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Title: A text-book of veterinary anatomy
Author: Septimus Sisson
Release date: April 30, 2025 [eBook #75996]
Language: English
Original publication: Philadelphia: W. B. Saunders, 1910
Credits: Richard Tonsing and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive)
*** START OF THE PROJECT GUTENBERG EBOOK A TEXT-BOOK OF VETERINARY ANATOMY ***
A TEXT-BOOK
of
VETERINARY ANATOMY
BY
SEPTIMUS SISSON, S.B., V.S.
PROFESSOR OF COMPARATIVE ANATOMY IN OHIO STATE UNIVERSITY, COLUMBUS,
OHIO MEMBER OF THE AMERICAN ASSOCIATION OF ANATOMISTS
_WITH 588 ILLUSTRATIONS
MANY IN COLORS_
PHILADELPHIA AND LONDON
W. B. SAUNDERS COMPANY
1911
COPYRIGHT, 1910, BY W. B. SAUNDERS COMPANY
Reprinted July, 1911
PRINTED IN AMERICA
PRESS OF
W. B. SAUNDERS COMPANY
PHILADELPHIA
TO
KATHERINE OLDHAM SISSON
IN GRATEFUL RECOGNITION OF CONSTANT
INSPIRATION AND ENCOURAGEMENT
THIS BOOK IS DEDICATED
BY THE AUTHOR
PREFACE
The lack of a modern and well-illustrated book on the structure of the
principal domestic animals has been acutely felt for a long time by
teachers, students, and practitioners of veterinary medicine. The work
here offered is the expression of a desire to close this gap in our
literature.
The study of frozen sections and of material which has been hardened by
intravascular injection of formalin has profoundly modified our views
concerning the natural shape of many of the viscera and has rendered
possible much greater precision in topographic statements. The
experience of the author during the last ten years, in which almost all
of the material used for dissection and for frozen sections in the
anatomical laboratory of this University has been hardened with
formalin, has demonstrated that many of the current descriptions of the
organs in animals contain the same sort of errors as those which
prevailed in regard to similar structures in man previous to the
adoption of modern methods of preparation.
While the method of treatment of the subject is essentially systematic,
topography is not by any means neglected either in text or
illustrations; it is hoped that this will render the book of value to
the student in his clinical courses and to the practitioner.
Embryological and histological data have been almost entirely excluded,
since it was desired to offer a text-book of convenient size for the
student and a work of ready reference for the practitioner. It is
believed that the use of black type for the names of important
structures and of small print for certain details or matter of secondary
importance will prove useful in this respect.
Veterinary anatomical nomenclature is at present quite chaotic in
English-speaking countries. In this work an attempt is made to eliminate
some terms which do not appear to the author to fulfil any useful
purpose, and others which are clearly erroneous or otherwise
undesirable. In many cases the terms agreed upon by the Congresses at
Baden and Stuttgart are adopted either in the original Latin or in
anglicized form; otherwise these terms are added in parenthesis. The
author favors the substantial adoption of this terminology, but
considered it desirable to offer a sort of transitional stage at
present.
The original illustrations are chiefly reproductions of photographs,
many of which were taken by Mr. F. H. Haskett. The preparation of the
pictures for reproduction was carried out by Messrs. J. V. Alteneder and
W. J. Norris. The author takes pleasure in expressing his appreciation
of the care and skill exercised by these gentlemen in this often
difficult task.
The author is under great obligation to Professors Ellenberger and Baum
in Dresden, to Professor Schmaltz in Berlin, and to their publishers for
permission to use or to copy figures from their most excellent works.
Their generosity in this matter has made it possible to supply this text
with a larger number of high-class illustrations than is to be found in
any other. A few figures have been taken from other sources, and proper
credit has been given in each case.
For checking over certain data and for assistance in the correction of
the proofs the author is much indebted to his associate, Dr. F. B.
Hadley.
The author desires to express his high appreciation of the determination
and constant effort of the publishers to do all in their power to render
the book worthy of favorable reception by the profession for whom it is
intended.
OHIO STATE UNIVERSITY, COLUMBUS, OHIO. SEPTIMUS SISSON.
CONTENTS
INTRODUCTION
OSTEOLOGY
PAGE
THE SKELETON 19
Structure of Bones 20
Development and Growth of Bone 22
Composition and Physical Properties of Bone 23
Descriptive Terms 23
The Vertebral Column 24
The Ribs and Costal Cartilages 25
Costal Cartilages 26
The Sternum 26
The Thorax 27
The Skull 27
Bones of the Thoracic Limb 27
Bones of the Pelvic Limb 29
SKELETON OF THE HORSE 31
Vertebral Column 31
Ribs 43
Sternum 45
Bones of the Skull 47
Cranium 47
Face 57
The Skull as a Whole 65
The Cranial Cavity 69
The Nasal Cavity 71
The Paranasal Sinuses 72
Bones of the Thoracic Limb 74
Bones of the Pelvic Limb 92
SKELETON OF THE OX 112
Vertebral Column 112
Ribs 114
Sternum 115
Bones of the Skull 115
The Skull as a Whole 123
Bones of the Thoracic Limb 127
Bones of the Pelvic Limb 131
SKELETON OF THE PIG 136
Vertebral Column 136
Ribs 138
Sternum 139
Bones of the Skull 139
The Skull as a Whole 144
Bones of the Thoracic Limb 146
Bones of the Pelvic Limb 148
SKELETON OF THE DOG 150
Vertebral Column 150
Ribs 153
Sternum 153
Bones of the Skull 153
The Skull as a Whole 159
Bones of the Thoracic Limb 162
Bones of the Pelvic Limb 165
ARTHROLOGY
SYNARTHROSES 169
DIARTHROSES 170
AMPHIARTHROSES 172
ARTICULATIONS OF THE HORSE 172
Joints and Ligaments of the Vertebræ 172
Atlanto-occipital Articulation 176
Costo-vertebral Articulations 177
Costo-chondral Articulations 178
Chondro-sternal Articulations 178
Sternal Joints and Ligaments 178
Articulations of the Skull 179
Articulations of the Thoracic Limb 180
Articulations of the Pelvic Limb 190
ARTICULATIONS OF THE OX, PIG, AND DOG 203
THE MUSCULAR SYSTEM—MYOLOGY
THE MUSCLES AND ACCESSORY STRUCTURES 211
FASCIÆ AND MUSCLES OF THE HORSE 213
Panniculus carnosus 213
Fasciæ and Muscles of the Head 213
Fasciæ and Muscles of the Neck 224
Fasciæ and Muscles of the Back and Loins 235
Fasciæ and Muscles of the Tail 238
Muscles of the Thorax 240
Muscles of the Abdomen 245
Muscles of the Thoracic Limb 250
Fasciæ and Muscles of the Pelvic Limb 273
MUSCLES OF THE OX 295
MUSCLES OF THE PIG 311
MUSCLES OF THE DOG 318
SPLANCHNOLOGY—THE DIGESTIVE SYSTEM
DIGESTIVE SYSTEM OF THE HORSE 330
The Mouth 330
The Tongue 335
The Teeth 338
The Salivary Glands 346
The Pharynx 348
The Œsophagus 350
The Abdominal Cavity 352
The Peritoneum 353
The Pelvic Cavity 354
The Stomach 357
The Small Intestine 360
The Large Intestine 363
The Pancreas 371
The Liver 373
The Spleen 377
The Peritoneum 379
DIGESTIVE SYSTEM OF THE OX 382
DIGESTIVE SYSTEM OF THE SHEEP 405
DIGESTIVE SYSTEM OF THE PIG 410
DIGESTIVE SYSTEM OF THE DOG 423
THE RESPIRATORY SYSTEM
RESPIRATORY SYSTEM OF THE HORSE 436
The Nasal Cavity 436
The Larynx 440
The Trachea 448
The Bronchi 450
The Thoracic Cavity 450
The Pleuræ 451
The Lungs 453
THE THYROID GLAND OF THE HORSE 457
THE THYMUS OF THE HORSE 458
RESPIRATORY SYSTEM OF THE OX 458
RESPIRATORY SYSTEM OF THE PIG 464
RESPIRATORY SYSTEM OF THE DOG 466
THE UROGENITAL SYSTEM
URINARY ORGANS OF THE HORSE 469
The Kidneys 469
The Ureters 475
The Urinary Bladder 475
THE ADRENAL BODIES 477
URINARY ORGANS OF THE OX 478
URINARY ORGANS OF THE PIG 481
URINARY ORGANS OF THE DOG 483
THE MALE GENITAL ORGANS
MALE GENITAL ORGANS OF THE HORSE 485
The Testicles 485
The Scrotum 487
The Vas Deferens 488
The Spermatic Cord 489
The Tunica Vaginalis 489
Descent of the Testicles 490
The Vesiculæ Seminales 491
The Prostate 493
The Uterus Masculinus 493
The Bulbo-urethral Glands 493
The Penis 494
The Prepuce 496
MALE GENITAL ORGANS OF THE OX 500
MALE GENITAL ORGANS OF THE PIG 504
MALE GENITAL ORGANS OF THE DOG 506
THE FEMALE GENITAL ORGANS
GENITAL ORGANS OF THE MARE 508
The Ovaries 508
The Uterine or Fallopian Tubes 511
The Uterus 511
The Vagina 514
The Vulva 514
The Urethra 515
The Mammary Glands 516
GENITAL ORGANS OF THE COW 517
GENITAL ORGANS OF THE SOW 521
GENITAL ORGANS OF THE BITCH 522
ANGIOLOGY
THE ORGANS OF CIRCULATION 524
BLOOD-VASCULAR SYSTEM OF THE HORSE 525
The Pericardium 525
The Heart 526
The Pulmonary Artery 535
The Systemic Arteries 535
The Coronary Arteries 537
The Brachiocephalic Trunk or Anterior Aorta 537
Arteries of the Thoracic Limb 556
Branches of the Thoracic Aorta 565
Branches of the Abdominal Aorta 566
Arteries of the Pelvic Limb 578
The Veins 585
The Pulmonary Veins 585
The Systemic Veins 585
The Anterior Vena Cava and its Tributaries 586
The Posterior Vena Cava and its Tributaries 595
THE LYMPHATIC SYSTEM 599
Lymphatic System of the Horse 600
The Lymph Glands and Vessels of the Head and Neck 601
The Lymph Glands and Vessels of the Thorax 603
The Lymph Glands and Vessels of the Abdomen and Pelvis 604
The Lymph Glands and Vessels of the Thoracic Limb 605
The Lymph Glands and Vessels of the Pelvic Limb 606
THE FŒTAL CIRCULATION 606
BLOOD-VASCULAR SYSTEM OF THE OX 608
The Pericardium and Heart 608
The Arteries 609
The Veins 621
LYMPHATIC SYSTEM OF THE OX 623
CIRCULATORY SYSTEM OF THE PIG 626
The Pericardium and Heart 626
The Arteries 627
The Veins 630
Lymphatic System of the Pig 630
CIRCULATORY SYSTEM OF THE DOG 632
The Pericardium and Heart 632
The Arteries 633
The Veins 641
Lymphatic System of the Dog 643
NEUROLOGY—THE NERVOUS SYSTEM
GENERAL CONSIDERATIONS 644
NERVOUS SYSTEM OF THE HORSE 648
The Spinal Cord 648
The Brain 652
The Cranial Nerves 676
The Spinal Nerves 692
SYMPATHETIC NERVOUS SYSTEM OF THE HORSE 710
NERVOUS SYSTEM OF THE OX 715
NERVOUS SYSTEM OF THE PIG 720
NERVOUS SYSTEM OF THE DOG 724
ÆSTHESIOLOGY
THE SENSE ORGANS AND SKIN OF THE HORSE 734
The Eye 734
The Ear 747
The Skin 761
The Olfactory and Gustatory Apparatus 772
THE SENSE ORGANS AND SKIN OF THE OX 772
THE SENSE ORGANS AND INTEGUMENT OF THE PIG 777
THE SENSE ORGANS AND INTEGUMENT OF THE DOG 779
INDEX 783
VETERINARY ANATOMY
INTRODUCTION
=Anatomy= is the branch of biological science which deals with the form
and structure of organisms, both animal and vegetal. It is therefore in
close correlation with physiology, which treats of the functions of the
body.
Etymologically the word “anatomy” signifies the cutting apart or
disassociating of parts of the body. In the earlier phases of its
development anatomy was necessarily a purely descriptive science, based
on such observations as were possible with the unaided eye and simple
dissecting instruments—the scalpel, forceps, and the like. At this time,
therefore, the term adequately expressed the nature of the subject. But
as the scope of the science extended and the body of anatomical
knowledge grew, subdivisions became necessary and new terms were
introduced to designate special fields and methods of work. With the
introduction of the microscope and its accessories it became possible to
study the finer details of structure and minute organisms hitherto
unknown, and this field of inquiry rapidly developed into the science of
=microscopic anatomy= or =histology= as conventionally distinguished
from =gross= or =macroscopic anatomy=. In the same way the study of the
changes which organisms undergo during their development soon attained
sufficient importance to be regarded on practical grounds as a separate
branch known as =embryology=.
This term is usually limited in its application to the earlier phases
of development during which the tissues and organs are formed. The
term =ontogeny= is used to designate the entire development of the
individual. The ancestral history or =phylogeny= of the species is
constituted by the evolutionary changes which it has undergone as
disclosed by the geological record.
=Comparative anatomy= is the description and comparison of the structure
of animals, and forms the basis for their classification. By this
means—including extinct forms in the scope of inquiry—it has been
possible to show the genetic relationship of various groups of animals
and to elucidate the significance of many facts of structure which are
otherwise quite obscure. The deductions concerning the general laws of
form and structure derived from comparative anatomical studies
constitute the science of =morphology= or =philosophical anatomy=. The
morphologist, however, deals only with such anatomical details as are
necessary to form a basis for his generalizations. The anatomical
knowledge required in the practice of medicine and surgery is evidently
of a different character and must include many details which are of no
particular interest to the morphologist.
=Special anatomy= is the description of the structure of a single type
or species, _e. g._, anthropotomy, hippotomy.
=Veterinary anatomy= is the branch which deals with the form and
structure of the principal domesticated animals. It is usually pursued
with regard to professional requirements, and is therefore largely
descriptive in character. As a matter of convenience the horse is
generally selected as the type to be studied in detail and to form a
basis for comparison of the more essential differential characters in
the other animals.
Two chief methods of study are employed—the =systematic= and the
=topographic=. In the former the body is regarded as consisting of
systems of organs or apparatus which are similar in origin and structure
and are associated in the performance of certain functions. The
divisions of =systematic anatomy= are:
1. Osteology
2. Arthrology
3. Myology
4. Splanchnology
(1) Digestive System
(2) Respiratory System
(3) Urogenital System
(_a_) Urinary Organs
(_b_) Genital Organs
5. Angiology
6. Neurology
7. Æsthesiology
(1) Sense Organs
(2) Common Integument.
The term =topographic anatomy= designates the methods by which the
relative positions of the various parts of the body are accurately
determined. It presupposes a fair working knowledge of systematic
anatomy.
=Descriptive Terms.=—In order to indicate precisely the position and
direction of parts of the body, certain descriptive terms are employed,
and must be understood at the outset. In the explanation of these terms
it is assumed here that they apply to a quadruped such as the horse in
the ordinary standing position. The surface directed toward the plane of
support (the ground) is termed =inferior= or =ventral=, and the opposite
surface is =superior= or =dorsal=; the relations of parts in this
direction are named accordingly. The longitudinal =median plane= divides
the body into similar halves. A structure or surface which is nearer
than another to the median plane is =internal= or =medial= to it, and an
object or surface which is further than another from the median plane is
=external= or =lateral= to it. Planes parallel to the median plane are
=sagittal=. =Transverse= or =segmental= planes cut the long axis of the
body perpendicular to the median plane, or an organ or limb at right
angles to its long axis. A =frontal= plane is perpendicular to the
median and transverse planes. The head end of the body is termed
=anterior=, =cephalic=, or =cranial=; and the tail end =posterior= or
=caudal=; relations of structures with regard to the longitudinal axis
of the body are designated accordingly. Certain terms are used in a
special sense as applied to the limbs. =Proximal= and =distal= express
relative distances of parts from the axis of the body. The anterior face
of the thoracic limb from the elbow downward is also termed =dorsal=,
and the opposite face =volar=. In the corresponding part of the pelvic
limb the terms are =dorsal= and =plantar= respectively. In the same
regions =radial= and =ulnar= (thoracic limb), =tibial= and =fibular=
(pelvic limb), may be used to designate that side of the extremity on
which the corresponding bone is situated; they are therefore equivalent
respectively to internal or medial and external or lateral in the
animals with which we are concerned.
It is evidently advantageous to employ terms which are as far as
possible independent of the position of the body in space and capable
of general application, _e. g._, dorsal, ventral, proximal, etc. It is
also desirable that the terms internal and external be reserved to
indicate relations of depth in cavities or organs, and medial and
lateral to designate relations to the median plane. Such terms are
coming into more extensive use in human and veterinary anatomy, but
the older nomenclature is very firmly established and cannot well be
discarded at once and entirely.
OSTEOLOGY
THE SKELETON
The term =skeleton= is applied to the framework of hard structures which
supports and protects the soft tissues of animals. In the descriptive
anatomy of the higher animals it is usually restricted to the bones and
cartilages, although the ligaments which bind these together might well
be included.
In zoölogy the term is used in a much more comprehensive sense, and
includes all the harder supporting and protecting structures. When the
latter are situated externally, they form an =exoskeleton=, derived
from the ectoderm. Examples of this are the shells and chitinous
coverings of many invertebrates, the scales of fishes, the shields of
turtles, and the feathers, hair, and hoofs of the higher vertebrates.
The =endoskeleton= (with which we have to deal at present) is embedded
in the soft tissues. It is derived chiefly from the mesoderm, but
includes the notochord or primitive axial skeleton, which is of
entodermal origin.
The skeleton may be divided primarily into three parts: (1) axial; (2)
appendicular; (3) splanchnic.
The =axial skeleton= comprises the vertebral column, ribs, sternum, and
skull.
The =appendicular skeleton= includes the bones of the limbs.
The =splanchnic skeleton= consists of certain bones developed in the
substance of some of the viscera or soft organs, _e. g._, the os penis
of the dog and the os cordis of the ox.
The =number= of the bones of the skeleton of an animal varies with age,
owing to the fusion during growth of skeletal elements which are
separate in the fœtus or the young subject. Even in adults of the same
species numerical variations occur, _e. g._, the tarsus of the horse may
consist of six or seven bones, and the carpus of seven or eight; in all
the domestic mammals the number of coccygeal vertebræ varies
considerably.
The bones are commonly divided into four classes according to their
shape and function.
(1) =Long bones= (Ossa longa) are typically of elongated cylindrical
form with enlarged extremities. They occur in the limbs, where they act
as supporting columns and as levers. The cylindrical part, termed the
shaft or body (Corpus), is tubular, and incloses the =medullary cavity=,
which contains the medulla or marrow.
(2) =Flat bones= (Ossa plana) are expanded in two directions. They
furnish sufficient area for the attachment of muscles and afford
protection to the organs which they cover.
(3) =Short bones= (Ossa brevia), such as those of the carpus and tarsus,
present somewhat similar dimensions in length, breadth, and thickness.
Their chief function appears to be that of diffusing concussion.
Sesamoid bones, which are developed in the capsules of some joints or in
tendons, may be included in this group. They diminish friction or change
the direction of tendons.
(4) =Irregular bones.= This group would include bones of irregular
shape, such as the vertebræ and the bones of the cranial base; they are
median and unpaired. Their functions are various and not so clearly
specialized as those of the preceding classes.
This classification is not entirely satisfactory; some bones, _e. g._,
the ribs, are not clearly provided for, and others might be variously
placed.
STRUCTURE OF BONES[1]
Bones consist chiefly of =bone tissue=, but considered as organs they
present also an enveloping membrane, termed the =periosteum=, the
=medulla= or =marrow=, =vessels=, and =nerves=.
The architecture of bone can be studied best by means of longitudinal
and cross-sections. These show that the bone consists of an external
shell of dense =compact substance=, within which is the more loosely
arranged =spongy substance=. In typical long bones the shaft is hollowed
to form the =medullary cavity= (Cavum medullare).
[Illustration:
FIG. 1.—FRONTAL SECTION OF LARGE METATARSAL BONE OF HORSE, POSTERIOR
PART.
]
[Illustration:
FIG. 2.—SAGITTAL SECTION OF LARGE METATARSAL BONE OF HORSE.
_S.C._, Compact substance; _S.s._, spongy substance; _C.m._, medullary
cavity; _F.n._, nutrient foramen. Note the greater thickness of the
compact substance of the inner and anterior parts of the shaft.
]
The =compact substance= (Substantia compacta) differs greatly in
thickness in various situations, in conformity with the stresses and
strains to which the bone is subjected. In the long bones it is thickest
in the middle part of the shaft and thins out toward the extremities. On
the latter the layer is very thin, and is especially dense and smooth on
joint surfaces.
The =spongy substance= (Substantia spongiosa) consists of delicate bony
plates and spicules which run in various directions and intercross.
These plates are definitely arranged with regard to mechanical
requirements, so that systems of pressure and tension plates can be
recognized, in conformity with the lines of pressure and the pull of
tendons and ligaments respectively. The intervals (marrow spaces)
between the plates are occupied by marrow. The spongy substance forms
the bulk of short bones and of the extremities of long bones; in the
latter it is not confined to the ends, but extends a variable distance
along the shaft also. Some bones (Ossa pneumatica) contain =air-spaces=
or =sinuses= within the compact substance instead of spongy bone and
marrow. In certain situations the two compact layers of flat bones are
not separated by spongy bone, but fuse with each other; in some cases of
this kind the bone is so thin as to be translucent, or may even undergo
absorption, producing an actual deficiency.
The flat bones of the cranial vault and sides are composed of an outer
layer of ordinary compact substance, an inner layer of very dense bone,
the =tabula vitrea=, and between these a variable amount of spongy bone,
here termed =diploë=.
The =periosteum= is the membrane which invests the outer surface of
bone, except where it is covered with cartilage. It consists of an outer
protective fibrous layer, and an inner cellular osteogenic layer. During
active growth the osteogenic layer is well developed, but later it
becomes much reduced. The fibrous layer varies much in thickness, being
in general thickest in exposed situations. The adhesion of the
periosteum to the bone also differs greatly in various places; it is
usually very thin and easily detached where it is thickly covered with
muscular tissue which has little or no attachment. The degree of
vascularity conforms to the activity of the periosteum.
The =marrow= (Medulla ossium) occupies the interstices of the spongy
bone and the medullary cavity of the long bones. There are two varieties
in the adult—red and yellow. In the young subject there is only =red
marrow= (Medulla ossium rubra), but later this is replaced in the
medullary cavity by =yellow marrow= (Medulla ossium flava). The red
marrow contains several types of characteristic cells and is a
blood-forming substance, while the yellow is practically ordinary
adipose tissue.
Since yellow marrow is formed by regressive changes in red marrow,
including fatty infiltration and degeneration of the characteristic
cells, we find transitional forms or stages in the process. In aged or
badly nourished subjects the marrow may undergo gelatinous
degeneration, resulting in the formation of gelatinous marrow.
=Vessels and Nerves.=—It is customary to recognize two sets of
=arteries=—the =periosteal= and the =medullary=. The former ramify in
the periosteum and give off innumerable small branches which enter
minute openings (Volkmann’s canals) on the surface and reach the
Haversian canals of the compact substance. Other branches enter the
extremities of the long bones and supply the spongy bone and marrow in
them. In the case of the larger bones—and especially the long bones—the
large =medullary= or =nutrient artery= enters at the so-called =nutrient
foramen= (Foramen nutricium), passes in a canal (Canalis nutricius)
through the compact substance, and ramifies in the marrow; its branches
anastomose with the central branches of the periosteal set. The larger
=veins= of the spongy bone do not, as a rule, accompany the arteries,
but emerge chiefly near the articular surfaces. Within the bone they are
destitute of valves.
The =lymph vessels= form perivascular channels in the periosteum and the
Haversian canals of the compact substance. Lymph-spaces exist at the
periphery of the marrow.
The =nerves= appear to be distributed chiefly to the blood-vessels.
Special nerve-endings (Vater-Pacini corpuscles) in the periosteum are to
be regarded as sensory, and probably are concerned in mediating the
muscle sense (Kopsch).
DEVELOPMENT AND GROWTH OF BONE[2]
The primitive embryonal skeleton consists of cartilage and fibrous
tissue, in which the bones develop. The process is termed =ossification=
or =osteogenesis=, and is effected essentially by bone-producing cells,
called =osteoblasts=. It is customary, therefore, to designate as
=membrane bones= those which are developed in fibrous tissue, and as
=cartilage bones= those which are preformed in cartilage. The principal
membrane bones are those of the roof and sides of the cranium and most
of the bones of the face. The cartilage bones comprise, therefore, most
of the skeleton. Correspondingly we distinguish =intramembranous= and
=endochondral ossification=.
[Illustration:
FIG. 3.—LEFT FEMUR OF YOUNG PIG, EXTERNAL VIEW, TO SHOW DIVISION OF A
LONG BONE INTO SHAFT (_s_) AND EXTREMITIES.
Proximal extremity consists of two parts, head (_h_) and trochanter
major (_t. m._), which have separate centers of ossification. Distal
extremity consists of trochlea (_t_) and condyles (_c_); _e.l._,
epiphyseal cartilages; _s.f._, supracondyloid fossa.
]
In intramembranous development the process begins at a definite =center
of ossification= where the cells (osteoblasts) surround themselves with
a deposit of bone. The process extends from this center to the periphery
of the future bone, thus producing a network of bony trabeculæ. The
trabeculæ rapidly thicken and coalesce, forming a bony plate which is
separated from the adjacent bones by persistent fibrous tissue. The
superficial part of the original tissue becomes periosteum, and on the
deep face of this successive layers of periosteal bone are formed by
osteoblasts until the bone attains its definitive thickness.
In endochondral ossification the process is fundamentally the same, but
not quite so simple. Osteoblasts emigrate from the deep face of the
perichondrium or primitive periosteum into the cartilage and cause
calcification of the matrix or ground-substance of the latter. Vessels
extend into the calcifying area, the cartilage cells shrink and
disappear, forming primary marrow cavities which are occupied by
processes of the osteogenic tissue. There is thus formed a sort of
scaffolding of calcareous trabeculæ on which the bone is constructed by
the osteoblasts. At the same time perichondral bone is formed by the
osteoblasts of the primitive periosteum. The calcified cartilage is
broken down and absorbed through the agency of large cells called
=osteoclasts=, and is replaced by bone deposited by the osteoblasts. The
osteoclasts also cause absorption of the primitive bone, producing the
marrow cavities; thus in the case of the long bones the primitive
central spongy bone is largely absorbed to form the medullary cavity of
the shaft, and persists chiefly in the extremities. Destruction of the
central part and formation of subperiosteal bone continue until the
shaft of the bone has completed its growth.
A typical long bone is developed from three primary centers of
ossification, one for the diaphysis or shaft and one for each epiphysis
or extremity. Many bones have secondary centers from which processes or
apophyses develop.
The foregoing outline accounts for the growth of bones except in regard
to length. Increase in length may be explained briefly as follows:
Provision for continued ossification at either end of the diaphysis is
made by a layer of actively growing cartilage—the =epiphyseal
cartilage=—which intervenes between the diaphysis and the epiphysis. It
is evident that so long as this cartilage persists and grows, new bone
may continue to be formed at its expense, and increase of length is
possible. When the epiphyseal cartilage ceases to grow, it undergoes
ossification, the bone is consolidated, and no further increase in
length is possible. This fusion takes place at fairly definite periods
in the various bones, and it is of value to know the usual times at
which it occurs in the larger bones of the limbs at least.
After the bones have reached their full size, the periosteum becomes
relatively reduced and inactive so far as its osteogenic layer is
concerned; the bone-forming function may be stimulated by various
causes, as is well seen in the healing of fractures and the occurrence
of bony enlargements.
CHEMICAL COMPOSITION OF BONE
Dried bone consists of =organic= and =inorganic= matter in the ratio of
1 ∶ 2 approximately. The animal matter gives toughness and elasticity,
the mineral matter hardness, to the bone tissue. Removal of the organic
matter by heat does not change the general form of a bone, but reduces
the weight by about one-third, and makes it very fragile. Conversely,
decalcification, while not affecting the form and size of the bone,
renders it soft and pliable. The animal matter when boiled yields
gelatin. The following table represents the composition in 100 parts of
ox bone of average quality:
Gelatin 33.30
Phosphate of lime 57.35
Carbonate of lime 3.85
Phosphate of magnesia 2.05
Carbonate and chlorid of sodium 3.45
——————
100.00
PHYSICAL PROPERTIES OF BONE
Fresh dead bone has a yellowish-white color; when macerated or boiled
and bleached, it is white. The specific gravity of fresh compact bone is
a little over 1.93. It is very hard and resistant to pressure; a
5-millimeter cube of compact bone of the ox will resist pressure up to
852 pounds, if the pressure be applied in the line of the lamellæ
(Rauber). Its tensile strength is estimated to be nearly twice that of
oak.
DESCRIPTIVE TERMS
The surfaces of the bones present a great variety of eminences and
depressions, as well as perforations. The prominences and cavities may
be articular, or non-articular, furnishing attachment to muscles,
tendons, ligaments or fascia. A number of descriptive terms are used to
designate these features, and the following are some of those in general
use:
=Process= (Processus) is a general term for a prominence.
A =tuberosity= (Tuber, Tuberositas) is a large, rounded projection; a
=tubercle= (Tuberculum) is a smaller one.
The term =trochanter= is applied to a few prominences, _e. g._, the
trochanters of the femur.
A =spine= (Spina) or =spinous process= (Processus spinosus) is a pointed
projection.
A =crest= (Crista) is a sharp ridge.
A =line= (Linea) is a very small ridge.
A =head= (Caput) is a rounded articular enlargement at the end of a
bone; it may be joined to the shaft by a constricted part, the =neck=
(Collum).
A =condyle= (Condylus) is an articular eminence which is somewhat
cylindrical; a non-articular projection in connection with a condyle may
be termed an =epicondyle=.
A =trochlea= is a pulley-like articular mass.
A =glenoid cavity= (Cavitas glenoidalis) is a shallow articular
depression, and a =cotyloid cavity= or =acetabulum= is a deeper one.
The term =facet= is commonly applied to articular surfaces of small
extent, especially when they are not strongly concave or convex.
The terms =fossa=, =fovea=, =groove= or =sulcus=, and =impression= are
applied to various forms of depressions.
A =foramen= is a perforation for the transmission of vessels, nerves,
etc.
A =sinus= or =antrum= is an air-cavity.
Other terms, such as =canal=, =fissure=, =notch=, etc., require no
explanation.[3]
VERTEBRAL COLUMN
The =vertebral column= (Columna vertebralis) is the fundamental part of
the skeleton. It consists of a chain of median, unpaired, irregular
bones which extends from the skull to the end of the tail. In the adult
certain vertebræ have become fused to form a single bony mass with which
the pelvic girdle articulates. Vertebræ so fused are termed =fixed= or
=“false” vertebræ= (Vertebræ immobiles), as distinguished from the
=movable= or =“true” vertebræ= (Vertebræ mobiles).
The column is subdivided for description into =five regions=, which are
named according to the part of the body in which they are placed. Thus
the vertebræ are designated as =cervical=, =thoracic= (or dorsal),
=lumbar=, =sacral=, and =coccygeal= or =caudal= (Vertebræ cervicales,
thoracales, lumbales, sacrales, coccygeæ). The number of vertebræ in a
given species is fairly constant in each region except the last, so that
the =vertebral formula= may be expressed (for the horse, for example) as
follows:
C_{7}T_{18}L_{6}S_{5}Cy_{15–21}.
[Illustration:
FIG. 4.—FIRST THORACIC VERTEBRÆ OF HORSE.
To illustrate plan of structure of vertebræ.
]
The vertebræ in a given region have special characters by which they may
be distinguished from those of other regions, and individual vertebræ
have characters which are more or less clearly recognizable. All typical
vertebræ have a common plan of structure, which must first be
understood. The parts of which a vertebra consists are the =body= or
=centrum=, the =arch=, and the =processes=.
The =body= (Corpus vertebræ) is the more or less cylindrical mass on
which the other parts are constructed. The anterior and posterior
extremities of the body are attached to the adjacent vertebræ by
intervertebral fibro-cartilages, and are usually convex and concave
respectively. The dorsal surface is flattened and enters into the
formation of the vertebral canal, while the ventral aspect is rounded
laterally, and is in relation to various muscles and viscera. In the
thoracic region the body presents two pairs of demifacets (Foveæ
costales) at the extremities for articulation with the heads of two
pairs of ribs.
The =arch= (Arcus vertebræ) is constructed on the dorsal aspect of the
body. It consists originally of two lateral halves, each of which is
considered to consist of a pedicle and a lamina. The pedicles form the
lateral parts of the arch, and are cut into in front and behind by the
=vertebral notches= (Incisura vertebralis cranialis, caudalis). The
notches of two adjacent vertebræ form =intervertebral foramina= for the
passage of the spinal nerves and vessels; in some vertebræ, however,
these are complete foramina instead of notches. The laminæ are plates
which complete the arch dorsally, uniting with each other medially at
the root of the spinous process.
The body and the arch form a bony ring which incloses the =vertebral
foramen= (Foramen vertebrale); the series of vertebral rings, together
with the ligaments which unite them, inclose the =vertebral canal=
(Canalis vertebralis), which contains the spinal cord and its coverings
and vessels.
The =articular processes=, two =anterior= and two =posterior= (Processus
articulares craniales, caudales), project from the borders of the arch
on either side. They present joint surfaces adapted to those of adjacent
vertebræ, and the remaining surface is roughened for muscular and
ligamentous attachment.
The =spinous process= (Processus spinosus) is single, and projects
dorsally from the middle of the arch. It varies greatly in form, size,
and direction in different vertebræ. It furnishes attachment to muscles
and ligaments.
The =transverse processes= (Processus transversi) are two in number and
project laterally from the side of the arch, or from the junction of the
arch and body. In the thoracic region each has a facet for articulation
with the tubercle of a rib (Fovea costalis transversalis). They also
give attachment to muscles and ligaments.
Some vertebræ have also a =ventral= or =hæmal spine=.
=Mammillary processes= (Processus mammillares) are found in most animals
on the last thoracic and anterior lumbar vertebræ between the transverse
and anterior articular processes or on the latter.
=Accessory processes= (Processus accessorii), when present, are situated
between the transverse and posterior articular processes.
=Development.=—The vertebræ are developed by ossification in the
cartilage which surrounds the notochord and forms the sides of the
neural canal. There are =three primary centers of ossification=, one for
the body and one for each side of the arch. =Secondary centers= appear
later for the summit of the spinous process (except in the cervical
region), the extremities of the transverse processes, and the thin
epiphyseal plates at the extremities of the body.
Sometimes there are at first two centers for the body which soon fuse.
The process of ossification extends from the lateral centers to form
not only the corresponding part of the arch, but also the processes
and a part of the body next to the root of the arch (Radix arcus). In
the horse and ox the body and arch are usually fused at birth, but the
epiphyses do not fuse till growth is complete. In the pig, sheep, and
dog the body and arch are united at birth by cartilage (neurocentral
synchondrosis), but fuse in the first few months.
THE RIBS
The ribs (Costæ) are elongated curved bones which form the skeleton of
the lateral thoracic walls. They are arranged serially in pairs which
usually correspond in number to the thoracic vertebræ. Each articulates
dorsally with the spine and is continued ventrally by a =costal
cartilage=. Those which articulate with the sternum by means of their
cartilages are termed =sternal= or =“true” ribs= (Costæ sternales s.
veræ); the remainder are =asternal= or =“false” ribs= (Costæ asternales
s. spuriæ). Ribs at the end of the series which have their ventral ends
free in the abdominal wall are named =floating ribs= (Costæ
fluctuantes). The intervals between the ribs are termed =intercostal
spaces= (Spatia intercostalia).
A typical rib[4] consists of a =shaft= and two =extremities=. The
=shaft= (Corpus costæ) is band-like and varies much in length, breadth,
and curvature. In the case of some ribs the curvature is not uniform,
but is most accentuated at a certain point, termed the =angle of the
rib= (Angulus costæ); this occurs at a variable distance from the
vertebral end, and is usually marked by a rough ridge. The direction
also varies; the first rib is almost vertical, while the remainder slope
backward in increasing degree. The =external= surface is convex, and the
=internal= flattened from edge to edge; on the latter, close to the
posterior border, is the =costal groove= (Sulcus costalis), which fades
out ventrally. It contains the intercostal vein. The =anterior= and
=posterior borders= are thin and sharp on some ribs, rounded on others.
The =vertebral extremity= (Extremitas vertebralis) consists of the
=head=, =neck=, and =tubercle=. The =head= (Capitulum costæ) is the
actual end of the rib, and is rounded and somewhat enlarged. It presents
two facets (Facies articularis capituli costæ) for articulation with the
bodies of two adjacent thoracic vertebræ; these surfaces are separated
by a groove in which the conjugal ligament is attached. The =neck=
(Collum costæ) joins the head to the shaft. It varies in length and
diameter. Its outer surface is rough, its inner smooth. The =tubercle=
(Tuberculum costæ) projects backward at the junction of the neck and
shaft. It has a facet (Facies articularis tuberculi costæ) for
articulation with the transverse process of the posterior vertebra of
the two with which the head articulates. The tubercle gradually
approaches the head in the posterior ribs, and eventually fuses with it.
The =sternal extremity= (Extremitas sternalis) is commonly slightly
enlarged, and has a rough depression in which the costal cartilage is
embedded.
=Development.=—The ribs are ossified in cartilage from three centers—one
each for the shaft (and sternal end), head, and tubercle; the third
center does not occur in the last two ribs.
THE COSTAL CARTILAGES
These (Cartilagines costales) are bars of hyaline cartilage which
continue the ribs. Those of the sternal ribs articulate with the
sternum, while the remainder overlap and are attached to each other to
form the =costal arch= (Arcus costalis).
THE STERNUM
The =sternum= or breast-bone is a median segmental bone which completes
the skeleton of the thorax ventrally, and articulates with the
cartilages of the sternal ribs laterally. It consists of six to eight
bony segments (Sternebræ) connected by intervening cartilage in the
young subject. Its form varies with that of the thorax in general and
with the development of the clavicles in animals in which they are
present. Its anterior extremity, the =manubrium sterni= or =presternum=,
is specially affected by the latter factor, being broad and strong when
the clavicles are well developed and articulate with it (as in man),
relatively small and laterally compressed when they are absent (as in
the horse) or rudimentary (as in the dog). The cartilages of the first
pair of ribs articulate with it. The =body= or =mesosternum= (Corpus
sterni) presents laterally, at the junction of the segments, concave
facets (Incisuræ costales) for articulation with the cartilages of the
sternal ribs. The posterior extremity or =metasternum= presents the
=xiphoid= (or ensiform) =cartilage= (Processus xiphoideus); this is thin
and plate-like, as in the horse and ox, or narrow and short, as in the
pig and dog.
=Development.=—The cartilaginous sternum is formed by the fusion
medially of two lateral bars which unite the ventral ends of the first
eight or nine costal cartilages, and is primitively unsegmented. The
manubrium ossifies from a single center, but the centers for the other
segments appear to be primitively paired. The sternum never becomes
completely ossified; details in regard to persisting cartilage will be
given in the special descriptions. The layer of compact tissue is for
the greater part very thin and the spongy substance is open-meshed and
very vascular.
THE THORAX
The skeleton of the thorax comprises the thoracic vertebræ dorsally, the
ribs and their cartilages laterally, and the sternum ventrally. The
=thoracic cavity= (Cavum thoracis) resembles in shape an irregular
truncated cone; it is compressed laterally, especially in front, and the
dorsal wall or roof is much longer than the ventral wall or floor. The
=anterior aperture= (Apertura thoracis cranialis) is bounded by the
first thoracic vertebra dorsally, the first pair of ribs and their
cartilages laterally, and the manubrium sterni ventrally. The =posterior
aperture= (Apertura thoracis caudalis) is bounded by the last thoracic
vertebra, the last pair of ribs, the costal arches, and the anterior
part of the xiphoid cartilage.
It may be noted here that the diaphragm (which forms the partition
between the thoracic and abdominal cavities) does not follow the
costal arches in its posterior attachment, so that the posterior ribs
enter also into the formation of the abdominal wall.
THE SKULL
The term skull is usually understood to include all of the bones of the
head. The head consists of the cranium and the face, and it is therefore
convenient to divide the bones into cranial and facial groups.
The =cranial bones= (Ossa cranii) inclose the brain with its membranes
and vessels and the essential organs of hearing. They concur with the
facial bones in forming the orbital and nasal cavities, in which the
peripheral organs of sight and of smell are situated.
The =facial bones= (Ossa faciei) form the skeleton of the oral and nasal
cavities, and also support the larynx and the root of the tongue.
Most of the bones of the skull are flat bones, developed in membrane;
those of the cranial base may be classed as irregular, and are cartilage
bones. Only two form permanent movable joints with other parts of the
skull. The mandible or lower jaw-bone forms diarthrodial joints with the
temporal bones, and the hyoid bone is attached to the latter by bars of
cartilage. The other bones form immovable joints, most of which
disappear with age.
In order to study the separate bones, skulls of young subjects are
necessary, since later most of the lines of demarcation become
effaced. The relations of each bone to its surroundings should be
specially noted, since the final object is to understand the skull as
a whole. In the descriptions which follow the skull is considered with
its long axis horizontal, and that of the horse will serve as a type.
THE BONES OF THE THORACIC LIMB
The thoracic limb consists of four chief segments, viz., the shoulder
girdle, the arm, the forearm, and the forefoot or manus.
The =shoulder girdle= (Cingulum extremitatis thoracicæ), when fully
developed, consists of three bones—the =scapula= or shoulder-blade, the
=coracoid=, and the =clavicle= or collar-bone. In the domesticated
mammals only the scapula, a large, flat bone, is well developed, and the
small coracoid element has fused with it, while the clavicle is either
absent or is a small rudiment embedded in the mastoido-humeralis muscle.
There is therefore no articulation of the shoulder with the axial
skeleton.
The shoulder girdle is fully developed in birds and the lower mammals
(monotremata). In the higher mammals the coracoid is reduced to the
coracoid process of the scapula, and the development of the clavicle
is in conformity with the function of the limb. Thus in typical
quadrupeds, such as the horse and ox, in which the forelimbs are used
only for support and locomotion, the clavicle is absent. Other animals
which use these limbs for grasping, burrowing, climbing, etc. (_e.g._,
man, apes, moles), have well-developed clavicles which connect the
scapula with the sternum.
The =arm= (Brachium) contains a single long bone, the humerus or arm
bone.
In the =forearm= (Antibrachium) are two long bones, the =radius= and
=ulna=. These vary in relative size and mobility. In the horse and ox
the two bones are fused, and the lower part of the limb is fixed in the
position of pronation. The radius is placed in front and supports the
weight. The ulna is well developed only in its upper part, which forms a
lever for the extensor muscles of the elbow. In the pig the ulna is the
larger and longer of the two bones, but is closely attached to the back
of the radius. In the dog the ulna is also well developed and a small
amount of movement is possible between the two bones.
The =forefoot= or =hand= (Manus) consists of three subdivisions, viz.,
the =carpus=, =metacarpus=, and =digit= or =digits=.
The =carpus=, popularly termed the “knee” in animals, and homologous
with the wrist of man, contains a group of short bones (Ossa carpi).
These are typically eight in number and are arranged in two transverse
rows—a proximal or antibrachial, and a distal or metacarpal. The bones
of the proximal row, named from the radial to the ulnar side (_i. e._,
from within outward), are the =radial=, =intermediate=, =ulnar=, and
=accessory= carpal bones. The bones of the distal row are designated
numerically, in the same direction, as =first=, =second=, =third=, and
=fourth= carpal bones.
This nomenclature, introduced by Gegenbaur, and now used largely by
comparative anatomists, seems decidedly preferable to the variety of
terms borrowed from human anatomy and based on the form of the bones
in man. The following table of synonyms in common use is appended for
comparison. The Latin terms and abbreviated notations are given in
parenthesis.
Radial (Os carpi radiale, Cr) Scaphoid
Intermediate (Os carpi intermedium, Ci) Semilunar
Ulnar (Os carpi ulnare, Cu) Cuneiform
Accessory (Os carpi accessorium, Ca) Pisiform
First carpal (Os carpale primum, C1) Trapezium
Second carpal (Os carpale secundum, C2) Trapezoid
Third carpal (Os carpale tertium, C3) Os magnum
Fourth carpal (Os carpale quartum, C4) Unciform
The central carpal bone (Os carpi centrale) is omitted, since it is
not a separate element in the animals under consideration here.
The =metacarpus= contains typically five =metacarpal bones= (Ossa
metacarpalia I–V), one for each digit; they are long bones and are
designated numerically from within outward. This arrangement occurs in
the dog, although the first metacarpal is much smaller than the others,
and the second and fifth are somewhat reduced. Further reduction has
taken place in the other animals, resulting in the perissodactyl and
artiodactyl forms. In the horse the first and fifth metacarpals are
absent, the third is the large supporting metacarpal bone and carries
the single digit, while the second and fourth are much reduced. In
artiodactyls (_e. g._, ox, sheep, pig) the third and fourth are the
chief metacarpals and carry the well developed digits; they are fused in
the ox and sheep. The others are variously reduced or absent as noted in
the special descriptions to follow.
The fossil remains of the ancestors of the existing Equidæ illustrate
in a most complete manner the reduction which has occurred in this
respect. The earliest known ancestor of the horse, Eohippus or
Hyracotherium of the Lower Eocene, had four well developed metacarpal
bones, each of which carried a digit; the first metacarpal bone was
small. Eleven intermediate stages show the gradual evolution of the
race from this primitive animal, which was about the size of the
domestic cat. There is reason to believe that earlier forms had five
digits.
The =digits= (Digiti manus) are homologous with the fingers of man, and
are typically five in number. They are designated numerically from the
radial to the ulnar side, in correspondence with the metacarpus. The
full number is present in the dog. In the ox and pig the third and
fourth are well developed and support the weight, while the second and
fifth are reduced. The existing horse has a single digit, the third of
his polydactyl ancestors. The skeleton of each fully developed digit
consists of three =phalanges= and certain =sesamoid bones=. The =first=
or =proximal phalanx= (Phalanx prima) articulates with the corresponding
metacarpal bone above and with the =second= or =middle phalanx= (Phalanx
secunda) below. The =third= or =distal phalanx= (Phalanx tertia) is
inclosed in the hoof or claw, and is modified to conform to the latter.
The =sesamoid bones= (Ossa sesamoidea) are developed along the course of
the flexor tendons or in the joint capsules. Two =proximal sesamoids=
(Ossa sesamoidea phalangis primæ) occur at the flexor side of the
metacarpo-phalangeal joint and form a pulley for the flexor tendon. The
=distal sesamoids= (Ossa sesamoidea phalangis tertiæ) are similarly
placed between the deep flexor tendon and the joint between the second
and third phalanx; they are absent in the dog, which has a small
sesamoid on the extensor side of the metacarpo-phalangeal joints, and
often at the proximal interphalangeal joint also.
Numerous cases are recorded of the occurrence of supernumerary digits
(hyperdactylism) in the horse and other animals. In some pigs, on the
other hand, the two chief digits are fused, and the condition appears
to be inherited.
THE BONES OF THE PELVIC LIMB
The pelvic limb, like the thoracic, consists of four segments, viz., the
pelvic girdle, thigh, leg, and the hind foot or pes; the last is
subdivided into tarsus, metatarsus, and digits.
The =pelvic girdle= (Cingulum extremitatis pelvinæ) consists of the =os
coxæ= or hip bone, which joins its fellow of the opposite side ventrally
at the symphysis pelvis, and articulates very firmly with the sacrum
dorsally. The two coxal bones, together with the sacrum and the first
two or three coccygeal vertebræ, constitute the bony pelvis. The os coxæ
consists originally of three flat bones, the =ilium=, =ischium=, and
=pubis=, which meet at the acetabulum, a large cotyloid cavity that
articulates with the head of the femur. These three parts are fused
before growth is complete, but are considered separately for convenience
of description. The =ilium= (Os ilium) is situated in the lateral wall
of the pelvis, the =pubis= (Os pubis) in the anterior part, and the
=ischium= (Os ischii) in the posterior part of the ventral wall.
The =thigh= (Femur), like the arm, contains a single large, long bone,
the =femur= or thigh bone (Os femoris). This articulates with the
acetabulum above and the tibia and patella below.
The skeleton of the leg (Crus) comprises three bones (Ossa cruris),
viz., the =tibia=, =fibula=, and =patella=. The =tibia= is a large
prismatic long bone which supports the weight, and articulates below
with the tibial tarsal bone. The =fibula= is situated along the outer
border of the tibia, from which it is separated by the =interosseous
space= of the leg. It is much more slender than the tibia and does not
articulate with the femur. In the pig and dog it has a complete shaft
and two extremities, but in the horse and ox it is much reduced and
otherwise modified. The =patella= or “knee-cap” is a short bone which
articulates with the trochlea of the distal end of the femur; it is to
be regarded as a large sesamoid bone intercalated in the tendon of the
quadriceps femoris muscle.
The =tarsus= or “hock” consists of a group of short bones (Ossa tarsi)
numbering five to seven in the different animals. The proximal or crural
row consists of two bones, the =tibial= and =fibular tarsals=; the
former is situated at the inner or tibial side, and has a trochlea for
articulation with the distal end of the tibia; the latter, situated
externally, has a process, the =tuber calcis=, which projects upward and
backward and constitutes a lever for the muscles which extend the hock
joint. The distal or metatarsal row consists of four bones when seven
tarsal elements are present, as in the pig and dog. They are best
designated numerically as =first tarsal=, =second tarsal=, etc. The
=central tarsal= is interposed between the rows.
The preceding terms are anglicized abbreviations of those introduced
by Gegenbaur into comparative anatomy. The Latin names and synonyms
are given in the following table.
Tibial (Os tarsi tibiale, Tt.) Astragalus or Talus
Fibular (Os tarsi fibulare, Tf.) Calcaneus or Os calcis
Central (Os tarsi centrale, Tc.) Scaphoid or Navicular
First Tarsal (Os tarsale primum, T1) First or internal cuneiform
Second Tarsal (Os tarsale secundum, T2) Second or middle cuneiform
Third Tarsal (Os tarsale tertium, T3) Third or external cuneiform
Fourth Tarsal (Os tarsale quartum, T4) Cuboid.
The =metatarsal= and =digital bones= resemble in general those of the
corresponding regions of the thoracic limb; the differential features
will be noted in the special descriptions.
[Illustration:
FIG. 5.—SKELETON OF HORSE, WITH OUTLINE OF CONTOUR OF BODY.
_1.H._, Atlas; _7.H._, seventh cervical vertebra; _1.R._, first
thoracic vertebra; _17.R._, seventeenth thoracic vertebra; _1.L._,
first lumbar vertebra; _6.L._, sixth lumbar vertebra; _K_, sacrum;
_1.S._, first coccygeal vertebra; _16.S._, sixteenth coccygeal
vertebra; _6.R._, sixth rib; _6.K._, costal cartilage; _18.R._, last
rib; 1, scapula; 1′, cartilage of scapula; 2, spine of scapula; 4,
humerus; 4′ external epicondyle of humerus; 5, external tuberosity
of humerus; 6, deltoid tuberosity; 7, shaft of ulna; 8, olecranon;
9, radius; 10, carpus; 11, accessory carpal bone; 12, metacarpus;
13, digit; 14, sternum; 14″, xiphoid cartilage; 15, ilium; 16, 16′,
external and internal angles of ilium; 17, ischium; 18, femur
(shaft); 19, trochanter major; 27, trochanter minor; 28, trochanter
tertius; 20, patella; 21, tibia (shaft); 21′, external condyle of
tibia; 23, fibula; 22, tarsus; 24, tuber calcis; 25, metatarsus; 26,
digit. (After Ellenberger-Baum, Anat. für Künstler.)
]
THE SKELETON OF THE HORSE
The skeleton of the horse consists of 205 bones, as shown in the
following table.
Vertebral column 54
Ribs 36
Sternum 1
Skull (including auditory ossicles) 34
Thoracic limbs 40
Pelvic limbs 40
————
205
In this enumeration the average number of coccygeal vertebræ is taken
to be 18, the temporal and os coxæ are not divided into parts, the
usual number of carpal and tarsal elements is taken, and the sesamoids
are included.
THE VERTEBRAL COLUMN
The vertebral formula of the horse is C_{7}T_{18}L_{6}S_{5}Cy_{15–21}.
[Illustration:
FIG. 6.—CERVICAL VERTEBRÆ OF HORSE, DORSAL VIEW. (After Schmaltz,
Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 7.—CERVICAL VERTEBRÆ OF HORSE, VENTRAL VIEW. (After Schmaltz,
Atlas d. Anat. d. Pferdes.)
]
THE CERVICAL VERTEBRÆ
These are quadrangular, massive, and longer than the vertebræ of other
regions; they decrease in length from the second to the last. The
=third=, =fourth=, and =fifth= are typical, and have the following
characters:
1. The =bodies= are long as compared with those of other vertebræ. Each
presents a median =ventral spine= or =crest=, which becomes more
prominent as it is traced backward, and is tuberculate at its posterior
end. The =lateral aspect= is concave. The =dorsal surface= has a flat
central area which is narrow in the middle of the vertebræ, and wide at
either end; it gives attachment to the superior common ligament. On
either side of this area is a groove which lodges the longitudinal
spinal vein. These lateral grooves are connected at the middle of the
surface by a transverse furrow, in which there are several foramina
through which veins emerge from the spongy substance of the body. The
=anterior extremity= presents a head which has an oval articular
surface, strongly convex, and wider above than below. The =posterior
extremity= is larger and has a nearly circular cotyloid cavity.
[Illustration:
FIG. 8.—LAST CERVICAL AND FIRST THORACIC VERTEBRÆ OF HORSE, LATERAL
VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
2. The =arches= are large and strong. They are perforated on either side
by a foramen which communicates with the foramen transversarium. The
vertebral notches are large.
3. The =articular processes= are large. Their articular surfaces are
extensive, oval in outline, and slightly concave; the anterior ones are
directed upward and inward, the posterior downward and outward. The
remaining surface is mainly roughened for ligamentous and muscular
attachment. A crest connects the articular processes of the same side on
the fourth and fifth; on the third it does not reach the anterior
process.
4. The =transverse processes= are large and plate-like. Each arises by
two roots, one from the arch and one from the body; between these is the
=foramen transversarium=, through which the vertebral artery passes. The
process divides externally into anterior and posterior branches, which
are thickened and rough for muscular attachment.
5. The =spinous process= is represented by a crest (Crista spinosa),
which widens behind, and is connected by ridges with the posterior
articular processes.
The =sixth= cervical vertebra has the following distinctive features: It
is shorter and wider than the fifth. The =arch= is large, especially
posteriorly. The =posterior articular= processes are shorter, thicker
and further apart; they are connected with the anterior ones by a thick
ridge. The =spinous process= is less rudimentary; it is half an inch or
more (ca. 1.5 cm.) in height. The =transverse processes= have three
branches; the third part is a thick, almost sagittal plate, which forms
with its fellow and the body a wide ventral groove on the posterior part
of the vertebra; the other branches correspond to those of the typical
vertebræ, but are short and thicker. The =foramen transversarium= is
large; below its posterior end is a fossa. The =ventral crest= is small
and is less prominent posteriorly.
The third branch of the transverse process and the fossa are sometimes
absent on one side.
The =seventh= cervical vertebra is readily distinguished by the
following characters: It is =shorter= and =wider= than the others. The
=body= is flattened dorso-ventrally and wide, especially behind; here it
has a =demifacet= on either side for articulation with part of the head
of the first rib. The =arch= and its =notches= are large. The =anterior
articular processes= are wider and longer than the posterior pair. The
=spinous process= is an inch or more (ca. 3 cm.) in height. The
=transverse process= is undivided, and has no foramen transversarium.
The ventral crest is replaced by a pair of tubercles.
In some specimens a large foramen transversarium is present on one
side or (rarely) on both.
[Illustration:
FIG. 9.—ATLAS OF HORSE, ANTERIOR VIEW. (After Schmaltz, Atlas d. Anat.
d. Pferdes.)
]
[Illustration:
FIG. 10.—ATLAS OF HORSE, POSTERIOR VIEW. (After Schmaltz, Atlas d.
Anat. d. Pferdes.)
]
THE ATLAS
This vertebra is decidedly atypical in form and structure. The body and
spinous process are absent. It has the form of a strong ring, from which
two curved plates, the =wings=, project laterally. The ring incloses a
very large vertebral foramen, and consists of two =lateral masses=
connected by =dorsal= and =ventral arches=.
The =lateral masses= (Massæ laterales) present two deep oval =anterior
articular cavities= (Foveæ articulares craniales) which receive the
occipital condyles; they are separated by a wide notch above and a
narrow one below. The outer margin is also notched, and a triangular
non-articular depression cuts into the inner part of each cavity. The
=posterior articular surfaces= (Facies articulares caudales) are
somewhat saddle-shaped; they are confluent on the ventral arch below,
but are widely separated above, and do not conform in shape to the
corresponding surfaces of the axis.
The =dorsal arch= (Arcus dorsalis) presents a median =dorsal tubercle=
(Tuberculum dorsale) and is concave below. It is perforated on either
side near its anterior margin by the =intervertebral foramen=. The
=anterior border= is deeply notched, and the =posterior= is thin and
concave.
The =ventral arch= (Arcus ventralis) is thicker, narrower, and less
curved than the dorsal. On its lower surface is the =ventral tubercle=
(Tuberculum ventrale), into which the terminal tendon of the longus
colli muscle is inserted. The upper face has posteriorly a transversely
concave articular surface (Fovea dentis), on which the dens or odontoid
process of the axis rests. In front of this is a transverse rough
excavation for the attachment of the odontoid ligament.
The =wings= (Alæ) are modified transverse processes. They are extensive
curved plates which project outward, downward, and backward from the
lateral masses. The dorsal surface is concave. Between the ventral
aspect of the wing and the lateral mass is a cavity, the =fossa
atlantis=; in this there is a foramen which opens into the vertebral
canal. The =border= is thick and rough. Two foramina perforate each
wing. The anterior one, the =foramen alare=, is connected with the
intervertebral foramen by a short groove. The posterior one is the
=foramen transversarium=.
=Development.=—The atlas ossifies from =three= or =four centers=, one or
two for the ventral arch, and one on either side for each lateral mass,
wing, and half of the dorsal arch. At birth the bone consists of three
pieces—the ventral arch and two lateral parts, which are separated by a
layer of cartilage in the dorsal median line. These parts are usually
fused at about six months.
[Illustration:
FIG. 11.—FIRST THREE CERVICAL VERTEBRÆ OF HORSE, LATERAL VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
THE AXIS
The =axis= (Epistropheus) is the longest of the vertebræ, and is
characterized by the presence of the odontoid process, which projects
from the anterior part of the body.
The =body= has a median ventral crest which terminates in a tubercle
behind. The anterior extremity presents centrally the =odontoid process=
(Dens); this has a convex articular surface ventrally for articulation
with the ventral arch of the atlas, and two rough depressions for the
attachment of the odontoid ligament dorsally. Flanking this on either
side are the modified =anterior articular processes=, which have
saddle-shaped articular surfaces confluent below with that of the dens.
The posterior extremity has the usual cavity.
The =arch= presents in the young subject a notch on each side of its
anterior border; this is converted into a foramen by a ligament which
usually ossifies later. The posterior border has the usual notches.
The =posterior articular processes= are typical.
The =transverse processes= are small, single, and project backward. The
=foramen transversarium= is small.
The =spinous process= is very large and strong. Its free border is
rough, thickens posteriorly, and is continued to the articular processes
by two ridges. The lateral surfaces are concave and rough for muscular
attachment.
=Development.=—The axis has =six= or =seven centers= of ossification. In
addition to the usual five, one or two appear for the dens, which is
regarded as the displaced body of the atlas. A nucleus behind the dens,
which remains distinct to three or four years of age, is considered by
Lesbre to be the head of the axis.
[Illustration:
FIG. 12.—OCCIPITAL BONE AND FIRST THREE CERVICAL VERTEBRÆ OF HORSE,
DORSAL VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
THE THORACIC VERTEBRÆ
These (Vertebræ thoracales) are usually eighteen in number in the horse,
but there are sometimes nineteen, rarely seventeen. As regional
characters we note the surfaces for articulation with the ribs and the
length and form of the spinous processes. Those in the middle of the
series are the most typical and present the following features:
1. The =bodies= are short and constricted in the middle. The ends are
expanded and have articular surfaces which are not strongly curved. On
the upper part of each side are anterior and posterior =costal facets=
(Fovea costalis cranialis, caudalis), which, with those of adjacent
vertebræ, form sockets for the heads of the ribs.
2. The =arches= are small. Their posterior notches are relatively large
and are often converted into foramina.
[Illustration:
FIG. 13.—THIRD, FOURTH, AND FIFTH THORACIC VERTEBRÆ OF HORSE, LATERAL
VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
3. The =articular processes= are small. The anterior pair are in fact
represented only by two oval facets on the anterior part of the laminæ
which face almost directly upward. The posterior pair spring from the
base of the spinous process; their facets face almost directly downward.
4. The =transverse processes= are short, thick, and tuberous at the free
end. Each has a =facet= (Fovea transversaria) for articulation with the
tuberosity of the rib which has the same serial number.
5. The =spinous process= is large, narrow, and slopes upward and
backward. The anterior border is thin, the posterior wider and furrowed.
The summit is expanded and rough.
The =first thoracic vertebra= is easily recognized by the following
specific characters: The body is wide and flattened dorso-ventrally. In
front it has a head like the cervical vertebræ, and behind a cavity
somewhat deeper than any other thoracic vertebra. Two =costal facets=
are found on either side, and a well-marked spine ventrally. The =arch=
is large and strong, and has large notches. The =articular processes=
are much larger than those of other thoracic vertebræ, and resemble a
good deal those of the seventh cervical in form. The =transverse
processes= are short and thick, and each has on its ventral aspect a
large concave facet for articulation with the tubercle of the first rib.
The spinous process is curved backward and tapers to a point. Its length
is usually about three or four inches (ca. 8 to 10 cm.). It may be
mistaken at first glance for the last cervical, but is promptly
identified by the three costal facets on each side and the length of the
spine.
The =last thoracic vertebra= is distinguished by the absence of the
posterior pair of costal facets, and the confluence of the anterior pair
with those on the transverse processes.
[Illustration:
FIG. 14.—THIRD THORACIC VERTEBRÆ AND UPPER PART OF RIB OF HORSE,
ANTERIOR VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 15.—LOWER PART OF NINTH THORACIC VERTEBRA OF HORSE, POSTERIOR
VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The serial position of others may be determined at least approximately
by the following data: (1) The bodies gradually diminish in length and
width to the middle of the region and then increase slightly. Their
costal facets become smaller and less concave from first to last. The
ventral crest is distinct on three or four vertebræ at either end of the
region. (2) The transverse processes diminish in size and are placed
lower down as they are traced backward. Their costal facets become
smaller and lower in position; on the last (and sometimes on its
predecessor also) it fuses with the costal facet of the body. The upper
non-articular part of the process gradually becomes more sharply
defined, and in the last four or five separates to form the =mammillary
process=. (3) The spinous processes increase in length to the third and
fourth, and then gradually diminish to the fifteenth, beyond which they
have about the same length. The backward inclination is most pronounced
in the second, the sixteenth is vertical, and the last two are directed
a little forward. The longest spines (_i. e._, those of the withers) are
the thickest and have expanded summits which remain more or less
cartilaginous; the others are more plate-like, and are surmounted by a
thick lip. The second spine is more than twice as large as the first.
The summits of the fourth and fifth usually form the highest point of
the withers.
=Development.=—There are =six= or =seven centers=, three for the body,
two for the arch, and one for the spinous process; some of the latter
have an additional center for the summit.
THE LUMBAR VERTEBRÆ
The =lumbar vertebræ= (Vertebræ lumbales) are usually six in number in
the horse. They are characterized by the size and form of their
transverse processes.
The =bodies= of the first three are triangular on cross-section, and
present a distinct ventral crest. From the fourth backward they become
wider and flatter and the ventral crest fades out.
[Illustration:
FIG. 16.—FIRST THORACIC VERTEBRA AND UPPER PART OF FIRST RIB OF HORSE,
ANTERIOR VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =arches= of the first two or three are about equal in size and
similar to that of the last thoracic; from the fourth they decrease
noticeably in breadth and height.
[Illustration:
FIG. 17.—LAST TWO THORACIC AND FIRST LUMBAR VERTEBRÆ OF HORSE, LATERAL
VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =anterior articular processes= are fused with the mammillary
processes, and present superiorly concave surfaces for articulation with
the posterior pair of the preceding vertebra. The =posterior articular
processes= project distinctly from the arch at the base of the spinous
process, and have ventrally convex articular surfaces, which fit into
the grooved surfaces of the anterior pair of the next vertebra.
The =transverse processes= are large plates, flattened dorso-ventrally,
which project outward and usually curve slightly downward; their length
increases to the third and fourth, and then diminishes to the last,
which is the shortest. The first one or two usually curve somewhat
backward, the last two decidedly forward. Those of the fifth have an
oval concave facet on the inner part of the posterior border for
articulation with the sixth process; the latter has a corresponding
convex facet on the anterior border, and a larger concave surface on the
posterior border for articulation with the wing of the sacrum. Sometimes
the fifth process has a small surface for articulation with the fourth.
The inner part of the sixth process is thick, the outer part thinner,
narrower, and curved forward. The inner part of the fifth is also
somewhat thickened.
The =spinous processes= resemble those of the last two thoracic
vertebræ. They are usually about equal in height, but minor differences
are common, and the width diminishes in the last three.
=Development.=—This is similar to that of the thoracic vertebræ. The
extremities of the transverse processes remain cartilaginous for some
time after ossification is otherwise complete.
[Illustration:
FIG. 18.—SECOND LUMBAR VERTEBRA OF HORSE, ANTERIOR VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The transverse processes of this region are considered equivalent to
the proper transverse process + the costal element, and hence the
distinctive term processus lateralis (s. costarius) has been proposed.
The occurrence of a lumbar rib in connection with the transverse
process of the first lumbar is not rare. Reduction of the number to
five has been observed frequently, and may or may not be compensated
by an additional thoracic vertebra. This variation is not more common
in certain races as Sanson and others have maintained. Very few cases
are recorded of seven lumbar vertebræ—especially with the normal
thoracic number. An anomalous vertebra with mixed thoracic and lumbar
characters sometimes occurs at the junction of the two regions.
THE SACRUM
The =sacrum= (Os sacrum) is formed by the fusion of five vertebræ
usually, and is conveniently described as a single bone. It is
triangular in form and is wedged in between the ilia, with which it
articulates very firmly on each side. Its long axis is gently curved,
and slightly oblique, so that the posterior end is a little higher than
the anterior. It presents two surfaces, two borders, a base, and an
apex.
The =dorsal surface= presents centrally the five sacral spines, which
are directed upward and backward, and have (with the exception of the
first) tuberous summits which are sometimes bifid.
The first spine is relatively thin and narrow, and is not so high as
the internal angle of the ilium. The second is the longest, and the
height diminishes rapidly to the last. The bases of the spines are
often fused in old subjects.
On either side of the spines is a groove, in which are the four =dorsal
sacral foramina= (Foramina sacralia dorsalia); the dorsal branches of
the sacral nerves emerge through them.
The =ventral= or =pelvic surface= (Facies pelvina) is concave in its
length, wide in front, narrow behind. It is marked by four more or less
distinct =transverse lines= (Linæ transversæ), which indicate the
demarcation of the bodies of the vertebræ. At the ends of these lines
are the =ventral sacral foramina= (Foramina sacralia ventralia), which
are larger than the dorsal series and diminish in size from first to
last; they transmit the ventral divisions of the sacral nerves.
The dorsal and ventral foramina communicate with the sacral canal and
are together equivalent to the usual intervertebral foramina.
[Illustration:
FIG. 19.—SACRUM OF HORSE, DORSO-LATERAL VIEW.
_C_, Body of first sacral vertebra; _A_, arch of first vertebra; _Cs_,
sacral canal; _P.s._ 1–5, sacral spines; _P.t._, wings of sacrum; 1,
1′, surfaces for articulation with transverse processes of last
lumbar vertebra; _F.a._, auricular surface; 2, 2′, articular
processes; 3–6, dorsal sacral foramina; 7, interarcuate space; 8,
lateral border; _h_, apex. (Struska, Anat. d. Haustiere.)
]
The =lateral borders= are rough, thick in front, thin behind.
The =base= (Basis ossis sacri) is directed forward, and is relatively
very wide. It presents centrally the =body= of the first sacral segment,
which is wide transversely, flattened dorso-ventrally, and has a rounded
surface which articulates with the last lumbar vertebra through the
medium of an intervertebral fibro-cartilage. The ventral margin projects
slightly, forming the =promontory= (Promontorium). Above the body is the
entrance to the sacral canal, flanked by a pair of =articular
processes=, which project upward and forward from the arch, and have
concave surfaces internally for articulation with those of the last
lumbar vertebra. On each side of these is a smooth notch which is
converted into a foramen by apposition with the last lumbar. The lateral
parts of the base, the =wings= or =alæ= (Alæ sacrales), are strong
prismatic masses with pointed ends, which result from the fusion of the
first with part of the second transverse process. Each has in front a
large, oval, slightly convex surface for articulation with the
transverse process of the last lumbar. Posteriorly there is an elongated
oval area which faces upward, backward, and outward. This is the
=auricular surface= (Facies auricularis), which articulates with the
ilium; it is slightly concave in its length, and somewhat rough and
irregular. The rest of the dorsal surface of the wing is roughened for
ligamentous attachment, while the ventral surface is smooth.
The =apex= (Apex ossis sacri) is the posterior aspect of the last sacral
vertebra and is quite small. It presents the elliptical flattened
surface of the body, above which is the triangular posterior opening of
the sacral canal, surmounted by the last sacral spine. There is a pair
of narrow notches between the arch and body, above which rudiments of
articular processes may occur.
The name =sacral canal= (Canalis sacralis) is applied to that part of
the vertebral canal which traverses the sacrum. Its anterior part is
large and has the form of a triangle with the angles rounded off; its
width is about twice its height. Traced backward it is seen to diminish
in size rapidly, and the posterior opening is quite small and
triangular.
The term =lateral part= (Pars lateralis) designates the portion external
to the foramina, which results from the fusion of the transverse
processes.
[Illustration:
FIG. 20.—FIRST COCCYGEAL VERTEBRA OF HORSE, LEFT VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 21.—FIRST COCCYGEAL VERTEBRA OF HORSE, DORSAL VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
=Development.=—The several sacral vertebræ ossify in the typical manner.
Separate centers for costal elements in the lateral parts have not yet
been found in the domesticated animals. Fusion begins in front, and is
usually not complete behind till near adult age. The lateral parts unite
before the bodies. It is rather curious that the epiphyseal plates of
adjacent segments unite with each other before they fuse with the main
portion of the bodies.
THE COCCYGEAL VERTEBRÆ
These (Vertebræ coccygeæ) vary considerably in number, but eighteen may
be taken as an average. From first to last they become reduced in size
and, with the exception of a few at the beginning of the series, consist
of bodies only. The first three have bodies which are somewhat flattened
dorso-ventrally, constricted in the middle, and have at the ends
slightly convex, elliptical, articular surfaces. The ventral surface has
a median groove for the coccygeal artery. The arch is small and
triangular; it is formed of two flat plates which are prolonged to form
a short spinous process with a thickened and often double summit. The
anterior notches are absent. Functional articular processes are not
present, but small rudiments of the anterior pair commonly occur. The
transverse processes are relatively large plates which project
horizontally outward. Further back the arch becomes incomplete, open
above, and soon disappears; the transverse processes gradually fade out,
and the vertebræ are reduced to cylindrical rods of diminishing size.
The last one has a pointed end.
=Variations.=—The number is said by good observers to vary between
fourteen and twenty-one. In old age the first is often fused with the
sacrum, and sometimes with the second. The arch of the third may be
open.
THE VERTEBRAL COLUMN AS A WHOLE
In the mid-dorsal line is the series of =spinous processes=, which are
low ridges in the cervical region with the exception of the second and
seventh, reach their maximum height at the fourth and fifth thoracic
vertebræ, and diminish to the fifteenth or sixteenth thoracic. Behind
this they are about equal in height as far as the last lumbar and first
sacral, which are somewhat lower. The second sacral spine is about as
high as the middle lumbar; behind this they diminish rather rapidly in
height and fade out about the third coccygeal. Their =inclination=
backward is most decided at the second thoracic, diminishes from the
sixth or seventh to the fifteenth or sixteenth, which is vertical and is
termed the =anticlinal= or =diaphragmatic vertebra.= Behind this they
are inclined a little forward until the sacrum is reached; here there is
an abrupt change to the backward inclination, so that a considerable
interspinous angle is formed.
On either side of the spinous processes is a =vertebral groove= which
contains the deep muscles of the spine. The floor of the groove is
formed by the laminæ and articular processes. It is wide in the neck and
narrows progressively in the back.
Viewed from the side, the column presents a series of curves. When the
head and neck are in the ordinary neutral position, the anterior part of
the cervical spine forms a gentle curve, concave ventrally. The
posterior cervical and first thoracic vertebræ form a more pronounced
curve in the opposite direction. At the junction of the cervical and
thoracic regions there is a marked change of direction, forming a
ventral projection or angle. At the second thoracic vertebra a gentle
curve, concave ventrally, begins. This is continued to the lumbo-sacral
junction, where there is a change of direction, and hence a promontory.
The sacrum has a variable, but never very pronounced, ventral concave
curvature, which is continued in a much accentuated form in the
coccygeal region. It may be remarked that a line through the summits of
the spines does not correspond to these curves formed by the bodies.
The =vertebral canal=, of course, corresponds in curvature to the
bodies. Its =caliber= varies greatly at different points. The greatest
diameter (ca. 5 cm.) is in the atlas, where it contains the dens of the
axis in addition to the spinal cord, and provision must be made for
extensive movement. It is very much smaller in the axis (ca. 2.5 cm.
wide, 3 cm. high). It widens considerably at the junction of the
cervical and thoracic regions to accommodate the cervical enlargement of
the spinal cord. Beyond this it diminishes, and is smaller in the middle
of the back than at any preceding point; this is correlated with the
small size of the spinal cord and the very limited movement of the
spine. At the middle of the lumbar region it again widens considerably
to contain the lumbar enlargement of the spinal cord. The caliber
diminishes very rapidly from the second sacral segment backward, and the
canal ceases to be complete at the fourth coccygeal vertebra.
The =articular processes= are very large and wide apart in the neck,
greatly reduced and much closer together in the back, larger and
interlocking in the lumbar region.
The =transverse processes= are large and outstanding in the neck, where
they form the outer boundary of a ventral groove occupied by the longus
colli muscle. In the back they are short and stout, and are
characterized by the facets for the tubercles of the ribs. On the first
thoracic vertebra this facet is large, deeply concave, and situated
almost directly outward from the cavity for the head of the rib; traced
backward it becomes smaller and flatter, and gradually comes to lie
behind the cavity for the head of the rib, with which it is fused on the
last and often also on the next to the last thoracic vertebra. The
processes in the lumbar region have a characteristic elongated
plate-like form. In the sacral region they are fused to form the wings
and lateral parts of the sacrum. In the coccygeal region they are at
first of considerable size relatively, but undergo rapid reduction, and
disappear at the fifth or sixth vertebra.
The cavities for the heads of the ribs diminish progressively in size
and depth from first to last.
The =mammillary processes= are usually distinct on the fourteenth to the
seventeenth thoracic vertebræ. In front of these they blend with the
transverse, behind with the anterior articular processes.
The length of the vertebral column (including the intervertebral
fibro-cartilages) in a horse of medium size is about 260 to 265 cm.
(ca. 8 feet 8 inches to 8 feet 10 inches). The relative lengths of the
various regions appear to vary most in the neck and back.
The table below gives the measurements in centimeters in a trotting
stallion of medium size and in an adult Percheron stallion. The
percentages are in round numbers.
─────────┬───────────┬───────────
│ TROTTER │ PERCHERON
─────────┼─────┬─────┼─────┬─────
Cervical │ 60.0│22.7%│ 74.0│25.4%
Thoracic │ 98.0│37.2%│100.0│34.4%
Lumbar │ 31.5│12.0%│ 36.5│12.5%
Sacral │ 20.0│ 7.6%│ 22.5│ 7.7%
Coccygeal│ 54.0│20.5%│ 58.0│20.0%
─────────┼─────┼─────┼─────┼─────
│263.5│100.0│291.0│100.0
─────────┴─────┴─────┴─────┴─────
THE RIBS
There are usually eighteen pairs of ribs in the horse, but a nineteenth
rib on one side or both is not at all rare. Eight are =sternal= or
“true” ribs, the remainder =asternal= or “false.” Ribs from different
parts of the series vary much in length, curvature, and other
characters. We will therefore consider as a type a rib from the middle
of the series first, and afterward note the chief serial differences. A
=typical rib= has the following characters:
The =shaft= or =body= (Corpus costæ) is elongated, relatively very
narrow, and strongly curved; the curvature is most pronounced in the
dorsal third, and the ventral part is twisted and inclined inward, so
that when a rib is laid with its outer surface on the table, the ventral
end is raised. The =external surface= is convex in its length and also
transversely; its anterior part is, however, grooved longitudinally. A
distinct angle, _i. e._, a point at which the curve of the rib changes
rather suddenly, as in man, can scarcely be said to exist in the horse.
The term is often applied, however, to a corresponding rough elevation
which gives attachment to the ilio-costalis muscle; it is most distinct
on the fourth to the eighth inclusive. The =internal surface= is smooth,
concave in its length, and rounded from side to side; the costal groove,
situated posteriorly, is very distinct above and fades out about the
middle. The =anterior border= is concave, the =posterior= convex.
The =vertebral extremity= (Extremitas vertebralis) consists of the head,
neck, and tubercle. The =head= (Capitulum costæ) has an articular
surface (Facies articularis capituli costæ), composed of two convex
facets, anterior and posterior, separated by a groove for the attachment
of the conjugal ligament. It articulates with the cavity formed by
facets on the bodies of two adjacent thoracic vertebræ and the
intervertebral fibro-cartilage. The _neck_ (Collum costæ) is roughened
above and in front. The =tubercle= (Tuberculum costæ) is placed above
and behind the junction of neck and shaft; it has a small surface
(Facies articularis tuberculi costæ) for articulation with the
transverse process of the corresponding thoracic vertebra.
The =sternal extremity= (Extremitas sternalis) is somewhat expanded, and
is continued by the costal cartilage.
The =first rib= is easily distinguished. It is the shortest and least
curved. At the lower part of the anterior border there is a smooth
impression where the brachial vein curves around it; above this is
usually the scalene tubercle. The costal groove is absent. The head is
large and has two facets of unequal extent which meet at an acute angle
in front; the smaller one faces forward and articulates with the last
cervical vertebra; the larger one is directed inward and articulates
with the first thoracic vertebra. The neck is thick and very short. The
tubercle is larger than that of any other rib and has an extensive
articular surface which is convex in its length. The sternal end is
larger than that of any other rib; it is thick and very wide, and is
turned a little forward.
[Illustration:
FIG. 22.—LEFT SEVENTH RIB OF HORSE, ANTERO-EXTERNAL VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =last rib= is the most slender and regularly curved. It is usually
but little longer than the second. The facet on the tubercle is
confluent with that of the head. (This feature, however, is usual on the
seventeenth also, and not rare on the sixteenth.)
The serial position of the other ribs may be determined approximately by
the following considerations: The =length= increases from the first to
the tenth and eleventh and then diminishes. The =width= increases
somewhat to the sixth and then diminishes. The =anterior border= is thin
and sharp from the second to the eighth, and behind this becomes thick
and rounded. The =external groove= is distinct on the fourth to the
eighth inclusive. The =curvature= increases in degree rapidly from the
first to the seventh, remains about the same to the sixteenth, and then
decreases very noticeably. In regard to dorso-ventral =direction=, the
first rib inclines a little forward, the second is about vertical, while
behind this they slope backward in increasing degree, so that a plane
tangent to the ventral ends of the last pair cuts the third lumbar
vertebra. The =head= and =tubercle= diminish in size from first to last.
Their relative positions change in that the tubercle of the first rib
lies almost directly outward from the head, while further back it
gradually comes to lie behind it. The =neck= is longest on the longest
ribs, and is absent on the last two or three. A costo-transverse foramen
is formed between the neck and the transverse process.
=Development.=—The ribs ossify in cartilage from =three centers=, one
each for the shaft, head, and tubercle; the third center is absent in
some of the posterior ribs.
=Variations.=—A nineteenth rib on one side or both is not rare. It is
usually imperfectly developed and quite variable. In some cases it is
a mere strip of cartilage connected by ligament with the first lumbar
transverse process; in other cases it is ossified, and may be fused
with the process; in others again it is connected with an additional
presacral vertebra which may be thoracic or lumbar or ambiguous in
character. It is commonly floating, but may be attached to the
eighteenth. Reduction in number is uncommon. Fusion of adjacent ribs
sometimes occurs.
THE COSTAL CARTILAGES
[Illustration:
FIG. 23.—STERNUM AND COSTAL CARTILAGES OF HORSE, VENTRAL VIEW. (After
Ellenberger-Baum, Anat. f. Künstler.)
]
The first costal cartilage is an inch or more (2.5 to 3 cm.) in length.
The upper part is very wide and thick. The sternal end is small. The two
articulate with each other as well as with the sternum. The cartilages
of the other sternal ribs increase progressively in length and become
more rounded. The sternal end is expanded and has an elliptical convex
facet for articulation with the sternum. The cartilages of the asternal
ribs are long, slender, and pointed. The ninth is the longest, and is
very firmly attached to the eighth; behind this they diminish
progressively in size, and are attached to each other by elastic tissue.
Except in the case of the first, the cartilage does not continue the
direction of the rib, but forms with the latter an angle which is open
in front, and decreases in obtuseness from second to last.
More or less extensive ossification is to be regarded as a normal
occurrence, especially in the cartilages of the sternal ribs.
THE STERNUM
The sternum of the horse is shaped somewhat like a canoe; it is
compressed laterally, except in its posterior part, which is flattened
dorso-ventrally. It is inclined obliquely so that the posterior end is
about six to eight inches (15 to 20 cm.) lower than the anterior.
The =dorsal surface= has the form of a very narrow isosceles triangle
with the apex in front. It is concave longitudinally, flattened
transversely.
The =lateral surfaces= are convex above, slightly concave below, and
diminish in extent behind. Each presents on its upper part seven
=articular cavities= (Foveæ costales), which receive the sternal ends of
the second to the eighth costal cartilages inclusive. These cavities are
situated in series at the intersternebral junctions. The first four are
elliptical in outline with the long diameter vertical, and are separated
by considerable regular intervals. The others are progressively smaller,
more circular, and closer together. The area below these cavities gives
attachment to the pectoral muscles.
[Illustration:
FIG. 24.—STERNUM OF HORSE, LATERAL VIEW.
The sternebræ are designated by Roman numerals and the costal facets
by ordinary figures.
]
The =dorso-lateral= borders separate the dorsal and lateral surfaces.
They give attachment to the lateral branches of the sternal ligament.
The =ventral border= forms the prominent keel-like crest of the sternum
(Crista sterni) which may be felt in the living animal; it fades out
behind.
[Illustration:
FIG. 25.—ANTERIOR APERTURE OF THORAX OF HORSE. (After Schmaltz, Atlas
d. Anat. d. Pferdes.)
]
The =anterior extremity= or =manubrium sterni=[5] can be distinctly felt
in the central furrow of the breast. It consists of a laterally
compressed cartilaginous prolongation, commonly called the =cariniform
cartilage=. Its lateral surfaces are flat and furnish attachment to
muscles of the breast and neck. The ventral border is rounded, and is
continued backward on the body of the bone. The dorsal border is concave
and has an articular cavity for the first pair of costal cartilages.
The =posterior extremity= is formed by the =xiphoid= or =ensiform
cartilage= (Processus xiphoideus). This is a thin plate, connected in
front with the last bony segment by a relatively thick, narrow neck, and
expanding in nearly circular form behind and laterally. Its dorsal
surface is concave, and gives attachment to the diaphragm. The ventral
surface is convex. The free margin is very thin.
=Development.=—At birth the sternum of the horse consists of seven bony
segments or sternebræ united by intersternebral cartilages. The last two
sternebræ fuse in the second month, but the others do not usually unite
completely even in old age. The sternebræ consist of very vascular
spongy bone covered by a very thin layer of compact substance. The adult
sternum thus consists to a very considerable extent of persisting
cartilage, viz., the intersternebral cartilages, the ventral keel, and
the extremities; in old age these undergo partial ossification.
THE THORAX
The bony thorax of the horse is remarkably compressed laterally in its
anterior part, but widens greatly behind. The =anterior aperture= is
oval and very narrow below; in a horse of medium size its greatest width
is about 4 inches (10 cm.), and its height 7 to 8 inches (ca. 18 to 20
cm.). The =ventral wall= or =floor= is about 10 inches (40 cm.) long,
and the =dorsal wall= or =roof= about 38 to 40 inches (95 to 100 cm.)
long. The height from the last segment of the sternum to the seventh or
eighth thoracic vertebra is about twice that of the anterior aperture;
this is due to the obliquity and divergence of the roof and floor. The
greatest width of the posterior aperture is about 20 to 24 inches (50 to
60 cm.). The intercostal spaces increase in width from the first to the
seventh or eighth, and then diminish. Their average width is about 1¼ to
1½ inches (3 to 3.5 cm.).
THE BONES OF THE SKULL
(A) BONES OF THE CRANIUM
The bones of the cranium (Ossa cranii) are the Occipital, Sphenoid,
Ethmoid, Interparietal, Parietal, Frontal, and Temporal. The first four
are single, the others paired.
[Illustration:
FIG. 26.—SKULL, ATLAS, AND AXIS OF HORSE, LATERAL VIEW.
8, Body of mandible; 28′, horizontal (molar) part of ramus; 30,
vertical part of ramus; 9, zygomatic process of squamous temporal;
11, coronoid process of mandible; 12, supraorbital process; 13″,
paramastoid (styloid) process of occipital; 19, orbit; 20, malar
bone; 21, lacrimal bone; 22, nasal bone; 23, premaxilla; 23′, nasal
process of premaxilla; 25, 29, canine teeth; 26, maxilla; 27, facial
crest; 31, condyle of mandible; 32, atlas; 33, axis; x, wing of
atlas; e, naso-maxillary notch. (After Ellenberger-Baum, Anat. für
Künstler.)
]
THE OCCIPITAL BONE
The =occipital bone= (Os occipitale) is situated at the posterior part
of the cranium, of which it forms the posterior wall and part of the
ventral wall or base.[6]
Its lower part is perforated centrally by a large, almost circular
opening, the =foramen magnum= (Foramen occipitale magnum), at which the
brain and spinal cord join. The foramen is bounded laterally and
dorsally by the =lateral parts= of the bone, and ventrally by the
=basilar part= or =process=. Above the lateral parts—but not entering
into the formation of the foramen magnum—is the =squamous part=.
[Illustration:
FIG. 27.—LINE DRAWING OF POSTERIOR HALF OF BASE OF SKULL OF HORSE,
WITHOUT MANDIBLE. (Key to Fig. 28.)
1, Incisura carotica; 2, incisura ovalis; 3, incisura spinosa; 4,
external orifice of parieto-temporal canal; 5, Eustachian canal; 6,
petro-tympanic fissure; 7, external auditory canal; 8, hyoid
process; 9, Vidian groove; 10, supraorbital process; _A_, basilar
part of occipital; _B_, body of sphenoid; _C_, temporal wing of
sphenoid; _D_, squamous temporal bone; _E_, petrous temporal bone;
_F_, orbital part of frontal bone.
]
The =lateral parts= (Partes laterales) bear the =occipital condyles=
(Condyli occipitales), which articulate with the atlas. The condyles are
obliquely placed, wide apart dorsally, and separated by a small interval
ventrally. The articular surface is curved so sharply in the
dorso-ventral direction as to form a blunt ridge externally. The cranial
surface is concave and smooth. External to the condyle is the
=paramastoid= or =styloid process= (Processus jugularis), a strong
flattened bar of bone which projects downward and backward; its external
surface is convex and roughened for muscular attachment. Between the
root of this process and the condyle is a smooth depression, the
=condyloid fossa= (Fossa condyloidea inferior); in this is the
=hypoglossal foramen= (Foramen hypoglossi), which transmits the nerve of
like name.
The =basilar part= or =process= (Pars basilaris) is a strong, somewhat
prismatic bar which extends forward from the ventral margin of the
foramen magnum. It is much narrower in front than behind. The ventral
surface is rounded. The cranial surface is concave and smooth; its
posterior part, supports the medulla, and its anterior part has a
shallow cavity on which the pons rests. The lateral borders are thin and
sharp, and form the inner margin of the =foramen lacerum= (Foramen
lacerum et jugulare). The anterior end has, in the young subject, a
semicircular, flat, pitted surface which is attached to the body of the
sphenoid bone by a layer of cartilage; in the adult there is complete
fusion. On the ventral aspect of the junction are tubercles for the
attachment of the ventral straight muscles of the head.
[Illustration:
FIG. 28.—VENTRAL SURFACE OF SKULL OF HORSE, POSTERIOR HALF WITHOUT
MANDIBLE.
The skull is inclined slightly. (Notation on key Fig. 27.)
]
The =squamous part= (Squama occipitalis) is the somewhat quadrilateral
mass situated above the lateral portions, from which it remains distinct
till the second year. The =outer surface= is crossed by a very prominent
ridge, the =occipital crest=; the middle part of this is thick,
transverse in direction, and forms the highest point of the skull when
the head is in the ordinary position; laterally it becomes thinner and
runs downward and forward to join the temporal crest.[7] The crest
divides the surface into two very unequal parts; the small anterior area
(Planum parietale) presents a median ridge which is the posterior part
of the external sagittal crest; the large area below the crest (Planum
nuchale) also has a central eminence, the =external occipital
protuberance=, on the sides of which the funicular part of the
ligamentum nuchæ is attached. The =internal surface= is concave and
presents a deep central depression and two shallower lateral ones which
adapt it to the surface of the cerebellum.
The occipital bone is connected by suture with the interparietal, two
parietals, and two temporals, and by synchondrosis with the sphenoid;
the condyles articulate with the atlas.
=Development.=—The occipital ossifies in cartilage from =four centers=,
and consists at birth of four pieces as described above.[8] The lateral
parts unite with the basilar at three to four months, and with the
squama in the second year, when the bone is consolidated.
The parieto-occipital suture and the spheno-occipital synchondrosis are
obliterated about the fifth year usually. The temporo-occipital suture
partially ossifies in old subjects.
THE SPHENOID BONE
The =sphenoid bone= (Os sphenoidale) is situated in the base of the
cranium, its central part lying in front of the basilar part of the
occipital. It consists of a central part, the body, two pairs of wings,
and two pterygoid processes.
The =body= (Corpus) is a cylindrical bar, flattened dorso-ventrally, and
wider in front than behind. Its =ventral surface= (Facies externa) is
convex in the transverse direction; and its anterior part is concealed
to a large extent by the vomer and pterygoid bones. The =cerebral
surface= (Facies cerebralis) presents the following features: (1) In
front is a raised, flattened part which is subdivided by a median
elevation into two slightly concave lateral areas; this part has a
posterior, thin, free margin (Limbus sphenoidalis), which overlies the
entrance to the optic foramina. (2) Just behind this and at a lower
level is a smooth transverse depression, the =optic groove= (Sulcus
chiasmatis), on which the optic chiasma rests. (3) From each end of this
groove the =optic foramen= passes forward and outward to terminate in
the posterior part of the orbital fossa.[9] (4) Near the posterior end
is a central depression, the =hypophyseal= or =pituitary fossa= (Fossa
hypophysea), which lodges the hypophysis cerebri or pituitary body. On
each side of this is an ill-defined groove for the internal carotid
artery and the cavernous sinus. The =anterior end= is expanded, and is
excavated to form the =sphenoidal sinuses.= These cavities extend back
as far as the optic groove, and are usually continuous in front with the
cavities in the vertical parts of the palate bones; they are separated
by a complete septum which is not always median.[10] The =posterior end=
is flat and is joined to the basilar part of the occipital; at the line
of junction there is dorsally a transverse elevation, the
=spheno-occipital= crest (Crista sphenooccipitalis).
The =orbital wings= (Alæ orbitales) curve upward and somewhat outward
from the sides of the body of the presphenoid. Their =inner= or
=cerebral surfaces= are concave, and are marked by =digital impressions=
(Impressiones digitatæ) for the gyri of the cerebrum. The =external
surface= is convex and is largely concealed by the overlapping temporal
wing and the squamous temporal and frontal bones; a narrow part of it
(Facies orbitalis) is uncovered on the inner wail of the orbital cavity
at the sphenoidal notch of the frontal bone. The =dorsal border= unites
with the frontal bone at the spheno-frontal suture. The =anterior
border= joins the ethmoid at the spheno-ethmoidal suture; at its lower
part it concurs with the frontal in the formation of the =ethmoidal= (or
internal orbital) =foramen=. The =posterior border= is overlapped by the
temporal wing and the squamous temporal. The =root= of the wing is
perforated by the =optic foramen=. Immediately below and behind the
latter (_i. e._, beneath the root) is the =foramen lacerum orbitale= or
=orbital fissure=. Below this, and separated from it usually by a thin
plate, is a larger opening, the =foramen rotundum=, which is bounded
externally by the root of the pterygoid process. Behind these foramina
is the =pterygoid crest= (Crista pterygoidea), which is continued
downward and forward on the pterygoid process; on its upper part may be
found the small and inconstant =trochlear= (or pathetic) =foramen=. Just
behind the crest is the =temporal foramen= (For. alare parvum), through
which the anterior deep temporal artery emerges from the alar canal of
the pterygoid process.
The =temporal wings= (Alæ temporales) extend outward and somewhat upward
from the body of the postsphenoid; they are irregularly quadrilateral in
outline. The =external surface= (Facies temporalis) enters into the
formation of the infratemporal fossa, and bears the pterygoid process on
its anterior part; at the junction with the body there is a small groove
for the pterygoid nerve. The =internal surface= (Facies cerebralis)
presents, at the junction with the body, two longitudinal =grooves=
(Sulci nervorum). The outer groove is the larger, and leads forward to
the foramen rotundum; it contains the maxillary nerve. The inner groove
conducts to the orbital fissure, and contains the third, sixth, and
ophthalmic nerves. The outer groove is bounded externally by a thin
overhanging crest, on which is a small groove for the fourth nerve. The
remainder of the surface is concave and supports the pyriform lobe of
the brain. The =dorsal border= joins the squamous temporal at the
spheno-squamous suture. The =anterior border= joins the orbital wing.
The =posterior border= forms the anterior boundary of the foramen
lacerum; it presents =three notches=, which are (from within outward)
the carotid, oval, and spinous (Incisura carotica, ovalis, spinosa). The
angle of junction of the dorsal and posterior borders articulates with
the parietal bone.
The =pterygoid processes= (Processus pterygoidei) arise from the
temporal wings and the body. They project downward and forward, and
curve outward at the lower part. The root is perforated by the =alar
canal= (Canalis alaris),[11] which transmits the internal maxillary
artery. From this canal a branch leads upward and forward to open at the
temporal foramen. The =external surface= is concave, and is marked by
lines for muscular attachment. The =internal surface= is largely
concealed by the overlapping palate and pterygoid bones, with which it
concurs in the formation of the =pterygoid= or =Vidian canal=.
=Development.=—The sphenoid is ossified in cartilage, and consists in
early life of two distinct parts, the presphenoid and postsphenoid. The
former develops from two centers, one in each wing; the latter has three
centers, one for the body and one for each wing. The pterygoid processes
ossify from the centers of the temporal wings.
=Variation.=—The dorsal border of the orbital wing may come to the
surface through a defect in the frontal bone at the place where the
horn process is situated in animals which have frontal horns.
THE ETHMOID BONE
The =ethmoid= (Os ethmoidale) is situated in front of the body and
orbital wings of the sphenoid. It projects forward between the orbital
plates of the frontal bones and enters into the formation of the
cranial, nasal, and paranasal cavities.[12] It consists of four
parts—the cribriform plate, two lateral masses, and the perpendicular
plate.
The =cribriform plate= (Lamina cribrosa) is a sieve-like partition
between the cranial and nasal cavities. Its margin joins the orbital
wings of the sphenoid laterally, and the cranial plate of the frontal
bones dorsally. Its =cranial surface= is divided into two parts by a
median ridge, the =crista galli=, which is the intracranial portion of
the perpendicular plate. Each half forms a deep oval cavity, the
=ethmoidal= or =olfactory fossa=, which lodges the olfactory bulb. The
plate is perforated by numerous small foramina for the passage of the
olfactory nerve filaments, and on either side is the much larger
=ethmoidal foramen.= The =nasal surface= is convex, and has the lateral
masses attached to it.
The =lateral masses= or =labyrinth= project forward from the cribriform
plate into the posterior part of the nasal cavity, which they nearly
fill. Each mass is somewhat conical in shape, with the base attached to
half of the cribriform plate. The =inner surface= is separated by a
narrow space from the perpendicular plate. The =outer surface= is convex
and faces chiefly into the frontal and maxillary sinuses, but is
attached behind to the inner wall of the orbital cavity; it is covered
by a very thin layer of bone, the =lamina papyracea.= The mass consists
of a large number of delicate, scroll-like plates of bone, termed
=ethmoturbinals= or =ethmoidal cells.= These are attached to the lamina
papyracea, and are separated by narrow intervals termed =ethmoidal
meatuses=, which communicate with the nasal cavity. In the living animal
the ethmoturbinals are covered with mucous membrane.
[Illustration:
FIG. 29.—CROSS-SECTION OF LATERAL MASS OF ETHMOID BONE OF HORSE.
]
The lateral mass is a very complex structure, the arrangement of which
may be studied on cross-sections of decalcified specimens with the
mucous membrane retained. Each mass consists of six turbinals which
extend almost to the perpendicular plate and are termed
=endoturbinals=. These diminish in size from above downward; the
largest is attached to the nasal bone, and is hence usually called the
naso-turbinal or superior turbinal; the second is much smaller, and is
very commonly termed the great ethmoid cell. Between the endoturbinals
are twenty-one small =ecto=turbinals, and all are beset with secondary
and tertiary coiled lamellæ.
The =perpendicular plate= or =mesethmoid= (Lamina perpendicularis) is
median, and forms the posterior part of the septum nasi. Its =lateral
surfaces= are nearly plane, but are marked below by some grooves and
ridges; they are covered by the nasal mucous membrane. The =anterior
border= is irregular and is continuous with the septal cartilage. The
=posterior border= projects into the cranial cavity as a ridge, the
=crista galli.= The =dorsal border= joins the frontal bones at their
line of junction—the frontal suture. The =ventral border= is received
into the groove of the vomer.
=Development.=—The ethmoid develops in cartilage from five centers, two
for each lateral mass, and one for the perpendicular plate; from the
latter ossification extends into the cribriform plate. At birth the
perpendicular and cribriform plates are entirely cartilaginous. By the
time ossification is complete the ethmoid has united with surrounding
bones to such an extent that it cannot be separated intact for study.
[Illustration:
FIG. 30.—SKULL OF HORSE, DORSAL VIEW.
12, Supraorbital process; 14, parietal bone; 14′, external sagittal
crest; 15, frontal bone; 15′, frontal crest; 21, lacrimal bone; 22,
nasal bone; 26, maxilla; 24, incisor teeth. (After Ellenberger-Baum,
Anat. für Künstler.)
]
THE INTERPARIETAL BONE
This bone (Os interparietale) is centrally placed between the squamous
part of the occipital and the parietal bones. It is usually described as
a single bone, although it ossifies from two chief lateral centers, and
is sometimes distinctly paired in skulls of young foals.
The =external surface= (Facies externa) is quadrilateral and is flat and
smooth in the very young foal; later it presents the median external
sagittal crest.
The =internal surface= (Facies cerebralis) presents the =internal
occipital protuberance=, a three-sided process which projects downward
and forward into the cranial cavity between the cerebral hemispheres and
the cerebellum; it has three concave surfaces and three sharp borders
which form part of the tentorium osseum.
The =posterior border= is thick; it joins the squamous part of the
occipital bone. The =lateral= and =anterior borders= are united by
suture with the parietal bones.
=Development.=—The interparietal ossifies in membrane from two chief
lateral centers.[13] It fuses first with the parietals, somewhat later
with the occipital, but the period at which this union takes place is
quite variable.
THE PARIETAL BONES
The two =parietal bones= (Ossa parietalia) form the greater part of the
roof of the cranium; they unite in the median line, forming the
=sagittal suture=. Each is quadrilateral in outline and has two surfaces
and four borders.
The =external surface= (Facies parietalis) is convex, and is marked by a
more or less prominent curved line, the =external sagittal crest=; this
is median in its posterior part, and is continuous with the crest of
like name on the occipital bone; in front it curves outward and is
continuous with the frontal crest. The surface external to the crest
(Planum temporale) enters into the formation of the temporal fossa, and
is roughened for the attachment of the temporal muscle.
The =internal= or =cerebral surface= (Facies cerebralis) is concave. It
presents numerous =digital impressions= (Impressiones digitatæ) which
correspond to the gyri of the cerebrum. There are also furrows (Sulci
vasculosi) for the meningeal arteries. Along the inner border there is a
=sagittal groove= (Sulcus sagittalis) for the superior longitudinal
sinus.
The =anterior border= joins the frontal bone at the =parieto-frontal
suture= (Sutura coronalis).
The =posterior border= meets the occipital bone at the
=parieto-occipital suture= (Sutura lambdoidea). Below this junction it
curves inward and concurs with the temporal bone in the formation of the
=parieto-temporal canal= (Meatus temporalis). A =transverse groove=
(Sulcus transversus) connects this canal with the sagittal sulcus.
The =internal border= is thick and serrated. It joins its fellow at the
=sagittal suture=, and (in the young subject) meets the interparietal at
the =interparietal suture=. The line of junction is marked internally by
the =internal sagittal crest= (Crista sagittalis interna).
The =external border= is beveled and is overlapped by the squamous
temporal bone, forming the parieto-temporal suture (Sutura
parieto-squamosa). The angle of junction of the external and posterior
borders articulates with the posterior angle of the temporal wing of the
sphenoid.
=Development.=—Each parietal bone ossifies in membrane from a single
center. In the young foal the central part of the bone is much more
convex than in the adult and forms a prominence similar to the
pronounced tuber parietale of the young child; the external sagittal
crest is not present, and the external surface is smooth.
The sagittal suture is usually closed at four years, the
parieto-occipital at five years, and the parieto-temporal at twelve to
fifteen years.
THE FRONTAL BONES
The =frontal bones= (Ossa frontalia) are situated on the limits of the
cranium and face, between the parietals behind and the nasal bones in
front. Each is irregularly quadrilateral, and consists of frontal,
orbital, and temporal parts.
The =frontal part= (Pars naso-frontalis) forms the basis of the
forehead. Its =external surface= (Facies frontalis) is nearly flat, and
is smooth and subcutaneous; it is separated from the temporal part by
the external frontal crest (Crista frontalis externa). At the junction
with the orbital part the =supraorbital= or =zygomatic process= (Proc.
zygomaticus) curves outward and downward to join the zygomatic arch. The
process partially separates the orbit from the temporal fossa; its root
is perforated by the =supraorbital foramen=, or presents instead a notch
on its anterior border; its upper surface is convex, while the lower or
orbital surface is concave and smooth, forming a shallow fossa for the
lacrimal gland (Fossa glandulæ lacrimalis). The =internal surface=
enters into the formation of the cranial cavity and the frontal sinus.
The cranial surface presents digital impressions for the cerebral gyri.
The two plates of the bone separate and diverge in front, and thus
inclose a large air-space which is part of the =frontal sinus=. The
cranial plate curves downward and articulates with the cribriform plate
of the ethmoid bone; the facial plate extends forward and joins the
nasal and lacrimal bones.
The =orbital part= (Pars orbitalis) forms the major part of the inner
wall of the orbital cavity. It is separated from the frontal part by a
prominent ridge which is part of the orbital margin. Its =external= or
=orbital surface= is concave and smooth, and presents superiorly a small
depression (Fovea trochlearis), which is bridged by a small bar of
cartilage, around which the superior oblique muscle of the eye is
reflected. The lower border concurs with the orbital wing of the
sphenoid in the formation of the ethmoidal or internal orbital foramen.
The =internal surface= faces into the frontal sinus and gives attachment
to the lateral mass of the ethmoid.
The =temporal part= is separated from the orbital part by the deep
=sphenoidal notch= (Incisura sphenoidalis), which is occupied by the
orbital wing of the sphenoid. Its =external surface= forms part of the
inner wall of the temporal fossa. The =internal surface= is largely
covered by the orbital wing of the sphenoid in the young subject, but
later forms part of the wall of the frontal sinus.
The principal connections of the frontal bone are as follows: (1) The
inner border joins its fellow at the =frontal suture=. (2) The
anterior border meets the nasal and lacrimal at the =naso-frontal= and
=fronto-lacrimal sutures=. (3) Laterally it forms the =spheno-frontal=
suture with the orbital wing of the sphenoid, and also joins the
palate bone and maxilla. (4) Posteriorly it meets the parietal at the
=parieto-frontal= (or coronal) =suture=, and articulates below this
with the squamous temporal. (5) The extremity of the supraorbital
process unites with the zygomatic process of the temporal bone.
=Development.=—Each ossifies in membrane from one center which appears
in the root of the supraorbital process. In the new-born foal there is a
slit between the cranial plate and the orbital and temporal plates which
receives the cartilaginous margin of the orbital wing of the sphenoid.
THE TEMPORAL BONES
The =temporal bone= (Os temporale) forms the greater part of the lateral
wall of the cranium. It is situated between the occipital behind, the
parietal above, the frontal in front, and the sphenoid below. It
consists of two distinct parts, =squamous= and =petrous=.
1. The =squamous temporal= (Squama temporalis) is a shell-like plate
which has two surfaces and four borders.
The =internal surface= (Facies cerebralis) is largely overlapped by the
surrounding bones, but its central part is free and presents digital
impressions and vascular grooves.
The =external surface= (Facies temporalis) is convex, and enters into
the formation of the temporal fossa. From its lower part there springs
the =zygomatic process= (Processus zygomaticus), which forms the
external boundary of the temporal fossa. It is at first directed
outward, and is wide and flattened dorso-ventrally. It then turns
forward, becomes narrower, and is twisted so that its surfaces are
internal and external. Its anterior end is pointed and joins the
zygomatic process of the malar bone, with which it forms the =zygomatic
arch= (Arcus zygomaticus). The narrow anterior part has a convex outer
surface and a concave inner one. Its upper border has a rough area for
articulation with the supraorbital process of the frontal. Its lower
border is wide and rough. The wide posterior part presents on its
ventral face a surface for articulation with the condyle of the
mandible. This surface consists of a transversely elongated =condyle=
(Tuberculum articulare), behind which is the =glenoid fossa= (Fossa
mandibularis). The fossa is limited behind by the =postglenoid process=,
the anterior surface of which is articular. Behind this process is a
fossa in which is the external opening of the parieto-temporal canal.
The dorsal surface is concave and forms the outer boundary of the
temporal fossa. The superior border is sinuous and is continuous behind
with the temporal crest.
The =posterior process= (Processus posterior) springs from the posterior
part of the squama. Its external surface is crossed by the temporal
crest, which forms here the outer limit of the temporal fossa. The
internal surface forms the outer boundary of the parieto-temporal canal,
and is elsewhere applied to the petrous portion. It divides into two
branches, upper and lower; the upper branch unites with the occipital
bone, while the lower one curves downward behind the external auditory
process and overlaps the mastoid process.
The =superior border= of the squamous temporal articulates with the
parietal, forming the =parieto-temporal suture=. The =inferior border=
joins the temporal wing of the sphenoid at the =spheno-squamous suture=.
The =anterior border= unites with the frontal bone, and the =posterior=
with the parietal.
2. The =petrous temporal= (Os petrosum) is placed between the occipital
behind and the parietal in front, and is largely overlapped externally
by the squamous temporal. It has the form of a four-sided pyramid, the
base of which is ventral.
The =external surface= is mainly concealed by the squamous temporal, but
two features are visible. A short tube of bone, the =external auditory
process=, protrudes from the lowest part through the notch of the
squamous temporal. The process is directed outward, upward, and a little
forward. It gives attachment to the annular cartilage of the ear. Its
lumen, the =external auditory meatus= (Meatus acusticus externus),
conducts to the cavity of the middle ear (tympanum) in the dry skull,
but is separated from it by the tympanic membrane in the natural state.
The =mastoid process= projects ventrally in the interval between the
posterior process of the squamous temporal and the root of the
paramastoid (or styloid) process of the occipital bone; its outer
surface is crossed by a curved groove which leads to the
parieto-temporal canal.
The =internal surface= faces into the cerebellar fossa of the cranium.
It is concave and smooth but irregular. In its lower part is the
entrance to a short canal, the =internal auditory meatus=, which
transmits the seventh and eighth cranial nerves.
The fundus of the meatus is divided by a crest into a superior and an
inferior fossa. In the superior one is the origin of the =facial
canal=, which curves through the bone and opens externally at the
stylo-mastoid foramen; it transmits the facial (seventh cranial)
nerve. The inferior fossa presents small foramina for the passage of
fibers of the auditory (eighth cranial) nerve.
Behind the meatus and near the posterior margin of the surface is the
slit-like opening of the aquæductus vestibuli, covered by a scale of
bone. Below this is a narrow fissure, the orifice of the aquæductus
cochleæ.
The =anterior surface= looks upward and forward. The outer part
articulates with the parietal bone and the inner part faces into the
cerebral fossa of the cranium. A sharp border, the =petrosal crest=
(Crista petrosa), separates this surface from the inner one.
The =posterior surface= joins the lateral part of the occipital bone.
The =base forms= the outer boundary of the foramen lacerum basis cranii.
It is very irregular and presents a number of important features. The
=hyoid process= is a short rod which projects downward and forward below
the base of the external auditory process, inclosed in a bony tube; it
is connected by a bar of cartilage with the hyoid bone. The
=stylo-mastoid foramen= is situated between the root of the hyoid
process and the mastoid process; it is the external opening of the
facial canal, through which the facial nerve emerges. The =bulla ossea=
is a considerable eminence situated centrally; it is thin-walled and
incloses a cavity which is part of the tympanum. The =muscular
process=[14] is a sharp spine which projects downward and forward from
the anterior part of the base; it gives origin to the tensor and levator
palati muscles. External to the root of the preceding is the small
=petro-tympanic= or =Glaserian fissure= (Fissura petro-tympanica) for
the passage of the chorda tympani nerve. The osseous =Eustachian tube=
is a semicanal at the inner side of the root of the muscular process; it
leads to the tympanum. At the inner side of the preceding is the
slit-like orifice of the petrosal canal, which communicates with the
facial canal.
The =apex= projects upward and backward between the squamous temporal
and the occipital bone.
=Development.=—The petrous temporal may be regarded as consisting of
petro-mastoid and tympanic parts. The latter includes the external
auditory process, the bulla ossea, and the muscular process; it is
developed in membrane. The petro-mastoid is developed in the
cartilaginous ear capsule. Its petrous part consists of very dense bone
which contains the labyrinth or internal ear and forms the inner wall of
the tympanum.
The =parieto-temporal canal= (Meatus temporalis) is a continuation of
the transverse groove which extends outward from the base of the
tentorium osseum. It is directed downward, forward, and somewhat
outward, and opens externally in front of the root of the auditory
process. It is bounded by the squamous temporal externally, the petrous
behind, and the parietal in front and internally. Several foramina open
from it into the temporal fossa. It contains a large vein (Vena
cerebralis dorsalis), the continuation of the transverse sinus of the
dura mater.
The =foramen lacerum basis cranii= (Foramen lacerum et jugulare) is a
large irregular opening in the cranial base, bounded internally by the
basilar part of the occipital bone, externally by the petrous temporal,
and in front by the temporal wing of the sphenoid. It consists of a
large anterior part (Foramen lacerum anterius), and a narrow posterior
part (Foramen lacerum posterius s. jugulare). It transmits the internal
carotid artery, the middle meningeal artery, the mandibular, ninth,
tenth, and eleventh cranial nerves, and the inferior cerebral vein.
In the fresh state the foramen is occupied by a dense fibrous membrane
which is perforated by apertures for the various structures
transmitted. Thus there are three openings in front for the internal
carotid artery, the mandibular nerve, and the middle meningeal artery;
these are (from within outward) the foramen caroticum, ovale,
spinosum.
(B) BONES OF THE FACE
The bones of the face (Ossa faciei) are the Maxilla, Premaxilla,
Palatine, Pterygoid, Nasal, Lacrimal, Malar, Superior Turbinal, Inferior
Turbinal, Vomer, Mandible, and Hyoid. The last three are single, the
others paired.
THE MAXILLAE
The =maxillæ= are the principal bones of the upper jaw and carry the
upper cheek teeth. They are situated on the lateral aspect of the face,
and articulate with almost all of the facial bones and the frontal and
temporal also. For description each may be divided into a body and two
processes.
The =body= (Corpus maxillæ) presents two surfaces, two borders, and two
extremities. The =external= or =facial surface= (Facies lateralis) is
somewhat concave in front and convex behind. On its posterior part is a
horizontal ridge, the =facial= or =zygomatic crest= (Crista facialis);
in a skull of medium size its anterior end is about an inch and a half
(3 to 4 cm.) above the third or fourth cheek tooth, and it is continued
behind by a corresponding ridge on the malar bone. About two inches (5
cm.) above and a little in front of the anterior end of the crest is the
=infraorbital foramen= (Foramen infraorbitale); this is the external
opening of the infraorbital canal.
In the young horse the anterior part of the surface is convex over the
embedded parts of the teeth. As the latter are extruded the surface
flattens and becomes concave in old subjects.
The =internal= or =nasal surface= (Facies nasalis) is concave
dorso-ventrally; it forms the greater part of the lateral wall of the
nasal cavity. Its upper part is crossed obliquely forward and downward
by the shallow =lacrimal groove= (Sulcus lacrimalis), which contains the
naso-lacrimal duct; in the adult the posterior part of the groove is
converted into a canal, which is continuous with that on the inner
surface of the lacrimal bone. Below the groove is the =inferior turbinal
crest= (Crista conchalis inferior), to which the inferior turbinal bone
is attached. Lower down and parallel with the turbinal crest is the
=palatine process=, which projects inward like a shelf. Behind this the
surface is rough for articulation with the palate bone; this area is
crossed by a groove which concurs with a furrow on the palate bone in
the formation of the =palatine canal=. The posterior part of the bone is
excavated to form part of the maxillary sinus.
The =superior border= is irregular and scaly. Its anterior part is
grooved and its posterior part beveled for articulation with the nasal
process of the premaxilla and the nasal and lacrimal bones.
The =inferior= or =alveolar border= (Processus alveolaris) is thick, and
presents six large cavities, the =alveoli=, for the cheek teeth. The
alveoli are separated by transverse =interalveolar septa=. There is
often a small alveolus for the first premolar (“wolf tooth”) close to
the first large one. Further forward the border is narrow and forms part
of the =interdental= or =interalveolar space= (Margo interalveolaris).
Behind the last alveolus is a rough area, the =alveolar tuberosity=.
The =anterior extremity= is pointed. It joins the premaxilla, and forms
with it the alveolus for the canine tooth.
The =posterior extremity= forms a rounded prominence, the =maxillary
tuberosity= (Tuber maxillare). Internal to the tuberosity is a deep
cavity, the maxillary hiatus, in which are three foramina. The upper
one, the =maxillary foramen=, leads into the infraorbital canal. The
lower one, the =posterior palatine foramen=, is the entrance to the
palatine canal. The =sphenopalatine foramen= perforates the inner wall
of the hiatus and opens into the nasal cavity.
The =zygomatic= or =temporal process= (Processus temporalis) projects
backward above and external to the tuberosity; it is overlapped by the
corresponding part of the malar and also articulates with the zygomatic
process of the temporal. A small curved plate extends inward from it and
joins the frontal and palate bones, forming part of the floor of the
orbit.
The =palatine process= (Processus palatinus) is a plate which projects
horizontally inward from the lower part of the inner surface of the
body. It forms the greater part of the basis of the hard palate. Its
=superior= or =nasal surface= is smooth and concave transversely; on its
anterior part, close to the inner border, is a shallow groove in which
the organ of Jacobson is situated. The inferior or =palatine surface= is
slightly concave from side to side, and presents along its outer part
the =palatine groove= (Sulcus palatinus). The groove is a continuation
of the palatine canal, and contains the palatine artery and nerve. The
=internal border= unites with its fellow to form the median palatine
suture; its nasal aspect bears the nasal crest, which forms, with that
of the opposite process, a groove for the vomer. The =posterior border=
unites with the horizontal part of the palate bone at the transverse
palatine suture.
[Illustration:
FIG. 31.—UPPER JAW OF HORSE ABOUT FOUR AND A HALF YEARS OLD, VENTRAL
VIEW.
1, 1, Posterior nares; 2, vomer; 3, horizontal part of palate bone; 4,
anterior palatine foramen; 5, palatine groove; 6, transverse
palatine suture; 7, median palatine suture; 8, palate process of
maxilla; 9, palate process of premaxilla; 10, foramen incisivum; 11,
malar bone; 12, maxilla; 13, anterior end of facial crest; 14,
interalveolar space; I. 1–3, incisor teeth; _C_, canine tooth; _P1_,
first premolar or “wolf” tooth.
]
The =infraorbital= or =superior dental canal= extends almost
horizontally from the maxillary foramen to the infraorbital foramen. It
is placed at the upper edge of the inner plate of the maxilla, and
traverses the maxillary sinus. Near the infraorbital foramen it gives
off a small canal (Canalis alveolaris incisivus) which lies above the
roots of the premolars and extends also into the premaxilla, carrying
vessels and nerves to the teeth there.
=Development.=—The maxilla ossifies in membrane below and external to
the cartilaginous nasal capsule. It has one chief center and a
supplementary one in the region of the deciduous canine tooth (Martin).
THE PREMAXILLAE
The =premaxillæ= (Ossa incisiva) form the anterior part of the upper jaw
and carry the incisor teeth. Each consists of a body and two processes,
nasal and palatine.
The =body= is the thick anterior part which carries the incisor teeth.
Its =labial= or =superior= surface is convex and smooth, and is related
to the upper lip. The =palatine= or =inferior surface= is concave and
presents a foramen a little behind its middle.[15] The =internal
surface= is rough, and joins the opposite bone; it is marked by a curved
groove, which forms with that on the opposed surface, the incisive
=foramen= (Foramen incisivum). The =alveolar border= (Limbus alveolaris)
separates the palatine and labial surfaces; it is curved and thick, and
presents three alveoli for the incisor teeth; behind the third alveolus
it is rounded and free, forming part of the =interalveolar space=.
The =nasal process= (Processus nasalis) projects backward and upward
from the body, forming here the lateral wall of the nasal cavity. The
two =surfaces=, =facial= and =nasal=, are smooth and rounded. The
=superior border= is free, thick, and smooth. The =inferior border= is
dentated and joins the maxilla; at its anterior end it forms with the
latter the alveolus for the permanent canine tooth.[16] The =posterior
extremity= fits into the interval between the nasal bone and the
maxilla.
The =palatine process= (Processus palatinus) is a thin plate which forms
the anterior part of the basis of the hard palate. Its =nasal= or
=superior surface= has a longitudinal ridge which forms with that of the
other side a groove for the septal cartilage. The =palatine= or
=inferior surface= is flat. The =internal border= is serrated and meets
its fellow at the median palatine suture. The =external border= is
separated from the maxilla and the nasal process by the =palatine cleft=
(Fissura palatina). The =posterior extremity= fits into the interval
between the vomer and the palatine process of the maxilla.
=Development.=—The premaxilla ossifies from a single center. Fusion of
the two bones is complete at the end of the third or the beginning of
the fourth year.
THE PALATINE BONES
The =palatine bones= (Ossa palatina) are situated on either side of the
posterior nares, and form the posterior margin of the hard palate. Each
is twisted so as to form a horizontal and a perpendicular part.
The =horizontal part= (Pars horizontalis) is a narrow plate which forms
the posterior part of the hard palate. It presents smooth =nasal= and
=palatine surfaces=. The =internal border= meets its fellow at the
median palatine suture, on the nasal aspect of which is the nasal crest.
The =anterior border= joins the palate process of the maxilla at the
transverse palatine suture, and forms with it the anterior palatine
foramen. The =posterior border= is concave and free; it gives attachment
to the aponeurosis of the soft palate.
The =perpendicular part= (Pars perpendicularis) is more extensive and
forms the outer boundary of the posterior nares. The =nasal= or
=internal surface= is in the greater part of its extent concave and
smooth; it is marked by a narrow rough area to which the pterygoid bone
is attached. Below this the bone curves outward, forming the pterygoid
process. The =maxillary= or =external surface= (Facies maxillaris)
presents three areas for consideration. The largest articulates with the
maxilla; it is rough and is crossed by a groove which enters into the
formation of the palatine canal. Behind this is a smooth part which
assists in forming the =pterygo-palatine fossa=. The rough area below
this is overlapped by the pterygoid process of the sphenoid bone. The
=superior border= is perforated by the =sphenopalatine foramen=. Behind
the foramen the two plates of the bone separate to inclose part of the
=sphenopalatine sinus=. The inner plate curves inward to articulate with
the vomer. The outer plate joins the maxilla and frontal and the orbital
wing of the sphenoid.
=Development.=—The palatine bone ossifies in membrane from a single
center.
THE PTERYGOID BONES
The =pterygoid bones= (Ossa pterygoidea) are narrow, thin, bent plates,
situated on either side of the posterior nares. Each has two surfaces
and two extremities. The =internal surface= is smooth, and forms part of
the boundary of the posterior nares. The =external surface= articulates
with the palatine, vomer, and sphenoid, concurring with the last in the
formation of the =pterygoid= or =Vidian canal=. The =anterior extremity=
is free, turned slightly outward, and forms the =hamulus=, a pulley
around which the tendon of the tensor palati muscle is reflected.
=Development.=—The pterygoid ossifies in membrane from a single center.
THE NASAL BONES
The =nasal bones= (Ossa nasalia) are situated in front of the frontal
bones and form the greater part of the roof of the nasal cavity. They
have an elongated triangular outline, wide behind, pointed in front.
Each presents two surfaces, two borders, a base, and an apex.
The =external= or =facial surface= is smooth and is convex transversely;
the profile contour is usually slightly wavy, with a depression about
its middle and a variably prominent area in front.
The =internal= or =nasal surface= is smooth and concave from side to
side. About in its middle it presents the =superior turbinal crest=
(Crista conchalis dorsalis), which is parallel with the inner border,
and has the superior turbinal bone attached to it. Most of this surface
faces into the nasal cavity, but its posterior part enters into the
formation of the frontal sinus; the latter area is marked off by an
oblique ridge.
The =internal border= is straight, and meets the opposite bone at the
=nasal suture=.
The =external border= is irregular. Its anterior third is free and
concurs with the nasal process in forming the =naso-maxillary notch=
(Incisura naso-maxillaris). Behind this it is scaly for articulation
with the end of the nasal process, the maxilla, and the lacrimal,
forming the =naso-maxillary= and =naso-lacrimal sutures=.
The =base= or posterior end is beveled and overlaps the frontal bone,
forming the =naso-frontal suture=.
The =apex= is pointed and thin.
=Development.=—Each nasal bone ossifies in membrane from a single
center. The nasal suture does not close completely even in old age. In
some cases the two plates separate to inclose a small air-space in the
posterior part.
THE LACRIMAL BONES
The =lacrimal bones= (Ossa lacrimalia) are situated at the anterior part
of the orbit, and extend forward on the face to the posterior border of
the maxilla. Each presents three surfaces and a circumference.
The external aspect is clearly divided into orbital and facial parts by
the orbital margin. The =orbital surface= (Facies orbitalis) is
triangular in outline, smooth and concave; it forms part of the inner
and front wall of the orbit. Near the orbital margin it presents a
funnel-like =fossa= for the lacrimal sac (Fossa sacci lacrimalis), which
is the entrance to the osseous lacrimal canal. Behind this is a
depression in which the inferior oblique muscle of the eye takes origin.
The =facial surface= (Facies facialis) is more extensive, and has the
form of an irregular pentagon. It is slightly convex and smooth in the
foal, flattened in the adult. It usually bears the small =lacrimal
tubercle=, situated nearly an inch (ca. 2 cm.) from the orbital margin.
The =nasal= or =internal surface= (Facies nasalis) faces into the
frontal and maxillary sinuses. It is concave and very irregular, and is
crossed almost horizontally by the =osseous lacrimal canal= (Canalis
lacrimalis osseus).
The =orbital margin= (Margo orbitalis) is concave, rough above, smooth
below.
The =circumference= articulates above with the frontal and nasal bones,
below with the malar and maxilla, in front with the maxilla, and behind
with the frontal. The various sutures so formed are designated by
combinations of the names of the bones.
=Development.=—Each ossifies in membrane from a single center.
THE MALAR BONES
The =malar= or =zygomatic bones= (Ossa zygomatica) are placed between
the lacrimal above and the maxilla below and in front. Each is
irregularly triangular in outline and presents three surfaces, three
borders, a base, and an apex.
The =facial surface= is smooth, slightly convex, wide in front, and
narrow behind. At its lower part it presents the =facial= or =zygomatic
crest=, which is continuous in front with the similar ridge on the
maxilla and behind with the zygomatic process of the temporal; the crest
is rough below, where the masseter muscle is attached to it.
The =orbital surface= is separated from the facial surface by the
concave =orbital margin=. It is concave and smooth, and forms part of
the lower and front wall of the orbit.
The =nasal surface= is concave and faces into the maxillary sinus. In
the young foal a considerable part of it articulates with the maxilla.
The =superior border= articulates with the lacrimal chiefly, but to a
small extent behind with the maxilla also.
The =inferior border= and the =base= articulate with the maxilla.
The =apex= is beveled above and is overlapped by the zygomatic process
of the temporal bone.
=Development.=—Each ossifies in membrane from one or two centers.
THE TURBINAL BONES
These (Ossa turbinata) are delicate, scroll-like bones, four in number,
which are attached to the lateral walls of the nasal cavity. They
project into the cavity and greatly diminish its extent. Each is
composed of a very thin lamina, cribriform in many places, and covered
on both sides with mucous membrane in the fresh state. They are arranged
in two pairs, superior and inferior.
The =superior= or =naso-turbinal= (Concha dorsalis)[17] is somewhat
cylindrical in form, small at its anterior part, and flattened
transversely. It is attached to the turbinal crest of the nasal bone and
the nasal plate of the frontal bone. The anterior part is rolled like a
scroll one and a half times, thus inclosing a cavity which communicates
with the middle meatus nasi. The arrangement is best seen on a
cross-section (Fig. 37). The posterior part is not rolled, but its lower
border is attached to the lateral nasal wall, thus helping to inclose a
large space which is part of the frontal sinus. This cavity is separated
from that of the scroll-like part by a transverse septum. The =internal
surface= is flattened, and is separated from the septum nasi by a narrow
interval, the =common meatus= (Meatus nasi communis). Another narrow
passage, the =superior meatus= (Meatus nasi superior), separates the
upper surface from the roof of the nasal cavity. The space between the
lower surface and the inferior turbinal is the =middle meatus= (Meatus
nasi medius). The anterior extremity is prolonged toward the nostril by
two small bars of cartilage.
The =inferior= or =maxillo-turbinal bone= (Concha ventralis) is shorter
and smaller posteriorly than the upper one. It is attached to the
inferior turbinal crest, and consists, like the upper one, of an
anterior coiled and a posterior uncoiled portion.
To express briefly the mode of coiling of the two bones of the same
side we may say that they are rolled toward the septum and each other.
The inferior and posterior borders of the posterior part are attached to
the maxilla, thus helping to inclose a cavity which is part of the
maxillary sinus. The lower surface is separated from the floor of the
nasal cavity by the =inferior meatus= (Meatus nasi inferior), which is
much larger than the other nasal passages. The anterior extremity is
prolonged to the nostril by a curved bar of cartilage.
=Development.=—Each ossifies in cartilage from a single center.
THE VOMER
The =vomer= is a median unpaired bone, which assists in forming the
lower part of the septum nasi. It is composed of a thin lamina which is
bent (except in its posterior part) so as to form a narrow groove
(Sulcus septi narium), in which the lower part of the perpendicular
plate of the ethmoid bone and the septal cartilage are received. The
=lateral surfaces=, right and left, are highest near the posterior end
and diminish gradually to the anterior end; they are slightly convex
dorso-ventrally, and are covered by the nasal mucous membrane during
life. The =inferior border= is thin and free in its posterior third, and
divides the posterior nares into right and left halves; in the remainder
of its extent it is wider and is attached to the nasal crest. The
=anterior extremity= lies above the ends of the palatine processes of
the premaxillæ. The =posterior extremity= consists of two =wings= (Alæ
vomeris) which extend outward below the body of the presphenoid;
posteriorly they form a notch (Incisura vomeris), and laterally join the
palate and pterygoid bones.
=Development.=—The vomer is primitively double, and ossifies from a
center on either side in the membrane covering the cartilaginous septum
nasi; the two laminæ then fuse below and form a groove.
THE MANDIBLE
The =mandible= or =inferior maxilla= (Mandibula) is the largest and the
only movable bone of the face. The two halves of which it consists at
birth unite during the second or third month, and it is usually
described as a single bone. It carries the lower teeth, and articulates
by its condyles with the squamous temporal on either side. It consists
of a body and two rami.[18]
The =body= (Corpus mandibulæ) is the thick anterior part which bears the
incisor teeth. It presents two surfaces and a border. The =lingual= or
=superior surface= (Facies lingualis) is smooth and slightly concave;
during life it is covered by mucous membrane, and the tip of the tongue
overlies it. The =labial= or =mental surface= (Facies mentalis) is
convex and is related to the lower lip. It is marked by a median furrow
which indicates the position of the primitive symphysis mandibulæ. The
curved =alveolar border= (Limbus alveolaris) presents six alveoli for
the incisor teeth, and a little further back two alveoli for the canine
teeth in the male; in the mare the latter are usually absent or small.
The =rami= (Rami mandibulæ) extend backward from the body and diverge to
inclose the =submaxillary space= (Spatium mandibulare). Each ramus is
bent so as to consist of a horizontal part (Pars molaris) which bears
the lower cheek teeth, and a vertical part (Ramus mandibulæ) which is
expanded and furnishes attachment to powerful muscles; the term =angle=
is applied to the most prominent part of the curve. The ramus presents
two surfaces, two borders, and two extremities. The =external surface=
is smooth and slightly convex from edge to edge on the horizontal part;
at the junction with the body it presents the =mental foramen= (Foramen
mentale), which is the external opening of the mandibular or inferior
dental canal. On the vertical part it is somewhat concave and presents a
number of rough lines for the attachment of the masseter muscle. The
=internal surface= of the horizontal part is smooth, and presents a
shallow longitudinal depression in its middle; above this there is often
a faint mylo-hyoid line for the attachment of the muscle of like name.
At the lower part of the junction with the body there is a small fossa
for the attachment of the genio-hyoid and genio-glossus muscles. On the
vertical part the surface is concave, and is marked in its lower and
posterior part by rough lines for the attachment of the internal
pterygoid muscle. In front of its middle is the =mandibular= or
=inferior maxillary foramen= (Foramen mandibulare), which is the
posterior orifice of the =mandibular= or =inferior dental canal=
(Canalis mandibulæ). The canal curves downward and passes forward below
the cheek teeth, opening externally at the mental foramen; it is
continued into the body of the bone as a small canal (Canalis alveolaris
incisivus), which carries the vessels and nerves to the incisor teeth.
The =superior= or =alveolar border= forms anteriorly part of the
interalveolar space; here it is thin. Behind this it is thick and is
excavated by six alveoli for the lower cheek teeth. Behind the last
alveolus it curves sharply upward and is narrow and rough. In the young
foal there is commonly a small alveolus for the vestige of the first
premolar (“wolf tooth”) close to the first large one. The =inferior
border= of the horizontal part is nearly straight; it is thick and
rounded in the young horse, becoming narrower and sharp in old subjects.
At its posterior part there is a smooth impression (Incisura vasorum)
where the facial vessels and parotid duct turn round the bone. Behind
this point the border curves sharply upward, forming the =angle=
(Angulus mandibulæ); this part is thick and has two roughened lips,
internal and external, separated by a considerable intermediate space;
near the condyle it becomes narrower. The =anterior extremity= joins the
body. The =superior extremity= comprises the =coronoid process= in front
and the =condyle= behind, the two being separated by the =sigmoid notch=
(Incisura mandibulæ), through which the nerve to the masseter muscle
passes. The =coronoid process= (Processus coronoideus) is thin
transversely and curved slightly inward and backward. It projects upward
in the temporal fossa, and furnishes insertion to the temporal muscle.
The =condyle= (Capitulum mandibulæ) lies at a much lower level than the
end of the coronoid process. It is elongated transversely and
articulates with the squamous temporal through the medium of an
articular disc. The part below the condyle is usually termed the =neck=
(Collum mandibulæ); on its antero-internal part is a depression (Fovea
pterygoidea) for the attachment of the external pterygoid muscle. The
middle of the vertical part of the ramus consists to a large extent of a
single plate of compact substance which may be so thin in places as to
be translucent.
=Development.=—The mandible develops from two chief centers in the
connective tissue which overlies the paired Meckel’s cartilages. At
birth it consists of two symmetrical halves which meet at a median
symphysis. Fusion usually occurs in the second or third month.
=Age changes.=—These are associated largely with the growth and later
with the reduction of the teeth. In the young horse, in which the
teeth are large and are in great part embedded in the bone, the body
is thick and strongly curved, and the horizontal part of the ramus is
also thick. Later, as the teeth are extruded from the bone, the body
becomes flattened and narrower, and the horizontal part of the ramus
is thinner, especially in its lower part; the angle and the impression
in front of it are more pronounced.
THE HYOID BONE
The =hyoid bone= (Os hyoideum) is situated chiefly between the vertical
parts of the rami of the mandible, but its upper part extends somewhat
further back. It is attached to the petrous temporal bones by rods of
cartilage, and supports the root of the tongue, the pharynx, and larynx.
It consists of a body, a lingual process, and three pairs of cornua.
The =body= or =basihyoid= (Basis ossishyoidei) is a short transverse
bar, compressed dorso-ventrally. The upper surface is concave and smooth
in its middle, and presents at each end a convex facet or tubercle for
articulation with the small cornu. The lower surface is slightly
roughened for muscular attachment. The anterior border carries medially
the lingual process. The posterior border is concave and smooth in its
middle, and carries on either side the thyroid cornu. The body, the
lingual process, and the thyroid processes are fused together, and may
be compared to a spur or a fork with a very short handle.
The =lingual process= (Processus lingualis) projects forward medially
from the body, and is embedded in the root of the tongue during life. It
is compressed laterally and has a blunt-pointed free end. The lateral
surfaces are slightly concave. The upper border is narrow, the lower
thick and irregular.
The =thyroid cornua= or =thyrohyoids= (Cornua laryngea)[19] extend
backward and upward from the lateral parts of the body. They are
compressed laterally (except at their junction with the body), and their
posterior ends are connected with the anterior cornua of the thyroid
cartilage of the larynx.
The =small cornua= or =keratohyoids= (Cornua minora) are short rods
which are directed upward and forward from either end of the upper
surface of the body. Each is somewhat constricted in its middle part and
has slightly enlarged ends. The lower end has a small concave facet
which articulates with the body. The upper end articulates with the
great cornu, or with the middle cornu when present.
[Illustration:
FIG. 32.—HYOID BONE OF HORSE, VIEWED FROM THE SIDE AND SOMEWHAT FROM
IN FRONT.
_a_, Body; _b_, lingual process; _c_, thyroid cornu; _c′_, cartilage
of _c_; _d_, small cornu; _e_, middle cornu; _f_, great cornu; _f′_,
muscular angle of great cornu; _g_, cartilage of great cornu.
(Ellenberger-Baum, Anat. d. Haustiere.)
]
The =great cornua= or =stylohyoids= are much the largest parts of the
bone. They are directed upward and backward, and are connected above
with the base of the petrous temporal bones. Each is a thin plate, seven
or eight inches (ca. 18 to 20 cm.) long, which is slightly curved in its
length, so that the external surface is concave and smooth. The internal
surface is convex and smooth. The borders are thin. The upper extremity
is large and forms two angles; the upper angle is connected by a rod of
cartilage with the hyoid process of the petrous temporal bone; the lower
angle is somewhat thickened and rough for muscular attachment. The lower
extremity is small, and articulates with the small or the middle cornu.
The =middle cornua= or =epihyoids= are small wedge-shaped pieces or
nodules interposed between the small and great cornua. They are usually
transitory, and unite with the great cornua in the adult.
=Development.=—The hyoid ossifies in the cartilages of the second and
third visceral arches. Each part has a separate center, except the
lingual process, which ossifies by extension from the body. The latter
has primarily two centers (Martin).
THE SKULL AS A WHOLE
The skull of the horse has the form of a long four-sided pyramid, the
base of which is posterior. It is convenient to exclude the mandible and
hyoid from present consideration. The division between the cranium
(Cranium cerebrale) and the face (Cranium viscerale) may be indicated
approximately by a transverse plane through the anterior margins of the
orbits.
The =superior= or =frontal surface= (Norma frontalis) is formed by the
upper part of the occipital, the interparietal, parietal, frontal, and
nasal bones. It may be divided into parietal, frontal, nasal, and
premaxillary regions. The parietal region extends from the occipital
crest to the parieto-frontal or coronal suture. It is marked medially by
the =external sagittal crest=, which bifurcates in front, the branches
becoming continuous with the =frontal crests=. The latter curve outward
to the root of the supraorbital process. The =frontal region= is the
widest part of the surface, and is smooth and almost flat. It is bounded
in front by the naso-frontal suture. On either side of it is the root of
the =supraorbital process=, pierced by the =supraorbital foramen=. The
=nasal region= is convex from side to side, wide behind, narrow in
front. Its profile is in some cases nearly straight; in others it is
undulating, with a variably marked depression about its middle and at
the anterior end. The =premaxillary region= presents the =osseous nasal
aperture= (Apertura nasalis ossea) and the =foramen incisivum=.
[Illustration:
FIG. 33.—CRANIAL AND ORBITAL REGIONS OF SKULL OF HORSE, LATERAL VIEW.
THE ZYGOMATIC ARCH AND SUPRAORBITAL PROCESSES HAVE BEEN SAWN OFF.
1, Occipital condyle; 2, condyloid fossa; 3, paramastoid or styloid
process; 4, occipital crest; 5, external occipital protuberance; 6,
external auditory meatus; 7, mastoid process; 8, hyoid process; 9,
stylo-mastoid foramen; 10, muscular process; 11, foramen lacerum
anterius; 12, postglenoid process; 13, glenoid cavity; 14, temporal
condyle; 15, Vidian groove; 16, alar canal of pterygoid process
indicated by arrow; 17, temporal foramen; 18, ethmoidal foramen; 19,
optic foramen; 20, foramen lacerum orbitale; 21, maxillary foramen;
22, sphenopalatine foramen; 23, posterior palatine foramen; 24,
supraorbital foramen (opened); 25, lacrimal fossa; 26, depression
for origin of obliquus oculi inferior; 27, facial crest; 28,
maxillary tuberosity; 29, alveolar tuberosity; 30, hamulus of
pterygoid bone; _S.o._, supraoccipital; _P_, parietal; _S_, squamous
temporal; _B.o._, basioccipital; _B.s._, basisphenoid; _A.t._,
temporal wing of sphenoid; _A.o._, orbital wing of sphenoid;
_Pt.p._, pterygoid process of sphenoid; _P.p._, perpendicular part
of palate bone; _F,F′_, facial and orbital parts of frontal bone;
_L,L′_, orbital and facial parts of lacrimal bone; _M_, facial part
of malar bone; _M.x._, maxilla; _a_, parieto-occipital suture; _b_,
parieto-temporal or squamous suture; _c_, _d_, spheno-squamous
suture; _e_, palato-frontal suture; _f_, fronto-lacrimal suture.
]
The =lateral surface= (Norma lateralis) may be divided into cranial,
orbital, and maxillary or preorbital regions.
The =cranial region= presents the temporal fossa, the zygomatic arch,
and the outer part of the petrous temporal bone.
The =temporal fossa= is bounded internally by the sagittal and frontal
crests, externally by the temporal crest and the zygomatic arch, and
behind by the occipital crest. Its upper and middle parts are rough for
the attachment of the temporal muscle. In its lower posterior part are
several =foramina= which communicate with the parieto-temporal canal.
The fossa is continuous in front with the orbital cavity.
The =zygomatic arch= is formed by the zygomatic processes of the
temporal, malar, and maxilla. Its ventral face presents the =condyle=
and =glenoid cavity= for articulation with the lower jaw, through the
medium of the articular disc. Behind the glenoid cavity is the
=postglenoid process=.
The =external auditory process= projects outward through a deep notch in
the lower margin of the squamous temporal below the temporal crest. A
little further back is the =mastoid process=, crossed in its upper part
by a groove for the mastoid artery.
The =orbital region= comprises the orbit and the pterygo-palatine
=fossa=.
The =orbit= is a cavity which incloses the eyeball, with the muscles,
vessels, and nerves associated with it. It is not separated in the
skeleton from the temporal fossa. The =long axis= of the cavity, taken
from the optic foramen to the middle of the =inlet=, is directed
forward, outward, and slightly upward. The =inner wall= (Paries
medialis) is complete and extensive. It is concave and smooth, and is
formed by the frontal and lacrimal and the orbital wing of the sphenoid.
In its extreme anterior part is the fossa for the lacrimal sac. Behind
this is a small depression in which the inferior oblique muscle of the
eye arises; here the plate which separates the orbit from the maxillary
sinus is very thin. The =upper wall= (Paries superior) is formed by the
frontal and to a small extent by the lacrimal bone. It presents the
supraorbital foramen, which perforates the root of the supraorbital
process. The =lower wall= (Paries inferior) is very incomplete, and is
formed by the malar, the zygomatic process of the temporal, and to a
small extent by the maxilla. The =external boundary= (Paries lateralis)
is the supraorbital process. At the extreme posterior part is the
=orbital group of foramina=. Four are situated in front of the pterygoid
crest. Of these, the uppermost is the =ethmoidal= or =internal orbital
foramen=, which transmits the ethmoidal vessels and nerve. The =optic
foramen= is situated a little lower and further back; it transmits the
optic nerve. Immediately below the optic is the =foramen lacerum
orbitale=, which transmits the ophthalmic, third, sixth, and sometimes
the fourth nerve; commonly there is a very small =trochlear= or
=pathetic foramen= in the crest for the last-named nerve. The =foramen
rotundum= is below the foramen lacerum, from which it is separated by a
thin plate; it transmits the superior maxillary nerve. The =alar canal=
opens in common with the foramen rotundum, and the anterior opening of
the pterygoid or Vidian canal is also found here. The =temporal foramen=
(For. alare parvum) is just behind the pterygoid crest and on a level
with the foramen lacerum. It is the upper opening of a canal which leads
from the alar canal, and through it the anterior deep temporal artery
emerges. The =inlet= of the orbital cavity (Aditus orbitæ) is
circumscribed by a complete bony ring, which is nearly circular. Its
antero-inferior part (Margo infraorbitalis) is smooth and rounded; the
remainder (Margo supraorbitalis) is rough and irregularly notched.
During life the cavity is completed by the periorbita or ocular sheath,
a conical fibrous membrane, the apex of which is attached around the
optic foramen.
Below the orbital cavity is the =pterygo-palatine fossa=. Its wall is
formed by the pterygoid process, the perpendicular part of the palate
bone, and the tuber maxillare. Its deep anterior part (maxillary hiatus)
contains three foramina. The upper one, the =maxillary foramen=, is the
entrance to the infraorbital canal, which transmits the infraorbital
nerve and vessels. The =sphenopalatine foramen= transmits vessels and
nerves of like name to the nasal cavity. The lower foramen, the
=posterior palatine=, transmits the palatine artery and nerve to the
palatine canal. The upper part of the fossa is smooth, and is crossed by
the internal maxillary artery and the maxillary nerve. The lower part is
chiefly roughened for the attachment of the internal pterygoid muscle,
but is crossed in front by a smooth groove in which the palatine vein
lies.
The =maxillary= or =preorbital region= is formed chiefly by the maxilla,
but also by the premaxilla, and the facial parts of the lacrimal and
malar bones. Its contour is approximately triangular, the base being
posterior. It offers two principal features. The =facial crest= extends
forward from the lower margin of the orbit, and ends abruptly at a point
about an inch and a half (3 to 4 cm.) above the third or fourth cheek
tooth;[20] its inferior aspect is rough for the attachment of the
masseter muscle. The =infraorbital foramen= is situated in a transverse
plane about an inch (ca. 2 to 3 cm.) in front of the end of the crest
and about two inches (5 cm.) above it. The foramen opens forward, and
through it the infraorbital artery and nerve emerge. The surface over
the premolar teeth varies greatly with age, in conformity with the size
of the embedded parts of the teeth. In the young horse the surface here
is strongly convex, the outer plate of bone is thin and even defective
sometimes in places, and the form of the teeth is indicated by eminences
(Juga alveolaria). In the old animal the surface is concave on account
of the extrusion of the teeth from the bone. The downward curve of the
premaxilla is pronounced in the young subject, very slight in the aged.
The =inferior= or =basal surface= (Norma basalis), exclusive of the
mandible, consists of cranial, guttural, and palatine regions.
The =cranial region= (Basis cranii externa) extends forward to the vomer
and pterygoid processes (Fig. 28). At its posterior end is the =foramen
magnum=, flanked by the =occipital condyles=. External to the latter is
the =condyloid fossa=, in which is the =hypoglossal foramen=, which
transmits the hypoglossal nerve and the condyloid artery and vein.
Further outward are the =paramastoid= or =styloid processes= (Processus
jugulares) of the occipital bone. Extending forward centrally is a
prismatic bar, formed by the basilar part of the occipital and the body
of the sphenoid bone; at the junction of these parts are tubercles for
the attachment of the ventral straight muscles of the head. On either
side of the basilar part of the occipital is the =foramen lacerum basis
cranii=, bounded externally by the base of the petrous temporal bone. In
front of these the region becomes very wide on account of the lateral
extension of the =zygomatic processes=, bearing on the ventral aspect
the =condyle= and =glenoid cavity= for articulation with the mandible.
Beyond this the process turns forward and joins the =zygomatic process=
of the malar, completing the zygomatic arch and the surface for the
attachment of the masseter muscle. On either side of the body of the
sphenoid is the infratemporal fossa, formed by the temporal wing and the
root of the pterygoid process of the sphenoid bone. It is bounded in
front by the pterygoid crest, which separates it from the orbit and the
pterygo-palatine fossa. In it is the =pterygoid= or =alar foramen=,
which transmits the internal maxillary artery. A little lower is the
entrance to the pterygoid (Vidian) =canal=.
The =guttural region= presents the pharyngeal orifice of the nasal
cavity. This is elliptical and is divided in its depth medially by the
vomer into two =posterior nares= or =choanæ=. It is bounded in front and
laterally by the palate and pterygoid bones, behind by the vomer. It is
flanked by the hamular process of the pterygoid bones. The plane of the
opening is nearly horizontal, and the length is about twice the width.
The =palatine region= comprises a little more than half of the entire
length of the base of the skull (Fig. 31). The =hard palate= (Palatum
durum) is concave from side to side, and in its length also in the
anterior part. It is formed by the palatine processes of the premaxillæ
and maxillæ, and the horizontal parts of the palate bones. It is
circumscribed in front and laterally by the =superior alveolar arch=, in
which the upper teeth are implanted. The =interalveolar space= (Margo
interalveolaris) is that part of the arch in which alveoli are not
present. Behind the last alveolus is the =alveolar tuberosity=, and
internal to this is a =groove= for the palatine vein. In the middle line
is the =median palatine suture= (Sutura palatina mediana). In the line
of the suture, a little behind the central incisors, is the =foramen
incisivum=, through which the palato-labial artery passes. On either
side, parallel with the alveolar part of the maxilla, is the =palatine
groove= (Sulcus palatinus), which contains the palatine vessels and
nerve. It is continuous at the anterior palatine foramen with the
palatine canal, which is situated between the maxilla and the palate
bone. The =palatine cleft= (Fissura palatina) is the narrow interval
along the outer margin of the palatine process of the premaxilla; it is
closed in the fresh state by cartilage. Scattered along each side of the
palate are several vascular foramina. The =transverse palatine suture=
(Sutura palatina transversa) is about half an inch from the posterior
border. The latter is in a plane through the last molar teeth, and is
concave and free.
[Illustration:
FIG. 34.—CRANIAL CAVITY OF HORSE AS SEEN ON SAGITTAL SECTION OF SKULL.
_O_, Frontal sinus; _r_, sphenoidal sinus; _t_, cerebral compartment
of cranium; 1–3, ridges (juga) corresponding to fissures of lateral
surface of cerebrum; 4, groove for middle cerebral artery; 5,
entrance to for. lacerum orbitale; 6, entrance to optic foramen; 7,
8, grooves on sphenoid bone; 9, incisura spinosa; 9′, groove for
middle meningeal artery; 10, fossa for pyriform lobe of cerebrum;
11, incisura ovalis; 12, incisura carotica; 13, internal auditory
meatus; 14, foramen lacerum basis cranii; 15, hypoglossal foramen;
16, petrous temporal; 17, orifice of aquæductus vestibuli; 18,
orifice of aquæductus cochleæ; 19, foramen magnum; 20, petrosal
crest; 21, two plates of frontal bone; 22, supraoccipital; 23,
basioccipital; 24, tentorium osseum; 25, body of sphenoid. (After
Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
The =posterior= or =nuchal surface= (Norma occipitalis) is formed by the
occipital bone. It is trapezoidal in outline, wider below than above,
concave dorso-ventrally, convex transversely. It is separated from the
superior surface by the =occipital crest=, and from the lateral surfaces
by the =superior curved lines= (Lineæ nuchæ superiores). Below the crest
are two rough areas for the attachment of the complexus muscles. A
little lower is a central eminence on the sides of which the ligamentum
nuchæ is attached. At the lowest part centrally is the =foramen magnum=,
at which the brain and spinal cord meet; this is bounded laterally by
the =occipital condyles=, which are flanked by the =paramastoid= or
=styloid processes= (Processus jugulares).
The =apex= of the skull is formed by the bodies of the premaxillæ and
mandible, carrying the incisor teeth.
THE CRANIAL CAVITY
This cavity incloses the brain, with its membranes and vessels. It is
relatively small and is ovoid in shape.
The =superior wall= or =roof= (Calvaria) is formed by the
supraoccipital, interparietal, parietal, and frontal bones. In the
middle line is the internal sagittal crest, which joins the crista galli
in front, and furnishes attachment to the falx cerebri. Posteriorly the
crest is continued by the sharp anterior margin of the =tentorium
osseum=, which projects downward and forward into the cavity, and gives
attachment to the tentorium cerebelli by its sharp lateral edges. Behind
this the roof is grooved centrally for the middle lobe or vermis of the
cerebellum. Transverse grooves pass from the base of the tentorium
osseum to the parieto-temporal canals. The anterior part of the roof is
hollowed by the frontal sinus. The occipital part is very thick and
strong.
The =lateral walls= are formed by the occipital, parietal, temporal, and
frontal bones, and in part by the orbital wings of the sphenoid. Each is
crossed obliquely by the =petrosal crest=, which concurs with the
projecting margin of the parietal bone and the tentorium osseum in
dividing the cavity into cerebral and cerebellar compartments. Behind
the crest is a depression for the lateral lobe (hemisphere) of the
cerebellum. Below this are the internal auditory meatus and the openings
of the aquæductus vestibuli and aquæductus cochleæ.
[Illustration:
FIG. 35.—FLOOR OF CRANIAL CAVITY OF HORSE.
The roots of the cranial nerves are shown on the left side and are
designated by number. _I_, Anterior cranial fossa; _II_, middle
cranial fossa; _III_, posterior cranial fossa; _a_, ethmoidal fossa;
_b_, ethmoidal foramen; _c_, foramen for nasal branch of ophthalmic
artery; _d_, orbital wing of sphenoid bone; _e_, optic fossa; _f_,
sella turcica; _g_, spheno-occipital crest; _h_, _h′_, dotted line
indicating contour of pituitary body; _h″_, slight elevation
representing dorsum sellæ; _i_, _k_, grooves for nerves and
cavernous sinus; _l_, depression for pyriform lobe of cerebrum; _m_,
groove for middle meningeal artery; _n_, depression for pons; _o_,
foramen lacerum anterius; _p_, foramen lacerum posterius; _q_,
incisura carotica; _q′_, incisura ovalis; _q″_, incisura spinosa;
_r_, depression for medulla oblongata; _s_, hypoglossal foramen;
_t_, internal auditory meatus; _u_, foramen magnum; _v_, frontal
sinus; _w_, zygomatic process of temporal bone; _x_, section of
petrous temporal; _y_, section of occipital bone; _z_, crista galli;
1, 1′, 1″, dotted lines indicating position of olfactory tracts and
peduncle. (After Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
The roof and lateral walls are marked by digital impressions and
vascular grooves.
The =inferior wall= or =floor= (Basis cranii interna) may be regarded as
forming three fossæ. The =anterior fossa= (Fossa cranii anterior)
supports the frontal and olfactory parts of the cerebrum. It is formed
chiefly by the presphenoid, and lies at a higher level than the middle
fossa. In front the fossa is divided medially by the =crista galli=,
lateral to which are the deep =ethmoidal= or =olfactory fossæ= for the
olfactory lobes. The =ethmoidal= or =internal orbital foramen=
perforates the cranial wall at the outer side of these fossæ. Further
back the central part of the surface is slightly elevated, and is
flanked by shallow depressions which support the olfactory peduncles.
Posteriorly is a bony shelf which covers the entrance to the =optic
foramina=; the edge of this shelf and the posterior borders of the
orbital wings of the sphenoid may be taken as the line of demarcation
between the anterior and middle fossæ. The =middle fossa= (Fossa cranii
media) is the widest part of the cavity. It extends backward to the
internal spheno-occipital and petrosal crests, thus corresponding to the
postsphenoid. In its middle is a small fossa, the sella turcica, in
which the pituitary body, or hypophysis cerebri, is situated. On either
side are two grooves for nerves; the inner one transmits the ophthalmic,
third, and sixth nerves to the foramen lacerum orbitale; the outer one
leads to the foramen rotundum, and lodges the maxillary nerve. External
to the grooves is a depression for the pyriform lobe of the cerebrum.
The =posterior fossa= (Fossa cranii posterior) corresponds to the
basilar part of the occipital bone. It contains the medulla, pons, and
cerebellum. In front is a median depression (Fossa pontis) for the pons.
The surface behind this is concave transversely and slopes gently
downward to the foramen magnum; it supports the medulla. On either side
are the =foramen lacerum basis cranii= and the =hypoglossal foramen=.
The =anterior= or =nasal wall= is formed by the cribriform plate of the
ethmoid, which separates the cranium from the nasal cavity. It is
perforated by numerous foramina for the passage of the olfactory
nerve-bundles.
[Illustration:
FIG. 36.—MEDIAN SECTION OF SKULL OF HORSE WITHOUT THE MANDIBLE.
The septum nasi is removed, but the mucous membrane on the turbinal
bones is retained. _a_, _a′_, Superior turbinal bone, dotted line
indicating limit between anterior coiled part and posterior uncoiled
part; _b_, _b′_, superior turbinal folds, inclosing bars of
cartilage; _c_, fold of mucous membrane formed by union of _b_ and
_b′_; _d_, _d′_, anterior coiled and posterior uncoiled part of
inferior turbinal, dotted line indicating septum between them; _e_,
_f_, inferior turbinal folds, former (alar fold) inclosing bar of
cartilage; _g_, _h_, _i_, superior, middle, inferior meatus; _o_,
_o′_, frontal sinus; partial septum between _o_ and _o′_; _q_, nasal
part of frontal sinus (nasal sinus); _r_, lateral mass of ethmoid
bone; _s_, sphenoidal sinus; _t_, cranial cavity; _u_, opening made
in superior turbinal bone at point where drainage of frontal sinus
may be obtained. (After Ellenberger, in Leisering’s Atlas.)
]
THE NASAL CAVITY
The =nasal cavity= (Cavum nasi) is a longitudinal passage which extends
through the upper part of the face. It is divided into right and left
halves by a median =septum nasi=. The =lateral walls= are formed by the
maxilla, premaxilla, and the perpendicular part of the palate bones.
Attached to them are the turbinal bones, which subdivide each nasal
fossa into three =meatuses= (Meatus nasi). This wall is crossed
obliquely by the =canal= and =groove= for the =naso-lacrimal duct=, and
its posterior part is perforated by the =sphenopalatine foramen=. The
=superior wall= or =roof= is formed by the frontal and nasal bones. It
is concave from side to side, and nearly straight longitudinally, except
in the posterior part, where it curves downward. It presents a median
elevation, the =nasal crest=. The =inferior wall= or =floor= is formed
by the palatine processes of the premaxillæ and maxillæ, and the
horizontal parts of the palate bones. It is wider but considerably
shorter than the roof. It is concave transversely, and nearly horizontal
from before backward, except in the posterior third, where there is a
slight declivity. The anterior part presents a median groove for the
cartilaginous septum, and a furrow for the organ of Jacobson on either
side. On either side of the palatine processes of the premaxillæ is the
=palatine cleft=.
The =septum nasi= is incomplete in the macerated skull. It is formed by
the perpendicular plate of the ethmoid behind, and the vomer below. In
the fresh state it is completed by a plate of cartilage.
The =superior meatus= (Meatus nasi superior) is a narrow passage between
the roof and the superior turbinal bone. It ends at the cribriform plate
of the ethmoid. The =middle meatus= (Meatus nasi medius) is the space
between the two turbinal bones. In its posterior part is the very narrow
opening into the maxillary sinus. The =inferior meatus= (Meatus nasi
inferior) is the channel along the floor which is overhung by the
inferior turbinal bone. It is much the largest and is the direct path
between the anterior and posterior nares.
The external aperture is bounded by the nasal bones and the premaxillæ.
[Illustration:
FIG. 37.—CROSS-SECTION OF NASAL REGION OF SKULL OF HORSE; THE SECTION
PASSES THROUGH THE ANTERIOR END OF THE FACIAL CREST, AND BETWEEN THE
THIRD AND FOURTH CHEEK TEETH.
_a_, Superior, _b_, inferior turbinal bone; _c_, _d_, cavities of _a_
and _b_; _e_, common meatus; _f_, _g_, _h_, superior, middle,
inferior meatus; _i_, _k_, passages to cavities of turbinal bones;
_l_, naso-lacrimal duct; _m_, infraorbital canal; _n_, anterior end
of maxillary sinus; _o_, septal cartilage. (After Ellenberger, in
Leisering’s Atlas.)
]
[Illustration:
FIG. 38.—CROSS-SECTION OF NASAL REGION OF SKULL OF HORSE; THE SECTION
IS CUT ABOUT HALFWAY BETWEEN THE ORBIT AND THE ANTERIOR END OF THE
FACIAL CREST, AND PASSES BETWEEN THE FIFTH AND SIXTH CHEEK TEETH.
_a_, Superior, _b_, inferior turbinal bone; _c_, _d_, cavities of _a_
and _b_; _e_, common meatus; _f_, superior, _g_, middle, _h_,
inferior meatus; _i_, placed over ridge in maxillary sinus; _k_,
communication between outer and inner (turbinal) part of maxillary
sinus; _l_, naso-maxillary opening; _m_, naso-lacrimal canal; _n_,
infraorbital canal. (After Ellenberger, in Leisering’s Atlas.)
]
The posterior extremity or fundus is separated from the cranial cavity
by the cribriform plate of the ethmoid, and is largely occupied by the
lateral masses of that bone.
THE PARANASAL SINUSES
Connected directly or indirectly with the nasal cavity, of which they
are diverticula, are four pairs of air-sinuses (Sinus paranasales),
viz., maxillary, frontal, sphenopalatine, and ethmoidal.
The =maxillary sinus= (Sinus maxillaris) is the largest. Its external
wall is formed by the maxilla, the lacrimal, and the malar. It is
bounded internally by the maxilla, the inferior turbinal, and the
lateral mass of the ethmoid bone. It extends backward to a transverse
plane in front of the root of the supraorbital process, and its anterior
limit is indicated approximately by a line drawn from the anterior end
of the facial crest to the infraorbital foramen. Its upper boundary
corresponds to a line drawn backward from the supraorbital foramen
parallel to the facial crest. The floor is formed by the alveolar part
of the maxilla; it is very irregular and is crossed by bony plates
running in various directions. The last three cheek teeth project up
into the cavity to an extent which varies with age; they are covered by
a thin plate of bone. The cavity is divided into anterior and posterior
parts by an oblique =septum=. The outer margin of the septum is commonly
about one and a half to two inches (ca. 3.5 to 5 cm.) from the anterior
end of the facial crest; from here it is directed inward, backward, and
upward. The upper part of the septum (formed by the posterior end of the
inferior turbinal bone) is very delicate and usually cribriform.
The position of the septum is quite variable. It is not rare to find
it further forward, and in some cases it is further back than is
stated above. In the recent state, _i. e._, when covered by the mucous
membrane on both surfaces, it is nearly always complete, but in very
exceptional cases there is an opening of variable size in the upper
part.
The =anterior compartment=, often called the =inferior maxillary sinus=,
is partially divided by the infraorbital canal into an external
maxillary part and an internal smaller turbinal part. The latter
communicates with the middle meatus by a very narrow slit situated at
its highest part. The =posterior compartment=, often called the
=superior maxillary sinus=, is also crossed by the infraorbital canal,
internal to which it opens freely into the sphenopalatine sinus. It
communicates dorsally with the frontal sinus through the large oval
=fronto-maxillary opening=, situated at the level of the osseous
lacrimal canal and the corresponding part of the inner wall of the
orbit; the orifice is commonly about one and a half to two inches (ca. 4
to 5 cm.) long and an inch or more (2 to 3 cm.) wide. Just in front of
this, and covered by a thin plate, is the narrow =naso-maxillary
fissure= (Aditus naso-maxillaris), by which the sinus opens into the
posterior part of the middle meatus.
The foregoing statements refer to the arrangement in the average adult
animal. In the foal the cavity (with the exception of its turbinal
part) is largely occupied by the developing teeth. In horses five to
six years of age the maxillary part of the sinus is still filled up to
a large degree by the embedded parts of the teeth. As the teeth are
extruded to compensate the wear, more and more of the cavity becomes
free, until in old age only the short roots project up in the floor,
covered by a layer of bone. Other facts in this connection will be
given in the description of the teeth. In exceptional cases the
posterior part of the inferior turbinal is smaller than usual and
leaves a considerable interval, through which the maxillary sinus
communicates with the nasal cavity.
[Illustration:
FIG. 39.—SKULL OF HORSE, LATERAL VIEW WITHOUT MANDIBLE. THE SINUSES
ARE OPENED UP.
_a_, Posterior part, _b_ and _c_, anterior part of frontal sinus; _d_,
roof of superior meatus; _e_, lateral mass of ethmoid bone; _f_,
_f′_, naso-lacrimal duct, exposed in its posterior part; _g_, _h_,
posterior and anterior compartments of maxillary sinus (also
designated as superior and inferior maxillary sinuses); _i_, septum
between _g_ and _h_; _k_, lower limit of upper thin and partly
membranous portion of septum; _l_, infraorbital canal; _m_, turbinal
part of maxillary sinus; _n_, bullous prominence of inferior
turbinal; _o_, orbit; _p_, infraorbital foramen; _q_, continuation
of infraorbital canal to premaxilla; _r_, limit of maxillary sinus.
(After Ellenberger, in Leisering’s Atlas.)
]
The =frontal sinus= (Sinus concho-frontalis) consists of frontal and
turbinal parts. The frontal part is bounded chiefly by the two plates of
the frontal bone, but its floor is formed in part by the lateral mass of
the ethmoid. It extends forward to a plane through the anterior margins
of the orbits, backward to one through the temporal condyles, and
outward into the root of the supraorbital process. It is separated from
the sinus of the opposite side by a complete =septum=. It is partially
subdivided by a number of bony plates. The turbinal part is situated in
the posterior part of the superior turbinal bone, roofed in by the nasal
and lacrimal bones. It extends forward to a transverse plane about
half-way between the anterior margin of the orbit and the end of the
facial crest. Behind it is in free communication with the frontal part
over the lateral mass of the ethmoid. It is separated from the nasal
cavity by the thin turbinal plate. The frontal and maxillary sinuses
communicate through the large opening described above.
The =sphenopalatine sinus= (Sinus sphenopalatinus) consists of two parts
which communicate under the lateral mass of the ethmoid. The sphenoidal
(posterior) part is excavated in the body of the presphenoid. The
palatine (anterior) part is between the two plates of the perpendicular
part of the palate bone, under the lateral mass of the ethmoid; it
communicates freely with the maxillary sinus. The septum between the
right and left sinuses is not usually median in the sphenoidal part.
In about one-third of the cases (according to Paulli) the sphenoidal
and palatine parts are separated by a transverse septum, and the
sphenoidal part then communicates only with the lower ethmoidal
meatuses.
The term =ethmoidal sinus= is often applied to the cavity of the largest
ethmoturbinal. It communicates with the maxillary sinus.
[Illustration:
FIG. 40.—SKULL OF HORSE, DORSAL VIEW, WITH SINUSES EXPOSED BY REMOVAL
OF THE OUTER PLATE OF BONE.
_1_, Frontal bone; _2_, nasal bone; _3_, lacrimal bone; _4_, maxilla;
_a_, posterior part of frontal sinus; _a′_, middle part of frontal
sinus; _b_, anterior (turbinal) part of frontal sinus; _c_, lateral
mass of ethmoid bone; _d_, roof of superior meatus; _e_,
fronto-maxillary opening; _f_, naso-maxillary opening below plate
which forms the anterior margin of _e_; _g_, _h_, posterior and
anterior compartments of maxillary sinus—often called the superior
and inferior maxillary sinuses; _i_, septum between _g_ and _h_;
_k_, orbit; _l_, point at which superior turbinal bone may be
perforated to obtain drainage into nasal cavity. (After Ellenberger,
in Leisering’s Atlas.)
]
THE BONES OF THE THORACIC LIMB THE SCAPULA
The =scapula= is a flat bone, situated on the anterior part of the
lateral wall of the thorax, and extending obliquely from the vertebral
end of the seventh or eighth rib to the sternal end of the first rib. It
is curved slightly and slopes outward in adaptation to the form of the
thoracic wall. It is triangular in outline, and has two surfaces, three
borders, and three angles.
The =external surface= or =dorsum= (Facies lateralis s. dorsalis) is
divided into two fossæ by the =spine= (Spina scapulæ), which extends
from the vertebral border to the neck of the bone, where it gradually
subsides. The free edge of the spine is thick, rough, and in great part
subcutaneous. A little above its middle is a variable prominence, the
=tubercle= of the spine (Tuber spinæ), to which the trapezius muscle is
attached. The =supraspinous fossa= (Fossa supraspinata) is situated in
front of the spine, and the =infraspinous fossa= (Fossa infraspinata)
behind it. The former is much the smaller of the two; it is smooth and
is occupied by the supraspinatus muscle. The infraspinous fossa lodges
the infraspinatus muscle; it is wide and smooth in its upper part,
narrower below, where it is marked by several rough lines for the
attachment of the teres minor muscle; near the neck is the nutrient
foramen, and a little lower is a vascular groove.
[Illustration:
FIG. 41.—LEFT SCAPULA OF HORSE, EXTERNAL VIEW. (After Schmaltz, Atlas
d. Anat. d. Pferdes.)
]
The =costal surface= or =venter= (Facies costalis) is hollowed in its
length by the =subscapular fossa= (Fossa subscapularis); this occupies
nearly the whole of the lower part of the surface, but is pointed above
and separates two rough triangular areas (Facies serrata), to which the
serratus magnus is attached. In the lower third there is a vascular
furrow with several branches.
The =anterior= or =cervical border= (Margo cranialis) is convex and
rough above, concave and smooth below.
The =posterior= or =dorsal border= (Margo caudalis) is slightly concave.
It is thick and rough in its upper third, thin in its middle, and
thickens again below.
The =superior= or =vertebral border= (Margo dorsalis s. basis) carries
the =scapular cartilage= (Cartilago scapulæ). In the young subject the
edge of the bone is thick, and is pitted by impressions into which the
cartilage fits. The cartilage is the unossified part of the fœtal
scapula. Its lower edge fits the depressions and elevations of the bone.
It thins out toward the free edge, which is convex and lies alongside of
the upper parts of the vertebral spines. In front it continues the line
of the scapula, but behind it forms a rounded projection. The lower part
of the cartilage undergoes more or less ossification, so that the
vertebral border of the bone in old subjects is thin, irregular, and
porous.
[Illustration:
FIG. 42.—LEFT SCAPULA OF HORSE, COSTAL SURFACE.—(After Schmaltz, Atlas
d. Anat. d. Pferdes.)
]
The =anterior= or =cervical angle= (Angulus cranialis) is at the
junction of the anterior and vertebral borders and lies opposite to the
second thoracic spine. It is relatively thin and is about a right angle.
The =posterior= or =dorsal angle= (Angulus caudalis) is thick and rough;
its position can be determined readily in the living animal.
The =inferior= or =articular angle= (Angulus glenoidalis) is joined to
the body of the bone by the =neck= of the scapula (Collum scapulæ). It
is enlarged, especially in the sagittal direction. It bears the =glenoid
cavity= (Cavitas glenoidalis) for articulation with the head of the
humerus. The cavity is oval in outline, and its margin is cut into in
front by the =glenoid notch= (Incisura glenoidalis), and is rounded off
externally; just above its postero-external part is a tubercle to which
a tendon of the teres minor is attached. The =bicipital tuberosity= or
=tuber scapulæ= is the large rough prominence in front, to which the
tendon of origin of the biceps brachii is attached; projecting from its
inner side is the small =coracoid process= (Processus coracoideus), from
which the coraco-brachialis muscle arises.
=Development.=—The scapula has four centers of ossification, viz., one
each for the body of the bone, the bicipital and coracoid processes, the
anterior part of the glenoid cavity, and the tuber spinæ. The last
ossifies after birth and fuses with the spine about the third year. The
bicipital tuberosity and coracoid fuse with the body of the bone about
the end of the first year.
In old subjects the spongy substance disappears at the middle part of
the fossæ, so that the bone consists here of a thin layer of compact
substance. Considerable ossification of the cartilage is usual, the
borders become much rougher, the muscular lines are more pronounced,
and a medullary cavity may appear in the neck. Much variation occurs
in dimensions and slope. The average ratio between the length and
breadth (scapular index) is about 1 ∶ 0.5, but in many cases the base
is relatively wider. The inclination on a horizontal plane varies from
50 to 65 degrees. Exceptionally the coracoid process reaches a length
of an inch or more (2½ to 3 cm.), and the chief nutrient foramen may
be on the posterior border or in the subscapular fossa.
[Illustration:
FIG. 43.—DISTAL END OF LEFT SCAPULA OF HORSE, END VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
THE HUMERUS
The =humerus= is a long bone which extends from the shoulder above,
where it articulates with the scapula, to the elbow below and behind,
where it articulates with the radius and ulna. It is directed obliquely
downward and backward, forming an angle of about 55 degrees with a
horizontal plane. It may be divided into a shaft and two extremities.
[Illustration:
FIG. 44.—PROXIMAL END OF LEFT HUMERUS OF HORSE, END VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =shaft= or =body= (Corpus humeri) is irregularly cylindrical and has
a twisted appearance. It may be regarded as having four surfaces. The
=external surface= is smooth and is spirally curved, forming the
=musculo-spiral groove= (Sulcus musculi brachialis), which contains the
brachialis muscle; the groove is continuous with the posterior surface
above and winds around toward the front below. The =internal surface= is
nearly straight in its length, rounded from side to side, and blends
with the anterior and posterior surfaces. Just above its middle is the
=internal= or =teres tubercle= (Tuberositas teres), to which the tendon
of the latissimus dorsi and teres major muscles is attached. The
=nutrient foramen= is in the lower third of this surface. The =anterior
surface= is triangular, wide and smooth above, narrow and roughened
below. It is separated from the external surface by a distinct border,
which bears on its upper part the =deltoid tuberosity= (Tuberositas
deltoidea). From the latter a rough line curves upward and backward to
the outer surface of the neck, and gives origin to the external head of
the triceps muscle. Below the tuberosity the border inclines forward,
becomes less salient, and ends at the coronoid fossa. The =posterior
surface= is rounded from side to side and smooth.
[Illustration:
FIG. 45.—LEFT HUMERUS OF HORSE, INTERNAL SURFACE. (After Schmaltz,
Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 46.—LEFT HUMERUS OF HORSE, EXTERNAL SURFACE. (After Schmaltz,
Atlas d. Anat. d. Pferdes.)
]
The =proximal extremity= consists of the head, neck, two tuberosities,
and the bicipital groove. The =head= (Caput humeri) presents an almost
circular convex articular surface, which is about twice as extensive as
the glenoid cavity of the scapula, with which it articulates. In front
of the head is a fossa, in which are several foramina. The neck (Collum
humeri) is well defined behind, but is practically absent elsewhere. The
=external tuberosity= (Tuberculum majus) is placed antero-externally,
and consists of two parts; the anterior part forms the outer boundary of
the bicipital groove and gives attachment to the external branch of the
supraspinatus muscle; the posterior part gives attachment to the short
insertion of the infraspinatus, while its outer surface is coated with
cartilage, over which the chief tendon of the same muscle passes to be
inserted into a triangular facet on the outer aspect of the anterior
part. The =internal tuberosity= (Tuberculum minus) is less salient, and
consists of anterior and posterior parts; the anterior part forms the
inner boundary of the bicipital groove, and furnishes insertion to the
inner branch of the supraspinatus above, and the posterior deep pectoral
muscle below; the posterior part gives attachment to the subscapularis
muscle. The =bicipital= or =intertubercular groove= (Sulcus
intertubercularis) is situated in front; it is bounded by the anterior
parts of the tuberosities, and is subdivided by an intermediate ridge.
The groove is covered in the fresh state by cartilage, and lodges the
tendon of origin of the biceps brachii muscle. Just below the
intermediate ridge is a small fossa in which several foramina open.
[Illustration:
FIG. 47.—LEFT HUMERUS OF HORSE, ANTERIOR VIEW. (After Schmaltz, Atlas
d. Anat. d. Pferdes.)
]
The =distal extremity= has an oblique surface for articulation with the
radius and ulna, which consists of two condyles of very unequal size,
separated by a ridge. The =internal condyle= (Condylus medialis) is much
the larger, and is crossed by a sagittal groove, on the anterior part of
which there is usually a synovial fossa. Posteriorly the groove extends
upward considerably above the rest of the articular surface and reaches
the olecranon fossa, and this part articulates with the semilunar notch
of the ulna. The =external condyle= (Condylus lateralis) is much smaller
and is placed somewhat lower and further back, giving the extremity an
oblique appearance; it is marked by a wide shallow groove. The =coronoid
fossa= (Fossa coronoidea) is situated in front above the groove on the
internal condyle; it furnishes origin to part of the extensor carpi, and
external to it is a rough depression from which the anterior or common
extensor of the digit arises. Behind and above the condyles are two
thick ridges, the epicondyles. The =internal= or =flexor epicondyle=
(Epicondylus medialis s. flexorius) is the more salient; it furnishes
origin to flexor muscles of the carpus and digit, and presents
internally a tubercle for the attachment of the internal lateral
ligament of the elbow joint. The =external= or =extensor epicondyle=
(Epicondylus lateralis s. extensorius) bears externally the =external
supracondyloid crest= (Crista condyloidea lateralis), which forms here
the outer boundary of the musculo-spiral groove, and gives origin to the
extensor carpi. Below this is a rough excavation in which the external
lateral ligament is attached. The lower border of the epicondyle gives
attachment to the flexor carpi externus. Between the epicondyles is the
deep =olecranon fossa= (Fossa olecrani).
=Development.=—The humerus ossifies from six centers, viz., three
primary centers for the shaft and epiphyses, and three secondary centers
for the external tuberosity, the deltoid tuberosity, and the internal
condyle. The proximal end fuses with the shaft at about three and
one-half years, the distal at about one and a half years of age.
THE RADIUS
The =radius= is much the larger of the two bones of the forearm in the
horse. It extends in a vertical direction from the elbow, where it
articulates with the humerus, to the carpus below. It is gently curved,
the convexity being anterior. It consists of a shaft and two
extremities.
The =shaft= (Corpus radii) is curved in its length, somewhat flattened
from before backward, and expanded at its ends. It presents for
description two surfaces and two borders. The =anterior surface= (Facies
dorsalis) is smooth, slightly convex in its length, and rounded from
side to side. The =posterior surface= (Facies volaris) is
correspondingly concave in its length and is flattened in the transverse
direction. At its upper part there is a smooth shallow groove, which
concurs with the ulna in the formation of the =interosseous space= of
the forearm; the nutrient foramen is in the lower part of this groove.
Below this there is in the young subject a narrow, rough, triangular
area to which the ulna is attached by an interosseous ligament; in the
adult the two bones are fused here. A variable rough elevation below the
middle of the surface and close to the internal border gives attachment
to the superior check ligament. The =internal border= (Margo medialis)
is slightly concave in its length and is largely subcutaneous; at its
proximal end there is a smooth area on which the tendon of insertion of
the brachialis muscle lies, and a small rough area just below gives
attachment to that muscle and the long internal lateral ligament of the
elbow joint. The =external border= (Margo lateralis) is more strongly
curved, but presents no special features.
The =proximal extremity= or =head= (Capitulum radii) is flattened from
before backward and wide transversely. It presents an articular surface
(Fovea capituli) which corresponds to that on the distal end of the
humerus; it is crossed by a central sagittal ridge, which has a synovial
fossa on its posterior part, and ends in front at a prominent lip, the
=coronoid process= (Processus coronoideus). Just below the posterior
border there are two concave facets for articulation with the ulna, and
between these and the interosseous space is a quadrilateral rough area
at which the two bones are united by an interosseous ligament. At the
inner side of the anterior surface is the =bicipital tuberosity=
(Tuberositas radii), into which the biceps tendon is inserted. The
=internal tuberosity= is continuous with the preceding eminence, and
furnishes attachment to the short part of the internal lateral ligament.
The =external tuberosity= is more salient; it gives attachment to the
external lateral ligament and to the anterior and lateral extensor
muscles of the digit.
[Illustration:
FIG. 48.—LEFT RADIUS AND ULNA OF HORSE, EXTERNAL VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 49.—LEFT RADIUS AND ULNA OF HORSE, POSTERIOR VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =distal extremity= is also compressed from before backward. It
presents the =carpal articular surface= (Facies articularis carpea)
which consists of three parts. The inner facet is the largest, is
quadrilateral, concavo-convex from before backward, and articulates with
the radial carpal bone (or scaphoid); the middle one is somewhat similar
in form but smaller, and articulates with the intermediate carpal bone
(or semilunar); the outer facet is smaller, is convex, and articulates
below with the ulnar carpal (or cuneiform) and behind with the accessory
carpal (or pisiform). The anterior surface presents three =grooves=,
separated by ridges. The middle one is vertical and gives passage to the
tendon of the extensor carpi radialis; the outer one is similar and
contains the tendon of the anterior extensor of the digit; the inner one
is small and oblique and lodges the tendon of the extensor carpi
obliquus. The posterior aspect is crossed by a rough ridge, below which
are three depressions. On either side is a tuberosity (Tuberculum
ligamenti) to which the lateral ligament is attached. The outer one is
marked by a small vertical groove for the passage of the lateral
extensor tendon.
=Development.=—The radius ossifies from four centers, viz., one each for
the shaft, the two extremities, and the outer part of the distal end;
the last is morphologically the distal end of the ulna which has fused
with the radius, and the line of fusion is often indicated by a distinct
groove on the carpal articular surface. The proximal extremity unites
with the shaft at about one and a half years, the distal end at about
three and a half years.
[Illustration:
FIG. 50.—UPPER HALF OF RADIUS AND ULNA OF HORSE, INTERNAL VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
THE ULNA
The =ulna= of the horse is a reduced long bone situated behind the
radius, with which it is partially fused in the adult.
The =shaft= (Corpus ulnæ) is three-sided and tapers to a point below.
The =anterior surface= (Facies dorsalis) is applied to the posterior
surface of the radius, and below the interosseous space the two bones
are fused in the adult. The surface which enters into the formation of
the space is smooth and usually presents a small nutrient foramen,
directed upward. Above the space it is rough and is attached to the
radius by an interosseous ligament which is usually permanent. The
=internal surface= (Facies medialis) is smooth and slightly concave. The
=external surface= (Facies lateralis) is flattened. The =internal= and
=external borders= are thin and sharp, except at the interosseous space.
The =posterior border= is slightly concave in its length and is rounded.
The lower end is pointed and is usually a little below the middle of the
radius. It is commonly continued by a fibrous cord to the distal
external tuberosity of the radius, but this band may be replaced in part
or entirely by bone.
The =proximal extremity= is the major part of the bone. It projects
upward and somewhat backward behind the lower end of the humerus, and
forms a lever arm for the extensor muscles of the elbow. The =internal
surface= is concave and smooth. The =external surface= is convex and is
roughened above. The =anterior border= bears on its middle a pointed
projection, the =processus anconæus= or “beak,” which overhangs the
=semilunar notch= or =sigmoid cavity= (Incisura semilunaris). The latter
is triangular in outline, concave from above downward, and articulates
with the humerus; in the middle of its lower part is an extensive
synovial fossa. Just below the notch are two convex =facets= which
articulate with those on the posterior aspect of the proximal end of the
radius. The =posterior border= is nearly straight, and is thick and
rounded. The free end or summit is a rough tuberosity, the =olecranon=,
which gives attachment to the triceps brachii and other muscles.
The primitive =distal extremity= has, as previously stated, fused with
the radius.
=Development.=—The ulna ossifies from three centers, of which one is for
the main part of the bone, one for the olecranon, and one for the distal
end. The cartilaginous embryonic ulna extends the entire length of the
forearm. The lower part of the shaft is usually reduced to a small
fibrous band or may disappear entirely; in some cases a variable remnant
of it ossifies. The distal extremity fuses early with the radius. The
olecranon unites with the rest of the bone at three to three and a half
years. A medullary canal appears to occur constantly in the
adult—contrary to the statements of some authors.
THE CARPUS
The =carpus= of the horse consists of seven or eight bones (Ossa carpi)
arranged in two rows, proximal or antibrachial, and distal or
metacarpal. The (abbreviated) names and relative positions of the bones
of the left carpus as seen from in front are indicated below.
_Proximal Row:_
Radial Intermediate Ulnar Accessory
_Distal Row:_
First Second Third Fourth
THE RADIAL CARPAL BONE
The =radial carpal= bone (Os carpi radiale, scaphoid) is the largest
bone of the upper row; it is somewhat compressed laterally, and is
clearly six-sided. The =superior= or =proximal surface= is convex in
front, concave behind, and articulates with the inner facet on the
distal end of the radius. The =inferior= or =distal surface= is also
convex in front and concave behind; it articulates with the second and
third carpal bones. The =external surface= bears upper and lower facets
on its anterior part for articulation with the intermediate; between and
behind these it is excavated and rough. The =anterior= or =dorsal
surface= is rough and slightly convex. The =internal surface= and the
=posterior= or =volar surface= are rough and tuberculate.
[Illustration:
FIG. 51.—SAGITTAL SECTION OF UPPER PART OF RADIUS AND ULNA OF HORSE.
_Cm_, Medullary cavity of ulna.
]
THE INTERMEDIATE CARPAL BONE
The =intermediate carpal= bone (Os carpi intermedium, semilunar, lunar)
is somewhat wedge-shaped, wider in front than behind. The =superior= or
=proximal surface= is saddle-shaped, and articulates with the middle
facet on the distal end of the radius. The =inferior= or =distal
surface= is smaller, convex in front, concave behind, and articulates
with the third and fourth carpal bones. The =internal surface= has upper
and lower facets for articulation with the radial carpal, and between
these it is excavated and rough. The =external surface= is similar to
the preceding and articulates with the ulnar carpal. The =anterior= or
=dorsal surface= is rough and slightly convex. The =posterior= or =volar
surface= bears a tuberosity on its lower part.
THE ULNAR CARPAL BONE
The =ulnar carpal= bone (Os carpi ulnare, cuneiform) is the smallest and
most irregular bone of the upper row. The =superior= or =proximal
surface= is concave, and fits the lower part of the outer facet on the
distal end of the radius. The =inferior= or =distal surface= is oblique
and undulating for articulation with the fourth carpal bone. The
=internal surface= has upper and lower facets for articulation with the
intermediate. The =anterior= or =dorsal= and =external surfaces= are
continuous, convex, and rough. The =posterior= or =volar surface= is
oblique, and bears a concave facet for articulation with the accessory
carpal bone; below this is a tubercle.
[Illustration:
FIG. 52.—LEFT CARPAL BONES OF HORSE, WITH DISTAL END OF RADIUS AND
PROXIMAL END OF METACARPUS; INTERNAL VIEW.
]
[Illustration:
FIG. 53.—LEFT CARPAL BONES OF HORSE, WITH ADJACENT ENDS OF RADIUS AND
METACARPUS; EXTERNAL VIEW.
_Ca_, Accessory carpal bone; _Cr_, radial carpal; _Ci_, intermediate
carpal; _Cu_, ulnar carpal; _C1–4_, first to fourth carpals; _Mc.
II_, _III_, _IV_, metacarpal bones; _1_, groove for tendon of
extensor carpi obliquus; _2_, groove for lateral extensor tendon;
_3_, groove for tendon of flexor carpi externus; _4_, metacarpal
tuberosity. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
THE ACCESSORY CARPAL BONE
The =accessory carpal= bone (Os carpi accessorium, pisiform) is situated
behind the ulnar carpal bone and the outer part of the distal end of the
ulna. It is discoid and presents for description two surfaces and a
circumference. The =internal surface= is concave and forms the outer
wall of the carpal groove. The =external surface= is convex and rough; a
smooth groove for the outer tendon of the flexor carpi externus crosses
its anterior part obliquely downward and slightly forward. The =anterior
border= bears two facets; the upper one is concave and articulates with
the back of the outer facet on the distal end of the radius; the lower
one is convex and articulates with the ulnar carpal bone. The remainder
of the circumference is rounded and rough.
The accessory does not directly bear weight, and may be regarded as a
sesamoid bone interposed in the course of the tendons of the middle
and external flexors of the carpus, which it enables to act at a
mechanical advantage. The posterior border furnishes attachment to the
transverse carpal ligament, which completes the carpal canal for the
flexors of the digit.
THE FIRST CARPAL BONE
The =first carpal= bone (Os carpale primum, trapezium) is a small
inconstant bone, commonly about the size and shape of a pea, which is
situated in the lower part of the internal lateral ligament behind the
second carpal bone.
This bone appears to be absent on both sides in about half of the
cases; in a good many subjects it is present on one side only. In size
it varies from a minute nodule to a discoid mass 10 to 12 mm. in
length. In exceptional cases it articulates with both the second
carpal and the second (inner) metacarpal bone, in other cases with the
former only, but in the majority of specimens no articular facet is
present.
THE SECOND CARPAL BONE
The =second carpal= bone (Os carpale secundum, trapezoid) is the
smallest constant bone of the lower row, and is irregularly
hemispherical in shape. The =superior= or =proximal surface= is a convex
facet which is continued upon the =posterior= or =volar surface= and
articulates with the posterior part of the radial carpal. The =external
surface= faces obliquely outward and forward, and bears three facets for
articulation with the third carpal bone. The =anterior= or =dorsal= and
the =internal surface= bear a tuberosity to which the lateral ligament
is attached. The =inferior= or =distal surface= is articular and
consists of a large flattened facet for the inner (second) metacarpal
bone, and a small one for the large (third) metacarpal bone. Some
specimens have a small facet on the lower part of the posterior surface
which articulates with the first carpal bone.
[Illustration:
FIG. 54.—CARPAL BONES OF HORSE, WITH ADJACENT ENDS OF RADIUS AND
METACARPUS; ANTERIOR VIEW. THE ACCESSORY AND FIRST CARPAL BONES ARE
NOT SHOWN.
]
[Illustration:
FIG. 55.—CARPAL ARTICULAR SURFACE OF RADIUS AND PROXIMAL ARTICULAR
SURFACES OF CARPAL AND METACARPAL BONES, LEFT SIDE. THE ACCESSORY
AND FIRST CARPAL BONES ARE NOT SHOWN.
_Cr_, Radial carpal; _Ci_, intermediate carpal; _Cu_, ulnar carpal;
_C2_, _C3_, _C4_, second, third, and fourth carpals; _Mc.II_, second
or inner small metacarpal bone; _Mc.III_, third or large metacarpal
bone; _Mc.IV_, fourth or outer small metacarpal bone; _1_, _2_,
grooves for tendons of anterior extensor and extensor carpi
radialis; _3_, metacarpal tuberosity. Arrows indicate relations of
facets. Short arrow points to facet on ulnar carpal for articulation
with accessory carpal. (After Schmaltz, Atlas. d. Anat. d. Pferdes.)
]
THE THIRD CARPAL BONE
The =third carpal= bone (Os carpale tertium, os magnum) is much the
largest bone of the lower row, forming more than two-thirds of the width
of the latter. It is flattened from above downward, and is twice as wide
in front as behind. The =superior= or =proximal surface= consists of two
facets separated by an antero-posterior ridge; the inner facet is
concave and articulates with the radial carpal; the outer facet—for the
intermediate carpal—is concave in front and convex behind, where it
encroaches on the posterior surface. The =inferior= or =distal surface=
is slightly undulating, and articulates almost entirely with the large
(third) metacarpal bone, but it usually bears a small oblique facet at
its inner side for the inner (second) metacarpal, and there is commonly
a non-articular depression externally. The _internal surface_ faces
backward and inward, and bears three facets for articulation with the
second carpal, between which it is excavated and rough. The =external
surface= has two facets for articulation with the fourth carpal, and is
depressed and rough in its middle. The =anterior= or =dorsal surface= is
convex and is crossed by a rough transverse ridge. The =posterior= or
=volar surface= is relatively small, and is rounded; its upper part is
encroached upon by the superior articular surface, below which it is
rough.
THE FOURTH CARPAL BONE
The =fourth carpal= bone (Os carpale quartum, unciform) is somewhat
wedge-shaped, and is readily distinguished from the second by its
greater size and its posterior tubercle. The =superior= or =proximal
surface= articulates with the intermediate and ulnar; it is convex and
curves outward, backward, and downward, encroaching on the external and
posterior surfaces. The =inferior= or =distal surface= bears two inner
facets for the large (third) metacarpal and an outer one for the
external (fourth) metacarpal bone. The =internal surface= has two or
three facets for articulation with the third carpal, between which it is
excavated and rough. The =anterior= or =dorsal surface= is convex and
rough. The =external surface= is small, being encroached upon by the
superior articular surface. The =posterior= or =volar surface= bears a
tubercle on its lower part.[21]
THE CARPUS AS A WHOLE
The bones of the carpus, exclusive of the accessory, form an irregular
quadrangular mass, the width of which is about twice the height or the
antero-posterior diameter. The =anterior= or =dorsal surface= is convex
from side to side, depressed along the line of junction of the two rows,
and prominent below. The =posterior= or =volar surface= is in general
slightly convex, but very irregular. It forms with the accessory the
=carpal groove= (Sulcus carpi), which in the recent state is rendered
smooth by the posterior ligament; it is converted into the =carpal
canal= (Canalis carpi) for the flexor tendons by the transverse carpal
ligament, which stretches across from the accessory bone to the inner
side. The =proximal surface= is widest internally and is elevated in
front, concave behind; it is entirely articular and adapted to the
carpal articular surface of the radius. The =distal surface= is also
articular and is irregularly faceted in adaptation to the surfaces of
the metacarpal bones; each of the lower bones usually articulates with
two metacarpal bones, but sometimes the third does not bear on the inner
metacarpal bone. The =lateral surfaces= are both irregular and rough,
the internal one being the wider. With the exception of the accessory,
ulnar, and second, each bone articulates with two bones of the other
row.
=Development.=—Each ossifies from a single center.
THE METACARPUS
Three =metacarpal bones= (Ossa metacarpalia) are present in the horse.
Of these, only one, the third or large metacarpal bone, is fully
developed and carries a digit; the other two, the second and fourth, are
much reduced, and are commonly called the internal and external small
metacarpal or “splint” bones.
[Illustration:
FIG. 56.—DISTAL ROW OF CARPAL BONES, METACARPUS, FIRST AND SECOND
PHALANGES, AND PROXIMAL SESAMOID BONES OF HORSE; POSTERIOR VIEW,
LEFT SIDE.
The fourth (external) metacarpal bone is wrongly numbered as I. (After
Schmaltz, Atlas. d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 57.—LEFT METACARPAL AND DIGITAL BONES OF HORSE, INTERNAL VIEW.
(After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
THE LARGE METACARPAL BONE
This (Os metacarpale tertium) is a very strong long bone, placed
vertically between the carpus above and the first phalanx below. It
consists of a shaft and two extremities.
The =shaft= (Corpus) is semicylindrical, and presents two surfaces and
two borders. The =anterior= or =dorsal surface= is smooth, convex from
side to side, and nearly straight in its length. The =posterior= or
=volar surface= is somewhat convex from side to side and, with the small
bones, forms a wide groove which lodges the suspensory ligament. On
either side of its upper two-thirds it is roughened for the attachment
of the small metacarpal bones. The =nutrient foramen= occurs at the
junction of the upper and middle thirds. The lower third is wider and
flattened. The borders are rounded.
The =proximal extremity= (Basis) bears an undulating articular surface
adapted to the lower row of carpal bones. The greater part supports the
third carpal bone; the oblique outer part, separated from the preceding
by a ridge, articulates with the fourth, and a small facet for the
second is usually found at the postero-internal angle. On either side is
a notch separating two small facets which articulate with the proximal
ends of the small metacarpal bones. Toward the inner side of the
anterior surface is the =metacarpal tuberosity=, into which the extensor
carpi radialis is inserted. The posterior surface is roughened for the
attachment of the suspensory ligament.
The =distal extremity= (Trochlea s. Capitulum) presents an articular
surface for the first phalanx and the proximal sesamoid bones, which is
composed of two condyles, separated by a sagittal ridge; the inner
condyle is slightly the larger. On either side is a small fossa,
surmounted by a tubercle, for the attachment of the lateral ligaments of
the fetlock joint.
The large metacarpal is one of the strongest bones in the skeleton.
The compact substance is specially thick in front and internally. The
medullary canal extends further toward the ends than in most of the
long bones of the horse and there is little spongy bone.
THE SMALL METACARPAL BONES
These are situated on either side of the posterior surface of the large
metacarpal bone, and form the sides of the metacarpal groove. Each
consists of a shaft and two extremities.
The =shaft= (Corpus) is three-sided and tapers to the distal end. It is
variably curved, convex toward the middle line of the limb. The anterior
surface is flattened and is rough, except in its lower part; it is
attached to the large metacarpal bone by an interosseous ligament,
except near the distal end. The abaxial surface is smooth and rounded
from side to side above, grooved below. The axial surface is smooth and
concave from edge to edge, except below, where it forms a rounded edge.
The =proximal extremity= or =head= (Basis) is relatively large. In the
case of the inner bone it usually bears two facets above which support
the second and third carpal bones, while the outer bone has here a
single facet for articulation with the fourth carpal bone. Each has also
two facets for articulation with the large metacarpal, and is elsewhere
roughened for the attachment of ligaments and muscles. The inner bone
may present a small facet behind for the first carpal bone.
The =distal extremity= (Capitulum) is usually a small nodule, which
projects to a variable extent in different subjects, and is easily felt
in the living animal. It is situated two-thirds to three-fourths of the
way down the region.
The small metacarpal bones vary much in length, thickness, and
curvature. In the majority of cases the inner bone is the longer; in
other subjects the outer one is the longer or there is no material
difference. Sometimes the curvature is very pronounced, so that the
distal end causes a decided projection. The distal end is very
variable in size and may be a mere point.
=Development.=—The large metacarpal bone ossifies from three centers.
The proximal extremity unites with the shaft before birth, the distal
extremity toward the middle of the second year. The small metacarpal
bones ossify from two centers, one of which is for the proximal
extremity. Their distal ends are cartilaginous at birth. Fusion of the
middle part of the shaft with the large metacarpal bone is common.
THE PHALANGES
THE FIRST PHALANX
The _first phalanx_ (Phalanx prima)[22] is a long bone, situated between
the large metacarpal bone above and the second phalanx below. It is
directed obliquely downward and forward, forming an angle of 50 to 55
degrees with the horizontal plane in well-formed limbs. It consists of a
shaft and two extremities.
The =shaft= (Corpus) is wider and much thicker above than below, and
presents two surfaces and two borders. The =anterior= or =dorsal
surface= is convex from side to side and smooth. The =posterior= or
=volar surface= is flattened, and bears a triangular rough area, bounded
laterally by ridges which begin at the tuberosities above and converge
below; this area furnishes attachment to the inferior sesamoidean
ligaments. The =borders=, =internal= and =external=, are rounded and
have a rough area or a tubercle on their middle parts.
The =proximal extremity= (Basis) is relatively large. It bears an
articular surface adapted to the distal end of the large metacarpal
bone, consisting of two glenoid cavities separated by a sagittal groove;
the inner cavity is a little larger than the outer one. The posterior
angles are formed by buttress-like tuberosities for ligamentous
attachment. The anterior surface has a slight elevation for the
attachment of the lateral extensor tendon.
The =distal extremity= is smaller, especially in its antero-posterior
diameter. It presents a trochlea for articulation with the second
phalanx, consisting of a shallow central groove and two lateral convex
areas or condyles; the inner area is a little the larger. On either
side, just above the margin of the articular surface, is a depression
surmounted by a tubercle, to both of which the lateral ligament is
attached. Behind the tubercle is a distinct facet to which the
superficial flexor tendon is attached.
=Development.= The first phalanx ossifies from three centers. The distal
end unites with the shaft before birth, the proximal end early in the
first year.
The first phalanx contains a small medullary canal in the middle of
the shaft. It may be remarked that the bone is twisted slightly; when
placed volar surface down on the table, it touches the latter by three
points only, the proximal tuberosities and the internal condyle.
THE SECOND PHALANX
The =second phalanx= (Phalanx secunda)[23] is situated between the first
and third phalanges, its direction corresponding to that of the first
phalanx. It is flattened from before backward, and its width is greater
than its height. It may be described as possessing four surfaces.
The =upper= or =proximal surface= presents two glenoid cavities
separated by a low ridge, and articulates with the first phalanx. The
middle of the anterior border is elevated and roughened in front for the
attachment of the anterior or common extensor tendon. The posterior
border is thick and overhanging; in the fresh state its middle part is
covered with cartilage, over which the deep flexor tendon passes. On
either side there is an eminence, to which the lateral ligament and the
superficial flexor tendon are attached.
The =inferior= or =distal surface= is trochlear, and articulates with
the third phalanx and third sesamoid bone. It resembles somewhat the
trochlea of the first phalanx, but is more extensive and encroaches more
on the anterior and posterior surfaces.
The =anterior= or =dorsal surface= is convex from side to side and
smooth in its middle; on its lower part are lateral rough depressions,
surmounted by tuberosities, to both of which ligaments are attached.
The =posterior= or =volar= surface is smooth, flattened, and slopes
obliquely downward and forward. The borders which separate the anterior
and posterior surfaces are concave from above downward, rounded from
before backward.
=Development.=—The second phalanx ossifies like the first, but the
proximal end unites with the shaft two or three months earlier.
[Illustration:
FIG. 58.—PHALANGES AND THIRD SESAMOID OF HORSE, DORSAL ASPECT.
]
THE THIRD PHALANX
The =third= or =ungual phalanx= (Phalanx tertia)[24] is entirely
inclosed by the hoof, to which it conforms in a general way. It presents
for examination three surfaces, three borders, and two angles or wings.
The =articular surface= (Facies articularis) faces upward and backward,
and is chiefly adapted to the distal surface of the second phalanx, but
a narrow flattened area along the posterior border articulates with the
third sesamoid. The =anterior= or =coronary border= forms a central
eminence, the =extensor= (or pyramidal) =process= (Processus
extensorius), to the front of which the anterior extensor tendon is
attached. On either side is a depression for the attachment of the
lateral ligament.
The =dorsal= or =wall surface= (Facies dorsalis) slopes downward and
forward. The angle of inclination on the ground plane is about 45 to 50
degrees in front. Laterally the height diminishes, and the slope becomes
steeper, especially on the inner side. From side to side the curvature
is almost semicircular. The surface is rough and porous, resembling
pumice stone somewhat. It is perforated by numerous foramina of various
sizes; a series of larger ones is situated on or near the lower border.
On either side the =dorsal= (or preplantar) =groove= (Sulcus dorsalis)
passes forward from the wing and ends at one of the larger foramina. In
the fresh state this surface is covered by the matrix of the wall of the
hoof. The =inferior= or =distal border= is thin, sharp, and irregularly
notched; there is commonly a wider notch in front.
The =volar= or =inferior surface= (Facies volaris) is arched, and
divided into two unequal parts by a curved rough line, the =semilunar
crest= (Crista semilunaris). The larger anterior area is
crescent-shaped, concave, and comparatively smooth; it corresponds to
the sole of the hoof, and may be termed the =sole surface=. The
posterior part is much smaller, and is semilunar; it is related to the
deep flexor tendon, and is hence called the =flexor= or =tendon surface=
(Facies flexoria). It presents a central prominent rough area, on either
side of which is the =volar= (or plantar) =foramen= (Foramen volare), to
which the =volar= (or plantar) =groove= (Sulcus volaris) conducts from
the wing. The foramina lead into the =semilunar canal= within the bone,
from which small canals lead to some of the foramina of the wall
surface. The deep flexor tendon is inserted into the semilunar crest and
the central rough area behind it.
The volar grooves and foramina transmit the terminations of the
digital arteries into the semilunar canal, where they meet and form a
terminal arch, from which branches pass through canals in the bone and
emerge through the foramina on the wall surface.
The =angles= or =wings= (Anguli) are prismatic masses which project
backward on either side; the inner one is usually the shorter. Each is
divided into upper and lower parts by a notch, or is perforated by a
foramen which leads to the vascular groove on the side of the wall
surface.[25] The upper border carries the lateral cartilage.
The =lateral cartilages= (Cartilagines ungulæ) are rhomboid curved
plates, which surmount the wings on either side. They are relatively
large and extend above the margin of the hoof sufficiently to be
distinctly palpable. The abaxial surface is convex, the axial concave.
The upper border is convex and thin; the lower is thicker and is in part
attached to the wing. The anterior end is attached by ligament to the
side of the second phalanx. The posterior end curves toward its fellow
at the heel, and is perforated by numerous foramina for the passage of
veins. The central part is mainly hyaline, the periphery mainly fibrous.
It will be noted that the size and form of the wings vary much in
different specimens. In the new-born foal the wing is a small, pointed
projection. Later the process of ossification invades the lower part
of the cartilage to a varying extent. In some cases the greater part
of the cartilage is ossified—a condition commonly termed “sidebone.”
=Development.=—The ossification of the terminal phalanx is peculiar.
While the proximal articular part is still cartilaginous, a
perichondrial cap of bone is formed in relation to the hoof. Later the
process extends into the upper part.
=Structure.=—The interior of this bone is channeled by numerous canals
for vessels, most of which radiate from the semilunar canal to the wall
surface; these are not canals for nutrient vessels of the bone, but
transmit arteries to the matrix of the hoof. Thick layers of compact
substance are found at the articular and flexor surfaces and the
extensor process, _i. e._, at the points of greatest pressure and
traction.
THE SESAMOID BONES
The two =proximal= or =great sesamoids= (Ossa sesamoidea phalangis
primæ) are situated behind the distal end of the large metacarpal bone,
and are closely attached to the first phalanx by strong ligaments. Each
has the form of a three-sided pyramid. The =anterior= or =articular
surface= conforms to the corresponding part of the distal end of the
large metacarpal bone. The =posterior= or =flexor surface= is flattened
and oblique; in the fresh state it is covered by a layer of cartilage
which also fills the interval between the opposed borders of the two
bones, and forms a smooth groove for the deep flexor tendon. The
=abaxial surface= is concave, and gives attachment to part of the
suspensory ligament; it is separated from the posterior surface by a
rough everted border. The =base= faces downward, and furnishes
attachment to the inferior sesamoidean ligaments. The =apex= is directed
upward and is rounded.
The =third sesamoid= or =navicular= bone (Os sesamoideum phalangis
tertiæ) is shuttle-shaped, and is situated behind the junction of the
second and third phalanges. Its long axis is transverse, and it
possesses two surfaces, two borders, and two extremities. The =articular
surface= (Facies articularis) faces upward and forward; it consists of a
central eminence, flanked by concave areas, and articulates with the
distal end of the second phalanx. The =flexor= or =tendon surface=
(Facies flexoria) is directed downward and backward. It resembles the
articular surface in form, but is more extensive and not so smooth. In
the fresh state it is coated with cartilage and the deep flexor tendon
plays over it. The =proximal border= (Margo liber) is wide and grooved
in its middle, narrower and rounded on either side. The =distal border=
(Margo ligamenti) bears in front a narrow facet for articulation with
the third phalanx. Behind this is a groove, which contains a number of
relatively large foramina, and is bounded behind by a prominent edge.
The =extremities= are blunt-pointed.
[Illustration:
FIG. 59.—THIRD SESAMOID OR NAVICULAR BONE OF HORSE. (After Schmaltz,
Atlas d. Anat. d. Pferdes.)
]
=Development.=—It ossifies from a single center.
THE BONES OF THE PELVIC LIMB
The =pelvic girdle= consists of the ossa coxæ, which unite ventrally at
the symphysis pelvis, and articulate with the sacrum dorsally.
OS COXÆ
The =os coxæ= (or os innominatum) forms the skeleton of the hip or
haunch, and is the largest of the flat bones. It consists primarily of
three parts, the =ilium=, =ischium=, and =pubis=, which meet to form the
=acetabulum=, a large cotyloid cavity for articulation with the head of
the femur. These parts are fused at about one year of age, but it is
convenient to describe them separately.
THE ILIUM
The =ilium= (Os ilium) is the largest of the three parts. It is
irregularly triangular and presents two surfaces, three borders, and
three angles.
The =gluteal surface= (Facies glutæa) faces upward, backward, and
outward. It is wide and concave in front, narrower and convex behind.
The wide part is crossed by the curved =gluteal line= (Linea glutæa),
which extends from the middle of the inner border toward the external
angle. This surface gives attachment to the middle and deep gluteal
muscles.
[Illustration:
FIG. 60.—OSSA COXARUM OF MARE, DORSAL VIEW.
_O.il._, Ilium; _O.p._, pubis; _O.is._, ischium; _A.o.i._, wing of
ilium; _C.o.i._, shaft of ilium; _Cr.o.i._, anterior border (crest)
of ilium; _1_, obturator foramen; _2_, acetabulum; _3_, internal
angle of ilium; _4_, external angle of ilium; _5_, gluteal line;
_6_, psoas tubercle; _7_, _8_, acetabular and symphyseal branches of
pubis; _9_, _10_, acetabular and symphyseal branches of ischium;
_12_, lesser sciatic notch; _13_, ischial arch; _14_, great sciatic
notch; _15_, symphysis pelvis; _17_, ilio-pectineal eminence; _18_,
anterior borders of pubic bones; _19_, posterior gluteal line.
(Struska, Anat. d. Haustiere.)
]
The =pelvic surface= (Facies pelvina) faces in the opposite direction;
it is convex, and consists of two distinct parts. The inner triangular
part (Pars articularis) is roughened for ligamentous attachment, and
bears an irregular facet, the =auricular surface= (Facies auricularis),
for articulation with the sacrum. The outer quadrilateral part (Pars
iliaca) is in general smooth. It is crossed by the =ilio-pectineal line=
(Crista iliopectinea), which begins below the auricular surface and is
continued on the shaft of the bone to join the anterior border of the
pubis. The line is interrupted by furrows for the iliaco-femoral
vessels, and below these it bears the =psoas tubercle= (Tuberculum
psoadicum), which gives attachment to the psoas minor muscle. The
iliacus muscle is attached to the surface external to the ilio-pectineal
line.
The =anterior border= or =crest= (Crista iliaca) is concave, thick, and
rough.
The =internal border= is deeply concave; its middle part forms the lower
boundary of the =great sciatic foramen=, and it is continuous behind
with the =superior ischiatic spine=.
The =external border= is concave and in great part rough. Its fore part
is crossed by grooves for the ilio-lumbar vessels, which are continued
on the pelvic surface. The =nutrient foramen= is usually situated on or
near the posterior part of this border.
[Illustration:
FIG. 61.—OSSA COXARUM OF MARE, VENTRAL VIEW.
_D_, Ilium; _Sch._, pubis; _S_, ischium; _a_, anterior border (crest)
of ilium; _b_, internal angle of ilium; _c′_, external angle of
ilium; _d_, great sciatic notch; _e_, external border of ilium; _f_,
iliac surface; _g_, linea arcuata; _h_, rough ligamentous area; _i_,
auricular surface; _k_, ilio-pectineal line; _l_, psoas tubercle;
_m_, transverse branch, and _n_, symphyseal branch of pubis; _o_,
_o′_, symphysis pelvis; _p_, anterior border of pubis (pecten); _q_,
tuberculum pubicum; _r_, ilio-pectineal eminence; _s_, tuber ischii;
_t_, ischial arch; _u_, lesser sciatic notch; _v_, acetabular
branch, and _w_, symphyseal branch of ischium; _x_, obturator
foramen; _y_, articular surface of acetabulum; _z_, fossa acetabuli;
_1_, groove for ilio-lumbar artery; _2_, groove for iliaco-femoral
artery; _3_, subpubic groove; _4_, depression for inner tendon of
origin of rectus femoris; _5_, rough area for attachment of adductor
muscles. (Ellenberger-Baum, Anat. d. Haustiere.)
]
The =internal= or =sacral angle= (Tuber sacrale) curves upward and a
little backward close to the first sacral spine, and forms here the
highest point of the skeleton. It is somewhat thickened and rough.
The =external= or =coxal angle= (Tuber coxæ) forms the basis of the
point of the hip. It is a large quadrangular mass, narrow in its middle,
and enlarged at either end, where it bears a pair of tuberosities. It is
roughened for muscular attachment.
The =posterior= or =acetabular angle= meets the other two bones at the
acetabulum, of which it forms about two-fifths. Its prominent upper
border forms part of the =superior ischiatic spine=, which is roughened
externally, smooth internally. Two depressions above and in front of the
acetabulum give attachment to the tendons of origin of the rectus
femoris muscle. This angle is connected with the ala or wide part of the
bone by a constricted part, often termed the =shaft=. The latter is of
three-sided prismatic form. Its external surface is convex and rough,
and gives attachment to the deep gluteus muscle. Its pelvic surface is
smooth and is grooved for the obturator vessels and nerves. Its ventral
surface is crossed by vascular grooves, below which is a rough area,
bounded internally by the psoas tubercle.
THE ISCHIUM
The =ischium= (Os ischii) forms the posterior part of the ventral wall
or floor of the bony pelvis. It slopes a little downward and inward, but
is practically horizontal in the longitudinal direction. It is
irregularly quadrilateral, and may be described as having two surfaces,
four borders, and four angles.
The =superior= or =pelvic surface= (Facies pelvina) is smooth and
slightly concave from side to side.
The =inferior surface= (Facies externa) is nearly flat, and is in great
part roughened for the attachment of the adductor muscles.
The =anterior border= forms the posterior margin of the obturator
foramen.
The =posterior border= is thick and rough. It slopes obliquely inward
and forward to meet the border of the other side, forming with it the
=ischial arch= (Arcus ischiadicus).
The =internal border= meets the opposite bone at the symphysis.
The =external border= is thick and rounded, but concave in =its length=;
it forms the =lesser sciatic notch=, the lower boundary of the lesser
sciatic foramen.
The =antero-internal angle= or =symphyseal branch= (Ramus symphyseos)
meets the pubis, with which it forms the inner boundary of the obturator
foramen.
The =antero-external angle= or =acetabular branch= joins the other two
bones at the acetabulum, of which it forms more than half. Superiorly it
bears part of the =superior ischiatic spine= (Spina ischiadica), and
internally it is grooved for the obturator vessels.
The =postero-external angle= is a thick three-sided mass, the =tuber
ischii= (Tuber ischiadicum); its lower border is the =inferior ischiatic
spine=, to which the biceps femoris and semitendinosus muscles are
attached.
THE PUBIS
The =pubis= (Os pubis) is the smallest of the three parts of the os
coxæ. It forms the anterior part of the pelvic floor, and may be
described as having two surfaces, three borders, and three angles.
The =superior= or =pelvic surface= (Facies pelvina) is convex in the
young subject and the stallion, concave and smooth in the mare and
usually in the gelding also. The urinary bladder rests on it.
The =inferior= or =ventral surface= (Facies externa) is convex, and in
great part rough for muscular attachment. Near the anterior border it is
crossed by the =subpubic groove=, the inner part of which is occupied by
a large vein, the outer part by the pubo-femoral ligament.
The =anterior border= is thin in its inner part (except in the young
subject and the stallion), forming the pecten ossis pubis. Externally it
bears the rough =ilio-pectineal eminence= (Eminentia iliopectinea),
beyond which it is continuous with the ilio-pectineal line.
The =internal border= joins the opposite bone at the symphysis pubis.
The =posterior border= forms the anterior margin of the obturator
foramen, and is marked externally by the obturator groove.
The =internal angle= meets its fellow at the anterior end of the
symphysis. This part is very thick in the young subject and the
stallion, but in the mare, and usually in the gelding also, it becomes
thin with advancing age.
The =external= or =acetabular angle= joins the ilium and ischium at the
acetabulum.
The =posterior angle= joins the ischium, with which it forms the inner
boundary of the obturator foramen.
The =pubis= may conveniently be regarded as consisting of two branches
which meet at a right angle; these are termed the =transverse= or
=acetabular branch= (Ramus acetabularis) and the =longitudinal= or
=symphyseal branch= (Ramus symphysecs).
The =acetabulum= is a cotyloid cavity which lodges the head of the
femur. It faces downward and outward, and consists of an articular and a
non-articular part. The =articular part= (Facies lunata) is crescentic,
and is cut into internally by the non-articular part, which lies at a
lower level, and is termed the =acetabular fossa= (Fossa acetabuli). The
inner part of the rim is correspondingly cut into by the =acetabular
notch= (Incisura acetabuli), which is converted into a foramen by the
transverse ligament in the fresh state, and transmits the pubo-femoral
and round ligaments to the head of the femur.
The =obturator foramen= (Foramen obturatum) is situated between the
pubis and ischium. It is oval in outline, the longer axis being directed
forward and outward. Its margin is grooved antero-externally for the
obturator nerve and vessels.
[Illustration:
FIG. 62.—OSSA COXARUM OF STALLION, DORSAL VIEW. (After
Ellenberger-Baum, Anat. für Künstler.)
]
=Development.=—Each division of the os coxæ ossifies from one chief
center. The center for the ilium appears first near the acetabulum,
followed quickly by one for the ischium, and a little later by the pubic
center. Secondary centers appear for the crest and external angle of the
ilium, the tuber and posterior border of the ischium, and the acetabular
part of the pubis. The pubis and ischium are united at birth or soon
after, but are not fused with the ilium until the second year. The
epiphyseal parts fuse with the main mass at four and a half to five
years of age.
The acetabular part of the pubis ossifies from a separate center. It
is most distinct in the embryo at three months, and is often called
the os acetabuli. Martin says that the ilium has a center for the
acetabular part, one for the shaft and wing, and a third for the
crest. He also states that there is a special center for the
acetabular part of the ischium, and a transitory nucleus in the
symphyseal part of the pubis.
THE PELVIS
The =bony pelvis= is composed of the ossa coxarum, the sacrum, and the
first three coccygeal vertebræ. The =dorsal wall= or =roof= is formed by
the sacrum and first three coccygeal vertebræ, and the =ventral wall= or
=floor= by the pubic and ischial bones. The =lateral walls= are formed
by the ilia and the acetabular part of the ischia. The defect in the
skeleton here is supplied in the fresh state by the sacro-sciatic
ligaments and semimembranosus muscles.
The =anterior aperture= or =inlet= (Apertura pelvis cranialis) is
bounded by the =terminal line= (Linea terminalis) or brim, composed of
the base of the sacrum dorsally, the ilio-pectineal lines laterally, and
the anterior border of the pubis ventrally. It is almost circular in the
mare, semi-elliptical in the stallion, and faces obliquely downward and
forward. It has two principal diameters. Of these, the =conjugate= or
=sacro-pubic diameter= (Conjugata) is measured from the sacral
promontory to the anterior end of the symphysis. The =transverse
diameter= (Diameter transversa) is measured at the greatest width, _i.
e._, just above the psoas tubercle.
The =posterior aperture= or =outlet= (Apertura pelvis caudalis) is much
smaller and is very incomplete in the skeleton. It is bounded above by
the third coccygeal vertebra and below by the ischial arch; in the fresh
state it is completed laterally by the sacro-sciatic ligament and the
semimembranosus muscle.
The =axis= of the pelvis is an imaginary line drawn through the centers
of the inlet, cavity, and outlet.
=Sexual Differences.=—Marked differences exist in the size and form of
the pelvis in the two sexes. The average =conjugate diameter= is about
9½ inches (ca. 23 to 24 cm.) in the mare, 7½ inches (ca. 18 to 20 cm.)
in the stallion. The =transverse diameter= of the inlet averages about 9
inches (ca. 22 to 23 cm.) in the mare, and 8 inches (ca. 20 cm.) in the
stallion. The =obliquity= of the inlet is greater in the female; the
difference is indicated by the fact that a vertical plane from the
pecten cuts the fourth sacral segment in the female, the second in the
male. The =outlet= is also larger in the mare, the =ischial arch= being
about one-third wider than in the stallion. The =cavity= is much more
roomy in the female; the transverse diameter between the middles of the
superior ischiatic spines is about 8 inches (20 cm.) in the mare, 6
inches (15 cm.) in the stallion. The pubic part of the =floor= in the
female is concave and lies considerably lower than the ischiatic part,
which is wide and relatively flat. In the stallion the pubis is very
thick centrally, and this part of the floor is convex, while the ischial
part is relatively narrow, and is concave from side to side. The
=obturator foramina= are correspondingly larger in the female. The ilium
is shorter, and the greater sciatic notch deeper and narrower in the
male. The pelvis of the gelding, when castration has been performed
early, resembles that of the mare; otherwise the male characters appear
to be retained to a large degree.
THE FEMUR
The =femur= or thigh bone (Os femoris) is the largest and most massive
of the long bones. It extends obliquely downward and forward,
articulating with the acetabulum above and the tibia and patella below.
It presents for examination a shaft and two extremities.
The =shaft= or =body= (Corpus femoris) is in general cylindrical, but
flattened behind, and larger above than below. The =anterior= and
=lateral surfaces= are continuous and strongly convex from side to side;
there is often a central vertical rough line on the proximal part, but
otherwise these surfaces are smooth. They are covered by the quadriceps
femoris muscle. The =posterior surface= is wide, flat, and smooth in its
proximal fourth. Below this part there is a rough elevation externally
for the attachment of the femoral tendon of the biceps femoris, and a
rough line internally to which the quadratus femoris is attached. The
middle third is narrower, and is rough for the attachment of the
adductor muscle. Just below this area an oblique groove crosses the
surface, indicating the position of the femoral vessels. The =internal
border= bears on its proximal part the =internal trochanter= or
=trochanter minor=, a thick rough ridge, to which the ilio-psoas muscle
is attached. From this a rough line curves up to the front of the neck
and indicates the limit of the attachment of the vastus internus muscle.
A narrow rough area about the middle gives attachment to the pectineus
muscle, and the =nutrient foramen= is usually found just in front of
this mark. The =supracondyloid crest= is situated below the groove for
the femoral vessels, and gives origin to the inner head of the
gastrocnemius. The =external border= is prominent in its upper part, and
bears at the junction of its proximal and middle thirds the =external=
or =third trochanter= (Trochanter tertius); this process is curved
forward, and furnishes insertion to the tendon of the superficial
gluteus muscle. At the lower part is found the =supracondyloid= or
=plantar fossa= (Fossa plantaris), in which the superficial flexor
arises; it is bounded externally by a thick rough margin, to which the
outer head of the gastrocnemius muscle is attached.
[Illustration:
FIG. 63.—RIGHT FEMUR OF HORSE, EXTERNAL VIEW.
]
[Illustration:
FIG. 64.—RIGHT FEMUR OF HORSE, POSTERIOR VIEW.
]
[Illustration:
FIG. 65.—RIGHT FEMUR OF HORSE, INTERNAL VIEW.
_1_, Anterior part, _1′_, posterior part of trochanter major; _2_,
neck; _3_, fovea capitis; _4_, crest; _5_, trochanteric fossa; _6_,
external or third trochanter; _7_, trochanter minor; _8_, eminence
for attachment of biceps femoris; _9_, internal border; _10_,
nutrient foramen; _11_, groove for femoral vessels; _12_,
supracondyloid crest; _13_, supracondyloid fossa; _14_, trochlea;
_15_, external epicondyle; _16_, external condyle; _17_, extensor
fossa; _18_, internal condyle; _19_, internal epicondyle; _20_,
intercondyloid fossa. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =proximal extremity= (Extremitas proximalis) is large and consists
of the head, neck, and great trochanter. The =head= (Caput femoris) is
placed at the inner side and is directed inward, upward, and somewhat
forward. It is approximately hemispherical and articulates with the
acetabulum. It is cut into internally by a deep notch, the =fovea
capitis=, in which the pubo-femoral and round ligaments are attached.
The articular surface is surrounded by a distinct margin. The =neck=
(Collum femoris) is most distinct in front and internally. The =great
trochanter= (Trochanter major) is situated externally; it presents three
features. The =anterior part= or =convexity= is situated opposite to the
head and rises little above the level of the latter; it gives attachment
to the deep gluteus muscle, and in the fresh state its outer surface is
coated with cartilage, over which a tendon of the middle gluteus passes,
to be inserted into the =crest=, which is placed below and behind the
convexity. The =posterior part= or =summit= is separated from the
convexity by a notch; it is situated behind the plane of the head and
rises to a much greater height. It furnishes insertion to part of the
middle gluteus muscle. Its posterior border is continued downward as the
=trochanteric ridge=, which forms the outer wall of the =trochanteric
fossa=. A number of foramina are found in the concave area internal to
the convexity.
[Illustration:
FIG. 66.—FRONTAL SECTION OF LEFT FEMUR OF HORSE, ANTERIOR VIEW.
The figure shows that the medullary cavity is traversed for the most
part by fine bony trabeculæ.
]
The =distal extremity= (Extremitas distalis) is large in both directions
and comprises the trochlea in front and two condyles behind. The
=trochlea= consists of two ridges separated by a groove, and forms an
extensive surface (Facies patellaris) for articulation with the patella.
It is very unsymmetrical; the inner ridge or lip is much wider, more
prominent, and extends up higher than the external one, and the two
converge below. The =condyles=, =internal= and =external= (Condylus
medialis, lateralis), are separated by the deep =intercondyloid fossa=
(Fossa intercondyloidea), and articulate with the condyles of the tibia
and the semilunar cartilages of the stifle joint. A ridge connects each
condyle with the lower part of the corresponding lip of the trochlea.
The intercondyloid fossa lodges the spine of the tibia and the crucial
ligaments of the stifle joint, which are attached here.
The condyles are obliquely placed, with their long axes directed
downward, forward, and inward. The articular surface of the external
condyle is more strongly convex from side to side than that of the
inner one, and the ridge which connects it with the trochlea is much
narrower.
The =internal epicondyle= (Epicondylus medialis) is a rounded prominence
on the internal surface of the internal condyle, to which the internal
lateral ligament and the adductor muscle are attached. The corresponding
=external epicondyle= (Epicondylus lateralis) is less distinct; it
presents a mark where the lateral ligament is attached, below and behind
which there is a depression (Fossa musculi poplitei) in which the
popliteus muscle arises. Between the external condyle and trochlea is
the =extensor fossa= (Fossa extensoria), in which the tendon of origin
of the anterior extensor and peroneus tertius is attached.
=Development.=—The shaft and the distal end each ossify from one center,
but the proximal end has two centers, one of which is for the great
trochanter. The edge of the external trochanter also has a separate
center. The proximal end fuses with the shaft at three to three and a
half years, the distal at about three and a half years.
[Illustration:
FIG. 67.—DISTAL EXTREMITY OF RIGHT FEMUR OF HORSE, END VIEW.
]
THE TIBIA
The =tibia= is a long bone which extends obliquely downward and backward
from the stifle to the hock. It articulates above with the femur, below
with the tarsus, and externally with the fibula. It possesses a shaft
and two extremities.
The =shaft= or =body= (Corpus tibiæ), large and three-sided above,
becomes smaller and flattened in the sagittal direction below, but
widens a little at the distal end. It presents for notice three surfaces
and three borders. The =internal surface= (Facies medialis) is broad
above, where it furnishes insertion to the internal lateral ligament and
the sartorius and gracilis muscles; below this it is convex and
subcutaneous. The =external surface= (Facies lateralis) is smooth and
somewhat spiral. It is wide and concave in its upper part, below which
it becomes narrower and slightly convex, and winds gradually to the
front of the bone; near the distal end it widens a little, becomes flat,
and faces forward. The =posterior surface= (Facies posterior) is
flattened, and is divided into two parts by the rough =popliteal line=,
which runs obliquely from the upper part of the external border to the
middle of the internal border. The triangular area above the line is
occupied by the popliteus muscle, while the area below is marked by
rough lines (Lineæ musculares) to which the deep flexor muscle of the
digit is attached; the lines fade out below, where the surface is smooth
and flat. The =nutrient foramen= is situated on or near the popliteal
line. The =anterior border= is very prominent in its upper third,
forming the =tibial crest= (Crista tibiæ); below it is reduced to a
rough line, which ends at a small elevation near the distal end of the
bone. The =internal border= (Margo medialis) is rounded in its upper
half, to which the popliteus muscle is attached, and a tubercle is found
on this part. The lower part is a rough line on well-marked bones. The
=external border= (Crista interossea) is concave in its upper part and
concurs with the fibula in the formation of the interosseous space of
the leg; a smooth impression indicates the course of the anterior tibial
vessels through the space to the front of the leg. Lower down the border
divides and incloses a narrow triangular surface.
[Illustration:
FIG. 68.—RIGHT TIBIA AND FIBULA OF HORSE, EXTERNAL VIEW.
]
The =proximal extremity= (Extremitas proximalis) is large and
three-sided. It bears two lateral eminences, the =internal= and
=external condyles= (Condylus medialis, lateralis). Each presents a
somewhat saddle-shaped surface for articulation with the condyle of the
femur and the semilunar cartilage. The =spine= or =intercondyloid
eminence= (Eminentia intercondyloidea) is the central prominence, upon
which the articular surfaces are continued; it consists of a high inner
part and a lower outer part (Tuberculum intercondyloideum mediale,
laterale). On, before, and behind the spine are the =anterior= and
=posterior intercondyloid fossæ=, in which the anterior crucial ligament
and the semilunar cartilages are attached. The condyles are separated
behind by the deep =popliteal notch= (Incisura poplitea), on the inner
side of which is a tubercle for the attachment of the posterior crucial
ligament. The external condyle has an overhanging outer margin, below
which is a =facet= for articulation with the fibula. The =large
anterior= eminence is the =tuberosity= of the tibia (Tuberositas tibiæ).
It is marked in front by a =groove=, the lower part of which gives
attachment to the middle patellar ligament, and the groove is flanked by
rough areas for the attachment of the internal and external patellar
ligaments. A semicircular smooth =notch= (Sulcus muscularis) separates
the tuberosity from the external condyle, and gives passage to the
tendon of origin of the anterior extensor and the peroneus tertius.
[Illustration:
FIG. 69.—RIGHT TIBIA AND FIBULA OF HORSE, POSTERIOR VIEW.
]
The =distal extremity= (Extremitas distalis) is much smaller than the
proximal; it is quadrangular in form and larger internally than
externally. It presents an =articular surface= (Cochlea tibiæ), which is
adapted to the trochlea of the tibial tarsal bone (astragalus), and
consists of two grooves separated by a ridge. The ridge and grooves are
directed obliquely forward and outward, and are bounded laterally by the
=malleoli=, to which the lateral ligaments of the hock joint are
attached. The =internal malleolus= (Malleolus tibialis) is the more
prominent of the two, and forms the anterior boundary of a groove for
the tendon of the inner head of the flexor perforans. The =external
malleolus= (Malleolus fibularis) is broader, and is marked by a vertical
groove for the passage of the lateral extensor tendon.
[Illustration:
FIG. 70.—RIGHT TIBIA AND FIBULA OF HORSE, ANTERIOR VIEW.
]
=Development.=—The tibia has the usual three chief centers of
ossification and supplementary ones for the tuberosity and the external
malleolus. The latter is really the distal end of the fibula; it is a
separate piece at birth, and the line of union is commonly quite evident
in the adult in the external articular groove. The proximal end unites
with the shaft at about three and a half years, and the distal end at
about two years of age.
THE FIBULA
The =fibula= of the horse is a much reduced long bone, situated along
the outer side of the tibia.
The =shaft= or =body= (Corpus fibulæ) is a slender rod which forms the
outer boundary of the interosseous space; it usually terminates below in
a pointed end about one-half to two-thirds of the way down the external
border of the tibia.
The =proximal extremity= or =head= (Capitulum fibulæ) is relatively
large, and is flattened transversely. Its internal surface presents a
narrow area along the upper border for articulation with the tibia. The
external surface is rough and gives attachment to the external lateral
ligament of the stifle joint. It has rounded anterior and posterior
borders.
[Illustration:
FIG. 71.—PROXIMAL EXTREMITY OF RIGHT TIBIA OF HORSE, END VIEW.
_l.c.a._, _l.c.p._, Depressions for attachment of anterior and
posterior crucial ligaments; _l_, _m_, _m_, depressions for
attachment of semilunar cartilages.
]
The =distal extremity= is fused with the tibia, constituting the
external malleolus.
=Development.=—This resembles that of the ulna. The embryonic
cartilaginous fibula extends the entire length of the leg, but does not
articulate with the femur. The lower part of the shaft is usually
reduced to a fibrous band. Three centers of ossification appear, one
each for the shaft and the extremities. The distal end unites early with
the tibia, forming the external malleolus.
It is interesting to note that in some cases the entire shaft of the
fibula develops, a reversion to the condition in the Miocene ancestors
of the present horse.
THE PATELLA
The =patella= is a large sesamoid bone which articulates with the
trochlea of the femur. It presents for description two surfaces, two
borders, a base, and an apex.
The =anterior= or =free surface= (Facies libera) is irregularly
quadrilateral, convex, and rough for muscular and ligamentous
attachment.
The =posterior= or =articular surface= is smaller and is triangular in
outline. It presents a vertical rounded ridge, which corresponds to the
groove on the trochlea of the femur, and separates two concave areas. Of
the latter, the inner cavity is much the larger, and is not very well
adapted to the inner lip of the trochlea; in the fresh state, however,
it is completed and rendered more congruent by the curved =accessory
fibro-cartilage=.
[Illustration:
FIG. 72.—FRONTAL SECTION OF RIGHT TIBIA OF HORSE, ANTERIOR VIEW.
]
The =lateral borders= converge to the apex below, and each forms a
prominence or angle at the base. The inner angle and the adjacent part
of the border give attachment to the fibro-cartilage of the patella,
which increases the articular surface. The external border is rounded
and its angle is less prominent.
The =base= (Basis patellæ) faces upward and backward, and is convex
transversely, concave from before backward.
The =apex= forms a blunt point directed downward.
=Development.=—The patella develops as a sesamoid bone from a single
center in a cartilaginous deposit in the tendon of the quadriceps
femoris muscle.
THE TARSUS
The =tarsus= or =hock= of the horse usually comprises six short bones
(Ossa tarsi), but exceptionally seven are present.
THE TIBIAL TARSAL BONE
The =tibial tarsal= bone (Os tarsi tibiale, astragalus, or talus) is the
inner bone of the proximal row. It is extremely irregular in form, but
may be considered as offering six surfaces for description.
[Illustration:
FIG. 73.—RIGHT PATELLA OF HORSE, ANTERIOR VIEW.
]
[Illustration:
FIG. 74.—RIGHT PATELLA OF HORSE, POSTERIOR VIEW.
]
The =superior= and the =anterior= or =dorsal surface= are continuous,
and form a =trochlea= for articulation with the distal end of the tibia.
The trochlea consists of two oblique ridges with a deep groove between
them, which curve spirally forward, downward, and outward. There is
usually a shallow =synovial fossa= in the groove. The =inferior surface=
is convex from before backward, and most of it articulates with the
central tarsal; externally it has an oblique facet for the fourth
tarsal, and a non-articular groove cuts into the surface to its middle.
The =posterior= or =plantar surface= is oblique and extremely irregular;
it presents four facets for articulation with the fibular tarsal bone;
the facets are separated by rough excavated areas, and the largest fossa
(Sulcus tali) forms with a corresponding one on the fibular tarsal a
cavity termed the =sinus tarsi=. The =internal surface= bears on its
lower part a large tuberosity, and on its upper part a small one for the
attachment of the internal lateral ligament. The =external surface= is
smaller than the internal, and is marked by a wide rough fossa in which
the external ligament is attached.
THE FIBULAR TARSAL BONE
[Illustration:
FIG. 75.—RIGHT TARSUS AND UPPER PART OF METATARSUS OF HORSE, INTERNAL
VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 76.—RIGHT TARSUS AND UPPER PART OF METATARSUS OF HORSE, POSTERIOR
(PLANTAR) VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =fibular tarsal= bone (Os tarsi fibulare, calcaneum, os calcis) is
the largest bone of the hock. It is elongated, flattened from side to
side, and forms a lever for the muscles which extend the hock joint. It
consists of a body and an inner process, the sustentaculum tali.
[Illustration:
FIG. 77.—RIGHT TIBIAL TARSAL BONE OF HORSE, ANTERIOR VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 78.—RIGHT TIBIAL TARSAL BONE OF HORSE, EXTERNAL VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =body= (Corpus calcanei) is enlarged at its proximal end to form the
=tuber calcis= or “point of the hock.” The posterior part of this
eminence gives attachment to the tendon of the gastrocnemius, while in
front and laterally it furnishes insertion to tendons of the flexor
perforatus, biceps, and semitendinosus muscles. The =inferior extremity=
bears a concave facet for articulation with the fourth tarsal bone. The
=internal surface= has on its lower part a strong process, the
=sustentaculum tali=, which projects inward. The process has a large,
oval, slightly concave facet in front for articulation with the tibial
tarsal, and sometimes a small articular surface below for the central
tarsal bone. Its plantar surface forms with the smooth inner surface of
the body a groove for the deep flexor tendon (Sulcus musculi flexoris
hallucis longi). Its inner surface has a prominence on the lower part
for the attachment of the lateral ligament. The =external surface= of
the body is flattened, except below, where there is a rough prominence
for the attachment of the lateral ligament. The =anterior= or =dorsal
border= is concave in its length, smooth and rounded in its upper part.
About its middle is a blunt-pointed projection (Processus cochlearis)
which bears facets on its inner and lower surfaces for articulation with
the tibial tarsal bone, and is roughened outwardly for ligamentous
attachment. Below this are two facets for the tibial tarsal, and an
extensive rough fossa which concurs in the formation of the sinus tarsi.
The =posterior= or =plantar border= is straight and thick, and widens a
little at either end; it is rough, and gives attachment to the long
plantar ligament.
[Illustration:
FIG. 79.—RIGHT FIBULAR TARSAL BONE OF HORSE, ANTERIOR VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 80.—RIGHT FOURTH TARSAL BONE OF HORSE, UPPER SURFACE. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 81.—RIGHT CENTRAL TARSAL BONE OF HORSE, UPPER SURFACE. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 82.—RIGHT FIRST, SECOND, AND THIRD TARSAL BONES OF HORSE, UPPER
SURFACE. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 83.—PROXIMAL ARTICULAR SURFACES OF LEFT METATARSAL BONES OF
HORSE. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
THE CENTRAL TARSAL BONE
The =central tarsal= bone (Os tarsi centrale, scaphoid, or navicular) is
irregularly quadrilateral, and is situated between the tibial tarsal
above and the third tarsal below. It is flattened from above downward,
and may be described as having two surfaces and four borders. The
=superior surface= is concave from before backward, and almost all of it
articulates with the tibial tarsal; a non-articular depression cuts into
its outer part, and sometimes there is a facet for the fibular tarsal
bone on the posterior angle. The =inferior surface= is convex, and is
crossed by a non-articular groove, which separates facets for
articulation with the third and the first and second (fused) tarsals.
The =anterior= or =dorsal border= and the =internal border= are
continuous, convex, and rough. The =posterior= or =plantar border= bears
two prominences, separated by a notch. The =external border= is oblique,
and bears anterior and posterior facets for articulation with the fourth
tarsal, between which it is excavated and rough.
[Illustration:
FIG. 84.—RIGHT TARSAL AND METATARSAL BONES OF HORSE. EXTERNAL VIEW.
(After Schmaltz, Atlas d. d. Anat. d. Pferdes.)
]
FIRST AND SECOND TARSAL BONES
The =first= and =second tarsal= bones (Os tarsale primum et secundum,
cuneiform parvum) are usually fused in the horse, forming a bone of very
irregular shape, situated in the inner and posterior part of the lower
row, below the central and behind the third tarsal. It is the smallest
of the tarsal bones, and may be described as having two surfaces, two
borders, and two extremities. The =internal surface= faces backward and
inward, and is convex. Its anterior part is ridged, and gives attachment
to the internal lateral ligament, and its posterior part bears an
imprint where the inner tendon of the tibialis anterior is inserted. The
=external surface= is marked by a deep notch which indicates the
division between the first and second tarsal elements; it bears on its
anterior part a large concave facet for the central tarsal. The
=superior border= is convex. The =inferior border= is broad in front,
where it articulates with the large and inner small metatarsal bones.
The =anterior extremity= has a small facet for articulation with the
third tarsal, and bears internally a ridge or tubercle. The =posterior
extremity= is a blunt point.
In some cases the first and second tarsal bones remain separate—a
remarkable reversion to the condition in the early ancestors of the
horse. In such specimens the first tarsal is a discoid bone,
articulating above with the central, below with the small metacarpal
bone. The second tarsal is quadrangular, equivalent to the thick
anterior part of the bone as described above, and overlapped by the
anterior part of the first tarsal.
THE THIRD TARSAL BONE
The =third tarsal= bone (Os tarsale tertium, third or great cuneiform)
resembles the central, but is smaller and triangular in outline. It is
situated between the central above and the large metatarsal bone below.
It possesses two surfaces and three borders.
The =superior surface= is concave, and is crossed by a non-articular
depression which divides it into two unequal facets; it articulates with
the central tarsal. The =inferior surface= is slightly convex, and rests
on the large metatarsal bone; it has an extensive central rough
excavation. The =anterior= or =dorsal border= is convex and bears a
rounded ridge on its inner part. The =internal border= is deeply notched
and has a small facet for the second tarsal on its anterior part. The
=external border= is also divided by a notch into two parts, and bears
two diagonally opposite facets for articulation with the fourth tarsal.
In some cases there is a facet for the inner small metatarsal bone.
[Illustration:
FIG. 85.—CROSS-SECTIONS OF METACARPAL AND METATARSAL BONES OF HORSE.
(After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
THE FOURTH TARSAL BONE
The =fourth tarsal= bone (Os tarsale quartum, cuboid) is the outer bone
of the lower row, and is equal in height to the central and third
together. It is cuboid in shape and presents six surfaces.
The =superior surface= is convex from side to side, and articulates
chiefly with the fibular tarsal, but to a small extent with the tibial
tarsal also. The =inferior surface= rests on the large and external
small metatarsal bones. The =internal surface= bears four facets for
articulation with the central and third tarsal bones. It is crossed from
before backward by a smooth groove, which by apposition with the
adjacent bones forms the =canal of the tarsus= (Canalis tarsi) for the
passage of the perforating tarsal vessels. The =anterior= or =dorsal=,
=external=, and =posterior= or =plantar surfaces= are continuous and
rough. A tuberosity behind gives attachment to the plantar ligament.
=Development.=—The fibular tarsal bone has two centers of ossification,
one for the main mass and the other for the tuber calcis; the latter
fuses with the rest of the bone at about three years of age. The first
and second tarsals have separate centers, but fusion usually occurs
before birth. Each of the other bones ossifies from a single center.
[Illustration:
FIG. 86.—DIGITAL BONES OF FORE LIMB OF HORSE, VOLAR ASPECT.
]
[Illustration:
FIG. 87.—DIGITAL BONES OF HIND LIMB OF HORSE, VOLAR ASPECT.
]
THE METATARSUS
The =metatarsal= bones (Ossa metatarsalia), three in number, have the
same general arrangement as the metacarpal bones, but present some
important differences. Their direction is slightly oblique, downward and
a little forward.
The =large= or =third metatarsal= bone is about one-sixth longer than
the corresponding metacarpal; in an animal of medium size the difference
is about two inches. The shaft is more cylindrical, and is almost
circular on cross-section, except in its lower part. At the upper part
of its external surface there is a groove, which is directed obliquely
downward and backward, and is continued by the furrow formed by the
apposition of the external metatarsal bone; it indicates the course of
the great metatarsal artery. A faint impression in a similar place on
the inner side marks the position of the corresponding vein. The
nutrient foramen is relatively higher than on the metacarpal bone. The
proximal extremity is much wider from before backward than that of the
metacarpal bone. Its articular surface is slightly concave, and is
marked by a large central non-articular depression, continued outward by
a deep notch. The greater part of the surface articulates with the third
tarsal, but there is an outer facet for the fourth, and usually a small
facet posterointernally for the second tarsal bone. Posteriorly there
are two pairs of facets for articulation with the small metatarsal
bones. The front is crossed by a rough ridge for insertion, which
becomes larger and turns downward on the outer side behind the vascular
groove. The distal extremity closely resembles that of the corresponding
metacarpal bone.
In some cases the lower part of the shaft is bent backward somewhat.
The articular surface extends a little higher behind than in the case
of the metacarpal bone. The large metatarsal bone is even more
strongly constructed than the metacarpal. The shell of compact
substance is very thick in the middle of the shaft, especially in
front and internally.
The =small metatarsal= bones are a little longer than the corresponding
metacarpals. The =external= (fourth) =metatarsal= is relatively massive,
especially in its upper part. The head is large and outstanding, and
bears two facets above for the fourth tarsal, and two in front and
internally for articulation with the large metatarsal; elsewhere it is
roughened for attachment. The =internal= (second) =metatarsal= is much
more slender than the outer one, especially in its upper part. The head
bears two facets above for the first and second tarsals, and sometimes
one for the third tarsal.
THE PHALANGES AND SESAMOIDS
The axis of the phalanges of the hind limb is about five degrees less
oblique than that of the fore limb, and the chief differences in the
form and size of the bones are as follows:
The =first phalanx= is a little shorter, wider above, and narrower
below.
The =second phalanx= is narrower and slightly longer.
The =third phalanx= is narrower, the angle of inclination of the wall
surface is a little (ca. 5 degrees) greater, the sole surface is more
concave, and the wings are less prominent and closer together.
The =proximal sesamoids= are a little smaller, except in thickness. The
=third sesamoid= or =navicular bone= is narrower and shorter.
SKELETON OF THE OX
VERTEBRAL COLUMN
The vertebral formula is C_{7}T_{13}L_{6}S_{5}Cy_{18–20}.
The =cervical vertebræ= are much shorter than those of the horse and are
smaller in their other dimensions. The =articular processes= are smaller
than in the horse, and a plate of bone connects each two of the same
side. The transverse processes of the third, fourth, and fifth are
double; the upper part projects backward, and is short and stout; the
lower part is directed downward and forward, and is longer and more
plate-like. The lower part of the sixth transverse process is a large,
thick, quadrilateral and almost sagittal plate, directed downward. The
seventh transverse process is single, short, and thick, and presents no
foramen transversarium; it is in series with the upper part of the
preceding processes. The =spinous processes= are well developed, and
increase in height from before backward. They are directed upward and
forward, with the exception of the last, which is nearly vertical and is
about four or five inches (ca. 10 to 12 cm.) in height. The summit of
that of the third bone is usually bifid. The =ventral spines= are
prominent and thick in their posterior part; they are absent on the last
two.
The =atlas= has a large rough =tuberosity= on its dorsal arch. The
=ventral arch= is very thick. The =wings= are less curved than in the
horse, and the foramen transversarium (posterior foramen) is absent. The
cavities for the occipital condyles are divided into upper and lower
parts by a non-articular area, and are separated by a narrow interval
below. The =posterior articular surfaces= are flattened behind and are
continued into the vertebral canal, forming an extensive area for the
odontoid process of the axis.
The =axis= is short. The =spine= projects a little in front, and
increases in height and thickness behind; its posterior border descends
abruptly. The =odontoid process= (dens) is wide, and its upper surface
is deeply concave from side to side. The =intervertebral foramen= is
circular and not so close to the anterior border of the arch as in the
horse. The =posterior notches= are not so deep. The =transverse
processes= are stouter, but the =foramen transversarium= is small and
sometimes absent.
The =thoracic vertebræ=, thirteen in number, are larger than those of
the horse. The =bodies= are longer and are distinctly constricted in the
middle. They bear a thin-edged ventral crest. The =arches=—in addition
to the usual notches, which are shallow—are perforated in the posterior
part by a foramen. The =transverse processes= are thick and strong, and
bear rounded mammillary processes (except at the posterior end of the
series); the last two, although prominent, do not always articulate with
the ribs. The =spinous processes= are long. The first is much higher
than in the horse, the next two are usually the most prominent, and
behind this there is a very gradual diminution in height. The backward
slope, slight at first, increases to the tenth; the last is vertical and
lumbar in character. The summit is usually pointed on the first, and the
thickening on those further back is less than in the horse. The width
diminishes from the fifth to the eleventh usually. Both borders of the
spines are in general thin and sharp, but the last three or four
sometimes have thick posterior margins.
[Illustration:
FIG. 88.—SKELETON OF COW.
_1.H._, Atlas; _7.H._, seventh cervical vertebra; _1.R._, first
thoracic vetrebra; _6.R._, sixth rib; _12.R._, twelfth thoracic
vertebra; _13.R._, last rib; _1.L._, first, _6.L._, last lumbar
vertebra; _K_, sacrum; _1.S._, first coccygeal vertebra; _6.K._,
sixth costal cartilage; _x_, wing of atlas; _1_, scapula; _1′_,
cartilage of scapula; _2_, spine of scapula; _3_, acromion; _4_,
humerus; _4′_, external condyle of humerus; _5_, external tuberosity
of humerus; _6_, deltoid tuberosity; _7_, ulna; _8_, olecranon; _9_,
radius; _10_, carpus; _11_, accessory carpal bone; _12_, metacarpus;
_13_, phalanges; _14_, sternum; _14′_, manubrium; _14″_, xiphoid
cartilage; _15_, ilium; _16_, external angle of ilium; _16′_,
internal angle of ilium; _17_, tuber ischii; _18_, femur; _19_,
trochanter major; _20_, patella; _21_, tibia; _21′_, external
condyle of tibia; _22_, tarsus; _23_, distal end of fibula; _24_,
tuber calcis; _25_, metatarsus; _26_, phalanges. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =lumbar vertebræ=, six in number, are much longer than in the horse.
The =bodies= are much constricted in the middle, expanded at either end,
and bear rudimentary ventral crests. The fourth and fifth are usually
the longest. The =intervertebral foramina= are often double in the
anterior part of the series, and are very large further back. The
=articular processes= are large, and their facets are more strongly
curved than in the horse. The =transverse processes= all curve forward.
They are separated by considerable intervals, and form no articulations
with each other or with the sacrum. Their borders are thin and
irregular, and often bear projections of variable size and form. The
first is the shortest and the length increases to the fifth, the last
being considerably shorter. The =spinous processes= are relatively low
and wide, the last being the smallest; their summits are moderately
thickened.
The =sacrum= is longer than that of the horse. It consists originally of
five segments, but fusion is more complete and involves the spinous
processes, which are united to form a =median sacral crest=, with a
convex thick and rough margin. =A lateral crest= is formed by the fusion
of the articular processes. The =pelvic surface= is concave in both
directions, and is marked by a central =groove=, which indicates the
course of the middle sacral artery. The =inferior sacral foramina= are
large. The =wings= are quadrangular, short, compressed from before
backward, and high dorso-ventrally. They have an extensive anterior
surface, which is concave from side to side, and non-articular. The
posterior surface is rough, and bears a triangular area below for
articulation with the ilium. The body of the first segment is very wide,
and the entrance to the sacral canal correspondingly wide and low. The
=anterior articular processes= are large, and are concave and
semicylindrical in curvature internally. The =lateral borders= are thin,
sharp, and irregular. The =apex= is wider than in the horse, and the
posterior end of the crest forms a pointed projection over the opening
of the sacral canal.
The =coccygeal vertebræ= are longer and better developed than in the
horse. The first five or six have complete arches and spinous processes.
The transverse processes are relatively large in the anterior part of
the series, in which there are also anterior articular processes (which
do not articulate), and a pair of ventral spines which form a hæmal
groove for the middle coccygeal artery.
Vertebral curves: The cervical curve is very slight and is concave
dorsally. The thoracic and lumbar regions form a gentle curve, concave
ventrally. The promontory is more pronounced than in the horse,
especially in subjects in which the sacrum is inclined upward behind.
Another promontory occurs at the junction of the sacrum and first
coccygeal vertebræ.
Length: The following table gives the lengths of the regions of a
shorthorn cow of medium size:
Cervical 47 cm.
Thoracic 75 cm.
Lumbar 40 cm.
Sacral 24 cm.
Coccygeal 75 cm.
———————
261 cm.
Variations: Sometimes fourteen thoracic vertebræ and fourteen pairs of
ribs are present; reduction to twelve with the normal number of lumbar
vertebræ is very rare. According to Franck, there are sometimes seven
lumbar vertebræ with the normal number in the thoracic region. The
number of coccygeal vertebræ may vary from sixteen to twenty-one.
THE RIBS
Thirteen pairs of ribs are normally present, of which eight are sternal
and five asternal. They are in general longer, wider, flatter, less
curved, and less regular in form than in the horse. The eighth, ninth,
and tenth are the longest and widest. The width of most of the ribs
increases considerably in the middle, and the breadth of the intercostal
spaces is correspondingly diminished. The neck is long, and forms
(except in the posterior part of the series) a smaller angle with the
shaft than in the horse. The articular surface of the tubercle is
concave transversely, except on the last two or three, where the facet
is small and flat or absent. The lower ends of the second to the tenth
or eleventh inclusive form diarthrodial joints with the costal
cartilages. The first costal cartilages are very short; they articulate
by their internal surfaces with the sternum, but not with each other.
The presence of a fourteenth rib is not very rare. It is usually
floating and may correspond to an additional thoracic vertebra or to
the first lumbar. Reduction of the thirteenth is more common. The
eighth cartilage often does not reach the sternum, but articulates
with the seventh.
The =sternum= consists of seven sternebræ, most of which are developed
from two lateral centers. It is wider, flatter, and relatively longer
than in the horse, and the ventral crest or “keel” is absent. The
manubrium is somewhat wedge-shaped and laterally compressed. Its base
forms a diarthrodial joint with the body of the bone, and laterally it
bears extensive facets for articulation with the first pair of costal
cartilages. The body widens from before backward, but behind the last
pair of costal facets it becomes much narrower. The ventral surface is
prominent on the second and third segments, concave further back. The
lateral borders are notched for the passage of vessels. The cariniform
cartilage is absent. The xiphoid cartilage is like that of the horse but
is smaller.
THE THORAX
The bony thorax is shorter than in the horse. The inlet is higher. The
roof is short, and the floor wider and relatively longer. The transverse
diameter is wider in the posterior part. The summits of the spinous
processes are almost in a straight line from the second thoracic to the
middle of the lumbar region.
BONES OF THE SKULL
BONES OF THE CRANIUM
The =occipital bone= is situated in the lower part only of the posterior
surface of the skull, and is separated from the highest part (the
frontal eminence) by the parietal and interparietal bones. The
supraoccipital, interparietals, and parietals fuse before birth or soon
after, and the mass so formed is separated from the lateral parts of the
occipital bone by a transverse suture in the skull of the calf. Above
this suture is a central tuberosity, to which the ligamentum nuchæ is
attached, and the surface on either side is depressed and rough for
muscular attachment. Below the suture the bone is much wider than that
of the horse. The foramen magnum is wide, so that the condyles are
further apart except below. The paramastoid processes are short and wide
and are bent inward. Two constant foramina are found in the condyloid
fossa; the anterior one is the hypoglossal, the other (sometimes double)
conducts a vein from the =condyloid canal=. The latter passes upward
from a foramen on the inner side of the condyle and opens into the
parieto-temporal canal. The cranial surface of the supraoccipital
presents a central depression, and above this is a variable but never
very pronounced eminence, which corresponds to the tentorium osseum of
the horse. On either side is a groove leading to the parieto-temporal
canal. The basilar process is short and wide; its cranial surface is
deeply concave, and the internal spheno-occipital crest is prominent.
Two large tubercles below mark the junction with the sphenoid. The
foramen lacerum is short and very narrow. In the adult animal the bone
is excavated to contain an air-cavity which is regarded as a part of the
frontal sinus.
The =sphenoid bone= is short. The cranial surface of the body presents a
deep sella turcica, in front of which it rises abruptly. The high
anterior part bears a central ridge (Rostrum sphenoidale), which joins
the crista galli of the ethmoid. Two foramina occur on either side. Of
these, the large anterior one is equivalent to the foramen rotundum,
lacerum orbitale, and patheticum of the horse. The posterior one is the
=foramen ovale=, which transmits the inferior maxillary nerve. The
orbital wing is thick and is overlapped by the frontal in such manner as
to appear externally to divide into two branches; the anterior part
joins the ethmoid close to the sphenopalatine foramen, and contains a
small sinus which communicates with an ethmoidal meatus. The temporal
wing is small, but forms a prominent thick pterygoid crest. The
pterygoid process is wide, and the pterygoid or alar foramen is absent.
The sphenoidal sinus is absent in the calf and small in the adult; it
communicates by one or two small openings with an ethmoidal meatus, and
so with the nasal cavity.
[Illustration:
FIG. 89.—SKULL AND ATLAS OF OX, LATERAL VIEW.
_9_, Zygomatic arch; _11_, coronoid process; _12_, supraorbital
process; _13″_, paramastoid or styloid process; _13‴_, occipital
condyle; _14_, parietal bone; _15_, frontal bone; _16_, squamous
temporal bone; _17_, external auditory meatus; _18_, temporal
condyle; _19_, orbital surface of lacrimal bone; _20_, malar bone;
_21_, facial surface of lacrimal bone; _22_, nasal bone; _23_, nasal
process of premaxilla; _24′_, incisor teeth; _26_, maxilla; _27_,
facial tuberosity; infraorbital foramen in front of _27_; _28′_,
molar part of ramus of mandible; _30_, broad vertical part of ramus;
_30′_, angle of jaw; _31_, condyle of mandible; _32_, atlas; _x_,
wing of atlas. (After Ellenberger-Baum, Anat. für Künstler.)
]
The =ethmoid bone= has an extensive perpendicular plate. The lateral
mass consists of five endoturbinals and eighteen ectoturbinals (Paulli).
The largest ethmoturbinal is so extensive as to be termed a third or
middle turbinal bone; it projects forward between the upper and lower
turbinals. The lamina papyracea appears to a small extent externally in
the pterygo-palatine fossa, forming part of the upper margin of the
sphenopalatine foramen.
The =interparietals= are primitively paired, but unite before birth. As
already mentioned, fusion occurs before or shortly after birth with the
parietals and supraoccipital. No distinct tentorium osseum is present.
[Illustration:
FIG. 90.—SKULL OF OX, BASAL VIEW, WITHOUT MANDIBLE.
_F_, Pterygoid bone; _G_, horizontal and _G′_, perpendicular part of
palate bone; _H_, occipital bone; _J_, malar bone; _K_, sphenoid
bone; _O_, maxilla; _P_, vomer; _Sch._, squamous temporal; _St._,
frontal bone; _Z_, premaxilla; _1_, for. magnum; _2_, occipital
condyle; _3_, paramastoid (styloid) process of occipital; _4_,
hypoglossal and condyloid foramina; _5_, for. lacerum; _6_,
pharyngeal tubercles; _7_, bulla ossea; _8_, muscular process (left
one is removed to expose for. ovale); _9_, hyoid process; _10_, ext.
auditory meatus; _11_, zygomatic process; _12_, external opening of
parieto-temporal canal; _13_, postglenoid process; _14_, temporal
condyle; _15_, for. ovale; _16_, for. lac. orbitale + for. rotundum;
_17_, optic foramen; _18_, ethmoidal foramen; _19_, orbital opening
of supraorbital canal; _20_, pterygoid crest; _21_, hamulus of
pterygoid bone; _22_, lacrimal bulla; _23_, temporal process of
malar; _24_, pterygoid process of maxilla; _25_, sphenopalatine
foramen; _26_, maxillary foramen; _27_, posterior palatine foramen;
_28_, anterior palatine foramen; _29_, accessory palatine foramina;
_30_, palate process of maxilla; _31_, interalveolar border; _32_,
palatine cleft; _33_, palate process of premaxilla; _34_, fissura
incisiva; _35_, facial tuberosity; _36_, posterior nares.
(Ellenberger-Baum, Anat. d. Haustiere.)
]
The =parietal bones= do not enter into the formation of the roof of the
cranium. They constitute the upper part of the posterior wall, and bend
sharply forward along the lateral wall, forming part of the wall of the
temporal fossa. The line of inflection is marked by the prominent
=parietal crest=, which is continuous with the temporal crest below. The
parietals are excavated to form part of the frontal sinuses in the adult
animal.
The condition in the young subject is as follows: The two parietals
are united with each other and also with the interparietal and
supraoccipital. The resulting mass is somewhat horseshoe-shaped. Its
occipital part (Planum occipitale) forms the greater part of the
posterior wall of the cranium and bears about its center the
tuberosity for the attachment of the ligamentum nuchæ. From either
side of this a line curves outward, and divides the surface into an
upper smooth area and a lower area which is rough for muscular
attachment. The upper border joins the frontal bone and concurs in the
formation of the frontal eminence. The temporal parts (Plana
temporalia) are much smaller and are concave externally; they join the
frontal above and the squamous temporal below.
[Illustration:
FIG. 91.—SKULL OF OX, DORSAL VIEW (WITH MANDIBLE).
_12_, Supraorbital process; _14_, parietal bone; _15_, frontal bone;
_16_, squamous temporal bone; _19_, orbit; _20_, malar bone; _21_,
lacrimal bone; _22_, nasal bone; _23_, premaxilla; _26_, maxilla;
_27_, facial tuberosity; _24_, incisor teeth. (After
Ellenberger-Baum, Anat. f. Künstler.)
]
[Illustration:
FIG. 92.—SKULL AND ATLAS OF OX, VENTRAL VIEW.
_13_, Basi-occipital; _13″_, paramastoid or styloid process; _13‴_,
occipital condyle; _24′_, incisor teeth; _28_, body of mandible;
_31_, condyle of mandible; _32_, ventral tubercle of atlas. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =frontal bones= are very extensive, forming about one-half of the
entire length of the skull, and all of the roof of the cranium. The
posterior borders form with the parietals a large central =frontal
eminence= (Torus frontalis), the highest point of the skull. At the
junction of the posterior and the lateral borders are the =processus
cornu= or “horn-cores,” for the support of the horns. These processes
are of elongated conical form, and vary greatly in size, length,
curvature, and direction. The external surface is rough and porous,
marked by numerous grooves and foramina; in the fresh state they are
covered by the matrix of the horns. The base has a constriction, the
neck. The interior is excavated to form a number of irregular
intercommunicating spaces, divided by bony septa, and communicating with
the frontal sinus. In the polled breeds these processes are absent, the
skull is narrower in this region, and the frontal eminence more
pronounced. The supraorbital process is situated about half-way between
the anterior and posterior margins; it is short and joins the frontal
process of the malar bone. The supraorbital foramen (often double) is
situated about an inch inward from the root of the process; it is the
external orifice of the =supraorbital canal= (Canalis supraorbitalis),
which passes downward and forward into the orbit. The foramen is in the
course of the =supraorbital groove= (Sulcus supraorbitalis), which marks
the course of the frontal vein. The anterior ends of the naso-frontal
parts form a notch which receives the nasal bones, and sutural or
Wormian bones are often found at this junction (naso-frontal suture).
The orbital part is extensive; it is perforated behind by the orbital
opening of the supraorbital canal, and below by the ethmoidal or
internal orbital foramen. It does not articulate with the palatine, from
which it is separated by the orbital wing of the sphenoid. The temporal
part is also more extensive than in the horse. The frontal sinus is very
extensive, being continued into the parietals and occipital, and the
horn processes when present.
The =squamous= and =petrous parts= of the =temporal bone= fuse early—in
fact, union is nearly complete at birth. The squamous part is relatively
small. Its external surface is divided into two parts by the prominent
temporal crest, which is continuous with the parietal crest above and
turns forward below, ending at a tubercle above the external auditory
meatus. The part behind the crest faces backward, and is partly free,
partly united with the occipital. The area in front of the crest is
concave and enters into the formation of the temporal fossa; it is
perforated by foramina which communicate with the parieto-temporal
canal. The zygomatic process is much shorter and weaker than in the
horse, and articulates with the malar only. The condyle is convex in
both directions. The postglenoid process is less prominent, and behind
it is the chief external opening of the parieto-temporal canal. The
internal surface is almost completely overlapped by the parietal and
sphenoid. The petrous part proper is small, but the tympanic part is
extensive. The external auditory meatus is smaller than in the horse and
is directed outward. From it a plate projects downward and helps to
inclose the deep depression in which the hyoid process is placed. Behind
this plate is the stylo-mastoid foramen. The muscular process is large
and often bifid at its free end. The bulla ossea is large and laterally
compressed. It is separated from the occipital bone by a narrow opening
which is equivalent to part of the foramen lacerum basis cranii of the
horse. The parieto-temporal canal is formed entirely in the temporal
bone. The facial canal, on the other hand, is bounded partly by the
occipital bone.
BONES OF THE FACE
The =maxilla= is shorter but broader and relatively higher than in the
horse. Its external surface bears instead of the facial crest a rough
=facial tuberosity= (Tuber malare), placed above the third cheek tooth;
a rough curved line often extends from it to the upper part of the malar
bone. The infraorbital foramen—often double—is situated above the first
cheek tooth. The tuber maxillare is small, laterally compressed, and
usually bears a small pointed process (Processus pterygoideus). The
zygomatic process is very small. The interalveolar border is concave,
and there is no alveolus for a canine tooth. The palatine process is
wider, but somewhat shorter than in the horse. It incloses a large
air-space, which is continuous behind with a like cavity in the
horizontal part of the palate bone, forming the =palatine sinus=. This
communicates externally (over the infraorbital canal) with the maxillary
sinus; in the macerated skull it communicates with the nasal cavity by a
large oval opening, which is closed by mucous membrane in the fresh
state. A median septum separates the two palatine sinuses. The alveoli
for the cheek teeth increase in size from before backward. The maxillary
sinus proper is small and is undivided. The maxillary foramen is a
narrow fissure, deeply placed at the inner side of the lacrimal bulla.
The maxilla takes no part in the formation of the palatine canal.
Sutural (or Wormian) bones may be found at its junction with the
lacrimal and malar bones.
The body of the =premaxilla= is thin and flattened, and has no alveoli,
since the canine and upper incisor teeth are absent. A deep notch takes
the place of the foramen incisivum. The nasal process is short, convex
externally, and is not closely attached to the nasal bone; the space
between the two processes is greater than in the horse. The palatine
process is narrow and is grooved on its nasal surface for the septal
cartilage and the vomer. The palatine cleft is very wide.
The =palatine bone= is very extensive. The =horizontal part= forms
one-fourth or more of the hard palate. The anterior palatine foramen
opens near the junction with the maxilla, about half an inch from the
median palatine suture and crest. =Accessory palatine foramina= are also
present. The palatine groove is usually not very distinct. The palatine
canal is formed entirely in this part, and there is no articulation with
the vomer. A rounded ridge occurs on the nasal side of the median
suture. The interior is hollow, forming part of the palatine sinus. The
=perpendicular part= is an extensive, quadrilateral, thin plate, which
forms the posterior part of the lateral wall of the nasal cavity and in
part bounds the narrow posterior nares. Its internal surface is nearly
flat, and is smooth and free, except behind, where it is overlapped by
the pterygoid bone. The external surface is attached to a small extent
to the pterygoid process behind, and is free elsewhere. The
sphenopalatine foramen is a long elliptical opening, formed by a deep
notch in the upper edge of the palate bone and completed by the ethmoid
and sphenoid. The edge behind this foramen articulates with the orbital
wing of the sphenoid, not the frontal as in the horse.
[Illustration:
FIG. 93.—MEDIAN SECTION OF SKULL OF OX, WITHOUT THE MANDIBLE.
The mucous membrane is retained. The septum nasi is removed. _a_,
Superior meatus; _b_, middle meatus, with _b′_ and _b″_, its upper
and lower divisions; _c_, inferior meatus; _d_, superior turbinal;
_e_, superior turbinal fold; _f_, inferior turbinal; _g_, alar fold;
_h_, inferior turbinal fold; _i_, lateral mass of ethmoid
(ethmoturbinals); _i′_, large ethmoturbinal or middle turbinal; _k_,
frontal sinus; _l_, sphenoidal sinus; _m_, cranial cavity; _n_,
palatine sinus; _o_, nasal bone; _o′_, parietal cartilage; _p_,
palate process of maxilla; _q_, palate bone (horizontal part); _1_,
sphenoid bone; _2_, _3_, inner and outer plates of frontal bone;
_4_, _4′_, outer and inner plates of parietal bone; _5_, _5′_,
occipital bone; _5″_, condyloid and hypoglossal foramina; _6_,
paramastoid or styloid process; _6′_, occipital condyle; _7_,
petrous temporal bone; _7′_, internal auditory meatus; _8_, squamous
temporal bone; _9_, muscular process; _10_, pterygoid bone
(hamulus). (After Ellenberger, in Leisering’s Atlas.)
]
The =pterygoid bone= is wider than in the horse, and forms the greater
part of the lateral boundary of the posterior nares. Its outer surface
is almost entirely united to the palate bone and the pterygoid process,
but a small part is free in the pterygo-palatine fossa. The hamulus is
distinctly hook-like, thin, and sharp.
The =nasal bone= is little more than half the length of that of the
horse. It is straight in its length, but strongly curved from side to
side. It does not fuse laterally with the adjacent bones, even in old
age. The posterior extremity is pointed and fits into the notch between
the frontal bones. The anterior end is broader, and is divided into two
parts by a deep notch. In old animals there is a small extension of the
frontal sinus into this bone.
The =lacrimal bone= is very large. The extensive facial part is concave
in its length, and bears no lacrimal tubercle. The orbital margin is
marked by several notches. The orbital part forms below the remarkable
=lacrimal bulla=; this is a large and very thin-walled protuberance,
which bulges backward into the lower part of the orbit, and contains an
extension of the maxillary sinus. The lacrimal fossa is small, and is
just behind the orbital margin.
The =malar bone= is relatively long. The facial surface is extensive; it
bears a curved crest (Crista facialis) just below the orbital margin,
and below this it is concave from above downward. The zygomatic process
divides into two branches; of these, the frontal process turns upward
and backward and joins the supraorbital process of the frontal bone; the
temporal process continues backward, and is overlapped by the zygomatic
process of the temporal bone, completing the zygomatic arch.
The =superior turbinal bone= is less cribriform and fragile than in the
horse, and is thickest in its middle, small at either end. It is
attached to the turbinal crest of the nasal bone, and curves downward,
outward, and upward to be applied outwardly to the frontal and lacrimal
bones. It thus incloses a cavity which communicates with the middle
meatus nasi. (In the macerated skull it opens into the frontal sinus,
but this communication is closed by mucous membrane in the fresh state.)
The =inferior turbinal bone= is shorter but much broader than in the
horse. It is attached to the maxilla by a basal lamella about an inch
(ca. 2 to 3 cm.) wide, which slopes downward and inward. At the inner
edge of this it splits into two plates which are rolled in opposite
directions, and inclose two separate cavities, subdivided by several
septa. The upper one opens into the middle meatus, the lower one into
the inferior meatus nasi.
The =vomer= forms a wider and deeper groove than in the horse. Its
anterior end rests in a groove formed by the ends of the palatine
processes of the premaxillæ. The anterior third of its thin lower edge
fits into the nasal crest of the maxilla; behind this it is free and
separated by a considerable interval from the nasal floor.
[Illustration:
FIG. 94.—HYOID BONE OF OX.
_a_, Body; _b_, lingual process; _c_, thyroid cornu and cartilage,
_c′_; _d_, small cornu; _e_, middle cornu; _f_, great cornu; _g_,
muscular angle of _f_. (Ellenberger-Baum, Anat. d Haustiere.)
]
The two halves of the =mandible= do not fuse completely even in advanced
age. The symphyseal surfaces are extremely rough and are marked by
reciprocal projections and cavities. The body is shorter, wider, and
flatter than in the horse, and has eight round and relatively shallow
alveoli for the lower incisors. The interalveolar border is long,
curved, thin and sharp. There are no alveoli for the canine teeth, which
are absent. The anterior part of the ramus constitutes a long narrow
neck. The mental foramen is further forward than in the horse, and is in
the posterior end of a fossa. The rami diverge more, so that the
submaxillary space is wider than in the horse. They are also more
strongly curved, and the angle is more pronounced. The molar part is not
so high, especially in its anterior part. Its lower border is convex in
its length. Its upper border bears six alveoli for the lower cheek
teeth; the first is quite small, and they increase in size from before
backward. The vertical part is much smaller than in the horse and its
posterior border is relatively thin below, concave and wider above. The
mandibular foramen is about in the middle of its inner surface, and a
groove for the lingual nerve curves downward and forward from it. The
condyle projects inward further than in the horse, and is concave from
side to side. The coronoid process is extensive and curves backward.
The =hyoid bone= has a short tuberous lingual process. The middle cornua
are almost, as large as the small cornua. The great cornua are narrow,
except at the ends. The upper end divides into two branches, which
correspond to the two angles of that of the horse. The thyroid cornua do
not fuse with the body.
SKULL OF THE OX AS A WHOLE
The skull of the ox is more clearly pyramidal than that of the horse,
and is shorter and relatively wider. The cranium is quadrangular and
larger externally than in the horse; its large size is due mainly to the
great extent of the frontal sinus, and does not affect the cranial
cavity, which is smaller than in the horse.
The =superior= or =frontal surface= is formed by the frontals, nasals,
and premaxillæ. The frontal part is quadrilateral and very extensive,
the greatest width being at the orbits. It presents a central depression
on its anterior part, and on either side are the supraorbital grooves
and foramina. Behind is the median frontal eminence, and at the lateral
angles the “horn-cores” project in horned cattle. The nasal part is very
short. The osseous nasal aperture is wide. The premaxillæ do not bend
downward as in the horse; they are relatively thin and weak, and are
separated by an interval which has a wide anterior part in place of the
foramen incisivum.
The =lateral surface= is more triangular than in the horse. The temporal
fossa is confined to this surface. It is deep and narrow, and its
boundaries are more complete. It is limited above by a crest which
extends from the postero-external angle of the frontal to the
supraorbital process, and is analogous to the sagittal crest of the
horse. Behind it is bounded by the temporal crest. It is clearly marked
off from the orbit by the rounded posterior orbital ridge and the
pterygoid crest. The zygomatic process is short, weak, and flattened,
and is formed by the temporal and malar only. Its condyle is convex and
is wide from before backward. The glenoid cavity and postglenoid process
are small. The orbit is encroached upon below by the lacrimal bulla, and
presents the orifice of the supraorbital canal behind. The margin is
completed behind by the frontal process of the malar; its lower part is
prominent and rough, not smooth and rounded as in the horse. The
pterygo-palatine fossa is much larger, deeper, and more clearly defined.
It has a long narrow forward extension (maxillary hiatus) between the
vertical plate of the palate bone internally and the maxilla and
lacrimal bulla externally; thus the sphenopalatine and maxillary
foramina are deeply placed. The preorbital region is short but
relatively high. A tuberosity and curved line take the place of the
facial crest. The infraorbital foramen is situated above the first cheek
tooth and is often double.
The =basal surface= is short and wide, especially in its cranial part.
The occipital condyles are limited in front by transverse ridges. The
tubercles at the junction of the occipital and sphenoid are large. The
condyloid fossæ contain two foramina, the hypoglossal below and in
front, and the condyloid above and behind; other inconstant ones occur.
The paramastoid processes are short and convergent. The foramen lacerum
is slit-like. The bulla ossea is a large, laterally compressed
prominence. The muscular processes are usually long and narrow
triangular plates, with one or two sharp points. The external auditory
process is directed almost straight outward. A curved plate extends
downward from it and joins the bulla ossea internally, completing the
deep cavity which receives the articular angle of the hyoid bone. The
chief external opening of the temporal canal is in front of this plate,
and an accessory one lies behind it. The infratemporal fossa is small,
and presents the foramen ovale. The posterior nares are very narrow, and
the vomer does not reach to the level of their margin. The hard palate
is wide, and forms about three-fifths of the entire length of the skull.
A small central part only of its posterior border enters into the
formation of the posterior nares; the lateral parts are notched and just
above them are the posterior palatine foramina. The anterior palatine
foramina are an inch or more from the posterior margin, and about the
same distance apart. The palatine grooves are distinct for a short
distance only. Just beyond the cheek teeth the palate narrows and
becomes concave; beyond this it widens and flattens.
The =posterior= or =nuchal surface= is extensive and somewhat pentagonal
in outline in the adult. About its center is the eminence for the
attachment of the ligamentum nuchæ. From this a median crest extends
toward the foramen magnum, and laterally two lines (Lineæ nuchæ
superiores) curve outward, marking the upper limit of the area which is
roughened for muscular attachment. The surface above the lines is
relatively smooth, and is covered only by the skin and the thin
auricular muscles in the living animal. It is separated from the cranial
roof by a thick border, which forms centrally the frontal eminence, and
bears at its extremities the processus cornu—except in the polled
breeds. The condyles are further apart, and the articular surfaces are
more clearly divided into upper and lower parts than in the horse.
[Illustration:
FIG. 95.—CROSS-SECTION OF SKULL OF OX. SECTION PASSES THROUGH FIFTH
CHEEK TOOTH.
]
[Illustration:
FIG. 96.—CROSS-SECTION OF SKULL OF OX. SECTION PASSES THROUGH SECOND
CHEEK TOOTH.
_a_, _b_, _c_, Superior, middle, inferior meatus; _b′_, communication
between middle meatus and cavity of upper part of inferior turbinal;
_c′_, communication between inferior meatus and lower part of
inferior turbinal; _d_, cavity of superior turbinal; _e_, _f_, outer
and inner walls of _d_; _g_, _h_, upper and lower cavities of
inferior turbinal bone; _i_, basal lamella of inferior turbinal;
_i′_, _i″_, upper and lower divisions of inferior turbinal bone;
_k_, floor of nasal cavity; _m_, lacrimal sinus; _n_, maxillary
sinus; _p_, palatine sinus; _q_, septum between maxillary and
palatine sinuses; _r_, infraorbital canal; _s_, septum between
palatine sinuses; _t_, common meatus; _u_, naso-lacrimal canal; _v_,
floor of nasal cavity and roof of palatine sinus; _1_, septum nasi;
_2_, posterior part of second cheek tooth; _3_, posterior part of
fifth cheek tooth; _4_, hard palate. (After Ellenberger, in
Leisering’s Atlas.)
]
The =cranial cavity= is shorter and its long axis is more oblique than
in the horse, but it is relatively high and wide. The anterior fossa
lies at a much higher level than the rest of the floor. The olfactory
fossæ are smaller, and the sella turcica is much deeper than in the
horse. A deep groove leads from the petrous temporal forward over the
foramen ovale to the foramen rotundum. Behind the sella there is often a
distinct prominence (Dorsum sellæ). The internal sagittal crest is
prominent anteriorly, but absent further back. A faintly marked
elevation takes the place of the tentorium osseum. The small petrous
temporal bone projects into the cavity laterally. The ridges and digital
impressions are very pronounced. The parieto-temporal canal is formed
entirely in the temporal bone, and opens at the apex of the petrous,
where it is joined by the condyloid canal. The foramen lacerum is
divided into two parts (For. lacerum anterius et posterius).
The =nasal cavity= is incompletely divided by the septum, which does not
reach the floor posteriorly. The floor is relatively long, and is more
concave from side to side than in the horse. In the dry skull it has a
large oval opening into the palatine sinus, which is closed during life
by mucous membrane. The middle meatus is divided behind into upper and
lower branches by the great ethmoturbinal. The posterior nares are
narrow and oblique.
[Illustration:
FIG. 97.—SKULL OF OX, DORSAL VIEW.
The outer plate of bone has been removed to show the sinuses. _a_,
Frontal sinus; _a′_, cranial plate of frontal bone; _a″_, anterior
part of frontal sinus, which is separated from remainder by a septum
(_b_); _c_, _c′_, communications between frontal sinus and nasal
cavity; _d_, supraorbital foramen; _e_, supraorbital canal; _f_,
cavity of superior turbinal bone, and _g_, its opening into the
nasal cavity; _h_, lacrimal sinus, _i_, its communication with the
maxillary sinus; _k_, maxillary sinus; _l_, orbit; _1_, frontal
bone; _1′_, processus cornu; _2_, nasal bone; _3_, premaxilla (nasal
process); _4_, maxilla; _5_, lacrimal bone; _6_, malar bone; _7_,
dotted line indicating course of naso-lacrimal duct. (After
Ellenberger, in Leisering’s Atlas.)
]
The =frontal sinus= is very large. It involves almost all of the frontal
bone and a large part of the posterior wall of the cranium. It also
extends for a variable distance into the horn processes when these are
present. A complete median septum separates the right and left sinuses.
The anterior limit is indicated by a transverse plane through the middle
of the orbits. It extends externally to the crest which limits the
temporal fossa above, and into the root of the supraorbital process. At
the highest part of the cranial cavity and at the tuberosity on the
posterior surface the two plates of the bone come together. The cavity
is very irregular and is subdivided into numerous spaces by ridges and
partial septa. This multilocular character is most marked in the
anterior part, and here several small spaces appear to be cut off from
the main cavity (Baum). The supraorbital canal passes through the sinus.
Several small openings lead from the sinus to the ethmoidal meatuses,
and thus indirectly to the upper division of the middle meatus nasi. The
communications with the cavity of the superior turbinal and with the
lacrimal part of the maxillary sinus which are seen in the macerated
skull are closed in the fresh state by mucous membrane.
[Illustration:
FIG. 98.—SKULL OF OX, LATERAL VIEW WITHOUT MANDIBLE.
The maxillary, lacrimal, and turbinal sinuses have been opened, and a
portion of the orbit removed, _a_, Cavity of superior turbinal bone;
_b_, lacrimal sinus; _c_, maxillary sinus; _d_, communication
between maxillary and palatine sinuses; _e_, opening between
maxillary and lacrimal sinuses; _f_, thin osseous bulla; _g_,
lacrimal bulla; _h_, orbit; _1–6_, cheek teeth; _7_, nasal bone;
_8_, premaxilla (nasal process); _9_, maxilla; _9′_, infraorbital
foramen; _10_, frontal bone; _11_, lacrimal bone; _12_, malar bone;
_13_, fissure between nasal bone and maxilla; _14_, temporal bone
(squamous); _15_, external auditory meatus; _16_, styloid or
paramastoid process; _17_, occipital condyle; _18_, palate bone
(perpendicular part); _19_, pterygoid bone (hamulus); _20_, tympanic
part of temporal; _20′_, muscular process of petrous temporal.
(After Ellenberger, in Leisering’s Atlas.)
]
The =maxillary sinus= is excavated chiefly in the maxilla, lacrimal, and
malar, and is not divided by a septum as in the horse. It extends
forward as far as the facial tuberosity, or a little further in old
animals. Its upper limit is indicated approximately by a line drawn from
the infraorbital foramen to the upper margin of the orbit. It is
continued directly backward into the lacrimal bulla to a point nearly
opposite to the bifurcation of the zygomatic process of the malar. It
also extends upward and backward through a large opening into a cavity
formed by the lacrimal, frontal, ethmoid, and turbinal bones, at the
inner side of the orbit.[26] The floor of the cavity is irregular and
the roots of the last three or four cheek teeth project up into it,
covered by a plate of bone. The sinus communicates with the palatine
sinus freely over the infraorbital canal through an oval opening about
two to three inches (ca. 5 to 7.5 cm.) long. Above this it communicates
by a shorter and much narrower opening with the middle meatus nasi.
The =palatine sinus= is excavated in the hard palate, and is separated
from that of the opposite side by a median septum. It extends from the
posterior border of the palate to a plane an inch or more (2.5 to 3 cm.)
in front of the first cheek tooth. As mentioned above, there is a large
communication with the maxillary sinus over the infraorbital canal, so
that the cavity is sometimes regarded as a part of that sinus. The large
defect in the bony roof of the sinus is closed by two layers of mucous
membrane in the fresh state. The palatine canal passes obliquely through
the posterior part of the sinus.
The =sphenoidal sinus= is almost entirely in the sphenoid bone and does
not communicate with the palatine and maxillary sinus. It has one or two
openings into the ventral ethmoidal meatuses. There is no cavity in the
perpendicular part of the palate bone.
There are several small air-cavities between the lateral mass of the
ethmoid and the anterior part of the frontal sinus, which communicate
separately with ethmoidal meatuses.
BONES OF THE THORACIC LIMB
The =scapula= is more regularly triangular than in the horse, relatively
wider at the vertebral end and narrower at the lower end. The scapular
index is about 1 ∶ 0.6. The spine is more prominent and is placed
further forward, so that the supraspinous fossa is narrow and does not
extend to the lower part of the bone. The spine is sinuous, bent
backward in its middle, forward below. Its free border is somewhat
thickened in its middle, but bears no distinct tubercle. Instead of
subsiding below as in the horse the spine becomes a little more
prominent, and is prolonged by a pointed projection, the =acromion=,
from which part of the deltoid muscle arises. The subscapular fossa is
shallow. The areas for the attachment of the serratus muscle are not
very distinct. The nutrient foramen is usually in the lower third of the
posterior border. The glenoid cavity is almost circular and without any
distinct notch. The tuberosity is small and close to the glenoid cavity.
The coracoid process is short and rounded. The cartilage resembles that
of the horse.
The =humerus= has a shallow musculo-spiral groove. The deltoid
tuberosity is less prominent than in the horse, and the curved line
running from it to the neck bears a well-marked tubercle on its upper
part. The nutrient foramen is usually in the lower third of the
posterior surface. The external tuberosity is very large, and rises an
inch or more (ca. 3 cm.) above the level of the head. Its anterior part
curves inward over the bicipital groove, and below it externally there
is a prominent circular rough area for the insertion of the tendon of
the supraspinatus. The anterior part of the internal tuberosity has a
small projection which curves over the groove. The groove is undivided.
The distal articular surface is decidedly oblique, and the grooves and
ridge are very well marked. The coronoid and olecranon fossæ are deep
and wide. The external condyloid crest is represented by a rough raised
area. The proximal end unites with the shaft at three and one-half to
four years, and the distal at about one and one-half years.
The =radius= is short and relatively broad. It is somewhat oblique, the
lower end being nearer the median plane than the upper. The curvature is
more pronounced below than above. The shaft is prismatic in its middle
part and has anterior, external, and posterior faces. There is a marked
increase in width and thickness below. The proximal articular surface
presents a synovial fossa which extends inward from the deep groove
between the two glenoid cavities. The bicipital tuberosity is
represented by a slightly elevated rough area. The posterior facets for
the ulna are larger than in the horse. The two bones commonly fuse above
the proximal interosseous space and always fuse below it, except near
the distal end, where there is a small distal interosseous space. A
groove connects the two spaces externally. The distal extremity is
large, and is thickest internally. Its articular surface is oblique in
two directions, _i. e._, from within upward and backward. The grooves
for the extensor tendons are shallow. The proximal end unites with the
shaft at one to one and one-half years, and the distal at three and
one-half to four years.
The approximation of the lower ends of the forearms and the carpi
gives the “knock-kneed” appearance in cattle. The obliquity of the
joint surfaces produces lateral deviation of the lower part of the
limb in flexion. The facets for the radial and intermediate carpals
are narrower than in the horse and run obliquely forward and outward.
The surface for the ulnar carpal is extensive and saddle-shaped; its
outer part is furnished by the ulna.
[Illustration:
FIG. 99.—SKELETON OF LEFT FORE LIMB OF OX, FROM SHOULDER DOWNWARD,
ANTERIOR VIEW. (After Ellenberger-Baum, Anat. für Künstler.)
]
The =ulna= is more fully developed than in the horse. The shaft is
complete, three-sided, and strongly curved. It is fused with the radius
in the adult, except at the two interosseous spaces mentioned above. Its
upper part contains a medullary canal which extends somewhat into the
proximal end. The olecranon is large and bears a rounded tuberosity
above. The distal end is fused with the radius; it projects below the
level of the latter, forming the =styloid process= (Processus styloideus
ulnæ), which furnishes part of the facet for the ulnar carpal. The
proximal and distal ends unite with the shaft at three and one-half to
four years.
[Illustration:
FIG. 100.—SKELETON OF LEFT FORE LIMB OF OX, FROM ELBOW DOWNWARD,
EXTERNAL VIEW. (After Ellenberger-Baum, Anat. für Künstler.)
]
The =carpus= consists of six bones, four in the upper row, and two in
the lower. The upper row is oblique in conformity with the carpal
articular surface of the radius. The radial and intermediate resemble in
general those of the horse, but are less regular in shape, and their
long axes are directed obliquely backward and inward. The radial is
narrower than in the horse and curves upward behind. The intermediate is
constricted in its middle, and wider behind than in front. The ulnar is
large and very irregular. Its proximal surface is extensive and sinuous
and articulates with both radius and ulna. Behind is a large oval facet
for articulation with the accessory carpal. The accessory is short,
thick, and rounded; it articulates with the ulnar carpal only. The first
carpal is absent. The second and third carpals are fused to form a large
quadrilateral bone. The fourth carpal is a smaller quadrilateral bone.
The =metacarpus= consists of a large metacarpal and an external small
metacarpal bone. The large metacarpal bone (Mc. 3 + 4) results from the
fusion of the third and fourth bones of the fœtus, and bears evidences
of its double origin even in the adult state. The shaft is shorter than
in the horse, and is relatively wider and flatter. The anterior surface
is rounded, and is marked by a vertical vascular groove connecting two
canals which traverse the ends of the shaft from before backward. The
posterior surface is flat and presents a similar but much fainter
groove. The borders are rough in the upper third. The proximal end bears
two slightly concave facets for articulation with the bones of the lower
row of the carpus; the inner area is the larger, and they are separated
by a ridge in front and a notch behind. The outer angle has a facet
behind for the small metacarpal bone. The inner part of the extremity
has anterior and posterior tuberosities. The distal end is divided into
two parts by a sagittal notch. Each division bears an articular surface
similar to that in the horse, but much smaller. The =medullary canal= is
divided into two parts by a =vertical septum= which is usually
incomplete in the adult.
The =small metacarpal= bone (Mc. 5) is a rounded rod about an inch and a
half (ca. 3.5 to 4 cm.) in length, which lies against the upper part of
the outer border of the large bone. Its upper end articulates with the
latter, but not with the carpus. The lower end is pointed.
Four cartilaginous metacarpals are present in the early fœtal state,
viz., the second, third, fourth, and fifth. The second commonly either
disappears or unites with the third; sometimes it develops as a small
rod of bone. The third and fourth gradually unite, but can be cut
apart at birth. Each has three centers of ossification; the proximal
epiphysis fuses with the shaft before birth, the distal at two to two
and one-half years.
Four =digits= are present in the ox. Of these, two—the third and
fourth—are fully developed and have three phalanges and three sesamoids
each. The second and fifth are vestiges and are placed behind the
fetlock; each contains one or two small bones which do not articulate
with the rest of the skeleton.
The =first phalanges= are shorter and narrower than in the horse and are
three-sided. The interdigital surface is flattened and its posterior
part bears a prominence for the attachment of the interdigital
ligaments. The proximal extremity is relatively large, and is somewhat
compressed from side to side. The articular surface is concave from
before backward and is divided by a sagittal groove into two areas, of
which the abaxial one is the larger and higher. Behind these are two
facets for articulation with the sesamoid bones. The posterior surface
bears two tuberosities separated by a deep depression. The distal
extremity is smaller than the proximal, especially in the
antero-posterior direction. Its articular surface is divided by a
sagittal groove into two convex facets, of which the abaxial one is
decidedly the larger. There are depressions on either side for
ligamentous attachment. The bone consists at birth of two pieces—the
distal end and the fused shaft and upper extremity. Union occurs at one
and one-half to two years.
The =second phalanges= are about two-thirds of the length of the first
and are distinctly three-sided. The proximal articular surface is
divided by a sagittal ridge into two glenoid cavities, of which the
abaxial one is much the larger. There is a central prominence in front
and two lateral tubercles behind. The distal extremity is smaller than
the proximal. Its articular surface encroaches considerably on the
anterior and posterior surfaces, and is divided into two lateral parts
by a groove. There is a deep depression for ligamentous attachment on
the interdigital side. The bone contains a small medullary canal. The
distal end unites with the rest of the bone about the middle of the
second year.
The =third phalanges= resemble in a general way one-half of the bone of
the horse. Each has four surfaces. The dorsal or wall surface is marked
in its lower part by a shallow groove, along which there are several
foramina of considerable size; the posterior one of the series is the
largest, and conducts to a canal in the interior of the bone. Below the
groove the surface is prominent, rough, and porous. Near and on the
extensor process are several relatively large foramina. The slope of the
surface is very steep posteriorly, but in front it forms an angle of 25
to 30 degrees with the ground plane. The articular surface is narrow
from side to side, and slopes downward and backward. It is also oblique
transversely, the interdigital side being the lower. It is adapted to
the distal surface of the second phalanx, with the exception of a facet
behind for the distal sesamoid. The extensor process is very rough. The
volar or sole surface is narrow and slightly concave, and presents two
or three foramina of considerable size. It is separated from the wall
surface by a border which is sharp in front, rounded behind. There is no
semilunar crest, since the deep flexor tendon is attached to the thick
posterior border of the sole surface. The interdigital surface is smooth
and grooved below, rough and porous above. At the upper angle it is
perforated by a large foramen, which is equivalent to the volar foramen
of the horse and leads to a cavity in the middle of the bone. The
surface is separated by a rounded border from the wall surface, and by a
sharp edge from the sole surface. The wing or angle is very short and
blunt, and there is no lateral cartilage.
Four =proximal sesamoids= are present, two for each digit. They are much
smaller than in the horse. The bones of each pair articulate with the
corresponding part of the distal end of the large metacarpal bone by
their anterior surfaces, with each other and with the first phalanx by
small facets.
The two =distal sesamoids= are short and their ends are but little
narrower than the middle.
BONES OF THE PELVIC LIMB
The =ilia= are almost parallel to each other and are also less oblique
with regard to the horizontal plane than in the horse. They are
relatively small. The gluteal line is prominent and is nearly parallel
to the external border; it joins the superior ischiatic spine. A rounded
ridge separates the two parts of the ventral surface. The surface for
articulation with the sacrum is triangular. The internal angle is
truncated, does not extend as high as the vertebral spines, and is
separated from the opposite angle by a wider interval than in the horse.
The external angle is relatively large and prominent; it is not so
oblique as in the horse, and is wide in the middle, smaller at either
end. The shaft is short and compressed from side to side.
The =ischium= is large. Its long axis is directed obliquely upward and
backward, forming an angle of about 45 to 50 degrees with the horizontal
plane. The transverse axis is oblique downward and inward at a similar
angle, so that this part of the pelvic floor is deeply concave from side
to side. The middle of the ventral surface bears a rough ridge or
imprint for muscular attachment. The superior ischiatic spine is high
and thin, and bears a series of almost vertical rough lines externally.
The tuber ischii is large and three-sided, bearing upper, lower, and
external tuberosities. The ischial arch is narrow and deep. The
symphysis bears a ventral ridge, which fades out near the ischial arch.
The acetabular branch of the =pubis= is narrow, and is directed outward
and a little forward. The anterior border is marked by a transverse
groove which ends below the rough ilio-pectineal eminence. The
longitudinal branch is wide and thin.
The =acetabulum= is smaller than in the horse. The rim is rounded and is
usually marked by two notches. One of these is postero-internal and is
narrow and deep; it leads to the deep acetabular fossa and is commonly
almost converted into a foramen by a bar of bone. The other notch is
antero-internal, small, and sometimes replaced by a foramen or absent.
The =obturator foramen= is large and elliptical. Its inner border is
thin and sharp.
[Illustration:
FIG. 101.—SKELETON OF LEFT HIND LIMB OF OX, FROM MIDDLE OF THIGH
DOWNWARD, POSTERIOR VIEW. _21_, Tibia; _24_, tuber calcis; _25_,
large metatarsal bone. (After Ellenberger-Baum, Anat. für Künstler.)
]
The =pelvic inlet= is elliptical and is more oblique than in the horse.
In a cow of medium size the =conjugate diameter= is about nine and a
half inches (ca. 23 to 24 cm.), and the transverse about seven inches
(ca. 18 cm.). The anterior end of the symphysis lies in a transverse
plane through the junction of the third and fourth sacral segments. The
roof is concave in both directions. The =floor= is deeply concave,
particularly in the transverse direction. The =cavity= is narrower and
its =axis= is inclined strongly upward in the posterior part. The
distance between the acetabulum and the external angle of the ilium is
only a little (ca. 3 to 4 cm.) more than the distance between the former
and the tuber ischii.
[Illustration:
FIG. 102.—FRONTAL SECTION OF LEFT FEMUR OF OX, FRONT VIEW.
]
[Illustration:
FIG. 103.—FRONTAL SECTION OF LEFT TIBIA OF OX, ANTERIOR VIEW.
These figures show the internal architecture of these bones, and
especially the great extent of the medullary cavity as compared with
those of the horse (Figs. 67 and 72).
]
The =femur= has a relatively small shaft, which is cylindrical in its
middle, prismatic below. The trochanter minor has the form of a rough
tuberosity, and is situated higher up than in the horse and encroaches
on the posterior surface. The trochanteric ridge (Crista
intertrochanterica posterior) connects it with the trochanter major. The
third trochanter is absent. The supracondyloid (plantar) fossa is
shallow. The proximal extremity is very wide. The head is smaller than
in the horse and the articular surface extends considerably on the upper
surface of the neck. Instead of the notch there is a small depression on
the middle of the head for the attachment of the round ligament. The
neck is well defined except above. The trochanter major is very massive
and is undivided; its external surface is very rough. The trochanteric
fossa is deep, but does not extend so far downward as in the horse. The
distal end presents no very striking differential features, but the lips
of the trochlea are less oblique than in the horse, and converge very
slightly below. The proximal extremity unites with the shaft at about
three and one-half years, the distal at three and one-half to four
years.
The =tibia= resembles that of the horse rather closely, but is somewhat
shorter. The shaft is distinctly curved, so that the inner side is
convex. The posterior surface is not divided into two areas, and the
lineæ musculares are fewer and extend up higher than in the horse. The
articular grooves and ridge of the distal end are almost sagittal in
direction, and present an extensive but shallow synovial fossa. The
external groove is separated by a sharp ridge from an outer area which
is for articulation with the external malleolus. The anterior part of
the internal malleolus is prolonged downward and has a pointed end. The
groove behind it is broad and well defined. Externally there is a deep
narrow groove which separates two prominences. The proximal extremity
fuses with the shaft at three and one-half to four years, the distal at
two to two and one-half years.
The =fibula= usually consists of the two extremities only. The head is
fused with the external condyle of the tibia and bears a small
blunt-pointed prolongation below. The distal end remains separate and
forms the external malleolus (sometimes called the os malleolare). It is
quadrilateral in outline and compressed from side to side. The proximal
surface articulates with the distal end of the tibia, and bears a small
spine which fits into the groove on that bone. The distal surface rests
on the fibular tarsal, and the inner articulates with the external ridge
of the tibial tarsal bone. The outer surface is rough and irregular.
The early cartilaginous fibula is complete, but later the shaft is
reduced and is usually represented by a fibrous cord which connects the
two ends. In some cases, however, the upper part undergoes partial
ossification, forming a slender rod which is usually united with the
outer border of the tibia and is joined to the head by fibrous tissue.
The =patella= is long, narrow, and very thick. The anterior surface is
strongly convex and very rough and irregular. The articular surface is
convex from side to side and nearly straight in the vertical direction.
The large prominence on the inner side for the attachment of the
accessory cartilage allows prompt determination of the side to which the
bone belongs. The apex is more pointed than in the horse.
The =tarsus= consists of five pieces; the central and fourth, and the
second and third tarsal bones are fused.
The =tibial tarsal= bone is relatively long and narrow, and is somewhat
flattened from before backward. It bears a trochlea at either end. The
groove and ridges of the proximal trochlea are not spiral, but almost
sagittal; the outer ridge is the wider, and articulates with both tibia
and fibula. The distal trochlea consists of two condyles divided by a
groove, and articulates with the combined central and fourth tarsals.
The posterior surface bears a large oval facet for articulation with the
fibular tarsal; this occupies most of the surface, and is convex and
grooved from above downward. The outer surface presents two facets for
articulation with the fibular tarsal, and is excavated and rough
elsewhere. The inner surface bears a tuberosity at its upper part, and
is flattened below.
The =fibular tarsal= bone is longer and more slender than in the horse.
The distal part of the body is compressed laterally, and bears a
projection in front which articulates with the external malleolus. The
tuber calcis is marked posteriorly by a wide shallow groove, which is
coated with cartilage in the fresh state.
The =central= and =fourth tarsals= are fused to form a large bone (Os
centrotarsale quartum, scapho-cuboid), which extends across the entire
width of the tarsus and articulates with all of the other bones. The
greater part of the upper surface is molded on the distal trochlea of
the tibial tarsal, and its inner part rises high above the rest
posteriorly. Externally there is a narrow undulating surface for
articulation with the distal end of the fibular tarsal bone. The
posterior surface bears two tuberosities, of which the outer one is
rounded, the inner more prominent and narrower.
The =first tarsal= bone is quadrilateral and small. It articulates with
the central above, the metatarsus below, and the second tarsal in front.
The =second= and =third tarsals= are fused to form a rhomboid piece. The
proximal surface is concavo-convex, and articulates with the central
component. The distal surface is undulating and rests on the metatarsus.
The external surface bears a small facet in front for the fourth tarsal
component, and the posterior surface a very small one for the first
tarsal bone.
The =large metatarsal= bone is about one-seventh (ca. 3 cm.) longer than
the corresponding metacarpal. Its shaft is compressed laterally and is
distinctly four-sided. The groove on the anterior surface is deep and
wide. The posterior surface is marked by variable grooves. The upper
foramen on this surface does not perforate the shaft, but passes
obliquely through the extremity, opening on the posterior part of its
proximal surface. The postero-internal angle of the proximal end bears a
facet for articulation with the small metatarsal bone.
[Illustration:
FIG. 104.—SKELETON OF DISTAL PART OF LEFT HIND LIMB OF OX, INTERNAL
VIEW. _24_, Tuber calcis; _25_, large metatarsal bone; _30_, first
phalanx; _31_, second phalanx; _32_, third phalanx. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =small metatarsal= bone is a quadrilateral disc a little less than
an inch in width and height. Its anterior face bears a facet for
articulation with the large metatarsal bone.
The large metatarsal bone is usually regarded as consisting of the
fused third and fourth metatarsal bones. The medullary cavity is
subdivided like that of the large metacarpal bone. Some anatomists,
however, consider that the ridges at the upper end of each border
represent the second and fifth metatarsals (Rosenberg and Retterer).
On this basis the small bone would be the first metatarsal.
The =phalanges= and =sesamoids= resemble those of the thoracic limb so
closely as to render separate description unnecessary.
SKELETON OF THE PIG
VERTEBRAL COLUMN
The =vertebral formula= is C_{7}T_{14–15}L_{6–7}S_{4}Cy_{20–23}.
[Illustration:
FIG. 105.—SKELETON OF PIG, LATERAL VIEW.
_a_, Cranium; _b_, upper jaw; _c_, lower jaw; _1H.-7H._, cervical
vertebræ; _1R.w._, first thoracic vertebra; _13 R.w._, thirteenth
thoracic vertebra (next to last); _1L._, first lumbar vertebra;
_6L._, sixth lumbar vertebra (next to last usually); _K._, sacrum;
_S._, coccygeal vertebra; _1R._, first rib; _14R._, last rib;
_R.kn._, costal cartilages; _St._, sternum; _d_, supraspinous fossa
of scapula; _d′_, infraspinous fossa; _1_, spine of scapula; _2_,
neck of scapula; _e_, humerus; _3_, head of humerus; _4_,
tuberosities of humerus; _5_, deltoid tuberosity; _6_, external
epicondyle of humerus; _f_, radius; _g_, ulna; _7_, olecranon; _h_,
carpus; _18–25_, carpal bones; _i-i⁗_, metacarpus; _k-k⁗_, proximal
phalanges; _l-l⁗_, middle phalanges; _m-m⁗_, distal phalanges; _n_,
_o_, sesamoids; _p_, ilium; _8_, external angle of ilium (tuber
coxæ); _9_, internal angle of ilium (tuber sacrale); _10_, superior
ischiatic spine; _q_, ischium; _11_, tuber ischii; _r_, pubis; _12_,
acetabulum; _s_, femur; _13_, trochanter major; _14_, trochanter
minor; _15_, external epicondyle; _t_, patella; _u_, tibia; _16_,
crest of tibia; _17_, external condyle of tibia; _v_, fibula; _w_,
tarsus; _26–31_, tarsal bones; _26′_, tuber calcis. (After
Ellenberger, in Leisering’s Atlas.)
]
The =cervical vertebræ= are short and wide. The bodies are elliptical in
cross-section, the long diameter being transverse. The anterior
articular surfaces are slightly convex from side to side and concave
dorso-ventrally; the posterior ones are slightly concave. A ventral
crest is not present. The arches are wide from side to side, but the
laminæ are narrow, so that a considerable interval (Spatium
interarcuale) separates adjacent arches dorsally. The pedicles are
perforated by a foramen on either side in addition to the usual
intervertebral foramina. The transverse processes divide into two
branches, both of which increase in size from the third to the sixth.
The upper branch projects outward and backward; it is short and is
thickened at its free end. The lower branch is a quadrilateral plate
directed ventrally; each overlaps the succeeding one to a small extent,
and the series forms the lateral boundary of a deep and wide groove
beneath the bodies. The spines increase in height from the third to the
last; the anterior ones are inclined backward, the posterior ones
forward. The last cervical is recognized by the great length of its
spine (ca. 10 cm. in the adult), the absence of the ventral plate of the
transverse process, and the flatness of the body, which bears a pair of
small facets on its posterior margin for the heads of the first ribs. It
has foramina transversaria, and usually two foramina in either side of
the arch.
The dorsal arch of the =atlas= bears a large tuberosity. The ventral
tubercle is long, compressed laterally, and projects back under the
axis. The wing is flattened and bears a posterior tuberosity. The
foramen transversarium passes through the posterior border of the wing
to the fossa under the latter, and is not visible dorsally; it is
sometimes very small or absent. The sides of the vertebral foramen bear
two lateral projections which partially divide it into a ventral narrow
part, which receives the odontoid process, and a dorsal larger part for
the spinal cord. In the fresh state the division is completed by the
transverse ligament, which is attached to the projections.
The =axis= has a large spinous process, which is directed upward and
backward. The odontoid process is a thick cylindrical rod. The
transverse process is very small and the foramen transversarium is often
incomplete.
[Illustration:
FIG. 106.—ATLAS OF PIG, DORSAL VIEW.
_a_, Wing; _b_, ventral tubercle; _c_, foramen transversarium; _d_,
alar foramen; _e_, intervertebral foramen; _f_, dorsal tuberosity;
_g_, articular surface corresponding to that of posterior articular
process of typical vertebra; _h_, facet on ventral arch for odontoid
process. (Ellenberger-Baum, Anat. d. Haustiere.)
]
[Illustration:
FIG. 107.—AXIS OF PIG, LEFT LATERAL VIEW.
_a_, Odontoid process (dens); _b_, spinous process; _c_, anterior
articular process; _d_, posterior articular processes; _e_,
transverse process; _f_, foramen transversarium; _g_, bar of bone
which bounds _h_, intervertebral foramen; _i_, vertebral foramen.
(Ellenberger-Baum, Anat. d. Haustiere.)
]
The =thoracic vertebræ= are often fifteen in number. Their bodies are
relatively long, constricted in the middle, and without ventral crests.
Their extremities are elliptical, depressed in the middle and prominent
at the periphery. The arch is perforated by a foramen on either side,
and in most of the series there is also a foramen in the posterior part
of the root of the transverse process which communicates with the former
or with the posterior intervertebral foramen. Sometimes there is a
foramen in the anterior part of the process also. There are mammillary
processes except on the first two; in the posterior five or six vertebræ
they project from the anterior articular processes. The facet for the
tubercle of the rib is absent or fused with that for the head in the
last five or six. The last transverse process is lumbar in character,
plate-like, and about an inch (2 cm.) long. Small accessory processes
occur in the posterior part of the region. The first spinous process is
broad, very high, and inclined a little forward. The others diminish
very gradually in length to the tenth, beyond which they are about
equal. The second to the ninth are inclined backward, the tenth is
vertical (anticlinal), and the rest incline forward. The width decreases
decidedly from the fourth to the tenth, beyond which there is a gradual
increase. The summits are slightly enlarged and lie almost in a straight
line.
The occurrence of fifteen thoracic vertebræ appears to be quite
common, and some observers have recorded the existence of sixteen and
even seventeen; a reduction to thirteen is rare.
The =lumbar vertebræ= are six or seven in number. The bodies are longer
than in the thoracic region and bear a ventral crest. They become wider
and flatter in the posterior part of the series. The arches are deeply
notched, and are separated by an increasing space dorsally. The
mammillary processes project outward and backward. The transverse
processes are bent downward and incline a little forward. Their length
increases to the fifth and is much diminished in the last. They form no
articulation with each other or with the sacrum. The posterior edge of
the root of the process is marked by a notch in the anterior part of the
series, a foramen in the posterior part. The spines are broad and
incline forward, with the exception of the last, which is narrow and
vertical.
Lesbre states that six and seven lumbar vertebræ occur with almost
equal frequency. The number may be reduced to five, and the number of
presacral vertebræ varies from twenty-six to twenty-nine.
The =sacrum= consists usually of four vertebræ, which fuse later and
less completely than in the other domesticated animals. It is less
curved than in the ox. The spines are absent, excepting small rudiments
on the last two segments. The middle of the dorsal surface is flattened
and smooth, and presents openings into the sacral canal between adjacent
arches (Spatia interarcualia). On either side are the superior sacral
foramina, and tubercles which indicate the fused articular processes.
The wings resemble those of the ox. The anterior articular processes are
very large. The pelvic surface resembles that of the ox, but is not so
strongly curved, and the transverse lines are very distinct.
[Illustration:
FIG. 108.—SACRUM OF PIG, DORSAL VIEW.
_a_, Wing; _b_, dorsal sacral foramina; _c_, articular process; _1–4_,
segments or sacral vertebræ. (Ellenberger-Baum, Anat. d. Haustiere.)
]
The =coccygeal vertebræ= are specially characterized by the presence of
functional articular processes on the first four or five, beyond which
these processes become non-articular and smaller. The arches of the
first five or six are complete. The transverse processes are broad and
plate-like in the anterior part of the series and diminish very
gradually.
The numerical variation here is twenty to twenty-six according to the
observation of several anatomists. Lesbre states that he has found
twenty-three most frequently.
=Curves.=—The cervical region is practically straight. The thoracic and
lumbar regions form a gentle curve, concave ventrally, the highest point
of which is at the junction of the two regions. The sacral promontory is
not so pronounced as in the ox, and the sacral curve is flatter.
THE RIBS
The =ribs= number fourteen or fifteen pairs, of which seven are sternal
and seven or eight asternal usually. They are in general strongly curved
in the improved breeds, so that there is a fairly distinct angle, except
toward the end of the series. The backward slope of the posterior ribs
is slight. The first rib is prismatic, has a large sternal end, and a
very short cartilage. The width is greatest in the third to the sixth,
and the length in the sixth and seventh usually. The tuberosity fuses
with the head on the last five or six. The second to the fifth form
diarthrodial joints with their cartilages, which are wide and
plate-like.
THE STERNUM
The =sternum= consists of six segments and resembles that of the ox in
general form. The first segment (Manubrium) is long, flattened
laterally, and bears a blunt-pointed cartilage on its anterior end; its
posterior end forms a diarthrodial joint with the body. The latter is
flattened, wide in its middle, narrow at either end. The widest segments
are formed of two lateral parts, which are not completely fused in the
adult. The last segment has a long narrow part which bears the xiphoid
cartilage.
The =thorax= is long and is more barrel-shaped than in the horse or ox,
since the ribs are more strongly curved and differ less in relative
length.
[Illustration:
FIG. 109.—SKULL OF PIG, LATERAL VIEW WITHOUT MANDIBLE.
_1_, Occipital condyle; _2_, paramastoid or styloid process; _3_,
bulla ossea; _4_, external auditory meatus, _5_, zygomatic process
of temporal bone; _6_, sphenoid bone; _7_, orbital opening of
supraorbital canal; _8_, malar bone; _9_, pterygoid bone; _10_,
pterygoid process of sphenoid; _11_, pterygoid process of palate
bone; _I1–3_, incisor teeth; _C_, canine tooth; _P1–4_, premolars;
_M1–3_, molars.
]
BONES OF THE SKULL
CRANIUM
The =occipital bone= has an extensive squamous part or supraoccipital,
which forms a very broad and prominent crest. The latter is concave, and
is thick and rough above, where it forms the highest part of the skull;
laterally it becomes thinner, turns downward, and is continuous with the
temporal crest. Two divergent ridges pass upward from the foramen
magnum, and the surface between them is concave and smooth. The greater
part of the inner (or anterior) surface of the supraoccipital is united
with the parietal bones, but a lower concave area faces into the cranial
cavity. The foramen magnum is almost triangular, and is narrow above,
where it is flanked by two small tuberosities. The paramastoid processes
are extremely long and project almost straight downward. The hypoglossal
foramen is at the inner side of the root of the process. The basilar
part is short and wide; its lower surface bears a thin median ridge and
two lateral imprints or tubercles which converge at the junction with
the sphenoid bone.
[Illustration:
FIG. 110.—SKULL OF PIG, DORSAL VIEW.
]
The =interparietal= fuses before birth with the occipital. The tentorium
osseum is absent.
The =parietal= is overlapped by the occipital bone behind and concurs in
the formation of the occipital crest. Its external surface is divided by
the parietal crest into two parts. The inner part (Planum parietale)
faces upward and forward, and is flattened and smooth. Its inner border
is short and straight and unites early with the opposite bone. Its
anterior border is concave and joins the frontal bone. The outer part
(Planum temporale) faces outward and is more extensive; it is concave,
forms a large part of the temporal fossa, and is overlapped below by the
squamous temporal. The parietal crest extends in a curve from the
occipital crest forward and outward to the supraorbital process. The
internal surface is concave and is marked by digital impressions. The
lower border projects into the cranial cavity and forms a crest which
separates the cerebral and cerebellar compartments laterally. The
interior forms part of the frontal sinus in the adult. There is no
parieto-temporal canal.
The =frontal bone= is long. The frontal surface slopes downward and
forward, the inclination varying in different subjects. The anterior
part is concave and is marked by the supraorbital foramen and the groove
leading forward from the foramen to the nasal bone. The supraorbital
canal opens into the orbit at the upper part of the inner wall of the
latter. The supraorbital process is short and blunt-pointed, and is not
connected with the zygomatic arch. The gap in the orbital margin is
closed by the orbital ligament in the fresh state. The orbital part is
extensive and forms the greater part of the inner wall of the orbit. Its
upper part is perforated by the orbital orifice of the supraorbital
canal, in front of which is the distinct fovea trochlearis. The
ethmoidal or internal orbital foramen is situated in the lower part near
the junction with the orbital wing of the sphenoid. The temporal part is
very narrow and is separated from the orbital plate by a ridge which
joins the pterygoid crest below. The interior of the bone is excavated
by the frontal sinus in practically its entire extent in the adult. In
the young subject the cavity is confined to the anterior part and the
rest of the bone is thick.
The =temporal bone= has a general resemblance to that of the ox. The
zygomatic process is short and stout and is bent at a right angle. The
upper border of the process is thin; traced from before backward it
curves sharply upward and forms a high prominence in front of the
external auditory meatus; beyond this it drops rather abruptly and is
then continued upward to the occipital crest. The anterior part of the
lower border joins the zygomatic process of the malar, which is deeply
notched. The condyle is concave in the transverse direction. The
postglenoid process is absent, but the articular surface is bounded
behind and internally by a crest. There is no parieto-temporal canal.
The external auditory canal is very long and is directed upward and
outward. The bulla ossea is large, compressed laterally, and bears a
pointed muscular process in front. A narrow space intervenes between the
bulla and the basilar part of the occipital bone, so that the foramen
lacerum resembles that of the horse. The small hyoid process is situated
in a deep depression in front of the root of the paramastoid process,
and the stylo-mastoid foramen is immediately external to it. The petrous
part presents no important differential features. The squamous part
(including the root of the zygomatic process) contains an air-cavity,
which is continuous with the sphenoidal sinus.
[Illustration:
FIG. 111.—BASAL SURFACE OF SKULL OF YOUNG PIG, WITHOUT THE MANDIBLE.
_Sq.o._, Supraoccipital; _E.o._, exoccipital; _B.o._, basioccipital;
_B.s._, body of sphenoid; _Sq._, squamous temporal bone; _V_, vomer;
_Mx._, maxilla; _Pa._, horizontal part of palate bone; _P.p._,
palate process of maxilla; _Z_, malar bone; _J_, premaxilla; _D.c._,
canine tooth; _J1–3_, incisor teeth; _O_, temporal fossa; _1_,
occipital crest; _2_, for. magnum; _3_, occipital condyle; _4_,
paramastoid (styloid) process; _5_, bulla ossea; _6_, for. lacerum
basis cranii; _7_, pterygoid process of sphenoid; _8_, posterior
nares; _9_, anterior palatine foramen; _10_, palatine cleft.
(Struska, Anat. d. Haustiere.)
]
The =sphenoid bone= is short and resembles that of the ox in general.
The body is narrow. The pituitary fossa is very deep, and is limited
behind by a prominent dorsum sellæ; the dorsum bears lateral
projections, the =posterior clinoid processes=. The foramen ovale is
absent, being included in the foramen lacerum anterius. The other
foramina are like those of the ox. The pterygoid process is broad and
twisted. Its base is not perforated and its free edge is thin and sharp.
It concurs with the pterygoid and palate bones in the formation of the
pterygoid fossa, which opens backward and is not present in the horse or
ox. The sphenoidal sinus is very large and occupies the body, the
temporal wings, and a great part of the pterygoid processes in the
adult; it is continued into the temporal bone as mentioned above.
The =ethmoid bone= has a relatively long perpendicular plate, which is
marked by ridges corresponding to the ethmoidal meatuses. The cribriform
plate is extensive and very oblique, so that it and the crista galli are
almost in line with the basi-cranial axis. A linear series of relatively
large foramina is found on either side of the crista. The lateral mass
consists of five endoturbinals and eighteen ectoturbinals (Paulli). The
lamina papyracea concurs in the formation of the pterygo-palatine fossa.
FACE
The =maxilla= is extensive. Its external surface forms a longitudinal
groove, which is continued upon the premaxilla in front and the facial
parts of the lacrimal and malar behind. The infraorbital
foramen—sometimes double—is large and is situated above the third or
fourth cheek tooth. The alveolus for the canine tooth produces a ridge
at the anterior end which is very pronounced in the boar. The facial
crest extends forward from the root of the zygomatic process and fades
out behind the infraorbital foramen; in some specimens it is prominent
and thin-edged, in others it is rounded and projects little. The
zygomatic process is short but stout and buttress-like; it is overlapped
externally by the malar. The maxillary tuberosity forms in the young
subject a long bulla, which occupies most of the pterygo-palatine fossa
and contains the developing permanent molars; after the eruption of the
teeth the tuberosity flattens and joins the vertical part of the palate
bone. The palatine process is very long and is marked in its anterior
part by transverse ridges corresponding with those of the mucous
membrane of the palate. The anterior palatine foramen is near the
junction with the palate bone; from it the palatine groove can be traced
distinctly along the entire length of the process. The alveolar border
presents a large alveolus for the canine tooth at its anterior end;
behind this are seven alveoli for the cheek teeth, which increase in
size from first to last. The maxillary foramen and infraorbital canal
are very large. The maxillary sinus is small.
The body of the =premaxilla= is narrow and prismatic. It presents three
alveoli for the incisor teeth, which are separated by short intervals
and diminish in size from before backward. As in the ox, a narrow space
separates the right and left bones and takes the place of the foramen
incisivum. The palatine process is long and narrow. The nasal process is
very extensive and is somewhat rhomboid in outline. Its upper border
forms a very long suture with the nasal bone, and the lower articulates
to about the same extent with the maxilla. The palatine fissure is
relatively wide.
The horizontal part of the =palate bone= forms a fourth to a fifth of
the length of the palate; its palatine surface is triangular, the apex
being anterior; its nasal surface is deeply grooved and smooth. A
pterygoid process (processus pyramidalis of man) projects backward and
downward, and its thick rounded end is received between the pterygoid
process of the sphenoid and the pterygoid bone. The perpendicular part
is largely overlapped externally by the maxilla and concurs in forming
part of the palatine canal. Superiorly the two plates separate and
inclose an air-cavity which opens into an ethmoidal meatus. The inner
plate curves inward and unites with the vomer and ethmoid to form a
horizontal plate (Lamina transversalis), which divides the posterior
part of the nasal cavity into an upper olfactory part and a lower
respiratory part.
The =pterygoid bone= is nearly vertical in direction, and is narrow in
its middle, wide at each end. The external surface is free below and
forms the inner wall of the pterygoid fossa. The lower end is notched
and forms a distinct hamulus.
The =nasal bone= is very long and its width is almost uniform, except at
the anterior end, which is pointed and reaches almost as far forward as
the premaxilla. The facial surface is flattened from side to side. In
profile it is nearly straight in some subjects, variably concave in
others. The external border is free to a small extent in front only;
otherwise it is firmly connected with the premaxilla and maxilla. In the
adult the frontal sinus extends into the posterior part of the bone.
The =lacrimal bone= is very sharply bent. Its facial surface presents a
deep depression, surmounted by a ridge or tubercle. On or close to the
orbital margin are two lacrimal foramina which lead to the lacrimal
canals. The orbital surface presents a fossa in which the inferior
oblique muscle of the eyeball arises, and its lower part bears a crest,
which is crossed obliquely by a vascular furrow. The upper border
articulates with the frontal only. The bone concurs in the formation of
the maxillary sinus.
The =malar bone= is strongly compressed from side to side. Its facial
surface is small and presents a fossa which is continuous with the
depressions of the maxilla and lacrimal. The orbital surface is still
smaller and is smooth and deeply grooved. The zygomatic process is very
extensive, especially in the vertical direction. Its external surface is
convex and free, and bears a rough eminence in its middle. Its internal
surface is concave; it is overlapped in front by the maxilla, and in the
remainder of its extent is free and smooth. The upper border is thick
and rounded in front, where it forms the lower part of the orbital
margin; behind this it forms an extensive notch which receives the
zygomatic process of the temporal. (It might be regarded as dividing
into frontal and temporal branches.) The lower border is convex and
becomes thinner behind.
The =turbinal bones= resemble those of the ox. The superior turbinal is,
however, relatively longer, less fragile, and more firmly attached to
the nasal bone. There is no middle turbinal.
The =vomer= is very long. The anterior extremity reaches to the body of
the premaxilla or very close to it. The lower border is received into a
groove formed by the nasal crest of the maxillæ and palate bones and in
front by the palatine processes of the premaxillæ. The posterior border
is concave, thin, and sharp.
The =os rostri= (or prenasal bone) is situated in the snout between the
nostrils. It has the form of a short three-sided prism. The upper
surface is convex and is notched at each end. The lateral surfaces are
concave, smooth, and converge below, forming a grooved lower border. The
posterior surface is triangular, notched centrally, and rough laterally.
The anterior surface is deeply pitted and is surrounded by an irregular
sharp border.
The =mandible= is very strong, and differs very much from that of the
horse or ox. The body narrows decidedly in front; the lingual surface is
deeply concave; the mental surface is strongly convex, slopes downward
and backward, and forms a distinct prominence at the point of divergence
of the rami. Above this prominence is a pair of foramina. The alveolar
border presents six alveoli for the incisor teeth, and a little further
back two large cavities for the canine teeth. There are two pairs of
mental foramina of considerable size and a variable number of smaller
ones. The rami diverge more than in the horse or ox, and the upper part
is somewhat incurved. The horizontal part is very thick and strong. Its
outer surface is strongly convex from above downward. The inner surface
is prominent over the roots of the molar teeth and overhangs the concave
lower part. The alveolar border is thin in front and widens behind; it
does not follow the axis of the ramus, but runs nearly straight and
produces the marked overhang noted above. There are seven alveoli for
the lower cheek teeth, which increase in size from before backward. The
first is small, not always present in the adult, and is separated by
short spaces from the second and the canine alveolus. The vertical part
is relatively wide above. The condyle is convex in both directions, wide
in front, narrow and declivitous behind. The very small and thin-edged
coronoid process is not quite so high as the condyle, from which it is
separated by a very wide notch. The mandibular foramen is large. The two
halves of the bone unite soon after birth in the improved breeds.
The body of the =hyoid bone= is broad from before backward, short
transversely, and bears on its ventral aspect a very short pointed
lingual process. The thyroid cornua are wide and curved, concave and
grooved dorsally; their ends are attached to the thyroid cartilage of
the larynx by rather long bars of cartilage. The small cornua are short,
wide, and flattened dorso-ventrally; they are attached to short bars
which project from the junction of the body and thyroid cornua. The
middle cornu is a little longer than the small cornu, but is relatively
slender; it is largely cartilaginous in the young subject and does not
ossify at either end. The great cornu is a very slender rod, slightly
enlarged at either end; the upper extremity is attached to the hyoid
process of the temporal by a rather long and wide bar of cartilage.
[Illustration:
FIG. 112.—MANDIBLE OF PIG.
_a_, Body of mandible; _b_, horizontal part of ramus; _f_, vertical
part of ramus; _c_, interalveolar border; _c′_, interval between
canine and corner incisor; _c″_, interval between first and second
premolars; _d_, mental foramina; _e_, vascular impression; _g_,
coronoid process; _h_, condyle; _i_, sigmoid notch; _k_, mandibular
foramen; _1–7_, cheek teeth, _8_, canine tooth; _9_, _10_, _11_,
incisors. (Ellenberger-Baum, Anat d. Haustiere.)
]
THE SKULL AS A WHOLE
The =length= and the =profile= contour vary greatly in different
subjects. Primitively the skull is long—especially in its facial
part—and the frontal profile is almost straight. The condition is very
pronounced in wild or semi-feral pigs, and exists also in the improved
breeds during extreme youth. Most of the latter are decidedly
brachycephalic when fully developed; the face is “dished” in a
pronounced fashion. The frontal region slopes sharply upward, and the
nasal region is shortened, and in some specimens even distinctly concave
in profile. The supraorbital foramina are about midway between the
orbital margin and the frontal suture. The supraorbital grooves extend
forward from the foramina to the nasal region and turn outward and
downward toward the infraorbital foramina over the ridges which separate
the nasal and lateral regions.
The =lateral surface= is triangular when the mandible is included. The
temporal fossa is entirely lateral and its long axis is almost vertical.
It is bounded above by the occipital crest, behind by the temporal
crest, in front by the parietal crest, and is marked off from the
orbital cavity by the supraorbital process and a curved crest which
extends from it to the root of the pterygoid process. The zygomatic arch
is strong, high, and flattened from side to side. Its root is notched
above and bears a projection below. It curves sharply upward behind and
forms a pointed recurved projection above and in front of the external
auditory meatus. The orbit is small. Its margin is deficient behind in
the dry skull, thick and rounded in front and below. The cavity is
limited below by a ridge on the frontal and lacrimal bones, and is
separated by a crest from the temporal fossa. The inner wall is
perforated above by the orbital opening of the supraorbital canal, and
below by the optic and ethmoidal foramina; on its antero-inferior part
is the fossa in which the inferior oblique muscle of the eye takes
origin. Two lacrimal foramina are found on or close to the anterior
margin. The pterygo-palatine fossa is well defined; its upper part forms
a deep groove which leads from the large foramen in the sphenoid (like
that of the ox) to the very large maxillary foramen. The preorbital
region is deeply grooved in its length and is clearly marked off by a
ridge from the nasal and frontal regions. The facial crest is short,
usually thin-edged, and lies above the fifth and sixth cheek teeth. A
little (ca. 2 cm.) in front of it is the infraorbital foramen. There is
a ridged prominence over the canine alveolus. In some skulls the
anterior part of the upper jaw is inclined upward.
The most striking features of the =basal surface= are as follows: The
paramastoid processes are extremely long, less flattened than in the
horse and ox, and nearly vertical. At the inner side of the root of each
is the hypoglossal foramen, and in front of it are the stylo-mastoid
foramen and a deep cavity in which the hyoid process is concealed. The
bulla ossea is long, compressed laterally, and bears a sharp, short,
muscular process. The basioccipital is wide and flattened; it bears a
median crest and two lateral tubercles. The posterior nares are small
and are wider below than above. On either side of them is the tuberosity
of the palate bone, and above this is the pterygoid fossa. The palate is
remarkably long and is relatively narrow. It constitutes about
two-thirds of the entire length of the skull. It is widest between the
canines and premolars and narrow at each end. It is marked by a crest
medially and by the palatine foramen and groove laterally. The anterior
part bears transverse ridges. It is moderately arched from side to side.
In some specimens it is nearly straight or slightly concave in its
length; in others it curves upward to a variable degree in front. The
posterior end always slopes upward more or less.
The =posterior= or =nuchal surface= is remarkable for its height and the
breadth of the occipital crest. The central part above the foramen
magnum is smooth and concave from side to side, and is bounded laterally
by ridges, which converge below and end on two tubercles at the upper
margin of the foramen magnum. The surface is separated from the temporal
fossæ by the temporal crests, which curve downward and outward and blend
with the external auditory canals. The mastoid process has the form of a
plate which overlaps the root of the paramastoid process and bears a
crest on its anterior part.
The =cranial cavity= is small, in spite of the great size of the
cranium; the discrepancy is due to the enormous development of the
frontal sinuses in the adult. It is relatively longer, but much lower
than that of the ox. Its width is greatly diminished between the orbits.
The olfactory fossæ are extensive and very oblique. The floor resembles
that of the ox, but the foramen ovale is absent, the dorsum sellæ is
more developed, and the foramen lacerum basis cranii is like that of the
horse. Two oblique lateral crests clearly mark the limit between the
cerebral and cerebellar compartments. The tentorium osseum and the
parieto-temporal canals are absent.
The =nasal cavity= is very long. Its posterior part is divided by a
horizontal plate into olfactory and respiratory parts. The olfactory
part or fundus is above, and contains the ethmoturbinals and ethmoidal
meatuses. The lower part is continuous with the inferior meatus and
leads to the pharyngeal orifice; hence it is sometimes called the
naso-pharyngeal meatus. The bony roof is almost complete in front on
account of the great length of the nasal bones.
The =frontal sinus= is a vast excavation in the adult animal. It
involves all of the roof and almost all of the sides of the cranium, and
extends forward into the roof of the nasal cavity a variable
distance—sometimes as far as a transverse plane through the infraorbital
foramina. The septum between the right and left sinuses is usually
deflected in an irregular manner in its middle part, but is practically
median at either end. Each sinus is subdivided by numerous septa, some
of which are complete. Thus the sinus is divided into compartments, each
of which communicates with an ethmoidal meatus.
In the young pig the sinus is small and is confined to the anterior
part of the frontal bone. Later it extends backward, outward, and to a
less extent forward. In the old subject it penetrates laterally into
the supraorbital process and the root of the zygomatic process of the
temporal bone, and behind almost down to the foramen magnum and the
occipital condyles. It then consists of six to eight compartments
usually.
The =maxillary sinus= is relatively small. Its anterior end is a little
less than an inch (ca. 2 cm.) behind the infraorbital foramen, and it
extends upward into the lacrimal and backward into the malar bone. The
infraorbital canal passes along its floor, and the roots of the molar
teeth do not project up into it. It does not communicate with the
frontal and sphenoidal sinuses, but with the posterior part of the
middle meatus by means of a considerable orifice.
The =sphenoidal sinus= is very large. It involves the body, pterygoid
processes, and temporal wings of the sphenoid bone, and extends into the
squamous temporal. It communicates with the ventral ethmoidal meatus.
There is a small sinus in the perpendicular part of the palate bone
which communicates with an ethmoidal meatus.
BONES OF THE THORACIC LIMB
The =scapula= is very wide, the index being about 1 ∶ 0.7. The spine is
triangular and is very wide in its middle, which curves backward over
the infraspinous fossa and bears a large tuberosity. Its lower part
bears a small projection (rudimentary acromion). The anterior border is
strongly convex in profile, sinuous when viewed from the front, and
thick and rough in its middle. The posterior border is wide, slightly
concave, and bears an outer rough lip. The vertebral border is convex,
and the cartilage is not so extensive as in the horse and ox. The
cervical angle is thin and bent inward a little. The dorsal angle is
thick and is about a right angle. The neck is well defined. The rim of
the glenoid cavity is rounded and not notched. The tuberosity is just
above the antero-internal part of the glenoid cavity and bears no
distinct coracoid process.
The =humerus= has an appearance in profile somewhat like an italic _f_
minus the cross-bar; this is due to the marked backward and forward
inclination of the proximal and distal ends respectively. The shaft is
decidedly compressed from side to side. The internal surface is
extensive and flattened; it is separated from the anterior surface by a
distinct border, and bears no teres tubercle. The musculo-spiral groove
is shallow. The deltoid tuberosity is small, and there is a larger
rounded eminence midway between it and the external tuberosity. The
nutrient foramen is on the posterior surface below its middle. The head
is more strongly curved and the neck better marked than in the horse or
ox. The external tuberosity is very large and extends upon the front of
the extremity. It is divided into two high prominences by a wide deep
groove. There is a third eminence below and externally for the
attachment of the supraspinatus muscle. The bicipital groove is at the
front of the inner side; it is undivided and is almost converted into a
canal. The outer groove on the distal articular surface is so shallow as
to give the appearance of two condyles of similar size. The olecranon
fossa is very deep, and the plate of bone which separates it from the
coronoid fossa is thin and sometimes perforated. The proximal end unites
with the shaft at three and a half years, the distal at one year.
The =radius= is short and narrow, but thick. The shaft increases in size
from above downward. The greater part of the posterior surface is in
apposition with the ulna; this part is marked by a vascular furrow which
runs downward from the upper interosseous space, and has the nutrient
foramen at its proximal end. The bicipital tuberosity is represented by
a rough area. The distal end is relatively large. Its carpal surface
consists of concavo-convex facets for the radial and intermediate carpal
bones. There is a wide shallow groove on the middle of the front. The
proximal end fuses with the shaft at one year, the distal at three and a
half years.
The =ulna= is massive. It is much longer and considerably heavier than
the radius. The shaft is curved. The anterior surface is convex and most
of it is rough and attached to the radius by the interosseous ligament.
There is a smooth area on the upper third, which concurs with the radius
in forming the upper interosseous space, and is marked in its upper part
by the nutrient foramen. From this space a vascular furrow passes
downward to the lower part of the shaft, where there is often a distal
interosseous space for the passage of vessels. The internal surface is
extensive, concave, and smooth. The external surface is slightly convex,
and its upper part is marked by an oblique rough line or ridge. The
proximal extremity is large and is bent inward somewhat; its length is
more than one-third of that of the entire bone. The distal extremity is
relatively small; it articulates with the ulnar and accessory carpal
bones, and is notched in front to accommodate the ridge on the radius.
The bone contains a considerable medullary canal. The bone is
consolidated at three to three and a half years.
The =carpus= comprises eight bones, four in each row. The bones of the
proximal row resemble those of the ox, with the exception of the
accessory, which is more like that of the horse, but has no external
groove. The first carpal is small, elongated from before backward,
rounded, and articulates in front with the second carpal. The latter is
high and narrow, and articulates with the second and third metacarpal
bones below. The third carpal articulates with the radial and
intermediate above, the third metacarpal bone below. The fourth is the
largest bone of the row; it articulates with the intermediate and ulnar
above, the fourth and fifth metacarpals below, and bears a tuberosity on
its volar aspect.
[Illustration:
FIG. 113.—SKELETON OF FOREARM AND MANUS OF PIG, ANTERO-EXTERNAL VIEW.
_a_, Radius; _b_, ulna; _c_, radial carpal; _d_, intermediate carpal;
_e_, ulnar carpal; _f_, accessory carpal; _g_, first carpal; _h_,
second carpal; _i_, third carpal; _k_, fourth carpal; _l-o_, second
to fifth metacarpal bones; _p-s_, second to fifth digits; _1_,
olecranon; _2_, beak of ulna (proc. anconeus); _3_, semilunar notch;
_4_, styloid process of ulna; _5_, styloid process of radius; _6_,
distal epiphyseal lines; _7_, first phalanx; _8_, second phalanx;
_9_, third phalanx. (Ellenberger-Baum, Anat. d. Haustiere.)
]
Four =metacarpal bones= are present. The first is absent, the third and
fourth are large and carry the chief digits, while the second and fifth
are much smaller and bear the accessory digits. Their proximal ends
articulate with each other and with the carpus as indicated above. The
bones are consolidated at about two years of age.
The third and fourth metacarpals are flattened from before backward,
three-sided, and placed close together. The distal end of each bears a
trochlea for articulation with the first phalanx and the sesamoids.
The third is the wider of the two, and articulates with all of the
lower row of the carpus except the first. The fourth articulates with
the fourth carpal chiefly, but has a small facet for the third. The
second and fifth metacarpals are placed further back than the chief
bones. The fifth is considerably the thicker of the two. The proximal
ends are small and articulate with the corresponding carpal and
metacarpal bones. The distal end is relatively large; its articular
surface is condyloid in front, trochlear behind.
Each chief digit comprises three =phalanges= and three =sesamoids=. The
bones of the chief digits resemble those of the ox in form, but there is
no foramen on the interdigital side of the extensor process and the
proximal sesamoids are narrow and ridged behind. The phalanges of the
accessory digits (which do not reach the ground ordinarily) are similar
in form but much smaller.
BONES OF THE PELVIC LIMB
The =os coxæ= is long and narrow. The ilium and ischium are almost in
line with each other and sagittal in direction. The wing of the =ilium=
bends outward much less than in the horse or ox. The gluteal surface is
divided into two fossæ by a ridge, which is continuous with the superior
ischiatic spine behind. The inner surface presents an extensive rough
area behind, which is in apposition with the wing of the sacrum. The
smooth iliac area is narrow, and is bounded above by a ridge. The crest
or anterior border is convex, and is thick, rough, and prominent in its
middle, which forms the highest point of the bone. The internal angle is
lower than the crest, is directed backward, and articulates internally
with the sacrum. The external angle is lower still and is very little
thickened. The =ischia= in the female are somewhat divergent and
flattened behind. The tubera are everted and bear three prominences.
There is a crest or tuberosity on the ventral surface. The superior
ischiatic spine is like that of the cow, but is slightly incurved and
the muscular ridges on its outer face are more pronounced. The
symphyseal part of the =pubis= is thick and the two bones are almost in
a horizontal plane. The ilio-pectineal eminence is prominent and the
psoas tubercle is well marked.
The =acetabulum= is placed a little further back than in the ox. The rim
is thick and is cut into posteriorly by a narrow fissure, which leads
into the deep fossa acetabuli. The three pieces of the os coxæ are fused
by the end of the first year, but the crest and the ischial tubera are
partially separate till the sixth or seventh year. The symphysis does
not usually undergo complete anchylosis. Interischial bones are present.
The =inlet= of the =pelvis= is elliptical and very oblique. In a sow of
full size the conjugate diameter is about five to six inches (10 to 12
cm.) and the transverse about three and a half to four inches (ca. 8.75
to 10 cm.). In the female the floor is relatively wide and flattened,
especially at the outlet, where the tubera are everted; it also has a
decided downward inclination behind. The pelvic axis is therefore
correspondingly oblique. The ischial arch is wide. In the boar the pubis
is much thicker and the ischia are not everted posteriorly. The inlet is
smaller. The floor is concave from side to side and slopes decidedly
less than in the sow. The superior ischiatic spines are more incurved,
and the ischial arch is much narrower and deeper.
The =femur= has a relatively wide and massive shaft, on which four
surfaces might be recognized. The principal nutrient foramen is situated
in the proximal third of the anterior surface. The posterior surface is
wide, and is limited outwardly by a ridge which extends from the
trochanter major to the large external supracondyloid crest. There is no
supracondyloid (plantar) fossa. The head is strongly curved, and is
marked toward the inner side by a rather large depression for the
attachment of the round ligament. The neck is distinct. The trochanter
major, although massive, does not extend up as high as the head. The
trochanteric ridge and fossa resemble those of the ox. The external
(third) trochanter is absent. The ridges of the trochlea are similar and
almost sagittal.
The shaft of the =tibia= is slightly curved, convex internally. The
tuberosity is grooved in front, and a narrow sulcus separates it from
the external condyle. The facet for the fibula is on the posterior
border of the latter, and is bounded internally by an eminence. The
upper part of the crest is very prominent and curves outward. The distal
end resembles in general that of the ox, but is relatively narrower
transversely and thicker from before backward.
The =fibula= extends the entire length of the region, and is separated
from the tibia by a wide interosseous space. The shaft is flattened from
side to side; the proximal part is wide and deeply grooved externally;
the lower part is narrower and thicker. The proximal end is flattened,
grooved externally, and articulates internally with the external condyle
of the tibia. The distal end forms the external malleolus. It is grooved
externally, and articulates with the tibia and tibial tarsal internally,
with the fibular tarsal bone distally.
The =patella= is very much compressed laterally and presents three
surfaces.
[Illustration:
FIG. 114.—COXAL BONES OF PIG, LEFT POSTERIOR VIEW.
_a_, Wing, _b_, shaft, _c_, external angle, _d_, anterior border, _e_,
internal angle, _f_, gluteal line of ilium; _g_, great sciatic
notch; _h_, smooth, _i_, rough part of ventral surface of ilium;
_k_, psoas tubercle; _l_, ilio-pectineal eminence; _m_, acetabular
branch, _n_, symphyseal branch of pubis; _o_, obturator foramen;
_p_, _p′_, ischium; _q_, _q′_, tuber ischii; _r_, symphysis; _s_,
ischial arch; _t_, _t′_, superior ischiatic spine; _u_, acetabulum;
_v_, epiphyseal line. (Ellenberger-Baum, Anat. d. Haustiere.)
]
The =tarsus= comprises seven bones. The tibial and the fibular tarsal
resemble in general those of the ox. The axis of the tibial is, however,
slightly oblique downward and inward, and its distal end bears a double
trochlea for articulation with the central and fourth tarsals. The tuber
calcis is deeply grooved posteriorly. The central tarsal is narrow
transversely and thick. Its proximal surface is deeply concave, and the
posterior bears a large tubercle. The first tarsal is high and narrow;
it articulates with the central and second tarsals and the second
metatarsal bone. The second tarsal is small and somewhat prismatic; it
articulates with the central above, the third in front, the first
behind, and the second and third metatarsals below. The third tarsal is
much larger, and is compressed from above downward, wide in front,
narrow behind. It articulates with the central tarsal above, the third
metatarsal below, the second tarsal internally, and the fourth tarsal
externally. The fourth tarsal is large. Its external face is crossed by
an oblique groove for the tendon of the peroneus longus. The internal
surface articulates with the central and third tarsals. The proximal
surface supports the tibial and fibular tarsal bones, and the distal
surface rests on the fourth and fifth metatarsals. It ossifies from two
centers.
The four =metatarsal bones= resemble the corresponding bones of the fore
limb, but are somewhat longer. The proximal ends of the third and fourth
each have a considerable projection behind; the process on the third has
a facet for articulation with a discoid sesamoid bone. The second and
fifth are placed more on the posterior aspect of the large bones than is
the case in the fore limb.
The first and second =phalanges= are a little longer and narrower than
those of the fore limb.
SKELETON OF THE DOG
VERTEBRAL COLUMN
The vertebral formula is C_{7}T_{13}L_{7(6)}S_{3}Cy_{20–23}.
The =cervical vertebræ= are relatively longer than in the ox and the
pig. The bodies of the typical vertebræ diminish in length from first to
last and are compressed dorso-ventrally. The anterior extremity is
moderately convex and the posterior slightly concave; both are oblique.
The median ridge and lateral grooves on the upper surface of the body
are very well marked. The second, third, and fourth have distinct
ventral spines. The spinous process of the third has the form of a long
low crest; in the remainder it is higher, blunt-pointed, and inclined
forward. The transverse processes of the third, fourth, and fifth
project downward and backward, and divide into two branches; of these,
the anterior one is thin, and the posterior is thick and tuberculate at
its free end. The process of the sixth has two parts; one of these is an
extensive quadrilateral plate directed downward and outward and ridged
on its inner surface; the other part is short and blunt, and is directed
outward and a little backward and upward. The seventh is readily
distinguished by its shortness, the length of its spine, and the single
transverse process. The posterior articular processes bear tubercles
which are large on the third, fourth, and fifth.
The ventral arch of the =atlas= is narrow from before backward, and
bears a small tubercle posteriorly. The upper surface of the dorsal arch
is strongly convex and rough centrally. The wings are wide, flattened,
and almost horizontal. The upper surface is rough. There is an alar
notch (Incisura alaris) on the anterior border instead of the anterior
foramen. The foramen transversarium is present.
The body of the =axis= is flattened dorso-ventrally, especially in
front. The odontoid process is rounded and relatively long, reaching
almost to the occipital bone; it is inclined upward a little. The
articular surfaces which flank it are condyloid in form and very
oblique. The inferior surface is wide, and is divided by a median crest
into two fossæ. The transverse processes are single, pointed, directed
backward and outward, and perforated by relatively large foramina
transversaria. The spinous process is thin and of moderate height, but
very long; it is prolonged forward so as to overhang the dorsal arch of
the atlas, and is terminated behind by a tuberosity which is connected
by two crests with the posterior articular processes. The anterior
notches are large and are never converted into foramina.
The bodies of the =thoracic vertebræ= are wide and compressed
dorso-ventrally, especially at each end of the region. Their convex
anterior surfaces are depressed in the middle. The posterior facets for
the heads of the ribs are absent on the last three or four. The
transverse processes resemble those of the horse. They bear mammillary
processes except at the anterior end of the region. The facets for the
tubercles of the ribs are large and concave in the anterior part of the
series, and become smaller and slightly convex further back. The last
three have accessory processes also. The first three or four spinous
processes are about equal in length. Behind this they become gradually
shorter to the tenth, and then remain equal. The backward slope is most
marked in the ninth and tenth. The eleventh is practically vertical
(anticlinal vertebra) and the last two incline slightly forward.
The bodies of the =lumbar vertebræ= are decidedly flattened
dorso-ventrally, and increase in width from first to last. The length
increases to the sixth. The transverse processes are plate-like and are
directed forward and downward. Their length increases to the fifth and
sixth. They form no joints with each other or with the sacrum. Their
extremities are enlarged, with the exception of the last. The accessory
processes project backward over the posterior notches of the first five.
The anterior articular processes are large, compressed laterally, and
bear mammillary processes. The spinous processes are broad below,
narrower above, and with the exception of the last, incline a little
forward. Their height diminishes behind the fourth.
[Illustration:
FIG. 115.—SKELETON OF DOG, LATERAL VIEW.
_a_, Cranium; _b_, face; _c_, mandible; _1H-7H_, cervical vertebræ;
_13B_, last thoracic vertebra; _1L-7L_, lumbar vertebræ; _K_,
sacrum; _S_, coccygeal vertebræ; _1R-13R_, ribs; _R.Kn._, costal
cartilages; _St._, sternum; _d_, scapula; _d′_, supraspinous fossa;
_d″_, infraspinous fossa; _1_, spine of scapula; _2_, acromion; _3_,
tuberosity of scapula; _3′_, articular end of scapula; _e_, humerus;
_4_, head of humerus; _5_, external tuberosity of humerus; _5′_,
deltoid ridge; _6_, _6′_, epicondyles of humerus; _7_, external
condyloid crest; _7′_, coronoid fossa; _f_, radius; _g_, ulna; _8_,
olecranon; _9_, “beak” of ulna; _h_, carpus; _i_, metacarpus; _k_,
proximal phalanges; _l_, middle phalanges; _m_, distal phalanges;
_n_, sesamoid; _p_, ilium; _10_, wing of ilium; _11_, shaft of
ilium; _12_, crest of ilium; _13_, external angle of ilium (tuber
coxæ); _14_, internal angle of ilium (tuber sacrale); _15_, superior
ischiatic spine; _q_, pubis; _r_, ischium; _16_, tuber ischii; _17_,
acetabulum; _s_, femur; _18_, head of femur; _19_, trochanter major;
_20_, trochanter minor; _21_, trochanter tertius; _22_, _23_,
condyles; _24_, _25_, epicondyles; _26_, trochlea; _t_, patella;
_u_, tibia; _27_, tuberosity of tibia; _28_, _29_, condyles of
tibia; _30_, internal malleolus; _v_, fibula; _31_, external
malleolus; _32_, head of fibula; _w_, tarsus; _x_, metatarsus; _y_,
phalanges; _33_, occipital bone; _34_, paramastoid (styloid)
process; _35_, parietal bone; _36_, frontal bone; _37_, lacrimal
bone; _38_, malar bone; _39_, squamous temporal; _40_, maxilla;
_40′_, infraorbital foramen; _41_, premaxilla; _42_, nasal bone;
_43_, external auditory meatus; _44_, canine tooth; _45_, masseteric
fossa; _46_, angular process of mandible. (After Ellenberger, in
Leisering’s Atlas.)
]
The =sacrum= results from the early fusion of three vertebræ. It is
short, wide, and quadrangular. The spines are fused to form a median
crest, which is notched, however, between the summits of the spines. On
either side are two tubercles, vestiges of the fused articular
processes. The pelvic surface is deeply concave and presents two pairs
of foramina. The wings are prismatic and very high. Their lateral
surfaces are extensive, face almost directly outward, and bear an
auricular surface on the lower part. The anterior surface of the body of
the first vertebra is extensive, depressed in its middle, and bears a
prominent lip below. The anterior articular processes are large and have
extensive, slightly concave facets which face upward and inward. The
posterior articular processes are small. The transverse processes of the
last vertebra project backward and may articulate or fuse with those of
the first coccygeal. The sacral canal is strongly compressed
dorso-ventrally.
[Illustration:
FIG. 116.—ATLAS OF DOG, VIEWED FROM ABOVE AND BEHIND.
_a_, Wing; _b_, dorsal arch and tubercle; _c_, ventral tubercle; _d_,
intervertebral foramen; _e_, foramen transversarium; _f_, articular
surface for axis. (Ellenberger-Baum, Anat. d. Hundes.)
]
[Illustration:
FIG. 117.—AXIS OF DOG, LEFT LATERAL VIEW.
_a_, Odontoid process; _b_, articular surface for atlas; _c_,
transverse process; _d_; foramen transversarium; _d′_, posterior
opening of _d_; _e_, spine; _f_, posterior articular process.
(Ellenberger-Baum, Anat. d. Hundes.)
]
The =coccygeal vertebræ= are fully developed in the anterior part of the
region. The arch is complete in the first six usually. The first three
or four have well developed articular processes at each end. Behind this
the posterior pair quickly disappears, and the anterior ones become
non-articular and gradually reduced in size. The transverse processes of
the first five or six are relatively large; behind this they quickly
disappear. =Hæmal arches= (or chevron bones) in the form of a =V= or =Y=
occur ventrally at the intercentral junctions of the third, fourth, and
fifth usually. They transmit the middle coccygeal artery, which passes
between pairs of ventral tubercles further back.
[Illustration:
FIG. 118.—SIXTH CERVICAL VERTEBRA OF DOG, LEFT VIEW.
_a_, Ventral plate, _b_, lateral part of transverse process; _c_,
foramen transversarium; _d_, anterior articular process; _f_,
accessory process; _g_, spinous process; _h_, articular head of
body. (Ellenberger-Baum, Anat. d. Hundes.)
]
[Illustration:
FIG. 119.—FOURTH THORACIC VERTEBRA OF DOG, LEFT VIEW.
_a_, Head; _b_, glenoid cavity; _c_, facet for head of rib; _d_,
transverse process; _e_, facet for tubercle of rib; _f_, mammillary
process; _g_, posterior articular process; _h_, spinous process.
(Ellenberger-Baum, Anat. d. Hundes.)
]
=Curves.=—A gentle curve, convex ventrally, is formed by the cervical
and the anterior part of the thoracic region. The posterior thoracic and
the lumbar vertebra form a second curve, concave ventrally. The sacral
promontory is well marked. The sacrum and the anterior part of the
coccygeal region constitute a third and more pronounced curve, concave
ventrally. In long-tailed dogs the sacro-coccygeal region is somewhat
=S=-shaped.
=Variations.=—Numerical variations are not common except in the
coccygeal region. The number of thoracic vertebræ may be twelve or
fourteen, with or without compensatory change in the lumbar region.
Girard recorded a case with eight lumbar and the usual number of
thoracic vertebra. Six lumbar with fourteen thoracic vertebræ have been
met with. The first coccygeal sometimes unites with the sacrum.
THE RIBS
Thirteen pairs of ribs are present, of which nine are sternal and four
asternal. They are strongly curved, narrow, and thick. Those in the
middle of the series are the longest. The first eight or nine increase
in width in their lower part. The last rib is usually floating. The
costal cartilages are long and curve forward; the length and curvature
of the first pair is a striking special feature.
[Illustration:
FIG. 120.—FOURTH LUMBAR VERTEBRA OF DOG, LEFT VIEW.
_a_, _b_, Articular surfaces of body; _c_, transverse process; _d_,
accessory process; _e_, anterior articular process; _e′_, mammillary
process; _f_, posterior articular process; _g_, spinous process.
(Ellenberger-Baum, Anat. d. Hundes.)
]
[Illustration:
FIG. 121.—SACRUM OF DOG, DORSAL VIEW.
_a_, Dorsal sacral foramina; _b_, articular surface of body of first
segment; _c_, _d_, anterior articular processes; _e_, wing; _f_,
rudiments of articular processes; _g_, lateral part; _h_, spinous
processes. (Ellenberger-Baum, Anat. d. Hundes.)
]
THE STERNUM
This is long, laterally compressed, and consists of eight sternebræ,
which fuse only in exceptional cases and in extreme old age. The first
segment is the longest; its anterior end is blunt-pointed and bears a
short conical cartilage. It widens at the point of articulation of the
first pair of cartilages. The last segment is also long, thinner than
its predecessors, wide in front, and narrow behind, where it bears a
narrow xiphoid cartilage.
The =thorax= is distinctly barrel-like and is not decidedly compressed
anteriorly like that of the horse and ox. The inlet is oval and is
relatively wide on account of the marked curvature of the first pair of
ribs and cartilages.
BONES OF THE SKULL
In the following descriptions of the separate bones an intermediate
type—_e. g._, a fox terrier—is selected, and the most striking
differences in the brachycephalic and dolichocephalic breeds will be
considered in the section on the skull as a whole.
CRANIUM
[Illustration:
FIG. 122.—BASE OF SKULL OF DOG, WITHOUT MANDIBLE.
_I_, Occipital; _II_, tympanic part of temporal; _IIa_, squamous part
of temporal; _IIb_, mastoid part of temporal; _III_, sphenoid; _IV_,
pterygoid; _V_, palate bone; _VI_, vomer; _VII_, malar; _VIII_,
zygomatic arch; _IX_, inner wall of orbit; _X_, palatine process of
maxilla; _XI_, premaxilla; _XII_, orbital cavity; _1_, _1_,
tubercles above foramen magnum; _2_, foramen magnum; _3_, occipital
condyle; _4_, notch between occipital condyles; _5_, condyloid
fossa; _6_, hypoglossal foramen; _7_, paramastoid (styloid, jugular)
process; _8_, for. lacerum and posterior opening of carotid canal;
_9_, petro-occipital synchondrosis; _10_, petro-tympanic fissure;
_11_, tubercle; _12_, bulla ossea; _13_, muscular process of
petrous; _14_, carotid foramen; _15_, osseous Eustachian tube; _16_,
postglenoid process; _17_, glenoid cavity; _18_, for. ovale; _19_,
posterior opening of alar canal; _20_, external opening of
parieto-temporal canal; _21_, stylo-mastoid foramen; _22_, external
auditory meatus; _23_, temporal crest; _24_, zygomatic process of
temporal bone; _25_, body of postsphenoid; _26_, body of
presphenoid; _27_, anterior opening of alar canal; _28_, for.
lacerum orbitale; _29_, optic foramen; _30_, hamulus of pterygoid;
_31_, horizontal part of palate bone; _32_, perpendicular part of
palate bone; _33_, median palatine suture; _34_, palato-maxillary
suture; _35_, posterior nasal spine; _36_, anterior palatine
foramen; _37_, palatine groove; _38_, alveolar border of maxilla;
_39_, palatine process of maxilla; _40_, pterygoid process of
maxilla; _41_, palatine fissure; _42_, body of premaxilla; _43_,
palatine process of premaxilla; _44_, alveolar border of premaxilla;
_45_, supraorbital process of frontal bone. (Ellenberger-Baum, Anat.
d. Hundes.)
]
The =occipital bone= is similar in position to that of the horse. The
crest, is prominent, angular, and directed backward. Just below the
crest are two rough imprints or tubercles for muscular attachment. The
surface below these is convex from side to side and concave from above
downward. On either side, at the junction with the squamous, there is a
foramen which communicates with the parieto-temporal canal. The condyles
are somewhat flattened and are widely separated above; at the inner side
of each is a short condyloid canal, which opens into the
parieto-temporal canal. The paramastoid processes are very short. The
basilar part is wide and joins the bulla ossea on either side; its lower
surface is flattened and the tubercles are at the junction with the
bulla. The hypoglossal foramen is small and is close to the foramen
lacerum posterius; the latter is bounded in front by the bulla ossea,
behind and internally by the occipital bone.
The =interparietal bone= fuses with the occipital before birth. It forms
the high posterior part of the sagittal crest, and is wedged in between
the two parietal bones. The tentorium osseum is thin and curved, concave
ventrally. Its base concurs with the occipital and parietal bones in the
formation of a transverse canal which is continuous with the
parieto-temporal canals.
[Illustration:
FIG. 123.—SKULL OF DOG, DORSAL VIEW.
_I_, Occipital; _II_, parietal; _III_, frontal; _IV_, lacrimal; _V_,
malar; _VI_, squamous temporal; _VII_, nasal; _VIII_, maxilla; _IX_,
premaxilla; _1_, supraoccipital; _2_, interparietal; _3_,
parieto-occipital suture; _4_, occipital crest; _5_, sagittal crest;
_6_, parieto-frontal suture; _7_, squamous suture; _8_, parietal
eminence; _9_, antero-external angle of parietal bone; _10_, frontal
crest; _11_, _14_, orbital margin; _12_, supraorbital process; _13_,
frontal fossa; _15_, temporal part of frontal bone; _16_, nasal
process of frontal bone; _17_, frontal suture; _18_, lacrimal
foramen; _19_, maxillary process of frontal bone; _20_,
lacrimo-maxillary suture; _21_, frontal process of malar bone; _22_,
lacrimal process of malar; _23_, zygomatic process of malar; _24_,
zygomatic process of squamous temporal; _24′_, posterior end of
nasal bone; _25_, nasal suture; _26_, anterior end of nasal bone;
_27_, infraorbital foramen; _28_, canine tooth; _29_, cheek tooth;
_30_, frontal process of maxilla; _31_, body, _32_, nasal process,
_33_, palatine process of premaxilla; _34_, palatine fissure; _35_,
incisor teeth. (Ellenberger-Baum, Anat. d. Hundes.)
]
The =parietal bone= is rhomboid in outline and is strongly curved. It is
extensive and forms the greater part of the roof of the cranial cavity.
At the junction of the right and left bones there is a prominent
sagittal crest which is continued upon the frontal bones. The lower
border articulates with the temporal wing of the sphenoid by its
anterior part and with the squamous temporal in the remainder of its
extent. The external surface enters into the formation of the temporal
fossa. The internal surface is marked by digital impressions, and by
grooves for the middle meningeal artery and its branches.
The external surface of the =frontal bone= is crossed by a frontal
crest, which extends in a curve from the sagittal crest to the
supraorbital process, and separates the frontal and temporal parts. The
frontal parts of the two bones form a central depression and slope
downward and forward. The supraorbital process is very short, so that
the orbital margin is incomplete as in the pig. The supraorbital foramen
is absent. In front there is a narrow pointed nasal part which fits in
between the nasal bone and the maxilla. The orbital and temporal parts
are relatively extensive. Two ethmoidal foramina are commonly present.
The frontal sinus is confined to the frontal bone.
The parts of the =temporal bone= fuse early. The zygomatic process
curves widely outward and forward. Its anterior part is beveled below
and articulates extensively with the corresponding process of the malar.
The articular surface for the condyle of the mandible consists of a
transverse groove which is continued upon the front of the large
postglenoid process. Behind the latter is the lower opening of the
parieto-temporal canal. There is no condyle. The mastoid part is small,
but bears a distinct mastoid process. The external auditory meatus is
large and the canal very short, so that one can see into the tympanum in
the dry skull. The India ossea is very large and is rounded and smooth;
the inner side is united to the basioccipital. Above this junction and
roofed in by the union of the petrous part and the basioccipital is the
=petro-basilar canal= (Canalis petrobasilaris); this transmits a vein
from the floor of the cranium to the foramen lacerum posterius. The
latter is in reality a depression and is situated behind the bulla
ossea. In its posterior part is a foramen which transmits the ninth,
tenth, and eleventh cranial nerves. The =carotid canal= branches off
from the petro-basilar, passes forward external to it through the inner
part of the bulla ossea, and opens in front at the =carotid foramen=; it
transmits the internal carotid artery. The Eustachian opening is
immediately external to the carotid foramen. The muscular and hyoid
processes are extremely rudimentary. The petrous part projects into the
cranial cavity and forms a sharp prominent petrosal crest. The inner
surface presents a deep =floccular fossa= above the internal auditory
meatus. The anterior surface is also free. The anterior angle is
perforated by a =canal= for the fifth cranial nerve (Canalis nervi
trigemini).
[Illustration:
FIG. 124.—CRANIAL CAVITY OF DOG, AS SEEN ON SAGITTAL SECTION OF SKULL.
_I_, Roof of cranium; _II_, base of cranium; _III_, posterior wall of
cranium; _IV_, anterior wall of cranium; _A_, anterior cranial
fossa; _B_, middle cranial fossa; _C_, posterior cranial fossa; _a_,
body of presphenoid; _a′_, body of postsphenoid; _c_, palate bone;
_d_, vomer; _e_, occipital; _f_, occipital condyle; _g_, sagittal
crest; _h_, frontal sinus; _h′_, cranial plate of frontal bone; _i_,
cribriform plate of ethmoid bone; _i′_, ethmoidal foramen; _k_,
ethmoturbinals; _l_, parietal bone; _l′_, _l″_, squamous temporal
bone; _l‴_, temporal wing of sphenoid bone; _m_, sella turcica;
_m′_, dorsum sellæ; _n_, optic foramen; _o_, foramen lacerum
orbitale; _p_, foramen rotundum; _q_, foramen ovale; _r_, _r′_,
carotid foramina; _s_, tentorium osseum; _t_, foramen lacerum; _u_,
_u′_, orifices of parieto-temporal canal; _v_, condyloid canal; _w_,
canal for trigeminal nerve; _x_, internal auditory meatus; _y_,
_y′_, orifices of canal for inferior occipital sinus; _z_, floccular
fossa. (After Ellenberger, in Leisering’s Atlas.)
]
The body of the =sphenoid bone= is flattened dorso-ventrally. The sella
turcica is shallow, but the dorsum sellæ is well developed and bears
=posterior clinoid processes=. A pair of =anterior clinoid processes=
project back from the roots of the orbital wings. The latter are
relatively small and are crossed externally by a crest, which is
continued forward upon the palate bone. The temporal wings are extensive
and articulate above with the parietals. Perforating the roots of the
wings are the following foramina, named from before backward: The optic
passes through the orbital wing. The foramen lacerum orbitale is a
little lower and is at the junction of the wings. The foramen rotundum
opens into the alar canal, which passes through the root of the short
but wide pterygoid process. The foramen ovale is near the posterior
border of the temporal wing. There is no sphenoidal sinus.
The =ethmoid bone= is highly developed. The cribriform plate is
extensive, and the olfactory fossæ are very deep. The crista galli is
little developed, and often incomplete. The perpendicular plate is long.
The lateral masses are greatly developed and bulge upward into the
frontal sinus. There are four large endoturbinals and six ectoturbinals.
The lamina papyracea is extensive and forms the inner wall of the
maxillary sinus. Its lower border joins the palatine process of the
maxilla and the horizontal part of the palate bone. A shelf-like plate
extends inward from its lower part and concurs with the similarly
incurved part of the palate bone in forming the =transverse lamina=
(Lamina transversalis), which divides the olfactory fundus of the nasal
cavity from the naso-pharyngeal meatus.
FACE
The =maxilla= is short, but very high posteriorly. The facial crest is
absent. The infraorbital foramen is over the alveolus for the third
premolar. The =frontal process= fits into a deep notch between the nasal
and orbital parts of the frontal bone, and the middle part of the
posterior border lies along the orbital margin. There are more or less
pronounced ridges, juga alveolaria, over the canine and molar teeth. The
zygomatic process is short and thin; it is completely overlapped
outwardly by the malar, and is perforated by a number of foramina
(Foramina alveolaria). A maxillary tuberosity is not present in the
adult, but there is a pointed projection, the pterygoid process, behind
the last alveolus. The internal surface bears a short turbinal crest on
its anterior part, behind which it is deeply concave and forms the outer
wall of the maxillary sinus. The palatine process is short, wide behind,
and moderately arched from side to side. The anterior palatine foramen
is situated at or close to the transverse palatine suture about midway
between the median suture and the alveolar border. The palatine groove
is distinct. The large alveolus for the canine tooth is completed by the
premaxilla. The small alveolus for the first premolar is separated from
the preceding one by a small interval. The next two consist of anterior
and posterior parts for the roots of the teeth. The fourth and fifth are
much larger and are divided into three parts. The last is small and
consists of three divisions. The infraorbital canal is short.
The body of the =premaxilla= is compressed dorso-ventrally, and contains
three alveoli for the incisor teeth, which increase in size from first
to third; it also completes the inner wall of the large alveolus for the
canine tooth. The foramen incisivum is very small except in large
skulls. The interalveolar border is wide and very short. The nasal
process is wide at its origin and tapers to a sharp point behind; the
anterior part curves upward, backward, and a little inward, and forms
the lateral margin of the osseous nasal aperture; the posterior part
extends backward a long distance between the nasal bone and the maxilla.
The palatine process turns upward and outward, forming with its fellow a
wide groove for the septal cartilage; the posterior end is pointed and
fits into a notch between the palatine processes of the maxillæ, and
supports the end of the vomer. The palatine fissure is short but wide.
The horizontal part of the =palate bones= is extensive, forming about
one-third of the hard palate. It presents a variable number of lesser
palatine foramina. There is usually a pointed posterior nasal spine at
the end of the median suture. The palatine canal is sometimes formed
entirely in this bone. The perpendicular part is even more extensive.
Its external surface is chiefly free and forms most of the inner wall of
the large pterygo-palatine fossa. The maxillary foramen is situated in a
deep recess between this bone and the zygomatic process of the maxilla.
Just above it there is commonly another foramen which opens into the
nasal cavity. The posterior palatine and sphenopalatine foramina are
situated further back and a little lower; the former is immediately
below the latter. A horizontal plate extends from the inner surface,
meets that of the opposite bone and completes the lamina transversalis
spoken of in the description of the ethmoid bone. There is no palatine
sinus.
The =pterygoid bones= are very wide and short. They form a considerable
part of the lateral boundaries of the posterior nares. The lower and
posterior holders are free and at their angle of junction there is a
variable hamulus.
The =nasal bones= are (in most breeds) long and wider in front than
behind. The external surface is variably concave in its length and is
inclined toward the median suture so as to form a central groove. The
inner borders turn downward and form an internal nasal crest which
becomes very prominent behind. The posterior parts fit into a notch
formed by the frontal bones. The anterior ends form an almost
semicircular nasal notch.
The =lacrimal bone= is very small. The facial part extends very little
or not at all beyond the orbital margin. The orbital surface is small
and triangular, and presents the entrance to the lacrimal canal.
[Illustration:
FIG. 125.—MANDIBLE OF DOG, RIGHT-ANTERIOR VIEW.
_a_, Right ramus; _b_, left ramus; _c_, body; _d_, alveolar border;
_e_, processus angularis; _f_, condyle; _g_, coronoid process; _h_,
masseteric fossa; _i_, _k_, crests which form the upper and lower
boundaries of fossa; _l_, mandibular foramen; _m_, mental foramina;
_n_, masseteric line; _o_, sigmoid notch. (Ellenberger-Baum, Anat.
d. Hundes.)
]
The large zygomatic process constitutes the bulk of the =malar bone=. It
is very long and is strongly curved. The upper border is convex, free in
front, where it forms part of the orbital margin, beveled behind for
articulation with the similar process of the temporal bone. Between
these it bears an eminence, the processus frontalis, to which the
orbital ligament is attached. The body of the bone may be considered to
consist of a =lacrimal process= directed upward and fitting in between
the lacrimal and maxilla, and a =maxillary process= directed downward.
The facial surface is convex.
The =superior turbinal bone= is in its anterior part a simple plate,
attached by one edge to the nasal bone; it curves downward and inward,
and its free border is thickened and everted. The posterior part is
wider and resembles the ethmoturbinals, with which it is connected.
The =inferior turbinal bone= is short and very complex. It is attached
to the nasal surface of the maxilla by a basal lamina, which divides
into two secondary lamellæ. The latter detach numerous tertiary lamellæ,
which are coiled and have thick free edges (Fig. 373).
The =vomer= is not in contact with the posterior part of the floor of
the nasal cavity, and does not divide the posterior nares. The posterior
end is narrow and deeply notched. Near the posterior nares the two
plates curve outward and join the palate bones and assist in forming the
lamina transversalis.
The two halves of the =mandible= do not fuse completely even in old age.
The body presents six alveoli for the incisor teeth and two for the
canines. The incisor alveoli increase in size from first to third. The
canine alveoli extend deeply downward and backward. There are usually
two or more foramina on the mental surface. The rami diverge less than
in the pig. The inferior border of the horizontal part is convex in its
length and is thick and rounded. The alveolar border slightly concave in
its length and is a little everted, especially in its middle; it
presents seven alveoli for the lower cheek teeth, which resemble those
of the upper jaw except that the fourth and sixth are much smaller and
the fifth is like the fourth of the upper series. The interalveolar
space is very short or even absent. There are two or three mental
foramina on either side. The vertical part is relatively small. Its
external surface presents a deep =masseteric fossa= which encroaches on
the coronoid process and is limited by ridges in front and below. The
internal surface is convex and is marked by the usual foramen. At about
the same level as the latter is the rough =angular process= (Processus
angularis), which projects backward from the posterior border, and is
equivalent to the angle of the other animals. The condyle is placed very
low—not much higher than the apex of the canine tooth when the bone is
resting on a flat surface. It is long transversely and the inner part of
the articular surface is much the wider and extends over the posterior
surface. Its long axis is a little oblique, the inner end being inclined
somewhat downward and forward. The coronoid process is very extensive
and is bent slightly outward and backward.
The body of the =hyoid bone= is a slightly curved transverse rod; it is
compressed from before backward, and bears no lingual process. The
thyroid cornua are permanently attached to the body by cartilage; they
diverge widely, curve inward, and are compressed laterally. The small
cornua are short, prismatic, and strong. The middle cornua are commonly
a little longer than the great cornua; they are compressed laterally,
and are slightly enlarged at the ends, which are joined by cartilage to
the adjacent cornua. The great cornua are bent outward and are somewhat
twisted.
THE SKULL AS A WHOLE
The different breeds of dog display great variations in the form and
size of the skull. Those which have a long narrow skull (_e. g._,
greyhound, collie) are designated =dolichocephalic=. Other dogs (_e.
g._, bulldog, small spaniels, pugs) have very broad, short skulls and
are termed =brachycephalic=. Intermediate forms (e. g., fox terrier,
dachshund) are =mesaticephalic=.
The length is usually measured from the occipital crest to the
anterior end of the premaxillary suture, and the breadth between the
summits of the zygomatic arches. The cephalic index is the relation of
the breadth to the length, assuming the latter equal 100; the formula
is: (breadth × 100)/(length) = cephalic index. The index of extreme
dolichocephalic breeds is about 50 or even less, as in the greyhound,
and that of brachycephalic specimens may be as high as 90, as in the
bulldog and pugs. Among the mesaticephalic types are the fox terrier,
with an index of about 70, and the white Pomeranian, with one about 72
to 75. The cranio-facial index is the relation of the distance from
the occipital crest to the fronto-nasal suture to that between the
latter and the nasal notch. It varies from 10 ∶ 3 in extreme
brachycephalic breeds to 10 ∶ 7 in extreme dolichocephalic subjects.
The =superior surface= shows the wide outward curve of the zygomatic
arches, and the great extent of the temporal fossæ. The latter are
separated by the sagittal crest, which in the larger breeds is very
strong and prominent, and is continued by the diverging frontal ridges
to the supraorbital processes. The frontal and nasal regions are
centrally depressed, and are more or less concave in profile. The nasal
region is narrow and is terminated in front by a nasal notch. In the
extreme brachycephalic breeds the differences are very striking. The
cranium is strongly convex in both directions and is considerably longer
than the face. The sagittal crest is more or less effaced and is formed
by the interparietal only. The parieto-frontal crests are separated by
an interval behind and diverge to the supraorbital processes, so that
the temporal fossæ are widely separated. The frontal region is wide,
strongly convex, and has a shallow central depression. The nasal region
is very short, relatively wide, and centrally depressed. In profile
there is a marked depression at the fronto-nasal junction, producing
what is termed by fanciers the “stop” of the face.
On the =lateral surface= the great extent of the temporal fossa is seen.
The orbit communicates freely with the fossa, the posterior part of the
orbital margin being absent in the dry skull. The axis of the orbital
cavity forms a much smaller angle with the median plane than in the
horse and ox. A distinct crest marks the limit between the orbital
cavity proper and the extensive pterygo-palatine fossa. The preorbital
region is somewhat triangular, concave in its length, and convex from
above downward. The infraorbital foramen is on its lower part above the
third cheek tooth. In extreme brachycephalic breeds the orbit is
relatively very large and the preorbital region extremely short but
high. In the bulldog the lower jaw protrudes beyond the upper—a
condition known as prognathism. The opposite condition, brachygnathism,
is seen in the dachshund.
[Illustration:
FIG. 126.—SKULL OF BRACHYCEPHALIC DOG, DORSAL VIEW WITHOUT MANDIBLE.
]
Striking features on the =basal surface= of the cranium are the width
and flatness of the basioccipital, the small size of the paramastoid
processes, the large size and rounded shape of the bulla ossea, and the
grooved form of the articular surfaces for the mandible. The posterior
nares are long and narrow and are not divided by the vomer. The hard
palate is usually about half the length of the skull. It is commonly
marked by a median crest or rough line, and on each side are the
anterior and accessory palatine foramina and the palatine grooves. The
width is greatest between the fourth pair of cheek teeth, and here there
is in most skulls a pronounced depression on either side. The length,
width, and contour vary greatly in different breeds.
The angle of divergence of the rami of the mandible varies from 25 to 30
degrees; it is smallest in the greyhound, largest in extreme
brachycephalic types, _e. g._, bulldog, pug.
The =posterior= or =nuchal surface= is somewhat triangular, with the
base below. The summit is formed by the occipital crest, which projects
very strongly backward in the large breeds. Below it there are two very
distinct rough imprints for muscular attachment. In some skulls there is
a thin median crest, in others a rounded elevation. Laterally are the
temporal crests and the mastoid processes. There is usually a foramen in
the temporo-occipital suture above the root of the paramastoid process.
The foramen magnum varies greatly in form; most often the transverse
diameter is the greater, but in some skulls it is equaled or exceeded by
the vertical diameter.
The =cranial cavity= (Fig. 124) corresponds in form and size with the
cranium, specially in those breeds in which the various crests are more
or less effaced and the frontal sinuses are small. The basi-cranial axis
is almost parallel with the palate, and the floor is flattened. The
anterior fossa is narrow and is only slightly higher than the middle
one. The olfactory fossæ are very deep and the crista galli is little
developed. The sella turcica is variable in depth, and the dorsum sellæ
is relatively high and bears clinoid processes laterally. The cerebral
and cerebellar compartments are well marked off laterally by the
petrosal crests and above by the tentorium osseum. The base of the
latter is traversed by a canal which connects the two parieto-temporal
canals. The anterior angle of the petrous temporal is perforated by a
canal for the fifth cranial nerve.
[Illustration:
FIG. 127.—SKULL OF BRACHYCEPHALIC DOG, LATERAL VIEW WITHOUT MANDIBLE.
]
The =nasal cavity= (Fig. 373) conforms to the shape of the face. Its
anterior aperture is large and nearly circular in most dogs. The complex
inferior turbinals occupy the anterior part of the cavity to a large
extent, except near the aperture. Behind the inferior turbinals is the
large opening of the maxillary sinus. Behind this the cavity is divided
by a horizontal plate (Lamina transversalis) into a large upper
olfactory region or fundus nasi and a lower naso-pharyngeal canal. The
fundus is occupied largely by the ethmoturbinals. The posterior nares
are undivided and are in general long and narrow, but vary with the
shape of the skull.
The =frontal sinus= is of considerable size in the large breeds, but is
confined to the frontal bone. It is usually divided into a small
anterior and a much larger posterior compartment, each of which opens
into the superior ethmoidal meatus. The sinus is very small in extreme
brachycephalic types.
The =maxillary sinus= is small, and is in such free communication with
the nasal cavity as to make it rather a recess than a true sinus. It is
bounded internally by the lamina papyracea of the ethmoid, and its outer
wall is crossed obliquely by the lacrimal canal. The roots of the molar
teeth do not project up into it.
BONES OF THORACIC LIMB
The =clavicle= is a small, thin, irregularly-triangular bony or
cartilaginous plate. It is embedded in the mastoido-humeralis muscle in
front of the shoulder joint and forms no articulation with the rest of
the skeleton. (It is nearly an inch long in a large cat and is a slender
curved rod.)
[Illustration:
FIG. 128.—RIGHT SCAPULA OF DOG, EXTERNAL VIEW.
_a_. Supraspinous fossa; _b_, infraspinous fossa; _c_, spine; _d_,
upper broad end of spine; _e_, acromion; _f_, glenoid cavity; _g_,
tuberosity; _h_, vertebral border; _i_, posterior angle; _k_,
scapular notch. (Ellenberger-Baum, Anat. d. Hundes.)
]
[Illustration:
FIG. 129.—LEFT SCAPULA OF DOG, COSTAL SURFACE.
_a_, Subscapular fossa; _b_, _b_, _b_, muscular lines; _c_, _c_,
limiting line between subscapular fossa and serratus area; _d_,
glenoid cavity; _e_, _f_, tuberosity; _g_, nutrient foramen.
(Ellenberger-Baum, Anat. d. Hundes.)
]
The =scapula= is relatively long and narrow. The spine increases
gradually in height from above downward and divides the external surface
into two nearly equal fossæ. Its free edge is thick and rough above, and
at the lower part is thin and bent backward. The =acromion= is short and
blunt and is opposite the rim of the glenoid cavity. The subscapular
fossa is very shallow and is marked by rough lines. The rough area above
it for the attachment of the serratus magnus is large and quadrilateral
in front, narrow and marginal behind. The anterior border is thin,
strongly convex, and sinuous. The posterior border is straight and
thick. The vertebral border is convex and thick and bears a band of
cartilage. The cervical angle is rounded. The dorsal angle is thick and
square. The neck is well defined and bears a rough eminence posteriorly.
The glenoid cavity is continued forward upon the lower face of the
scapular tuberosity, which is blunt and bears no distinct coracoid
process. There is a rough eminence on the posterior surface of the neck,
from which the long head of the triceps arises. The cervical angle is
opposite the first thoracic spine, the dorsal angle lies above the
vertebral end of the fourth rib, and the articular angle at a point just
in front of the sternal end of the first rib in the ordinary standing
position. The shoulder has a great range of movement on the chest-wall.
The =humerus= is relatively very long, rather slender, and has a slight
spiral twist. The shaft is somewhat compressed laterally, especially in
its upper two-thirds; this part is curved in varying degree, convex in
front. The deltoid tuberosity has the form of a low ridge, and it is
continued by a crest which runs upward and backward and bears a tubercle
on its upper part. Another line runs from it down the anterior aspect
and forms the inner boundary of the very shallow musculo-spiral groove.
The nutrient foramen is about in the middle of the posterior surface. A
slight elevation on the proximal third of the inner surface represents
the teres tubercle. The head is long and strongly curved from before
backward. The neck is better marked than in the horse. The undivided
external tuberosity is placed well forward and extends little above the
level of the head. The internal tuberosity is small. The bicipital
groove is undivided and is displaced to the inner side by the extension
forward of the external tuberosity. The distal end bears an oblique
trochlear articular surface for articulation with the radius and ulna,
the outer part of which is the more extensive and is faintly grooved.
The epicondyles are prominent. The coronoid and olecranon fossæ often
communicate through a large =supratrochlear foramen=.
[Illustration:
FIG. 130.—LEFT HUMERUS OF DOG, EXTERNAL VIEW.
_a_, Head; _b_, neck; _c_, crest; _d_, external tuberosity; _e_, mark
for insertion of infraspinatus tendon; _f_, external condyle; _g_,
external condyloid crest; _h_, coronoid fossa; _i_, olecranon fossa.
(Ellenberger-Baum, Anat. d. Hundes.)
]
[Illustration:
FIG. 131.—LEFT RADIUS AND ULNA OF DOG, ANTERO-EXTERNAL VIEW.
_A_, Radius; _B_, ulna; _a_, groove for tendon of extensor carpi
radialis: _b_, groove for common extensor tendon; _c_, proximal
articular surface of radius; _d_, olecranon; _e_, beak (proc.
anconeus) of ulna; _f_, semilunar notch; _g_, coronoid process; _h_,
facet for radius; _i_, groove for lateral extensor tendon; _k_,
groove for tendon of extensor carpi obliquus. (Ellenberger-Baum,
Anat. d. Hundes.)
]
The two bones of the forearm are relatively long and articulate with
each other at either end in such a manner as to allow of slight
movement. A narrow interosseous space separates their shafts. The
=radius= is flattened from before backward and increases in size from
above downward. The shaft forms two curves; one of these, an anterior
convexity, involves the whole shaft; the other, an inner convexity,
affects the upper part. The anterior surface is convex in both
directions and is marked by a groove for the oblique extensor of the
carpus. The posterior surface presents the nutrient foramen in its upper
third, and bears a rough line (Crista interossea) externally for the
attachment of the interosseous ligament. The proximal end (Capitulum
radii) is relatively small and is supported by a distinct neck (Collum
radii). It bears a concave surface (Fovea capituli) above for
articulation with the humerus, and a convex marginal area
(Circumferentia articularis) behind for the ulna. The bicipital
tuberosity is small. There is a large external tuberosity and below this
a rough eminence. The distal extremity is much wider. It has an
extensive concave carpal articular surface. Its inner border projects
downward, forming the =styloid process= of the radius. Externally there
is a concave facet (Incisura ulnaris radii) for the ulna. In front are
three distinct grooves for the extensor tendons. The =ulna= is well
developed, but diminishes in size from above downward. It crosses the
posterior surface of the radius from within outward. The shaft is large
and three-sided in its upper two-thirds, smaller and more rounded below.
Its anterior surface is in general rough. The nutrient foramen is near
the proximal end. A vascular groove descends from it and indicates the
course of the interosseous artery. The proximal end is relatively short.
It is concave and smooth internally, convex and rough externally. The
olecranon is grooved and bears three prominences, of which the posterior
one is large and rounded. The semilunar notch is wide below and
completes the surface for articulation with the trochlea of the humerus.
Below it is a concave surface (Incisura radialis) which articulates with
the back of the head of the radius, and below this is a fossa, which
receives a tuberosity of the radius. The distal end (Capitulum ulnæ) is
small and is produced to a blunt point (Processus styloideus ulnæ). It
articulates with the ulnar carpal below, and has a convex facet on its
antero-internal aspect for the radius.
[Illustration:
FIG. 132.—SKELETON OF DISTAL PART OF THORACIC LIMB OF DOG, EXTERNAL
VIEW.
_4_, Radial + intermediate carpal bone; _5_, ulnar carpal; _6_,
accessory carpal; _7_, second carpal; _8_, third carpal; _9_, fourth
carpal; _10–14_, first to fifth metacarpals; _15_, first phalanx;
_16_, second phalanx; _17_, third phalanx. (After Leisering’s
Atlas.)
]
The =carpus= comprises seven bones, three in the proximal row and four
in the distal. The numerical reduction in the upper row is apparently
due to the fusion of the radial and intermediate, constituting a large
bone which articulates with almost all of the distal surface of the
radius and with the bones of the lower row. It projects prominently on
the posterior surface of the carpus. The ulnar carpal is long; it
articulates with the radius and ulna above and the accessory behind;
below it rests on the fourth carpal and is prolonged downward to
articulate with the fifth metacarpal also. The accessory is cylindrical,
constricted in its middle and enlarged at each end; the anterior
extremity articulates with the ulna and ulnar carpal bone. The first
carpal is the smallest bone of the lower row; it articulates with the
second carpal externally and the first metacarpal distally. The second
carpal is wedge-shaped, the base being posterior; its upper surface is
convex, and its lower is concave and rests on the second metacarpal. The
third carpal is somewhat like the second; its lower surface is concave
and articulates chiefly with the third metacarpal. The fourth carpal is
the largest of the row; it articulates with the fourth and fifth
metacarpals below. Two small bones or cartilages may be found at the
junction of the two rows behind, and a third small bone articulates with
the inner side of the radiointermediate.[27]
Five =metacarpal bones= are present. The first is much the shortest; the
third and fourth are the longest, and are about one-fifth longer than
the second and fifth. The fifth is the widest at the proximal end and is
slightly shorter than the second. They are close together above, but
diverge somewhat below; the first is separated from the second by a
considerable interosseous space. They are so arranged as to form a
convex dorsal surface, and a concave volar surface, which corresponds to
the hollow of the palm of the hand in man. Each consists of a shaft and
two extremities. The shaft is compressed from before backward. In the
third and fourth it is almost four-sided, in the second and fifth
three-sided, in the first rounded. The proximal ends (Bases) articulate
with each other and with the corresponding carpal bones. The carpal
articular surface formed by them is concave from side to side, convex
from before backward. The distal ends (Capitula) have articular surfaces
of the nature of a head, but bear a sagittal ridge behind, except the
first, which is grooved.
[Illustration:
FIG. 133.—SECOND AND THIRD PHALANGES OF DOG.
_a_, Wing of third phalanx; _b_, coronary ridge; _c_, foramen for
digital artery; _d_, ungual surface of third phalanx; _e_, second
phalanx; _f_, first phalanx; _g_, elastic dorsal ligaments. (From
Leisering’s Atlas.)
]
The five =digits= have three phalanges each, except the first, which has
two. The third and fourth digits are the longest; the first is very
short and does not come in contact with the ground in walking. The
=first phalanges= of the chief digits have four-sided shafts, which are
slightly curved forward. The proximal end of each has a concave surface
for articulation with the metacarpal bone and is deeply notched behind.
The distal end has a trochlea for articulation with the second phalanx,
and lateral depressions for ligamentous attachment. The =second
phalanges= are about two-thirds of the length of the first phalanges.
The proximal articular surface consists of two cavities separated by a
sagittal ridge. The distal extremity is wider and flatter than that of
the first. The =third phalanges= correspond in general to the form of
the claws. The base has an articular surface adapted to the second
phalanx and is encircled by a collar of bone. The volar surface bears a
wing or tuberosity, and on either side of this is a foramen. The ungual
part is a curved rod with a blunt-pointed free end. It is rough and
porous. Its base forms with the collar previously mentioned a deep
groove, into which the proximal border of the claw is received. The two
phalanges of the first digit resemble in arrangement the first and third
phalanges of the other digits.
Nine =volar sesamoids= are usually present. Two are found at each
metacarpo-phalangeal joint of the chief digits. They are high and
narrow, articulate with the distal end of the metacarpal bone in front,
and have a small facet on the base for the first phalanx. On this joint
of the first digit there is usually a single flattened sesamoid, but
exceptionally two are present. The distal volar sesamoids remain
cartilaginous. A nodular =dorsal sesamoid= occurs in the anterior part
of the capsule of the metacarpo-phalangeal joints, and cartilaginous
nodules are found in a similar position in connection with the joints
between the first and second phalanges.
BONES OF THE PELVIC LIMB
The =ilium= is nearly parallel with the median plane and its axis is
only slightly oblique with regard to the horizontal plane. The gluteal
surface is concave. The iliac surface is almost flat. The auricular
surface faces almost directly inward, and in front of it there is an
extensive rough area. The ilio-pectineal line is very distinct and is
uninterrupted. The anterior border or crest is strongly convex, thick,
and rough. The internal angle is represented by a thickened part which
bears two eminences, homologous with the posterior superior and
posterior inferior iliac spines of man. The external angle also has two
prominences, which are equivalent to the two anterior spines present in
man. The shaft is almost sagittal and is compressed laterally. Above it
is smooth and rounded, and below it bears a crest externally which
terminates at a tuberosity in front of the acetabulum.
The =ischium= has a twisted appearance owing to the fact that its
acetabular part is nearly sagittal while the posterior part is almost
horizontal. The two bones also diverge behind and the tubera are
flattened and everted. The superior ischiatic spine is low and thick;
its posterior part is marked by transverse grooves and has a prominent
outer lip. There is no lesser sciatic notch. The ischial arch is
relatively small and is semi-elliptical.
[Illustration:
FIG. 134.—OSSA COXARUM OF DOG, LEFT POSTERIOR VIEW.
_a_. Crest; _b_, _c_, internal angle; _d_, great sciatic notch; _e_,
_f_, external angle; _g_, posterior gluteal line; _h_, gluteal fossa
of wing; _i_, shaft of ilium; _k_, anterior gluteal line; _l_,
auricular surface; _m_, ilio-pectineal line; _n_, depression for
origin of rectus femoris; _o_, acetabulum; _p_, acetabular, and _q_,
symphyseal branch of pubis; _r_, psoas tubercle; _s_, obturator
foramen; _s′_, obturator notch; _t_, line for origin of coccygeus;
_u_, superior ischiatic spine; _v_, external border of ischium; _w_,
tuber ischii; _x_, ischial arch. (Ellenberger-Baum, Anat. d.
Hundes.)
]
[Illustration:
FIG. 135.—LEFT FEMUR OF DOG, ANTERIOR VIEW.
_a_, Head; _b_, neck; _c_, trochanter major; _d_, trochanter minor;
_e_, rudimentary trochanter tertius; _f_, rough line; _g_, trochlea;
_h_, _i_, condyles; _k_, suprapatellar fossa. (Ellenberger-Baum,
Anat. d. Hundes.)
]
[Illustration:
FIG. 136.—LEFT TIBIA AND FIBULA OF DOG, ANTERO-EXTERNAL VIEW.
_A_, Tibia; _B_, fibula; _a_, external condyle of tibia; _b_, spine;
_c_, crest of tibia; _d_, muscular notch; _e_, internal malleolus;
_f_, head of fibula; _g_, interosseous space; _h_, external
malleolus (distal end of fibula); _i_, groove for tendon.
(Ellenberger-Baum, Anat. d. Hundes.)
]
The symphyseal part of the =pubis= is thick and fuses late with the
opposite bone. There is no subpubic groove.
The =acetabulum= is about twice as far from the external angle of the
ilium as from the tuber ischii. The fossa acetabuli is deep, and is
bounded internally by a flat plate of bone; its floor is so thin as to
be translucent. There is a small notch behind.
The =obturator foramen= resembles in outline an equilateral triangle
with the angles rounded off.
[Illustration:
FIG. 137.—SKELETON OF DISTAL PART OF PELVIC LIMB OF DOG, EXTERNAL
VIEW.
_6_, Tibial tarsal bone; _7_, fibular tarsal; _8_, central tarsal;
_9_, second tarsal; _10_, third tarsal; _11_, fourth tarsal; _12_,
metatarsal bones; _13_, first phalanx. The first tarsal bone is not
visible in the figure. (After Leisering’s Atlas.)
]
The inlet of the =pelvis= is very oblique. It is almost circular in the
female, but in the male it is elliptical and the conjugate diameter is
the longer. The cavity is narrowest between the acetabula, and very wide
behind. The floor is concave and relatively narrow in front, wide and
flat behind.
The =femur= is relatively much longer than in the horse or ox. The shaft
is regularly cylindrical, except near the extremities, where it is wider
and compressed from before backward. It is strongly curved in its lower
two-thirds, convex in front. The posterior surface is flattened
transversely, narrow in the middle, and widens toward each end. It is
bounded by two rough lines (Labium laterale, mediale) which diverge
toward the extremities. The third trochanter and the plantar
(supracondyloid) fossa are absent. There are two supracondyloid crests,
the inner one being small. The nutrient foramen is in the upper third of
the posterior surface. The head is a little more than a hemisphere and
has a shallow depression behind and external to its center. The neck is
well defined. The trochanter major does not extend as high as the head;
a thick ridge runs from its anterior surface to the neck. The internal
trochanter has the form of a blunt tuberosity. The trochanteric fossa is
round and deep. The ridges of the trochlea are practically sagittal in
direction and are almost similar. The intercondyloid fossa is wide. Just
above each condyle posteriorly there is a facet for articulation with
the sesamoid (of Vesal), which is developed in the origin of the
gastrocnemius muscle.
The =tibia= is about the same length as the femur. The shaft forms a
double curve; the upper part is convex internally, the lower part
externally. The proximal third is prismatic, but is compressed laterally
and is long from before backward. The remainder is almost regularly
cylindrical. The crest is short but very prominent. The nutrient foramen
is usually in the upper third of the external border. The tuberosity is
not grooved, but bears a distinct mark where the ligamentum patellæ is
attached. There is a small facet for the fibula on the postero-external
part of the external condyle, and a small sesamoid bone in the tendon of
origin of the popliteus is in contact with the posterior angle of the
latter. The distal end is quadrangular and relatively small. The
articular grooves and ridge are almost sagittal. There is a facet
externally for articulation with the fibula. There is a vertical groove
internally and a shallower one behind—both for tendons.
The =fibula= extends the entire length of the region. It is slender,
somewhat twisted, and enlarged at either end. The upper part of the
shaft is separated from the tibia by a considerable interosseous space,
but the lower part is flattened and closely applied to the tibia. The
proximal end is flattened and articulates with the external condyle of
the tibia. The distal end is somewhat thicker and forms the external
malleolus. It articulates internally with the tibia and the tibial
tarsal bone. Externally it bears two tubercles.
The =patella= is long and narrow. The anterior surface is convex in both
directions. The articular surface is convex from side to side and
slightly concave from above downward.
The =tarsus= comprises seven bones. The tibial tarsal consists of a
body, neck, and head, like the bone in man. The body presents a trochlea
above for articulation with the tibia and fibula. The posterior surface
has three facets for articulation with the fibular tarsal bone. The head
is directed a little inward and articulates with the central. The
fibular tarsal has a long anterior process or “beak,” but the inner
process (sustentaculum) is short. The tuber calcis is grooved from
before backward. The central has a concave proximal surface adapted to
the head of the tibial tarsal. Its distal surface articulates with the
first, second, and third tarsals. It bears two tubercles posteriorly.
The first tarsal is flattened and irregularly quadrangular; it
articulates above with the central and below with the first metatarsal.
The second tarsal is the smallest and is wedge-shaped; it articulates
below with the second metatarsal bone. The third tarsal is also
wedge-shaped, the base being in front; it articulates with the third
metatarsal below. The fourth tarsal is remarkably high, and resembles a
quadrangular prism; it articulates with the fibular tarsal above, the
fourth and fifth metatarsal below, and the central and third tarsal
bones internally. A groove for the tendon of the peroneus longus crosses
its outer and posterior surface, and above it are one or two tubercles.
Five =metatarsal bones= are present. The first is commonly very small
and has the form of a blunt cone, somewhat compressed laterally. It
articulates with the first tarsal and furnishes insertion to the
tibialis anterior muscle. In some cases it fuses with the first tarsal;
when the first digit is well developed, its metatarsal may resemble the
others (except in size) or be reduced in its proximal part to a fibrous
band. The other metatarsals are a little longer than the corresponding
metacarpals. Their proximal ends are elongated from before backward and
have posterior projections, which in the case of the third and fourth
usually bear facets for articulation with two small rounded sesamoid
bones. In other respects they resemble the metacarpals.
The first digit is often absent. When present, its development varies
and it contains one or two phalanges. In other cases the digit is
double. The phalanges of the other digits resemble those of the fore
limb.
ARTHROLOGY
THE ARTICULATIONS OR JOINTS
An =articulation= or =joint= is formed by the union of two or more bones
or cartilages by other tissue. Bone is the fundamental part of most
joints; in some cases a bone and a cartilage, or two cartilages, form a
joint. The uniting medium is chiefly fibrous tissue or cartilage, or a
mixture of these. Union of parts of the skeleton by muscles
(Synsarcosis), as in the attachment of the thoracic limb in the horse,
will not be considered in this section.
Joints may be classified—(_a_) anatomically, according to their mode of
development, the nature of the uniting media, and the form of the joint
surfaces; (_b_) physiologically, with regard to the amount and kind of
movement or the absence of mobility in them; (_c_) by a combination of
the foregoing considerations.
The classification of joints is still in a very unsatisfactory state,
and, unfortunately, the same term is used in various senses by
different authors. The two main subdivisions proposed by Hepburn are:
(1) Those in which the uniting medium is coextensive with the opposed
joint surfaces, and in which a direct union of these surfaces is
thereby effected. (2) Those in which the uniting medium has undergone
interruption in its structural continuity, and in which a cavity of
greater or less extent is thus formed in the interior of the joint.
This distinction is of considerable importance clinically.
Three chief subdivisions of joints are usually recognized—viz.,
=synarthroses=, =diarthroses=, and =amphiarthroses=.
SYNARTHROSES
In this group the segments are united by fibrous tissue or cartilage, or
a mixture of the two in such a manner as practically to preclude
movement; hence they are often termed fixed or immovable joints. There
is no joint cavity. Many of these joints are temporary, the uniting
medium being invaded by the process of ossification, with a resulting
ankylosis or synostosis. The chief classes in this group of joints are
as follows:
(1) =Suture.=—This term (Sutura) is applied to those joints in the skull
in which the adjacent bones are closely united by fibrous tissue—the
sutural ligament. In many cases the edges of the bones have irregular
interlocking margins, forming the =sutura serrata=, _e. g._, the frontal
suture. In others the edges are beveled and overlap, forming the =sutura
squamosa=, _e. g._, the parieto-temporal suture. If the edges are plane
or slightly roughened, the term =sutura harmonia= is applied to the
joint, _e. g._, the nasal suture.
(2) =Synchondrosis.=—In these the two bones are united by cartilage, _e.
g._, the joint between the basioccipital and the sphenoid bone. Very few
of these joints are permanent.
(3) =Symphysis.=—This term is usually limited to a few median joints
which connect symmetrical parts of the skeleton, _e. g._, symphysis
pelvis, symphysis mandibulæ. The uniting media are cartilage and fibrous
tissue. In some cases a cleft-like rudimentary joint cavity occurs.
(4) =Gomphosis.=—This term is applied to the implantation of the teeth
in the alveoli.
DIARTHROSES
These joints are characterized by the presence of a joint cavity and by
their mobility. They are often called movable or true joints. The
structures which enter into their formation are:
1. The =joint surfaces= (Facies articulares), which are usually more or
less expanded. They are in most cases smooth, and vary much in form.
They are formed of specially dense bone, which differs histologically
from ordinary compact substance. In certain cases (_vide_ Osteology) the
surface is interrupted by non-articular cavities known as =synovial
fossæ=.
2. The =articular cartilages= (Cartilagines articulares), usually
hyaline in type, form a covering over the articular surfaces of the
bones. They vary in thickness in different joints; they are thickest on
the areas of the greatest pressure, and usually tend to accentuate the
curvature of the bone, _i. e._, on a concave surface the peripheral part
is the thickest, while on a convex surface the central part is the
thickest. The articular cartilages are non-vascular, very smooth, and
have a bluish tinge in the fresh state. They diminish the effects of
concussion and greatly reduce friction.
[Illustration:
FIG. 138.—DIAGRAM OF SECTION OF DIARTHROSIS.
_f.l._, Fibrous layer, _s.l._, synovial layer of joint capsule. The
articular cartilages are white, bones dotted, and the joint cavity
black in the figure.
]
3. The =joint capsule= (Capsula articularis) is, in its simplest form, a
sac, the margins of which are attached around the articulating surfaces.
It consists of two layers—an external one, composed of fibrous tissue
(Stratum fibrosum), and an internal one, the synovial layer or membrane
(Stratum synoviale). The =fibrous layer=, sometimes termed the capsular
ligament, is attached either close to the margins of the articular
surfaces or at a variable distance from them. Its thickness varies
greatly in different situations: in certain places it is extremely
thick, and sometimes cartilage or bone develops in it; in other places
it is practically absent, the capsule then consisting only of the
synovial membrane. Parts of the capsule may undergo thickening and so
form ligaments, which are not separable, except artificially, from the
rest of the capsule. The =synovial layer= lines the joint cavity except
where this is bounded by the articular cartilages; it stops normally at
the margin of the latter. It is a thin membrane, and is richly supplied
by close networks of vessels and nerves. It frequently forms =folds=
(Plicæ synoviales) and =villi= (Villi synoviales), which project into
the cavity of the joint. The folds commonly contain pads of fat which
fill up interstices and vary in form and position in various phases of
movement. The synovial membrane secretes a fluid, the =synovia=, which
resembles white-of-egg and lubricates the joint.[28] In many places the
membrane forms extra-articular pouches, which facilitate the play of
muscles and tendons.
The =joint cavity= (Cavum articulare) is inclosed by the synovial
membrane and the articular cartilages. Normally, it is, strictly
speaking, only a potential cavity, which contains nothing but a small
amount of synovia.
The student must guard against a false conception of the joint cavity
which may result from dissections and diagrams, in which an actual
cavity of considerable extent appears to exist. A correct idea of the
intimate apposition of the parts is best obtained from the study of
frozen sections. It is also instructive to examine joints which have
been injected so as to distend the capsule fully. It is then seen that
the cavity is often of much greater potential extent than one might
suppose, and that the capsule is often very irregular in form, _i.
e._, forms a variety of sacculations.
The foregoing are constant and necessary features in all diarthroses.
Other structures which enter into the formation of these joints are
ligaments, articular discs or menisci, and marginal cartilages.
4. =Ligaments.=—These are strong bands or membranes, usually composed of
white, fibrous tissue, which bind the bones together. They are pliable,
but practically inelastic. In a few cases, however, _e. g._, ligamenta
flava, ligamentum nuchæ, they are composed of elastic tissue. They may
be subdivided, according to position, into =periarticular= and
=intraarticular=. Periarticular ligaments are frequently blended with or
form part of the fibrous capsule; in other cases they are quite
distinct. Strictly speaking, intraarticular ligaments, though within the
fibrous capsule, are not in the joint cavity; the synovial membrane is
reflected over them. The term seems justifiable, however, on practical
grounds. Ligaments which connect directly opposed surfaces of bones are
termed interosseous. The special names are based usually on their
position, form, and attachments, _e. g._, lateral or collateral,
cruciate, sacro-iliac, etc. In many places muscles, tendons, and
thickenings of the fasciæ function as ligaments and increase the
security of the joint. Atmospheric pressure and cohesion play a
considerable part in keeping the joint surfaces in apposition.
5. =Articular discs= or =menisci= are plates of fibro-cartilage or dense
fibrous tissue placed between the articular cartilages, and divide the
joint cavity partially or completely into two compartments. They render
certain surfaces congruent, _e. g._, femoro-tibial joint, allow greater
range or variety of movement, and diminish concussion.
6. A =marginal cartilage= (Labrum glenoidale) is a ring of
fibro-cartilage which encircles the rim of an articular cavity. It
enlarges the cavity and tends to prevent fracture of the margin.
=Vessels and Nerves.=—The =arteries= form anastomoses around the larger
joints, and give off branches to the extremities of the bones and to the
joint capsule. The synovial membrane has a close-meshed network of
capillaries; the latter form loops around the margins of the articular
cartilages, but do not usually enter them. The =veins= form plexuses.
The synovial membrane is also well supplied with lymphatics.
Nerve-fibers are especially numerous in and around the synovial membrane
and there are special nerve-endings, _e. g._, Pacinian bodies and the
articular end-bulbs described by Krause.
=Movements.=—The movements of a joint are determined chiefly by the form
and extent of the joint surfaces and the arrangement of the ligaments.
They are usually classified as follows:
1. =Gliding.=—This refers to the sliding of one practically plane
surface on another, as in the joints between the articular processes of
the cervical vertebræ.
2. =Angular Movements.=—In these cases there is movement around one or
more axes. Motion which diminishes the angle included by the segments
forming the joint is termed =flexion=, while that which tends to bring
the segments into line with each other is called =extension=.
With reference to the joints of the lower parts of the limbs, it seems
advisable to employ the terms =dorsal= and volar or =plantar flexion=,
since these joints can be “overextended.” Similarly, the terms =dorsal=
and =ventral flexion= should be applied to the corresponding movements
of the spinal column. The meaning of the term =lateral flexion= is
evident. These movements are all rotations around axes which are
approximately either transverse or vertical. Depression, elevation, and
lateral movement of the lower jaw fall in this category.
3. =Circumduction.=—This designates movements in which the distal part
of the limb describes a circle or a segment of one. In man such movement
is easily performed, but in quadrupeds it is possible to a limited
degree only, and is to be regarded usually as an indication of disease.
4. =Rotation.=—As a matter of convenience, this term is reserved to
indicate rotation of one segment around the longitudinal axis of the
other segment forming the joint. It is seen typically in the
atlanto-axial joint.
5. =Adduction= and =abduction= designate respectively movement of a limb
toward and away from the median plane, or of a digit toward and away
from the axis of the limb.
=Classification.=—This is based on the form of the joint surfaces and
the movements which occur. The following chief classes may be
recognized:
1. =Arthrodia=, or gliding joint. In these the surfaces are practically
flat, admitting of gliding movement. Examples: carpo-metacarpal joints;
joints between the articular processes of the cervical and thoracic
vertebræ.
2. =Ginglymus=, or hinge-joint. In this class the joint surfaces consist
usually of two condyles, or of a segment of a cylinder or cone, which
are received by corresponding cavities. In typical cases the movements
are flexion and extension, _i. e._, around a single transverse axis.
Examples: occipito-atlantal and elbow joints.
3. =Trochoid=, or pivot joint. In these the movement is limited to
rotation of one segment around the longitudinal axis of the other.
Example: atlanto-axial joint.
4. =Enarthrosis=, or ball-and-socket joint. These are formed by a
surface of approximately spherical curvature, received into a
corresponding cavity. They are multiaxial, and allow of the greatest
variety of movement, _e. g._, flexion, extension, rotation, abduction,
adduction, circumduction. Examples: hip and shoulder joints.[29]
AMPHIARTHROSES
These joints, as the name indicates, share some characters with both of
the preceding groups. In them the segments are directly united by a
plate of fibro-cartilage, and usually by ligaments also. The amount and
kind of movement are determined by the shape of the joint surfaces and
the amount and pliability of the uniting medium.[30] These joints are
all medial in position, and are best illustrated by the joints between
the bodies of the vertebræ. There is usually no joint cavity, but in
certain situations a rudimentary one exists.
THE ARTICULATIONS OF THE HORSE
JOINTS AND LIGAMENTS OF THE VERTEBRÆ
The movable vertebræ form two sets of articulations, viz., those formed
by the bodies, and those formed by the articular processes of adjacent
vertebræ; the former are termed =intercentral=, and the latter,
=interneural=. Associated with these are ligaments uniting the arches
and processes; some of these are =special=, _i. e._, confined to a
single joint, while others are =common=, _i. e._, extend along the
entire vertebral column or a considerable part of it. The joints between
the atlas and axis and between the former and the skull require separate
consideration.
INTERCENTRAL ARTICULATIONS
These are =amphiarthroses=, formed by the junction of the extremities of
the bodies of adjacent vertebræ. The =articular surfaces= in the
cervical region consist of a cavity on the posterior end of the body of
the anterior vertebra, and a corresponding convexity or head of the
succeeding vertebra. In the other regions the surfaces are much
flattened. The uniting media are:
1. The =intervertebralfibro-cartilages= (Fibrocartilagines
intervertebrales). Each of these is a disc which fits into the space
between the bodies of two adjacent vertebræ, to which it is intimately
attached. The discs are thinnest in the middle of the thoracic region,
thicker in the cervical and lumbar regions, and thickest in the
coccygeal region. Each consists of a dense fibrous peripheral part
(Annulus fibrosus), and a soft pulpy central part (Nucleus pulposus).
[Illustration:
FIG. 139.—SAGITTAL SECTION OF LAST TWO THORACIC AND FIRST LUMBAR
VERTEBRÆ, SHOWING LIGAMENTS AND SPINAL CORD (MEDULLA). (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The fibrous ring consists of laminæ of fibrous tissue and
fibro-cartilage, which pass obliquely between the two vertebræ and
alternate in direction, forming an X-shaped arrangement. The central
part of the ring is largely cartilaginous, and gradually assumes the
character of the pulpy center. The latter is very elastic and is
compressed, so that it bulges considerably from the surface of
sections; it consists of white and elastic fibers, connective-tissue
cells, and peculiar clear, transparent cells of various sizes. It is a
remnant of the notochord. There are joint cavities in the cervical
intercentral joints, and in those between the last cervical and the
first thoracic, and between the last lumbar and the sacrum. In the
latter the cavity is coextensive with the extremities of the bodies;
in the former, it is usually not so extensive.
2. The =inferior common ligament= (Ligamentum longitudinale ventrale)
lies on the ventral surface of the bodies of the vertebræ and the
intervertebral fibro-cartilages, to which it is firmly attached. It
begins about the fourteenth or fifteenth thoracic vertebra, and is at
first a narrow, thin band. Further back it becomes gradually thicker and
wider, and terminates on the pelvic surface of the sacrum by spreading
out and blending with the periosteum. It is strongest in the lumbar
region, where the tendons of the crura of the diaphragm fuse with it.
3. The =superior common ligament= (Ligamentum longitudinale dorsale)
lies on the floor of the vertebral canal from the dens or odontoid
process to the sacrum. It is narrow over the middles of the vertebral
bodies, and widens over the intervertebral fibro-cartilages, to which it
is very firmly attached.
This ligament is in relation with the spinal veins on either side, and
in the middle of each vertebra a transverse anastomotic branch passes
under the ligament.
INTERNEURAL ARTICULATIONS
Each typical vertebra presents two pairs of articular processes, which
form diarthroses with the two adjacent vertebræ. The =articular
surfaces= are extensive, flat, and oval in the cervical region, small
and flat in the thoracic region, while in the lumbar region the anterior
ones are concave and the posterior convex. The joint capsule is strong
and ample in the cervical region, in conformity with the large size and
greater mobility of these joints in the neck. In the thoracic and lumbar
regions the capsule is small and close. These joints are arthrodia.
Associated with these joints are the =ligamenta flava=, which connect
the arches of adjacent vertebræ. They are membranous and consist largely
of elastic tissue.
[Illustration:
FIG. 140.—LIGAMENTUM NUCHÆ OF HORSE.
_1_, Scapula; _1′_, cartilage of scapula; _4_, lamellar part of
ligamentum nuchæ; _x_, wing of atlas. (After Ellenberger-Baum, Anat.
für Künstler.)
]
The =supraspinous ligament= extends medially from the occipital bone to
the sacrum. From the withers backward it consists of a strong cord of
fibrous tissue, attached to the summits of the vertebral spines. In the
neck and withers it is remarkably modified to form the ligamentum nuchæ,
which requires more extended notice.
The =ligamentum nuchæ= is a powerful elastic apparatus, the principal
function of which is to assist the extensor muscles of the head and
neck. It extends from the occipital bone to the withers, where it is
directly continuous with the supraspinous ligament. It consists of two
parts—funicular and lamellar. The =funicular part= (Pars occipitalis)
arises from the external occipital protuberance and the fossa below it,
and is inserted into the summits of the vertebral spines at the withers.
Two =bursæ= are usually found under it in the adult. The =supra-atloid
bursa= lies between the ligament and the dorsal arch of the atlas. The
=supraspinous bursa= occurs usually over the fourth thoracic spine, but
may be over the third and may extend to the fifth.[31] In the neck the
funicular part consists for the greater part of two bands closely
applied and attached to each other. Near and at the withers it broadens
greatly, forming an expansion three to five inches (ca. 8 to 12.5 cm.)
in width, the lateral margins of which are thin and overlie the
trapezius and rhomboideus muscles. Behind the higher spines it becomes
narrower and thinner, and is continued by the white fibrous lumbo-dorsal
ligament.[32] A mass of fat and elastic tissue lies upon the ligament as
far back as the withers. It varies greatly in amount in different
subjects, and is most developed in stallions of draft breeds, in which
it forms the basis of the “crest.” The =lamellar portion= (Pars
cervicalis) consists of two laminæ separated medially by a layer of
loose connective tissue. Each lamina is formed of digitations which
arise from the second and third thoracic spines and from the funicular
portion, are directed downward and forward, and end on the spines of the
cervical vertebræ, except the first and last. The digitation which is
attached to the spine of the axis is very thick and strong. Behind this
they diminish in size and strength; that to the sixth cervical is quite
thin and feeble, or may be absent.
The =interspinous ligaments= (Ligamenta interspinalia) extend between
the spines of contiguous vertebræ. In the cervical region they are
narrow elastic bands, and in the thoracic and lumbar regions they
consist of white fibers directed obliquely downward and forward.
The =intertransverse ligaments= (Ligamenta intertransversaria) are
membranes which connect adjacent transverse processes in the lumbar
region.
INTERTRANSVERSE ARTICULATIONS
These joints (peculiar to equidæ) are diarthroses formed by the
transverse processes of the last two lumbar vertebræ and the alæ of the
sacrum. A similar joint between the fourth and fifth lumbar processes is
frequently present. The =articular surfaces= have an elongated oval
form, the anterior one being concave and the posterior one convex. The
capsule is tight, and is reinforced ventrally.
SACRAL AND COCCYGEAL ARTICULATIONS
In the foal the bodies of the five sacral vertebræ form joints which
resemble somewhat those in the posterior part of the lumbar region.
These joints are invaded by the process of ossification early, so that
the consolidation of the sacrum is usually complete, or nearly so, at
three years.
The coccygeal vertebræ are united by relatively thick intervertebral
fibro-cartilages, which have the form of biconcave discs. Special
ligaments are not present, but there is a continuous sheath of fibrous
tissue. The movement in this region is extensive and varied. In old
horses the first coccygeal vertebra is often fused with the sacrum.
MOVEMENTS OF THE VERTEBRAL COLUMN
The movements of the spine, exclusive of those at the atlanto-axial
joint, are dorsal, ventral, and lateral flexion, and rotation. The range
of movement at a single joint is very small, but the sum of the
movements is considerable. The movements are freest in the cervical and
coccygeal regions. Rotation is extremely limited in the thoracic and
lumbar regions.
ATLANTO-AXIAL ARTICULATION
This is a trochoid or pivot joint, of a rather peculiar character. The
articular surfaces are: (1) On the lateral masses of the atlas, two
somewhat saddle-shaped facets, which are usually confluent ventrally;
(2) on the axis, reciprocal saddle-shaped surfaces which extend upon the
odontoid process and are confluent on its ventral aspect. It will be
observed that the joint surfaces are not at all accurately adapted to
each other, so that only limited areas are in contact at any time.
The =joint capsule= is attached around the margins of the articular
surfaces. It is loose and ample enough laterally to allow extensive
movement.
The =superior atlanto-axial ligament= (Ligamentum interarcuale) is
membranous and reinforces the capsule dorsally.
The =interspinous ligament= (Ligamentum inter-spinale) consists of two
elastic bands which extend from the dorsal arch of the atlas to the
spine of the axis.
The =inferior atlanto-axial ligament= (Ligamentum dentis externum)
arises from the ventral tubercle of the atlas and is attached by two
branches on the ventral spine of the axis.
The =odontoid ligament= (Ligamentum dentis internum) is short, very
strong, and somewhat fan-shaped. It extends from the rough concave
dorsal surface of the dens or odontoid process, widens in front, and is
attached to the transverse rough area on the inner surface of the
ventral arch of the atlas.
=Movements.=—The atlas and the head rotate upon the axis; the axis of
rotation passes through the center of the odontoid process and body of
the axis.
[Illustration:
FIG. 141.—ATLANTO-OCCIPITAL AND ATLANTO-AXIAL JOINTS OF HORSE, DORSAL
VIEW AFTER REMOVAL OF DORSAL ARCH OF ATLAS.
_a_, Joint capsule of left part of atlanto-occipital joint; _b_,
lateral ligament of same; _c_, _c′_, odontoid ligament; _d_,
atlanto-occipital joint capsule; _e_, joint capsule of articulation
between axis and third cervical vertebra; _f_, interspinous
ligament; _1_, occipital bone; _2_, atlas; _3_, axis; _4_, third
cervical vetrebra. (Ellenberger-Baum, Anat. d. Haustiere.)
]
THE ATLANTO-OCCIPITAL ARTICULATION
This joint may be classed as a ginglymus. The =articular surfaces= of
this joint are: (1) On the atlas, two deep oval cavities; (2) the
corresponding condyles of the occipital bone.
The joint surfaces are oblique, coming very close to the median line
ventrally, but separated by a considerable interval dorsally.
Posteriorly, a triangular rough area cuts into the middle of each
articular surface on the atlas.
There are two roomy =joint capsules=, which sometimes communicate
ventrally, especially in old subjects.
The =superior atlanto-occipital membrane= extends from the dorsal arch
of the atlas to the upper margin of the foramen magnum. It is blended
with the capsules and contains many elastic fibers.
The =inferior atlanto-occipital membrane= extends from the ventral arch
of the atlas to the lower margin of the foramen magnum. It is narrower
and thinner than the superior membrane, and also fuses with the joint
capsules.
The =lateral ligaments= are two short bands which are partially blended
with the capsules. Each is attached to the border of the wing of the
atlas near the intervertebral foramen, and to the outer surface of the
paramastoid or styloid process of the occipital bone.
=Movements.=—These are chiefly flexion and extension. A small amount of
lateral oblique movement is also possible.
ARTICULATIONS OF THE THORAX
COSTO-VERTEBRAL ARTICULATIONS
Each typical rib forms two joints with the vertebral column, one by its
head, and one by its tubercle. They are termed respectively
costo-central and costo-transverse joints.
[Illustration:
FIG. 142.—COSTO-VERTEBRAL ARTICULATION, ANTERIOR VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
I. The =costo-central articulations= (Articulationes capitulorum) are
trochoid or rotatory joints, formed by the junction of the head of the
rib with the bodies of two adjacent vertebræ and the intervertebral
fibro-cartilage. The two facets on the head of the rib are separated by
a non-articular groove, and correspond to the two concave facets (Foveæ
costales) on the vertebral bodies. The capsules are rather tight, and
are covered by the accessory ligaments, which are as follows: 1. The
=radiate ligament= (Ligamentum capituli costæ radiatum) extends
ventrally from the neck of the rib to spread out on the vertebral bodies
and the intervertebral fibro-cartilage. 2. The =conjugal ligament=
(Ligamentum conjugale)—absent from the first joint—is attached to the
groove on the head of the rib, passes transversely into the vertebral
canal, and divides under the superior common ligament into two branches;
one of these is attached to the body of the anterior vertebra; the other
is continued across to the head of the opposite rib, and is attached to
the intervertebral fibro-cartilage. The joint cavity is divided into two
compartments by the conjugal ligament. 3. The =ligament of the neck= of
the rib (Ligamentum colli costæ) is a strong band which crosses the
joint dorsally. It is attached on the vertebra above the costal facet
and on the neck of the rib.
II. The =costo-transverse articulations=. These occur between the
facets on the tubercles of the ribs and those on the transverse
processes of the vertebræ. They are gliding joints. The =capsule= is
reinforced by the =superior costo-transverse ligament= (Ligamentum
costo-transversarium dorsale), a distinct strong band which arises on
the transverse process and ends on the non-articular part of the
tubercle. It is covered by the levator costæ muscle, and begins to be
quite distinct at the fifth joint.
The cavity for the head of the first rib is formed by concave facets
on the bodies of the last cervical and first thoracic vertebræ. The
conjugal ligament is absent, but the ligament of the neck is short and
strong. The radiate ligament is very strong, and consists of two
bands. In the case of the last two or three ribs the costo-central and
costo-transverse joints are confluent, and the various structures are
correspondingly modified.
=Movements.=—The chief movement is rotation around an axis which
connects the centers of the head and tubercle of the rib. The movement
is very limited in the anterior part of the series of joints, but very
considerable in the posterior part.
In the case of the first rib, the movement is evidently extremely
limited. The facet for the tubercle of the rib is deeply concave, and
the axis of rotation is almost transverse. Further back the facets on
the transverse processes become flat, and the axis of rotation
gradually approaches a longitudinal direction. This, in connection
with the mobility of the ventral ends of the asternal ribs and their
elasticity, allows a great increase here in the range of movement, the
effect of which is to enlarge (chiefly) the transverse diameter of the
thorax.
COSTO-CHONDRAL ARTICULATIONS
The costo-chondral junctions are synarthroses. The rib has a concave
surface which receives the convex end of the cartilage. They are united
by the continuity of the strong periosteum and perichondrium.
CHONDRO-STERNAL ARTICULATIONS
These joints (Articulationes sternocostales) are diarthroses formed by
the junction of the cartilages of the sternal ribs with the sternum. The
articular ends of the cartilages (except the first) are somewhat
enlarged, and present surfaces of cylindrical curvature. The articular
surfaces on the sternum for the first pair of cartilages are placed
close together on the dorsal border of the cariniform cartilage
(Manubrium sterni); the other seven are placed laterally at the junction
of the segments. The capsules are strong and tight; the first pair of
joints has a common capsule, and the cartilages articulate with each
other medially. The lower ends of the first pair of ribs are firmly
attached to each other by dense fibrous tissue, which is prolonged
forward along the upper margin of the cariniform cartilage and is
continuous behind with the sternal ligament. Each of the other capsules
is reinforced dorsally by the =superior costo-sternal ligament=
(Ligamentum sternocostale radiatum), composed of radiating fibers which
blend with the sternal ligament. The movement is rotation around a
nearly vertical axis, except in the case of the first pair of joints.
INTERCHONDRAL LIGAMENTS
The eighth and ninth costal cartilages are firmly united by fibrous
tissue. The chondro-xiphoid ligament attaches the ninth costal cartilage
to the xiphoid cartilage. The remaining cartilages are rather loosely
attached to each other by elastic tissue.
STERNAL ARTICULATIONS
In the new-born foal the sternum has seven bony segments (Sternebræ),
united by persisting cartilage. The last two segments coalesce within a
few weeks after birth. In old subjects there is more or less
ossification of the intersegmental cartilage, which may lead to partial
fusion of adjacent segments, especially posteriorly. The =sternal
ligament= (Ligamentum sterni proprium internum) lies on the thoracic
surface of the sternum. It arises on the first segment, and divides
opposite the second chondro-sternal joint into three bands. The median
band passes backward and spreads out on the last segment and the xiphoid
cartilage. The lateral branches—thicker and wider—lie along the lateral
borders above the chondro-sternal joints, and end at the cartilage of
the eighth rib; they are covered by the transversus thoracis muscle.
THE ARTICULATIONS OF THE SKULL
TEMPORO-MANDIBULAR ARTICULATION
This joint (Articulatio mandibularis) is the only diarthrosis formed
between bones of the skull.
The =articular surfaces= are dissimilar in form and size. That on the
squamous temporal bone is concavo-convex, and the long axis is directed
outward and somewhat forward; it consists of a glenoid cavity, which is
continued upon the postglenoid process behind, and a condyle in front.
The mandible presents a transversely elongated condyle.
The =articular disc= is placed between the joint surfaces, which it
renders congruent. Its upper and lower surfaces are molded upon the
temporal and mandibular surfaces respectively, and its circumference is
attached to the joint capsule; thus it divides the joint cavity into
upper and lower compartments, the former being the more roomy.
The =joint capsule= is strong and tight. It is reinforced by two
ligaments. The =external ligament= (Ligamentum laterale) extends
obliquely across the anterior part of the outer surface of the capsule,
from which it is not distinctly separable. The =posterior ligament=
(Ligamentum posterius) is an elastic band which is attached above to the
postglenoid process, and below to a line on the posterior face of the
neck of the mandible.
=Movements.=—The chief movements take place around a transverse axis
passing through both joints. Associated with this hinge-like action is
slight gliding movement, as in opening and shutting the mouth. When the
mouth is shut, the condyle lies under the glenoid cavity. When the
mandible is depressed, the condyle moves forward under the articular
eminence of the temporal bone, carrying the disc with it. In protrusion
and retraction of the lower jaw the gliding movement just described
occurs without the hinge-like rotation of the condyle. These movements
are similar in both joints. In the lateral movements (as usually
performed in mastication) the action consists of rotation of the
condyles around a vertical axis, while the disc glides forward on one
side and backward on the other.
THE SYNARTHROSES OF THE SKULL
Most of the bones of the skull are united with the adjacent bones by
=sutures=; a few are united by cartilage. The difference in the uniting
medium depends on the fact that most of these bones are developed in
membrane, but some are preformed in cartilage. Most of these joints are
temporary, and are obliterated at various periods during development and
growth. Their importance rests on the fact that so long as they persist,
continuous growth is possible. They are usually designated according to
the bones which enter into their formation, _e. g._, spheno-squamous,
naso-frontal, internasal, etc. Special names (borrowed from human
anatomy) are sometimes used; thus the interparietal, the
parieto-occipital, and the parieto-frontal sutures are often called the
sagittal, lambdoid, and coronal respectively.
Detailed description of the sutures has not sufficient clinical value
to justify much addition to the statements made in the osteology in
this connection. The obliteration or closure of the sutures is,
however, worthy of brief mention. The cranial sutures are usually all
closed at seven years, but the apex only of the petrous temporal is
fused with the occipital and squamous temporal. Most of the facial
sutures are practically closed at ten years, although complete
synostosis may in some be delayed for years or may not occur at all;
the nasal suture, for example, often persists even in advanced age, so
far as its anterior part is concerned.
The principal =synchondroses= are: (1) That between the basioccipital
and the body of the sphenoid (Synchondrosis sphenooccipitalis); (2) that
between the presphenoid and postsphenoid (Synchondrosis
intersphenoidalis); (3) those between the parts of the occipital bone
(Synchondroses intraoccipitales). The first is usually ossified at four
years, the second at three years, and the occipital bone is consolidated
at two years.
The =symphysis= of the lower jaw (Symphysis mandibulæ) ossifies at one
to six months.
THE HYOIDEAN ARTICULATIONS
The =temporo-hyoid articulation= is an amphiarthrosis, in which the
dorsal angle of the proximal end of the great cornu (Stylo-hyal) is
attached by a short bar of cartilage to the hyoid process of the petrous
temporal bone. The cartilage (Arthrohyal) is about half an inch (ca. 1
to 1.5 cm. ) in length. The chief movement is hinge-like, the axis of
motion passing transversely through both joints.
The =intercornual articulation= is an amphiarthrosis formed by the
junction of the distal extremity of the great cornu with the proximal
end of the small cornu (kerato-hyal). They are united by a very short
piece of cartilage, in which there is usually a small nodule of bone in
the young subject. This nodule, the epihyal or middle cornu, is usually
fused with the great cornu in the adult. The chief movement here is also
hinge-like, the angle between the cornua being increased or diminished.
The =basi-cornual articulation= is a diarthrosis formed by the junction
of each small cornu (kerato-hyal) with the body (basi-hyal). The small
cornu has a concave facet which articulates with the convex facet on
either end of the dorsal surface of the body. The capsule is ample
enough to allow considerable movement, which is chiefly hinge-like. The
movements of the hyoid bone are concerned chiefly in the acts of
mastication and swallowing. In the latter the distal parts of the hyoid
bone are moved forward and upward, carrying the root of the tongue and
the larynx with them, and then return to their former position.
THE ARTICULATIONS OF THE THORACIC LIMB
In the absence of the clavicle the thoracic limb forms no articulation
with the trunk, unless we regard as such the union by muscles. The
movement of the shoulder on the chest-wall is chiefly rotation around a
transverse axis passing through the scapula behind the upper part of the
spine.
THE SHOULDER JOINT
The shoulder or scapulo-humeral joint (Articulatio scapulo-humeralis) is
formed by the junction of the distal end of the scapula with the
proximal end of the humerus. The =articular surfaces= are: (1) On the
scapula, the glenoid cavity; (2) on the humerus, the head. Both surfaces
are approximately spherical and similar in curvature, but the humeral
surface is much more extensive than that of the scapula.
The =joint capsule= is ample enough to allow the bones to be drawn apart
about an inch (ca. 2 to 3 cm.); but this requires a very considerable
amount of force unless air is admitted into the joint cavity. The
fibrous layer (or capsular ligament) is not attached to the margin of
the joint surfaces, but at a distance of one to two centimeters from it.
It is strengthened in front by two diverging elastic bands, which arise
on the scapular tuberosity and end on the lips of the bicipital groove.
A pad of fat is interposed between the capsule and the tendon of the
biceps.
Ligaments are absent from this joint, but the muscles and tendons around
it afford remarkable security, so that dislocation seldom or never
occurs. The large extent of the head of the humerus is also of
importance in this regard.
The principal muscles which are attached around the joint and act as
ligaments are: externally, the supraspinatus, infraspinatus, and teres
minor; internally, the subscapularis; in front, the biceps and
supraspinatus; behind, the triceps.
=Movements.=—While it is a typical enarthrosis in structure, and capable
of the various movements of the ball-and-socket joint, the chief normal
movements are flexion and extension. In the position of rest the angle
formed between the scapula and humerus posteriorly is about 110° to
120°; in flexion it is reduced to about 80°, and in extension it is
increased to about 145°. Adduction and abduction are very restricted,
the former being limited chiefly by the infraspinatus, the latter by the
subscapularis and the low insertion of the superficial pectoral muscles.
Rotation is somewhat freer, but does not exceed 33°, when all the
muscles are removed (Franck).
THE ELBOW JOINT
This, the cubital articulation (Articulatio cubiti), is a ginglymus
formed between the distal extremity of the humerus and the proximal ends
of the bones of the forearm.
[Illustration:
FIG. 143.—LEFT ELBOW JOINT OF HORSE, POSTERIOR VIEW. THE CAPSULE IS
REMOVED. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =articular surfaces= are: (1) A trochlear surface formed by the
condyles of the humerus and the groove between them; (2) the
corresponding glenoid cavities and ridge on the proximal extremity of
the radius, together with the semilunar notch of the ulna.
The articular surface of the condyles does not extend upon the back of
the extremity, but the groove which receives the semilunar notch of
the ulna extends up into the olecranon fossa. In the fore part of the
groove there is a synovial fossa. The surface on the outer condyle is
smaller than that of the inner one, and is subdivided into two unequal
parts by a shallow furrow. On the lower part of the semilunar notch
and the adjacent part of the ridge on the radius are synovial fossæ.
The =joint capsule= is extremely thin behind, where it forms a pouch in
the olecranon fossa under the anconeus muscle and a pad of fat. In front
it is strengthened by oblique fibers (Ligamentum obliquum or anterior
ligament), and laterally it fuses with the lateral ligaments. Small
pouches of the =synovial membrane= lubricate the origins of the flexors
of the carpus and digit and the small radio-ulnar joints. There are two
lateral ligaments.
The =internal lateral ligament= (Ligamentum collaterale radiale) is
attached above to an eminence on the internal epicondyle of the humerus,
and divides into two parts: the long, superficial part ends on the inner
border of the radius, just below the level of the interosseous space;
the deep, short part is inserted into the internal tuberosity of the
radius. (The superficial part represents the pronator teres muscle,
which is only exceptionally present in the horse.)
The =external lateral ligament= (Ligamentum collaterale ulnare) is short
and strong. It is attached above to a depression on the external
epicondyle of the humerus, and below to the external tuberosity of the
radius, just below the margin of the articular surface.
=Movements.=—This joint is a typical ginglymus, the only movements being
flexion and extension around an axis which passes through the upper
attachments of the lateral ligaments. In the standing position the
articular angle (in front) is about 140° to 150°. The range of movement
is about 55° to 60°. Complete extension is prevented chiefly by the
tension of the lateral ligaments and the biceps muscle. (The axis of
movement is slightly oblique, so that in flexion the forearm is carried
somewhat outward.)
[Illustration:
FIG. 144.—LEFT CARPAL JOINTS OF HORSE, EXTERNAL VIEW.
The capsule has been removed, _g_, Radius; _12_, large metacarpal
bone. (After Ellenberger-Baum, Anat. f. Künstler.)
]
[Illustration:
FIG. 145.—LEFT CARPAL JOINTS OF HORSE, ANTERIOR VIEW.
The capsule has been removed. The smaller ligaments are shown. (After
Ellenberger-Baum, Anat. f. Künstler.)
]
THE RADIO-ULNAR ARTICULATION
In the foal the shaft of the ulna is attached to the radius above and
below the interosseous space by the =interosseous ligament=. Below the
space the two bones become fused before adult age is reached. Above the
space the ligament usually persists, but may undergo more or less
ossification in extreme old age. The =transverse= or =arciform
ligaments= (Ligamentum transversum ulnare et radiale ulnæ et radii)
consist of fibers which pass above the interosseous space from either
border of the shaft of the ulna to the posterior surface of the radius.
The proximal radio-ulnar articulation, formed by two small convex facets
on the ulna and the corresponding facets on the posterior surface of the
proximal extremity of the radius, is inclosed in the capsule of the
elbow joint and does not require separate consideration. The distal
extremity of the ulna fuses early with the radius, and is, therefore,
regarded usually as a part of the latter.
=Movement.=—This is inappreciable, the forearm being fixed in the
position of pronation.
THE CARPAL JOINTS
These joints taken together constitute the composite =articulatio
carpi=, or what is popularly termed the “knee-joint” in animals.[33]
This consists of three chief joints, viz., (1) The =radio-carpal joint=,
formed by the distal end of the radius and the proximal row of the
carpus; (2) the =intercarpal joint=, formed between the two rows of the
carpus; (3) the =carpo-metacarpal joint=, formed between the distal row
of the carpus and the proximal ends of the metacarpal bones. The
proximal and middle joints may be regarded as ginglymi, although they
are not typical or pure examples of hinge-joints. The distal joint is
arthrodial. In addition there are arthrodial joints formed between
adjacent bones of the same row (Articulationes interosseæ). All these
constitute a very composite joint, with numerous ligaments. The
articular surfaces have been described in the Osteology.
The =joint capsule= may be regarded, so far as the fibrous part is
concerned, as being common to all three joints. It is attached close to
the margin of the articular surface of the radius above and the
metacarpus below; its deep face is also attached to a considerable
extent to the carpal bones and to the small ligaments. Its anterior
part, the =dorsal= or =anterior common ligament=, is rather loose, and
assists in forming the fibrous canals for the extensor tendons. Its
posterior part, the =volar= or =posterior common ligament=, is very
thick and dense, and is closely attached to the carpal bones. It levels
up the irregularities of the skeleton here, and forms the smooth
anterior wall of the carpal canal. It is continued downward to form the
=subcarpal= or =inferior check ligament=, which blends with the tendon
of the flexor perforans about the middle of the metacarpus.
[Illustration:
FIG. 146.—FRONTAL SECTION OF CARPAL JOINTS OF HORSE (RIGHT SIDE).
_l.u._, External, _l.r._, internal, lateral ligament; _Cr_, radial
carpal; _Ci_, intermediate carpal; _Cu_, ulnar carpal; _C2_, second
carpal; _C3_, third carpal; _C4_, fourth carpal; _Mc2_, second
(internal) metacarpal; _Mc3_, third (large) metacarpal; _Mc4_,
fourth (external) metacarpal.
]
The =synovial membrane= forms three sacs corresponding to the three
joints. The =radio-carpal sac= is the most voluminous; it includes the
joints formed by the accessory carpal bone, and also those between the
proximal carpal bones as far as the interosseous ligaments. The
=intercarpal sac= sends extensions upward and downward between the bones
of the two rows as far as the interosseous ligaments; it communicates
between the third and fourth carpal bones with the =carpo-metacarpal
sac=. The latter is very limited in extent, and is closely applied to
the bones; it incloses the carpo-metacarpal joint, and lubricates also
the lower parts of the joints between the distal carpal bones and the
intermetacarpal joints.
The =external lateral ligament= (Ligamentum carpi collaterale ulnare) is
attached above to the external tuberosity of the distal end of the
radius. Its long superficial part is attached below to the proximal end
of the external small metacarpal chiefly, but some fibers end on the
large metacarpal bone. A canal for the lateral extensor tendon separates
a short deep band which ends on the ulnar carpal bone. Other deep fibers
connect the latter with the fourth carpal bone, and the fourth carpal
with the metacarpus.
The =internal lateral ligament= (Ligamentum carpi collaterale radiale)
resembles the preceding in general, but is stronger and wider distally.
It is attached above to the internal tuberosity of the distal end of the
radius and ends below on the proximal ends of the large and inner small
metacarpal bones. Deep fasciculi are detached to the radial and second
carpal bones. The first carpal bone, when present, is usually embedded
in the posterior part of the distal end of the ligament. The posterior
part of the ligament is fused with the posterior annular ligament
(Ligamentum carpi transversum), and concurs in the formation of a canal
for the tendon of the flexor carpi internus.
A number of special short ligaments connect two or more adjacent
bones; only the most distinct of these will be described here.
The accessory carpal bone is connected with adjacent bones by three
ligaments (Fig. 444). The proximal one is a short band which extends
from the accessory carpal in front of the groove on its outer face and
is inserted into the distal end of the radius behind the groove for
the lateral extensor tendon. A middle band connects the accessory with
the ulnar carpal. The distal ligament consists of two strong bands
which pass from the lower margin of the accessory to the fourth carpal
and the proximal end of the outer metacarpal bone; these bands
transmit the action of the muscles, which are inserted into the
accessory carpal bone. The other bones of the proximal row are
connected by two anterior or dorsal ligaments, which are transverse in
direction, and two interosseous ligaments. An oblique ligament passes
from an eminence on the posterior surface of the radial carpal bone to
a small depression on the radius internal to the facet for the
accessory carpal bone.
Two ligaments connect the proximal and distal rows posteriorly. The
inner one joins the radial to the second and third carpal, and the
outer one attaches the ulnar to the third and fourth carpals.
The bones of the distal row are connected by two strong transverse
anterior or dorsal ligaments and two interosseous ligaments.
There are four carpo-metacarpal ligaments. Two oblique anterior bands
connect the third carpal with the large metacarpal. Two interosseous
ligaments pass downward from the interosseous ligaments of the distal
row to end in depressions in the interstices between the proximal ends
of the metacarpal bones.
[Illustration:
FIG. 147.—LEFT CARPAL JOINTS OF HORSE, INNER VIEW.
_g_, Radius; _12_, large (third) metacarpal bone. (After
Ellenberger-Baum, Anat. für Künstler.)
]
=Movements.=—Taking the joint as a whole, the chief movements are
flexion and extension. In the standing position the joint is extended.
When the joint is flexed, slight lateral movement and rotation can be
produced by manipulation. The anterior part of the capsule is, of
course, tense during flexion, the posterior part in extension.
The movement practically all occurs at the radio-carpal and
intercarpal joints, the articular surfaces of which are widely
separated in front during flexion, but remain in contact behind. The
distal row remains in contact with the metacarpus. The intermediate
and ulnar carpals move together as one piece, but the radial does not
move so far as the intermediate, so that the anterior and interosseous
ligaments connecting these bones become tense and oblique in
direction.
THE FETLOCK JOINT
This, the =metacarpo-phalangeal articulation= (Articulatio
metacarpo-phalangea), is a ginglymus formed by the junction of the
distal end of the large (third) metacarpal bone, the proximal end of the
first phalanx, and the proximal sesamoid bones.
=Articular Surfaces.=—The surface on the large metacarpal bone is
approximately cylindrical in curvature, but is divided into two slightly
unequal parts by a sagittal ridge. This is received into a sort of
socket formed by the first phalanx below and the two sesamoids together
with the intersesamoid ligament behind. The latter is a mass of
fibro-cartilage in which the sesamoid bones are largely embedded. It
extends above the level of the sesamoids, and is grooved to receive the
ridge on the metacarpal bone; its posterior surface forms a smooth
groove for the deep flexor tendon.
[Illustration:
FIG. 148.—SAGITTAL SECTION OF DISTAL PART OF LIMB OF HORSE.
_1_, Large metacarpal bone; _3_, fetlock joint; _4_, proximal sesamoid
bone; _5_, first phalanx; _6_, pastern joint; _7_, second phalanx;
_8_, coffin joint; _9_, third phalanx; _10_, distal sesamoid
(navicular bone); _12_, suspensory ligament; _14_, deep flexor
tendon; _15_, superficial flexor tendon; _16_, posterior annular
ligament of fetlock; _20_, inferior sesamoidean ligaments; _21_,
extensor tendon; _24_, plantar cushion; _25_, periople; _28_, wall
of hoof; _29_, sole of hoof; _A_, navicular bursa, proximal part.
(After Ellenberger-Baum, Anat. für Künstler.)
]
[Illustration:
FIG. 149.—ARTICULAR SURFACES OF FIRST PHALANX AND SESAMOIDS AT
FETLOCK, WITH INTERSESAMOID AND SUSPENSORY LIGAMENTS. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =joint capsule= is attached around the margin of the articular
surfaces. It is thick and ample in front; here a bursa is interposed
between it and the extensor tendons, but the tendons are also attached
to the capsule. Posteriorly it forms a thin-walled pouch which extends
upward between the metacarpal bone and the suspensory ligament about as
high as the point of bifurcation of the latter. The capsule is
reinforced by two lateral ligaments.
The =lateral ligaments=, =external= and =internal= (Ligamentum
collaterale ulnare, radiale) are partially divided into two layers: the
=superficial layer= arises from the eminence on the side of the distal
end of the large metacarpal bone, and passes straight to the rough
lateral area below the margin of the articular surface of the first
phalanx; the =deep layer=, shorter and much stronger, arises in the
lateral depression on the distal end of the metacarpal bone, and passes
obliquely downward and backward to be inserted into the outer surface of
the sesamoid and the proximal end of the first phalanx.
The capsule is further strengthened by a layer of oblique fibers which
pass over the lateral ligament on either side and end on the extensor
tendon and the proximal extremity of the first phalanx. It may
properly be regarded as fascia rather than ligament.
[Illustration:
FIG. 150.—LIGAMENTS AND TENDONS OF DISTAL PART OF LIMB OF HORSE.
Mc.III, Large metacarpal bone; Ph.I, first phalanx; Ph.II, second
phalanx; Ph.III, third phalanx; 1, deep flexor tendon; 2, band from
first phalanx to plantar cushion. (After Schmaltz, Atlas d. Anat. d.
Pferdes.)
]
=Movements.=—These are of the nature of flexion and extension, the axis
of motion passing through the upper attachments of the lateral
ligaments. In the ordinary standing position the joint is in a state of
partial =dorsal flexion=, the articular angle (in front) being about
140° to 150°. (In the hind limb it is about 5° greater.) Diminution of
this angle (sometimes termed “overextension”) is normally very limited
on account of the resistance offered by the sesamoidean apparatus, but
it varies considerably in amount in different subjects. =Volar flexion=
is limited only by contact of the heels with the metacarpus. During
volar flexion a small amount of lateral flexion is possible.
THE SESAMOIDEAN LIGAMENTS
Under this head will be described a number of important ligaments which
are connected with the sesamoid bones and form a sort of stay apparatus
or brace.
The =intersesamoidean ligament= (Ligamentum intersesamoideum) not only
fills the space between and unites the sesamoid bones, but also extends
above them, entering into the formation of the articular surface of the
fetlock joint. Other facts in regard to it have been given above.
The =lateral sesamoidean ligaments=, outer and inner (Ligamenta
sesamoidea ulnare et radiale), arise on the abaxial surface of each
sesamoid bone, pass forward, and divide into two branches, one of which
ends in the depression on the distal end of the large metacarpal bone,
the other on the eminence on the proximal end of the first phalanx. They
are partly covered by the branches of the suspensory or superior
sesamoidean ligament.
[Illustration:
FIG. 151.—DEEP DISSECTION OF DISTAL PART OF RIGHT FORE LIMB OF HORSE,
SHOWING JOINTS AND LIGAMENTS, POSTERIOR VIEW.
1, Lateral cartilage; 2, tendon surface of navicular bone; 3, inferior
navicular or interosseous ligament; 4, insertion of deep flexor
tendon. Small arrows point to openings made in capsules of pastern
and coffin joints. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =suspensory= or =superior sesamoidean ligament= (Musculus
interosseus medius) lies for the greater part in the metacarpal groove,
where it has the form of a wide, thick band. It is attached above to the
upper part of the posterior surface of the large metacarpal bone and to
the distal row of carpal bones. At the lower fourth of the metacarpus it
divides into two diverging branches. Each branch passes to the abaxial
face of the corresponding sesamoid, on which a considerable part, is
attached. The remainder passes obliquely downward and forward to the
anterior surface of the first phalanx, where it joins the extensor
tendon. This ligament possesses considerable elasticity, and is the
highly modified interosseous medius muscle. It consists mainly of
tendinous tissue, but contains a variable amount of striped muscular
tissue, especially in its deep part and in young subjects. Its principal
function is to support the fetlock, _i. e._, to prevent excessive dorsal
flexion of the joint when the weight is put on the limb. The branches
which join the common extensor tendon limit volar flexion of the
interphalangeal joints in certain phases of movement.
The =inferior sesamoidean ligaments= are three in number—superficial,
middle, and deep. The =superficial= or =straight ligament= (Ligamentum
sesamoideum rectum) is a flat band and is somewhat wider above than
below.[34] It is attached above to the bases of the sesamoid bones and
the intersesamoid ligament, below to the complementary fibro-cartilage
of the proximal end of the second phalanx. The =middle ligament= is
triangular, with thick, rounded margins (Ligamenta obliqua) and a thin
central portion.[35] Its base is attached to the sesamoid bones and
intersesamoid ligament, and its deep face to the triangular rough area
on the posterior surface of the first phalanx. The =deep= or =cruciate
ligament= (Ligamenta sesamoidea cruciata) consists of two thin layers of
fibers which arise on the base of the sesamoid bones, cross each other,
and end on the opposite eminence on the proximal end of the first
phalanx.
The =short sesamoidean ligaments= (Ligamenta sesamoidea brevia) are best
seen by opening the joint in front and pushing the sesamoid bones
backward; they are covered by the synovial membrane. Each is a short
band which extends from the anterior part of the base of the sesamoid
bone outward to the posterior margin of the articular surface of the
first phalanx.
The inferior sesamoidean ligaments may be regarded as digital
continuations of the suspensory ligament, the sesamoid bones being
intercalated in this remarkable stay apparatus by which the fetlock is
supported and concussion diminished.
THE PASTERN JOINT
This, the =proximal interphalangeal articulation= (Articulatio phalangis
secundæ), is a ginglymus formed by the junction of the distal end of the
first phalanx and the proximal end of the second phalanx.
The =articular surfaces= are: (1) On the first phalanx, two slightly
unequal convex areas with an intermediate shallow groove; (2) on the
second phalanx, a corresponding surface, completed behind by a plate of
fibro-cartilage.
The =joint capsule= is close fitting in front and laterally, where it
blends with the extensor tendon and the lateral ligaments respectively.
Behind it pouches upward a little and is reinforced by the straight
sesamoidean ligament and the branches of the superficial flexor tendon.
There are two lateral and four volar ligaments.
The =lateral ligaments=, internal and external (Ligamentum collaterale
radiale, ulnare) are very short and strong bands which are attached
above on the eminence and depression on each side of the distal end of
the first phalanx, and below on the eminence on either side of the
proximal end of the second phalanx. The direction of the ligaments is
about vertical and, therefore, does not correspond to the digital axis.
The =volar= or =posterior ligaments= consist of central and lateral
pairs of bands which are attached below to the posterior margin of the
proximal end of the second phalanx and its complementary
fibro-cartilage. The lateral pair is attached above to the middle of the
borders of the first phalanx, the central pair lower down and on the
margin of the triangular rough area.
These ligaments are very commonly thickened as a result of chronic
inflammation, and then are not well defined. The central ones blend
below with the branches of the superficial flexor tendon and with the
straight sesamoidean ligament.
=Movements.=—These are very limited, and consist of flexion and
extension. The axis of motion passes transversely through the distal end
of the first phalanx. In the standing position the joint is extended. A
small amount of volar flexion is possible, and in this position slight
lateral flexion and rotation can be produced by manipulation. Dorsal
flexion is prevented by the lateral, volar, and straight sesamoidean
ligaments.
THE COFFIN JOINT
This joint, technically termed the =distal interphalangeal articulation=
(Articulatio phalangis tertiæ), is a ginglymus formed by the junction of
the second and third phalanges and the third sesamoid bone.
=Articular Surfaces.=—The surface on the distal end of the second
phalanx is convex from before backward, concave transversely. The
articular surface of the third phalanx slopes sharply upward and
forward; its central part is prominent, and is flanked by two glenoid
cavities. It is completed behind by the articular surface of the third
sesamoid or navicular bone.
[Illustration:
FIG. 152.—LATERAL LIGAMENTS OF PASTERN JOINT AND SUSPENSORY LIGAMENTS
OF NAVICULAR BONE. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
=Joint Capsule.=—This is attached around the margins of the articular
surfaces. In front and laterally it is tight, and is blended with the
extensor tendon and the lateral ligaments respectively. Posteriorly, it
forms a considerable pouch which extends upward to about the middle of
the second phalanx, where it is separated by a fibrous membrane from the
digital synovial sheath. Laterally small pouches project outward
(especially during volar flexion) against the lateral cartilages, just
behind the lateral ligaments.[36]
=Ligaments.=—The =lateral ligaments=, external and internal (Ligamentum
collaterale ulnare, radiale), are short strong bands which are attached
above in the depressions on either side of the lower part of the second
phalanx, under cover of the lateral cartilage. They widen below and end
in the depressions on either side of the extensor process and on the
anterior end of the lateral cartilages.
The =suspensory navicular ligaments=, external and internal (Ligamentum
sesamoideum collaterale ulnare, radiale),[37] are strong, somewhat
elastic bands, which form a sort of suspensory apparatus for the third
sesamoid. They are attached superiorly in and above the depressions on
either side of the distal end of the first phalanx and are here partly
blended with the lateral ligaments of the pastern joint. They are
directed obliquely downward and backward, and end chiefly on the ends
and proximal border of the third sesamoid, but detach a branch to the
inner surface of each lateral cartilage and wing of the third phalanx.
The =inferior navicular ligament= (Ligamentum phalangeo-sesamoideum)
reinforces the capsule interiorly. It is a strong layer of fibers which
extend from the distal border of the third sesamoid to the tendon
surface of the third phalanx, near the posterior margin of the articular
surface.
=Movements.=—The chief movements are flexion and extension. In the
standing position the joint is extended. During volar flexion a very
small amount of lateral movement and rotation can be produced by
manipulation. Dorsal flexion is very limited.
Dorsal flexion appears to be checked mainly by the deep flexor tendon,
since in cases of rupture of the latter the toe turns up. The slight
mobility of the posterior part of the socket for the second phalanx
(formed by the third sesamoid) diminishes concussion when the weight
comes on the foot.
LIGAMENTS OF THE LATERAL CARTILAGES
In addition to the bands mentioned above, which attach the lateral
cartilages to the extremities of the navicular bone, there are three
ligaments on either side which attach the cartilages to the phalanges.
An ill-defined elastic band passes from the middle part of the border of
the first phalanx to the upper part of the cartilage, detaching a branch
to the plantar cushion.
A short strong band connects the anterior extremity of the cartilage
with the rough eminence on the second phalanx in front of the attachment
of the lateral ligament of the coffin joint.
The lower border of the cartilage is covered externally by fibers which
attach it to the wing of the third phalanx.
THE ARTICULATIONS OF THE PELVIC LIMB
THE SACRO-ILIAC ARTICULATION
This joint (Articulatio sacro-iliaca) is a diarthrosis formed between
the auricular surfaces of the sacrum and ilium. These surfaces are not
smooth in the adult, but are marked by eminences and depressions, and
are covered by a thin layer of cartilage. The joint cavity is a mere
cleft, and is often crossed by fibrous bands.
The =capsule= is very close fitting, and is attached around the margins
of the articular surfaces. It is reinforced by the =ventral sacro-iliac
ligament= (Ligamentum sacro-iliacum ventrale), which surrounds the
joint, and is exceedingly strong above.
The =movements= are inappreciable in the adult—stability, not mobility,
being the chief desideratum.
The following ligaments may be regarded as accessory to the joint,
although not directly connected with it.
The =dorsal sacro-iliac ligament= (Ligamentum sacro-iliacum dorsale
breve) is a strong band which is attached to the internal angle (Tuber
sacrale) of the ilium and the summits of the sacral spines.
The =lateral sacro-iliac ligament= (Ligamentum sacro-iliacum dorsale
longum) is a triangular, thick sheet which is attached in front to the
internal angle and border of the ilium above the great sciatic notch,
and below to the lateral border of the sacrum. It blends above with the
dorsal sacro-iliac ligament, below with the sacro-sciatic ligament, and
behind with the coccygeal fascia.
The =sacro-sciatic ligament= (Ligamentum sacrospinosum et tuberosum) is
a quadrilateral sheet which completes the lateral pelvic wall. Its upper
border is attached to the border of the sacrum and the transverse
processes of the first and second coccygeal vertebræ. Its lower border
is attached to the superior ischiatic spine and tuber ischii. Between
these it bridges over the external border of the ischium and completes
the lesser sciatic foramen. The anterior border is concave, and
completes the greater sciatic foramen. The posterior border is fused
with the vertebral head of the semimembranosus muscle.
The =ilio-lumbar ligament= (Ligamentum ilio-lumbale) is a triangular
sheet which attaches the ends of the lumbar transverse processes to the
ventral surface of the ilium below the attachment of the longissimus
muscle (Fig. 184).
[Illustration:
FIG. 153.—LEFT OS COXÆ AND ADJACENT PARTS OF SACRUM AND FEMUR OF
HORSE. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
SYMPHYSIS PELVIS
The =symphysis pelvis= is formed by the junction of the two ossa coxarum
at the ventral median line. In the young subject the bones are united by
a layer of cartilage; in the adult the latter is gradually replaced by
bone, the process beginning in the pubic portion and extending backward.
The union is strengthened by white fibrous tissue above and below, and a
transverse band also covers the anterior border of the pubis (pecten).
No appreciable movement occurs even before synostosis takes place.
OBTURATOR MEMBRANE
This (Membrana obturatoria) is a thin layer of fibrous tissue which
covers the obturator foramen, leaving, however, a passage (Canalis
obturatorius) for the obturator vessels and nerve.
THE HIP JOINT
This joint (Articulatio coxæ) is an enarthrosis formed by the proximal
end of the femur and the acetabulum.
=Articular Surfaces.=—The head of the femur presents an almost
hemispherical articular surface, which is continued a short distance on
the upper surface of the neck. It is more extensive than the socket
which receives it. Internally it is cut into by a deep notch for the
attachment of the round and pubo-femoral ligaments. The acetabulum is a
typical cotyloid cavity. Its articular surface is somewhat crescentic,
being deeply cut into internally by the acetabular notch and fossa. It
is increased and deepened by a ring of fibro-cartilage, the =cotyloid
ligament= (Labrum glenoidale), which is attached to the bony margin;
that part of the ligament which crosses the notch is called the
=transverse ligament= (Fig. 456).
[Illustration:
FIG. 154.—PELVIC LIGAMENTS AND HIP JOINT.
_1_, Dorsal sacro-iliac ligament; _2_, lateral sacro-iliac ligament;
_3_, sacro-sciatic ligament; _4_, greater sciatic foramen; _5_,
lesser sciatic foramen; _6_, line of attachment of intermuscular
septum between biceps femoris and semitendinosus; _7_, capsule of
hip joint; _8_, rectus parvus or capsularis muscle; _9_, outer
tendon of origin of biceps femoris; _10_, internal, _11_, external,
angle of ilium; _12_, shaft of ilium; _13_, superior ischiatic
spine; _14_, pubis; _15_, tuber ischii; _16_, trochanter major;
_17_, semimembranosus; _18_, fifth lumbar spine; _19_, _20_, first
and second coccygeal vertebræ.
]
The =joint capsule= is roomy. It is attached around the margin of the
acetabulum and the neck of the femur. It is thickest externally.
The attachment on the femur is about 1 cm. from the margin of the
articular surface, except above, where 2 to 3 cm. of the neck is
intracapsular. A thin oblique band corresponding in direction with the
rectus parvus muscle reinforces the antero-external part of the
capsule; this appears to be the feeble homologue of the very strong
ilio-femoral ligament of man. The capsule is very thin under the
ilio-psoas, and is adherent to the muscle. Internally, its fibrous
part is perforated by the pubo-femoral and round ligaments and the
articular vessels.
The =round ligament= (Ligamentum teres) is a strong hand which is
attached in the subpubic groove close to the acetabular notch, passes
outward, and ends in the notch on the head of the femur (Fig. 456).
The =pubo-femoral ligament= (Ligamentum accessorium) does not occur in
the domestic animals other than the equidæ. It is a strong band detached
from the prepubic tendon of the abdominal muscles (Fig. 456). It is
directed outward, backward, and upward, passes through the acetabular
notch above the transverse ligament, and ends behind the round ligament
in the notch on the head of the femur. The origin of the pectineus
muscle is perforated by the ligament, which furnishes attachment to the
greater part of the fibers of the muscle.
[Illustration:
FIG. 155.—LEFT STIFLE JOINT OF HORSE, EXTERNAL VIEW, IN PARTIAL
FLEXION.
The capsules have been removed. _18_, Femur; _20_, patella; _21_,
tibia; _a″_, internal patellar ligament; _b_, external
femoro-patellar ligament; _d_, external semilunar cartilage. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =synovial membrane= is reflected over the intracapsular parts of
these ligaments and covers the fossa acetabuli. A pouch also extends
from the acetabular notch for a variable distance along the subpubic
groove above the pubo-femoral ligament.
=Movements.=—This joint is capable of all the movements of a
ball-and-socket joint, viz., flexion, extension, abduction, adduction,
rotation, and circumduction. The greatest range of movement is displayed
in flexion and extension. When standing at rest, the joint is partially
flexed, the articular angle (in front) being about 100° to 115°. The
other movements occur to a very limited extent in normal action.
Abduction appears to be checked by tension of the round ligament. The
pubo-femoral ligament is tensed most promptly by inward rotation of
the thigh.
THE STIFLE JOINT
This joint (Articulatio genu), which corresponds to the knee-joint of
man, is the largest and most elaborate of all the articulations. Taken
as a whole, it may be classed as a ginglymus, although it is not a
typical example of the group. In reality it consists of two joints—the
=femoro-patellar= and the =femoro-tibial=.
The =femoro-patellar articulation= (Articulatio femoro-patellaris) is
formed between the trochlea of the femur and the articular surface of
the patella.
[Illustration:
FIG. 156.—LEFT STIFLE JOINT OF HORSE, LATERAL VIEW.
The capsules are distended and the external patellar ligament is
removed.
]
=Articular Surfaces.=—The trochlea consists of two slightly oblique
ridges, with a wide and deep groove between them. The inner ridge is
much the larger of the two, especially at its upper part, which is wide
and rounded. The outer ridge is much narrower, and is more regularly
curved; its upper part lies about an inch behind a frontal plane tangent
to the inner ridge. The articular surface of the patella is much smaller
than that of the trochlea. It is completed internally by a supplementary
plate of fibro-cartilage (Fibrocartilago patellæ), which curves over the
internal surface of the inner lip of the trochlea. A narrow strip of
cartilage is found along the outer border also. The articular cartilage
on the trochlea completely covers both surfaces of the inner ridge, but
only a narrow marginal area on the external surface of the outer ridge.
=Joint Capsule.=—This is thin and is very capacious. On the patella it
is attached around the margin of the articular surface, but on the femur
the line of attachment is at a varying distance from the articular
surface. On the inner side it is an inch or more from the articular
cartilage; on the outer side and above, about half an inch. It pouches
upward under the quadriceps femoris for a distance of two or three
inches, a pad of fat separating the capsule from the muscle. Below the
patella it is separated from the straight ligaments by a thick pad of
fat, but inferiorly it is in contact with the femoro-patellar capsules.
The joint cavity is the most extensive in the body. It usually
communicates with the inner femoro-tibial joint cavity by a slit-like
opening situated at the lowest part of the inner ridge of the trochlea.
A similar, but smaller, communication with the outer femoro-patellar
capsule is often found at the lowest part of the outer ridge.
The inner communication appears to be constant in adult horses, but is
liable to be overlooked on account of the fact that it is covered by a
valvular fold of the synovial membrane. It is about half an inch wide,
and lies under the narrow articular area which connects the trochlea
and internal condyle. The outer communication occurs in 18 to 25 per
cent. of cases, according to Baum. It is instructive to distend this
capsule and thus obtain an idea of its potential capacity and
relations ([Fig. 156]).
[Illustration:
FIG. 157.—STIFLE JOINT OF HORSE, FRONT VIEW, IN EXTENSION.
The capsules are removed. _18_, Femur; _20_, patella; _21_, tibia.
(After Ellenberger-Baum, Anat. für Künstler.)
]
=Ligaments.=—The =lateral femoro-patellar ligaments=, external and
internal (Ligamentum femoro-patellare fibulare, tibiale), are two thin
bands which reinforce the capsule on either side. The external ligament
is fairly distinct; it arises from the external epicondyle of the femur
just above the lateral femoro-tibial ligament, and ends on the external
border of the patella. The internal ligament is thinner and is not
distinct from the capsule; it arises above the internal epicondyle, and
ends on the patellar fibro-cartilage.
The =patellar ligaments= (Ligamenta patellæ), also called the straight
ligaments of the patella, are three very strong bands which attach the
patella to the tuberosity of the tibia. The =external patellar ligament=
is attached above to the outer part of the anterior surface of the
patella, and below to the outer part of the tuberosity. It receives a
strong tendon from the biceps femoris muscle. The =middle patellar
ligament= extends from the front of the apex of the patella to the lower
part of the groove on the tuberosity of the tibia, a bursa being
interposed between the ligament and the upper part of the groove. The
=internal patellar ligament= is attached above to the patellar
fibro-cartilage, and ends on the tuberosity of the tibia, internally to
the groove. It is joined by the common aponeurosis of the gracilis and
sartorius. These so-called ligaments are, in reality, the tendons of
insertion of the quadriceps femoris muscle, and transmit the action of
the latter to the tibia; they also function similarly for the other
muscles attached to them as noted above.
It will be noticed that the upper attachments are further apart than
the lower ones, so that the ligaments converge below. The inner
ligament is especially oblique. The middle ligament is more deeply
placed than the others, and therefore cannot usually be felt
distinctly in the living animal.
[Illustration:
FIG. 158.—SEMILUNAR CARTILAGES AND CRUCIAL LIGAMENTS OF RIGHT STIFLE
OF HORSE.
_F_, Femoral ligament of external cartilage. (After Schmaltz, Atlas d.
Anat. d. Pferdes.)
]
The =femoro-tibial articulation= (Articulatio femoro-tibialis) is formed
between the condyles of the femur, the proximal end of the tibia, and
the interposed semilunar cartilages.
=Articular Surfaces.=—The condyles of the femur are slightly oblique in
direction. The articular surface of the outer one is more strongly
curved than that of the inner one; the latter is confluent below with
the inner ridge of the trochlea, while the narrow ridge which connects
the external condyle with the trochlea is usually non-articular. The
saddle-shaped surfaces of the condyles of the tibia are not adapted to
the femoral condyles, and are in contact with only a small part of them.
[Illustration:
FIG. 159.—PROXIMAL ENDS OF RIGHT TIBIA AND FIBULA OF HORSE, WITH
SEMILUNAR CARTILAGES AND CRUCIAL LIGAMENTS, EXTERNAL VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =semilunar cartilages= (Meniscus lateralis, medialis) are two
C-shaped or crescentic discs of fibro-cartilage which produce congruence
in the articular surfaces. Each has an upper concave surface adapted to
the condyle of the femur, and a lower surface which fits the
corresponding condyle of the tibia. The external cartilage does not
cover the outer and posterior part of the condyle, over which the tendon
of origin of the popliteus muscle plays. The peripheral border is thick
and convex, the central one very thin and concave. The fibrous ends or
=cornua= are attached to the tibia in front of and behind the spine. The
external cartilage has a third attachment by means of an oblique band
(Ligamentum femorale menisci lateralis) which passes from the posterior
cornu to the posterior part of the intercondyloid fossa of the femur.
The cornua of the internal cartilage (Ligamenta tibiæ anterius et
posterius menisci medialis) are attached in front of and behind the
inner eminence of the spine. The anterior cornu of the external
cartilage (Ligamentum tibiæ anterius menisci lateralis) is attached in
front of the outer eminence of the spine. The posterior cornu
bifurcates; the lower branch (Ligamentum tibiæ posterius menisci
lateralis) is inserted at the popliteal notch, the upper (Ligamentum
femorale menisci lateralis) in a small fossa in the extreme posterior
part of the intercondyloid fossa.
The =joint capsule= is attached to the margin of the tibial articular
surface, but on the femur the line of attachment is for the greater part
about half an inch from the articular margin. It is also attached to the
convex borders of the semilunar cartilages and to the crucial ligaments.
It is strong posteriorly, but in front it practically consists only of
the synovial layer. There are two synovial sacs, corresponding to the
double nature of the articular surfaces; they do not usually
communicate, and each is partially divided into an upper and a lower
compartment by the semilunar cartilage. The inner sac pouches upward
about half an inch over the condyle of the femur. The external sac
invests the tendon of origin of the popliteus muscle, and also pouches
downward about three or four inches (ca. 8 to 10 cm.) beneath the
peroneus tertius and long extensor muscles (Fig. 156). As stated above,
the outer sac sometimes communicates with the femoro-patellar joint
cavity, and the inner sac usually, if not always, does so in the adult.
[Illustration:
FIG. 160.—LEFT STIFLE JOINT OF HORSE, INTERNAL VIEW IN EXTREME
EXTENSION.[38]
_18_, Femur; _20_, patella (base); _21_, tibia; _d_, internal
semilunar cartilage. (After Ellenberger-Baum, Anat. für Künstler.)
]
=Ligaments.=—There are four of these—two lateral and two crucial.
The =internal lateral ligament= (Ligamentum collaterale tibiale) is
attached above to the prominent internal epicondyle of the femur, and
below to a rough area below the margin of the internal condyle of the
tibia.
The =external lateral ligament= (Ligamentum collaterale fibulare) is
somewhat thicker; it arises from the upper depression on the external
epicondyle, and ends on the head of the fibula. It covers the tendon of
the origin of the popliteus muscle, and a bursa is interposed between
the lower part of the ligament and the margin of the external condyle of
the tibia.
The =crucial ligaments= are two strong rounded bands situated mainly in
the intercondyloid fossa of the femur, between the two synovial sacs.
They cross each other somewhat in the form of an X, and are named
according to their tibial attachments. The =anterior crucial ligament=
(Ligamentum cruciatum anterius) arises in the central fossa on the
tibial spine, extends upward and backward, and ends on the upper part of
the inner surface of the external condyle of the femur. The =posterior
crucial ligament= (Ligamentum cruciatum posterius) is internal to the
preceding, and is somewhat larger. It is attached to an eminence at the
popliteal notch of the tibia, is directed upward and forward, and ends
in the anterior part of the intercondyloid fossa of the femur.
[Illustration:
FIG. 161.—RIGHT STIFLE JOINT OF HORSE; SAGITTAL SECTION PASSING
THROUGH OUTER PART OF INNER RIDGE OF TROCHLEA AND INTERCONDYLOID
FOSSA.
_1_, Anterior crucial ligament; _2_, posterior crucial ligament; _3_,
posterior cornu of internal semilunar cartilage; _4_, femoral
ligament of external semilunar cartilage; _5_, articular artery;
_6_, part of vastus internus.
]
It may be added that these ligaments do not lie in a sagittal plane,
but are somewhat twisted across each other; outward rotation of the
leg untwists and slackens them.
=Movements.=—The principal movements of the stifle joint as a whole are
flexion and extension. In the ordinary standing position the articular
angle (behind) is about 140° to 150°. Flexion is limited only by contact
of the leg with the thigh if the hock is also flexed. Extension is
incomplete, _i. e._, the femur and tibia cannot be brought into the same
straight line. Rotation is limited, and is freest during semiflexion.
The patella glides on the femoral trochlea upward in extension, downward
in flexion.
Extension is checked mainly by tension of the crucial and lateral
ligaments. In extreme extension, which is accompanied by slight
outward rotation of the leg, the patella can be pushed upward and
inward so that its fibro-cartilage hooks over the upper end of the
inner ridge of the trochlea, but it will not remain there unless held
in position. When pressure is removed, the base of the patella tips
forward and the cartilage lies upon the most prominent part of the
trochlear ridge. During flexion, which is accompanied by slight inward
rotation of the leg, the condyles of the femur and the semilunar
cartilages glide backward on the tibia; the movement of the external
condyle and cartilage is greater than that of the inner one. In
extreme flexion the patellar and posterior crucial ligaments are
tense; the other ligaments are relaxed. The movement of the patella is
gliding with coaptation, _i. e._, different parts of the opposing
articular surfaces come into contact successively. Only a narrow
transverse strip (ca. 1.5 to 2 cm. wide) of the patella is in contact
with the trochlea at a time.
TIBIO-FIBULAR ARTICULATION
The head of the fibula articulates with a crescentic facet just below
the outer margin of the external condyle of the tibia. The =joint
capsule= is strong and close. The shaft of the fibula is attached to the
external border of the tibia by the =interosseous membrane= of the leg
(Membrana interossea cruris); this is perforated about an inch from its
proximal end by an opening which transmits the anterior tibial vessels
to the front of the tibia. A fibrous cord usually extends from the
distal end of the shaft of the fibula to the external malleolus. The
latter is the distal end of the fibula which has fused with the tibia.
No appreciable movement occurs in this joint.
[Illustration:
FIG. 162.—LEFT HOCK JOINT OF HORSE, EXTERNAL VIEW.
]
[Illustration:
FIG. 163.—LEFT HOCK JOINT OF HORSE, INTERNAL VIEW.
_21_, Tibia; _24_, tuber calcis; _25_, large metatarsal bone; _47_,
long external lateral ligament; _51_, long internal lateral
ligament. (After Ellenberger-Baum, Anat. für Künstler.)
]
THE HOCK JOINT
This is a composite joint made up of a number of articulations
(Articulationes tarsi). These are: (1) The tibio-tarsal articulation;
(2) the intertarsal articulations; (3) the tarso-metatarsal
articulation.
The =tibio-tarsal articulation= (Articulatio talo-cruralis) is a typical
ginglymus formed by the trochlea of the tibial tarsal bone (astragalus
or talus) and the corresponding surface of the distal end of the tibia.
The ridges and grooves of these surfaces are directed obliquely forward
and outward at an angle of about 12° to 15°, with a sagittal plane. The
trochlear surface is about twice as extensive as that on the tibia, and
its ridges have a spiral curvature. The other articulations are
arthrodia, which have joint surfaces and ligaments of such a nature as
to allow only a minimal amount of gliding motion.
As in the case of the carpal joints, it is convenient to describe first
the common capsule and ligaments, which are the more important
practically, and then to consider very briefly the special ligaments.
The fibrous part of the =joint capsule= is attached around the margin of
the tibial articular surface above and the metatarsal surfaces below; it
is also attached in part to the free surface of the bones which it
covers, and blends with the lateral ligaments. Its anterior part
(anterior ligament) is rather thin; in distention of the capsule, as in
“bog-spavin,” its antero-internal part, which is not bound down by the
tendons passing over the joint, forms a fluctuating swelling over the
inner ridge of the trochlea. The posterior part (posterior and
tarso-metatarsal ligaments) is very thick, and is intimately attached to
the tarsal bones. Its superficial face is in part cartilaginous, and
forms a smooth surface for the perforans tendon. Superiorly, it pouches
upward behind the distal end of the tibia for a distance of about two
inches (ca. 5 cm.). Interiorly, it is continued downward, forming the
=subtarsal= or =check ligament=, which unites with the perforans tendon
about the middle of the metatarsus.
[Illustration:
FIG. 164.—LEFT HOCK JOINT OF HORSE, ANTERIOR VIEW.
_21_, Tibia; _22_, trochlea of tibial tarsal bone; _25_, large
metatarsal bone; _50_, dorsal or oblique ligament. (After
Ellenberger-Baum, Anat. für Künstler.)
]
There are four =synovial sacs=: 1. The =tibio-tarsal sac= lubricates the
proximal joint, and is much the largest and most important. It is
chiefly involved in the swelling produced by excess of fluid in the
joint cavity, when the capsule bulges antero-internally and
postero-superiorly. 2. The =first intertarsal sac= lines the joints
formed by the tibial and fibular tarsal bones above, and the central and
fourth tarsals below; it communicates in front with the proximal
synovial capsule. 3. The =second intertarsal sac= lubricates the joints
formed between the central tarsal and the bones below and on either
side. 4. The =tarso-metatarsal sac= lubricates the joints formed between
the tarsal and metatarsal bones, those between the proximal ends of the
metatarsal bones, and those formed by the third tarsal with the bones on
either side.
=Common Ligaments.=—The =external lateral ligament= (Ligamentum
collaterale fibulare longum et breve) consists of two distinct bands
which cross each other. The =long= (superficial) =ligament= arises on
the posterior part of the external malleolus, is directed almost
straight downward, and is attached to the fibular and fourth tarsal
bones and the large and external small metatarsal bones. It forms a
canal for the lateral extensor tendon. The =short= (deep) =ligament=
arises on the anterior part of the external malleolus, is directed
chiefly backward, and ends on the rough excavation on the external
surface of the tibial tarsal and the adjacent surface of the fibular
tarsal bone.
[Illustration:
FIG. 165.—LEFT HOCK JOINT OF HORSE, POSTERIOR VIEW.
_21_, Tibia; _24_, tuber calcis. (After Ellenberger-Baum, Anat. für
Künstler.)
]
The =internal lateral ligament= (Ligamentum collaterale tibiale longum
et breve) also consists of two parts which cross each other. The =long
ligament= arises on the posterior part of the internal malleolus,
becomes wider below, and is attached on the lower tuberosity of the
tibial tarsal, the large and outer small metatarsal bones, and the inner
surface of the lower tarsal bones which it covers. The =short ligament=
lies largely under cover of the long one. It extends from the anterior
part of the internal malleolus, runs backward and somewhat downward, and
divides into two branches; one of these ends on the upper tuberosity on
the inner surface of the tibial tarsal bone, the other on the
sustentaculum tali.
The =plantar= or =calcaneo-metatarsal ligament= (Ligamentum tarsi
plantare) is a very strong flat band which covers the outer part of the
posterior surface of the tarsus. It is attached to the posterior surface
of the fibular and fourth tarsal bones and the proximal end of the
external metatarsal bone.
The =dorsal= or =oblique ligament= (Ligamentum tarsi dorsale) is a
triangular sheet which is attached above to the lower tuberosity on the
inner face of the tibial tarsal bone, and spreads out below on the
central and third tarsal bones, and the proximal ends of the large and
inner small metatarsal bones, to all of which it is attached.
=Special Ligaments.=—A considerable number of short bands which connect
adjacent bones of the tarsus and metatarsus are described by various
authors; some of these are quite distinct; others are difficult to
isolate. Most of them are not of sufficient importance to justify
detailed description.
(1) The =tibial= and =fibular tarsal= bones are united by four bands
(astragalo-calcaneal ligaments). The =internal ligament= extends from
the sustentaculum tali to the adjacent part of the tibia tarsal,
blending with the short lateral ligament. The =external ligament=
extends from the anterior process of the fibular tarsal to the
adjacent part of the external ridge of the trochlea. The =superior
ligament= extends from the posterior margin of the trochlea to the
fibular tarsal. The =interosseous ligament= is deeply placed in the
sinus tarsi between the two bones, and is attached in the rough areas
of the opposed surfaces.
(2) The smaller bones are attached to each other as follows: The
central and third tarsal are united by an interosseous and an oblique
anterior ligament (scaphoido-cunean ligaments). The central and fourth
tarsal are united by an interosseous and a transverse external
ligament (cuboido-scaphoid ligament). The third and fourth tarsals are
similarly connected (cuboido-cunean ligaments). The third tarsal is
joined by an interosseous (intercunean) ligament to the (fused) first
and second tarsals; the latter are connected with the fourth tarsal by
a transverse posterior ligament.
(3) The smaller bones are connected with the upper row as follows: The
central is attached to the tibial tarsal by posterior and interosseous
(astragalo-seaphoid) ligaments, and to the fibular tarsal by a short
oblique (calcaneo-scaphoid) band. The fourth is attached to the
fibular tarsal by interosseous and posterior (calcaneo-cuboid)
ligaments. The (fused) first and second tarsals are connected with the
fibular tarsal by a posterior (calcaneo-cunean) ligament.
(4) The lower tarsal bones are connected with the metatarsus by
tarso-metatarsal ligaments, which are not distinct from the common
ligaments, except in the case of the interosseous ligament between the
third tarsal and metatarsal bones.
[Illustration:
FIG. 166.—SAGITTAL SECTION OF HOCK OF HORSE.
]
=Movements.=—These are flexion and extension, which take place at the
tibio-tarsal joint. The movements between the tarsal bones, and between
the latter and the metatarsus, are so limited as to be negligible so far
as the action of the joint as a whole is concerned. In the standing
position the articular angle (in front) is about 150° to 160°. Complete
extension is prevented by tension of the lateral ligaments. Flexion is
checked only by contact of the metatarsus with the leg, provided the
stifle joint is also flexed. Owing to the fact that the axis of motion
is slightly oblique, the lower part of the limb deviates somewhat
outward during flexion.
The movements of the hock joint must correspond with those of the
stifle on account of the tendinous bands in front and behind (peroneus
tertius and flexor perforatus), which extend from the lower part of
the femur to the tarsus and metatarsus.
The remaining joints differ in no material respect from those of the
thoracic limb.
COMPARATIVE ARTHROLOGY[39]
JOINTS AND LIGAMENTS OF THE VERTEBRÆ
=Ox.=—The ligamentum nuchæ is better developed than in the horse. The
funicular part is clearly divided into two lateral halves, which are
round at their occipital attachment, but from the axis backward become
rapidly wider and flat. This wide portion is almost sagittal, lies on
either side of the vertebral spines, and is covered by the trapezius and
rhomboideus muscles. From the highest part of the withers (third
thoracic spine) it gradually diminishes in size and fades out in the
lumbar region. The lamellar part is thick, and consists of anterior and
posterior parts. The anterior part is double; its fibers proceed from
the funicular part to the second, third, and fourth cervical spines. The
posterior part is single; its fibers extend from the first thoracic
spine to the fifth, sixth, and seventh cervical spines.
[Illustration:
FIG. 167.—LIGAMENTUM NUCHÆ OF OX.
_a_, Funicular part; _b_, wide portion; _c_, _d_, lamellar part; _e_,
interspinous ligaments; _1_, spinous process of first thoracic
vertebra; _2_, axis. (Ellenberger-Baum, Anat. d. Haustiere.)
]
The inferior common ligament is very strong in the lumbar region.
The intervertebral fibro-cartilages are thicker than in the horse.
The interspinous ligaments of the back and loins consist largely of
elastic tissue.
There are no intertransverse joints in the lumbar region.
=Pig.=—The ligamentum nuchæ is represented by a fibrous raphé and thin
layers of elastic tissue which extend between the cervical spines.
The atlanto-occipital and atlanto-axial joints resemble those of the
dog.
The interspinous ligaments of the neck are elastic.
=Dog.=—The ligamentum nuchæ consists of a small fibrous band which
extends from the spine of the axis to the anterior thoracic spines; it
may be regarded as a mere fibrous raphé between the right and left
muscles.
There are interspinous muscles instead of ligaments in the neck.
There are three ligaments in connection with the odontoid process. The
two alar ligaments (Ligamenta alaria) arise on either side of the
odontoid process, diverge, and end on either side of the foramen magnum.
The transverse ligament of the atlas (Ligamentum transversum atlantis)
stretches across the dorsal surface of the odontoid process and binds it
down on the ventral arch of the atlas, a bursa being interposed. It is
attached on either side to the lateral masses of the atlas.
The two capsules of the atlanto-occipital joint communicate with each
other, and usually with the capsule of the atlanto-axial joint also.
ARTICULATIONS OF THE THORAX
=Ox.=—The second to the eleventh costo-chondral joints inclusive are
diarthroses with close capsules, reinforced externally. (They are
synchondroses in the sheep.) The upper parts of the cartilages are
attached to each other by distinct elastic ligaments (Ligamenta
intercostalia).
The first pair of chondro-sternal joints are separate from each other;
intercrossing fibers unite the costo-chondral junctions above the
joints.
The first segment of the sternum forms a diarthrosis with the body. The
anterior joint surface is concave, the posterior convex. The joint
(Articulatio intersternalis) is surrounded by a close capsule, and the
joint surfaces are attached to each by a small intraarticular ligament.
Limited lateral movement is possible. (In the sheep the joint is a
synchondrosis.)
Both surfaces of the sternum are covered by a layer of fibrous tissue.
=Pig.=—The second to the fifth or sixth costo-chondral joints are
diarthroses. The intersternal articulation and the sternal ligaments
resemble those of the ox.
=Dog.=—The first chondro-sternal joints do not coalesce.
The internal sternal ligament divides into three bands.
TEMPORO-MANDIBULAR ARTICULATION
=Ox.=—The articular surfaces are of such a character as to permit more
extensive lateral movement than in the horse.
The condyle of the mandible is relatively small and is concave
transversely. The temporal articular surface is extensive and is
convex in both directions. The postglenoid process is small.
=Pig.=—The considerable longitudinal diameter of the temporal articular
surfaces and the very small size of the postglenoid process allow great
freedom of protraction and retraction of the lower jaw. Lateral movement
is limited. The posterior ligament is absent.
=Dog.=—The articular surfaces allow extremely little lateral or gliding
movement. They are cylindrical in curvature, and the interarticular disc
is very thin. The posterior ligament is absent.
The other articulations of the skull are sufficiently described in the
Osteology.
Articulations of the Thoracic Limb
SHOULDER JOINT
=Ox.=—The articular angle is about 100°.
=Pig and Dog.=—The joint capsule communicates freely with the bicipital
bursa. There is a rudimentary marginal cartilage around the rim of the
glenoid cavity. In the dog there is usually a strong band extending from
the acromion to the outer part of the capsule; another band (Ligamentum
coraco-acromiale) often stretches between the scapular tuberosity and
the acromion.
ELBOW JOINT
=Ox.=—No important differences exist. The upper part of the interosseous
radio-ulnar ligament is commonly ossified in the adult.
=Pig.=—There are no important differences. The radius and ulna are so
firmly united by the interosseous ligament as to prevent any appreciable
movement between them.
=Dog.=—The joint capsule is reinforced in front by an oblique ligament
which arises on the front of the external condyle of the humerus above
the joint surface, and joins the terminal part of the biceps and
brachialis below. The external lateral ligament is thick and divides
into two parts; the anterior part is attached to the radius and blends
with the annular ligament; the posterior part widens below, forming a
sort of cap, and is attached to the ulna. The internal lateral ligament
also divides into two branches; the anterior branch ends on the inner
surface of the neck of the radius; the posterior enters the interosseous
space and is attached to both bones. An elastic band (Ligamentum
olecrani) extends from the outer surface of the internal epicondyle to
the anterior border of the ulna.
There are two radio-ulnar joints. The proximal radio-ulnar joint is
included in the capsule of the elbow, but is provided with an annular
ligament which extends from the lower part of the external ligament
across the front of the proximal end of the radius to the ulna, blending
with the biceps and brachialis tendons. The distal joint is formed by a
concave facet on the radius and a convex one on the radius, and is
surrounded by a tight capsule. The interosseous membrane unites the
shafts of the two bones. The movements consist of limited rotation of
the radius (ca. 20°), carrying the paw with it. The ordinary position is
termed pronation; outward rotation is supination.[40]
THE CARPAL JOINTS
These have the same general arrangement as in the horse. Numerous minor
differences naturally exist, but must be excluded from this brief
account, which contains only important special features.
The lateral movements are freer, especially in the dog, but flexion is
not so complete: the anatomical explanation of these facts lies in the
nature of the articular surfaces and certain ligamentous differences.
The lateral ligaments are much weaker, the long external one being
especially small in the ox. Two oblique, somewhat elastic, bands cross
the front of the radio-carpal and intercarpal joints. The proximal one
is attached to the distal end of the radius and passes downward and
outward to the ulnar carpal bone; the other one connects the radial and
fourth carpal bones in a similar fashion.
In the ox the short lateral ligaments are well defined, a ligament
connects the accessory carpal with the distal end of the ulna, and
strong bands connect the distal bones with the metacarpus.
The interosseous and interordinal ligaments vary with the number of
carpal bones present in the different species.
INTERMETACARPAL JOINTS
In the ox the small (fifth) metacarpal bone articulates with the large
metacarpal, but not with the carpus. The joint cavity is connected with
that of the carpo-metacarpal sac. The proximal end of the small
metacarpal bone is attached by a ligament to the fourth carpal, and
another band extends from its distal part to the side of the large
metacarpal. There is also an interosseous ligament, which is permanent
and allows a small amount of movement.
The chief metacarpal bones of the pig, and the second to the fifth of
the dog, articulate with each other at their proximal ends, and are
connected by interosseous ligaments, which do not, however, unite them
closely, as in the horse.
[Illustration:
FIG. 168.—DISTAL PART OF LIMB OF OX, SHOWING LIGAMENTS AND TENDONS.
ONE DIGIT AND CORRESPONDING ARTICULAR PART OF METACARPAL BONE ARE
REMOVED.
_a_, Suspensory ligament; _a′_, branch of _a_ to superficial flexor
tendon; _a″_, _a‴_, lateral and central branches of _a_; _b_, deep
flexor tendon; _b′_, branch of _b_ to digit removed; _c_, _c′_,
superficial flexor tendon; _d_, _d′_, intersesamoid ligament (cut);
_e_, interdigital lateral ligament of fetlock joint; _f_, tendon of
common extensor; _g_, proximal interdigital ligament; _h_, digital
annular ligament; _i_, posterior annular ligament of fetlock; _k_,
lateral ligament of pastern joint; _l_, distal interdigital
ligament; _m_, crucial interdigital ligament (cut); _m′_, _m″_,
attachments of _m_ to second phalanx and distal sesamoid bone; _n_,
suspensory ligament of distal sesamoid; _o_, anterior elastic
ligament; _p_, lateral volar ligament of pastern joint; _1_,
metacarpus, sawn off at _1′_; _2_, first phalanx; _3_, second
phalanx; _4_, third phalanx. (Ellenberger-Baum, Anat. d. Haustiere.)
]
METACARPO-PHALANGEAL JOINTS
=Ox.=—There are two joints, one for each digit. The two capsules
communicate posteriorly. The two interdigital lateral ligaments
(Ligamenta collateralia interdigitalia) result from the bifurcation of a
band which arises in the furrow between the divisions of the distal end
of the large metacarpal bone; they spread out and end on the proximal
ends of the first phalanges. A strong =superior interdigital ligament=
(Ligamentum interdigitale), consisting of short intercrossing fibers,
unites the middles of the interdigital surfaces of the first phalanges.
Crucial ligaments (Ligamenta phalango-sesamoideæ) connect the sesamoids
with the proximal end of the opposite first phalanx.
The intersesamoid ligament connects all four sesamoids, and extends
upward much less than in the horse.
The lateral sesamoidean ligaments end almost entirely on the first
phalanges.
The superficial inferior sesamoidean ligament is absent. The middle
inferior sesamoidean ligaments of each digit are two short strong bands
which extend from the distal margins of the sesamoids to the proximal
ends of the first phalanges. The deep inferior sesamoidean ligaments are
strong and distinctly crucial.
[Illustration:
FIG. 169.—LIGAMENTS AND TENDONS OF DIGITS OF PIG, VOLAR VIEW.
_a_, Superficial flexor tendon; _b_, deep flexor tendon; _b′_,
branches of _b_ to accessory digits; _c_, _c′_, annular ligaments;
_d-d‴_, ligaments of accessory digits; _e_, cruciate interdigital
ligaments; _f_, _f′_, spiral band around the flexor tendons of the
accessory digits; _g_, abductor of accessory digit.
(Ellenberger-Baum, Anat. d. Haustiere.)
]
[Illustration:
FIG. 170.—LIGAMENTS AND TENDONS OF PAW OF DOG, HIND LIMB, VOLAR VIEW.
_a_, _a′_, Superficial flexor tendon; _b_, tendon to large pad; _c_,
lumbricales muscles; _d_, interossei muscles; _e_, _f_, annular
ligaments at metatarsophalangeal joints; _g_, suspensory ligament of
large pad; _h_, digital annular ligaments; _i_, deep flexor tendon;
_k_, distal sesamoid; _l_, suspensory ligament of _k_; _m_,
suspensory ligament of digital pad; _n_, digital pads.
(Ellenberger-Baum, Anat. d. Haustiere.)
]
The suspensory or superior sesamoidean ligament is more distinctly
muscular than in the horse—indeed in the young animal it consists almost
entirely of muscular tissue. At the distal third of the metacarpus it
divides into three branches. These give rise to five subdivisions,
either by bifurcation of the lateral branches or trifurcation of the
middle branch. The four lateral bands end on the sesamoid bones and the
distal end of the large metacarpal bone, and detach slips to the
extensor tendons. The middle band passes through the groove between the
two divisions of the distal end of the metacarpus, and divides into two
branches which join the tendons of the proper extensors of the digits;
it sends fibers also to the interdigital lateral ligaments and to the
central sesamoids. About the middle of the metacarpus the suspensory
ligament detaches a band which unites lower down with the superficial
flexor tendon, thus inclosing the tendon of the deep flexor of the
digit; it also blends with the thick fascia of the region. The latter
gives off a band on either side to the accessory digits, and a tendinous
band descends from each accessory digit to the third phalanx and
sesamoid bone, blending with the tendon of the corresponding proper
extensor.
=Pig.=—There are four metacarpo-phalangeal joints, each of which has a
capsule, lateral, intersesamoidean, and crucial sesamoidean ligaments.
Since distinct interosseous muscles are present, there are, of course,
no suspensory ligaments.
=Dog.=—There are five metacarpo-phalangeal joints, each having its own
capsule and indistinct lateral ligaments. A small sesamoid bone occurs
in the anterior part of each capsule, over which the corresponding
extensor tendon plays. The intersesamoidean ligaments do not extend
above the sesamoids. The cruciate ligaments are present, as well as a
fibrous layer which attaches the distal margins of the sesamoids to the
posterior surface of the proximal end of the first phalanx.
INTERPHALANGEAL JOINTS
=Ox.=—The two proximal joints have separate capsules, and broad, but
rather indistinct, lateral ligaments. Each joint has also two central
and two lateral volar ligaments. The central ligaments are largely fused
to form a strong band. The lateral ones extend from the borders of the
first phalanx to the proximal end of the second phalanx.
The distal interphalangeal joints have, in addition to the capsules and
lateral ligaments, bands which reinforce them on either side. The
central or interdigital pair arise in the depressions on the distal ends
of the first phalanges, receive fibers from the second phalanges, and
end on the interdigital surfaces of the third phalanges at the margin of
the articular surface. The lateral pair have a similar course, but are
thinner, and end on the corresponding third sesamoid. An elastic band
crosses the front of the second phalanx obliquely, from the distal end
of the first phalanx to the extensor process of the third phalanx.
The =crucial= or =inferior interdigital ligaments= (Ligamenta cruciata
interdigitalia) are two strong bands which limit the separation of the
digits. They are attached above to the lateral (or abaxial) eminences on
the proximal ends of the second phalanges (blending with the lateral
ligaments), cross the deep flexor tendon obliquely, and reach the
interdigital space, where they intercross and blend. Most of the fibers
end on the third sesamoid of the opposite side, but some are attached to
the interdigital aspect of the second phalanx and the third sesamoid of
the same side. In the sheep there is, instead of the foregoing, a
transverse ligament which is attached on either side to the interdigital
surfaces of the second and third phalanges and the third sesamoid bone.
It is related below to the skin, above to a pad of fat.
=Pig.=—The interphalangeal joints of the chief digits resemble in
general those of the ox. The inferior interdigital ligament resembles,
however, that of the sheep, and is intimately adherent to the skin.
There is, besides, a remarkable arrangement of ligaments which connect
the small digits with each other and with the chief digits.
This apparatus is somewhat complex, but its chief features are as
follows: A superior interdigital ligament is attached on either side
to the third phalanges of the small digits, while centrally it blends
with the annular ligaments of the flexor tendons behind the
metacarpo-phalangeal joints of the chief digits. Two bands (central
longitudinal interdigital ligaments) arise on the bases of the small
digits, cross the flexor tendons obliquely downward and inward, pass
through the superior interdigital ligament, and blend below with the
inferior interdigital ligament. Two lateral bands (lateral
longitudinal interdigital ligaments) are attached in common with the
superior interdigital ligaments to the third phalanges of the small
digits, and blend below with the outer part of the inferior
interdigital ligament.
=Dog.=—Each joint has a capsule and two lateral ligaments. The distal
joints have also two elastic =dorsal ligaments= (Ligamenta dorsalia),
which extend from the proximal end of the second phalanx to the ridge at
the base of the third phalanx (Fig. 133). They produce dorsal flexion of
the joint, and thus raise or retract the claws when the flexor muscles
relax. The distal sesamoids are represented by complementary cartilages
attached to the volar margins of the articular surfaces of the third
phalanges.
Three interdigital ligaments restrict the spreading apart of the digits.
Two of these cross the volar surface of the proximal parts of the chief
digits, _i. e._, one for the second and third, the other for the fourth
and fifth; they blend with the annular ligaments on either side. The
third ligament is attached on either side to the foregoing ligaments and
the annular ligaments of the third and fourth digits, and curves
downward centrally, ending in the large pad on the paw.
ARTICULATIONS OF THE PELVIC LIMB
SACRO-ILIAC JOINT
This joint and the pelvic ligaments present no very striking differences
in the other animals. The sacro-sciatic ligament in the dog is a narrow
but strong band which extends from the posterior part of the lateral
margin of the sacrum to the tuber ischii; it is the homologue of the
ligamentum sacro-tuberosum of man.
HIP JOINT
=Ox.=—The shallowness of the acetabulum is compensated by the greater
size of the marginal cartilage. The head of the femur has a smaller
radius of curvature than that of the horse, and the articular surface
extends a considerable distance outward on the upper surface of the
neck. The round ligament is entirely intraarticular; it is small, and
sometimes absent. The pubo-femoral or accessory ligament is absent.
There are no important differences in the other animals.
STIFLE JOINT
=Ox.=—There is a considerable communication between the femoro-patellar
and inner femoro-tibial joint cavities; this is situated as in the
horse, but is wider. A small communication with the external
femoro-tibial capsule sometimes occurs. The two femoro-tibial capsules
usually communicate. The middle patellar ligament is not sunken, as
there is no groove on the tuberosity of the tibia where it is attached.
The external patellar ligament fuses completely with the tendon of
insertion of the biceps femoris, and a synovial bursa is interposed
between them and the external condyle of the femur.
In the other animals there is a single ligamentum patellæ, and the
synovial sacs communicate so freely as to constitute a common joint
cavity. In the dog the semilunar cartilages are united anteriorly by a
transverse ligament, and the posterior part of the capsule contains the
two Vesalian sesamoids, which articulate with the condyles of the femur.
TIBIO-FIBULAR JOINTS
=Ox.=—The proximal end of the fibula fuses with the external condyle of
the tibia. The distal end remains separate, and forms an arthrosis with
the distal end of the tibia; the movement here is imperceptible, as the
two bones are closely united by strong peripheral fibers.
=Pig.=—The superior joint is provided with a capsule which is reinforced
in front and behind by fibrous tissue.
The interosseous ligament attaches the shaft of the fibula to the outer
border of the tibia.
The inferior joint is included in the capsule of the hock joint, and is
strengthened by oblique anterior and posterior ligaments. There is also
an interosseus ligament.
=Dog.=—The arrangement is essentially the same as in the pig, but there
is no interosseous ligament in the inferior joint.
HOCK JOINT
=Ox.=—There is very considerable mobility at the first intertarsal
joint, the capsule of which is correspondingly roomy. The short external
lateral ligament is attached below on the tibial tarsal only. A strong
transverse ligament attaches the external malleolus (distal end of the
fibula) to the back of the tibial tarsal bone. The dorsal or oblique
ligament is narrow and thin.
=Pig.=—The arrangement in general resembles that of the ox.
=Dog.=—The long lateral ligaments are very small, and the short ones
double. The plantar ligament is weak, and ends on the fourth metacarpal
bone. No distinct dorsal (or oblique) ligament is present. Movement
occurs almost exclusively at the tibio-tarsal joint.
The remaining joints resemble those of the thoracic limb.
THE MUSCULAR SYSTEM
MYOLOGY
The =muscles= (Musculi) are the active organs of motion. They are
characterized by their property of contracting when stimulated. Muscular
tissue is of three kinds: (_a_) =Striated= or striped; (_b_)
=non-striated=, unstriped, or smooth; and (_c_) =cardiac=. Only the
first of these varieties will be considered in this section. The striped
muscles, being for the most part directly or indirectly connected with
the skeleton, are often termed =skeletal= or somatic, while unstriped
muscle may be spoken of as =visceral= or splanchnic. The former cover
the greater part of the skeleton, and thus in a large measure determine
the form of the animal. They are red in color, the shade varying in
different muscles and under various conditions.
Muscles vary greatly in =form=, and may be classified as—(_a_) =Long=;
(_b_) =short=; (_c_) =flat=; (_d_) =ring-like= or =orbicular=. Long
muscles are found chiefly in the limbs, while the flat or broad muscles
occur principally in the trunk, where they assist in forming the walls
of the body cavities. The ring-like or orbicular muscles circumscribe
orifices which they close, and are hence termed =sphincters=.
=Attachments.=—The muscles are attached to =bones=, =cartilages=,
=ligaments=, =fasciæ=, or the =skin=. In all cases the attachment is by
means of fibrous tissue, the muscle-fibers not coming into direct
relation with the bone or cartilage. The perimysium of the muscle may
fuse directly with the periosteum or perichondrium (fleshy attachment),
or the union may be by means of intermediary fibrous structures called
=tendons= or =aponeuroses= (tendinous attachment). Tendons may be
funicular, ribbon-like, or in the form of membranous sheets; to the
latter the term aponeurosis is commonly applied.
In certain positions, especially where tendons play over joints or are
subjected to great pressure, =sesamoid bones= develop in the original
tendon tissue. Some of these are large and constant, as the patella and
the great sesamoids of the fetlock.
The accessory structures connected with the muscles are the =synovial
membranes= and the =fasciæ=.
[Illustration:
FIG. 171.—DIAGRAMS OF CROSS-SECTIONS OF TENDON SHEATH (A) AND BURSA
(B); T, TENDON.
]
The =synovial membranes= are arranged in two principal forms: (_a_)
=Bursal=; (_b_) =vaginal=. A =bursa= (Bursa mucosa) is a simple sac
interposed between the tendon or muscle and some deeper seated
structure—most commonly a bony prominence. A =vagina tendinis= or
=tendon sheath= differs from a bursa in the fact that the synovial sac
is folded around the tendon more or less completely, so that two layers
can be distinguished; of these, the inner one adheres closely to the
tendon, while the outer lines the groove or canal in which the tendon
lies. The two layers are continuous along a fold termed the
=mesotendon=. The arrangement is shown in Fig. 171.[41] The articular
synovial membranes in some places form extra-articular pouches, which
facilitate the play of tendons.
The =fasciæ= are sheets of connective tissue, mainly of the white
fibrous variety, with a greater or less admixture of elastic fibers in
certain cases. Two layers may usually be recognized. Of these, the
=superficial fascia= (Fascia subcutanea) is composed of loose connective
tissue which may contain more or less fat and is subcutaneous. The =deep
fascia= is composed of one or more layers of dense fibrous tissue spread
over the surface of the muscles chiefly. Its deep face may be very
loosely attached to the underlying structures or may fuse with the
epimysium, tendons, bones, or ligaments. In some parts, especially the
limbs, septal plates pass between the muscles and are attached to the
bones or ligaments; these are termed =intermuscular septa=. In this way
many muscles are inclosed in fibrous sheaths which hold them in
position. Not uncommonly special bands stretch across the grooves in
which tendons play, converting these into canals. Such bands are termed
=vaginal= or =annular ligaments=. The deep fascia is often so distinctly
tendinous in structure, furnishing attachment to special tensor muscles,
as to render the distinction between fascia and aponeurosis quite
arbitrary. Bursæ occur in certain situations between the fascia and
underlying structures (subfascial bursæ), or between the fascia and the
skin (subcutaneous bursæ).
It is convenient to divide the description of a muscle into seven heads,
viz.: (1) Name, followed by important synonyms; (2) position and form;
(3) attachments; (4) action; (5) structure; (6) relations; (7) blood and
nerve supply.
1. The =name= is determined by various factors, viz.: (_a_) The action,
_e. g._, extensor, adductor, etc.; (_b_) the shape, _e. g._, quadratus,
triangularis; (_c_) the direction, _e. g._, rectus, obliquus; (_d_) the
position, _e. g._, the subscapularis, iliacus; (_e_) the division (into
heads, etc.), _e. g._, biceps, triceps, etc.; (_f_) the size, _e. g._,
major, minor, etc.; (_g_) the attachments, _e. g._, sterno-cephalicus,
mastoido-humeralis; (_h_) the structure, _e. g._, semitendinosus. In
most cases two or more of these factors have combined to produce the
name, _e. g._, adductor magnus, longus colli, obliquus externus
abdominis.
2. The =shape= is, in many cases, sufficiently definite to allow the use
of such terms as triangular, quadrilateral, fan-shaped, long, flat,
fusiform, ring-like, etc.
3. The =attachments= are in most cases to bone, but many muscles are
attached to cartilage, ligaments, fascia, the skin, etc. It is usual to
apply the term =origin= to the attachment which always or more commonly
remains fixed when the muscle contracts. The term =insertion= designates
the movable attachment. Such a distinction cannot always be made, as the
action may be reversible, or both attachments may be freely movable.
4. The =action= belongs rather to physiological study, but is briefly
indicated in anatomical descriptions.
5. The =structure= includes the direction of the muscle-fibers, the
arrangement of the tendons, the synovial membranes, and any other
accessory structures, _e. g._, annular ligaments and reinforcing sheaths
and bands. The relation of the muscle-fibers to the tendon varies, and
this fact has given rise to special terms. Thus a muscle in which the
fibers converge to either side of the tendon is termed =bipennate=;
while one in which this arrangement exists only on one side of the
tendon is called =unipennate=. The terms fleshy and tendinous are used
to indicate the relative amounts of muscular and tendinous tissue. The
muscular tissue is often spoken of as the =belly= (Venter) of the
muscle. In the case of the long muscles, the origin is often termed the
=head= (Caput). Muscles having two or more heads are called biceps,
triceps, etc. =Digastric= muscles are those which have two bellies
joined by an intermediate tendon. Ring-like muscles which circumscribe
openings are termed =sphincters=, on account of their action.
6. The =relations= are, of course, important on surgical grounds.
7. The =nerve-supply= is of clinical interest, and is important for the
determination of homologies.
FASCIÆ AND MUSCLES OF THE HORSE
PANNICULUS CARNOSUS
The =panniculus carnosus= (Musculus cutaneus) is a thin muscular layer
developed in the superficial fascia. It is intimately adherent in great
part to the skin, but has very little attachment to the skeleton. It
does not cover the entire body, and may be conveniently divided into
facial, cervical, thoracic, and abdominal portions, each of which will
be described with the muscles of the corresponding region.
THE FASCIÆ AND MUSCLES OF THE HEAD
The muscles of the head may be divided into three groups, viz.: (1)
Superficial muscles, including the panniculus and those of the lips,
cheeks, nostrils, eyelids, and external ear; (2) the orbital muscles;
(3) the muscles of mastication.
The =superficial fascia= forms an almost continuous layer, but is very
scanty around the natural orifices. It contains a number of the thin
superficial muscles, so that care must be exercised in removing the
skin. Over the frontal and nasal bones the fascia blends with the
periosteum.
The =deep fascia= is of special interest in three regions. The =temporal
fascia= covers the temporalis muscle, and is attached to the parietal
and frontal crests internally, and to the zygomatic arch externally. The
=buccal fascia= covers the buccinator muscle and the free part of the
outer surface of the ramus of the jaw. Superiorly it is attached to the
facial crest, and posteriorly it forms a band (Ligamentum
pterygomandibulare) which stretches from the hamulus of the pterygoid
bone to the mandible behind the last molar tooth. It is directly
continuous with the =pharyngeal fascia=, which is attached to the great
and thyroid cornua of the hyoid bone, covers the lateral walls of the
pharynx, and blends dorsally with the median raphé of the constrictor
muscles of the latter.
SUPERFICIAL MUSCLES
1. =Panniculus carnosus.=—The facial panniculus (M. cutaneus faciei)
consists of a thin and usually incomplete muscular stratum, which covers
the submaxillary space and the masseter muscle. A branch from it passes
forward to the angle of the mouth and blends with the orbicularis oris;
this part (M. cutaneus labiorum) retracts the angle of the mouth. (A
number of the superficial muscles of the face may be considered modified
parts of the panniculus, _e. g._, the corrugator supercilii, malaris,
zygomaticus, etc.)
MUSCLES OF THE LIPS AND CHEEKS
1. =Orbicularis oris.=—This is the sphincter muscle of the mouth; it is
continuous with the other muscles which converge to the lips. It lies
between the skin and the mucous membrane of the lips, and is intimately
adherent to the former. Most of the fibers run parallel to the free
edges of the lips and have no direct attachment to the skeleton.
_Action._—It closes the lips.
_Blood-supply._—Palato-labial, facial, and mental arteries.
_Nerve-supply._—Facial nerve.
[Illustration:
FIG. 172.—MUSCLES OF HEAD OF HORSE, LATERAL VIEW. THE PANNICULUS IS
REMOVED.
_a_, Levator labii superioris proprius; _b_, levator nasolabialis;
_c_, mastoido-humeralis; _d_, sterno-cephalicus; _d′_, tendon of
_d_; _e_, omo-hyoideus; _f_, dilatator naris lateralis; _g_,
zygomaticus; _h_, buccinator; _i_, depressor labii inferioris; _k_,
orbicularis oris; _l_, dilatator naris superior; _m_, masseter; _n_,
parotido-auricularis; _o_, zygomatico-auricularis; _p_,
interscutularis; _p′_, fronto-scutularis, pars temporalis; _q_,
cervico-auricularis profundus major; _r_, cervico-auricularis
superficialis; _s_, obliquus capitis anterior; _t_, splenius; v,
stylo-maxillaris; _y_, mastoid tendon of mastoido-humeralis; _2_,
posterior, _3_, anterior, border of external ear; _8_, scutiform
cartilage; _9_, zygomatic arch; _10_, depression behind supraorbital
process; _18_, temporo-mandibular articulation; _27_, facial crest;
_30′_, angle of jaw; _37_, external maxillary vein; _38_, jugular
vein; 39, facial vein; _40_, parotid duct; _41_, transverse facial
vein; _42_, masseteric vein; _43_, facial nerve; _44_, parotid
gland; _45_, chin; _x_, wing of atlas. (After Ellenberger-Baum,
Anat. für Künstler.)
]
2. =Levator nasolabialis= (Levator labii superioris alæque nasi).—This
thin muscle lies directly under the skin, and chiefly on the lateral
surface of the nasal region.
_Origin._—The frontal and nasal bones.
_Insertion._—(1) The upper lip and the outer wing of the nostril; (2)
the commissure of the lips.
_Action._—(1) To elevate the upper lip and the commissure; (2) to dilate
the nostril.
_Structure._—The muscle arises by a thin aponeurosis. The belly is also
thin, and divides into two branches, between which the lateral dilator
of the nostril passes. The dorsal branch reaches the nostril and upper
lip, blending with the lateral dilator; the ventral one is much smaller,
and blends at the labial commissure with the orbicularis and buccinator.
_Relations._—Superficially, the skin, fascia, and lateral dilator (in
part); deeply, the levator labii superioris proprius, lateral dilator
(in part), buccinator, branches of the facial vessels and nerve, and the
infraorbital artery and nerve.
_Blood-supply._—Facial and palato-labial arteries.
_Nerve-supply._—Facial nerve.
[Illustration:
FIG. 173.—MUSCLES OF HEAD OF HORSE, DORSAL VIEW. THE PANNICULUS IS
REMOVED.
_a_, Levator labii superioris proprius; _a′_, common tendon of a with
opposite muscle; _b_, levator nasolabialis; _f_, dilatator naris
lateralis; _g_, zygomaticus; _l_, dilatator naris superior; _n_,
parotido-auricularis; _o″_, scutulo-auricularis superficialis
superior; _p_, interscutularis; _p′_, fronto-scutularis, pars
temporalis; _r_, cervico-auricularis superficialis; _u_, corrugator
supercilii; _x_, transversus nasi; _2_, posterior, _3_, anterior,
border of external ear; _8_, scutiform cartilage; _9_, zygomatic
arch; _10_, supraorbital depression; _35_, inner wing of nostril,
containing lamina of alar cartilage; _39_, facial vein. (After
Ellenberger-Baum, Anat. für Künstler.)
]
3. =Levator labii superioris proprius.=—This lies on the dorso-lateral
aspect of the face, partly covered by the preceding muscle.
_Origin._—The lacrimal, malar, and maxillary bones at their junction.
_Insertion._—The upper lip, by a common tendon, with its fellow.
_Action._—Acting with its fellow, to elevate the upper lip. This action,
if carried to the fullest extent, results in eversion. In unilateral
action the lip is drawn upward and to the side of the muscle acting.
_Structure._—The muscle has a short, thin tendon of origin. The belly is
at first flattened, but becomes narrower and thicker, then tapers over
the false nostril, to terminate in a tendon. The tendons of the two
muscles unite over the alar cartilages of the nostrils, forming an
expansion which spreads out in the substance of the upper lip.
_Relations._—Superficially, the skin, the levator nasolabialis, and the
angular vessels of the eye; deeply, the superior and transverse dilators
of the nostril and the infraorbital artery and nerve.
_Blood-supply._—Facial artery.
_Nerve-supply._—Facial nerve.
4. =Zygomaticus.=—This very thin muscle lies immediately under the skin
of the cheek.
_Origin._—The fascia covering the masseter muscle below the facial
crest.
_Insertion._—The commissure of the lips, blending with the buccinator.
_Action._—To retract and raise the angle of the mouth.
_Structure._—Fleshy, with a thin aponeurotic origin.
_Relations._—Superficially, the skin; deeply, the buccinator.
_Blood-supply._—Facial artery.
_Nerve-supply._—Facial nerve.
5. =Incisivus superior= (Depressor labii superioris).—This lies under
the mucous membrane of the upper lip.
_Origin._—The alveolar border of the premaxilla from the second incisor
to the first cheek tooth.
_Insertion._—The upper lip.
_Action._—To depress the upper lip.
6. =Incisivus inferior.=—This is arranged in the lower lip like the
preceding muscle in the upper one.
_Origin._—The alveolar border of the mandible from the second incisor to
a point near the first cheek tooth.
_Insertion._—The skin of the lower lip and the prominence of the chin.
_Action._—To raise the lower lip.
7. =Mentalis= (Levator menti).—This is situated in the prominence of the
chin. Its fibers arise from each side of the body of the mandible and
are inserted into the skin of the chin. It is mingled with fat and
strands of connective tissue, in which the roots of the tactile hairs
are embedded. It raises and corrugates the skin to which it is attached.
8. =Depressor labii inferioris.=—This muscle lies on the outer surface
of the ramus of the mandible, along the ventral border of the
buccinator.
_Origin._—The alveolar border of the mandible near the coronoid process
and the maxillary tuberosity, in common with the buccinator.
_Insertion._—The lower lip.
_Action._—To depress and retract the lower lip.
_Structure._—The tendon of origin and the belly are fused with the
buccinator as far forward as the first cheek tooth. From this point
forward the belly is distinct and rounded, terminating in a tendon which
spreads out in the lower lip, blending with the orbicularis and the
muscle of the opposite side.
_Relations._—Superficially, the skin, masseter, facial vessels, and
parotid duct; deeply, the mandible and inferior labial artery.
_Blood-supply._—Facial artery.
_Nerve-supply._—Facial nerve.
9. =Buccinator.=—This muscle lies in the lateral wall of the mouth,
extending from the angle of the mouth to the maxillary tuberosity.
_Origin._—The external surface of the maxilla above the interdental
space and the molar teeth; the alveolar border of the mandible at the
interdental space and also posteriorly where it turns upward to the
coronoid process; the pterygo-mandibular ligament.
_Insertion._—The angle of the mouth, blending with the orbicularis oris.
_Action._—To flatten the cheeks, thus pressing the food between the
teeth; also to retract the angle of the mouth.
_Structure._—Two layers may be recognized. The =superficial layer= (Pars
buccalis) extends from the angle of the mouth to the masseter. It is
incompletely pennate, having a longitudinal raphé on which most of the
muscle-fibers converge. The upper fibers are directed chiefly downward
and backward, the lower ones upward and backward. The =deep layer= (Pars
molaris) consists mainly of longitudinal fibers. It blends in part with
the superficial layer of the orbicularis; it has a small tendinous
attachment to the coronoid process behind, and is united below with the
depressor labii inferioris.
_Relations._—Superficially, the skin and fascia, the zygomaticus,
levator nasolabialis, lateral dilator of the nostril, the superior
buccal glands, the parotid duct, the facial vessels, and branches of the
facial nerve; deeply, the mucous membrane of the mouth and the inferior
buccal glands.
_Blood-supply._—Facial and buccinator arteries.
_Nerve-supply._—Facial nerve.
MUSCLES OF THE NOSTRILS
1. =Levator nasolabialis.=—This has been described (p. 214).
2. =Dilatator naris lateralis= (M. caninus).—This thin, triangular
muscle lies on the lateral nasal region, and passes between the two
branches of the levator nasolabialis.
_Origin._—The maxilla, close to the anterior extremity of the facial
crest.
_Insertion._—The outer wing of the nostril.
[Illustration:
FIG. 174.—NASAL AND SUPERIOR LABIAL MUSCLES OF HORSE.
_a_, _a′_, Dilatator naris transversus; _b_, levator labii superioris
proprius; _b′_, tendon of _b_; _b″_, common tendon of two levatores
labii superioris proprii; _c_, _c′_, dilatator naris inferior; _d_,
_e_, dilatator naris superior; _f_, orbicularis oris; _g_, levator
nasolabialis, a portion of which is removed; _h_, dilatator naris
lateralis (cut); _i_, cornu of alar cartilage; _k_, nostril; _k′_,
false nostril; _l_, nasal diverticulum; _m_, nasal bone. (After
Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
_Action._—To dilate the nostril.
_Structure._—The muscle has a flat tendon of origin, passes between the
two branches of the levator nasolabialis, and spreads out in the
external wing of the nostril. The lower fibers blend with the
orbicularis oris.
_Relations._—Superficially, the skin, fascia, and the labial branch of
the levator nasolabialis; deeply, the maxilla and the nasal branch of
the levator nasolabialis.
_Blood-supply._—Facial artery.
_Nerve-supply._—Facial nerve.
3. =Dilatator naris transversus= (M. transversus nasi).—This is an
unpaired, quadrilateral muscle, which lies between the nostrils. It
consists of two layers.
_Attachments._—Superficial layer, the superficial faces of the laminæ of
the alar cartilages; deep layer, the convex edges of the cornua of the
same.
_Action._—To dilate the nostrils.
_Structure._—It is composed of transverse fleshy fibers, which blend
below with the orbicularis.
_Relations._—Superficially, the skin, fascia, and tendinous expansion of
the levator labii superioris proprius; deeply, the alar cartilages, the
extremity of the septum nasi, and the palato-labial artery.
_Blood-supply._—Palato-labial artery.
_Nerve-supply._—Facial nerve.
4. =Dilatator naris superior= (Pars dorsalis m. lateralis nasi).—This
very thin muscle occupies the angle between the nasal process of the
premaxilla and the nasal bone.
_Origin._—The lateral border of the nasal bone.
_Insertion._—The inner wall of the false nostril and the parietal lamina
of the septal cartilage.
_Action._—To dilate the vestibule of the nasal cavity.
_Structure._—Fleshy.
_Relations._—Superficially, the skin, fascia, and levator labii
superioris proprius; deeply, the parietal cartilage and false nostril.
_Blood-supply._—Facial artery.
_Nerve-supply._—Facial nerve.
5. =Dilatator naris inferior= (Pars ventralis m. lateralis nasi).—This
is a similar but thicker muscle, which lies on the nasal process of the
premaxilla.
_Origin._—The maxilla and the nasal process of the premaxilla.
_Insertion._—The cartilaginous prolongations of the turbinal bones and
the inner wall of the false nostril.
_Action._—To rotate the turbinal outward and dilate the nostril and the
vestibule of the nasal cavity.
_Structure._—Fleshy. A division into two or more parts may be
recognized. A small part posteriorly is inserted into the cartilage of
the dorsal turbinal bone, while the bulk of the muscle is inserted into
the cartilage of the ventral turbinal bone. A few fibers also pass
between the cornu of the alar cartilage and the outer wing of the
nostril.
_Relations._—Superficially, the levator labii superioris proprius, the
levator nasolabialis, and the lateral nasal artery; deeply, the maxilla,
the premaxilla, and the anterior nasal branch of the infraorbital nerve.
_Blood-supply._—Facial artery.
_Nerve-supply._—Facial nerve.
MUSCLES OF THE EYELIDS
1. =Orbicularis oculi.=—This is a flat, elliptical, sphincter muscle,
situated in and around the eyelids, the portion in the upper lid being
much broader than that in the lower. The chief attachment is to the skin
of the lids, but some bundles are attached to the palpebral ligament at
the inner canthus and to the lacrimal bone. Its action is to close the
lids.
2. =Corrugator supercilii.=—This is a very thin, small muscle, which
arises over the root of the supraorbital process and spreads out in the
upper eyelid, blending with the orbicularis. Its action is to assist in
raising the upper lid or, especially in pathological conditions, to
wrinkle the skin.
3. =Malaris.=—This is a very thin muscle, which varies much in different
subjects. It extends from the fascia in front of the orbit to the lower
lid. Its action is to depress the lower lid.
The foregoing muscles receive their blood-supply from the facial,
transverse facial, supraorbital, and infraorbital arteries; the
nerve-supply is derived from the facial nerve.
4. =Levator palpebræ superioris.=—This slender, flat muscle is almost
entirely within the orbital cavity. It arises on the pterygoid crest,
passes forward above the rectus oculi superior and below the lacrimal
gland, and terminates in a thin tendon in the upper lid.
_Action._—To elevate the upper lid.
_Blood-supply._—Ophthalmic artery.
_Nerve-supply._—Oculomotor nerve.
MUSCLES OF MASTICATION
The muscles of this group are six in number in the horse. They arise
chiefly from the upper jaw and the base of the cranium, and are all
inserted into the mandible.
1. =Masseter.=—This muscle extends from the zygomatic arch and facial
crest over the broad part of the mandibular ramus. It is semi-elliptical
in outline.
_Origin._—By a strong tendon from the zygomatic arch and the facial
crest.
_Insertion._—The outer surface of the broad part of the ramus of the
mandible.
_Action._—Its action is to bring the jaws together. Acting singly, it
also carries the lower jaw toward the side of the contracting muscle.
_Structure._—The superficial face of the muscle in its upper part is
covered by a strong, glistening aponeurosis, and several tendinous
intersections partially divide the muscle into layers. The fibers of the
superficial layer take origin from the malar and maxilla only, and
diverge somewhat to their insertion close to the thick ventral border of
the lower jaw. The fibers of the deep layer arise from the entire area
of origin, and pass straight to the border of the mandible; it will be
noted that a small part, near the temporo-maxillary joint, is not
covered by the superficial layer. The two layers are separable only
above and behind; elsewhere they are fused.
_Relations._—Superficially, the skin and panniculus, the parotid gland,
the transverse facial and masseteric vessels, and the facial nerve;
deeply, the ramus of the mandible, the buccinator, depressor labii
inferioris, and mylo-hyoideus muscles, the superior buccal glands, the
buccinator nerve, and two large varicose veins which join the facial
vein at the anterior edge of the muscle. The facial vessels and parotid
duct run along the anterior edge of the muscle; the duct, however, bends
forward about the middle of the border and leaves the muscle.
_Blood-supply._—Transverse facial and masseteric arteries.
_Nerve-supply._—Mandibular nerve.
2. =Temporalis.=—This muscle occupies the temporal fossa.
_Origin._—The rough part of the temporal fossa and the crests which
surround it.
_Insertion._—The coronoid process of the mandible, which it envelops.
_Action._—Chiefly to raise the lower jaw, acting with the masseter and
internal pterygoid muscles.
_Structure._—The surface of the muscle is covered with a glistening
aponeurosis, and strong tendinous intersections are found in its
substance. The inner edge of the muscle is quite thin, but as the fibers
converge toward the much smaller area of insertion, the muscle becomes
nearly an inch thick. It fuses somewhat with the masseter.
_Relations._—Superficially, the scutiform cartilage and anterior muscles
of the external ear and the orbital fat; deeply, the temporal fossa and
the deep temporal vessels and nerves.
_Blood-supply._—Superficial and deep temporal, and mastoid arteries.
_Nerve-supply._—Mandibular nerve.
3. =Pterygoideus internus= (s. medialis).—This muscle occupies a
position on the inner surface of the ramus of the mandible similar to
that of the masseter on the outside.
_Origin._—The crest formed by the pterygoid process of the sphenoid and
the palate bone.
_Insertion._—The concave inner surface of the broad portion of the ramus
of the mandible, and the inner lip of the lower border.
_Action._—Acting together, to raise the lower jaw; acting singly, to
produce also lateral movement of the jaw.
_Structure._—The muscle is capable of division into two parts. The
principal part is superficial (internal), and its fibers are, for the
most part, vertical in direction. It contains much tendinous tissue
(septa). The smaller portion is external to the foregoing, and its
fibers are directed downward and backward.
[Illustration:
FIG. 175.—SAGITTAL SECTION OF HEAD OF HORSE, SHOWING DEEP
PTERYGO-MAXILLARY REGION, AND NASAL AND CRANIAL CAVITIES.
_1_, Cerebral compartment of cranial cavity; _2_, cerebellar
compartment of same; _3_, tentorium osseum; _4_, tentorium
cerebelli; _5_, sphenoidal sinus; _6_, hamulus of pterygoid
bone-tendon of tensor palati cut off short at anterior border of
hamulus; _7_, mylo-glossus. The olfactory mucous membrane is shaded.
]
_Relations._—Externally, the ramus of the mandible, the external
pterygoid muscle, the inferior alveolar vessels and nerve, and the
lingual and mylo-hyoid nerves; internally, the great cornu of the hyoid
bone, the tensor palati, pterygo-pharyngeus, palato-pharyngeus,
mylo-hyoideus, digastricus, and stylo-hyoideus muscles, the guttural
pouch, the external maxillary vessels, the ninth and twelfth nerves, the
submaxillary salivary gland, the submaxillary and parotid ducts, and the
submaxillary and pharyngeal lymph glands.
_Blood-supply._—Internal maxillary, masseteric, and inferior alveolar
arteries.
_Nerve-supply._—Mandibular nerve.
4. =Pterygoideus externus= (=s. lateralis=).—This muscle is considerably
smaller than the preceding one, and is situated external to its upper
part.
_Origin._—The external surface of the pterygoid process of the sphenoid
bone.
_Insertion._—The inner surface of the neck and the inner part of the
anterior border of the condyle of the mandible.
_Action._—Acting together, to draw the lower jaw forward; acting singly,
to move the jaw laterally, _i. e._, toward the side opposite to the
muscle acting. The latter action is due to the fact that the origin is
nearer to the median plane than the insertion.
[Illustration:
FIG. 176.—SUBMAXILLARY AND LARYNGEAL REGIONS OF HORSE, AFTER REMOVAL
OF SKIN AND PANNICULUS.
_c_, Mastoido-humeralis; _d_, sterno-cephalicus; _e_, omo-hyoideus and
sterno-hyoideus; _h_, buccinator; _i_, depressor labii inferioris;
_m_, masseter; _v_, stylo-maxillaris; _w_, mylo-hyoideus; _2_,
posterior, _3_, anterior, border of external ear; _30′_, angle of
jaw; _36_, submaxillary lymph glands; _37_, external maxillary vein;
_39_, facial continuation of _37_; _40_, parotid duct; _44_, parotid
gland; _45_, prominence of chin; _x_, wing of atlas. (After
Ellenberger-Baum, Anat. für Künstler.)
]
_Structure._—The muscle is almost entirely fleshy, and the fibers are
almost longitudinal in direction. Some of them are inserted into the
edge of the interarticular meniscus.
_Relations._—Externally, the temporo-maxillary articulation and the
temporalis muscle; internally, the internal pterygoid and tensor palati
muscles. The internal maxillary artery crosses the lower face of the
muscle and dips in between it and the tensor palati. The mandibular
nerve lies on the ventral surface, and the buccinator nerve perforates
the origin of the muscle.
_Blood-supply._—Internal maxillary and inferior alveolar arteries.
_Nerve-supply._—Mandibular nerve.
5. =Stylo-maxillaris= (s.-mandibularis) (M. jugulomandibularis).—This is
a short muscle extending from the paramastoid or styloid process of the
occipital bone to the posterior border of the lower jaw; it is covered
by the parotid gland.
_Origin._—The paramastoid or styloid process of the occipital bone, in
common with the posterior belly of the digastricus.
_Insertion._—The posterior border of the ramus of the mandible.
_Action._—To depress the lower jaw and open the mouth.
_Structure._—The muscle contains a good deal of tendinous tissue. It
blends with the posterior belly of the digastricus.
_Relations._—Superficially, the parotid gland, the tendon of the
sterno-cephalicus, and the fibrous expansion which connects it with the
tendon of the mastoido-humeralis; deeply, the guttural pouch, the
external carotid artery, the ninth and twelfth nerves, the pharynx, and
the submaxillary gland.
_Blood-supply._—External carotid artery.
_Nerve-supply._—Facial nerve.
6. =Digastricus.=—This muscle is composed of two fusiform, flattened
bellies, united by a round tendon.
_Origin._—The paramastoid or styloid process of the occipital bone, in
common with the preceding muscle.
_Insertion._—The inner surface of the lower border of the mandible
behind the symphysis.
_Action._—It assists in depressing the lower jaw and opening the mouth.
If the mandible be fixed and both bellies contract, the hyoid bone and
the base of the tongue are raised, as in the first phase of deglutition.
_Structure._—The posterior belly has the appearance of a branch detached
from the inner surface of the stylo-maxillaris. It passes downward and
forward, and is succeeded by a small rounded tendon. The latter
perforates the tendon of insertion of the stylo-hyoideus, and is
provided with a =synovial sheath=. The anterior belly is larger and
terminates by thin tendinous bundles.
_Relations._—The posterior belly has practically the same relations as
the stylo-maxillaris. The intermediate tendon is in contact externally
with the internal pterygoid muscle, the submaxillary gland and duct, and
the external maxillary artery. The anterior belly lies in the
submaxillary space between the ramus of the jaw and the mylo-hyoideus
muscle; the sublingual vessels run along its upper border.
_Blood-supply._—External carotid and sublingual arteries.
_Nerve-supply._—Facial and mandibular nerves.
THE HYOID MUSCLES
This group consists of eight muscles, one of which, the hyoideus
transversus, is unpaired.
1. =Mylo-hyoideus.=—This muscle, together with its fellow, forms a sort
of sling between the two rami of the lower jaw, in which the tongue is
supported.
_Origin._—The inner surface of the alveolar border of the mandible.
_Insertion._—(1) A median fibrous raphé extending from the symphysis to
the hyoid bone; (2) the lingual process and body of the hyoid bone.
_Action._—It raises the floor of the mouth, the tongue, and the hyoid
bone.
_Structure._—Each muscle consists of a thin curved sheet, the fibers
passing downward from their origin and then curving toward the median
raphé. It is chiefly fleshy, and is thickest behind. The anterior
superficial part of the muscle is termed the mylo-glossus.
_Relations._—On the superficial surface of the muscles are the ramus,
the internal pterygoid and digastricus muscles, and the submaxillary
lymph glands. The deep surface is in contact with the mucous membrane of
the mouth, the stylo-glossus, hyo-glossus, and genio-hyoideus muscles,
the sublingual gland and vessels, the submaxillary duct, and the lingual
and hypoglossal nerves.
_Blood-supply._—Sublingual artery.
_Nerve-supply._—Mylo-hyoid branch of the mandibular nerve.
2. =Stylo-hyoideus.=—This is a slender, fusiform muscle, having a
direction nearly parallel to that of the great cornu of the hyoid bone
(Fig. 436).
_Origin._—The heel-like prominence on the proximal extremity of the
great cornu of the hyoid bone.
_Insertion._—The anterior part of the thyroid cornu of the hyoid bone.
_Action._—It draws the base of the tongue and the larynx upward and
backward.
_Structure._—It arises by a thin, short tendon, and has a fusiform
belly. The tendon of insertion is perforated for the passage of the
intermediate tendon of the digastricus, and at this point there is a
small synovial sheath.
_Relations._—Superficially, the internal pterygoid muscle and the
parotid gland; deeply, the guttural pouch, the pharynx, the external
carotid and maxillary arteries, and the hypoglossal nerve.
_Blood-supply._—External carotid artery.
_Nerve-supply._—Facial nerve (stylo-hyoid branch).
3. =Occipito-hyoideus= (M. jugulo-hyoideus; occipito-styloideus).—This
is a small triangular muscle, which lies in the space between the
paramastoid process and the great cornu of the hyoid bone.
_Origin._—The paramastoid (styloid) process of the occipital bone.
_Insertion._—The proximal extremity and ventral edge of the great cornu
of the hyoid bone.
_Action._—It carries the distal extremity of the great cornu backward
and upward. Acting with the genio-hyoideus and digastricus, it raises
the hyoid bone and the larynx.
_Structure._—The muscle is somewhat triangular, its fibers being longer
as the ventral border is approached. It blends with the posterior belly
of the digastricus.
_Relations._—Superficially, the parotid gland; deeply, the guttural
pouch.
_Blood-supply._—Occipital artery.
_Nerve-supply._—Facial nerve.
4. =Genio-hyoideus.=—This is a long, spindle-shaped muscle, which lies
under the tongue in contact with its fellow of the opposite side (Fig.
243).
_Origin._—The angle of union of the rami of the mandible.
_Insertion._—The extremity of the lingual process of the hyoid bone.
_Action._—It draws the hyoid bone and tongue forward.
_Structure._—The muscle arises by a short tendon, which is succeeded by
the belly, composed of long bundles of parallel fibers.
_Relations._—Below, the mylo-hyoideus; above, the hyo-glossus,
stylo-glossus, genio-glossus, the sublingual gland, submaxillary duct,
and the lingual nerve.
_Blood-supply._—Sublingual artery.
_Nerve-supply._—Hypoglossal nerve.
5. =Kerato-hyoideus.=—This small triangular muscle lies in the space
between the thyroid and small cornu, under cover of the hyo-glossus
(Fig. 243).
_Origin._—The posterior edge of the small cornu and the adjacent part of
the ventral border of the great cornu.
_Insertion._—The dorsal edge of the thyroid cornu.
_Action._—It raises the thyroid cornu and the larynx.
_Relations._—The muscle is crossed outwardly by the lingual artery.
_Blood-supply._—Lingual artery.
_Nerve-supply._—Glosso-pharyngeal nerve.
6. =Hyoideus Transversus.=—This is a thin, unpaired muscle, which
extends transversely between the two small cornua of the hyoid bone.
_Attachments._—The small cornua close to the junction with the great
cornua.
_Action._—When relaxed, its upper surface is concave; when it contracts,
it elevates the root of the tongue.
_Structure._—Fleshy, composed of parallel transverse bundles.
_Blood-supply._—Lingual artery.
_Nerve-supply._—Glosso-pharyngeal nerve.
7. =Sterno-thyro-hyoideus=, and
8. =Omo-hyoideus.=—These are described with the muscles on the ventral
surface of the neck.
THE FASCIÆ AND MUSCLES OF THE NECK
It is convenient to divide the muscles of the neck into ventral and
lateral groups, the two lateral groups being separated from each other
by the ligamentum nuchæ.
THE FASCIÆ OF THE NECK
The =superficial fascia= is in part two-layered, and contains the
cervical portion of the panniculus. The fasciæ of the right and left
sides are attached along the dorsal line of the neck to the ligamentum
nuchæ, while along the ventral line they meet in a fibrous raphé. A deep
layer is detached which passes underneath the panniculus, bridges over
the jugular furrow, and crosses over the deep face of the
mastoido-humeralis and omo-hyoideus to join the superficial layer. It
again separates to pass under the cervical trapezius, and become
attached to the ligamentum nuchæ. Along the ventral line a septum is
detached which separates the sterno-cephalici. Two other layers in front
of the shoulder inclose the prescapular lymph glands.
The =deep fascia= also forms two layers. The =superficial layer= is
attached to the wing of the atlas and the lower edge of the
trachelo-mastoideus and scalenus. Passing downward, it incloses the
trachea, and, together with the deep layer, furnishes sheaths for the
vagus and sympathetic nerves and the carotid artery. Passing upward it
detaches septa between the extensor muscles of the spine. Anteriorly it
covers the thyroid gland, the guttural pouch, the adjacent vessels and
nerves and the larynx, and is attached to the mastoid process of the
temporal bone and the thyroid cornu of the hyoid bone. Posteriorly, it
is attached to the first rib and the cariniform cartilage of the
sternum. The =deep layer= (prevertebral fascia) covers the ventral
surface of the longus colli, and incloses the trachea and œsophagus.
Anteriorly, it forms, with the corresponding layer of the opposite side,
a septum between the guttural pouches; posteriorly, it becomes
continuous with the endothoracic fascia. A =fascia propria= forms a
tubular sheath around the trachea, inclosing also the recurrent nerves.
VENTRAL MUSCLES
This group consists of eleven pairs of muscles which lie almost entirely
ventral to the vertebræ.
1. =Panniculus carnosus.=—The =cervical panniculus= (platysma myoides of
man) has a fleshy origin on the cariniform cartilage (manubrium) of the
sternum. it passes forward, outward, and upward, crossing over the
sterno-cephalicus and jugular furrow obliquely. On reaching the surface
of the mastoido-humeralis it adheres closely to this muscle, and soon
thins out, to be continued over the splenius and trapezius by an
aponeurosis which is difficult to remove from the latter muscle.
Scattered bundles may be traced on the ventral surface of the neck to
the facial portion. The right and left muscles meet at a ventral median
raphé in pennate fashion.
[Illustration:
FIG. 177.—ANTERO-LATERAL VIEW OF MUSCLES AND SKELETON OF HORSE.
_a_, Trapezius; _c_, mastoido-humeralis; _d_, sterno-cephalicus; _f_,
long head of triceps; _f′_, external head of triceps; _g_, anterior
superficial pectoral muscle; _g′_, posterior superficial pectoral;
_h′_, anterior deep pectoral; _v_, cervical panniculus; _z_,
supraspinatus; _29_, omo-hyoideus; _30_, sterno-thyro-hyoideus;
_31_, jugular vein; _32_, cephalic vein; _1_, scapula; _1′_,
cartilage of scapula; _2_, spine of scapula; _4_, shaft of humerus;
_4′_, external epicondyle; _5_, external tuberosity of humerus; _6_,
deltoid tuberosity; _14_, ventral border (“keel”) of sternum; _14′_,
cariniform cartilage; l.R., first rib. (After Ellenberger-Baum,
Anat. für Künstler.)
]
2. =Mastoido-humeralis.=—This is described on p. 252.
3. =Sterno-cephalicus= (Sterno-maxillaris s.-mandibularis).[42]—This is
a long, narrow muscle, extending along the ventral and lateral aspects
of the trachea from the sternum to the angle of the jaw. It forms the
ventral boundary of the jugular furrow.
_Origin._—The cariniform cartilage of the sternum.
_Insertion._—The posterior border of the lower jaw.
_Action._—Acting together, to flex the head and neck; acting singly, to
incline the head and neck to the side of the muscle contracting.
_Structure._—The two muscles are fused at their origin, which is fleshy.
Near the middle of the neck they separate, and, becoming thinner, each
muscle passes under the parotid gland and terminates in a flat tendon.
_Relations._—Superficially, the cervical panniculus; deeply, the
sterno-thyro-hyoideus and omo-hyoideus muscles. The upper edge of the
muscle is related to the jugular vein, which lies in the jugular furrow.
The carotid artery, the vagus, sympathetic, and recurrent nerves also
lie along the upper edge at the root of the neck. The tendon passes
under the submaxillary vein and the parotid gland, having the
submaxillary gland and stylo-maxillaris muscle on its inner side.
_Blood-supply._—Carotid artery.
_Nerve-supply._—Ventral branches of the spinal accessory and first
cervical nerves.
4. =Sterno-thyro-hyoideus= (Sterno-thyroideus et sterno-hyoideus).—This
is a long, slender, digastric muscle, applied to the ventral surface of
the trachea and its fellow of the opposite side.
_Origin._—The cariniform cartilage of the sternum.
_Insertion._—(1) The external surface of the thyroid cartilage of the
larynx; (2) the body of the hyoid bone.
_Action._—To depress and retract the hyoid bone, the base of the tongue,
and the larynx, as in deglutition. It may also fix the hyoid bone when
the depressors of the tongue are acting, as in suction.
_Structure._—The origin of the muscle is fleshy, and as far as the
middle of the neck it blends with its fellow. The common belly is then
interrupted by a tendon, or sometimes two tendons, from which arise
three or four fleshy bands. The lateral bands diverge to reach their
insertion into the thyroid cartilage; while the inner bands, closely
applied to each other and blending with the omo-hyoideus, pass straight
forward to reach the ventral surface of the hyoid bone.
_Relations._—At the root of the neck the common belly has the
sterno-cephalicus below, and the carotid arteries and recurrent nerves
above. Further forward the trachea becomes the upper relation, and near
the head the skin and fascia, the lower one.
_Blood-supply._—Carotid artery.
_Nerve-supply._—Ventral branch of the first cervical nerve.
5. =Omo-hyoideus= (Subscapulo-hyoideus).—This is a thin, ribbon-like
muscle, almost entirely fleshy, which crosses the trachea very obliquely
under cover of the mastoido-humeralis.
_Origin._—The subscapular fascia close to the shoulder joint.
_Insertion._—The body of the hyoid bone, in common with the hyoid branch
of the preceding muscle.
_Action._—To depress the hyoid bone.
_Structure._—The muscle is composed of parallel fleshy fibers, except at
its origin, where it has a thin tendon.
_Relations._—In the first part of its course the muscle passes forward
between the supraspinatus, anterior deep pectoral, mastoido-humeralis
(outwardly), and the scalenus (inwardly). It is intimately adherent to
the mastoido-humeralis. In the middle of the neck it is related
superficially to the mastoido-humeralis, sterno-cephalicus, and the
jugular vein; deeply, to the rectus capitis anterior major, the carotid
artery, the vagus, sympathetic, and recurrent nerves, the trachea, and,
on the left side, the œsophagus. In its anterior part the muscle blends
with the hyoid part of the sterno-thyro-hyoideus, the two covering the
thyroid portion of the latter muscle, the thyroid gland, and the ventral
face of the larynx.
_Blood-supply._—Carotid and inferior cervical arteries.
_Nerve-supply._—Ventral branches of the cervical nerves.
6. =Scalenus= (M. scalenus primæ costæ).—This muscle is deeply situated
on the side of the posterior half of the neck. It is composed of two
parts, between which the roots of the brachial plexus of nerves emerge.
_Origin._—The anterior border and outer surface of the first rib.
_Insertion._—(1) The dorsal (smaller) portion is attached to the
transverse process of the seventh cervical vertebra; (2) the ventral
portion is attached to the transverse processes of the sixth, fifth, and
fourth cervical vertebræ.
_Action._—The neck is flexed or inclined laterally, according as the
muscles act together or singly. If the neck be the fixed point, the
muscle may have a respiratory action by pulling forward or fixing the
first rib.
_Structure._—The dorsal portion is composed of three or four fleshy
bundles.[43] The ventral portion, which is much larger, is almost
entirely fleshy, and not so divided.
_Relations._—Superficially, the anterior deep pectoral,
mastoido-humeralis, and omo-hyoideus muscles, the phrenic nerve, and the
other branches of the brachial plexus; deeply, the vertebræ, the longus
colli and intertransversales muscles, the œsophagus (on the left side),
the trachea (on the right side), the vertebral vessels, the vagus,
sympathetic, and recurrent nerves. The roots of the brachial plexus form
a flat anastomosis, which lies between the two portions of the muscle.
The brachial vessels cross the ventral edge close to the first rib.
_Blood-supply._—Carotid, vertebral, and inferior cervical arteries.
_Nerve-supply._—Ventral branches of the cervical nerves.
7. =Rectus capitis anterior major= (M. longus capitis).—This is the
largest of the three special flexors of the head, and lies along the
ventro-lateral surface of the anterior cervical vertebræ and the base of
the cranium.
_Origin._—The transverse processes of the fifth, fourth, and third
cervical vertebræ.
_Insertion._—The tubercles at the junction of the basilar process of the
occipital bone with the body of the sphenoid.
_Action._—Acting together, to flex the head; acting singly, to incline
it to the same side also.
_Structure._—The origin of the muscle is by fleshy digitations. The
belly increases in size by the union of these digitations, reaching its
maximum at the axis. It then diminishes, passes toward the median plane,
and terminates on a rounded tendon.
_Relations._—Superficially, the mastoido-humeralis, omo-hyoideus, and
rectus capitis anticus minor, the submaxillary gland, the carotid artery
(which lies along the lower border), the occipital and internal carotid
arteries, and the tenth, eleventh, and sympathetic nerves; deeply, the
vertebræ, the longus colli, intertransversales, and the small straight
muscle. The terminal part of the muscle lies in contact with its fellow
above the pharynx and between the guttural pouches.
_Blood-supply._—Carotid, vertebral, and occipital arteries.
_Nerve-supply._—Ventral branches of the cervical nerves.
8. =Rectus capitis anterior minor= (M. rectus capitis ventralis).—This
is a small muscle which lies under cover of the preceding one.
_Origin._—The ventral arch of the atlas.
_Insertion._—The basilar process, close to the preceding muscle.
_Action._—To flex the occipito-atlantal articulation.
_Structure._—Fleshy.
_Relations._—Below, to the preceding muscle; above, to the atlas,
occipito-atlantal articulation, and the basilar process; externally, to
the rectus capitis lateralis and the guttural pouch.
_Blood-supply._—Occipital artery.
_Nerve-supply._—Ventral branch of the first cervical nerve.
9. =Rectus capitis lateralis.=—This is a still smaller, entirely fleshy
muscle, which lies for the most part under the small oblique muscle.
_Origin._—The atlas, external to the preceding muscle.
_Insertion._—The paramastoid or styloid process of the occipital bone.
_Action._—The same as the preceding muscle.
_Structure_.—Fleshy.
_Relations._—Superficially, the small oblique muscle, the occipital
vessels, and the ventral branch of the first cervical nerve.
_Blood-supply._—Occipital artery.
_Nerve-supply._—Ventral branch of the first cervical nerve.
10. =Longus colli.=—This muscle covers the ventral surface of the
vertebræ, from the sixth thoracic to the atlas, and is united with its
fellow. It consists of two portions, thoracic and cervical.
_Origin._—(1) Thoracic portion, the bodies of the first six thoracic
vertebræ; (2) cervical portion, the transverse processes of the cervical
vertebræ.
_Insertion._—(1) Thoracic portion, the bodies and transverse processes
of the last two cervical vertebræ; (2) cervical portion, the bodies of
the cervical vertebræ and the tubercle on the ventral surface of the
atlas.
_Action._—To flex the neck.
_Structure._—The muscle is composed of a succession of bundles. The
largest of these constitute the thoracic part of the muscle, which has a
strong tendon inserted into the last two cervical vertebræ. A bursa is
interposed between the tendon and the spine at the first costo-vertebral
articulation. The cervical portion consists of a number of smaller
bundles, each of which passes from its origin on the transverse process
of one vertebra forward and inward to its insertion into a vertebra
further forward. The most anterior bundle is inserted by a strong tendon
into the ventral tubercle of the atlas.
_Relations._—The principal relations of the two muscles in the thorax
are: ventrally, the pleura, and, further forward, the trachea and
œsophagus; dorsally, the vertebræ and the costo-vertebral joints;
laterally, the dorsal, superior cervical, and vertebral vessels, the
sympathetic nerve, and the thoracic roots of the brachial plexus. In
the neck, important relations are: ventrally, the trachea and
œsophagus, the carotid artery, the vagus, sympathetic and recurrent
nerves; dorsally, the vertebræ and, in the middle third of the neck,
the intertransversales muscles; laterally, the scalenus, the rectus
capitis anticus major, and the intertransversales (in the anterior
third). The terminal part of the muscle is separated from the trachea
by the œsophagus, which is here median in position.
_Blood-supply._—Subcostal and vertebral arteries.
_Nerve-supply._—Ventral branches of the spinal nerves.
11. =Intertransversales colli= (Mm. intertransversarii cervicis).—These
are six fasciculi which occupy the spaces between the lateral aspects of
the vertebræ and the transverse and articular processes. There is thus a
bundle for each intervertebral articulation except the first. Each
bundle consists of a dorsal and ventral portion.
_Attachments._—The dorsal bundles pass from transverse process to
articular process; the ventral bundles extend between adjacent
transverse processes.
_Action._—To bend the neck laterally.
_Structure._—They contain strong tendinous intersections.
_Relations._—Superficially, the mastoido-humeralis, rectus capitis
anterior major, complexus, trachelo-mastoideus, splenius, scalenus, and
longissimus muscles; deeply, the vertebræ, the longus colli muscle, and
the vertebral vessels. The muscles are perforated by branches of these
vessels and by the primary branches of the cervical nerves.
_Blood-supply._—Vertebral artery.
_Nerve-supply._—The cervical nerves.
LATERAL MUSCLES
This group consists of twelve pairs of muscles arranged in layers.
FIRST LAYER
1. =Trapezius cervicalis.=—Described on p. 250.
SECOND LAYER
2. =Rhomboideus cervicalis.=—Described on p. 251.
3. =Serratus magnus= (M. serratus cervicis).—Described with the thoracic
part on p. 254.
THIRD LAYER
4. =Splenius.=—This is an extensive, flat, triangular muscle, partly
covered by the preceding three muscles.
_Origin._—The second, third, and fourth thoracic spines by means of the
dorso-scapular ligament, and the funicular portion of the ligamentum
nuchæ.
_Insertion._—The occipital crest, the mastoid process, the wing of the
atlas, and the transverse processes of the third, fourth, and fifth
cervical vertebræ.
_Action._—Acting together, to elevate the head and neck; acting singly,
to incline the head and neck to the side of the muscle acting.
_Structure._—The muscle arises in the withers from the anterior part of
the dorso-scapular ligament, which also affords attachment to the
rhomboideus, serratus anticus, and complexus muscles. The fibers pass
upward and forward toward the head and the first cervical vertebra. The
insertion on the occipital bone and the mastoid process is by means of a
thin aponeurosis common to the splenius, trachelo-mastoideus, and
mastoido-humeralis. The atlantal insertion is by a strong, flat tendon,
also in common with these muscles. The remaining insertions are fleshy
digitations.
_Relations._—Superficially, the skin and fascia, the trapezius
rhomboideus, cervicalis, serratus magnus, and posterior auricular
muscles; deeply, the complexus, trachelo-mastoideus, and longissimus
muscles.
_Blood-supply._—Deep cervical and dorsal arteries.
_Nerve-supply._—Dorsal branches of the last six cervical nerves.
FOURTH LAYER
5. =Trachelo-mastoideus= (M. longissimus capitis et atlantis).—This
muscle consists of two parallel, fusiform portions. It lies between the
deep face of the splenius and the ventral part of the complexus.
_Origin._—(1) The transverse processes of the first two thoracic
vertebræ; (2) the articular processes of the cervical vertebræ.
_Insertion._—(1) The mastoid process; (2) the wing of the atlas.
[Illustration:
FIG. 178.—SUPERFICIAL MUSCLES OF HORSE.
The panniculus, except the cervical part, has been removed. _a_,
Trapezius cervicalis; _a′_, trapezius thoracalis; _c_, _c′_,
mastoido-humeralis; _d_, sterno-cephalicus; _e_, deltoid; _f_, long
head of triceps; _f′_, external head of triceps; _g_, anterior
superficial pectoral; _h_, posterior deep pectoral; _h′_, anterior
deep pectoral; _i_, serratus thoracis; _i′_, serratus cervicis; _k_,
latissimus dorsi; _l_, obliquus abdominis externus; _l′_,
aponeurosis of _l_; _m_, serratus posticus; _m′_, lumbo-dorsal
fascia; _o_, tensor fasciæ latæ; _o′_, fascia lata; _o″_, gluteus
superficialis; _q_, _q′_, _q″_, biceps femoris; _r_, semitendinosus;
_s_, sacro-coccygeus superior; _t_, sacro-coccygeus lateralis; _u_,
coccygeus; _v_, cervical panniculus; _w_, splenius; _x_,
rhomboideus; _y_, tendon of trachelo-mastoideus and
mastoido-humeralis; _z_, suprasinatus; _X_, wing of atlas; _2_,
spine of scapula; _4′_, external epicondyle of humerus; _6_, deltoid
tuberosity; _8_, olecranon; _16_, external angle of ilium; _20_,
patella; _21′_, external condyle of tibia. (After Ellenberger-Baum,
Anat. für Künstler.)
]
_Action._—Acting together, to extend the head and neck; acting singly,
to flex the head and neck laterally or to rotate the atlas.
_Structure._—The origin from the thoracic vertebræ is by aponeurotic
slips which blend with the complexus. The succeeding fleshy portion, in
passing along the neck, receives fasciculi from each of the cervical
vertebræ except the first two. The dorsal division of the muscle is
inserted into the mastoid process by a flat tendon which fuses with that
of the splenius; the ventral division is inserted into the wing of the
atlas by a ribbon-like tendon in common with the splenius and
mastoido-humeralis.
_Relations._—Superficially, the splenius muscle and dorsal branches of
the cervical nerves; deeply, the complexus, the spinalis colli, and the
oblique muscles of the head. The superior cervical vessels cross the
deep face of the muscle obliquely at the level of the sixth and seventh
cervical vertebræ.
_Blood-supply._—Vertebral and superior cervical arteries.
_Nerve-supply._—Dorsal branches of the last six cervical nerves.
6. =Complexus= (M. semispinalis capitis).—This is a large triangular
muscle which lies chiefly on the ligamentum nuchæ, under cover of the
splenius and trachelo-mastoideus muscles.
_Origin._—(1) The second, third, and fourth thoracic spines, in common
with the splenius and serratus anticus; (2) the transverse processes of
the first six or seven thoracic vertebræ; (3) the articular processes of
the cervical vertebræ.
_Insertion._—The posterior surface of the occipital bone, external to
the funicular portion of the ligamentum nuchæ.
_Action._—It is the chief extensor of the head and neck. Acting singly,
the muscle inclines the head to the same side.
_Structure._—The origin of the muscle at the withers is aponeurotic. In
the neck the bundles arising from the articular processes run obliquely
upward and forward, giving the lower part of the muscle a distinct
pennate character. The upper part of the belly is crossed obliquely by
four or five tendinous intersections. The insertion is by a strong
tendon.
_Relations._—Superficially, the rhomboideus, serratus magnus, splenius,
and trachelo-mastoideus muscles; deeply, the ligamentum nuchæ, the
multifidus cervicis, longissimus, and the oblique and posterior straight
muscles of the head, the deep or superior cervical vessels, and the
dorsal cutaneous branches of the cervical nerves.
_Blood-supply._—Deep cervical, vertebral, and occipital arteries.
_Nerve-supply._—Dorsal branches of the last six cervical nerves.
7. =Multifidus cervicis= (M. semispinalis colli; transverse spinous
muscle of neck).—This muscle lies on the arches of the last five
cervical vertebræ. It consists of five or six segments.
_Origin._—The articular processes of the last five (or four) cervical
and the first thoracic vertebræ.
_Insertion._—The spinous processes of the cervical vertebræ.
[Illustration:
FIG. 179.—DEEPER MUSCLES OF HORSE.
_f_, Long head of triceps; _f′_, external head of triceps; _g_,
anterior superficial pectoral; _h_, posterior deep pectoral; _h′_,
anterior deep pectoral; _i_, serratus thoracis; _i′_, serratus
cervicis; _l_, obliquus abdominis externus, and _l′_, its
aponeurosis, the posterior part of which has been removed; _m_,
serratus posticus; _p_, gluteus medius; _r_, semitendinosus; _s_,
sacro-coccygeus superior; _t_, sacro-coccygeus lateralis; _u_,
coccygeus; _v′_, biceps brachii; _x_, rhomboideus; _y_, _y′_,
trachelo-mastoideus; _z_, supraspinatus; _z′_, infraspinatus; _1_,
cartilage of scapula; _2_, spine of scapula; _5_, external
tuberosity of humerus; _6_, deltoid tuberosity; _8_, olecranon;
_16_, external angle of ilium; _19_, trochanter major; _20_,
patella; _21′_, external condyle of tibia; _26_, articular processes
of cervical vertebræ; _27_, parotido-auricularis; _28_, vastus
externus; _28′_, rectus femoris; _28″_, trochanter tertius; _29_,
semimembranosus; _30_, gastrocnemius; _31_, sacro-sciatic ligament;
_32_, omo-hyoideus; _33_, complexus; _34_, rectus capitis anterior
major; _35_, spinalis dorsi; _36_, longissimus dorsi; _37_,
transversalis costarum; _38_, teres minor; _39_, brachialis; _40_,
external intercostal; _41_, obliquus abdominis internus; _42_,
iliacus; _43_, transversus abdominis. (After Ellenberger-Baum, Anat.
für Künstler.)
]
_Action._—Acting together, to extend the neck; acting singly, to flex
and rotate the neck to the opposite side.
_Structure._—The muscle is composed of two sets of bundles. The
superficial bundles are directed obliquely forward and inward, each
passing from an articular process to the spine of the preceding
vertebra. The deep bundles are shorter and run straight from an
articular process to that of the preceding vertebra.
_Relations._—Superficially, the complexus, longissimus,
trachelo-mastoideus, and great oblique muscles; deeply, the spinalis
muscle, the ligamentum nuchæ, and the arches of the vertebræ.
_Blood-supply._—Deep cervical and vertebral arteries.
_Nerve-supply._—Dorsal branches of the last six cervical nerves.
8. =Spinalis.=—Described with the longissimus on p. 237.
9. =Obliquus capitis posterior= (s. caudalis) (great oblique muscle of
the head).—This is a strong, quadrilateral muscle, which covers the
dorso-lateral aspect of the atlas and axis.
_Origin._—The side of the spine and the posterior articular process of
the axis.
_Insertion._—The dorsal surface of the wing of the atlas.
_Action._—Chiefly to rotate the atlas, and with it the head, to the same
side; also to assist in extending and fixing the atlanto-axial joint.
_Structure._—The muscle is composed almost entirely of parallel fleshy
fibers directed obliquely forward and outward.
_Relations._—Superficially, the skin, the splenius, complexus,
trachelo-mastoideus, and mastoido-humeralis muscles; deeply, the arch
and spine of the axis, the wing of the atlas, the atlanto-axial joint,
the multifidus cervicis, the posterior straight muscles, the occipital
and vertebral vessels, and the first and second cervical nerves. The
terminal part of the vertebral artery joins the posterior branch of the
occipital artery under cover of the muscle.
_Blood-supply._—Occipital and vertebral arteries.
_Nerve-supply._—Dorsal branch of the second cervical nerve.
10. =Obliquus capitis anterior= (s. cranialis) (small oblique muscle of
the head).—A short, thick, quadrilateral muscle which lies on the side
of the occipito-atlantal articulation.
_Origin._—The anterior edge of the wing of the atlas and the fossa
atlantis.
_Insertion._—The styloid process and crest of the occipital bone, and
the mastoid process.
_Action._—Acting together, to extend the head on the atlas; acting
singly, to flex the head laterally.
_Structure._—The muscle contains a good deal of tendinous tissue. The
direction of its fibers is forward, upward, and inward.
_Relations._—Superficially, the posterior auricular muscles, artery, and
nerve, the aponeurosis of the splenius, trachelo-mastoideus and
mastoido-humeralis, and the parotid gland; deeply, the straight muscles,
the complexus, the occipito-hyoideus, the occipito-atlantal
articulation, branches of the occipital artery, and a branch of the
occipital nerve.
_Blood-supply._—Occipital artery.
_Nerve-supply._—Dorsal branch of the first cervical nerve.
11. =Rectus capitis posterior major= (s. dorsalis major) (great
posterior straight muscle of the head).—This muscle extends from the
axis to the occipital bone, in contact with the ligamentum nuchæ.
_Origin._—The edge of the spinous process of the axis.
_Insertion._—The occipital bone, below and external to the complexus and
ligamentum nuchæ.
_Action._—To extend the head.
[Illustration:
FIG. 180.—DEEPEST LAYER OF MUSCLES OF NECK OF HORSE.
_a_, Obliquus capitis anterior; _b_, obliquus capitis posterior; _c_,
rectus capitis lateralis; _d_, rectus capitis anterior minor; _e_,
rectus capitis anterior major; _f_, longus colli; _g_, _g′_,
scalenus; _h_, transversalis costarum; _i_, longissimus dorsi; _k_,
spinalis et semispinalis; _l_, multifidus dorsi; _m_, multifidus
cervicis; _n_, intertransversales; _o_, _o′_, rectus capitis
posterior major; _p_, rectus capitis posterior minor; _q_, tendon of
insertion of complexus; _1_, lamellar part, _1′_, funicular part of
ligamentum nuchæ; _2_, occipital crest; _3_, paramastoid process;
_4_, edge of wing of atlas; _5_, transverse, and _6_, articular,
processes of cervical vertebræ; _7_, nerves of brachial plexus
(cut); _8_, first rib. (Ellenberger-Baum, Anat. d. Haustiere.)
]
_Structure._—The muscle is fleshy and may be divided into two parallel
portions, superficial and deep. The former blends somewhat with the
terminal part of the complexus. The deep portion may be termed the
rectus capitis posterior medius.
_Relations._—Superficially, the anterior oblique, splenius, and
complexus; internally, the ligamentum nuchæ; deeply, the atlas, the
occipito-atlantal articulation, and the rectus capitis posterior minor.
The dorsal branch of the first cervical nerve appears between this
muscle and the small oblique.
_Blood-supply._—Occipital artery.
_Nerve-supply._—Dorsal branch of the first cervical nerve.
12. =Rectus capitis posterior minor= (s. dorsalis minor) (small
posterior straight muscle of the head).—This small muscle lies under
cover of the preceding.
_Origin._—The dorsal surface of the atlas.
_Insertion._—The occipital bone beneath the preceding muscle.
_Action._—To assist the preceding muscle.
_Structure._—It is fleshy and varies a good deal in volume, being
sometimes small and difficult to recognize.[44] On the other hand, it is
sometimes double.
_Relations._—Superficially, the preceding muscle and the small oblique;
deeply, the atlas and the occipito-atlantal articulation.
_Blood-supply._—Occipital artery.
_Nerve-supply._—Dorsal branch of the first cervical nerve.
THE FASCIÆ AND MUSCLES OF THE BACK AND LOINS
The =superficial fascia= presents no special features. The =lumbo-dorsal
fascia= (Fascia lumbo-dorsalis) closely invests the muscles, but is
easily stripped off the longissimus. It is attached medially to the
supraspinous ligament and the spinous processes of the vertebræ;
laterally, it divides into two layers. The superficial layer is
practically the aponeurosis of the latissimus dorsi. The deep layer
gives origin to the serratus anticus and posticus, the lumbar part of
the obliquus externus abdominis, the transversus abdominis, and the
retractor costæ. Its lateral edge curves under the longissimus and is
attached to the ribs and lumbar transverse processes. Posteriorly, it is
continuous with the gluteal fascia. At the withers it forms an important
structure, the =dorso-scapular ligament=. This is a strong tendinous
sheet, attached to the third, fourth, and fifth thoracic spines. Its
upper part is very thick and gives origin by its superficial surface to
the rhomboideus dorsi, by its anterior part to the splenius. The lower
part is thin and elastic, and furnishes numerous lamellæ which intersect
the scapular part of the serratus and are attached with it to the
scapula. Three lamellæ are detached from the deep face of the ligament.
The deepest of these passes between the longissimus and spinalis and is
attached to the transverse processes of the first seven thoracic
vertebræ; it gives attachment to the complexus. The middle one dips in
between the longissimus and transversalis costarum. The superficial one
gives origin to the serratus anticus. A strong fascial layer, the
ilio-lumbar ligament, extends from the last rib to the external angle of
the ilium.
There are nine pairs of muscles in this region, arranged in four layers.
FIRST LAYER
1. =Trapezius thoracalis.=
2. =Latissimus dorsi.=
SECOND LAYER
3. =Rhomboideus thoracalis.=
The foregoing are described with the other muscles which attach the
thoracic limb to the trunk (p. 251).
4. =Serratus anticus= (M. serratus dorsalis inspiratorius).—This is a
thin quadrilateral muscle, named from its toothed ventral border. It
lies beneath the rhomboideus, serratus magnus, and latissimus dorsi.
_Origin._—The lumbo-dorsal fascia and dorso-scapular ligament.
_Insertion._—The external surfaces of the fifth to the eleventh or
twelfth ribs inclusive.
_Action._—To draw the ribs on which it is inserted forward and outward,
thus assisting in inspiration.
_Structure._—The muscle arises by means of a thin aponeurosis which
blends with the lumbo-dorsal fascia and the aponeurosis of the
latissimus dorsi. The muscle-fibers pass downward and backward to be
attached to the ribs by seven or eight digitations below the outer edge
of the transversalis costarum.
_Relations._—Superficially, the rhomboideus, serratus magnus, latissimus
dorsi, and serratus posticus; deeply, the longissimus dorsi,
transversalis costarum, external intercostal muscles, and the ribs.
_Blood-supply._—Intercostal arteries.
_Nerve-supply._—Thoracic nerves.
5. =Serratus posticus= (M. serratus dorsalis exspiratorius).—This muscle
resembles the preceding one, which it partly covers.
_Origin._—The lumbo-dorsal fascia.
_Insertion._—The outer surfaces of the last seven or eight ribs.
_Action._—To draw the ribs backward, thus assisting in expiration.
_Structure._—Similar to the preceding muscle. The fibers are directed
downward and forward and terminate in seven or eight digitations, one or
two of which cover the posterior teeth of the anticus. The aponeurosis
blends with that of the latissimus dorsi.
_Relations._—Superficially, the latissimus dorsi and external oblique;
deeply, the longissimus dorsi, transversalis costarum, external
intercostals, serratus anticus, and the ribs.
_Blood-supply._—Intercostal and lumbar arteries.
_Nerve-supply._—Thoracic nerves.
THIRD LAYER
6. =Transversalis costarum= (M. ilio-costalis).—This long, segmental
muscle extends, as its name indicates, across the series of ribs, in
contact with the outer edge of the longissimus dorsi.
_Origin._—(1) The transverse processes of the second and third lumbar
vertebræ and the deep layer of the lumbo-dorsal fascia. (2) The anterior
borders and external surface of the last fifteen ribs.[45]
_Insertion._—The posterior borders of the ribs and the transverse
processes of the last two or three cervical vertebræ.
_Action._—Chiefly to depress and retract the ribs and so help in
expiration. Acting together, they may assist in extending this spine,
acting singly in inclining it laterally.
_Structure._—This muscle presents a distinct segmental arrangement. It
is composed of a series of bundles, the fibers of which are directed
forward and a little downward and outward. From these are detached two
sets of tendons. The superficial tendons spring from the outer edge of
the muscle. They are flat and are about half an inch in width. Each
crosses two or three intercostal spaces, to be inserted on the posterior
border of a rib. The deep tendons are detached from the dorsal part of
the deep face of the muscle. Each passes backward across one or two
intercostal spaces to its origin on the anterior border or outer surface
of a rib. Small bursæ may be found between the ribs and tendons.
_Relations._—Superficially, the dorsal serrati and the complexus;
deeply, the external intercostals and the ribs. The lumbar origin is
covered by the longissimus. The superior (deep) cervical and dorsal
vessels cross the surface of the muscle at the first and second
intercostal spaces respectively, and branches of the intercostal vessels
and nerves emerge between the transversalis and longissimus; here a
fascial layer dips in between the two.
_Blood-supply._—Intercostal arteries.
_Nerve-supply._—Dorsal branches of the thoracic nerves.
7. =Longissimus.=[46]—This is the largest and longest muscle in the
body. It extends from the sacrum and ilium to the neck, filling up the
space between the spinous processes medially and the lumbar transverse
processes and the upper ends of the ribs below; consequently it has the
form of a three-sided prism.
_Origin._—(1) The internal angle, crest, and adjacent part of the
ventral surface of the ilium; (2) the first three sacral spines; (3) the
lumbar and thoracic spines and the supraspinous ligament.
_Insertion._—(1) The lumbar transverse and articular processes; (2) the
thoracic transverse processes; (3) the spinous and transverse processes
of the last four cervical vertebræ; (4) the outer surfaces of the ribs,
except the first.
_Action._—Acting with its fellow, it is the most powerful extensor of
the back and loins; by its cervical attachment it assists in extending
the neck. By its costal attachment it may also assist in expiration.
Acting singly, it flexes the spine laterally.
[Illustration:
FIG. 181.—RIGHT PORTION OF CROSS-SECTION OF BACK OF HORSE. SECTION IS
CUT THROUGH SEVENTH THORACIC VERTEBRA.
_a_, Ligamentum nuchæ; _b_, trapezius muscle; _c_, cartilage of
scapula; _d_, latissimus dorsi; _e_, panniculus carnosus; _f_,
rhomboideus dorsi; _g_, serratus magnus; _h_, serratus anticus;
_h′_, lumbo-dorsal fascia, which divides below into three layers;
_i_, transversalis costarum; _k_, levator costæ; _k′_, internal
intercostal muscle; _l_, longissimus dorsi; _m_, _m′_, seventh
thoracic vertebra; _n_, head of eighth thoracic vertebra; _o_, head
of eighth rib; _p_, seventh rib; _r_, intercostal artery and nerve;
_s_, skin. The fasciæ are indicated by dotted lines. (After
Ellenberger, in Leisering’s Atlas.)
]
_Structure._—This is quite complex. The posterior part of the muscle is
greatly developed and constitutes the common mass of the loins. This is
covered by a strong aponeurosis which blends with the supraspinous and
sacro-iliac ligaments, and is attached to the crest and inner (sacral)
angle of the ilium and the first and second sacral spines; it furnishes
origin to the lumbar portion of the middle gluteus. In its course
further forward the muscle receives fasciculi from the lumbar and
thoracic spines, but diminishes somewhat in volume. At the withers it
divides into two parts. The dorsal division (spinalis et semispinalis),
reinforced by bundles from the first four thoracic spines, passes
forward under the complexus to be inserted into the spines of the last
four cervical vertebræ. The ventral division passes forward and downward
underneath the serratus magnus to be inserted into the ribs and the
transverse processes of the last four cervical vertebræ. Three sets of
fasciculi may be distinguished, viz.: (1) spinal, which are superficial
and internal; (2) transverse, attached to the transverse and articular
processes, which are internal and deep; (3) costal, which are external.
_Relations._—Superficially, the middle gluteus, the lumbo-dorsal fascia,
the latissimus dorsi, dorsal serrati, serratus magnus, and complexus;
deeply, the multifidus, intertransversales, external intercostals,
levatores costarum, the ligamentum nuchæ, and its fellow of the opposite
side (in the neck).
_Blood-supply._—Dorsal, superior cervical, intercostal, and lumbar
arteries.
_Nerve-supply._—Dorsal branches of the thoracic and lumbar nerves.
8. =Multifidus dorsi= (semispinalis of the back and loins).—This is a
long segmental muscle which covers the sides of the spinous processes of
the vertebræ from the sacrum to the neck.
_Origin._—(1) The lateral portion of the sacrum; (2) the articular
processes of the lumbar vertebræ; (3) the transverse processes of the
thoracic vertebræ.
_Insertion._—The spinous processes of the first two sacral, the lumbar,
thoracic, and last cervical vertebræ.
_Action._—Acting with its fellow, it is an extensor of the spine; acting
singly, it flexes it laterally.
_Structure._—It is composed of a series of bundles which are directed
obliquely forward and upward. Each fasciculus passes over several
vertebræ to its insertion. In the posterior part of the series the
bundles cross two or three vertebræ and are inserted into the summits of
the spines. Anteriorly, the bundles have a more horizontal direction,
cross three to five vertebræ, and are inserted into the sides of the
spines considerably below their summits. A further complication consists
in the fusion of several bundles into a common insertion.
_Relations._—Superficially, the longissimus; deeply, the vertebral
spines.
_Blood-supply._—Intercostal and lumbar arteries.
_Nerve-supply._—Dorsal branches of the thoracic and lumbar nerves.
9. =Intertransversales lumborum.=—These are very thin muscular and
tendinous strata, which occupy the spaces between the transverse
processes of the lumbar vertebræ except the fifth and sixth.
_Action._—To assist in flexing the loins laterally.
_Relations._—Superficially, the longissimus; deeply, the quadratus
lumborum.
_Blood-supply._—Lumbar arteries.
_Nerve-supply._—Lumbar nerves.
THE FASCIA AND MUSCLES OF THE TAIL
The muscles of the tail are inclosed in the strong =coccygeal fascia=,
which is continuous in front with the gluteal fascia and blends with the
lateral sacro-iliac ligament. At the root of the tail it is loosely
attached to the subjacent muscles, but further back it is intimately
adherent to them. From its deep face are detached septa which pass
between the muscles to become attached to the vertebræ.
1. =Coccygeus= (Compressor coccygis; ischio-coccygeus).—This is a flat,
triangular muscle which lies chiefly between the sacro-sciatic ligament
and the rectum.
_Origin._—The pelvic surface of the sacro-sciatic ligament near the
ischiatic spine.
_Insertion._—The first four coccygeal vertebræ and the coccygeal fascia.
_Action._—Acting together, to depress (flex) the tail, compressing it
over the perineum; acting singly, to depress and incline it to the same
side.
_Structure._—The origin of the muscle is aponeurotic. Becoming fleshy,
its fibers pass upward and backward and divide into two layers. The
outer layer is attached to the vertebræ, the inner to the fascia;
included between the two lie the intertransversales. When the tail is
raised, the ventral edges of the muscles produce a distinct ridge at
either side of the anus.
_Relations._—Outwardly, the sacro-sciatic ligament and the
semimembranosus; inwardly, the rectum and the sacro-coccygeus ventralis
muscle. The internal pudic artery crosses the outer face of the origin
of the muscle.
2. =Sacro-coccygeus superior= (M. sacro-coccygeus dorsalis medialis;
erector s. extensor coccygis).—This muscle lies along the dorso-median
aspect of the tail, in contact with its fellow.
_Origin._—The last three sacral spines and some of the coccygeal spines.
_Insertion._—The dorsal surface of the coccygeal vertebræ.
_Action._—Acting together, to elevate (extend) the tail; acting singly,
to elevate and incline it laterally.
_Structure._—The muscle has a strong rounded belly. It is inserted by
means of short tendons which fuse with those of the next muscle.
_Relations._—Superficially, the coccygeal fascia; internally, its
fellow; laterally, the sacro-coccygeus lateralis; deeply, the vertebræ.
3. =Sacro-coccygeus lateralis= (M. sacro-coccygeus dorsalis lateralis;
curvator coccygis).—This muscle lies immediately lateral to the
preceding.
[Illustration:
FIG. 182.—CROSS-SECTION OF TAIL OF HORSE CLOSE TO ANUS.
_34_, Coccygeal vertebra; _35_, sacro-coccygeus superior; _36_,
intertransversalis; _37_, sacro-coccygeus inferior; _38_, coccygeus;
_39_, recto-coccygeus; _40_, coccygeal fascia. (After
Ellenberger-Baum, Anat. für Künstler.)
]
[Illustration:
FIG. 183.—MUSCLES OF PERINEUM OF HORSE.
_a_, Coccygeus; _b_, retractor ani; _c_, _c′_, sphincter and externus;
_d_, recto-coccygeus; _e_, sacro-coccygeus inferior lateralis; _f_,
retractor penis; _g_, bulbo-cavernosus; _h_, ischio-cavernosus; _i_,
internal pudic artery; _k_, anus; _l_, penis. (After
Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
_Origin._—The sides of the sacral spines, with the multifidus, and the
transverse processes of the sacral and coccygeal vertebræ.
_Insertion._—The lateral surface of the coccygeal vertebræ, except the
first four.
_Action._—Acting with its fellow, to assist the preceding muscle in
elevating the tail; acting singly, to incline it to the same side.
_Structure._—This muscle appears to be a direct continuation of the
multifidus dorsi. The belly is fusiform and receives reinforcing
fasciculi from the transverse processes of the sacrum. This is succeeded
by bundles of tendons, as many as four lying alongside of each other.
_Relations._—Superficially, the lateral sacro-iliac ligament and the
coccygeal fascia; dorsally, the sacro-coccygeus superior; ventrally, the
intertransversales; deeply, the vertebræ and a branch of the lateral
coccygeal artery and accompanying vein and nerve.
4. =Intertransversales caudæ= (Mm. intertransversarii caudæ).—These
consist of muscular bundles which lie on the lateral aspect of the tail,
between the preceding muscle and the sacro-coccygeus inferior. They
begin on the lateral edge of the sacrum and occupy the spaces between
the transverse processes, to which they are attached. They are, however,
not arranged in a strict segmental manner.
_Action._—Acting together, to fix the coccygeal vertebræ; acting singly,
to assist in lateral flexion.
5. =Sacro-coccygeus inferior= (Mm. sacro-coccygei ventrales; depressor
coccygis).—This muscle lies on the ventral aspect of the sacrum and
coccyx. It is composed of two portions, described by Bourgelat and the
German anatomists as separate muscles.
(_a_) The =outer portion= (M. coccygeus ventralis lateralis) is much the
larger of the two. It arises from the outer part of the ventral surface
of the sacrum, about as far forward as the third foramen, and is
inserted into the transverse processes and ventral surface of the
coccygeal vertebræ.
(_b_) The =inner portion= (M. sacro-coccygeus ventralis medialis) arises
from the ventral surface of the sacrum internal to the preceding muscle
and the first eight coccygeal vertebræ, and is inserted into the ventral
surfaces of the coccygeal vertebræ.
_Action._—Acting together, to depress (flex) the tail; acting singly, to
incline it laterally also.
_Structure._—The outer portion has a somewhat compressed belly, and
receives bundles from the transverse processes of the coccygeal
vertebræ. The inner portion is much smaller and shorter, reaching only
about to the middle of the tail.
_Relations._—Ventrally, the pelvic and coccygeal fasciæ; dorsally, the
sacrum, coccygeal vertebræ, and the intertransversales; laterally, the
sacro-sciatic ligament, the coccygeus, and the coccygeal fascia;
medially, its fellow, the recto-coccygeus, and the middle coccygeal
vessels. Branches of the lateral coccygeal vessels and nerves lie
between the outer division of the muscle and the intertransversales.
_Blood-supply._—Middle and lateral coccygeal arteries.
_Nerve-supply._—Coccygeal nerves.
THE MUSCLES OF THE THORAX
These consist of seven muscles or sets of muscles, which are attached to
the thoracic vertebræ, to the ribs and their cartilages, and to the
sternum. Functionally, they are muscles of respiration.
1. =Levatores costarum.=—These constitute a series of small muscles
which occupy and overlie the upper ends of the intercostal spaces.
_Origin._—The transverse processes of the thoracic vertebræ.
_Insertion._—The external surfaces of the upper ends of the ribs
posterior to the vertebral origin.
_Action._—To draw the ribs forward in inspiration.
_Structure._—Arising by tendinous fibers, each muscle passes backward
and outward and expands at its insertion. Some fibers pass over one rib
and are inserted on a succeeding one. At the first and last spaces the
muscle cannot be distinguished from the external intercostal, of which
it is in reality only a specially developed part.
_Relations._—Superficially, the longissimus dorsi; deeply, the ribs,
internal intercostal muscles, and the intercostal vessels and nerves.
_Blood-supply._—Intercostal arteries.
_Nerve-supply._—Intercostal nerves.
2. =External intercostals= (Mm. intercostales externi).—Each of these
occupies an intercostal space, from the levatores to the sternal
extremity of the rib. They do not occupy the intercartilaginous spaces.
_Origin._—The posterior borders of the ribs.
_Insertion._—The anterior borders and external surfaces of the
succeeding ribs.
_Action._—To draw the ribs forward in inspiration.
_Structure._—The fibers are directed downward and backward. There is a
considerable admixture of tendinous tissue. The thickness of the muscles
gradually diminishes toward the lower ends of the spaces.
[Illustration:
FIG. 184.—DORSAL AND LUMBAR REGIONS OF HORSE, DORSAL VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
_Relations._—Superficially, the serratus magnus, latissimus dorsi,
serratus anticus and posticus, longissimus dorsi, transversalis
costarum, rectus thoracis, deep pectorals, obliquus abdominis externus,
and panniculus; deeply, the internal intercostals and (in the upper part
of the spaces) the intercostal vessels and nerves.
_Blood-supply._—Intercostal and internal thoracic arteries.
_Nerve-supply._—Intercostal nerves.
3. =Internal intercostals= (Mm. intercostales interni).—These occupy the
entire length of the intercostal spaces, including their interchondral
portion.
_Origin._—The anterior borders of the ribs and their cartilages.
_Insertion._—The posterior borders of the preceding ribs and cartilages.
_Action._—To draw the ribs backward in expiration. It seems probable,
however, that the intercartilaginous portion is inspiratory.[47]
_Structure._—The direction of the fibers is oblique downward and
forward. There is a smaller amount of tendinous tissue than in the
external set, and the thickness diminishes from below upward. In the
upper part of the spaces fibers sometimes cross a rib in a fashion
similar to the subcostals of man. A thin aponeurosis separates the
internal from the external intercostal muscle in each space.
_Relations._—Superficially, the levatores costarum and the external
intercostals; deeply, the endothoracic fascia and pleura, the
transversus thoracis, diaphragm, transversus abdominis, and the internal
thoracic and asternal vessels. In the upper part of the intercostal
spaces the intercostal vessels and nerves lie between the internal and
external intercostal muscle, but below they lie chiefly on the deep face
of the inner muscle.
_Blood-supply._—Intercostal and internal thoracic arteries.
_Nerve-supply._—Intercostal nerves.
4. =Retractor costæ.=—This is a small triangular muscle which lies
behind the last rib, chiefly under cover of the serratus posticus.
_Origin._—The transverse processes of the first three or four lumbar
vertebræ by means of the lumbar fascia.
_Insertion._—The posterior border of the last rib.
_Action._—To retract the last rib.
_Structure._—The muscle arises by a thin aponeurosis. Its fibers are
parallel to those of the adjacent internal oblique.
_Relations._—Superficially, the serratus posticus and external oblique;
deeply, the transversus abdominis.
_Blood-supply._—Lumbar arteries.
_Nerve-supply._—Lumbar nerves.
5. =Rectus thoracis= (M. transversus costarum; lateralis sterni).—This
is a thin muscle which lies under cover of the deep pectoral muscles. It
is directed obliquely backward and downward, and crosses the lower part
of the first three intercostal spaces.
_Origin._—The outer surface of the first rib, below the scalenus.
_Insertion._—The cartilage of the third or fourth rib. The aponeurosis
usually joins the rectus abdominis. It may reach the sternum.
_Action._—It may assist in inspiration or concur with the rectus
abdominis.
_Relations._—Superficially, the deep pectoral muscles; deeply, the
intercostal muscles and the ribs.
6. =Transversus thoracis= (Triangularis sterni).—This is a flat muscle
situated on the thoracic surface of the sternum and the cartilages of
the sternal ribs.
_Origin._—The sternal ligament.
_Insertion._—The cartilages of the ribs, from the second to the eighth
inclusive.
_Action._—It draws the costal cartilages inward and backward, thus
assisting in expiration.
_Structure._—Each muscle has the form of a scalene triangle, of which
the base is the strongly serrated external border. The muscle contains a
good deal of tendinous tissue. The anterior bundles are directed forward
and outward; the posterior backward and outward.
_Relations._—Superiorly, the endothoracic fascia and pleura; inferiorly,
the costal cartilages, the internal intercostal muscles, and the
internal thoracic vessels.
_Blood-supply._—Internal thoracic artery.
_Nerve-supply._—The intercostal nerves.
7. =Diaphragm.=—This is a broad, unpaired muscle which forms a partition
between the thoracic and abdominal cavities.[48] In outline it has some
resemblance to a palm-leaf fan. In form it is dome-shaped, compressed
laterally. On a median section it is seen to have a general direction
downward and forward from the lumbar vertebræ to the xiphoid cartilage.
The thoracic surface is strongly convex, and is covered by the pleura.
The abdominal surface is deeply concave, and is covered for the most
part by the peritoneum. The muscle consists of a peripheral fleshy
portion, two muscular crura, and a tendinous center.
_Attachments._—(1) =Costal part=: The cartilages of the ninth to the
fifteenth ribs, and the last three ribs at an increasing distance from
their sternal ends.
(2) =Sternal part=: The upper surface of the xiphoid cartilage.
(3) =Lumbar part=: (_a_) The =right crus= is attached to the inferior
common ligament, and by this means to the first four or five lumbar
vertebræ. (_b_) The =left crus= is attached in a similar fashion to the
first and second lumbar vertebræ.
_Action._—It is the principal muscle of inspiration and increases the
longitudinal diameter of the chest. The contraction produces a general
lessening of the curvature of the diaphragm. In the expiratory phase the
costal part and crura lie directly on the body walls, so that the bases
of the lungs are in contact with the tendinous center and sternal
portion only. In ordinary inspiration the fleshy rim recedes from the
chest-wall, so that the bases of the lungs move backward to a line about
parallel with the curve formed by the cartilages of the asternal ribs,
and about four or five inches (ca. 10 to 12 cm.) therefrom. It is stated
that the inspiratory movement affects the tendinous center much less
than the fleshy part, since the posterior vena cava is firmly attached
to the former. It should be noted, however, that the direction of the
thoracic part of the vena cava in the expiratory phase is oblique upward
and backward. Thus it would seem that there is no anatomical reason why
the diaphragm should not move as a whole in ordinary inspiration at
least.
_Structure._—The =costal part= (Pars costalis) consists of a series of
digitations which meet, or are separated by a very narrow interval from,
the transversus abdominis; between the two are the asternal vessels.
From the tenth rib backward the attachments are to the ribs at an
increasing distance above the costo-chondral junctions. Thus at the last
rib the attachment is four to five inches (10 to 12 cm.) from the lower
end. Anteriorly, the origin extends along the ninth costal cartilage to
the xiphoid cartilage. From these points of origin the fibers curve
inward and forward to join the tendinous center. The =right crus= (Crus
dextrum) is about twice as thick as the left one and is also longer. It
arises by a strong tendon from the lumbar vertebræ (by means of the
inferior common ligament). The tendon is succeeded by a rounded belly
which leaves the vertebral column, at the last thoracic vertebra.
Passing downward and forward, its fibers spread out and join the
tendinous center. The =left crus= (Crus sinistrum) arises by a thin
tendon from the inferior common ligament at the first and second lumbar
vertebræ. This is succeeded by a triangular belly which joins the
central tendon. Between the crura and the attachment to the last rib the
edge of the muscle crosses the ventral surface of the psoas muscles
without attachment, forming the so-called lumbo-costal arch; here the
thoracic and abdominal cavities are separated only by the serous
membranes and some areolar tissue. The =tendinous center= (Centrum
tendineum) resembles the periphery in outline, but is more elongated. It
is partially divided into right and left halves by the descent of the
crura into it. It is composed largely of radiating fibers, but many
interlace in various directions; this is specially evident around the
foramen venæ cavæ, which is encircled by fibers. A strong tendinous
layer extends across below the hiatus œsophageus.
[Illustration:
FIG. 185.—DIAPHRAGM OF HORSE, ABDOMINAL SURFACE.
_1_, Inferior common ligament; _2_, _2′_, tendons of crura; _3_,
lumbar sympathetic trunks; _4_, external spermatic nerve; _5_, _5′_,
great splanchnic nerves; _6_, cisterna chyli (opened); _7_, _7′_,
œsophageal continuations of vagus nerves; _8_, lymph gland; _9_,
coronary ligament of liver (cut); _10_, right lateral ligament of
liver (cut); _11_, left lateral ligament of liver (cut); _12_,
falciform ligament of liver (cut); _A.l._, lumbo-costal arch;
_N.i._, intercostal nerve; _C.d._, right crus; _C.s._, left crus;
_A_, aorta; _Ca_, cœliac artery; _Oe._, œsophagus; _V.c._, posterior
vena cava; _V.p._, phrenic veins. (After Schmaltz, Atlas d. Anat. d.
Pferdes.)
]
The diaphragm is pierced by three foramina. (1) The =hiatus aorticus= is
an interval between the two crura and below the last thoracic vertebra.
It contains the posterior aorta, vena azygos, and cisterna chyli. (2)
The =hiatus œsophageus= (or foramen sinistrum) perforates the right crus
near its junction with the tendinous center. It is situated a little to
the left of the median plane and two or three inches below the
thirteenth thoracic vertebra (in expiration). It transmits the
œsophagus, the vagus nerves, and the œsophageal branch of the gastric
artery. (3) The =foramen venæ cavæ= (s. dextrum) pierces the tendinous
center about an inch to the right of the median plane, and about six
inches below the twelfth thoracic vertebra (in expiration). The vena
cava is firmly attached to the margin of the opening.[49]
_Relations._—The thoracic surface is related to the endothoracic fascia,
pleuræ, pericardium, the bases of the lungs, and the ribs in part. The
abdominal surface is in great part covered by the peritoneum, and is
related chiefly to the liver, stomach, spleen, pancreas, kidneys and
adrenals, and the anterior flexures of the colon. The sympathetic and
splanchnic nerves pass between the crus and the psoas muscles on each
side. The asternal vessels perforate the edge of the muscle at the ninth
costo-chondral joint.
_Blood-supply._—Phrenic and asternal arteries.
_Nerve-supply._—Phrenic nerves (from the fifth, sixth, and seventh
cervical nerves).
THE ABDOMINAL MUSCLES
The =superficial fascia= covering the lateral and ventral walls of the
abdomen is continuous dorsally with the lumbo-dorsal fascia, in front
with the thoracic fascia, and behind with the gluteal fascia. In the
inguinal region it forms part of the fascia of the penis or of the
mammary glands. At the lower part of the flank it forms a fold which is
continuous with the fascia of the thigh near the stifle joint. In this
fold are the precrural lymph glands. Medially it blends with the linea
alba. It contains the abdominal portion of the panniculus carnosus.
The =abdominal panniculus= (M. cutaneus maximus) covers a large part of
the lateral surface of the abdomen and thorax. The general direction of
its fibers is longitudinal. Its posterior extremity forms the basis of
the fold of the flank. Its anterior extremity is inserted by a thin
tendon into the internal tuberosity of the humerus, with the posterior
deep pectoral muscle. Its dorsal edge may be indicated by a line drawn
from the upper end of the thirteenth rib to the fold of the flank. Its
ventral limit corresponds to a line drawn from the fold to a point about
a handbreadth external to the umbilicus, and from here to a point a
little above the level of the elbow. Behind the shoulder the fibers
become oblique and blend with the scapular portion. The aponeurosis
extends ventrally to the linea alba, dorsally to the supraspinous
ligament. The muscle is intimately adherent to the skin, so that special
care is necessary in removing the latter. Its deep face, on the other
hand, is loosely attached to the underlying structures by a quantity of
areolar tissue which is more or less loaded with fat (panniculus
adiposus) in animals in good condition. The large external thoracic
(“spur”) vein is partially embedded in the lower part of the muscle. Its
action is to twitch the skin.
The =deep fascia= is represented chiefly by the =abdominal= tunic
(Tunica flava abdominis). This is a sheet of elastic tissue which
assists the muscles in supporting the great weight of the abdominal
viscera. It is practically coextensive with the obliquus externus, which
it covers. Ventrally it is thick, and is intimately adherent to the
aponeurosis of the muscle. Laterally it becomes thinner and is more
easily separated, although fibers from it dip in between the
muscle-bundles. It is continued for some distance upon the intercostals
and serratus magnus. Traced forward, it passes as a thin layer beneath
the posterior deep pectoral muscle. Posteriorly it is attached to the
external angle of the ilium. In the inguinal region it forms the deep
fascia of the prepuce or of the mammary glands.
The =linea alba= is a median fibrous raphé which extends from the
xiphoid cartilage to the symphysis pubis. It is formed chiefly by the
junction of the aponeuroses of the oblique and transverse muscles, but
partly by longitudinal fibers. A little behind its middle is a cicatrix
which indicates the position of the umbilical opening of the fœtus.
1. =Obliquus abdominis externus= (great oblique; external oblique of the
abdomen).—This is the most extensive of the abdominal muscles. It is a
broad sheet, irregularly triangular in shape, widest behind. Its fibers
are directed chiefly downward and backward.
_Origin._—(1) The outer surfaces of the last fourteen ribs, and the
fascia over the external intercostal muscles; (2) the lumbo-dorsal
fascia.
_Insertion._—(1) The linea alba and the prepubic tendon; (2) the
external angle and shaft of the ilium; (3) the internal femoral fascia.
_Action._—(1) To compress the abdominal viscera, as in defecation,
micturition, parturition, and expiration; (2) to flex the trunk (arch
the back); (3) acting singly, to flex the trunk laterally.
_Structure._—The muscle is composed of a fleshy portion and an
aponeurosis. The =muscular portion= lies on the lateral wall of the
thorax and abdomen. It arises by a series of digitations, the anterior
four of which alternate with those of the serratus magnus. The origin
may be indicated by a slightly curved line (concave above) drawn from
the lower part of the fifth rib to the external angle of the ilium. The
fibers are directed downward and backward and terminate on the
aponeurosis, except in the flank, where they are almost horizontal in
direction. The line of junction is a curve (concave above) extending
from the upper edge of the posterior deep pectoral muscle toward the
external angle of the ilium. The =aponeurosis= is intimately attached to
the abdominal tunic, and its fibers are largely interwoven ventrally
with those of the aponeurosis of the internal oblique. By this fusion is
formed the outer sheath of the rectus abdominis, which blends at the
linea alba with that of the opposite side. In the inguinal region the
aponeurosis divides into two chief layers; one of these curves upward
and backward and is inserted into the external angle of the ilium and
the prepubic tendon. Between these points the aponeurosis is much
strengthened and is called the =inguinal= (Poupart’s) =ligament=
(Ligamentum inguinale). This curves upward and somewhat forward, becomes
thin, and blends with the iliac fascia. It forms the posterior wall of
the inguinal canal. About an inch (ca. 2 to 3 cm.) in front of the pubis
and about two inches (ca. 4 to 5 cm.) from the median plane the
aponeurosis is pierced by a slit-like opening,[50] the =external
inguinal ring= (Annulus inguinalis subcutaneus). This is the external
orifice of the inguinal canal. Its long axis is directed outward and
forward, and is about four inches (ca. 10 cm.) in length. The inner
angle is rounded and is well defined by the junction of the inguinal
ligament with the prepubic tendon, but the outer angle is not so sharply
defined. The borders or pillars are constituted by arciform fibers of
the aponeurosis of the external oblique (Crus mediale, laterale). The
=femoral layer= of the aponeurosis (Lamina femoralis) passes on to the
inner surface of the thigh, where it blends with the femoral fascia. A
thin =iliac layer= (Lamina iliaca) passes over the outer margin of the
iliacus to the external border of the ilium.
_Relations._—Superficially, the skin, the panniculus carnosus, the
abdominal tunic, and the posterior deep pectoral muscle; deeply, the
ribs and their cartilages, the intercostal muscles, the internal
oblique, the contents of the inguinal canal, and the sartorius and
gracilis.
_Blood-supply._—Intercostal and lumbar arteries.
_Nerve-supply._—Intercostal and lumbar nerves.
2. =Obliquus abdominis internus= (small oblique; internal oblique of the
abdomen).—This muscle is situated under the preceding one. Its fibers
are directed downward, forward, and inward. It forms a triangular curved
sheet with the base behind.
[Illustration:
FIG. 186.—VENTRAL MUSCLES OF HORSE, AFTER REMOVAL OF GREATER PART OF
PANNICULUS CARNOSUS AND ABDOMINAL TUNIC. SARTORIUS AND GRACILIS
REMOVED FROM RIGHT THIGH.
_c_, Mastoido-humeralis; _g_, anterior superficial pectoral; _g′_,
posterior superficial pectoral; _h_, posterior deep pectoral; _l′_,
aponeurosis of obliquus abdominis externus; _t_, pectineus; _u_,
ilio-psoas; _v_, semimembranosus; _w_, gracilis; _x_, sartorius;
_y_, vastus internus; _z_, _z′_, adductor; _14_, sternum; _14′_,
cariniform cartilage. (After Ellenberger-Baum, Anat. f. Künstler.)
]
_Origin._—The external angle of the ilium and the adjacent part of the
inguinal (Poupart’s) ligament.
_Insertion._—(1) The cartilages of the last four or five ribs; (2) the
linea alba and the prepubic tendon.
_Action._—Similar to that of the preceding muscle.
_Structure._—Like the external oblique, it is composed of a fleshy
portion and an aponeurosis. The fleshy portion is fan-shaped, and is
situated chiefly in the flank. At its iliac origin it is covered by a
glistening aponeurosis. Traced inward and downward along the abdominal
surface of the inguinal ligament, the muscular origin is found to become
much thinner, and also becomes loosely attached to the ligament. About
four or five inches (ca. 10 to 12 cm.) from the linea alba the muscle
separates from the ligament and forms the anterior wall of the inguinal
canal. The abdominal orifice of the canal, the =internal inguinal
ring=[51] (Annulus inguinalis abdominalis), is found here. It is
normally a narrow slit, bounded in front by the edge of the internal
oblique, and behind by the inguinal ligament. The =aponeurosis= is to a
great extent blended with that of the external oblique, being, indeed,
considerably interwoven with it ventrally. Where it covers the rectus
abdominis it is attached to the tendinous inscriptions of that muscle.
_Relations._—Superficially, the external oblique; deeply, the rectus
abdominis, transversus abdominis, and the peritoneum.
_Blood-supply._—Circumflex iliac, lumbar, and intercostal arteries.
_Nerve-supply._—Ventral branches of the lumbar nerves.
3. =Rectus Abdominis.=—This muscle is confined to the ventral part of
the abdominal wall; it extends from the lower part of the chest-wall to
the pubis.
_Origin._—The cartilages of the fifth to the ninth ribs inclusive, and
the adjacent surface of the sternum.
_Insertion._—The pubis, by means of the prepubic tendon.
_Action._—Similar to that of the oblique muscles. It is specially
adapted to flex the lumbo-sacral joints and the lumbar and thoracic
parts of the spine.
_Structure._—The fibers of the muscle are directed longitudinally. Nine
to eleven transverse bands of fibrous tissue extend in an irregular
manner across the muscle. These are termed =inscriptiones tendineæ=.
They strengthen the muscle and serve to prevent separation of its
fibers. The width of the muscle is greatest about its middle.
_Relations._—Superficially, the aponeuroses of the oblique muscles
(which constitute the external rectus sheath), and the posterior deep
pectoral; deeply, the transversus, intercostals, the cartilages of the
ribs, and the sternum. The posterior abdominal artery runs along the
outer edge of the muscle posteriorly, and the anterior abdominal artery
on or in its anterior part.
_Blood-supply._—Anterior and posterior abdominal arteries.
_Nerve-supply._—Intercostal and lumbar nerves.
4. =Transversus abdominis.=—This muscle, named from the general
direction of its fibers, is a triangular curved sheet. Its lateral part
is muscular, its ventral aponeurotic.
_Origin._—(1) The inner surfaces of the distal ends or the cartilages of
the asternal ribs, meeting the costal attachment of the diaphragm; (2)
the transverse processes of the lumbar vertebræ, by means of the deep
layer of the lumbo-dorsal fascia.
_Insertion._—The xiphoid cartilage and the linea alba.
_Action._—Similar to that of the oblique muscles.
_Structure._—The =muscular part= is a sheet of parallel bundles of
fibers, directed downward and inward. It is thickest over the cartilages
of the ribs, and from here it thins out greatly toward the aponeurosis
and the lumbar region. The fibers of the =aponeurosis= directly continue
those of the fleshy part. Posteriorly it becomes extremely thin and
blends with the aponeuroses of the oblique muscles. It covers the deep
face of the rectus, so forming the internal rectus sheath.
_Relations._—Superficially, the oblique and straight muscles, the
retractor costæ, the cartilages of the asternal ribs, and the internal
intercostal muscles; deeply, the transversalis fascia and the
peritoneum. The =transversalis fascia= is little developed in the horse,
and is very thin in emaciated subjects, but in animals in good condition
it contains a good deal of fat. It blends with the iliac fascia and
descends into the inguinal canal. The asternal artery runs along the
interval between the origin of the transversus and the costal part of
the diaphragm. The intercostal nerves pass down over the external
surface of the muscle, to which they give branches. Branches of the
first three lumbar nerves are similarly disposed further back.
_Blood-supply._—Intercostal, lumbar, and asternal arteries.
_Nerve-supply._—Intercostal and lumbar nerves.
5. =Cremaster externus.=—This small muscle may be regarded as a detached
portion of the internal oblique, with which it blends at its origin
(Figs. 272, 450).
_Origin._—The iliac fascia, near the origin of the sartorius.
_Insertion._—The tunica vaginalis communis.
_Action._—To raise the tunica vaginalis, and with it the testicle.
_Structure._—The muscle arises by a thin aponeurosis which is succeeded
by a flat muscular belly about one and a half to two inches (ca. 4 to 5
cm.) in width.[52] It passes down the inguinal canal on the
postero-external surface of the tunica vaginalis, to which it is rather
loosely attached. On reaching the point where the tunic is reflected on
to the tail of the epididymis, the muscle is firmly attached to the
outer surface of the tunic by short tendinous fibers.
_Relations._—The muscle lies between the peritoneum and the fascia
transversalis in front and the iliac fascia and inguinal ligament
behind. On reaching the internal ring it descends the inguinal canal on
the postero-external surface of the tunica vaginalis communis.
_Blood-supply._—External spermatic or cremasteric artery.
_Nerve-supply._—External spermatic nerve.
=The Inguinal Canal.=—This term (Canalis inguinalis) is applied to an
oblique passage through the posterior part of the abdominal wall.[53] It
begins at the internal inguinal or abdominal ring, and extends obliquely
downward, inward, and somewhat forward, to end at the external inguinal
or subcutaneous ring. Its anterior wall is formed by the fleshy
posterior part of the internal oblique muscle, and the posterior wall by
the strong tendinous inguinal (Poupart’s) ligament. The average length
of the canal, measured along the spermatic cord, is about four inches
(ca. 10 cm.). The =internal inguinal ring= (Annulus inguinalis
abdominalis) is bounded in front by the thin margin of the internal
oblique muscle, and behind by the inguinal ligament. It is directed
approximately from the edge of the prepubic tendon toward the external
angle of the ilium. Its length is about four or five inches (ca. 10 to
12 cm.). The edge of the muscle is attached to the surface of the
ligament here by delicate connective tissue, except where structures
intervene between the walls of the canal. Consequently the limits of the
ring are not very clearly defined. The =external inguinal ring= (Annulus
inguinalis subcutaneus) is a well defined slit in the aponeurosis of the
external oblique muscle, situated lateral to the prepubic tendon. Its
long axis is directed from the edge of the prepubic tendon outward and
forward, and its average length is about four inches (ca. 10 cm.). The
canal contains in the male the spermatic cord, the tunica vaginalis, the
external cremaster muscle, the external pudic artery and a small
satellite vein, and the inguinal lymph vessels and nerves. In the female
it contains the mammary vessels and nerves; in the bitch it also lodges
the round ligament of the uterus, inclosed in a tubular process of
peritoneum.
The two rings do not correspond in direction, so that the length of
the canal varies greatly when measured at different points. The inner
angle of the internal ring lies almost immediately above that of the
external ring, but the outer angle is situated five to six inches (ca.
12 to 15 cm.) from that of the external ring. The inner angles of the
external rings are well defined and distinctly palpable in the living
subject; they are about three to four inches (ca. 8 to 10 cm.) apart.
=The Prepubic Tendon.=—The =prepubic tendon= is essentially the tendon
of insertion of the two recti abdominis, but also furnishes attachment
to the obliqui, the graciles, and the pectinei. It is attached to the
anterior borders of the pubic bones, including the ilio-pectineal
eminences. It has the form of a very strong thick band, with concave
lateral borders which form the inner boundaries of the external inguinal
rings. Its direction is oblique upward and backward.[54] Its structure
is somewhat complex. Most of the fibers of the posterior part extend
from one ilio-pectineal eminence to the other. The fibers which belong
to the recti curve in to the median line. The aponeuroses of the
internal oblique muscles are inserted into its abdominal surface, and
the inguinal ligaments are attached to and continue across it in
arciform fashion. The anterior part of the tendon of origin of the
gracilis is fused with it ventrally, and many of the fibers of the
pectineus arise from it. It gives off on either side a strong round
band, the so-called =pubo-femoral= or =accessory ligament=, which is
inserted into the fossa of the head of the femur with the round ligament
(_vide_ hip joint).
MUSCLES OF THE THORACIC LIMB
I. THE MUSCLES OF THE SHOULDER GIRDLE (Figs. 177, 178, 179, 186)
This group consists of those muscles which connect the thoracic limb
with the head, neck, and trunk. The group naturally falls into two
divisions—dorsal and ventral.[55]
A. DORSAL DIVISION
This division consists of two layers which overlie the proper muscles of
the neck and back.
FIRST LAYER
1. =Trapezius.=—This is a flat, triangular muscle, the base of the
triangle corresponding with the spine. It is divided by an aponeurotic
portion into two divisions:
(=a=) =Trapezius cervicalis.=—_Origin._—The funicular portion of the
ligamentum nuchæ, from the second cervical to the third thoracic
vertebra.
_Insertion._—The spine of the scapula and the fascia of the shoulder and
arm.
(=b=) =Trapezius thoracalis s. dorsalis.=—_Origin._—The supraspinous
ligament, from the third to the tenth thoracic vertebra.
_Insertion._—The tubercle of the spine of the scapula.
_Action._—Acting as a whole, to elevate the shoulder; the cervical
portion draws the scapula forward and upward and the thoracic portion
draws it backward and upward.
_Structure._—The muscle arises by a short, thin aponeurosis, from which
the fibers of the flat fleshy portion converge to the spine of the
scapula and the aponeurosis which separates the two portions. The
cervical fascia joins the ventral edge of the cervical portion to the
mastoido-humeralis, or the two muscles may unite here.
_Relations._—Superficially, the skin and fascia; deeply, the
rhomboideus, latissimus dorsi, supraspinatus, infraspinatus, deltoid,
splenius, serratus magnus, and anterior deep pectoral muscles, and the
cartilage of the scapula.
_Blood-supply._—Deep cervical and intercostal arteries.
_Nerve-supply._—Spinal accessory nerve.
SECOND LAYER
This consists of two muscles—the rhomboideus and the latissimus dorsi.
2. =Rhomboideus.=—This consists of two portions:
(=a=) =Rhomboideus cervicalis s. cervicis.=—_Origin._—The funicular
portion of the ligamentum nuchæ, from the second cervical to the second
thoracic vertebra.
_Insertion._—The internal surface of the cartilage of the scapula.
(=b=) =Rhomboideus thoracalis s. dorsalis.=—_Origin._—The spinous
processes of the second to the seventh thoracic vertebra by means of the
dorso-scapular ligament.
_Insertion._—The inner surface of the cartilage of the scapula.
_Action._—To draw the scapula upward and forward. When the limb is fixed
the cervical portion will elevate the neck.
_Structure._—The cervical portion is narrow, pointed at its anterior
extremity, and lies along the funicular part of the ligamentum nuchæ, to
which it is attached by short tendon bundles. The fibers are directed
for the most part longitudinally. The thoracic portion is quadrilateral
in shape, and its fibers are nearly vertical. Its deep face is
intimately attached to the dorso-scapular ligament.
_Relations._—Superficially, the skin and fascia (over a small area), the
trapezius, and the cartilage of the scapula; deeply, the dorso-scapular
ligament, the splenius, complexus, longissimus dorsi, and serratus
anticus.
_Blood-supply._—Dorsal and superior cervical arteries.
_Nerve-supply._—Sixth cervical nerve.
3. =Latissimus Dorsi.=—This is a wide muscle which has the form of a
right-angled triangle. It lies for the most part under the skin and
panniculus, on the lateral wall of the thorax, from the spine to the
arm.
_Origin._—The lumbo-dorsal fascia—and by this means from the lumbar and
thoracic spines as far forward as the highest point of the withers.
_Insertion._—The internal tubercle of the humerus, in common with the
teres major.
_Action._—To draw the humerus upward and backward and flex the shoulder
joint. If the limb is advanced and fixed, it draws the trunk forward.
_Structure._—The muscle arises by a wide aponeurosis, which fuses with
that of the serratus posticus and with the lumbo-dorsal fascia. The
muscular portion is at first rather thin, but by the convergence of its
fibers becomes thicker as it approaches the arm. The anterior fibers
pass almost vertically downward over the dorsal angle of the scapula and
its cartilage. The posterior fibers are directed downward and forward.
The thick belly formed by the convergence of these passes under the
triceps to end on the flat tendon of insertion, which is common to this
muscle and the teres major.
_Blood-supply._—Subscapular, intercostal, and lumbar arteries.
_Nerve-supply._—Brachial plexus (eighth cervical and dorsal roots).
B. VENTRAL DIVISION
1. =Mastoido-humeralis= (M. brachiocephalicus; levator humeri).—This
muscle extends along the side of the neck from the head to the arm. It
is incompletely divisible into two portions.
_Origin._—(1) The mastoid process of the petrous temporal bone and the
occipital crest; (2) the wing of the atlas and the transverse processes
of the second, third, and fourth cervical vertebræ.
_Insertion._—The deltoid tuberosity and the curved rough line which
extends from this to the distal extremity of the humerus.
_Action._—When the head and neck are fixed, to draw the limb forward,
extending the shoulder joint. When the limb is fixed, to extend the head
and neck, if the muscles act together; acting separately, to incline the
head and neck to the same side.
_Structure._—As already mentioned, the muscle is capable of incomplete
division into two parts, the line of division being indicated by the
emergence of superficial branches of the ventral divisions of the
cervical nerves. The mastoid portion (M. cleido-mastoideus) partly
overlaps the other portion (M. cleido-transversarius), which lies dorsal
to it. The former is attached to the mastoid process and the occipital
bone by a broad tendon which fuses with that of the splenius and
trachelo-mastoideus; it is also attached to the tendon of insertion of
the sterno-cephalicus by aponeurosis. The dorsal portion is attached to
the transverse processes by four fleshy digitations. The belly of the
muscle is adherent superficially to the cervical fascia and the
panniculus, and deeply to the subscapulo-hyoideus. In front of the
shoulder its deep face is marked by a tendinous intersection of variable
development.[56] Here the muscle becomes wider, covers the shoulder
joint, passes between the brachialis and biceps, and is inserted by
means of a wide tendon which it shares with the superficial pectoral
muscle.
_Relations._—Superficially, the skin, cervical fascia, the parotid
gland, the panniculus, brachialis, and branches of the cervical nerves;
deeply, the splenius, trachelo-mastoideus, rectus capitis anterior
major, omo-hyoideus, serratus magnus, anterior deep pectoral and biceps
muscles, the inferior cervical artery, the prescapular lymph glands, and
branches of the cervical nerves. The ventral edge of the muscle forms
the dorsal boundary of the jugular furrow. The dorsal border may be in
contact with the cervical trapezius, or separated from it by a variable
interval.
_Blood-supply._—Inferior cervical, carotid, and vertebral arteries.
_Nerve-supply._—Spinal accessory and cervical nerves.
The =pectoral fascia= is a thin membrane covering the surface of the
pectoral muscles, to which it is, for the most part, pretty intimately
attached. It detaches a layer which passes between the superficial and
deep pectorals. At the posterior edge of the triceps another layer is
given off, which passes on the outer surface of this muscle to blend
with the scapular fascia; the deeper layer becomes continuous with the
subscapular and cervical fasciæ.
The =pectoral muscles= form a large fleshy mass which occupies the space
between the ventral part of the chest-wall and the shoulder and arm.
They are clearly divisible into a superficial and a deep layer. The
superficial layer may be subdivided into two portions by careful
dissection; the deep layer is clearly made up of two muscles.
2. =Superficial pectoral= (M. pectoralis superficialis).
(=a=) =Anterior superficial pectoral= (portio clavicularis s.
descendens; pectoralis anticus).—This is a short, thick, somewhat
rounded muscle, which extends between the anterior part of the sternum
and the front of the arm. It forms a distinct prominence on the front of
the breast, which is easily recognized in the living animal.
_Origin._—The cariniform cartilage of the sternum.
_Insertion._—(1) The curved line of the humerus with the
mastoido-humeralis; (2) the fascia of the arm.
_Action._—To adduct and advance the limb.
_Structure._—The belly of the muscle is convex on its superficial face,
but deeply it is flattened where it overlaps the posterior superficial
pectoral. Here the two muscles are usually pretty intimately attached to
each other, and care must be exercised in making the separation. The
tendon of insertion blends with that of the mastoido-humeralis and with
the fascia of the arm. At the middle line of the breast a furrow occurs
between the two muscles; laterally, another furrow, containing the
cephalic vein, lies between the muscle and the mastoido-humeralis.
_Relations._—Superficially, the skin, fascia, and panniculus; deeply,
the posterior division, the deep pectoral, and the biceps. The cephalic
vein lies in the groove between this muscle and the mastoido-humeralis.
(=b=) =Posterior superficial pectoral= (portio sternocostalis;
pectoralis transversus).—This is a wide muscular sheet which extends
from the ventral edge of the sternum to the fascia on the inner surface
of the forearm.
_Origin._—(1) The ventral edge of the sternum as far back as the sixth
cartilage; (2) a fibrous raphé common to the two muscles.
_Insertion._—(1) The fascia on the proximal third of the forearm; (2)
the curved line of the humerus with the preceding muscle.
_Action._—To adduct the limb and to tense the fascia of the forearm.
_Structure._—It is thin and pale, and mixed with a good deal of fibrous
tissue. The right and left muscles fuse at a median fibrous raphé. The
tendon of insertion unites with the fascia on the inner side of the
forearm for the most part; only a small part in front, about an inch in
width, is attached to the humerus.
_Relations._—Superficially, the skin, fascia, and the preceding muscle;
deeply, the deep pectoral, the biceps, and the brachialis; at the elbow,
the posterior radial vessels, the median nerve, and the inner and middle
flexors of the carpus.
3. =Deep pectoral= (M. pectoralis profundus).—This muscle is much
thicker and more extensive in the horse than the superficial pectoral.
It consists of two distinct portions.
(=a=) =Anterior deep pectoral= (portio prescapularis; pectoralis
parvus).—This division is prismatic and extends from the anterior part
of the lateral surface of the sternum to the cervical angle of the
scapula.
_Origin._—The anterior half of the lateral surface of the sternum and
the cartilages of the first four ribs.
_Insertion._—The aponeurosis which covers the supraspinatus at its
dorsal end, and the scapular fascia.
_Action._—To adduct and retract the limb; when the limb is advanced and
fixed, to draw the trunk forward.
_Structure._—The muscle is almost entirely fleshy. It describes a curve
(convex anteriorly), passing at first forward, then upward over the
front of the shoulder, a little to its inner side, and finally upward
and backward along the anterior border of the supraspinatus. It is
loosely attached to the latter muscle, and terminates in a pointed end
which becomes more firmly attached near the cervical angle of the
scapula.
_Relations._—Superficially, the skin and fascia, the panniculus,
superficial pectoral, trapezius, and mastoido-humeralis muscles, the
cephalic vein, and the inferior cervical artery; deeply, the posterior
deep pectoral, biceps, supraspinatus, omo-hyoideus, and serratus magnus
muscles, the brachial vessels, and the branches of the brachial plexus
of nerves.
(=b=) =Posterior deep pectoral= (portio humeralis s. ascendens;
pectoralis magnus).—This is much the largest of the pectoral group in
the horse. It is somewhat triangular or fan-shaped.
_Origin._—(1) The abdominal tunic; (2) the xiphoid cartilage and ventral
aspect of the sternum; (3) the cartilages of the fourth to the ninth
ribs.
_Insertion._—(1) The internal tuberosity of the humerus; (2) the
external lip of the bicipital groove; (3) the tendon of origin of the
coraco-brachialis.
_Action._—To adduct and retract the limb; if the limb is advanced and
fixed, to draw the trunk forward.
_Structure._—This muscle is also almost entirely fleshy. Its posterior
part is wide and thin, but as the muscle is traced forward, it becomes
narrower and much thicker. It passes forward and slightly upward in a
gentle curve to its insertion. The humeral insertion is just below that
of the inner division of the supraspinatus. Part of the fibers are
inserted by means of a tendinous band which binds down the tendon of the
biceps and is attached to the external lip of the bicipital groove, and
a small part is attached to the tendon of origin of the
coraco-brachialis.
_Relations._—Superficially, the skin, panniculus, and superficial
pectoral; deeply, the abdominal tunic, the external oblique, the rectus
abdominis et thoracis, the brachial vessels, and branches of the
brachial plexus of nerves. The external thoracic vein lies along the
outer or upper border.
_Blood-supply._—Internal and external thoracic, inferior cervical,
anterior circumflex, and intercostal arteries.
_Nerve-supply._—Pectoral (or thoracic) nerves, from the brachial plexus.
4. =Serratus magnus= (M. serratus ventralis).—This is a large,
fan-shaped muscle, situated on the lateral surface of the neck and
thorax. It derives its name from the serrated ventral edge of its
thoracic portion. It consists of a cervical and a thoracic portion.
(=a=) =Cervical part= (M. serratus cervicis; levator scapulæ hominis).
_Origin._—The transverse processes of the last four or five cervical
vertebræ.
_Insertion._—The anterior triangular area on the costal surface of the
scapula and the adjacent part of the cartilage.
(=b=) =Thoracic part= (M. serratus thoracis; serratus anterior hominis).
_Origin._—The external surfaces of the first eight or nine ribs.
_Insertion._—The posterior triangular area on the costal surface of the
scapula and the adjacent part of the cartilage.
_Action._—The two muscles form a sort of sling in which the trunk is
suspended. Contracting together, they raise the thorax; contracting
singly, the weight is shifted to the limb on the side of the muscle
acting. The two parts can contract separately and are antagonistic in
their action on the scapula. The cervical part draws the base of the
scapula toward the neck, while the thoracic part has the opposite
action; these effects concur in the backward and forward swing of the
limb respectively. With the limb fixed, the cervical part extends
(raises) the neck or inclines it laterally. The thoracic part may act as
a muscle of forced inspiration.
_Structure._—In the domesticated animals there is no such clear division
of the muscle as is found in man and the apes. On account of the
difference in action, however, it seems desirable to distinguish the two
portions. The cervical part is thick and almost entirely fleshy. The
thoracic part has on its superficial face a thick, tendinous layer which
may sustain the weight of the trunk when the muscle substance relaxes.
The ventral edge presents distinct digitations, the last four of which
alternate with those of the obliquus externus abdominis, and are covered
by the abdominal tunic. The fourth, fifth, and sixth digitations extend
nearly to the distal ends of the ribs. The last digitation is small and
may be absent. Exceptionally additional digitations may be attached to
the tenth or eleventh rib or to the fascia over the intercostal muscles.
The fibers converge to the insertion, which is thick and is intersected
by elastic lamellæ derived from the dorso-scapular ligament.
_Relations._—Superficially, the mastoido-humeralis, trapezius, deep
pectoral, subscapularis, teres major, latissimus dorsi, panniculus
carnosus, the abdominal tunic, the brachial vessels, and the long
thoracic nerve; deeply, the splenius, complexus, longissimus,
transversalis costarum, the ribs and external intercostal muscles, and
branches of the superior cervical and dorsal arteries.
_Blood-supply._—Superior cervical, dorsal, vertebral, and intercostal
arteries.
_Nerve-supply._—Brachial plexus.
II. THE MUSCLES OF THE SHOULDER
Under this head will be described those muscles which arise on the
scapula and end on the arm; they may be divided into two groups—one
covering the dorsum, the other the venter of the scapula.
The =superficial fascia= of the shoulder and arm contains the panniculus
carnosus of this region, and may be considered to be continued on the
inner side of the limb by the subscapular fascia.
The =thoracic= or =scapulo-humeral portion= of the =panniculus= (M.
cutaneus scapulæ et humeri) arises by a thin aponeurosis from the
ligamentum nuchæ at the withers. The fleshy portion begins over the
upper part of the scapula and extends to the elbow. Its fibers have in
general a dorso-ventral direction. It is continuous behind with the
abdominal portion.
The =deep fascia= of the shoulder and arm (Fascia omobrachialis) is much
more developed and important. It is strong and tendinous, and is
intimately adherent to the muscles on the outer surface of the scapula,
between which it detaches =intermuscular septa=, which are attached to
the spine and borders of the scapula. The brachial portion is, for the
most part, only loosely attached to the underlying muscles, for which it
forms sheaths; it is attached to the humerus, especially to the lips of
the bicipital groove and the deltoid tuberosity. It blends distally with
the tendon of insertion of the biceps, and is continued by the
antibrachial fascia.
A. EXTERNAL GROUP (Figs. 178, 179)
1. =Deltoid= (M. deltoideus; long abductor of the arm; scapular portion
of the deltoid of man).—This lies partly on the triceps in the angle
between the scapula and humerus, partly on the infraspinatus and teres
minor.
_Origin._—(1) The upper part of the posterior border of the scapula; (2)
the spine of the scapula, by means of the strong aponeurosis which
covers the infraspinatus.
_Insertion._—The deltoid tuberosity of the humerus.
_Action._—To flex the shoulder joint and abduct the arm.
_Structure._—The origin of the muscle is partly aponeurotic, partly
fleshy. The aponeurosis fuses with that of the infraspinatus; the
posterior part is attached to the scapula immediately in front of the
origin of the long head of the triceps. The belly of the muscle lies for
the most part in a cavity formed in the triceps. It is widest about its
middle.
_Relations._—Superficially, the skin, fascia, panniculus, and
mastoido-humeralis; deeply, the infraspinatus, teres minor, triceps, and
brachialis muscles, and branches of the posterior circumflex artery and
axillary nerve.
_Blood-supply._—Subscapular artery (chiefly through the posterior
circumflex).
_Nerve-supply._—Suprascapular and axillary nerves.
2. =Supraspinatus.=—This muscle occupies the supraspinous fossa, which
it fills, and beyond which it extends, thus coming in contact with the
subscapularis.
_Origin._—The supraspinous fossa, the spine, and the lower part of the
cartilage of the scapula.
_Insertion._—The inner and outer lips of the bicipital groove.
_Action._—To extend the shoulder joint. It also assists in preventing
dislocation.
_Structure._—The surface of the muscle is covered by a strong
aponeurosis, from the deep face of which many fibers arise. The muscle
is thin at its origin from the cartilage, but becomes considerably
thicker below. At the neck of the scapula it divides into two branches,
between which the tendon of origin of the biceps emerges. These
branches, fleshy superficially, tendinous deeply, are inserted into the
lips of the bicipital groove. They are united by a fibrous membrane
already mentioned in connection with the deep pectoral muscle; some
fibers are attached to this membrane and the capsule of the shoulder
joint.
_Relations._—Superficially, the skin, fascia, panniculus, trapezius, and
mastoido-humeralis; deeply, the scapula and its cartilage, the
subscapularis muscle, and the suprascapular vessels and nerve; in front,
the anterior deep pectoral muscle; behind, the spine of the scapula and
infraspinatus muscle.
_Blood-supply._—Suprascapular and posterior circumflex arteries.
_Nerve-supply._—Suprascapular nerve.
3. =Infraspinatus.=—This muscle occupies the greater part of the
infraspinous fossa.
_Origin._—The infraspinous fossa and the scapular cartilage.
_Insertion._—(1) The outer tuberosity of the humerus, distal to the
outer insertion of the supraspinatus; (2) the posterior eminence of the
outer tuberosity.
_Action._—To abduct the arm and rotate it outward.[57] It also plays the
part of a lateral ligament.
_Structure._—This muscle is also covered by a strong aponeurosis, from
which many fibers arise, and by means of which the deltoid is attached
to the spine of the scapula. A thick tendinous layer partially divides
the muscle into two strata, and, coming to the surface at the shoulder
joint, constitutes the chief means of insertion. This tendon, an inch or
more (3 cm.) in width, passes over the posterior eminence of the
external tuberosity of the humerus; it is bound down by a fibrous sheet,
and a =synovial bursa= is interposed between the tendon and the bone.
When the long insertion is cut and reflected, the short insertion,
partly tendinous, partly fleshy, is exposed.
_Relations._—Superficially, the skin, fascia, panniculus, trapezius, and
deltoid; deeply, the scapula and its cartilage, the shoulder joint and
capsule, the long head of the triceps, the teres minor, and the nutrient
artery of the scapula.
_Blood-supply._—Subscapular artery.
_Nerve-supply._—Suprascapular and axillary nerves.
4. =Teres minor.=—This is a much smaller muscle than the foregoing. It
lies chiefly on the triceps, under cover of the deltoid and
infraspinatus.
_Origin._—(1) The rough lines on the distal and posterior part of the
infraspinous fossa; (2) a small part of the posterior border of the
scapula, about its middle; (3) a tubercle near the rim of the glenoid
artery.
_Insertion._—The deltoid tuberosity and a small area just above it.
_Action._—To flex the shoulder joint and to abduct the arm; also to
assist in outward rotation.
_Structure._—The muscle is not rounded in the horse and ox, but flat and
triangular. Its origin from the posterior border of the scapula is by
means of an aponeurosis which also gives origin to fibers of the
infraspinatus and triceps. A =bursa= is commonly found between the
terminal part of the muscle and the capsule of the shoulder joint, and
is often continuous with that of the infraspinatus.
_Relations._—Superficially, the deltoid and infraspinatus muscles;
deeply, the scapula, the shoulder joint, and the triceps muscle.
_Blood-supply._—Subscapular artery (circumflex branches).
_Nerve-supply._—Axillary nerve.
B. INTERNAL GROUP
1. =Subscapularis.=—This muscle occupies the subscapular fossa, beyond
which, however, it extends both before and behind.
_Origin._—The subscapular fossa.
_Insertion._—The posterior eminence of the internal tuberosity of the
humerus.
_Action._—To adduct the humerus.
[Illustration:
FIG. 187.—MUSCLES OF THORACIC LIMB OF HORSE, INTERNAL VIEW.
_3_, _4_, Rhomboideus; _5_, latissimus dorsi; _8_, posterior deep
pectoral; _9_, anterior deep pectoral; _11_, supraspinatus; _15_,
subscapularis; _16_, teres major; _20_, long head of triceps; _22a_,
_22b_, tensor fasciæ antibrachii; _23_, internal head of triceps.
(After Ellenberger, in Leisering’s Atlas.)
]
_Structure._—The muscle is flat and triangular, with the base upward.
The latter is thin and interdigitates with the scapular attachments of
the serratus. Below this the belly thickens and becomes narrower. It is
covered by an aponeurosis, and contains a considerable amount of
tendinous tissue. The tendon of insertion is crossed by the tendon of
origin of the coraco-brachialis; it is intimately adherent to the
capsule of the shoulder joint, and may be regarded as replacing the
internal ligament of the latter. A small bursa may occur here.
_Relations._—Superficially, the scapula and shoulder joint, the
supraspinatus, triceps, and teres major muscles; deeply, the serratus
magnus muscle, the brachial vessels, and the chief branches of the
brachial plexus. The subscapular vessels run along or near the posterior
edge of the muscle.
_Blood-supply._—Subscapular artery.
_Nerve-supply._—Subscapular nerves (from the brachial plexus).
2. =Teres major= (Teres internus; adductor of the arm).—This muscle is
flat, widest about its middle, and lies chiefly on the deep face of the
triceps.
_Origin._—The dorsal angle and the adjacent part of the posterior border
of the scapula.
_Insertion._—The tubercle on the inner surface of the shaft of the
humerus, in common with the latissimus dorsi.
_Action._—To flex the shoulder joint and adduct the arm.
_Structure._—It is for the most part fleshy, but the origin consists of
an aponeurosis which blends with that of the tensor fasciæ antibrachii.
The insertion is by a flat tendon which fuses with that of the
latissimus dorsi.
_Relations._—Superficially, the triceps, infraspinatus, and deltoid
muscles; deeply, the serratus magnus muscle. The subscapular vessels lie
in a groove between the anterior edge of this muscle and the posterior
border of the subscapularis; near the shoulder joint the posterior
circumflex artery and the axillary nerve emerge between the two muscles.
The deep face of the muscle is crossed by the thoracic branches of the
brachial plexus, and by the branch of the subscapular artery which
supplies the latissimus dorsi.
_Blood-supply._—Subscapular artery.
_Nerve-supply._—Axillary nerve.
3. =Coraco-brachialis= (Coraco-humeralis).—This muscle lies on the inner
surface of the shoulder joint and the arm.
_Origin._—The coracoid process of the scapula.
_Insertion._—(1) A small area above the internal tubercle of the
humerus; (2) the middle third of the anterior surface of the humerus.
_Action._—To adduct the arm and to flex the shoulder joint.
_Structure._—The long tendon of origin emerges between the subscapularis
and the inner branch of the supraspinatus. It passes over the terminal
part of the subscapularis and is provided with a =synovial sheath=. The
muscular part spreads out and divides into two portions. The smaller and
shorter portion is inserted into the proximal third of the shaft of the
humerus, close to the origin of the lateral head of the triceps; the
larger and longer portion is inserted into the middle third of the
humerus, in front of the internal tubercle and the inner head of the
triceps.
_Relations._—Externally, the subscapularis muscle and the humerus;
internally, the deep pectoral and brachialis muscles. The anterior
circumflex artery and the nerve to the biceps usually emerge between the
two insertions, and the brachial vessels lie along the posterior border
of the muscle.
_Blood-supply._—Anterior circumflex artery.
_Nerve-supply._—Musculo-cutaneous nerve.
4. =Capsularis= (Scapulo-humeralis posticus s. gracilis).—This is a very
small muscle, which lies on the back of the capsule of the shoulder
joint.
_Origin._—The scapula, close to the rim of the glenoid cavity.
_Insertion._—The posterior surface of the shaft of the humerus, a short
distance below the head.
_Action._—It may perhaps tense the capsule of the shoulder joint and
prevent its being pinched during flexion.
_Structure._—It is fleshy and usually about the breadth of a finger. It
may, however, consist of only a few bundles of fibers; sometimes it is
double. Its attachment to the joint capsule is slight. It passes through
the brachialis muscle to reach its insertion.
_Relations._—Superficially, the teres minor and triceps muscles; deeply,
the teres major and subscapularis muscles, and the capsule of the joint.
_Blood-supply._—Posterior circumflex artery.
_Nerve-supply._—Axillary nerve.
III. THE MUSCLES OF THE ARM
This group consists of five muscles which are grouped around the
humerus. They arise from the scapula and the humerus, and are inserted
into the forearm. They act on the elbow joint and the fascia of the
forearm.
[Illustration:
FIG. 188.—BICEPS AND BRACHIALIS MUSCLES OF HORSE. (After
Ellenberger-Baum, Anat. für Künstler.)
]
1. =Biceps brachii= (Coraco-radialis; flexor brachii).—This is a strong,
somewhat rounded muscle, which lies on the anterior surface of the
humerus.
_Origin._—The tuberosity of the scapula.
_Insertion._—(1) The bicipital tuberosity of the radius; (2) the
internal lateral ligament of the elbow joint; (3) the fascia of the
forearm and the tendon of the extensor carpi radialis.
_Action._—To flex the elbow joint, to fix the shoulder, elbow, and
carpus in standing, and to tense the fascia of the forearm.
_Structure._—The muscle is inclosed in a double sheath of fascia, which
is attached to the lips of the bicipital groove and the deltoid ridge of
the humerus. The tendon of origin is moulded on the bicipital groove; it
is very strong and dense and is partly cartilaginous. Its play over the
groove is facilitated by the large =bicipital bursa= (Bursa
intertubercularis). The synovial membrane covers not only the deep face
of the tendon, but extends somewhat over the edges to the superficial
face. A well-marked tendinous intersection runs through the belly of the
muscle and divides distally into two portions. Of these, the short,
thick one is inserted into the bicipital tuberosity and detaches fibers
to the internal lateral ligament. The long tendon (Lacertus fibrosus) is
thinner, blends with the fascia of the forearm, and ends by fusing with
the tendon of the extensor carpi radialis.
_Relations._—Externally, the mastoido-humeralis and brachialis muscles;
internally, the posterior deep pectoral and the superficial pectoral
muscles; in front, the anterior deep pectoral muscle; behind, the
humerus, the coraco-brachialis muscle, the anterior circumflex and
anterior radial vessels, and the musculo-cutaneous nerve.
_Blood-supply._—Branches of the brachial and anterior radial arteries.
_Nerve-supply._—Musculo-cutaneous nerve.
2. =Brachialis= (Humeralis obliquus s. externus; brachialis
anticus).—This muscle occupies the musculo-spiral groove of the humerus.
_Origin._—The proximal third of the posterior surface of the humerus.
_Insertion._—The inner surface of the neck of the radius (under cover of
the lateral ligament) and the arciform ligament.
_Action._—To flex the elbow joint.
_Structure._—The peculiar spiral course of this muscle gave rise to the
name often applied to it—humeralis obliquus. Beginning on the posterior
surface of the shaft, close to the head of the humerus, it winds over
the lateral surface, crosses the biceps very obliquely, and finally
reaches the inner side of the forearm by passing between the biceps and
the extensor carpi. It is entirely fleshy, with the exception of its
relatively slender tendon of insertion.
_Relations._—Externally the skin and fascia, the teres minor, deltoid,
triceps (lateral head), biceps, and mastoido-humeralis muscles. The
anterior radial artery crosses the deep face of the muscle in its distal
third, and the radial nerve accompanies the muscle in the distal half of
the musculo-spiral groove.
_Blood-supply._—Brachial artery.
_Nerve-supply._—Radial nerve.
3. =Tensor fasciæ antibrachii= (Fig. 187)[58] (Scapulo-ulnaris; long
extensor of the forearm; accessory anconeus of the latissimus
dorsi).—This is a thin muscle which lies on the inner surface of the
triceps.
_Origin._—The tendon of insertion of the latissimus dorsi and the
posterior border of the scapula.
_Insertion._—(1) The fascia of the forearm; (2) a small eminence on the
posterior border of the olecranon.
_Action._—(1) To tense the fascia of the forearm and to extend the elbow
joint.
_Structure._—The origin consists of a very thin aponeurosis which blends
with those of the caput longum and the latissimus dorsi. The muscular
portion is quite thin in its anterior part, somewhat thicker behind, and
is narrower than the aponeurotic origin. It is succeeded by an
aponeurotic insertion, which ends chiefly by blending with the fascia of
the forearm a little below the elbow. There is, however, a small but
constant tendinous attachment to the olecranon.
_Relations._—Externally, the panniculus, triceps (long and internal
heads), the inner and middle flexors of the carpus, and the ulnar
vessels and nerve; internally, the latissimus dorsi, serratus magnus,
and posterior pectoral muscles.
_Blood-supply._—Subscapular, ulnar, and deep brachial arteries.
_Nerve-supply._—Radial nerve.
4. =Triceps brachii= (Figs. 178, 179, 187) (Brachial triceps; triceps
extensor cubiti).—This, together with the preceding muscle, constitutes
the large muscular mass which fills the angle between the posterior
border of the scapula and the humerus. It is clearly divisible into
three heads, as described below.
(=a=) =Long head= (Caput longum tricipitis; anconeus longus; caput
magnum).—This, the largest and longest of the three heads, is a
powerful, thick, triangular muscle, which extends from the posterior
border of the scapula to the olecranon.
_Origin._—The posterior border of the scapula.
_Insertion._—The outer and posterior part of the summit of the
olecranon.
_Action._—(1) To extend the elbow joint; (2) to flex the shoulder joint.
_Structure._—The muscle arises by a wide, strong aponeurosis from the
posterior border of the scapula. From this the bundles of the fleshy
portion converge to the short, strong tendon of insertion. A careful
examination will show that the muscle is penetrated by a tendinous
intersection from which many fibers take origin obliquely. The
superficial face is covered by an aponeurosis which is specially
developed at its distal part. A small =bursa= occurs under the tendon of
insertion.
_Relations._—Externally, the panniculus, deltoid, infraspinatus, teres
minor, and the external head; internally, the tensor fasciæ antibrachii,
teres major, latissimus dorsi, and posterior deep pectoral muscles, and
the subscapular vessels; in front, the brachialis, and the inner head,
the deep brachial and posterior circumflex vessels, and the axillary and
radial nerves; behind, the skin and fascia.
_Blood-supply._—Subscapular and deep brachial arteries.
_Nerve-supply._—Radial nerve.
(=b=) =External head= (Caput laterale tricipitis s. anconeus lateralis
s. externus; caput medium).—This is a strong, quadrilateral muscle,
which lies on the outer surface of the arm. Its proximal third is
covered by the deltoid and teres minor muscles; the remainder only by
the thin panniculus and the skin.
_Origin._—The deltoid tuberosity and the curved rough line which extends
from it to the neck of the humerus.
_Insertion._—(1) A small prominent area on the outer surface of the
olecranon; (2) the tendon of the long head.
_Action._—To extend the elbow joint.
_Structure._—The origin consists of short tendinous fibers. The belly is
thick, and is composed of parallel bundles which are directed obliquely
downward and backward. They are inserted partly into the tendon of the
long head and partly into the olecranon below and in front of that
tendon.
_Relations._—Externally, the deltoid, teres minor, and panniculus
muscles; internally, the long and inner heads and the brachialis muscle.
Branches of the circumflex vessels and axillary nerve emerge between the
posterior edge of the muscle and the long head. The deep face of the
muscle is related to the branches of the deep brachial artery and of the
radial nerve.
_Blood-supply._—Posterior circumflex and deep brachial arteries.
_Nerve-supply._—Radial nerve.
(=c=) =Internal head= (Fig. 193) (Caput mediale tricipitis; anconeus
medialis s. internus; caput parvum).—This is much the smallest of the
three heads. It is situated on the inner surface of the arm, and extends
from the middle third of the humerus to the olecranon.
_Origin._—The middle third of the inner surface of the shaft of the
humerus, behind and below the internal tubercle.
_Insertion._—The inner and fore part of the summit of the olecranon,
between the insertion of the long head and the origin of the ulnar head
of the flexor perforans.
_Action._—To extend the elbow joint.
_Structure._—The muscle is fleshy except at its insertion, where it has
a flat tendon, under which a small bursa may be found.
_Relations._—Externally, the humerus, brachialis, anconeus, and the
external head; internally, the posterior deep pectoral,
coraco-brachialis, teres major, latissimus dorsi, and tensor fasciæ
antibrachii muscles, the brachial and deep brachial vessels, and the
median and ulnar nerves; behind, the long head, branches of the deep
brachial vessels, and the radial nerve.
_Blood-supply._—Deep brachial and ulnar arteries.
_Nerve-supply._—Radial nerve.
5. =Anconeus= (M. anconeus parvus s. subanconeus).—This is a small
fleshy muscle which covers the olecranon fossa and is covered by the
triceps. It is somewhat difficult to separate from the outer head.
_Origin._—The distal third of the posterior surface of the humerus.
_Insertion._—The outer surface of the olecranon.
_Action._—To extend the elbow joint, and to raise the capsule of the
joint and prevent its being pinched during extension.
_Structure._—It is almost entirely fleshy, and is adherent by its deep
face to the joint capsule.
_Relations._—Superficially, the triceps muscle; deeply, the humerus and
the elbow joint.
_Blood-supply._—Deep brachial artery.
_Nerve-supply._—Radial nerve.
[Illustration:
FIG. 189.—DIGIT OF HORSE, POSTERIOR VIEW.
_14_, Deep flexor tendon; _15_, superficial flexor tendon; _16_,
posterior annular ligament of fetlock; _17_, proximal annular or
vaginal ligament of digit; _11_, lateral cartilage; _24_, plantar
cushion. (After Ellenberger-Baum, Anat. für Künstler.)
]
IV. FASCIÆ AND MUSCLES OF THE FOREARM AND MANUS
The forearm is covered on three sides by the muscles of this group,
leaving the inner surface of the radius for the most part subcutaneous.
The extensors of the carpus and digit lie on the anterior (dorsal) and
external part of the region, while the flexors occupy the posterior
(volar) surface.
The =fascia= of the =forearm= (Fascia antibrachii) forms a very strong
and complete investment for all the muscles of the region. The
=superficial fascia= is thin, and disappears at the carpus by fusing
with the deep fascia. The =deep fascia= is very strong and tendinous in
character. It furnishes insertion at its upper and inner part to the
tensor fasciæ antibrachii and posterior superficial pectoral muscles; at
its upper anterior and outer part, to aponeuroses from the
mastoido-humeralis and biceps. It is attached at the elbow by its deep
face to the outer tuberosities of the humerus and radius, to the ulna,
and to the lateral ligaments. On the inner surface of the forearm it
blends with the periosteum on the subcutaneous surface of the radius. It
is closely adherent to the surface of the extensor muscles, but is
rather loosely attached to the flexors. From its deep face are detached
=intermuscular septa=, which form sheaths for the muscles and are
attached to the underlying bones. The principal septa are: (_a_) One
which passes between the common extensor (in front) and the lateral
extensor and flexor carpi externus (behind); (_b_) one between the
common extensor and the extensor carpi radialis; (_c_) one between the
inner and middle flexors of the carpus.
The =carpal fascia= (Fascia carpi) is a direct continuation of that of
the forearm. It is attached chiefly to the tuberosities at the distal
end of the radius, to the accessory carpal (pisiform) bone, and to the
lateral ligaments. In front it forms the so-called =anterior annular
ligament= (Ligamentum carpi dorsale), bridging over the grooves and
binding down the extensor tendons and their synovial sheaths. Behind it
is greatly thickened and forms the =posterior annular= or =transverse
ligament= of the carpus (Ligamentum carpi transversum). This stretches
across from the accessory carpal bone to the internal lateral ligament
and the proximal extremity of the inner metacarpal bone. It thus
completes the carpal canal, in which lie the flexor tendons, their
synovial sheath, and the principal vessels and nerves of the region.
The =fascia= of the =metacarpus= and =digit= (Fascia metacarpea et
digitalis) is, in general, thinner than the preceding. It is attached to
the tendons, ligaments, and the exposed bony prominences—especially to
the small metacarpal bones. On the flexion surface of the fetlock joint
it is much thickened by fibers passing transversely from one sesamoid
bone to the other, forming an =annular ligament= which binds down the
flexor tendons in the sesamoid groove or canal. Distal to this is a
second thick quadrilateral sheet (Ligamentum vaginale) which covers and
is adherent to the tendon of the flexor perforatus. It is attached on
either side by two bands to the borders of the first phalanx, thus
firmly binding down the flexor tendons. A little further down a
crescentic =fibro-elastic sheet= covers the terminal expansion of the
deep flexor tendon. It is attached on either side by a strong band to
the side of the first phalanx about its middle.
A. EXTENSOR DIVISION
1. =Extensor carpi radialis= (M. extensor carpi radialis s. radialis
dorsalis; extensor metacarpi magnus; anterior extensor of the
metacarpus).—This is the largest muscle of the extensor division, and
lies on the anterior (dorsal) surface of the radius.
_Origin._—(1) The external condyloid crest of the humerus; (2) the
coronoid fossa.
_Insertion._—The tuberosity on the anterior (dorsal) surface of the
proximal extremity of the large (third) metacarpal bone.
_Action._—To extend and fix the carpal joint and to flex the elbow
joint.
_Structure._—The belly of the muscle is rounded, and runs out to a point
at the distal third of the forearm. The tendon, which runs nearly the
whole length of the fleshy portion, appears on the surface of the latter
about its middle; here the muscle shows a distinctly pennate
arrangement. The tendon passes through the middle groove at the distal
extremity of the radius and over the capsule of the carpal joint, bound
down by the anterior annular ligament and invested with a =synovial
sheath=. The latter begins three to four inches (ca. 8 to 10 cm.) above
the carpus and extends almost to the insertion of the tendon. In the
lower half of the forearm the deep fascia blends with the tendon, and
here the latter is joined by the long tendon of the biceps.
_Relations._—Superficially, the skin, fascia, and the oblique extensor;
deeply, the capsule of the elbow joint, the biceps tendon, the radius,
the carpal joint capsule, the anterior radial artery, and the radial
nerve; externally, the anterior or common extensor; internally, at the
elbow, the brachialis and biceps.
_Blood-supply._—Anterior radial artery.
_Nerve-supply._—Radial nerve.
2. =Anterior= or =common digital extensor= (M. extensor digitalis
communis; anterior extensor of the phalanges; extensor pedis).—This
muscle lies external to the foregoing, which it resembles in general
form, although less bulky.
_Origin._—(1) The front of the distal extremity of the humerus, just
external to the coronoid fossa; (2) the external tuberosity on the
proximal extremity of the radius, the external lateral ligament of the
elbow, and the external border of the radius at the junction of its
proximal and middle thirds; (3) the external surface of the shaft of the
ulna; (4) the fascia of the forearm.
[Illustration:
FIG. 190.—MUSCLES OF LEFT THORACIC LIMB OF HORSE, FROM ELBOW DOWNWARD,
ANTERIOR VIEW.
_a_, Extensor carpi radialis; _g′_, superficial pectoral muscle.
(After Ellenberger-Baum, Anat. für Künstler.)
]
_Insertion._—(1) The extensor (or pyramidal) process of the third
phalanx; (2) the anterior surface of the proximal extremities of the
first and second phalanges.
_Action._—To extend the digital and carpal joints, and to flex the elbow
joint.
_Structure._—The muscle is a compound one, representing the common
extensor, together with vestiges of the proper extensors of the digits.
Usually at least =two heads= may be distinguished. The principal or
humeral head (Caput humerale) arises from the front of the extensor
epicondyle of the humerus in common with the extensor carpi. Its belly
is fusiform, and terminates in a point near the distal third of the
radius. The tendon appears on the surface of the muscle about the middle
of the belly, the arrangement being pennate. The tendon passes downward
through the outer of the two large grooves on the front of the distal
end of the radius, and over the capsule of the carpal joint. Passing
down over the front of the metacarpus, it inclines gradually inward,
reaching the middle line of the limb near the fetlock. A little below
the middle of the first phalanx it is joined by the branches of the
suspensory ligament, and the tendon thus becomes much wider. Two
=synovial membranes= facilitate the play of the tendon. The proximal one
is a =sheath= which begins about three inches (ca. 7 to 8 cm.) above the
carpus, and terminates at the proximal end of the metacarpus. At the
fetlock a =bursa= occurs between the tendon and the joint capsule, but
otherwise the two are adherent. The smaller head, arising chiefly from
the radius and ulna, is often divisible into two parts (Fig. 443). The
larger of these (Caput radiale, muscle of Phillips)[59] arises from the
outer tuberosity and outer border of the radius, and from the lateral
ligament of the elbow joint. The flat belly is succeeded by a delicate
tendon, which accompanies the principal tendon over the carpus (included
in the same sheath), and then passes outward to fuse with the tendon of
the lateral extensor. Usually a slip is detached which is inserted on
the proximal extremity of the first phalanx, or ends in the fascia here.
The smaller and deeper division (Caput ulnare, muscle of Thiernesse)[60]
is usually somewhat difficult to isolate. It arises from the ulna close
to the interosseous space. It has a small rounded belly and is provided
with a delicate tendon which may fuse with the principal tendon or may
be inserted into the capsule and the fascia in front of the fetlock
joint.
_Relations._—The chief relations of the belly of the muscle are:
superficially, the skin and fascia; deeply, the elbow joint, the radius
and ulna, the extensor carpi obliquus, and the anterior radial vessels
and radial nerve; in front and internally, the extensor carpi radialis;
behind, the lateral extensor and the interosseous vessels.
_Blood-supply._—Radial and interosseous arteries.
_Nerve-supply._—Radial nerve.
3. =Lateral digital extensor= (M. extensor digitalis lateralis s. digiti
quinti proprius; lateral extensor of the phalanges; extensor
suffraginis).—This muscle is much smaller than the preceding, behind
which it is situated.
_Origin._—The external tuberosity of the radius and the lateral ligament
of the elbow joint, the shaft of the ulna, the outer border of the
radius, and the intermuscular septum.
_Insertion._—An eminence on the front of the proximal extremity of the
first phalanx.
_Action._—To extend the digit and carpus.
_Structure._—The muscle is pennate, and is inclosed in a sheath formed
by the deep fascia, from which many fibers arise. The belly is thin and
fusiform and terminates at the lower third of the forearm. From here the
tendon (at first small and round) passes downward through the groove on
the outer tuberosity of the distal end of the radius, then over the
carpus, and, gradually inclining toward the front, but not reaching the
middle line of the limb, it passes over the metacarpus and fetlock to
its insertion. Two =synovial membranes= occur in connection with the
tendon. A =sheath= envelops the tendon, beginning about three inches
(ca. 6 to 8 cm.) above the carpus, and reaching to the proximal end of
the metacarpus. At the fetlock a small bursa lies between the tendon and
the joint capsule, but otherwise the tendon is adherent to the capsule.
The tendon becomes flat and much larger below the carpus, having
received the tendon of the radial head of the anterior extensor and a
strong band from the accessory carpal bone.
[Illustration:
FIG. 191.—MUSCLES OF LEFT THORACIC LIMB OF HORSE FROM ELBOW DOWNWARD;
EXTERNAL VIEW.
_a_, Extensor carpi radialis; _g_, brachialis; _g′_, anterior
superficial pectoral; _c_, anterior or common digital extensor; _e_,
flexor carpi externus. (After Ellenberger-Baum, Anat. für Künstler.)
]
_Relations._—Superficially, the skin and fascia; deeply, the outer face
of the radius and ulna; in front, the common extensor, the oblique
extensor, and the interosseous artery; behind, the external flexor of
the carpus and the deep flexor of the digit.
_Blood-supply._—Interosseous artery.
_Nerve-supply._—Radial nerve.
4. =Extensor carpi obliquus= (M. abductor pollicis longus et extensor
pollicis brevis; oblique extensor of the metacarpus; extensor metacarpi
obliquus).—This is a small muscle which curves obliquely over the distal
half of the radius and the carpus.
_Origin._—The external border and adjacent part of the anterior surface
of the radius (the attachment area beginning at a point above the middle
of the bone and extending down to its lower fourth).
_Insertion._—The head of the inner (second) metacarpal bone.
_Action._—To extend the carpal joint.
_Structure._—The muscle is pennate and has a flat belly which curves
downward, forward, and inward over the distal part of the radius. The
tendon continues the direction of the muscle, crossing obliquely over
the tendon of the extensor carpi radialis; it then occupies the oblique
groove at the distal end of the radius, and crosses the inner face of
the carpus. It is provided with a =synovial sheath=.
[Illustration:
FIG. 192.—CROSS-SECTION OF MIDDLE OF RIGHT FOREARM OF HORSE.
_a_, Accessory cephalic vein; _b_, cutaneous branch of median nerve;
_c_, extensor carpi obliquus; _d_, posterior radial artery; _e_,
satellite vein; _f_, median nerve; _g_, _g′_, ulnar vessels; _h_,
ulnar nerve; _i_, cephalic vein; _k_, tendon of ulnar head of deep
flexor; _l_, interosseous artery; _m_, extensor carpi radialis; _n_,
anterior digital extensor; _o_, lateral digital extensor; _p_,
flexor carpi externus; _q_, _q_, _q_, humeral heads of deep digital
flexor; _r_, radial head of same; _s_, superficial digital flexor;
_t_, flexor carpi medius; _u_, flexor carpi internus; _v_, radius;
_w_, skin; _x_, anterior radial artery. (After Ellenberger, in
Leisering’s Atlas.)
]
_Relations._—Superficially, the skin and fascia, the lateral extensor,
and the common extensor; deeply, the radius, the extensor carpi
radialis, the carpal capsule, and the internal lateral ligament.
_Blood-supply._—Interosseous and anterior radial arteries.
_Nerve-supply._—Radial nerve.
B. FLEXOR DIVISION
1. =Flexor carpi internus= (M. flexor carpi radialis s. radialis
volaris; internal flexor of the metacarpus).—This muscle lies on the
inner surface of the forearm, immediately behind the inner border of the
radius.
_Origin._—The flexor (internal) epicondyle of the humerus, below and
behind the lateral ligament.
_Insertion._—The proximal end of the internal (second) metacarpal bone.
_Action._—To flex the carpal joint and to extend the elbow.
_Structure._—The muscle has a short tendon of origin, which is succeeded
by a somewhat flattened, fusiform belly. The tendon of insertion begins
near the distal fourth of the radius. It is provided with a synovial
sheath which begins two or three inches (ca. 5 to 8 cm.) above the
carpus and extends almost to the insertion of the tendon.
_Relations._—Superficially, the skin and fascia, the posterior
superficial pectoral and the tensor fasciæ antibrachii; deeply, the
elbow joint, the radius, the deep flexor, the flexor carpi medius, the
posterior radial vessels, and the median nerve. At the elbow the artery
and nerve lie in front of the muscle, but below they dip beneath it.
_Blood-supply._—Posterior radial artery.
_Nerve-supply._—Median nerve.
On removing the deep fascia on the inner surface of the elbow the
student may notice a small muscle lying along the lateral ligament.
This is the =pronator teres=, which is usually not present or a mere
vestige in the horse. It arises by a small, flat tendon from the
flexor epicondyle of the humerus, and is inserted into the internal
lateral ligament of the elbow. On account of its small size and the
fact that the forearm is fixed in the position of pronation, the
muscle can have no appreciable function. It is usually represented by
the long portion of the internal lateral ligament.
2. =Flexor carpi medius= (M. flexor carpi ulnaris s. ulnaris medialis;
oblique or middle flexor of the metacarpus).—This muscle lies on the
inner and posterior aspect of the forearm partly under, partly behind,
the preceding muscle. It arises by two heads—humeral and ulnar.
_Origin._—(1) The flexor (internal) epicondyle of the humerus just
behind the preceding muscle; (2) the inner surface and posterior border
of the olecranon.
_Insertion._—The upper edge of the accessory carpal (pisiform) bone.
_Action._—To flex the carpal joint, and to extend the elbow.
_Structure._—The humeral head is much the larger, constituting, in fact,
the bulk of the muscle. It is flattened, curved, and tapers at both
ends. The ulnar head, much smaller and very thin, is covered by an
aponeurosis from which many of its fibers arise. It joins the large head
a little above the middle of the forearm. The tendon of insertion is
short and strong; it blends with the posterior annular ligament of the
carpus.
_Relations._—Superficially, the tensor fasciæ antibrachii, superficial
pectoral, and flexor carpi internus, the skin and fascia, and cutaneous
branches of the ulnar nerve; deeply, the superficial and deep flexors of
the digit. In the distal half of the forearm the ulnar vessels and nerve
lie between the outer edge of this muscle and the external flexor of the
carpus.
_Blood-supply._—Ulnar and posterior radial arteries.
_Nerve-supply._—Ulnar and median nerves.
[Illustration:
FIG. 193.—DEEPER MUSCLES OF FOREARM OF HORSE, INTERNAL VIEW.
_23_, Internal head of triceps; _30_, flexor carpi medius; _31_,
flexor carpi internus; _31′_, tendon of _31_; _32_, superficial
digital flexor; _32′_, radial check ligament; _32″_, tendon of
superficial flexor; _33a_, _33b_, _33c_, humeral heads of deep
flexor; _33′_, deep flexor tendon; _33″_, subcarpal check ligament;
_34_, ulnar head of deep flexor; _35_, radial head of deep flexor;
_36_, suspensory ligament. (After Ellenberger, in Leisering’s
Atlas.)
]
3. =Flexor carpi externus= (M. extensor carpi ulnaris[61] s. ulnaris
lateralis; external flexor of the metacarpus).—This muscle lies on the
outer face of the forearm, behind the lateral extensor of the digit.
_Origin._—The extensor (external) epicondyle of the humerus, behind and
below the lateral ligament.
_Insertion._—(1) The outer surface and upper edge of the accessory
carpal bone; (2) the proximal extremity of the outer (fourth) metacarpal
bone.
_Action._—To flex the carpal joint and to extend the elbow.
_Structure._—The belly of the muscle is flattened and is intersected by
a good deal of tendinous tissue. There are two tendons of insertion. The
short tendon is inserted into the accessory carpal bone. The long tendon
is detached just above the carpus; it is smaller and rounded; it passes
downward and a little forward through a groove on the outer surface of
the accessory carpal bone, enveloped by a =synovial sheath=, to reach
its insertion on the outer metacarpal bone. A synovial pouch lies under
the origin of the muscle at the elbow joint, with the cavity of which it
communicates.
[Illustration:
FIG. 194.—CROSS-SECTION OF PROXIMAL PART OF LEFT CARPUS OF HORSE.
The tendons have been removed to show the canals in which they lie.
The joint cavity is black. By an oversight the carpal canal for the
two flexor tendons behind the posterior ligament of the carpus is
not marked. _Cr_, Radial, _Ci_, intermediate, _Cu_, ulnar, _Ca_,
accessory carpal bones.
]
_Relations._—Superficially, the skin, fascia, and cutaneous branches of
the ulnar nerve; deeply, the elbow joint, the ulna, and the flexors of
the digit; in front, the lateral extensor of the digit; behind, the
middle flexor of the carpus, the ulnar head of the deep flexor, and the
ulnar vessels and nerve.
_Blood-supply_.—Interosseous, ulnar, and median arteries.
_Nerve-supply._—Radial nerve.
4. =Superficial digital flexor= or =flexor perforatus= (M. flexor
digitalis sublimis; superficial flexor of the phalanges).—This muscle is
situated in the middle of the flexor group, chiefly under cover of the
middle flexor of the carpus.
_Origin._—(1) The flexor epicondyle of the humerus, between the flexor
carpi internus and the deep flexor of the digit; (2) a ridge on the
posterior surface of the radius, below its middle and near the internal
border.
_Insertion._—(1) The eminences on the proximal extremity of the second
phalanx behind the lateral ligaments; (2) the distal extremity of the
first phalanx, also behind the lateral ligaments.
_Action._—To flex the digit and carpus, and to extend the elbow.
[Illustration:
FIG. 195.—SYNOVIAL SHEATHS AND BURSÆ OF LOWER PART OF RIGHT FORE LIMB
OF HORSE, INTERNAL VIEW.
_a_, Sheath of extensor carpi obliquus; _b_, sheath of flexor carpi
internus; _c_, carpal sheath; _d_, _d′_ _d″_, _d‴_, digital sheath;
_e_, bursa under anterior extensor tendon; _f_, capsule of fetlock
joint; _1_, extensor carpi radialis; _2_, tendon of extensor carpi
obliquus; _3_, flexor carpi internus; _4_, flexor carpi medius; _5_,
superficial flexor tendon; _6_, deep flexor tendon; _7_, suspensory
ligament; _8_, small metacarpal bone; _9_, large metacarpal bone;
_10_, posterior annular ligament of fetlock; _11_, proximal digital
annular ligament; _12_, radius; _13_, radio-carpal joint; _14_,
fetlock joint; _15_, lateral cartilage; _16_, band from first
phalanx to lateral cartilage. (After Ellenberger, in Leisering’s
Atlas.)
The synovial sheaths (colored yellow) and the joint capsules (colored
pink) are injected.
]
[Illustration:
FIG. 196.—SYNOVIAL SHEATHS AND BURSÆ OF LOWER PART OF RIGHT FORE LIMB
OF HORSE, EXTERNAL VIEW.
_a_, Sheath of extensor carpi radialis; _b_, sheath of anterior
extensor; _c_, sheath of lateral extensor; _d_, sheath of outer
tendon of flexor carpi externus; _e_, _e′_, carpal sheath; _f_, _f′_
_f″_, digital sheath; _g_, bursa under anterior extensor tendon;
_h_, bursa under lateral extensor tendon; _i_, capsule of fetlock
joint; _1_, extensor carpi radialis; _2_, anterior digital extensor;
_3_, lateral digital extensor; _4_, flexor carpi externus; _4′_
_4″_, tendons of _4_; _5_, superficial flexor tendon; _6_, deep
flexor tendon; _7_, suspensory ligament; _8_, external metacarpal
bone; _9_, large metacarpal bone; _10_, posterior annular ligament
of fetlock; _11_, digital annular ligament; _12_, fetlock joint;
_13_, lateral cartilage; _14_, band from first phalanx to lateral
cartilage. (After Ellenberger, in Leisering’s Atlas.)
]
_Structure._—The fleshy portion of the muscle or =humeral head= takes
origin from the humerus. The =radial head= (Caput tendineum) consists of
a strong fibrous band, usually termed the =radial= or =superior check
ligament=, which fuses with the tendon near the carpus. The belly of the
muscle is intersected by tendinous strands, and fuses more or less with
that of the deep flexor. Near the carpus it is succeeded by a strong,
thick tendon which passes down through the carpal canal, formed by the
posterior ligament of the carpus, the accessory carpal bone, and the
posterior annular ligament (Ligamentum carpi transversum). Here it is
enveloped by a synovial sheath, in common with the deep flexor. This
=carpal sheath= (Vagina carpea) begins three or four inches (8 to 10
cm.) above the carpus, and extends downward nearly to the middle of the
metacarpus. Below the carpus the tendon becomes flattened and broader.
Near the fetlock it forms a ring through which the tendon of the deep
flexor passes (Fig. 150). Here the two tendons are bound down in the
sesamoid groove by the posterior annular ligament, which fuses more or
less with the superficial flexor tendon. At the distal end of the first
phalanx the tendon divides into two branches which diverge to reach
their points of insertion, and between these branches the tendon of the
deep flexor emerges (Fig. 189). A second =synovial sheath=, the
=digital= or =sesamoidean= (Vagina digitalis), begins at the distal
third of the metacarpus, three to four inches (8 to 10 cm.) above the
fetlock, and extends to the middle of the second phalanx.
[Illustration:
FIG. 197.—CROSS-SECTION OF DISTAL PART OF LEFT METACARPUS OF HORSE,
JUST ABOVE SESAMOIDS.
]
_Relations._—The belly of the muscle is related superficially to the
ulnar head of the deep flexor, the flexor carpi medius, and, at its
origin, to the ulnar vessels and nerve; deeply to the humeral head of
the deep flexor. The tendon is related superficially to the skin and
fascia; deeply to the deep flexor tendon.
_Blood-supply._—Posterior radial artery.
_Nerve-supply._—Median nerve.
5. =Deep digital flexor= or =flexor perforans= (M. flexor digitalis
profundus; deep flexor of the phalanges).—The fleshy part of this muscle
lies on the posterior surface of the radius, under cover of the
preceding muscles. It is the largest muscle of the flexor group.
_Origin._—(1) The flexor (internal) epicondyle of the humerus; (2) the
inner surface of the olecranon; (3) the middle of the posterior surface
of the radius and a small adjacent area of the ulna.
_Insertion._—The semilunar crest of the third phalanx, and the adjacent
surface of the lateral cartilage.
_Action._—To flex the digit and carpus, and to extend the elbow.
_Structure._—This muscle consists of three principal heads. The =humeral
head= (Caput humerale) constitutes the bulk of the muscle. It is marked
by tendinous intersections, and is separable into three secondary heads.
The =ulnar head= (Caput ulnare, ulnaris accessorius) is much smaller,
and is at first superficially situated between the outer and middle
flexors of the carpus, the =radial head= (Caput radiale, radialis
accessorius) is the smallest, and is not always present; it is situated
on the distal two-thirds of the posterior surface of the radius, under
the humeral head. Each of these heads is provided with a tendon. The
principal tendon—that of the humeral head—begins about three or four
inches (8 to 10 cm.) above the carpus. It is soon joined by the small
tendon of the ulnar head, which begins about the middle of the forearm.
The tendon of the radial head fuses with the principal tendon close to
the carpus. The conjoined tendon passes downward through the carpal
canal, being included in the =carpal synovial sheath= with the
superficial flexor tendon, as previously described. Continuing downward,
it is joined about the middle of the metacarpus by a strong fibrous
band, the so-called =inferior= or =subcarpal check ligament= (Caput
tendineum). This is a direct continuation of the posterior ligament of
the carpus. Below this the tendon passes through the ring formed by the
perforatus, then in succession over the sesamoid groove, the inferior
sesamoidean ligaments, and the tendon surface of the third sesamoid, to
its insertion (Figs. 150 and 151). Its terminal part is much widened.
From the distal third of the metacarpus to the distal end of the second
phalanx it is inclosed in the =digital synovial sheath= described in
connection with the perforatus. The =navicular bursa= or =bursa
podotrochlearis= is found between the tendon and the third sesamoid or
navicular bone. The terminal part of the tendon is bound down by the
fibrous sheet described with the fascia.
[Illustration:
FIG. 198.—DIGIT OF HORSE, LATERAL VIEW.
_1_, Large metacarpal bone; _2_, distal end of small metacarpal bone;
_3_, fetlock joint; _5_, first phalanx; _6_, pastern joint; _7_,
second phalanx; _8_, coffin joint; _9_, third phalanx; _11_, lateral
cartilage; _11′_, upper (subcutaneous) border of cartilage; _12_,
suspensory ligament; _13_, branch of _12_ to extensor tendon; _14_,
deep flexor tendon; _15_, superficial flexor tendon; _15′_, branch
of _15_; _16_, posterior annular ligament of fetlock; _17_, proximal
annular or vaginal ligament of digit; _18_, distal annular ligament
or reinforcing sheath of deep flexor tendon; _19_, lateral ligament
of coffin joint; _21_, tendon of common or anterior extensor; _22_,
tendon of lateral extensor; _23_, digital vein. (After
Ellenberger-Baum, Anat. für Künstler.)
]
_Relations._—The belly of the muscle is related posteriorly to the
perforatus and the middle flexor of the carpus; internally, to the
internal carpal flexor, the radial check ligament, and the posterior
radial vessels and median nerve; externally, to the external flexor of
the carpus; anteriorly, to the radius and ulna and branches of the
posterior radial artery and median nerve. Below the carpus the tendon is
accompanied by the vessels and nerves of the digit. It may also be noted
that the muscle is not entirely covered by the other flexors; it comes
in contact with the skin and fascia on the postero-external aspect of
the proximal half of the forearm, and also on the outer aspect of the
distal fourth.
_Blood-supply._—Posterior radial and ulnar arteries.
_Nerve-supply._—Median and ulnar nerves.
METACARPAL MUSCLES
The five muscles of this group are either reduced to vestiges or
modified greatly in structure.
1, 2. =Lumbricales= (internus et externus).—These are two small muscles
which lie on either side of the flexor tendons above the fetlock. They
arise from the deep flexor tendon, and are lost in the fibrous tissue
which lies under the nodule of horn or ergot at the fetlock (Fig. 447).
Their action is inappreciable. The size of these muscles is subject to
much variation. Often very little muscular tissue can be found, but the
small tendon is constantly present.
_Blood-supply._—Metacarpal arteries.
_Nerve-supply._—Median and ulnar nerves.
3, 4, 5. =Interossei.=—These are three in number in the horse, and are
situated chiefly in the metacarpal groove. Two, the =internus= and
=externus=, are very small muscles, each of which arises from the
corresponding small metacarpal bone near its proximal extremity, and is
provided with a delicate tendon which is usually lost in the fascia at
the fetlock (Fig. 150). They have no appreciable action. Their blood-
and nerve-supply is the same as that of the preceding muscles.
The =interosseus medius= is so much modified that it is usually termed
the =suspensory=, or =superior sesamoidean ligament=. It contains little
muscular tissue, being transformed very largely into a strong tendinous
band, bifurcate below, and having for its chief function the supporting
of the fetlock. It has been described, in deference to common usage,
with the ligaments.
FASCIÆ AND MUSCLES OF THE PELVIC LIMB
THE FASCIÆ
The =iliac fascia= (Fascia iliaca) covers the ventral surface of the
iliacus and psoas muscles, over which it is tightly stretched (Fig.
450). It is attached internally to the tendon of the psoas minor,
externally to the inguinal (Poupart’s) ligament and the external angle
of the ilium. Its anterior part is thin. Posteriorly, it is in part
attached to the ilium, in part becomes continuous with the pelvic
fascia. It furnishes surfaces of origin for the sartorius, cremaster
externus, and transversus abdominis muscles.
The =pelvic fascia= (Fascia pelvis) lines the cavity (parietal layer)
and is reflected on the viscera at the pelvic outlet (visceral layer).
Laminæ are detached from it to strengthen the various peritoneal folds.
The =superficial fascia= of the =gluteal region= is continuous with the
aponeurosis of the panniculus. It covers and partly blends with the deep
fascia. The =gluteal fascia= (Fascia glutea) covers the superficial
muscles of the region, and detaches intermuscular septa, which pass
between the muscles. It is attached to the sacral spines, the dorsal
sacro-iliac ligament, and the angles of the ilium, and is continuous in
front with the lumbo-dorsal fascia, behind with the coccygeal fascia.
Its deep face gives origin to fibers of the superficial and middle
glutei, the biceps femoris, and the semitendinosus, so that care is
necessary in dissecting it off these muscles. The chief =intermuscular
septa= are: (1) One which passes between the superficial gluteus and the
biceps femoris; (2) one between the biceps and semitendinosus, from
which a lamella is detached which passes between the middle and
posterior portions of the biceps and is attached to the tuber ischii;
(3) one between the semitendinosus and semimembranosus, which is
attached to the sacro-sciatic ligament and tuber ischii; it furnishes
origin for fibers of the long head of the semimembranosus.
The =fascia lata= is continuous with the preceding, and covers the
muscles on the outer surface and front of the thigh. It is tendinous and
very strong, and for the most part easily separable from the underlying
muscles. It furnishes insertion to the tensor fasciæ latæ and to the
biceps femoris (in part), by both of which it is tensed. At the stifle
it is attached to the patella and the inner and outer straight
ligaments. Internally it is continuous with the internal femoral fascia.
It furnishes the following =intermuscular septa=: (1) One which passes
between the vastus externus and biceps femoris to be attached to the
external trochanter of the femur; (2) two which pass between the three
branches of the biceps femoris; (3) a fourth between the biceps femoris
and semitendinosus.
The =internal femoral fascia= (Fascia femoralis medialis) covers the
superficial muscles on the inner surface of the thigh. At its upper part
it is joined by part of the aponeurosis of the external oblique muscle
(Lamina femoralis) (Fig. 450). The posterior part is thin. It is
continuous with the fascia lata in front and the crural fascia below. At
the stifle it fuses with the tendons of the sartorius and gracilis.
The =crural fascia=, or fascia of the leg (Fascia cruris), consists of
three layers. Two of these invest the entire region and may, therefore,
be termed the =common fasciæ=. The superficial layer is a continuation
of the fasciæ of the thigh, while the second layer may be regarded
chiefly as a continuation of the tendons of the superficial muscles of
the hip and thigh (biceps femoris, semitendinosus, tensor fasciæ latæ,
sartorius, and gracilis). The two layers frequently fuse, and are
attached chiefly to the patellar ligaments and the crest and internal
surface of the tibia. About the middle of the leg the two layers unite
behind the deep flexor of the digit and form a strong band which passes
downward in front of the tendons of the gastrocnemius and superficial
flexor, to be attached with the latter to the anterior and inner part of
the tuber calcis. This may be regarded as an accessory or tarsal tendon
of insertion of the biceps femoris and semitendinosus. The third layer
forms sheaths for the muscles, furnishing origin in part to their
fibers. Two important =intermuscular septa= are detached, viz.: (1) One
which passes between the anterior and lateral digital extensors to be
attached to the fibula and the external border of the tibia; (2) one
between the lateral extensor and the deep flexor.
The =tarsal fascia= (Fascia tarsi) fuses with the ligaments and bony
prominences of the region. It is strong and tendinous in front, and
joins the tendon of the anterior extensor below the joint. Laterally, it
is thin and fuses with the ligaments. Posteriorly, it is very thick and
strong, forming an annular ligament which stretches from the internal
lateral ligament to the fibular tarsal bone and the plantar ligament.
This converts the groove at the back of the hock into a canal, in which
are the deep flexor tendon with its synovial sheath and the plantar
nerves. In front of the tarsus and above and below it there are three
=annular ligaments= (Ligamenta transversa). The proximal one binds down
the tendons of the anterior extensor, peroneus tertius, and tibialis
anterior on the distal end of the tibia. The middle one stretches from
the fibular tarsal bone to the outer tendon of the peroneus tertius,
forming a loop around the tendon of the anterior extensor. The distal
band stretches across the proximal extremity of the large metatarsal
bone and incloses the tendons (and sheaths) of the two extensors of the
digit.
The =metatarsal= and =digital fasciæ= do not differ materially from
those of the corresponding regions of the thoracic limb.
THE MUSCLES
I. THE SUBLUMBAR MUSCLES (Figs. 450, 456)
The muscles of this group are not confined to the sublumbar region, but
extend beyond it both before and behind. Their chief function is to flex
the hip joint. Two, however,—the psoas minor and the quadratus
lumborum,—have not this action.
1. =Psoas minor= (s. parvus).—This is a fusiform, flattened, pennate
muscle, which lies along the ventro-lateral aspect of the bodies of the
last three thoracic and the lumbar vertebræ.
_Origin._—The bodies of the last three thoracic and first four or five
lumbar vertebræ, and the vertebral ends of the sixteenth and seventeenth
ribs.
_Insertion._—The psoas tubercle on the shaft of the ilium.
_Action._—To flex the pelvis on the loins, or to incline it laterally.
_Structure._—The muscle arises by a series of digitations which pass
backward and outward to be inserted at an acute angle on the tendon. The
latter lies along the outer border of the fleshy portion and is
flattened. It appears on the surface of the muscle at the third lumbar
process and increases gradually in width until it reaches the pelvic
inlet, where it becomes narrower.
_Relations._—The ventral surface of the thoracic portion of the muscle
is related to the pleura, crura of the diaphragm, and sympathetic nerve.
In the abdomen, the chief ventral relations are the peritoneum, the vena
cava (right side), the aorta and left kidney (left side), the
sympathetic nerves, and the ureters. Dorsally, the chief relations are
the vertebræ, the psoas major, and lumbar nerves. Near its insertion the
tendon is crossed internally by the external iliac artery, and
externally by the femoral nerve.
_Blood-supply._—Intercostal and lumbar arteries.
_Nerve-supply._—Lumbar nerves.
2. =Psoas major= (s. magnus).—This is much larger than the preceding
muscle, by which it is partly covered. It is triangular, with the base
anterior.
_Origin._—The ventral surfaces of the vertebral ends of the last two
ribs and the transverse processes of the lumbar vertebræ.
_Insertion._—The internal trochanter of the femur, by a common tendon
with the iliacus.
_Action._—To flex the hip joint and to rotate the thigh outward.
_Structure._—The origin of the muscle is fleshy, the belly being in
general flattened, thick in its middle, thin at its edges. The thoracic
portion is small, the abdominal part much thicker and wider, extending
laterally beyond the extremities of the lumbar transverse processes.
From the lumbo-sacral articulation it lies in a deep groove formed in
the iliacus (with which it is partly united), becomes smaller and
rounded, and passes downward and backward to terminate by a strong
tendon common to it and the iliacus.[62]
_Relations._—Dorsally, the last two ribs and thoracic vertebræ, the
lumbar vertebræ, the internal intercostals, quadratus lumborum,
longissimus dorsi, and iliacus, and the lumbar vessels and nerves;
ventrally, the pleura and peritoneum, the iliac fascia, inguinal
ligament, the diaphragm, psoas minor, and sartorius, the kidneys, the
spleen, the intestine (duodenum, cæcum, etc.) and the circumflex iliac
vessels.
_Blood-supply._—Lumbar and circumflex iliac arteries.
_Nerve-supply._—Lumbar and femoral nerves.
3. =Iliacus.=—This muscle covers the ventral surface of the ilium
external to the sacro-iliac articulation, and extends outward beyond the
external border of the bone, underneath the middle gluteus.
_Origin._—The ventral surface of the ilium external to the
ilio-pectineal line, the ventral sacro-iliac ligament, the wing of the
sacrum, and the tendon of the psoas minor.
_Insertion._—The internal trochanter of the femur, by a common tendon
with the psoas major.
_Action._—To flex the hip joint and to rotate the thigh outward.
_Structure._—The belly of the muscle is so deeply grooved for the psoas
major as to give the appearance of being completely divided into outer
and inner portions. When the psoas is removed, it is seen, however, that
the two heads are not entirely separated. The outer, larger head arises
from the wing of the ilium chiefly; the inner, smaller head arises
chiefly from a small area on the shaft of the ilium, between the psoas
tubercle and the depression for the inner tendon of the rectus femoris,
and from the tendon of the psoas minor. The two portions inclose the
psoas major in front of the hip joint.
_Relations._—Dorsally, the ilium, sacrum, sacro-iliac articulation, the
gluteus medius, the ilio-lumbar and external circumflex vessels;
ventrally, the iliac fascia, inguinal ligament, the psoas major,
sartorius, and abdominal muscles. At the hip joint the chief relations
are: internally, the femoral vessels, the femoral nerve, and the
sartorius muscle; externally, the rectus femoris and tensor fasciæ latæ;
in front, the abdominal muscles; behind, the hip joint.
_Blood-supply._—Lumbar, circumflex iliac, and deep femoral arteries.
_Nerve-supply._—Lumbar and femoral nerves.
4. =Quadratus lumborum.=—This thin muscle lies on the outer part of the
ventral surfaces of the lumbar transverse processes.
_Origin._—The ventral surface of the upper part of the last two ribs and
the lumbar transverse processes.
_Insertion._—The ventral surface of the wing of the sacrum and the
ventral sacro-iliac ligament.
_Action._—Acting together, to fix the last two ribs and the lumbar
vertebræ; acting singly, to produce lateral flexion of the loins.
_Structure._—The muscle is pennate, and is curved with the convexity
outward. It is thin, largely mixed with tendinous fibers, and is, in
general, little developed in the horse in comparison with some of the
other animals (_e. g._, dog, sheep).
_Relations._—Ventrally, the psoas major and the last intercostal and
first three lumbar nerves; dorsally, the last two ribs, the lumbar
transverse processes, and the lateral branches of the lumbar arteries.
_Blood-supply._—Lumbar arteries.
_Nerve-supply._—Lumbar nerves.
5. =Intertransversales lumborum= (M. intertransversarii lumborum).—These
are described with the other spinal muscles. (See p. 238.)
II. THE EXTERNAL MUSCLES OF THE HIP AND THIGH
Under this head will be described the muscles of the outer surface of
the pelvis and thigh, and those which form the posterior contour of the
latter. They are given in the order in which they may be conveniently
examined.
1. =Tensor fasciæ latæ= (Fig. 178).—This is the most anterior muscle of
the superficial layer. It is triangular in form, with its apex at the
external angle of the ilium.
_Origin._—The external angle of the ilium.
_Insertion._—The fascia lata, and thus indirectly to the patella, the
external straight ligament, and the crest of the tibia.
_Action._—To tense the fascia lata, flex the hip joint, and extend the
stifle joint.
_Structure._—The muscle arises by a rather small head, about two inches
(ca. 5 cm.) wide, on the antero-inferior eminence of the external angle
of the ilium. Below this the belly spreads out and terminates about
midway between the point of the hip and the stifle in the aponeurosis.
The belly fuses to a considerable extent with the superficial gluteus.
The aponeurosis fuses with the fascia lata, and detaches a lamina which
passes with the tendon of insertion of the superficial gluteus to the
external border of the femur.
_Relations._—Externally, the skin and fascia; internally, the obliquus
abdominis externus, the iliacus, superficial gluteus, rectus femoris,
and vastus externus, branches of the circumflex iliac, ilio-lumbar, and
iliaco-femoral arteries, and the anterior gluteal nerve; anteriorly, the
precrural lymph glands. A considerable quantity of connective tissue is
found between the deep face of the muscle and the abdominal wall.
_Blood-supply._—Circumflex iliac, ilio-lumbar, and iliaco-femoral
arteries.
_Nerve-supply._—Anterior gluteal nerve.
2. =Gluteus superficialis= (Figs. 178, 199) (Superficial gluteus;
gluteus externus).—This muscle lies behind and partly underneath the
tensor fasciæ latæ. It is triangular and consists of an anterior and a
posterior head united by the gluteal fascia.
_Origin._—(1) The external angle and the adjacent part of the external
border of the ilium (anterior head); (2) the gluteal fascia (posterior
head).
_Insertion._—The third (external) trochanter of the femur.
_Action._—To abduct the limb, flex the hip joint, and tense the gluteal
fascia.
_Structure._—The anterior head of the muscle is not completely separable
(except artificially) from the tensor fasciæ latæ. The attachment to the
border of the ilium is by means of an intermuscular septum, which passes
beneath the thick outer border of the gluteus medius. The posterior head
arises from the deep face of the gluteal fascia, and so indirectly from
the dorsal sacro-iliac ligament. The two heads unite and terminate on a
strong flat tendon, which is inserted into the edge of the third
trochanter of the femur, beneath the biceps femoris.
_Relations._—Superficially, the skin, fascia, and biceps femoris;
deeply, the gluteus medius, iliacus, rectus femoris, and branches of the
iliaco-femoral artery; in front, the tensor fasciæ latæ; behind, the
biceps femoris.
_Blood-supply._—Gluteal and iliaco-femoral arteries.
_Nerve-supply._—Anterior gluteal nerve.
3. =Gluteus medius= (Figs. 178, 179) (Middle gluteus; gluteus
maximus).—This is a very large muscle which covers the dorsal surface of
the ilium and the greater part of the lateral wall of the pelvis, and
extends forward also on the lumbar part of the longissimus.
_Origin._—(1) The aponeurosis of the longissimus, as far forward as the
first lumbar vertebra; (2) the gluteal or dorsal surface and internal
and external angles of the ilium; (3) the dorsal and lateral sacro-iliac
and sacro-sciatic ligaments, and the gluteal fascia.
_Insertion._—(1) The summit of the trochanter major of the femur; (2)
the crest below the trochanter; (3) the outer aspect of the trochanteric
ridge.
_Action._—To extend the hip joint and abduct the limb. By its connection
with the longissimus a muscular mass is formed which is one of the chief
factors in rearing, kicking, and propulsion.
_Structure._—The anterior extremity of the muscle is relatively thin,
and lies in a depression on the surface of the longissimus, from the
strong aponeurosis of which the fibers take origin. The pelvic portion
of the muscle is very voluminous, and forms the bulk of the muscular
mass which gives the haunch its rounded contour. This part of the muscle
is intersected by several tendinous sheets. One of these is particularly
distinct, and is attached to the gluteal line on the ilium. This divides
the muscle incompletely into superficial and deep strata. The
superficial part is inserted by a strong tendon into the summit of the
great trochanter, and by a pointed fleshy mass with a tendinous border
into the trochanteric ridge. The deep part (Gluteus accessorius) is
smaller, and arises entirely from the ilium between the gluteal line and
the external angle (Fig. 455). It has a strong flat tendon which passes
over the convexity of the trochanter to be inserted into the crest below
it. The convexity is covered with cartilage, and the =trochanteric
bursa= (Bursa trochanterica) is interposed between the tendon and the
cartilage.[63]
_Relations._—Superficially, the skin, lumbo-dorsal and gluteal fasciæ,
the tensor fasciæ latæ, gluteus superficialis, and biceps femoris;
deeply, the longissimus, the ilium, sacro-iliac and sacro-sciatic
ligaments, the gluteus profundus, iliacus and rectus femoris, the
iliaco-femoral artery, the gluteal and internal pudic vessels and
nerves, and the great sciatic nerve.
_Blood-supply._—Gluteal, ilio-lumbar, lumbar, and iliaco-femoral
arteries.
_Nerve-supply._—Gluteal nerves.
4. =Gluteus profundus= (Deep gluteus; gluteus internus;
scansorius).—This much smaller, quadrilateral muscle lies under the
posterior part of the preceding muscle, and extends over the hip joint,
from the superior ischiatic spine to the anterior part of the great
trochanter (Fig. 455).
_Origin._—The superior ischiatic spine and the adjacent part of the
shaft of the ilium.
_Insertion._—The edge of the anterior part or convexity of the
trochanter major of the femur.
_Action._—To abduct the thigh and to rotate it inward.
_Structure._—The muscle is short and thick and contains numerous
tendinous intersections. The fibers are directed almost transversely
outward over the capsule of the hip joint and converge at the convexity
of the trochanter.
_Relations._—Superficially, the gluteus medius and branches of the
gluteal vessels and nerves; deeply, the shaft of the ilium, the hip
joint, and the rectus femoris and capsularis.
_Blood-supply._—Gluteal artery.
_Nerve-supply._—Anterior gluteal nerve.
5. =Biceps femoris= (Gluteo-biceps s. paramero-biceps).—This large
muscle lies behind and in part upon the superficial and middle glutei.
It extends in a curved direction from the sacral and coccygeal spines to
the outer surface of the stifle and leg (Figs. 178, 199, 200, 201, 202).
_Origin._—(1) The dorsal sacro-iliac ligament, the gluteal and coccygeal
fasciæ, and the intermuscular septum between this muscle and the
semitendinosus; (2) the tuber ischii.
_Insertion._—(1) A tubercle on the posterior surface of the femur near
the external trochanter; (2) the anterior surface and external straight
ligament of the patella; (3) the tibial crest; (4) the anterior and
internal surface of the tuber calcis.
_Action._—The action is somewhat complex, because the muscle is composed
of three portions, has several points of insertion, and acts on all the
joints of the limb except those of the digit. The general action is to
extend the limb, as in propelling the body, rearing or kicking, and to
abduct it. The anterior part, by its attachment to the posterior surface
of the femur and to the patella, would extend the stifle and hip joints
and abduct the limb. The middle part, being inserted chiefly on the
tibial crest and the external straight ligament, would extend the hip,
and, with the semitendinosus, flex the stifle. The posterior part, by
virtue of its attachment to the tuber calcis, assists in extending the
hock.
[Illustration:
FIG. 199.—MUSCLES OF PELVIC LIMB OF HORSE, POSTERO-EXTERNAL VIEW.
_17_, Position of tuber ischii; _o′_, superficial gluteus; _q_, _q′_,
_q″_, biceps femoris; _r_, semitendinosus; _t_, sacro-coccygeus
lateralis; _v_, semimembranosus; _w_, gracilis; _f_, gastrocnemius.
(After Ellenberger-Baum, Anat. f. Künstler.)]
]
_Structure._—The muscle has two heads of origin:[64] The long or
vertebral head arises chiefly from the dorsal and lateral sacro-iliac
ligaments, the coccygeal fascia, and the intermuscular septum. There is
often a large =bursa= between this head and the trochanter major. The
short or ischiatic head arises by a strong tendon from the ventral spine
on the tuber ischii. They unite, and a short tendon is detached from the
deep face of the muscle, to be inserted into the posterior surface of
the femur near the third trochanter (Fig. 455), a =bursa= being
interposed between the tendon and the bone. The muscle then divides into
three portions, which terminate on a strong aponeurosis over the
junction of the thigh and leg. The anterior branch is directed toward
the patella, the middle toward the tibial crest, while the posterior one
assists in the formation of the posterior contour of the limb. The
aponeurosis blends with the deep layer of the fascia cruris, as already
described. A synovial =bursa= occurs under the patellar insertion.
_Relations._—Superficially, the skin and fascia; deeply, the sacro-iliac
and sacro-sciatic ligaments, the coccygeal fascia, the femur, the
obturator, gemellus, quadratus femoris, adductor, semimembranosus,
vastus externus, and gastrocnemius muscles, branches of the lateral
sacral, gluteal, obturator, femoral and deep femoral vessels, the great
sciatic, tibial, peroneal, and posterior gluteal nerves; in front, the
superficial and middle glutei; behind and internally, the
semitendinosus.
_Blood-supply._—Gluteal, obturator, and femoro-popliteal arteries.
_Nerve-supply._—Posterior gluteal and great sciatic nerves.
6. =Semitendinosus= (Biceps rotator tibialis).—This is a long muscle
which extends from the first two coccygeal vertebræ to the proximal
third of the inner surface of the tibia. It lies at first behind the
biceps, then passes downward on the back of the thigh, between that
muscle and the semimembranosus (Figs. 178, 179, 199). It has two heads
of origin.
_Origin._—(1) The transverse processes of the first and second coccygeal
vertebræ, the coccygeal fascia, and the intermuscular septum between
this muscle and the biceps femoris; (2) the ventral surface of the tuber
ischii.
_Insertion._—(1) The tibial crest; (2) the crural fascia and the tuber
calcis.
_Action._—To flex the stifle and rotate the leg inward; also to extend
the hip and hock joints, acting with the biceps and semimembranosus in
propulsion of the trunk, rearing, etc.
_Structure._—The long or vertebral head is small at its origin, but
becomes larger by the accession of fibers arising on the intermuscular
septum. Below the tuber ischii it is joined by the short head, which
arises partly by fleshy fibers, partly by a common tendon with the
biceps. The muscle then passes downward on the back of the thigh, and
terminates on a wide tendon on the inner surface of the proximal third
of the leg. A distinct band passes forward to be inserted on the tibial
crest (a =bursa= lying between the tendon and the tibia), part fuses
with the fascia of the leg, while the remainder joins the biceps tendon
and concurs in the formation of the tendinous band, which, as before
described, terminates on the tuber calcis (Fig. 458). A _bursa_ may
occur under the long head where it passes over the tuber ischii.
_Relations._—Externally, the skin and fascia, the biceps, and the
internal head of the gastrocnemius; internally, the coccygeal fascia,
the sacro-sciatic ligament, the semimembranosus; anteriorly, the biceps
femoris, branches of the femoral artery, and the great sciatic nerve.
_Blood-supply._—Posterior gluteal, obturator, and femoro-popliteal
arteries.
_Nerve-supply._—Posterior gluteal and great sciatic nerves.
7. =Semimembranosus=[65] (Figs. 179, 186, 199, 451).—This muscle lies on
the inner surface of the preceding muscle and the gastrocnemius, and has
two heads of origin.
_Origin._—(1) The posterior border of the sacro-sciatic ligament; (2)
the ventral surface of the tuber ischii.
_Insertion._—The internal epicondyle of the femur, behind the lateral
ligament.
_Action._—To extend the hip joint and to adduct the limb.
_Structure._—The long head, small and pointed above, extends toward the
root of the tail, fusing with the sacro-sciatic ligament. Passing
downward, it becomes larger and covers in part the posterior aspect of
the tuber ischii. A =bursa= may be found here. Below this it joins the
short head, which is much larger. The large belly so formed passes
downward and forward, covered in great part by the gracilis, and
terminates on a short, flat tendon of insertion at the distal end of the
femur.
_Relations._—The upper part of the muscle assists in forming the lateral
boundary of the pelvic outlet. It is related posteriorly and externally
to the skin and fascia and the semitendinosus; internally, to the anus
and its muscles, the vulva in the female, and the internal pudic artery
and nerve (Figs. 452, 453). Below the pelvis the chief relations are:
externally, the semitendinosus, biceps, and gastrocnemius, branches of
the obturator, femoral, and femoro-popliteal arteries, and the great
sciatic nerve and its chief branches; internally, the crus penis and
ischio-cavernosus muscle (in the male), and the gracilis; in front, the
adductor and the femoral vessels; behind, the skin and fascia.
_Blood-supply._—Obturator and femoral arteries.
_Nerve-supply._—Great sciatic nerve.
IV. THE INTERNAL MUSCLES OF THE THIGH
The muscles of this group are arranged in three layers.
FIRST LAYER
1. =Sartorius= (Figs. 180, 202, 203).—This long and rather narrow muscle
is the most anterior one of the first layer. It extends from the
sublumbar region to the lower and inner part of the stifle.
_Origin._—The iliac fascia and the tendon of the psoas minor.
_Insertion._—The internal straight ligament of the patella and the
adjacent part of the tuberosity of the tibia.
_Action._—To flex the hip joint and adduct the limb.
_Structure._—The muscle is very thin at its origin, but becomes thicker
and narrower as it passes downward and a little backward. It terminates
near the stifle joint on an aponeurosis which blends with that of the
gracilis and with the fascia of the leg.
_Relations._—Superficially, the inguinal (Poupart’s) ligament, the
abdominal muscles, the skin and fascia, and the saphenous vessels and
nerve; deeply, the ilio-psoas, quadriceps femoris, and adductor. It
forms the anterior boundary of the femoral canal, in which the femoral
artery and vein and the deep inguinal lymph glands are situated (Fig.
451).
_Blood-supply._—Femoral artery.
_Nerve-supply._—Femoral and saphenous nerves.
2. =Gracilis= (Figs. 186, 199, 202, 203).—This is a wide, flat,
quadrilateral muscle, situated behind the sartorius, which it exceeds
greatly in extent.
_Origin._—The middle third of the pelvic symphysis, the prepubic tendon
and pubo-femoral ligament, and the ventral surface of the pubis behind
the prepubic tendon.
_Insertion._—The internal straight ligament of the patella, the internal
surface of the tibia in front of the lateral ligament of the stifle
joint, and the fascia of the leg.
_Action._—To adduct the limb. It may also rotate it inward.
_Structure._—The muscle arises by a strong tendon, chiefly in common
with the opposite muscle. Its direct attachment to the ventral surface
of the pelvis is not so extensive as a superficial inspection would
suggest. The origin of the muscle presents anteriorly a round
perforation for the passage of the external pudic vein. The belly is
composed of parallel bundles, and is marked by a superficial furrow
which, however, does not indicate a muscular division. It terminates on
the inner surface of the stifle on a thin wide tendon which blends in
front with that of the sartorius, below with the crural fascia.
_Relations._—Superficially, the skin and fascia, the penis or mammary
gland, and the saphenous vessels and nerve; deeply, the pectineus,
adductor, semimembranosus and semitendinosus, and, at the middle of the
femur, the femoral vessels; anteriorly, the sartorius. In the upper
third of the thigh the sartorius and gracilis are separated by a
triangular interval (femoral triangle), in which lie the deep inguinal
lymph glands and the femoral vessels.
_Blood-supply._—Femoral and deep femoral arteries.
_Nerve-supply._—Obturator and saphenous nerves.
SECOND LAYER
1. =Pectineus= (Figs. 180, 451, 456).—This muscle is fusiform and
extends from the anterior border of the pubis to the middle of the inner
border of the femur.
_Origin._—The prepubic tendon, the pubo-femoral ligament, and the
anterior border of the pubis.
_Insertion._—The middle of the internal border of the femur, near the
nutrient foramen.
_Action._—To adduct the limb and flex the hip joint.
_Structure._—The belly is cylindrical and contains little fibrous
tissue. Its origin is perforated by the pubo-femoral ligament, and is
thus divided into two unequal parts. The large upper part arises mainly
from the prepubic tendon—only a very small part gaining direct
attachment to the pubis. The small lower part does not reach the bone.
The insertion is pointed and tendinous.
_Relations._—Superficially, the gracilis; deeply, the femur, the vastus
internus, the terminal tendon of the psoas major and iliacus, and the
deep femoral artery; anteriorly, the sartorius, the femoral vessels, the
saphenous nerve, and the deep inguinal lymph glands; posteriorly, the
adductor, obturator externus, and quadratus femoris, and the obturator
nerve (anterior division).
_Blood-supply._—Femoral and deep femoral arteries.
_Nerve-supply._—Femoral and obturator nerves.
The _femoral canal_ is exposed in the dissection of the preceding
muscles (Figs. 200, 451). It is bounded anteriorly by the sartorius,
posteriorly by the pectineus, and externally by the iliacus and vastus
internus. Its internal wall is formed by the femoral fascia and the
gracilis. Its upper or abdominal opening (Lacuna vasorum) lies behind
and a little internal to the internal inguinal ring and is bounded
anteriorly by the inguinal ligament, posteriorly by the anterior
border of the pubis, and externally by the tendon of the psoas minor.
The canal terminates below at the insertion of the pectineus. It
contains the deep inguinal lymph glands, the femoral artery and vein,
and the saphenous nerve.
2. =Adductor=[66] (Figs. 179, 186, 451) (Great and small adductors of
the thigh).—This fleshy, prismatic muscle lies behind the pectineus and
vastus internus. It extends downward and forward from the ventral
surface of the pelvis to the internal condyle of the femur.
_Origin._—The ventral surface of the pubis and ischium and the tendon of
the gracilis.
_Insertion._—(1) The posterior surface of the femur from the level of
the external trochanter to the groove for the femoral vessels; (2) the
internal epicondyle of the femur and the internal lateral ligament of
the stifle joint.
_Action._—To adduct the limb and assist in extending the hip joint. It
may also rotate the femur outward.
_Structure._—It is almost entirely fleshy, and is composed of parallel
bundles united rather loosely. It is usually possible to separate from
the principal mass a small anterior short portion,[67] which is inserted
into the femur behind the pectineus. The principal mass[68] is
perforated below its middle by the femoral vessels, and is thus divided
into two branches. The outer branch is inserted into the back of the
femur with the short portion, while the inner branch is attached to the
internal epicondyle and lateral ligament. There is often a superficial
slip which reaches the internal straight patellar ligament. Some fibers
pass under the lateral ligament and end on the tendon of the
semimembranosus.
_Relations._—Internally, the gracilis, and branches of the femoral
artery and of the obturator nerve; externally, the femur, the obturator
externus, quadratus femoris, biceps femoris, and gastrocnemius, and the
femoral, deep femoral, and obturator arteries; anteriorly, the
pectineus, vastus internus, and a large branch of the obturator nerve;
posteriorly, the semimembranosus and the great sciatic nerve.
_Blood-supply._—Femoral, deep femoral, and obturator arteries.
_Nerve-supply._—Obturator nerve.
3. =Semimembranosus.=—Described on p. 280.
THIRD LAYER
1. =Quadratus femoris= (Ischio-femoralis).—This is a narrow, flat
muscle, which lies under cover of the upper part of the adductor (Figs.
455, 456).
_Origin._—The ventral surface of the ischium, just in front of the
semimembranosus.
_Insertion._—An oblique line on the posterior surface of the femur, near
the lower part of the internal trochanter.
_Action._—To extend the hip joint, and to adduct the thigh and rotate it
outward.
_Structure._—It is composed of parallel bundles of fibers directed
downward, forward, and outward.
_Relations._—Internally, the adductor, semimembranosus, and the
obturator vessels; externally, the obturator externus and biceps
femoris, the deep femoral artery, and the great sciatic nerve.
_Blood-supply._—Deep femoral and obturator arteries.
_Nerve-supply._—Great sciatic nerve.
2. =Obturator Externus= (Fig. 456).—This is a pyramidal muscle which
extends across the back of the hip joint from the obturator foramen to
the trochanteric fossa.
_Origin._—The ventral surface of the pubis and ischium, and the margin
of the obturator foramen.
_Insertion._—The trochanteric fossa.
_Action._—To adduct the thigh and to rotate it outward.
_Structure._—It is almost entirely fleshy, the muscle-bundles being
rather loosely connected. The insertion is pointed, flattened, and
partly tendinous. The origin is perforated by the obturator vessels and
nerve.
_Relations._—Internally, the adductor and quadratus femoris and the deep
femoral vessels; externally, the gemellus, the tendon of the obturator
internus, the biceps femoris, and the great sciatic nerve; anteriorly,
the hip joint, the pectineus, and the external pudic vein.
_Blood-supply._—Deep femoral and obturator arteries.
_Nerve-supply._—Obturator nerve.
3. =Obturator internus= (Fig. 451).—This arises by two heads within the
pelvic cavity, the tendon emerging through the lesser sciatic foramen.
_Origin._—(1) The pelvic surface of the pubis and ischium around the
obturator foramen; (2) the pelvic surface of the shaft of the ilium and
the wing of the sacrum.
_Insertion._—The trochanteric fossa.
_Action._—To rotate the femur outward.
_Structure._—The ischio-pubic head lies on the pelvic floor and covers
the obturator foramen. It is thin and fan-shaped. The iliac head extends
along the lateral wall of the pelvis, and is pennate, with a central
tendon throughout. Both terminate on a flat tendon which passes outward
through the lesser sciatic foramen to be inserted into the trochanteric
fossa. A synovial bursa facilitates the play of the tendon over the
external border of the ischium.[69]
_Relations._—The pelvic surface is covered by the pelvic fascia and the
peritoneum. The obturator vessels and nerve lie between the two heads,
and the internal pudic vessels and nerve lie along the dorsal edge of
the iliac head.
_Blood-supply._—Obturator and internal pudic arteries.
_Nerve-supply._—Great sciatic nerve.
4. =Gemellus=[70] (Fig. 455).—This is a thin, triangular muscle, which
extends from the external border of the ischium to the trochanteric
fossa.
_Origin._—The external border of the ischium near the ischiatic spine.
_Insertion._—The trochanteric fossa.
_Action._—To rotate the femur outward.
_Structure._—Fleshy, some fibers being inserted into the tendon of the
obturator internus.
_Relations._—Dorsally, the tendon of the obturator internus and the
gluteus profundus; ventrally, the obturator externus.
_Blood-supply._—Obturator artery.
_Nerve-supply._—Sciatic nerve.
III. ANTERIOR MUSCLES OF THE THIGH
This group consists of the sartorius, quadriceps femoris, and
capsularis.
1. =Sartorius.=—This is described on p. 281.
2. =Quadriceps femoris= (Figs. 179, 186, 200) (Crural triceps).—This
constitutes the large muscular mass which covers the front and sides of
the femur. It has four heads, one of which, the rectus, arises from the
ilium; the other three arise from the femur. All are inserted into the
patella.
(1) =Rectus femoris.=—This is fusiform and rounded. It arises by two
tendons.
_Origin._—Two depressions on the shaft of the ilium above and in front
of the acetabulum.
_Insertion._—The base and anterior surface of the patella.
_Action._—To extend the stifle joint and to flex the hip joint.
_Structure._—It has two short strong tendons of origin; beneath the
outer one is a =bursa=. The belly is rounded and rests in a groove
formed by the other portions of the quadriceps. Its sides are covered by
a strong tendinous layer which furnishes insertion to fibers of the
vasti. The tendon of insertion is formed by the fusion of these
tendinous layers on the lower part of the muscle. The lower portion of
the muscle is pennate, the fibers on either side converging on the
tendon at an acute angle.
_Relations._—Internally, the iliacus, sartorius, and vastus internus;
externally, the tensor fasciæ latæ, glutei, and vastus externus;
posteriorly, the hip joint and the vastus intermedius; anteriorly, the
fascia lata and the skin. The anterior femoral artery and branches of
the femoral nerve descend into the interspace between the upper part of
the rectus and the vastus internus; similarly, the iliaco-femoral artery
dips in between the rectus femoris and vastus externus.
_Blood-supply._—Femoral and iliaco-femoral arteries.
_Nerve-supply._—Femoral nerve.
(2) =Vastus externus= (s. lateralis).—This lies on the outer surface of
the thigh, extending from the great trochanter to the patella. It is
thick and wide in its upper part, and becomes much thinner and narrow
below.
[Illustration:
FIG. 200.—CROSS-SECTION OF MIDDLE OF RIGHT THIGH OF HORSE.
]
_Origin._—The external border and surface of the femur, from the great
trochanter to the supracondyloid fossa.
_Insertion._—(1) The outer part of the anterior surface of the patella;
(2) the tendon of the rectus femoris.
_Action._—To extend the stifle joint.
_Structure._—The fibers are directed downward and forward, many being
inserted into the tendinous sheet which covers the side of the rectus. A
=bursa= is often found between the distal end and the patella.
_Relations._—Externally, the fascia lata and skin, tensor fasciæ latæ,
superficial gluteus, and biceps femoris; internally, the femur and
femoro-patellar joint capsule, the rectus femoris, vastus intermedius,
and the iliaco-femoral artery.
_Blood-supply._—Iliaco-femoral artery.
_Nerve-supply._—Femoral nerve.
(3) =Vastus internus= (s. medialis).—This is smaller than the preceding
muscle, and lies in a similar position on the inner side of the thigh.
_Origin._—The internal surface of the femur, from the neck to the distal
third.
_Insertion._—(1) The upper part of the inner border of the patella and
its cartilage; (2) the tendon of the rectus femoris.
_Action._—To extend the stifle joint.
_Structure._—This is very similar to that of the vastus externus. It is,
however, more difficult to separate from the intermedius, because many
fibers of the latter arise on the tendinous sheet which covers the
contact surface of the inner vastus. Its insertion into the patella is
chiefly by means of a broad strong tendon. From the deep face fleshy
fibers are inserted also into the femoro-patellar capsule.
_Relations._—Internally, the skin and fascia lata, the iliacus,
sartorius, pectineus, and adductor, the femoral vessels and saphenous
nerve; externally, the femur, femoro-patellar joint capsule, rectus
femoris, and vastus intermedius, the anterior femoral artery, and
branches of the femoral nerve.
_Blood-supply._—Femoral and anterior femoral arteries.
_Nerve-supply._—Femoral nerve.
(4) =Vastus intermedius= (Crureus).—This muscle is deeply situated on
the anterior face of the femur, and is entirely covered by the preceding
heads.
_Origin._—(1) The anterior and external surfaces of the femur, from the
proximal to the distal fourth; (2) the aponeurosis of the vastus
internus.
_Insertion._—(1) The base of the patella; (2) the femoro-patellar joint
capsule.
_Action._—(1) To extend the stifle joint; (2) to tense (raise) the
femoro-patellar capsule during extension of the joint.
_Structure._—The muscle is usually quite difficult to isolate from the
other vasti, so that many since Günther have declared it an
artefact.[71] It is entirely fleshy, and is small at its proximal end,
but when traced downward increases in bulk by the accession of fibers
arising on the femur and the tendinous covering of the vastus internus.
The terminal part is intimately adherent to the femoro-patellar joint
capsule, where the latter bulges upward above the level of the patella.
_Relations._—Internally, the vastus internus; externally, the vastus
externus; anteriorly, the rectus; posteriorly, the femur and
femoro-patellar capsule.
_Blood-supply._—Iliaco-femoral and anterior femoral arteries.
_Nerve-supply._—Femoral nerve.
The straight ligaments of the patella are to be regarded as tendons of
the quadriceps which communicate the action of the latter to the
tibia, the patella being intercalated as a sesamoid bone.
3. =Capsularis= (Fig. 154) (Rectus parvus).—This is a small muscle
(scarcely as large as one’s finger), which arises on the ilium
immediately above the outer tendon of the rectus femoris, and passes
down between the vastus internus and externus to be inserted into the
anterior surface of the femur. It passes over the front of the hip
joint, to the capsule of which some fibers are attached. Sometimes the
muscle has two distinct heads, in which case the additional head arises
between the two tendons of origin of the rectus femoris. Its action may
be to raise the capsule during flexion of the joint.
IV. THE MUSCLES OF THE LEG AND FOOT
[Illustration:
FIG. 201.—MUSCLES OF LOWER PART OF THIGH, LEG, AND FOOT OF HORSE,
EXTERNAL VIEW.
_o′_, Fascia lata; _q_, _q′_, _q″_, biceps femoris; _r_,
semitendinosus; _21′_, external condyle of tibia. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The muscles of this region cover almost all of the tibia except its
internal face, which is largely subcutaneous. As in the forearm, the
muscles fall into two groups, an anterior or dorso-lateral, and a
posterior or plantar. The muscles of the first group are extensors of
the digit and flexors of the hock, those of the second have the opposite
action.
A. ANTERIOR GROUP
1. =Anterior= or =long digital extensor= (M. extensor digitalis longus;
extensor pedis; anterior extensor of the phalanges).—This muscle is
situated superficially on the antero-external aspect of the leg, and is
provided with a long tendon which passes down over the front of the
tarsus, metatarsus, and digit.
_Origin._—The small fossa (Fossa extensoria) between the external
condyle and the trochlea of the femur.
_Insertion._—(1) The extensor process of the third phalanx; (2) the
anterior surface of the proximal extremities of the first and second
phalanges.
_Action._—To extend the digit and flex the hock. It also assists in
fixing the stifle joint.
_Structure._—The origin is by means of a strong tendon in common with
the peroneus tertius, on which also many fibers arise. The common tendon
passes downward in the groove between the outer condyle and the
tuberosity of the tibia, where a pouch from the femoro-tibial capsule
descends four or five inches (ca. 10 to 12 cm.) beneath the tendon. The
belly is fusiform and somewhat flattened. The long tendon of insertion
begins in the belly about its middle, and is clear of the fleshy part
near the tarsus. It passes downward over the front of the hock, bound
down by the three annular ligaments already described (see crural
fascia), and enveloped by a =synovial sheath= which begins a little
above the level of the external malleolus, and extends nearly to the
junction with the lateral extensor tendon. This union occurs usually
about a hand’s breadth below the tarsus. In the angle of union the
extensor brevis also joins the principal tendon. Beyond this point the
arrangement is the same as in the fore limb.
_Relations._—Superficially, the skin and fascia; deeply, the
femoro-tibial capsule, peroneus tertius, and tibialis anterior; behind,
the lateral extensor and the superficial and deep peroneal nerves. In
front of the tarsus the anterior tibial artery crosses the deep face of
the tendon (Fig. 460).
_Blood-supply._—Anterior tibial artery.
_Nerve-supply._—Peroneal nerve.
2. =Lateral digital extensor= (M. extensor digitalis lateralis;
peroneus; lateral extensor of the phalanges).—This muscle lies on the
outer surface of the leg, behind the preceding one.
_Origin._—The external lateral ligament of the stifle joint, the fibula,
the external border of the tibia, and the interosseus ligament.
_Insertion._—The tendon of the anterior extensor, about a third of the
way down the metatarsus.
_Action._—To assist the anterior extensor.
_Structure._—The belly is fusiform, flattened, and pennate. The tendon
runs through the entire length of the belly and becomes free from it at
the lower fourth of the tibia. It passes downward through the groove on
the external malleolus, bound down by an annular ligament, and,
inclining forward, blends (usually) with the tendon of the anterior
extensor. It is provided with a =synovial sheath=, which begins about
one inch (ca. 2 to 3 cm.) above the external malleolus and ends about
one and one-half inches (ca. 3 to 4 cm.) above the junction. Sometimes
the fusion does not occur, and the tendon then passes down the
metatarsus, alongside of that of the long extensor, to lie inserted into
the first phalanx like the corresponding muscle of the thoracic limb.
_Relations._—Externally, the skin and fascia and the superficial
peroneal nerve; internally, the tibia and fibula; anteriorly, the
intermuscular septum, the long extensor, and the tibialis anterior;
posteriorly, the deep flexor and the soleus.
_Blood-supply._—Anterior tibial artery.
_Nerve-supply._—Peroneal nerve.
3. =Peroneus tertius= (Tendinous part of the flexor metatarsi; tendo
femorotarseus [Schmaltz]).—This consists in the horse of a strong tendon
which lies between the anterior extensor and the tibialis anterior.[72]
[Illustration:
FIG. 202.—MUSCLES OF PELVIC LIMB OF HORSE, ANTERIOR VIEW. _y_, Rectus
femoris; _20_, patella. (After Ellenberger-Baum, Anat. für
Künstler.)
]
_Origin._—The fossa extensoria (between the external condyle and the
trochlea of the femur), in common with the anterior extensor.
_Insertion._—(1) The proximal extremities of the large (third) and
external small (fourth) metatarsal bones, and the third tarsal bone; (2)
the fibular and fourth tarsal bones.
_Action._—Mechanically to flex the hock when the stifle joint is flexed.
_Structure._—This is entirely tendinous. The proximal end and the
underlying prolongation of the synovial membrane of the femoro-tibial
joint have been mentioned in the description of the anterior extensor.
Fibers of the latter muscle and of the tibialis anterior arise on the
tendon as it passes downward to the front of the hock. At the distal end
of the tibia the tendon divides into two branches, between which the
tendon of the tibialis anterior emerges. The anterior branch is attached
to the third tarsal and third and fourth metatarsal bones, while the
outer one curves outward, bifurcates, and is inserted into the fibular
and fourth tarsal bones (Fig. 460).
_Relations._—Superficially, the anterior extensor; deeply, the tibialis
anterior. The anterior tibial vessels cross the deep face of the outer
branch.
4. =Tibialis anterior= (Muscular portion of the flexor metatarsi).—This
lies on the antero-external face of the tibia; it is wide and flattened
above, pointed below.
_Origin._—The external condyle and border of the tibia and a small area
on the external surface of the tuberosity.
_Insertion._—(1) The metatarsal tuberosity; (2) the first and second
tarsal bones.
_Action._—To flex the hock joint.
_Structure._—The origin is fleshy, and is divided by the groove in which
lie the common tendon of the long extensor and peroneus tertius and a
synovial pouch. Passing downward on the tibia, the belly is united by
tendinous and fleshy fibers with the peroneus tertius, and terminates
close to the tarsus in a point on the tendon of insertion. The latter
emerges between the branches of the peroneus tertius and bifurcates, the
anterior branch being inserted into the metatarsal tuberosity, the inner
one (cunean tendon) into the fused first and second tarsal bones
(cuneiform parvum). The tendon is provided with a =synovial sheath= at
its emergence, and a =bursa= (cunean bursa) is interposed between the
inner branch and the internal lateral ligament.
_Relations._—Superficially, the anterior and lateral extensors, the
peroneus tertius, and the deep peroneal nerve; deeply, the tibia, the
deep flexor, and the anterior tibial vessels.
_Blood-supply._—Anterior tibial artery.
_Nerve-supply._—Peroneal nerve.
B. POSTERIOR GROUP
1. =Gastrocnemius= (Figs. 179, 201, 203).—This muscle extends from the
lower third of the femur to the point of the hock. It arises by two
heads.
_Origin._—(1) Outer head, from the external rough margin of the
supracondyloid fossa (Fossa plantaris); (2) inner head, from the
supracondyloid crest.
_Insertion._—The posterior part of the tuber calcis.
_Action._—To extend the hock.
_Structure._—The two bellies are thick, fusiform, and somewhat
flattened. They are covered by a strong aponeurosis and contain
tendinous intersections. They terminate toward the middle of the leg on
a common tendon (Tendo calcaneus s. Achillis), which at first lies
posterior to that of the superficial flexor, but, by a twist in both,
comes to lie in front of the latter. The deep fascia blends with the
tendon throughout its length, and the soleus muscle is inserted into its
anterior edge. A small =bursa= (Bursa tendinis calcanei) lies in front
of the insertion on the tuber calcis, and a large =bursa= is interposed
between the two tendons from the twist downward. The superficial flexor
lies between the two heads and is adherent to the outer one (Fig. 459).
_Relations._—Anteriorly, the stifle joint, the superficial flexor,
popliteus, deep flexor, popliteal vessels, and tibial nerve; internally
(above), the semitendinosus, semimembranosus, and adductor, (below) the
fascia and skin; externally (above), the biceps femoris and peroneal
(anterior tibial) nerve, (below) the fascia and skin.
[Illustration:
FIG. 203.—MUSCLES OF LEG AND FOOT OF HORSE, INTERNAL VIEW.
_r′_, Tendon of semitendinosus; _w_, gracilis; _x_, sartorius; _y_,
vastus internus. (After Ellenberger-Baum, Anat. für Künstler.)
]
_Blood-supply._—Popliteal artery.
_Nerve-supply._—Tibial nerve.
2. =Soleus= (Fig. 201).—This muscle is very small in the horse. It lies
immediately under the deep fascia, on the proximal half of the outer
surface of the leg, and is directed obliquely downward and backward.
_Origin._—The head of the fibula.
_Insertion._—The tendon of the gastrocnemius, about the middle of the
leg.
_Action._—To assist the gastrocnemius.
_Structure._—It is a thin, fleshy band, about an inch (ca. 2 to 3 cm.)
in width, terminating on a thin tendon which fuses with that of the
gastrocnemius.[73]
_Relations._—Superficially, the skin, fascia, and peroneal nerve;
deeply, the lateral extensor and deep flexor.
_Blood-supply._—Posterior tibial artery.
_Nerve-supply._—Tibial nerve.
3. =Superficial digital flexor= or =flexor pedis perforatus= (Figs. 199,
201, 203) (M. flexor digitalis pedis sublimis; superficial flexor of the
phalanges).—The proximal part of this muscle lies between and under
cover of the two heads of the gastrocnemius (Fig. 459). It consists
almost entirely of a strong tendon, the belly being very little
developed.
[Illustration:
FIG. 204.—CROSS-SECTION OF LEFT LEG OF HORSE; SECTION IS CUT A LITTLE
ABOVE MIDDLE OF REGION.
_a_, Tibia; _b_, fibula; _c_, tibialis anterior; _d_, peroneus
tertius; _e_, anterior or long digital extensor; _f_, lateral
extensor; _g_, deep head of deep flexor (flexor hallucis longus);
_h_, inner head of deep flexor (flexor accessorius _s_, digitorum
longus); _i_, superficial head of deep flexor (tibialis posterior);
_k_, popliteus; _l_, superficial flexor tendon; _m_, gastrocnemius
tendon; _n_, soleus; _o_, skin; _p_, anterior tibial artery; _q_,
superficial peroneal nerve; _q′_, deep peroneal nerve; _r_, branch
of _q_; _s_, posterior tibial artery; _t_, cutaneous nerve; _u_,
tibial nerve; _v_, recurrent tibial vein; _w_, saphenous artery;
_x_, saphenous vein; _y_, branches of saphenous nerve. (After
Ellenberger, inl Leisering’s Atlas.)
]
_Origin._—The supracondyloid fossa (Fossa plantaris) of the femur.
_Insertion._—(1) The front and sides of the tuber calcis; (2) the
eminences on the proximal extremity of the second phalanx, and the
distal extremity of the first phalanx behind the lateral ligament.
_Action._—To flex the digit and extend the hock joint. On account of the
exceedingly small amount of muscular tissue the action is to be regarded
chiefly as a mechanical effect, resulting from the action of other
muscles on the stifle joint.
_Structure._—The origin is by means of a strong round tendon which is
incompletely covered with fleshy fibers as far as the upper third of the
leg. It is pretty intimately attached to the gastrocnemius, especially
to the outer head. At the distal third of the tibia it winds around the
inner surface of the gastrocnemius tendon, and then occupies a position
behind the latter. At the point of the hock it widens out, forming a
sort of cap over the tuber calcis, detaching on either side a strong
band which is inserted into the tuber calcis with the tarsal tendon of
the biceps and semitendinosus. It then passes downward over the plantar
(Calcaneo-metatarsal) ligament, becomes narrower, and is arranged below
as in the thoracic limb. A large synovial bursa lies under the tendon
from the distal fourth of the tibia to the middle of the tarsus. A
=subcutaneous bursa= is sometimes found on the wide part of the tendon
at the point of the hook. (Either or both of these bursæ may be involved
in so-called “capped hock.”)
_Relations._—Posteriorly, the gastrocnemius, fascia, and skin;
anteriorly, the femoro-patellar capsule, the popliteus, the deep flexor,
and the popliteal vessels; internally, the tibial nerve.
_Blood-supply._—Femoro-popliteal artery.
_Nerve-supply._—Tibial nerve.
[Illustration:
FIG. 205.—INJECTED SYNOVIAL SHEATHS AND BURSÆ OF TARSAL REGION OF
HORSE, INNER VIEW.
_a_, Synovial sheath of peroneus tertius and tibialis anterior; _b_,
bursa under inner (cunean) tendon of tibialis anterior; _c_,
synovial sheath of flexor longus s. accessorius; _d_, tarsal sheath
of deep flexor; _e_, _e′_, bursa under superficial flexor tendon;
_f_, _f′_, tibio-tarsal joint capsule; _1_, anterior extensor; _2_,
tibialis anterior; _2′_, inner (cunean) tendon of _2_; _3_, flexor
longus; _4_, deep digital flexor; _5_, superficial flexor tendon;
_6_, gastrocnemius tendon; _7_, tibia; _8_, tarsus; _9_, tuber
calcis; _10_, large metatarsal bone; _11_, inner small metatarsal
bone; _12_, _12′_, fascial bands. (After Ellenberger, in Leisering’s
Atlas.)
]
[Illustration:
FIG. 206.—INJECTED SYNOVIAL SHEATHS AND BURSÆ OF TARSAL REGION OF
HORSE, EXTERNAL VIEW.
_a_, Synovial sheath of anterior or long digital extensor; _b_,
synovial sheath of lateral digital extensor; _c_, _c′_, bursa under
superficial flexor tendon; _d_, capsule of hock joint; _1_, anterior
or long extensor; _2_, lateral extensor; _3_, _3_, _3_, annular
ligaments; _4_, deep digital flexor; _5_, tendon of gastrocnemius;
_6_, superficial flexor tendon; _7_, tibia; _8_, tarsus; _9_, tuber
calcis; _10_, metatarsus. (After Ellenberger, in Leisering’s Atlas.)
]
4. =Deep digital flexor= or =flexor pedis perforans= (M. flexor
digitalis pedis profundus; deep and oblique flexors of the
phalanges).—The belly of this muscle lies on the posterior surface of
the tibia, and is divisible into three parts or heads, which, however,
finally unite on a common tendon of insertion.
_Origin._—(1) The posterior edge of the external condyle of the tibia;
(2) the external border of the external condyle of the tibia, just
behind the facet for the fibula; (3) the middle third of the posterior
surface and the upper part of the external border of the tibia, the
posterior border of the fibula, and the interosseous ligament.[74]
_Insertion._—The semilunar crest of the third phalanx and the adjacent
surface of the lateral cartilage.
_Action._—To flex the digit and to extend the hock joint.
_Structure._—(1) The inner head (M. flexor digitalis longus s. flexor
accessorius) is easily isolated (Figs. 203, 459). It has a fusiform
belly, which crosses the leg obliquely and lies in a groove formed by
the other heads and the popliteus. This terminates near the lower third
of the tibia on a round tendon which passes downward, partly embedded in
the internal lateral ligament of the hock, and joins the common tendon
about a third of the way down the metatarsus. In its course over the
inner surface of the hock the tendon lies in a canal formed by the
strong tarsal fascia, the tibia, and the lateral ligament, and is
provided with a =synovial sheath= which extends from the distal fourth
of the tibia to the junction with the principal tendon. (2) The
superficial head (M. tibialis posterior) is only partially separable. It
has a flattened belly, terminating near the lower third of the tibia on
a flat tendon which soon fuses with the principal tendon. (3) The deep
head (M. flexor hallucis longus) is much the largest. It lies on the
posterior surface of the tibia, from the popliteal line outward and
downward. The belly contains much tendinous tissue, and terminates
behind the distal end of the tibia on a strong round tendon. The latter
receives the tendon of the tibialis posterior, passes downward in the
tarsal groove, bound down by the strong tarsal fascia (Ligamentum
laciniatum) and enveloped in a synovial sheath, receives the tendon of
the inner head below the hock, and, a little further down, the so-called
check ligament (Caput tendineum [Schmaltz]). The =tarsal sheath= (Vagina
tarsea) begins about two to three inches (ca. 5 to 7.5 cm.) above the
level of the internal malleolus, and extends about one-fourth of the way
down the metatarsus. (Distention of the sheath, as in “thoroughpin,”
affects chiefly its proximal end.) The check ligament resembles that of
the fore limb, except that it is longer and very much weaker; it may be
absent. The remainder of the tendon is arranged like that of the
thoracic limb.
_Relations._—Anteriorly, the tibia and fibula, the popliteus, lateral
extensor, tibialis anterior, and the tibial vessels; posteriorly, the
gastrocnemius, superficial flexor, and the tibial nerve; externally, the
fascia, skin, and the soleus; internally, the fascia and skin.
_Blood-supply._—Posterior tibial artery.
_Nerve-supply._—Tibial nerve.
5. =Popliteus= (Fig. 203).—This thick and triangular muscle lies on the
posterior surface of the femoro-tibial articulation and the posterior
surface of the tibia above the popliteal line.
_Origin._—A small depression on the external epicondyle of the femur,
close to the articular surface and under the lateral ligament.
_Insertion._—A triangular area on the posterior surface of the tibia,
above and internal to the popliteal line; also the proximal half of the
inner border and a narrow adjacent part of the internal surface of the
tibia.
_Action._—To flex the femoro-tibial joint and to rotate the leg inward.
_Structure._—The strong tendon of origin lies at first under the lateral
ligament, and curves backward and inward over the external condyle of
the tibia and its semilunar cartilage, being invested by a reflection of
the synovial capsule of the joint (Fig. 459). The tendon is succeeded by
a thick triangular belly, the fibers of which are directed obliquely
downward and inward.
_Relations._—Superficially, the fascia and skin, semitendinosus,
gastrocnemius, superficial flexor; deeply, the femoro-tibial joint, the
tibia, the popliteal vessels and their divisions. The saphenous vessels
and nerve lie along the inner border of the muscle, separated from it,
however, by the deep fascia.
_Blood-supply._—Popliteal and posterior tibial arteries.
_Nerve-supply._—Tibial nerve.
MUSCLES OF THE METATARSUS AND DIGIT
=Extensor pedis brevis= (M. extensor digitalis brevis).—This small
muscle lies in the angle of union of the long and lateral extensors of
the digit. (Shown in Fig. 201, but not marked.)
_Origin._—The outer tendon of the peroneus tertius, the middle annular
ligament, and the outer lateral ligament of the hock.
_Insertion._—The tendon of the anterior or long extensor.
_Action._—To assist the anterior or long extensor.
_Structure._—It is principally fleshy, having a superficial origin from
the annular ligament, and a deep one (by a thin tendon) from the outer
tendon of the peroneus tertius. The insertion is by a thin tendon.
_Relations._—Superficially, the skin and fascia and the tendons of the
anterior and lateral extensors; deeply, the joint capsule, the great
metatarsal artery, and the deep peroneal nerve.
_Blood-supply._—Great metatarsal artery.
_Nerve-supply._—Deep peroneal nerve.
The =interossei= and =lumbricales= are arranged like those of the
thoracic limb, the only noticeable difference being the greater
development of the lumbricales in the pelvic limb.
THE MUSCLES OF THE OX
MUSCLES OF THE FACE
The =panniculus= is much more developed than in the horse, presenting as
a special feature the extensive =frontalis= muscle, which covers the
frontal and nasal regions.
The =orbicularis oris= does not form a complete ring, the defect being
in the middle of the upper lip.
The =levator nasolabialis= is extensive, thin, and not very distinct
from the frontalis; it divides into two layers, between which the
levator labii superioris proprius and the lateral dilator of the nostril
pass. The superficial layer ends in the nostril and upper lip, the deep
layer on the accessory (lateral) nasal cartilages and on the nasal
process of the premaxilla.
The =levator labii superioris proprius= arises on and before the facial
tuberosity and terminates by several tendons in the muzzle. It passes
between the two layers of the preceding muscle, blending in part with
the deep layer.
The =zygomaticus= is much stronger than in the horse. It arises on the
masseteric fascia, and ends chiefly in the upper lip.
The =depressor labii superioris= does not resemble the muscle of the
same name in the horse. It arises just in front of the facial
tuberosity, and divides usually into two branches, which terminate in a
number of tendons that form a network in the muzzle and upper lip.
The =incisivus inferior= is a small, rounded muscle, which arises on the
body of the mandible below the second and third incisors, and ends in
the lower lip, blending with the orbicularis.
The =depressor labii inferioris= is thin, and does not extend as far
backward as in the horse; only the anterior end is distinct from the
buccinator.
The =buccinator= shows no marked variation, but its superficial layer is
well developed.
The =dilatator naris lateralis= arises in front of the facial
tuberosity, passes forward between the branches of the levator
nasolabialis, and terminates in the outer wing of the nostril.
The dilatator naris transversus is replaced by the =dilatator naris
apicalis=, which is situated in the muzzle and joins its fellow at a
median raphé. It arises on the border and upper surface of the body of
the premaxilla, the fibers passing obliquely upward and outward to the
inner wing of the nostril.
The =dilatator naris superior= arises from the alar cartilage of the
nostril and ends in the inner wing of the nostril.
[Illustration:
FIG. 207.—MUSCLES OF HEAD OF OX, LATERAL VIEW.
_a_, Levator labii superioris proprius; _b_, levator nasolabialis;
_c_, trapezius; _c′_, mastoido-humeralis; _d_, _d′_,
sterno-cephalicus; _e_, omo-hyoideus; _f_, dilatator
naris lateralis; _g_, zygomaticus; _g′_, malaris; _h_,
buccinator; _i_, depressor labii inferioris; _k_, orbicularis
oris; _m_, masseter; _n_, parotido-auricularis; _o′_,
zygomatico-auricularis and scutulo-auricularis superficialis
inferior; _o″_, scutulo-auricularis superficialis superior; _o‴_,
scutulo-auricularis superficialis accessorius; _p_, _p′_,
scutularis; _u_, frontalis; _w_, mylo-hyoideus; _1_, concha; _2_,
_3_, posterior and anterior borders of _1_; _8_, scutiform
cartilage; _9_, zygomatic arch; _28′_, ramus of mandible; _37_,
external maxillary vein; _38_, jugular vein; _39_, facial vein;
_44_, parotid gland; _50_, _50′_, submaxillary gland; dotted line at
_50_ indicates position of large lymph gland, and another lies
partly under parotid gland, just in front of _44_; _58_, internal
palpebral ligament; _59_, laryngeal prominence. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =dilatator naris inferior= consists of two layers which arise on the
nasal process of the premaxilla and the lateral nasal cartilage and end
in the outer wing of the nostril.
The =orbicularis oculi= is well developed.
The corrugator supercilii is not present as a separate muscle, its place
and function being taken by the frontalis.
The =malaris= is broad, and spreads out below on the fascia over the
buccinator and masseter; it is divided into two parts.
MUSCLES OF MASTICATION
The =masseter= is not so large as in the horse; a considerable part of
it arises on the facial tuberosity and is directed obliquely backward
and downward, so that it would draw the lower jaw forward as well as
upward.
The =temporalis= conforms to the temporal fossa, and is therefore longer
and entirely lateral in position.
The =pterygoidei= are not quite clearly separated; their direction is
more oblique, and the origin of the pterygoideus internus is nearer the
median plane than in the horse.
[Illustration:
FIG. 208.—MUSCLES OF HEAD OF OX, DORSAL VIEW.
_a_, _a′_, Levator labii superioris proprius; _b_, levator
nasolabialis; _f_, dilatator naris lateralis; _g′_, malaris; _o_,
zygo-inatico-auricularis and scutulo-auricularis superficialis
inferior; _o″_, scutulo-auricularis superficialis superior; _o‴_,
scutulo-auricularis superficialis accessorius; _p_, scutularis; _u_,
frontalis; _z_, orbicularis oculi; _1_, concave surface of concha;
_3_, _2_, anterior and posterior borders of concha; _8_, scutiform
cartilage; _34_, parietal cartilage; _39_, facial vein; _49_,
muzzle; _58_, internal palpebral ligament. (After Ellenberger-Baum,
Anat. für Künstler.)
]
The =stylo-mandibularis= is absent.
The =digastricus= has a tendinous origin on the paramastoid or styloid
process of the occipital bone; its bellies are short and thick. It does
not perforate the stylo-hyoideus. The two digastrici are connected
beneath the root of the tongue by a layer of transverse muscle-fibers
(Transversus mandibulæ).
HYOID MUSCLES
The =mylo-hyoideus= is thicker and more extensive than in the horse.
The =stylo-hyoideus= has a long thin tendinous origin and is not
perforated by the digastricus.
The =genio-hyoideus= is more developed.
The =kerato-hyoideus= has an additional attachment on the middle cornu
of the hyoid bone.
The =hyoideus transversus= is bifid.
The =sterno-thyro-hyoideus= has no intermediate tendon and is thicker.
The =omo-hyoideus= arises as a thin band from the fascia over the third
and fourth cervical vertebræ. It blends here with the rectus capitis
anterior major. The =occipito-hyoideus= is thick.
[Illustration:
FIG. 209.—MUSCLES OF HEAD OF OX, VENTRAL VIEW.
_d_, _d′_, Sterno-cephalicus; _e_, omo-hyoideus; _g_, zygomaticus;
_h_, buccinator; _i_, depressor labii inferioris; _k_, orbicularis
oris; _m_, masseter; _n_, parotido-auricularis; _o′_,
zygomatico-auricularis; _w_, mylo-hyoideus; _1_, concha, convex
surface; _2_, anterior border of concha; _30′_, angle of jaw; _39_,
facial vein; _44_, parotid gland; _45_, lower lip; _48_, angle of
mouth; _50_, _50′_, submaxillary gland; _59_, larynx; _x_, wing of
atlas. (After Ellenberger-Baum, Anat. für Künstler.)
]
MUSCLES OF THE NECK
A. VENTRAL GROUP
The =sterno-cephalicus= consists of two muscles. They arise from
the manubrium sterni and first rib. The superficial muscle
(Sterno-mandibularis) is inserted on the anterior border of the
masseter, the ramus of the mandible, and the buccal fascia. The
deep muscle (Sterno-mastoideus) crosses under the preceding and
ends on the mastoid process, the mandible, and, in common with the
rectus capitis anterior major, on the basilar process of the
occipital bone.
[Illustration:
FIG. 210.—SUPERFICIAL MUSCLES OF OX, AFTER REMOVAL OF PANNICULUS.
_a_, Trapezius; _b_, omo-transversarius; _c_, _c′_, mastoido-humeralis
(_c_, cleido-mastoideus; _c′_, cleido-occipitalis); _d_,
sterno-cephalicus; _e_, deltoid; _f_, long head, _f′_, external head
of triceps; _g_, superficial pectoral; _h_, posterior deep pectoral;
_i_, serratus magnus; _k_, latissimus dorsi; _l_, obliquus abdominis
externus; _l′_, aponeurosis of _l_; _m_, serratus posterior; _m′_,
lumbo-dorsal fascia; _n_, obliquus abdominis internus; _o_, tensor
fasciæ latæ; _o′_, fascia lata; _p_, gluteus medius; _q_, _q′_,
biceps femoris; _r_, semitendinosus; _s_, sacro-coccygeus superior;
_t_, sacro-coccygeus lateralis; _u_, coccygeus. (After
Ellenberger-Baum, Anat. f Künstler.)
]
There are two scaleni. The =scalenus ventralis= (s. primæ costæ) arises
on the first rib and ends on the transverse processes of the third to
the seventh cervical vertebræ. It is traversed by the roots of the
brachial plexus, which partially divide it into a small dorsal and a
large ventral part. The brachial vessels lie below the latter. The
=scalenus dorsalis= (s. supracostalis) arises usually on the second,
third, and fourth ribs, and ends on the transverse processes of the
third to the sixth cervical vertebræ.
The =rectus capitis anterior major= arises on the third to the sixth
cervical transverse processes, and blends at its insertion with the
sterno-mastoideus and the mastoid portion of the mastoido-humeralis.
The =rectus capitis anterior minor= is larger than in the horse.
The =rectus capitis lateralis= and =longus colli= resemble those of the
horse.
The =intertransversales= are large. From the sixth cervical vertebra
forward they form a muscular mass (M. intertransversarius longus) which
is inserted into the wing of the atlas.
B. LATERAL GROUP
The =splenius= is thin. It arises directly from the first three or four
thoracic spines, and ends by a thin tendon on the occipital bone, the
wing of the atlas, and the transverse process of the axis, blending with
the mastoido-humeralis, trachelo-mastoideus, and omo-transversarius. The
remaining muscles present no very marked differential features.
MUSCLES OF THE THORAX
The =levatores costarum= number ten or eleven pairs.
The =diaphragm= presents several important differential features. Its
slope is much steeper and its width is greater than in the horse. The
costal attachment extends almost in a straight line from the upper
fourth of the last rib to the junction of the eighth rib with its
cartilage, and along the latter to the sternum. The mid-line slopes from
the twelfth thoracic vertebra obliquely as far as the vena cava, beyond
which it is almost vertical. The right crus divides into two branches,
which circumscribe the œsophageal opening, unite below, and then spread
out in the tendinous center. The left crus is small. The œsophageal
opening is situated about four to five inches (10 to 12 cm.) below the
eighth thoracic vertebra, a little to the left of the median plane. The
foramen venæ cavæ is a little more ventral and almost in the median
plane. The other muscles resemble those of the horse.
MUSCLES OF THE BACK AND LOINS
The =serratus anticus= is very thin. It is inserted on the fifth to the
eighth ribs. It may be reduced to two or three digitations or may be
absent. The =serratus posticus= is usually inserted on the last three or
four ribs.
The =transversalis costarum= (Iliocostalis) has a distinct lumbar
portion which is attached to the lumbar transverse processes and the
external angle of the ilium.
The =longissimus= resembles that of the horse, but it is more fleshy
anteriorly, and the spinalis dorsi is clearly distinguishable from the
common mass. In the lumbar region the tendons meet across the summits of
the spines.
=Intertransversales= are present in the back, and =interspinales= in the
back and loins.
MUSCLES OF THE TAIL
These resemble those of the horse; the coccygeus is, however, much more
developed.
ABDOMINAL MUSCLES
The =obliquus abdominis externus= is somewhat thinner and has a less
extensive origin, which begins at the lower part of the fifth
intercostal space and ends on the last rib above its middle. The
direction of the fibers in the flank is horizontal, and they do not
reach to the external angle of the ilium, nor as high as the lumbar
transverse processes. (In this region the abdominal tunic has a strong
attachment to the point of the hip and the lumbo-dorsal fascia.) The
aponeurosis is intimately united with the abdominal tunic, and does not
detach a layer on the inner surface of the thigh.
[Illustration:
FIG. 211.—DEEPER MUSCLES OF NECK, SHOULDER, AND THORAX OF OX.
_c′_, Cleido-occipitalis muscle; _d_, sterno-cephalicus; _f_, _f′_,
long and external heads of triceps; _g_, superficial pectoral
muscle; _h_, _h′_, posterior and anterior deep pectoral muscles;
_i_, _i′_, serratus magnus; _k_, latissimus dorsi; _l_, obliquus
abdominis externus; _v′_, biceps brachii; _w_, splenius; _x_,
rhomboideus; _y_, trachelo-mastoideus; _z_, supraspinatus; _z′_,
infraspinatus; _z″_, tendon of insertion of _z′_; _1′_, cartilage of
scapula; _2_, tuberosity of spine of scapula; _3_, acromion; _5_,
external tuberosity of humerus; _6_, deltoid tuberosity; _8_,
olecranon; _26_, transverse processes of cervical vertebræ; _27_,
posterior auricular muscles; _X_, wing of atlas. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =obliquus abdominis internus= is more developed and has an
additional origin from the lumbo-dorsal fascia. The aponeurosis blends
with that of the external oblique near the linea alba, and detaches a
layer which assists in the formation of the internal sheath of the
rectus.
The =rectus abdominis= arises on the lateral border of the sternum as
far forward as the third costal cartilage. The two muscles are
separated, except near the pelvis, by an interval varying from two to
four inches (ca. 5 to 10 cm.), so that this part of the abdominal wall
is entirely fibrous. (The umbilicus is in a transverse plane through the
third lumbar vertebra.) There are five tendinous inscriptions, on the
third of which is a foramen for the passage of the subcutaneous
abdominal vein (milk vein). The prepubic tendon has, in addition to
branches inserted into the ilio-pectineal eminences, a strong attachment
to the median common tendon of the adductors of the thigh, so that the
abdominal wall is strongly retracted and almost vertical at its junction
with the pelvis.
The =transversus abdominis= presents no striking differential features.
The transversalis fascia is strong and distinct except over the
diaphragm.
MUSCLES OF THE THORACIC LIMB
I. MUSCLES OF THE SHOULDER GIRDLE
The =trapezius= is much thicker and broader than in the horse, and is
undivided. It arises on the ligamentum nuchæ and supraspinous ligament,
from the atlas to the twelfth thoracic vertebra.
The =omo-transversarius= is a muscle (not present in the horse) which
arises on the wing of the atlas, and, inconstantly, the transverse
process of the second cervical vertebra, and is inserted into the
scapular spine and fascia.
The =rhomboideus= is clearly divided into cervical and dorsal portions,
the latter extending further than in the horse.
The =latissimus dorsi= has a broad tendon of origin, which blends with
the lumbo-dorsal fascia; it is also attached to the eleventh and twelfth
ribs, the fascia over the external intercostal and oblique abdominal
muscles, and by a tendinous slip to the deep pectoral muscle.
The =mastoido-humeralis= has two distinct parts. The dorsal division (M.
cleido-occipitalis) arises on the occipital bone and the ligamentum
nuchæ. The ventral part (M. cleido-mastoideus) is smaller and arises by
a round tendon on the mastoid process and the rectus capitis anterior
major, and by a thin tendon on the mandible. At the shoulder a small
muscle which arises on the first rib blends with the deep face of the
mastoido-humeralis.[75]
The =superficial pectoral= muscle does not present any striking
difference.
The =deep pectoral= arises as far forward as the second rib and is
undivided. However, the scapular portion may be considered to be
represented by a small branch extending over the lower part of the
supraspinatus. A tendon is detached from the dorsal edge, which blends
with the latissimus dorsi and coraco-brachialis.
The =serratus magnus= is clearly divided into cervical and thoracic
portions. The former is large and extends from the third (or second)
cervical vertebra to the fifth rib, being overlapped behind by the
thoracic part. The thoracic part is relatively thin and is covered by a
very strong aponeurosis; it is attached to the fourth to the ninth ribs
by six digitations, and is inserted by a flat tendon into the inner face
of the dorsal angle of the scapula.
II. MUSCLES OF THE SHOULDER
The =deltoid= is clearly divided into acromial and scapular portions.
The former arises on the acromion, the latter on the posterior border of
the scapula and the aponeurotic covering of the infraspinatus. The
scapular part of the muscle is largely inserted into the fascia covering
the triceps.
The =supraspinatus=, =infraspinatus=, and =teres minor= do not differ
materially from those of the horse.
The =subscapularis= consists of three portions with a common tendon of
insertion.
The =teres major= and =coraco-brachialis= resemble those of the horse.
III. MUSCLES OF THE ARM
The =biceps= is smaller and less tendinous, and is situated more
internally than in the horse. The tendon of origin is flat, and is bound
down in the bicipital groove by a fibrous band. (In the sheep the tendon
is round and passes through the shoulder joint.)
[Illustration:
FIG. 212.—MUSCLES OF ANTIBRACHIUM AND MANUS OF OX, ANTERIOR VIEW.
_a_, Extensor carpi radialis; _b_, extensor digiti tertii; _c_,
extensor digitalis communis; _d_, extensor digiti quarti (tendon);
_f_, extensor carpi obliquus; _g_, brachialis; _12′_, metacarpal
tuberosity. (After Ellenberger-Baum, Anat. für Künstler.)
]
[Illustration:
FIG. 213.—MUSCLES OF ANTIBRACHIUM AND MANUS OF OX, EXTERNAL VIEW.
_a_, Extensor carpi radialis; _b_, extensor digiti tertii; _c_, common
or anterior digital extensor; _d_, extensor digiti quarti; _e_,
flexor carpi externus; _f_, extensor carpi obliquus; _f′_, ulnar
head of flexor carpi medius; _g_, brachialis; _h_, interosseus
medius or suspensory ligament; _i_, flexor tendons; _i′_, branch of
_h_, to superficial flexor tendon; _8_, olecranon; _11_, accessory
carpal bone; _12′_, metacarpal tuberosity. (After Ellenberger-Baum,
Anat. für Künstler.)
]
[Illustration:
FIG. 214.—MUSCLES OF ANTIBRACHIUM AND MANUS OF OX, INTERNAL VIEW.
_a_, Extensor carpi radialis; _b_, tendon of extensor digiti tertii;
_f_, tendon of extensor carpi obliquus; _g_, brachialis; _h_,
interosseus medius or suspensory ligament; _i_, flexor tendons;
_i′_, branch of _h_; _k_, flexor carpi internus; _l_, flexor carpi
medius; _m_, superficial digital flexor. (After Ellenberger-Baum,
Anat. für Künstler.)
]
The internal head of the =triceps= is more developed than in the horse.
The =tensor fasciæ antibrachii= is a slender muscle.
IV. MUSCLES OF THE FOREARM
A. EXTENSOR DIVISION
The =extensor carpi radialis= is like that of the horse. There is
sometimes a small muscle lying along its inner border, which may
represent the extensores pollicis.
There are three =digital extensors=: 1. The =common= or =anterior
digital extensor= (M. extensor digitalis communis) arises by two heads
from the extensor epicondyle and the ulna. The heads fuse about the
middle of the forearm, and terminate soon on a tendon which passes over
the carpus and metacarpus, gradually inclining forward. At the fetlock
joint it divides into two branches, which are inserted into the third
phalanges. 2. The =internal digital extensor= (M. extensor digiti tertii
proprius) arises on the extensor epicondyle, and is inserted by two
branches into the second and third phalanges of the inner digit. The
tendon receives two reinforcing slips from the suspensory ligament. 3.
The =lateral digital extensor= (M. extensor digitalis lateralis s.
digiti quarti proprius) arises from the external lateral ligament of the
elbow joint, the external tuberosity of the radius, and the ulna. The
tendon terminates like that of the preceding muscle.
[Illustration:
FIG. 215.—RIGHT CARPUS OF OX WITH BURSÆ AND SYNOVIAL SHEATHS INJECTED,
EXTERNAL VIEW.
]
[Illustration:
FIG. 216.—RIGHT CARPUS OF OX WITH BURSÆ AND SYNOVIAL SHEATHS INJECTED,
INTERNAL VIEW.
_1_, Extensor carpi radialis, with synovial sheath (_1′_) and bursa
(_1″_); _2_, extensor carpi obliquus, with synovial sheath (_2′_)
and bursa (_2″_); _3_, extensor digiti tertii proprius; _4_,
extensor digitalis communis; _3′_, common synovial sheath of _3_ and
_4_; _5_, extensor digiti quarti proprius, with synovial sheath
(_5′_); _6_, _6′_, flexor carpi externus, with bursa (_6″_); _7_,
flexor carpi internus, with synovial sheath; _8_, deep digital
flexor, with synovial sheath (_8′_); _9_, flexor carpi medius; _10_,
superficial digital flexor, with synovial sheath _10′_; _a_, radius;
_b_, carpus; _c_, metacarpus; _d_, cut edge of annular ligament.
(After Schmidtchen.)
]
The =extensor carpi obliquus= resembles that of the horse.
The extensor tendons are bound down at the carpus by an annular
ligament, and are furnished with synovial sheaths (Figs. 215, 216).
B. FLEXOR DIVISION
The three =flexors of the carpus= are like those of the horse.
The =superficial digital flexor= is somewhat blended at its origin with
the middle flexor of the carpus. It divides into two bellies,
superficial and deep, terminating on tendons at the distal part of the
forearm. The superficial tendon passes over the posterior annular
ligament (Ligamentum carpi transversum), perforates the metacarpal
fascia, and joins the deep tendon about the middle of the metacarpus.
The deep belly is connected with the deep flexor by a strong fibrous
band. Its tendon passes under the annular ligament in a groove on the
deep flexor, from which it receives fibers. The conjoined tendon soon
bifurcates, each branch receiving a reinforcing band from the suspensory
ligament, and forming near the fetlock a ring for the corresponding
branch of the deep flexor tendon. Passing under two digital annular
ligaments, they are inserted into the volar surfaces of the second
phalanges by three slips.
The =deep digital flexor= has the same heads as in the horse, the
humeral head, as before mentioned, being connected with the deep portion
of the superficial flexor. The tendon divides near the distal end of the
metacarpus into two branches which are inserted into the volar surfaces
of the third phalanges.
The synovial sheaths at the carpus present the following special
features: One is found in connection with the tendon of the superficial
part of the superficial flexor of the digits. There is a common sheath
for the tendons of the common extensor and the inner extensor.
Bursæ may occur under the tendons of the proper extensors of the digits
at the fetlock; they are constant only in old animals (Schmidtchen). The
branches of the tendon of the common extensor are provided with synovial
sheaths from their origin to the middle of the second phalanx. There are
two digital synovial sheaths for the flexor tendons; they may
communicate at their upper part, and extend from the distal third of the
metacarpus nearly to the distal sesamoids. Bursæ occur between the
latter and the branches of the deep flexor tendon.
METACARPAL MUSCLES
The =lumbricales= are absent, unless we regard as such the muscular
bundles which arise on the deep flexor and are inserted into the
superficial flexor tendon at the carpus.
The =interosseus medius= or suspensory ligament is somewhat more
muscular than in the horse; indeed, in the young subject it may be
almost entirely fleshy. Its arrangement is somewhat complex. Single at
its origin, it detaches about the middle of the metacarpus a band which
joins the tendon of the superficial flexor and concurs near the fetlock
in the formation of the ring for the deep flexor tendon. A little lower
down it divides into three and then into five branches. The lateral
branches (two pairs) are attached to the corresponding sesamoids and
tendons of the proper extensors, while the middle branch passes through
the sulcus at the distal end of the metacarpus and bifurcates, each
division fusing with the tendon of the corresponding proper extensor.
[Illustration:
FIG. 217.—CROSS-SECTION OF DISTAL THIRD OF METACARPUS OF OX.
_b_, Tendon of extensor digiti tertii; _c_, tendon of common extensor;
_d_, tendon of extensor digiti quarti; _h_, interosseus medius or
suspensory ligament; _i_, tendons of digital flexors; _i′_, branch
of _h_; _12_, metacarpal bone. (After Ellenberger-Baum, Anat. für
Künstler.)
]
It is to be noted that the fascia on the posterior face of the
metacarpus and digit is very thick. It is continuous above with the
ligamentum carpi transversum, and is attached on either side to the
metacarpal bone. At the fetlock it forms the fibrous basis for the small
claws, and below this it detaches two strong bands which diverge to be
inserted into the second and third phalanges, blending with the lateral
ligaments.
THE MUSCLES OF THE PELVIC LIMB
I. THE SUBLUMBAR MUSCLES
The =psoas minor= begins at the disc between the twelfth and thirteenth
thoracic vertebræ.
The =psoas major= has a fleshy origin on the posterior border of the
last rib, and a thin tendon attached to the twelfth rib.
The =iliacus= begins under the body of the sixth lumbar vertebra, and is
more closely united with the psoas major than in the horse.
The =quadratus lumborum= extends as far forward as the body of the tenth
or eleventh thoracic vertebra.
II. EXTERNAL MUSCLES OF THE HIP AND THIGH
The =tensor fasciæ latæ= is large, and the fleshy part extends further
down than in the horse.
The gluteus superficialis is not present as such; apparently its
anterior part has fused with the tensor fasciæ latæ and its posterior
with the biceps femoris.
The =gluteus medius= is small, the lumbar portion being insignificant
and extending forward only to the fourth lumbar vertebra. Its deep
portion (Gluteus accessorius) is easily separable, and its strong tendon
is inserted into the femur below the trochanter major, under cover of
the upper part of the vastus externus.
The =gluteus profundus= is thin, but extensive, arising as far forward
as the external angle of the ilium, and from the lower part of the
sacro-sciatic ligament. The fibers converge on a tendon which passes
under the upper part of the vastus externus, and is inserted into a
tubercle a short distance below the great trochanter.
[Illustration:
FIG. 218.—GLUTEAL AND FEMORAL REGIONS OF OX, AFTER REMOVAL OF
SUPERFICIAL MUSCLES.
_p_, Gluteus medius; _r_, semitendinosus; _u_, coccygeus; _28_, vastus
externus; _28′_, rectus femoris; _29_, semimembranosus; _30_,
gastrocnemius; _31_, sacro-sciatic ligament; _16_, tuber coxæ; _17_,
tuber ischii; _19_, trochanter major; _20_, patella; _21′_, external
condyle of tibia. (After Ellenberger-Baum. Anat. für Künstler.)
]
The =biceps femoris= is very wide at its upper part, having apparently
absorbed the posterior part of the superficial gluteus. It is divided in
the thigh into two portions, which end on a wide aponeurosis. There is
no femoral attachment. A large bursa occurs between the muscle and the
great trochanter in the adult. The part of the tendon which fuses with
the external patellar ligament presents a fibro-cartilaginous
thickening, and an extensive bursa is interposed between it and the
external condyle of the femur.
The =semitendinosus= and =semimembranosus= arise on the ischium only.
The latter has a branch attached to the internal condyle of the tibia.
III. ANTERIOR MUSCLES OF THE THIGH
The =quadriceps femoris= resembles that of the horse; the =vastus
intermedius= is more clearly separable, and consists of two parts. Bursæ
occur under the insertions of the internal and external vasti, and often
under the end of the biceps in the adult.
[Illustration:
FIG. 219.—MUSCLES OF LEFT LEG AND FOOT OF OX, ANTERIOR VIEW.
_a_, Peroneus tertius; _a′_, tibialis anterior; _b_, anterior or long
digital extensor; _b′_, extensor digiti tertii; _c_, peroneus
longus; _d_, extensor digiti quarti; _i_, _i_, annular ligaments;
_k_, external lateral ligament of hock joint; _l_, branch of
suspensory ligament; _20_, patella; _21′_, external condyle of
tibia; _28_, tuberosity of tibia. (After Ellenberger-Baum, Anat. für
Künstler.)
]
[Illustration:
FIG. 220.—MUSCLES OF LEG AND FOOT OF OX, EXTERNAL VIEW.
_a_, Peroneus tertius; _a′_, tibialis anterior; _b_, anterior or long
digital extensor; _b′_, tendon of _b_; _c_, peroneus longus; _d_,
extensor digiti quarti; _e_, deep digital flexor; _e′_, tendon of
_e_; _e″_, branch of interosseus medius or suspensory ligament; _f_,
gastrocnemius (the soleus lies just in front of _f_); _f′_, tendon
of _f_; _g_, tendon of superficial digital flexor; _h_, interosseus
medius or suspensory ligament; _i_, _i_, annular ligaments; _20_,
patella; _21′_, external condyle of tibia; _28_, crest of tibia.
(After Ellenberger-Baum, Anat. für Künstler.)
]
The =articularis genu= or subcrureus is a small muscle which lies under
the lower part of the vastus intermedius, and is inserted on the
suprapatellar cul-de-sac of the synovial membrane.
The =capsularis= is absent.
IV. INTERNAL MUSCLES OF THE THIGH
The =sartorius= arises by two heads, one from the tendon of the psoas
minor and the iliac fascia, the other from the shaft of the ilium. The
femoral vessels pass between them.
The =gracilis= is more extensively united with its fellow than in the
horse.
[Illustration:
FIG. 221.—LEFT TARSUS OF OX WITH SYNOVIAL SHEATHS AND BURSÆ INJECTED,
EXTERNAL VIEW.
_1_, Peroneus tertius; _1′_, tendon of _1_ and its sheath, _1″_; _2_,
extensor digiti tertii proprius; _2′_, tendon of _2_; _2″_, common
sheath of tendons of extensor digiti tertii and extensor digitalis
longus (_3_, _3′_); _4_, peroneus longus and its sheath, _4′_; _5_,
extensor digiti quarti and its sheath, _5′_; _6_, tendon of
gastrocnemius; _7_, superficial digital flexor and its sheath, _7′_;
_8_, tendon of tibialis anterior; _a_, tibia; _b_, proximal annular
ligament; _c_, tarsus; _d_, distal annular ligament; _e_,
metatarsus; _f_, external lateral ligament. (After Schmidtchen.)
]
[Illustration:
FIG. 222.—LEFT TARSUS OF OX WITH SYNOVIAL SHEATHS AND BURSÆ INJECTED,
INTERNAL VIEW.
_1_, Peroneus tertius; _2_, tendon of tibialis anterior with sheath,
_2′_, and bursa, _2″_; _3_, long digital flexor and _3′_, its
sheath; _4_, tibialis posterior; _5_, deep digital flexor and its
sheath, _5′_; _6_, tendon of gastrocnemius and bursa, _6′_; _7_,
superficial digital flexor and its sheath, _7′_; _8_, subcutaneous
bursa; _a_, tibia; _b_, proximal annular ligament; _c_, tarsus; _d_,
metatarsus. (After Schmidtchen.)
]
The =pectineus= is large, and arises by a single head from the pubic
crest and prepubic tendon. It divides into two branches, one of which is
inserted as in the horse, while the other extends to the internal
epicondyle of the femur.
The =adductor= resembles that of the horse, but does not reach to the
internal condyle.
The =quadratus femoris= and =obturator externus= resemble those of the
horse.
The =obturator internus= arises from the ischium only, and its tendon
passes through the obturator foramen.
The =gemellus= is large.
V. MUSCLES OF THE LEG AND FOOT
There are four =digital extensors=, two of which are fused with each
other and the peroneus tertius in the upper third of the leg.
1. The =anterior= or =long digital extensor= (M. extensor digitalis
longus) arises by the common tendon in the extensor fossa of the femur,
and separates from the other muscles near the middle of the leg. At the
distal end of the tibia it terminates on a tendon which passes down over
the hock (bound down by two annular ligaments) and ends like that of the
thoracic limb.
[Illustration:
FIG. 223.—MUSCLES OF LEG AND FOOT OF OX, INNER VIEW.
_a_, Peroneus tertius; _b′_, tendon of anterior or long extensor; _e_,
deep digital flexor; _e′_, tendon of _e_; _e″_, branch of _h_ to
superficial flexor tendon; _f_, gastrocnemius; _g_, tendon of
superficial digital flexor; _h_, interosseus medius or suspensory
ligament; _i_, annular ligaments; _l_, branch of _h_; _m_, long
digital flexor; _o_, popliteus; _20_, patella; _28_, tuberosity of
tibia. (After Ellenberger-Baum, Anat. für Künstler.)
]
2. The =internal digital extensor= (M. extensor digiti tertii proprius)
arises in common with the preceding muscle and the peroneus tertius, and
is covered by them to the distal third of the tibia. Its tendon passes
under the annular ligaments between those of its cogeners and ends on
the second phalanx of the inner digit.
3. The =lateral digital extensor= (M. extensor digitalis lateralis s.
digiti quarti proprius) arises on the external lateral ligament of the
stifle joint and the external condyle of the tibia. Its tendon passes
over the outer surface of the hock, and terminates on the anterior
surface of the second phalanx of the external digit.
The reinforcing bands from the suspensory ligament are arranged as in
the fore limb.
4. The =extensor brevis= resembles that of the horse, but is inserted on
the tendon of the anterior extensor only.
The =peroneus longus= (not present in the horse) is situated in front of
the lateral extensor. It arises on the external condyle of the tibia and
the fibrous band which represents the shaft of the fibula. Its tendon
passes downward and backward over the outer surface of the hock, crosses
over that of the lateral extensor and under the lateral ligament, and
ends on the first tarsal bone (Cuneiform parvum). It is enveloped by a
synovial sheath. It would apparently act as an inward rotator at the
hock joint.
[Illustration:
FIG. 224.—DISTAL PART OF LIMB OF OX WITH SYNOVIAL SHEATHS AND BURSÆ
INJECTED, ANTERIOR VIEW.
_1_, Tendon of extensor digiti tertii, with bursa (_1′_); _2_, tendon
of anterior extensor; _2′_, branch of _2_, with synovial sheath
(_2″_); _3_, tendon of extensor digiti quarti, with bursa (_3′_);
_a_, metatarsus; _b_, first phalanx; _c_, second phalanx. (After
Schmidtchen.)
]
[Illustration:
FIG. 225.—DISTAL PART OF LIMB OF OX WITH SYNOVIAL SHEATHS INJECTED,
POSTERIOR VIEW.
_1_, Superficial flexor tendon; _1′_, _1′_, branches of _1_; _1″_,
_1‴_, upper part of synovial sheaths of _1′_, _1′_; _2_, deep flexor
tendon; _2′_, _2″_, branches of _2_; _2″_, upper part of synovial
sheath of _2′_; _3_, _3_, lateral branches of interosseus medius or
suspensory ligament; _3′_, branch of same to superficial flexor
tendon; _a_, fetlock joint; _b_, pastern joint; _c_, coffin joint;
_d_, _e_, annular ligaments; _f_, crucial interdigital ligament.
(After Schmidtchen.)
]
The =peroneus tertius= is a well-developed muscle which arises on the
common tendon with the long and internal extensors. It has a large,
fusiform belly, which is superficially situated on the front of the leg.
Close to the tarsus it ends on a flat tendon, which is perforated by
that of the tibialis anterior, and ends on the large metatarsal and
second and third (fused) tarsal bones (Cuneiform magnum).
The =tibialis anterior= is smaller, and arises by two heads. The larger
head springs from the outer surface of the tuberosity of the tibia; the
outer, smaller one (M. extensor hallucis longus), from the upper part of
the external border of the tibia and the fibrous band which replaces the
shaft of the fibula. The tendon perforates that of the preceding muscle
and ends on the metatarsal and second and third tarsal bones.
B. POSTERIOR GROUP
The =gastrocnemius= and =soleus= resemble those of the horse. The
=superficial flexor= is more fleshy than in the horse. Its tendon
terminates as in the fore limb.
The =deep flexor= has in its upper part a close resemblance to that of
the horse, but the superficial head (tibialis posterior) is larger and
distinct. The tendon ends like that on the fore limb.
MUSCLES OF THE PIG
MUSCLES OF HEAD
The =facial panniculus= is pale, thin, and difficult to separate from
the skin.
The =orbicularis oris= is little developed.
The =levator nasolabialis= is thin and pale, and is undivided.
The =levator labii superioris proprius= may well be termed the =levator
rostri=. It has a large penniform belly, which arises in the fossa on
the lacrimal bone and maxilla. The tendon ends on the anterior part of
the os rostri. A muscular slip connects it with the premaxilla.
The =zygomaticus= arises on the fascia over the masseter and ends at the
angle of the mouth.
The =depressor labii inferioris= separates from the buccinator only near
the angle of the mouth; it ends by a number of tendinous branches in the
lower lip.
The =dilatator naris lateralis= is well developed. It arises under the
levator rostri and ends by a tendinous network around the nostril.
The =dilatator naris transversus= is represented only by a few fibers
which cross over the os rostri.
The =depressor rostri= arises on the facial crest. It has a long strong
tendon which passes below the nostril and turns up and inward to meet
the tendon of the opposite side and end in the skin of the snout. It
depresses the snout and contracts the nostril.
The malaris is absent, and the other palpebral muscles present no
special features.
MUSCLES OF MASTICATION
The =digastricus= has only one belly. It ends on the inner and lower
surface of the mandible, in front of the groove for the facial vessels.
The other muscles have no important differential features.
The same is true of the oral hyoid muscles.
MUSCLES OF THE NECK
The =panniculus carnosus= consists of two layers which cross each other
obliquely. The fibers of the superficial layer are directed nearly
vertically, those of the deep layer toward the face, on which they are
continued to form the facial portion.
The =mastoido-humeralis= is described on p. 314.
The =sterno-cephalicus= (Sterno-mastoideus) arises on the sternum and is
inserted by a long round tendon on the mastoid process.
The thyroid portion of the =sterno-thyro-hyoideus= has a peculiar
arrangement. It arises (separately from the opposite muscle) on the
manubrium sterni. About the middle of the neck it has an oblique
tendinous intersection, beyond which it divides into two branches; one
of these is inserted in the usual fashion, the other ends on the
laryngeal prominence. The hyoid portion is well developed.
The =omo-hyoideus= is thin. It arises as in the horse, but has no
connection with the mastoido-humeralis nor with the opposite muscle.
The =omo-transversarius= arises on the first or second cervical vertebra
(under cover of the mastoido-humeralis), and is inserted into the lower
part of the scapular spine.
There are two =scaleni=. The =scalenus ventralis= (s. primæ costæ)
resembles that of the ox, is attached to the last four cervical
vertebræ, and is perforated by the nerves of the brachial plexus. The
=scalenus dorsalis= (s. supracostalis) arises on the transverse
processes of the third to the sixth cervical vertebra, and ends on the
third rib.
[Illustration:
FIG. 226.—SUPERFICIAL MUSCLES OF PIG, AFTER REMOVAL OF PANNICULUS
CARNOSUS.
_a_, Levator nasolabialis; _b_, levator labii superioris proprius;
_b′_, fleshy slip of _b_ which comes from premaxilla; _c_,
dilatator naris lateralis; _d_, depressor rostri; _e_, orbicularis
oris; _f_, depressor labii inferioris; _g_, zygomaticus; _h_,
masseter; _i_, _i′_, _i″_, brachiocephalicus (cleido-occipitalis,
cleido-mastoideus, pars clavicularis); _k_, sterno-cephalicus;
_l_, sterno-hyoideus; _m_, omo-transversarius; _n_, _n′_,
trapezius; _o_, anterior deep pectoral; _p_, latissimus dorsi;
_q_, lumbo-dorsal fascia; _r_, obliquus abdominis externus; _r′_,
aponeurosis of _r_; _s_, serratus posticus; _t_, serratus magnus;
_u_, posterior deep pectoral; _v_, supraspinatus; _w_, _w′_,
deltoideus; _x_, long head of triceps; _y_, external head of
triceps; _z_, tensor fasciæ antibrachii; _1_, brachialis; _2_,
extensor carpi radialis; _3_, extensor digiti quarti; _4_,
extensor digiti quinti; _5_, extensor carpi ulnaris; _6_, ulnar
head of deep flexor; _7_, gluteus medius; _8_, tensor fasciæ latæ;
_9_, _10_, _10′_, biceps femoris; _11_, semitendinosus; _12_,
semimembranosus; _13_, caudal muscles; _14_, panniculus adiposus
in section. (After Ellenberger, in Leisering’s Atlas.)
]
The =straight muscles= of the head present no special features.
The =longus colli= is separated from the opposite muscle, so that part
of the bodies of the cervical vertebræ is exposed as in man.
The =intertransversales= resemble those of the ox.
The =splenius= is thick and extensive. It ends in three parts on the
occipital, the temporal, and the wing of the atlas (inconstant).
The =trachelo-mastoideus= is small, and its atlantal portion is blended
with the longissimus.
The =complexus= is large, and is clearly divided into two portions: the
dorsal portion (Biventer cervicis) is marked by several tendinous
intersections; the ventral part is the complexus proper.
The =obliquus capitis posterior= is relatively thin.
The =recti capitis= are thick and more or less fused.
MUSCLES OF THE THORAX
The =levatores costarum= and =rectus thoracis= present no special
features.
The =external intercostal= muscles are absent under the serratus anticus
and posticus and the digitations of the external oblique.
The =internal intercostals= are thick between the cartilages of the
sternal ribs.
The =retractor costæ= and the =transversus thoracis= resemble those of
the horse; the latter extends back to the eighth cartilage and fuses
with the transversus abdominis.
The =diaphragm= has seven costal digitations on each side, the posterior
ones being attached to the ribs at some distance (ca. one-third to
one-fourth of rib-length) from the costo-chondral junction. The line of
attachment reaches the latter at the tenth rib, and passes along the
eighth cartilage to the xiphoid process. The tendinous center is more
rounded than in the horse. The crura are well developed. The right crus
is very large, and is perforated by the extensive slit-like opening for
the œsophagus, which is median in position, and lies about two and
one-half to three inches (ca. 6 to 8 cm.) below the twelfth thoracic
vertebra. The hiatus aorticus is between the crura.
ABDOMINAL MUSCLES
The =abdominal tunic= is little developed.
The =obliquus abdominis externus= has an extensive fleshy portion and a
correspondingly narrow aponeurosis; the latter does not detach a femoral
lamina, but is reflected in toto to form the inguinal (Poupart’s)
ligament.
The =obliquus abdominis internus= resembles that of the ox; a small
fusiform muscle, which crosses the inguinal canal obliquely and is
attached on the abdominal surface of the inguinal ligament, is
apparently a detached slip of the internal oblique.
The =rectus abdominis= is extensive and thick. It has seven to ten
intersections. Its tendon of insertion fuses largely with the common
tendon of the gracilis, and does not give off an accessory band to the
head of the femur.
The fleshy part of the =transversus abdominis= is well developed. It
blends in front with the transversus thoracis.
The =cremaster externus= is present in the female as well as in the
male.
MUSCLES OF THE BACK AND LOINS
The =serratus anticus= is inserted into the fifth to the eighth ribs
inclusive, the serratus posticus into the last four or five ribs. There
are usually no digitations attached to the ninth and tenth ribs.
The =transversalis costarum= (Iliocostalis) extends to the wing of the
atlas.
The =spinalis et semispinalis= can be separated without much difficulty
from the longissimus dorsi, the division from the common mass of the
loins beginning about the first lumbar vertebra.
The =multifidus= resembles that of the horse.
=Interspinales= are present, as well as distinct =intertransversales= of
the back and loins.
MUSCLES OF THE TAIL
The superior and lateral =sacro-coccygei= arise as far forward as the
last lumbar vertebra. Gurlt explains the twist of the tail as being due
to the spiral arrangement of the insertions of the tendons.
MUSCLES OF THE THORACIC LIMB
MUSCLES OF THE SHOULDER GIRDLE
The =trapezius= is very wide, its line of origin extending from the
occipital bone to the tenth thoracic vertebra. There is no clear
division between its two parts, which are both inserted into the
scapular spine.
The =omo-transversarius= resembles that of the ox.
The =rhomboideus= consists of three portions. The =cervical portion=
(Rhomboideus cervicalis) is greatly developed, its origin extending from
the second cervical to the sixth thoracic vertebra. The =cephalic
portion= (Rhomboideus capitis) arises with the splenius on the occipital
bone, and is inserted with the cervical part. The =dorsal portion=
(Rhomboideus thoracalis) extends as far back as the ninth or tenth
thoracic vertebra.
The =latissimus dorsi= is attached to the four ribs preceding the last.
It is inserted into the internal lip of the bicipital groove.
The =mastoido-humeralis= divides into two parts, the =cleido-mastoideus=
and =cleido-occipitalis=, which arise on the mastoid process and
occipital crest respectively, and unite at the fibrous vestige of the
clavicle.
The =anterior superficial pectoral= is thin. The =posterior superficial
pectoral= is divided into parts, one of which ends on the humerus, the
other on the fascia of the forearm.
The =deep pectoral= is clearly divided into two parts. The =scapular
portion= resembles that of the horse, but its origin does not extend
behind the first two chondro-sternal joints. The =posterior deep
pectoral= is very long.
The cervical portion of the =serratus magnus= is greatly developed, its
origin extending from the wing of the atlas to the upper part of the
fifth rib, and passing under the thoracic portion; the latter resembles
that of the ox.
MUSCLES OF THE SHOULDER
The =deltoid= is undivided; it arises from the aponeurosis covering the
infraspinatus, and it ends largely on the deltoid ridge, but partly on
the fascia of the arm.
The =supraspinatus= is large; it ends chiefly on the external tuberosity
of the humerus.
The =infraspinatus= is inserted into a depression below the posterior
division of the external tuberosity.
The =teres minor= is well developed; it ends on a tubercle between the
external and deltoid tuberosities of the humerus.
The =subscapularis= and =teres major= have no remarkable features.
The =coraco-brachialis= is short and undivided.
The =capsularis= is very small and frequently absent.
MUSCLES OF THE ARM
The =biceps brachii= is fusiform and not greatly developed. Its tendon
of origin is rounded and passes through the capsule of the shoulder
joint. The tendon of insertion is bifid, ending on the radius and ulna.
The =brachialis= is well developed, and also ends on the radius and
ulna.
The =tensor fascias antibrachii= resembles that of the horse.
The =long head of the triceps= is divided into two parts, except at its
distal end, under which there is a synovial bursa. The =external head=
is inserted into a crest on the outer surface of the olecranon by a thin
tendon, under which there is a bursa. The =internal head= arises near
the head of the humerus, beneath the coraco-brachialis.
There are two =anconei=.
MUSCLES OF THE FOREARM AND DIGITS
The =extensor carpi radialis= is a strong, fleshy muscle, the tendon of
which is inserted into the proximal end of the third metacarpal bone. It
may be divided into two parts (M. extensor carpi radialis longus,
brevis).
The =extensor carpi obliquus= is well developed; it ends on the second
metacarpal bone.
There are three (or four) =digital extensors=.
1. The =common= or =anterior digital extensor= (M. extensor digitalis
communis) arises on the extensor epicondyle of the humerus and the
lateral ligament of the elbow, and divides into three parts. The tendon
of the =inner part= divides into two branches which end on the =second=
and =third digits=; the tendon to the second digit is small and often
absent. The tendon of the =middle part= divides lower down into two
branches for the =third= and =fourth= (chief) =digits=; above this
bifurcation it detaches a small branch to the =second digit=, which
usually unites with the tendon of the extensor indicis. The tendon of
the =deep head= divides into two branches, the inner one joining the
tendon of the middle head, while the outer one ends on the =fifth
digit=.
[Illustration:
FIG. 227.—MUSCLES OF ANTIBRACHIUM AND MANUS OF PIG, ANTERO-EXTERNAL
VIEW.
_a_, _a′_, Extensor carpi radialis; _b_, extensor carpi obliquus (s.
abductor pollicis longus); _c_, _d_, _e_, common or anterior digital
extensor; _c′_, _c″_, tendons of insertion of _c_; _d′_, _d″_,
tendons of _d_; _e′_, _e″_, tendons of _e_; _f_, tendon of extensor
indicis; _g_, extensor digiti quarti; _h_, extensor digiti quinti;
_h′_, tendon of _h_; _i_, tendinous, and _k_, fleshy part of flexor
carpi externus; _k′_, tendon of _k_; _l_, ulnar head of deep digital
flexor; _m_, superficial digital flexor; _n_, brachialis. (After
Ellenberger, in Leisering’s Atlas.)
]
2. The =extensor of the second digit= (M. extensor indicis proprius) is
covered by the preceding muscle, with which it is partially fused. It
arises on the ulna. Its delicate tendon usually unites with the tendon
of the middle head of the common extensor which goes to the =second
digit=.
3. The =lateral digital extensor= (M. extensor digitalis lateralis)
consists of two distinct parts: (1) The large =dorsal= (anterior)
=muscle= (M. extensor digiti quarti proprius) has a long tendon which
ends on the =fourth digit=, and often sends a slip to the fifth digit.
(2) The small =volar= (posterior) =muscle= (M. extensor digiti quinti
proprius) ends by a long tendon on the lateral aspect of the =fifth
digit=.
The =supinator= has been found by Arloing and Lesbre, but is usually
absent in the pig.
The =pronator teres= is a small muscle which lies on the internal
lateral ligament of the elbow. It arises from the internal epicondyle of
the humerus, and reaches about to the middle of the inner border of the
radius.
The =flexor carpi internus= is well developed. It arises on the flexor
epicondyle of the humerus, and is inserted into the third metacarpal
bone.
The =flexor carpi medius= is narrow and has no ulnar head.
The =flexor carpi externus= (M. extensor carpi ulnaris) is covered by a
thick, tendinous band, which extends from the extensor epicondyle to the
accessory carpal bone and outer aspect of the carpus. The tendon of the
muscle perforates this band in the distal part of the forearm and ends
on the proximal end of the fifth metacarpal bone.
The =superficial digital flexor= has two bellies. The tendon of the
=superficial head= passes down behind the posterior annular ligament of
the carpus (bound down by a special annular ligament), forms a ring at
the fetlock for a tendon of the deep flexor, and ends by two branches on
the second phalanx of the =fourth digit=. The tendon of the =deep head=,
after detaching a slip to the tendon of the deep flexor, passes down
with the latter (for which it forms a ring), and ends on the =third
digit=.
The =deep digital flexor= has three heads—humeral, ulnar, and radial.
The common tendon divides into four branches, the larger central pair
ending on the third phalanges of the principal digits, the smaller pair
on the accessory digits. The latter are bound down by a peculiar spiral
band. There is no check ligament.
The =lumbricales= are represented by bundles which extend from the deep
flexor tendon to the tendon of the deep head of the superficial flexor.
The third and fourth =interossei= are present. Each sends two slips to
the corresponding sesamoid bones and extensor tendon.
There are =flexors=, =adductors=, and =abductors= of the =second= and
=fifth digits=.
MUSCLES OF THE PELVIC LIMB
SUBLUMBAR MUSCLES
The =psoas minor= is intimately united with the psoas major in front,
and has a long small tendon which ends on the psoas tubercle. It has no
thoracic part.
The =psoas major= is large and rounded. It begins at the last rib.
The =quadratus lumborum= is well developed, and extends forward as far
as the twelfth rib.
MUSCLES OF THE HIP AND THIGH
The =tensor fasciæ latæ= is broad, and its fleshy part reaches almost to
the patella.
The =gluteus superficialis= has a sacral head only; it blends with the
biceps femoris.
The =gluteus medius= has a small lumbar part which does not extend so
far forward as in the horse. The deep part (Gluteus accessorius) is
pretty clearly marked.
The =gluteus profundus= is extensive, reaching nearly to the external
angle of the ilium.
The =biceps femoris= has a narrow origin from the sacro-sciatic ligament
and tuber ischii. It ends below like that of the ox.
The =semitendinosus= resembles that of the horse.
The =semimembranosus= has two insertions as in the ox.
The =sartorius= has two heads of origin, between which the external
iliac vessels are situated. The inner arises from the tendon of the
psoas minor, the outer one from the iliac fascia.
The =graciles= are united at their origin even more than in the ox.
The =pectineus= is well developed and is flattened from before backward.
The =adductor= shows no division and is partially fused with the
gracilis. It ends on the femur just above the origin of the
gastrocnemius.
The =quadratus femoris= is large.
The =obturator externus= resembles that of the horse.
The =obturator internus= is extensive and strong; its tendon emerges
through the obturator foramen.
The =gemellus= is fused in part with the obturator internus.
The =quadriceps femoris= is more clearly divided than in the horse, and
its action is transmitted by a single patellar ligament.
The =capsularis= is absent.
MUSCLES OF THE LEG AND FOOT
The =peroneus tertius= resembles that of the ox, but its tendon is not
perforated by that of the tibialis anterior, and ends on the inner
(second) large metatarsal bone, detaching a strong branch to the first
and second tarsal bones.
The =tibialis anterior= arises on the tibial crest. Its tendon passes
over the hock along the inner border of the tendon of the peroneus
tertius (both being bound down by an annular ligament), and is inserted
into the inner (second) metatarsal and first tarsal bones.
[Illustration:
FIG. 228.—MUSCLES OF LEG AND FOOT OF PIG, ANTERO-EXTERNAL VIEW.
_a_, Tibialis anterior; _a′_, tendon of preceding; _b_, peroneus
tertius; _b′_, tendon of _b_; _c_, anterior or long digital
extensor; _d_, _e_, _f_, _f′_, _f″_, tendons of _c_; _g_, peroneus
longus; _g′_, tendon of _g_; _h_, extensor digiti quarti; _h′_,
tendon of _h_, which receives _h″_, from the interosseus medius;
_i_, extensor digiti quinti; _k_, deep digital flexor; _l_, soleus;
_m_, gastrocnemius; _n_, extensor brevis. (After Ellenberger, in
Leisering’s Atlas.)
]
The =peroneus longus= lies partly on the outer surface of the peroneus
tertius. Its tendon crosses those of the lateral extensor, passes along
a groove on the plantar surface of the fourth tarsal bone, and ends on
the first tarsal and second metatarsal bones.
The =anterior= or =long digital extensor= arises with the peroneus
tertius and is largely covered by it and the peroneus longus. It divides
into three parts. The tendon of the =inner division= (M. extensor digiti
tertii) ends on the =inner chief= (third) =digit=; that of the =middle
division= by two branches on the =principal digits=; and that of the
=outer division= by three branches on the =second=, =fourth=, and =fifth
digits=.
The =lateral digital extensor= divides into proper extensors of the
=fourth= and =fifth digits= (Extensores digiti quarti et quinti).
The =extensor hallucis longus= arises on the fibula and ends on the
=inner small= (second) =digit=.
The =extensor digitalis brevis= is well developed and consists of three
parts. The inner and outer tendons end on the first phalanges of the
chief digits, the middle one joins the common extensor tendon of the
same.
The =gastrocnemius= presents nothing special.
The =soleus= is wide, and is partly blended with the external head of
the gastrocnemius.
The =superficial digital flexor= has a large belly. Its tendon ends on
the two chief digits, and is also connected with the ligaments of the
accessory digits.
The =inner head= of the =deep digital flexor= (flexor digitalis longus)
is relatively small. The common tendon ends as in the thoracic limb.
The =popliteus= presents no special features.
The =plantar muscles= resemble their homologues of the fore limb, except
that the adductors of the accessory digits and the lumbricales are
absent.
THE MUSCLES OF THE DOG
MUSCLES OF THE FACE
The =panniculus carnosus= is well developed and presents two distinct
bands, one of which is inserted into the lower lip, the other into the
scutiform cartilage of the ear.
The =orbicularis oris= is poorly developed. In the upper lip it is
divided centrally, and in the lower it is distinct only near the angles
of the mouth.
The =levator nasolabialis= is wide and undivided, and ends in the upper
lip.
The =levator labii superioris proprius= arises behind the infraorbital
foramen, runs forward under the preceding muscle, and ends in numerous
small tendons around the nostril, some blending with those of the
opposite side.
The =zygomaticus=, long and narrow, arises on the scutiform cartilage,
and ends at the angle of the mouth.
[Illustration:
FIG. 229.—MUSCLES OF HEAD OF DOG
_a_, Scutularis; _b_, _c_, anterior auricular muscles; _d_, helicis;
_e_, antitragicus; _f_, _f_, zygomaticus, out of which a portion is
cut; _g_, slip of panniculus; _h_, parotido-auricularis; _i_,
masseter; _k_, malaris; _l_, levator nasolabialis; _m_, levator
labii superioris proprius; _n_, dilatator naris lateralis; _o_, _p_,
buccinator (buccalis, molaris); _q_, retractor anguli oris; _r_,
digastricus; _s_, mylo-hyoideus; _1_, base of concha; _2_, parotid
gland; _2′_, parotid duct; _3_, submaxillary gland; _4_,
submaxillary lymph glands; _5_, buccal glands; _6_, zygomatic arch;
_7_, maxilla; _8_, dorsum nasi; _9_, parotid lymph gland.
(Ellenberger-Baum, Anat. d. Hundes.)
]
The =depressor labii inferioris= is absent, unless we recognize as such
a thin stratum arising on the body of the mandible and spreading out in
the orbicularis.
There are no special =nasal muscles=, the homologue of the lateral
dilator ending almost entirely in the upper lip.
The =buccinator= is wide and very thin, and the two planes of fibers
cross each other.
The =palpebral muscles= present no very noteworthy special characters.
MUSCLES OF MASTICATION
The =masseter= is large. It arises from the zygomatic arch, and extends
beyond the branch of the jaw below and behind. Three strata may be
recognized in its structure.
The =temporalis= is very large and strong, and contains much tendinous
tissue. It arises from the temporal fossa and the orbital ligament.
The =digastricus= is usually not digastric, but is a strong, round,
fleshy muscle, which arises on the paramastoid or styloid process and is
inserted into the border and inner surface of the ramus at the level of
the last molar teeth.
The stylo-mandibularis is absent.
HYOID MUSCLES
The =mylo-hyoideus= is well developed.
The =stylo-hyoideus= is very slender, and is inserted into the body of
the hyoid bone: it is not perforated by the digastricus.
[Illustration:
FIG. 230.—SUPERFICIAL MUSCLES OF DOG, AFTER REMOVAL OF PANNICULUS
CARNOSUS.
_1_, Levator nasolabialis; _2_, levator labii superioris proprius;
_3_, dilatator naris lateralis; _4_, _4′_, buccinator; _5_,
retractor anguli oris s. risorius; _6_, zygomaticus; _7_, malaris;
_8_, masseter; _9_, digastricus; _10_, scutularis; _11_, other
auricular muscles; _12_, parotido-auricularis; _13_, mylo-hyoideus;
_14_, sterno-hyoideus; _15_, sterno-thyroideus; _16_, splenius;
_17_, lumbo-dorsal fascia; _18_, rectus abdominis; _19_, obliquus
abdominis externus; _19′_, aponeurosis of preceding; _20_,
intercostal muscle; _21_, sacro-coccygeus accessorius; _22_,
sacro-coccygeus superior; _23_, sacro-coccygeus inferior; _24_,
great trochanter; _25_, jugular vein; _a_, _b_, _c_,
brachiocephalicus; _d_, clavicle; _e_, _f_, trapezius; _g_, serratus
cervicis; _h_, omo-transversarius; _i_, latissimus dorsi; _k_,
posterior deep pectoral; _l_, supraspinatus; _m_, _m′_, deltoid;
_n_, infraspinatus; _o_, triceps, long head; _o′_, triceps, external
head; _p_, brachialis; _q_, extensor carpi radialis; _r_, gluteus
medius; _s_, gluteus superficialis; _t_, _t′_, tensor fascia latæ;
_u_, sartorius; _v_, biceps femoris; _v′_, fascia lata; _w_,
semitendinosus; _x_, semimembranosus; _y_, sartorius; _z_, gracilis;
_26_, pronator teres; _27_, flexor carpi radialis; _28_, flexor
carpi ulnaris; _29_, tibialis anterior; _30_, popliteus; _31_,
_31′_, deep digital flexor; _32_, superficial digital flexor; _33_,
gastrocnemius; _34_, spine of scapula; α, parotid gland, with α′,
its duct; β, submaxillary gland; δ, submaxillary lymph glands; η,
parotid lymph gland; ζ, inferior buccal glands. (After Ellenberger,
in Leisering’s Atlas.)
]
The hyoideus transversus and =omo-hyoideus= are absent.
The =sterno-thyro-hyoideus= is large and arises chiefly on the first
costal cartilage.
MUSCLES OF THE THORACIC LIMB
The =trapezius= is thin, and is not clearly divided into cervical and
thoracic portions. Its line of origin extends from about the middle of
the neck to the ninth or tenth thoracic spine, the right and left
muscles meeting on a median fibrous raphé.
The =omo-transversarius= arises by a tendon on the lower part of the
spine of the scapula (often partially blended with the trapezius), and
is inserted into the wing of the atlas.
The =rhomboideus= consists of three parts. The =dorsal portion=
(Rhomboideus thoracalis) is small; it arises from the fourth to the
sixth or seventh thoracic spine, and is inserted into the inner surface
(chiefly) of the dorsal angle of the scapula. The =cervical portion=
(Rhomboideus cervicalis) arises from the ligamentum nuchæ as far forward
as the second or third cervical vertebra, and is inserted into the inner
surface of the cervical angle of the scapula. The =cephalic portion=
(Rhomboideus capitis) is a continuation of the preceding which is
inserted into the occipital crest.
[Illustration:
FIG. 231.—VENTRAL MUSCLES OF HEAD, NECK, AND THORAX OF DOG.
_a_, Mylo-hyoideus; _b_, digastricus; _c_, sterno-hyoideus; _c′_,
sterno-thyroideus; _d_, sterno-cephalicus; _e_, brachiocephalicus;
_f_, subscapularis; _g_, superficial pectoral; _h_, deep pectoral;
_i_, rectus abdominis; _k_, obliquus abdominis externus; _l_, long
head of triceps; _m_, internal head of triceps; _n_, biceps brachii;
_o_, brachialis; _1_, _1′_, _1″_, submaxillary lymph glands; _2_,
thyroid gland; _3_, external jugular vein. (Ellenberger-Baum, Anat.
d. Hundes.)
]
The =latissimus dorsi= is extensive, and has a fleshy attachment to the
last two ribs. Its lower edge blends near the shoulder with the
panniculus.
The =mastoido-humeralis= contains in front of the shoulder a fibrous
mass in which the clavicle is embedded. Anterior to this it separates
into two diverging portions. The =dorsal portion= (M. cleido-cervicalis)
is attached to the median raphé of the neck and to the occipital bone.
The =ventral portion= (M. cleido-mastoideus) is attached to the mastoid
process. The common mass posterior to the clavicle and the fibrous
intersection, which is attached to the humerus, is homologous with the
clavicular portion of the deltoid of man.
The =superficial pectoral= muscle is small. It arises on the sternum
from the first to the third costal cartilage, and is inserted into the
anterior surface of the humerus. A superficial slip detached from it is
inserted into the fascia of the forearm. The =deep pectoral= has no
prescapular portion. It arises on the sternum and costal cartilages from
the second costal to the xiphoid cartilage. It is inserted chiefly into
the internal tuberosity of the humerus, but also by small slips into the
external tuberosity and the fascia of the arm.
The =serratus magnus= shows no clear division into cervical and thoracic
portions. It arises from the last five cervical vertebræ and the first
seven or eight ribs, and is inserted into the upper part of the costal
surface of the scapula.
The =deltoid= is clearly divided into scapular and acromial parts, the
former arising on the spine, the latter on the acromion of the scapula.
Both end on the deltoid tuberosity.
The =supraspinatus= ends chiefly on the external tuberosity of the
humerus, but has a small attachment to the internal tuberosity also.
The =infraspinatus= is inserted into the outer surface of the external
tuberosity of the humerus.
[Illustration:
FIG. 232.—MUSCLES OF THORACIC LIMB OF DOG, INTERNAL VIEW.
(Ellenberger-Baum, Anat. des Hundes.)
]
The =teres minor= arises on a tubercle on the posterior border of the
scapula, just above the glenoid cavity, and is inserted into the deltoid
ridge.
The =subscapularis= is wide and is somewhat multipennate in structure,
being intersected by fibrous septa which are attached to the rough lines
on the costal surface of the scapula.
The =teres major= is thick. It arises on the upper part of the posterior
border of the scapula and on the subscapularis.
The =coraco-brachialis= is short and undivided, and is inserted into the
upper part of the postero-internal surface of the humerus.
The capsularis is absent.
[Illustration:
FIG. 233.—MUSCLES OF ANTIBRACHIUM AND MANUS OF DOG, EXTERNAL VIEW.
_a_, Triceps brachii; _b_, brachialis; _c_, extensor carpi radialis;
_d_, common or anterior digital extensor; _d′_, _d″_, _d‴_, _d⁗_,
tendons of preceding; _e_, lateral digital extensor; _e′_, _f_,
tendons of preceding; _g_, extensor carpi ulnaris; _h_, _h′_, flexor
carpi ulnaris; _i_, extensor carpi obliquus (s. abductor pollicis
longus); _k_, interossei; _l_, branches from preceding to extensor
tendons; _1_, olecranon; _2_, radius; _3_, extensor epicondyle of
humerus. (After Ellenberger, in Leisering’s Atlas.)
]
The =biceps brachii= lies almost entirely on the inner surface of the
humerus. It is long and fusiform. The tendon of origin is round, and
passes through the capsule of the shoulder joint. The tendon of
insertion is bifid, one branch being attached to the ulnar, the other to
the radial tuberosity.
The =brachialis= is very little curved, and is inserted chiefly into the
tuberosity and inner border of the ulna.
The =tensor fasciæ antibrachii= is thin and narrow. It arises on the
outer surface of the latissimus dorsi, and ends on the olecranon and the
fascia of the forearm.
The =triceps= has an additional deep head (Caput accessorium), which
arises just below the head of the humerus.
The =brachio-radialis= is a long, narrow, delicate muscle, situated
superficially on the anterior surface of the forearm. It arises with the
extensor carpi on the crest above the extensor epicondyle of the
humerus, and is inserted into the distal part of the inner border of the
radius. It is often much reduced, and is sometimes absent. It rotates
the forearm and paw outward.
The =extensor carpi= divides into two parts. The larger outer part, the
=extensor carpi radialis brevis=, ends on the proximal end of the third
metacarpal bone. The inner and more superficial part, the =extensor
carpi radialis longus=, ends on the second metacarpal bone. (A tendon to
the fourth metacarpal may occur.)
The =extensor carpi obliquus= or =abductor pollicis longus= arises from
the outer border and anterior surface of the ulna, the interosseous
ligament, and the outer border of the radius. It is inserted into the
first metacarpal bone by a tendon which contains a small (sesamoid?)
bone. It abducts the first digit.
There are three (or four) =extensors of the digits=.
1. The =common digital extensor= (M. extensor digitalis communis) arises
on the extensor epicondyle of the humerus and the lateral ligament of
the elbow joint. It has four bellies, each terminating in a tendon.
These are inserted into the third phalanges of the second, third,
fourth, and fifth digits.
2. The =extensor of the first and second digits= (M. extensor pollicis
longus et extensor indicis proprius) is small, and is covered by the
common and lateral extensors. It arises on the proximal part of the
ulna. Its tendon passes down with that of the common extensor and
divides into two branches. The delicate inner branch ends on the first
digit, while the other blends with the tendon of the common extensor for
the second digit.
3. The =lateral digital extensor= (M. extensor digitalis lateralis)
consists of two muscles which are not rarely fused. They arise on the
extensor epicondyle of the humerus and the lateral ligament of the elbow
joint. The larger, =superficial belly= (M. extensor digiti tertii et
quarti) terminates on a tendon which divides at or near the carpus into
two branches, which are inserted into the third phalanges of the third
and fourth digits, blending with the corresponding tendons of the common
extensor. The =posterior belly= (M. extensor digiti quinti) terminates
by a tendon which fuses with that of the common extensor for the fifth
digit.
The =ulnaris lateralis= or =extensor carpi ulnaris= corresponds to the
flexor carpi externus of the horse, but is an extensor of the carpus. It
is a large flat muscle which lies on the outer surface of the ulna. It
arises on the extensor epicondyle of the humerus, and is inserted into
the proximal end of the fifth metacarpal and the accessory carpal bone.
[Illustration:
FIG. 234.—VOLAR MUSCLES OF FORE PAW OF DOG.
_a_, Abductor pollicis brevis et opponens pollicis; _b_, flexor
pollicis brevis; _c_, adductor pollicis; _d_, adductor digiti
secundi; _e_, adductor digiti quinti; _f_, flexor digiti quinti
brevis; _g_, abductor digiti quinti; _h_, interossei; _1_,
accessory carpal bone; _2_, first digit; _3–6_, sesamoids of
metacarpo-phalangeal joints. (Ellenberger-Baum, Anat. d. Hundes.)
]
The =ulnaris medialis= or =flexor carpi medius= (s. ulnaris) consists of
two quite distinct heads. The larger, =humeral head= arises on the
flexor epicondyle, while the smaller, superficial =ulnar head= arises on
the posterior border of the ulna. The tendons of the two end together on
the accessory carpal bone.
The =radialis volaris= or =flexor carpi internus= (s. radialis) arises
on the flexor epicondyle of the humerus and is inserted by a bifid
tendon into the second and third metacarpal bones.
The tendons of the foregoing muscles are provided with synovial sheaths
at the carpus.
The =pronator teres= is a round muscle, which is situated superficially
on the inner border of the proximal part of the radius. It arises on the
flexor epicondyle of the humerus, and is inserted into the internal
border of the radius. Its action is to flex the elbow and rotate the
forearm inward.
The =superficial digital flexor= is situated superficially on the
posterior and inner surfaces of the forearm. It arises on the flexor
epicondyle of the humerus and terminates near the carpus on a tendon
which passes downward outside of the carpal canal and receives below the
carpus two reinforcing bands, one from the accessory carpal, the other
from the sesamoid bone at the inner side of the carpus. Below this it
divides into four branches, which are inserted into the second phalanges
of the second, third, fourth, and fifth digits.
The =deep digital flexor= has =humeral=, =ulnar=, and =radial heads=,
the latter arising from the inner border of the radius. They unite on a
common tendon which passes down through the carpal canal, gives off a
branch to the first digit, and divides into four branches. These
perforate the tendons of the superficial flexor and are inserted into
the third phalanges of the second to the fifth digits. The tendons are
provided with synovial sheaths from the middle of the metacarpus
downward, and are held in place by three digital annular ligaments.
The =palmaris longus accessorius= (?) is a small muscle which arises
from the deep flexor below the middle of the forearm and ends by two
tendons which unite with those of the superficial flexor for the third
and fourth digits.
The =supinator= is a short, wide muscle which arises on the humerus
beneath the external lateral ligament, crosses the anterior surface of
the radius, and is inserted into the inner border of the radius. (A
pouch of the capsule of the elbow joint lies under the tendon of
origin.) Its action is to rotate the forearm outward (supination).
The =pronator quadratus= consists of fibers which cross the inner
surface of the interosseous ligament of the forearm, except at the two
extremities of the latter. It is attached to the inner border of the
ulna and the anterior surface of the radius. It rotates the forearm
inward (pronation).
The =palmaris brevis= (?) is a very small muscle, which arises on the
tendon of the superficial digital flexor for the fifth digit, and is
inserted at the fifth metacarpo-phalangeal joint into the sheath and
annular ligament of the deep flexor.
The =lumbricales= are three very delicate muscles, which arise on the
tendons of the deep flexor, and are inserted into the first phalanges of
the third, fourth, and fifth digits.
The =abductor pollicis brevis et opponens pollicis=, a very small pale
muscle, arises on the fibrous band which connects the superficial flexor
tendon with the inner carpal sesamoid, and ends on the distal end of the
first metacarpal bone and the first phalanx of the first digit. It
abducts the first digit.[76]
The =flexor pollicis brevis= arises on the posterior carpal ligament
over the second metacarpal bone, and ends on the volar sesamoid of the
first digit.
The =adductor pollicis=, situated externally to the preceding, is the
largest of the thumb muscles. It arises between the preceding and the
second interosseous muscle, and is inserted into the first phalanx of
the first digit.
The =adductor digiti secundi= is situated between the second
interosseous muscle and the adductor digiti quinti. It arises on the
carpal ligament, and ends on the first phalanx of the second digit.
The =adductor digiti quinti= arises close to the preceding muscle, and
passes outward to end on the first phalanx of the fifth digit.
The =flexor digiti quinti= arises on the ligament connecting the
accessory carpal to the third and fourth metacarpal bones, crosses the
corresponding interosseous muscle, and ends on the fifth digit with the
next muscle.
The =abductor digiti quinti= is larger than the two preceding muscles;
it arises on the accessory carpal bone, and ends on the outer sesamoid
of the fifth digit and on the lateral ligament.
There are four =interossei= which lie on the volar (posterior) surface
of the metacarpus. They are well developed and fleshy. They arise on the
distal row of the carpus and on the proximal ends of the metacarpals.
Each divides distally into two branches, which are inserted by small
tendons on the corresponding sesamoid bones, and detach slips to the
extensor tendons.
MUSCLES OF THE NECK
The =sterno-cephalicus= is well developed. It arises on the manubrium
sterni and ends on the mastoid process, blending with the
cleido-cervicalis.
The =scalenus ventralis= (s. primæ costæ) arises on the last four
cervical transverse processes, and is inserted into the first rib.
The =scalenus dorsalis= (s. supracostalis) is large. Anteriorly it
blends with the preceding muscle, while posteriorly it divides into two
parts. The upper part is inserted on the third and fourth ribs, the
=lower part= by a long, thin tendon on the eighth rib.
The =longus colli= resembles that of the horse.
The =rectus capitis anterior major= arises on the transverse processes
of the second to the sixth cervical vertebræ and ends as in the horse.
The =rectus minor= and =lateralis= resemble those of the horse.
The =intertransversales= resemble those of the ox.
The =splenius= is strong and extensive. It arises on the first four or
five thoracic spines and the median raphé of the neck, and is inserted
into the occipital crest and mastoid process.
The =complexus= is composed of two parts—the biventer cervicis and the
complexus major proper. The =biventer cervicis= arises from the
transverse processes of the fifth and sixth, and the spines of the
second to the fifth (or sixth) thoracic vertebræ, from the ligamentum
nuchæ, and the median raphé. It has four tendinous intersections. The
=complexus major= arises on the transverse processes of the first three
or four thoracic vertebræ and the articular processes of the last five
cervical. Both end on a strong common tendon which is inserted into the
occipital crest and the depression below it.
The =trachelo-mastoideus= consists of two unequal portions. The large
=dorsal part= (M. longissimus capitis) arises on the transverse
processes of the first four thoracic and the articular process of the
last three or four cervical vertebræ, and ends with the splenius on the
mastoid process of the temporal bone. The small =ventral part= (M.
longissimus atlantis) arises on the articular processes of the third,
fourth, and fifth cervical vertebræ, and ends on the wing of the atlas.
The other muscles present no striking differential features, but it may
be noted that distinct =interspinales= are present.
MUSCLES OF THE THORAX
There are twelve pairs of =levatores costarum=.
The =external intercostals= do not occupy the spaces between the costal
cartilages.
The =diaphragm= has a small tendinous center. The =œsophageal opening=
is between the pillars. The fleshy rim is attached at the costo-chondral
junctions from the eighth backward, and along the thirteenth rib nearly
its entire length.
MUSCLES OF THE BACK AND LOINS
The =serratus anticus= arises from the median raphé of the neck and the
first six or seven thoracic spines, and is inserted into the second to
the ninth ribs. It is well developed. The =serratus posticus=—much
weaker—arises on the lumbo-dorsal fascia, and is inserted into the last
three or four ribs. Thus one or two ribs intervene between the two.
The =transversalis costarum= (Iliocostalis) is well developed, and
extends from the ilium to the sixth, fifth, or fourth cervical vertebra.
The =longissimus= resembles that of the other animals, but the spinalis
et semispinalis separates clearly at the sixth or seventh thoracic
vertebra. It is inserted into the articular and spinous processes of the
last six cervical vertebræ. It has no depression in the lumbar region
for the gluteus medius.
The =intertransversales= are fleshy, as in the ox.
The =interspinales= are distinct, especially in the lumbar region.
MUSCLES OF THE TAIL
These present the same general arrangement as in the horse. The
=sacro-coccygei=, however, arise on the lumbar vertebræ also, and the
=coccygeus= on the ischiatic spine. There is found a =sacro-coccygeus
accessorius=, which arises on the internal border of the ilium, the edge
of the sacrum, and the transverse processes of the first coccygeal
vertebræ, and is inserted between the superior and lateral
sacro-coccygei. It is homologous with the intertransversales.
MUSCLES OF THE ABDOMEN
The abdominal tunic is practically absent.
The =obliquus abdominis externus= has an extensive fleshy portion. It
arises from the last eight or nine ribs and the lumbo-dorsal fascia.
The =obliquus abdominis internus= arises from the external angle of the
ilium and the lumbo-dorsal fascia. The fibers have an almost vertical
direction, and there is a fleshy attachment to the last rib.
The =rectus abdominis= is attached by a long tendon on the first five or
six costal cartilages, and by fleshy fibers on the xiphoid cartilage. It
has three to six indistinct tendinous inscriptions.
The =transversus abdominis= presents no special features except that the
posterior part of its aponeurosis splits into two layers which include
the rectus between them.
MUSCLES OF THE PELVIC LIMB
[Illustration:
FIG. 235.—MUSCLES OF TAIL, ANUS, AND GENITAL ORGANS OF DOG.
_1_, Ilium; _2_, femur; _3_, tuber ischii; _4_, sacro-sciatic lig.;
_5_, sacral region; _6_, tail; _7_, penis; _8_, anus; _9_, rectum;
_a_, sacro-coccygeus superior; _b_, sacro-coccygeus accessorius;
_c_, coccygeus; _d_, sacro-coccygeus inferior; _e_, retractor ani;
_f_, _f′_, sphincter ani externus; _g_, retractor penis; _h_,
bulbo-cavernosus; _i_, transversus perinei (?); _k_, _m_,
ischio-urethrales; _l_, ischio-cavernosus; _n_, tendon of obturator
internus; _o_, gemellus; _p_, urethral muscle. (After Ellenberger,
in Leisering’s Atlas.)
]
The =psoas minor= arises on the last thoracic and first four or five
lumbar vertebræ, and is inserted into the ilio-pectineal line.
The =psoas major= is short, arising from the last four lumbar vertebræ.
The outer head of the =iliacus= is small, while the inner head is large
and fuses with the psoas major.
The =quadratus lumborum= is well developed, and extends laterally beyond
the outer edge of the ilio-psoas. It arises from the last four ribs and
the lumbar transverse processes, and ends on the pelvic surface of the
wing of the ilium.
The =tensor fasciæ latæ= consists of two parts. The anterior part is
long and rounded; the posterior is shorter and fan-like.
The =gluteus superficialis= is small. It arises on the sacrum, first
coccygeal vertebræ, and sacro-sciatic ligament. It is inserted below and
behind the trochanter major of the femur, on the outer branch of the
linea aspera.
The =gluteus medius= has no lumbar portion. It is inserted into the
trochanter major by a strong tendon.
The =gluteus profundus= is broad and fan-shaped. It arises on the
superior ischiatic spine and on the ilium as far forward as the gluteal
line, and is inserted into the trochanter major below the medius.
The =pyriformis= is not blended with the gluteus medius. It arises from
the border of the sacrum and from the sacro-sciatic ligament, and ends
on the trochanter major.
The =biceps femoris= has two heads of origin which soon fuse. The larger
head arises from the sacro-sciatic ligament and tuber ischii, the
smaller one from the tuber ischii. The aponeurosis of insertion ends on
the patella, the patellar ligament, and the tibial crest. There is also
a tendinous band, which comes from the deep face of the muscle and
terminates at the tarsus, as in the horse.
The =abductor cruris posterior= may be regarded as an accessory head of
the biceps femoris. It is a thin, muscular band which arises on the
sacro-sciatic ligament, passes downward between the biceps and
semimembranosus, and ends by blending with the former.
The =semitendinosus= arises from the tuber ischii only. It ends as in
the horse.
[Illustration:
FIG. 236.—MUSCLES OF PELVIC LIMB OF DOG, INTERNAL VIEW.
_a_, Ilio-psoas; _b_, tendon of psoas minor; _c_, sacro-coccygeus
ventralis lateralis; _d_, coccygeus; _e_, pyriformis; _f_, obturator
internus; _g_, origin of retractor ani; _h_, _h′_, sartorius; _i_,
rectus femoris; _k_, vastus internus; _l_, pectineus; _m_, adductor;
_n_, gracilis; _o_, semitendinosus; _p_, semimembranosus; _q_,
gastrocnemius, inner head; _q′_, tendon of gastrocnemius; _r_,
superficial digital flexor; _r′_, tendon of _r_; _s_, tarsal tendon
of biceps femoris; _t_, popliteus; _u_, deep digital flexor, outer
head (flexor hallucis longus); _u′_, long digital flexor; _u″_,
common tendon of u and _u′_; _v_, tendon of tibialis posterior; _w_,
tibialis anterior; _x_, tendon of anterior or long digital extensor;
_1_, pelvic surface of ilium; _2_, section of symphysis pelvis; _3_,
tuber ischii; _4_, internal condyle of femur; _5_, ligamentum
patellæ; _6_, _7_, internal surface of tibia; _8_, tarsus; _8′_,
fibular tarsal bone; _9_, metatarsus. (Ellenberger-Baum, Anat. d.
Hundes.)
]
The =semimembranosus= is large and arises from the ischium only. It
divides into two portions: the anterior portion ends on the tendon of
the pectineus, on the femur above the internal condyle, and on the inner
(Vesalian) sesamoid bone; the posterior portion ends on the internal
condyle of the tibia, the tendon passing under the internal lateral
ligament of the stifle joint.
The =rectus femoris= has only one tendon of origin. The single patellar
ligament acts as the tendon of insertion of the quadriceps.
The =capsularis= is usually present, but is small and pale.
The =sartorius= consists of two portions. It arises from the external
angle and border of the ilium. The anterior portion ends on the patella,
the posterior on the internal surface of the tibia, its tendon blending
with that of the gracilis.
The =graciles= are not so much fused at their origin as in the other
animals.
The =pectineus= is long and slender. It arises from the ilio-pectineal
eminence and ends on the internal branch of the linea aspera above the
distal end of the femur.
There are two distinct =adductors=. The small anterior one ends on the
proximal third of the femur, the posterior one on the distal part of the
femur and on the inner face of the stifle joint.
The =quadratus femoris= is short and strong. The other external rotators
of the thigh present no special features.
The =peroneus tertius= is represented by a tendinous band which arises
on the internal surface of the tibia below the crest. It passes downward
on the inner surface of the tibialis anterior, blends with the annular
ligament above the tarsus, and is attached to the joint capsule and the
proximal end of the third metatarsal bone.
Arloing and Lesbre say: “The third peroneus is a proper extensor of
the fifth digit; it is a very feeble, fleshy band, situated behind the
peroneus brevis, which it partially covers. It is attached to the
upper part of the fibula, and is continued by a long, delicate tendon
which passes in the same malleolar groove with the muscle mentioned;
it then crosses behind the tendon of the peroneus longus and extends
to the phalanges of the outer digit, where it joins one of the
branches of the common extensor.”
The =tibialis anterior= is large and superficial. It arises on the
external condyle and crest of the tibia, and is inserted into the first
metatarsal bone, or into the first tarsal and second metatarsal.
There are four =extensors of the digits=.
1. The =anterior= or =long digital extensor= (M. extensor digitalis
longus) is fusiform, and lies largely under the preceding muscle. It
arises from the extensor fossa of the femur. The tendon is bound down by
two annular ligaments, and divides below the tarsus into four branches,
which end on the distal phalanges of the digits (second to fifth).
2. The =lateral digital extensor= (M. extensor digitalis lateralis) is
feeble and semipennate. It arises on the fibula below the head. The
tendon passes under the lateral ligament of the tarsus and joins the
branch of the tendon of the long extensor for the fifth digit.
3. The =extensor hallucis longus= is a very thin muscle which arises
from the fibula under the long extensor. Its delicate tendon accompanies
that of the tibialis anterior to the first metatarsal bone, or becomes
lost in the fascia.
4. The =extensor digitalis brevis= has three divisions. It arises on the
fibular tarsal bone and the adjacent ligaments. The three tendons are
inserted into the second, third, and fourth digits, blending with the
interossei. (Sometimes there is found a tendon to the rudimentary first
digit, which may represent the extensor hallucis brevis. There may be a
fourth belly for the tendon to the second digit.)
The =peroneus longus= arises on the external condyle of the tibia, the
head of the fibula, and the lateral ligament. The long tendon passes
down the leg parallel to the fibula, crosses the plantar (posterior)
surface of the tarsus transversely, and ends on the first metatarsal
bone. A short branch is detached to the external metatarsal bone.
The =peroneus brevis= is semipennate and arises from the distal half or
more of the outer face of the tibia and the fibula. Its tendon
accompanies that of the lateral extensor over the external malleolus of
the tibia, and ends on the proximal end of the fifth metatarsal bone.
The soleus is absent. (It is present and large in the cat.)
The =gastrocnemius= arises on the rough lines above the condyles of the
femur. The heads of origin each contain a bone about the size of a
pea—the sesamoid of Vesal—which articulates with the corresponding
condyle of the femur. The tendon comports itself as in the horse.
The =superficial digital flexor= has a large round belly. It arises in
common with the outer head of the gastrocnemius from the external rough
line and Vesalian sesamoid bone, and from the aponeurosis of the vastus
externus. The tendon winds around that of the gastrocnemius, passes over
the tuber calcis (where it is arranged as in the horse), and divides
below the tarsus into two branches. Each of these divides into two
branches which end as in the fore limb. The outer and inner branches
detach slips to the suspensory ligaments of the large digital pad.
Muscle-fibers often occur in the tendon in the metatarsal region.
[Illustration:
FIG. 237.—MUSCLES OF LEG AND FOOT OF DOG, EXTERNAL VIEW.
_a_, Quadriceps femoris; _b_, gastrocnemius, external head; _c_,
superficial digital flexor; _d_, deep digital flexor; _e_, peroneus
longus; _f_, tendon of lateral extensor; _g_, peroneus brevis; _h_,
long or anterior digital extensor; _h′_, _h″_, _h‴_, tendons of
preceding; _i_, tibialis anterior; _k_, extensor brevis; _l_, slips
from interossei (_m_); _1_, external condyle of femur; _2_, patella;
_3_, tibia; _4_, tuber calcis; _5_, _6_, annular ligaments. (After
Ellenberger, in Leisering’s Atlas.)
]
The =deep digital flexor= has two heads. The large outer head, the
=flexor hallucis longus=, arises from the tibia and fibula, filling the
interosseous space. The small inner head, =flexor digitalis pedis
longus=, also arises from the tibia and fibula, its tendon joining that
of the large head below the tarsus. The common tendon detaches a branch
to the large digital pad and terminates as in the fore limb.
The =tibialis posterior= is a small but distinct muscle, which arises on
the proximal part of the fibula. The thin tendon accompanies that of the
flexor longus and ends on the internal lateral ligament of the tarsus.
The tendon of the =popliteus= contains a small sesamoid bone.
The =adductors of the second and fifth digits=, the =lumbricales=, and
the =interossei= are arranged as in the thoracic limb.
The =quadratus plantæ= arises on the outer surface of the distal end of
the fibular tarsal bone and on the lateral tarsal ligament, passes
downward and inward, and terminates on a thin tendon which fuses with
that of the deep flexor.
The =abductor digiti quinti= is a very small muscle which consists of
two parts. One of these is a tendinous slip which extends from the
posterior surface of the proximal part of the fibular tarsal bone to the
head of the fifth metatarsal bone; the other part arises from the inner
surface of the fibular tarsal bone (or from the tendinous part) and ends
on the first phalanx of the fifth digit.
In case the skeleton of the first digit is well developed, there are
found three muscles homologous with those of the same digit in the fore
limb. These are the =abductor hallucis=, =adductor hallucis=, and
=flexor hallucis brevis=.
THE DIGESTIVE SYSTEM
This system consists of the organs directly concerned in the reception
and digestion of the food, its passage through the body, and the
expulsion of the unabsorbed portion. These organs are conveniently
grouped under two heads, viz.: (1) the =alimentary canal=; (2) the
=accessory organs=.
The =alimentary canal= (Tractus alimentarius) is a tube, about 100 feet
(ca. 30 m.) in length in the horse, and extends from the lips to the
anus. It has a complete lining of mucous membrane, external to which is
an almost continuous muscular coat. The abdominal portion of the tube is
largely covered with a serous membrane—the visceral peritoneum. The
canal consists of the following consecutive segments:
1. Mouth.
2. Pharynx.
3. Œsophagus.
4. Stomach.
5. Small intestine.
6. Large intestine.
The =accessory organs= are the teeth, tongue, salivary glands, liver,
and pancreas.
DIGESTIVE SYSTEM OF THE HORSE
THE MOUTH
The =mouth=[77] (Cavum oris) is the first part of the alimentary canal.
In the horse it is a long cylindrical cavity, and when closed, it is
almost entirely filled up by the contained structures. The entrance to
it (Rima oris) is closed by the lips. Laterally it is bounded by the
cheeks; above, by the hard palate; below, by the body of the mandible
and the mylo-hyoid muscles; behind, by the soft palate.
The =cavity= of the mouth is subdivided into two parts by the teeth and
alveolar processes. The space external to these and inclosed externally
by the lips and cheeks is termed the vestibule of the mouth (Vestibulum
oris). In the resting state of the parts the walls of this cavity are in
contact, and the space is practically obliterated. Its existence becomes
very evident in facial paralysis, when the food tends to collect in it
laterally, pouching out the cheeks. The space within the teeth and
alveolar processes is termed the mouth cavity proper (Cavum oris
proprium). When the teeth are in contact, it communicates with the
vestibule only by the interdental spaces and the intervals behind the
last molar teeth. Posteriorly it communicates with the pharynx through
the isthmus of the fauces.
The =mucous membrane= lining the mouth (Tunica mucosa oris) is
continuous at the margin of the lips with the common integument, and
behind with the mucous lining of the pharynx. During life it is chiefly
of a pink color.
The =lips= (Labia oris) are two musculo-membranous folds which surround
the orifice of the mouth. Their angles of union (Anguli oris s.
commissuræ labiorum) are situated near the first cheek tooth and are
rounded. Each lip presents two surfaces and two borders. The outer
surface is covered by the skin, which presents long tactile hairs in
addition to the ordinary fine hair. The upper lip shows a shallow median
furrow (Philtrum), the lower a rounded prominence, the chin (Mentum).
The inner or oral surface is covered with mucous membrane which is
commonly more or less pigmented. The small papillæ on this surface show
on their summits the openings of the ducts of the labial glands. Small
folds of mucous membrane which pass from the lip to the gum represent
the frænula labii (superioris, inferioris). The free border of the lip
is dense and presents short, very stiff hairs. The attached border is
continuous with the surrounding structures, and is adherent to the
alveolar borders of the bones of the jaws.
[Illustration:
FIG. 238.—SAGITTAL SECTION OF HEAD OF HORSE. THE SECTION IS ABOUT 1
CM. TO THE LEFT OF THE MEDIAN PLANE.
_1_, Hard palate; _2_, soft palate; _3_, posterior pillar of soft
palate; _4_, Eustachian opening; _5_, great cornu of hyoid bone;
_6_, stylo-pharyngeus muscle; _9_, glosso-pharyngeal nerve; _10_,
hypoglossal nerve; _11_, perpendicular plate of ethmoid; _12_,
presphenoid; _13_, sphenoidal sinus; _14_, occipital bone; _15_,
median surface of cerebral hemisphere; _16_, corpus callosum; _17_,
septum lucidum; _18_, fornix; _19_, thalamus opticus; _20_, corpora
quadrigemina; _21_, pons; _22_, medulla oblongata; _23_, spinal
cord; _24_, cerebellum; _25_, pituitary body; _26_, hyo-epiglottic
muscle; _27_, superior longitudinal muscle of tongue; _28_,
omo-hyoideus; _29_, hyo-glossus; _30_, hyoideus transversus; _31_,
thyroid cartilage (body); _S. f._, frontal sinus; _L. n._, lig.
nuchæ; _C I_, atlas; _C II_, axis; _R. c. m._, rectus cap. ant.
major and minor; _E p._, epiglottis; _A r._, arytenoid cartilage; _P
m._, premaxilla; _M._, mandible. The leader line for the guttural
pouch points to the external carotid artery.
]
=Structure.=—The lips are covered externally by the skin, and are lined
by mucous membrane; between these are muscular tissue and glands. The
skin lies directly on the muscles, many fibers of which are inserted
into the former. The muscles have been described (page 214). The =labial
glands= (Glandulæ labiales) form a compact mass near the angles; they
are numerous in the upper lip, fewer in the lower. The mucous membrane
is often pigmented, and is reflected upon the bones of the jaws to form
the gums.
=Blood-vessels and Nerves.=—The arteries are derived from the superior
and inferior labial and palato-labial arteries. The sensory nerves come
from the trigeminus, and the motor from the facial nerve.
The =cheeks= (Buccæ) form the sides of the mouth, and are continuous in
front with the lips. They are attached above and below to the alveolar
borders of the bones of the jaws.
=Structure.=—This comprises: (1) The skin; (2) the muscular and
glandular layer; (3) the mucous membrane. The skin offers nothing in
particular to notice. The muscular tissue is formed mainly by the
buccinator, but also by parts of the panniculus, zygomaticus, dilatator
naris lateralis, levator nasolabialis, and depressor labii inferioris.
The =buccal glands= (Glandulæ buccales) are arranged in two rows. The
upper row (superior buccal or molar glands) is found on the outer
surface of the buccinator muscle, near its upper border. The anterior
part of the row consists of scattered lobules; the posterior part, which
lies under cover of the masseter muscle, is more developed and compact.
The lower row (inferior buccal or molar glands), less voluminous than
the upper, is situated in the submucous tissue at the lower border of
the buccinator muscle. The mucous membrane is reflected above and below
upon the gums, and is continuous behind with that of the soft palate. It
is reddish in color and frequently shows pigmented areas. Opposite the
third upper cheek tooth is the opening of the parotid (Stenson’s) duct,
surrounded by a circular fold of the mucous membrane. A linear series of
small papillæ above and below indicates the orifices of the small ducts
from the buccal glands.
=Blood-vessels and Nerves.=—The blood-supply is derived from the facial
and buccinator arteries. The sensory nerves come from the trigeminus and
the motor from the facial nerve.
The =gums= (Gingivæ) are composed of a dense fibrous tissue intimately
united with the periosteum of the alveolar processes, and blending at
the edges of the alveoli with the alveolar periosteum, which fixes the
teeth in their cavities. They are covered by a smooth mucous membrane,
destitute of glands, and of a low degree of sensibility.
The =hard palate= (Palatum durum) is bounded in front and on the sides
by the alveolar arches; behind it is continuous with the soft palate.
Its osseous basis is formed by the premaxilla, maxilla, and palate
bones. The mucous membrane is smooth, and is attached to the bones by a
submucosa which contains in its anterior part an exceedingly rich venous
plexus, constituting an erectile tissue. A central raphé (Raphé palati)
divides the surface into two equal portions. Each of these presents
about eighteen transverse curved ridges (Rugæ palatini) which have their
concavity and their free edges directed backward. They are further apart
and more prominent anteriorly. There are no glands in the submucosa.
=Vessels and Nerves.=—The blood-supply is derived chiefly from the
palatine arteries and the nerves from the trigeminus.
The =soft palate= (Palatum molle) is a musculo-membranous curtain which
separates the cavity of the mouth from that of the pharynx. It slopes
downward and backward from its junction with the hard palate. The =oral
surface= faces downward and forward, and is covered with a mucous
membrane continuous with that of the hard palate. It is corrugated and
presents numerous small orifices (of gland-ducts) and two sagittal
ridges. On each side a short, thick fold passes to join the base of the
tongue; this is the =anterior pillar= of the soft palate (Arcus
glossopalatinus). The =pharyngeal surface= looks upward and backward and
is covered by a mucous membrane continuous with that of the nasal
cavity. The =free border= (Arcus palatinus) is concave and thin; it is
in contact (except during deglutition) with the epiglottis. It is
continuous with a fold of the mucous membrane, which passes on each side
along the lateral wall of the pharynx and unites with its fellow over
the beginning of the œsophagus; this fold is termed the =posterior
pillar= of the soft palate (Arcus pharyngopalatinus). The space between
the diverging anterior and posterior pillars (Sinus tonsillaris) is
occupied by the faucial =tonsil=. In the horse, however, there is not a
compact tonsil, as in man, dog, etc., but a somewhat extended group of
mucous glands and masses of lymphoid tissue. These cause elevations of
the surface, on which are seen numerous depressions (crypts) in which
the gland-ducts open. The soft palate is greatly developed in equidæ,
its length being five to six inches (12 to 15 cm.). Its length and
contact with the epiglottis account for the fact that in these animals
mouth-breathing does not occur under normal conditions, and that in
vomiting the ejected matter escapes usually through the nasal
cavity.[78]
[Illustration:
FIG. 239.—HARD PALATE AND PART OF SOFT PALATE OF HORSE.
_1_, Raphé palati; _2_, ridges of palate; _3_, anterior end of soft
palate, showing orifices of ducts of palatine glands.
]
=Structure.=—The soft palate consists of: (1) The oral mucous membrane,
continuous with that of the hard palate; (2) the =palatine glands=
(Glandulæ palatinæ), which form a layer about half an inch in thickness;
(3) the aponeurotic and muscular layer; (4) the pharyngeal mucous
membrane, continuous with that of the nasal cavity.
The =muscles= proper to the soft palate are the azygos uvulæ, the
levator palati, and the tensor palati.
The =azygos uvulæ= (M. palatinus) consists of two small muscular bundles
which lie together at the median line. It is attached through the medium
of the palatine aponeurosis to the palatine arch, and terminates near
the free edge of the soft palate. Its action is to shorten and raise the
soft palate.
The =levator palati= (M. levator veli palatini) arises from the muscular
process of the petrous temporal bone and from the Eustachian tube, and
passes forward and downward externally to the latter, to spread out on
the pharyngeal surface of the soft palate. It raises the soft palate,
thus closing the posterior nares during deglutition.
The =tensor palati= (M. tensor veli palatini) is larger than the
levator, and is fusiform and flattened. It arises from the muscular
process of the petrous temporal bone and the Eustachian tube, and passes
forward external to the levator. Its tendon is then reflected around the
hamulus of the pterygoid bone, being held in position by a fibrous band
and lubricated by a bursa. It turns inward and expands in the
aponeurosis of the soft palate. It tenses the soft palate.
=Vessels and Nerves.=—The blood-supply of the soft palate is derived
from the internal and external maxillary arteries. The nerves come from
the trigeminus, vagus, and glosso-pharyngeal nerves.
[Illustration:
FIG. 240.—CROSS-SECTION OF HEAD OF HORSE JUST IN FRONT OF FACIAL
CREST.
_1_, Cavity of superior turbinal; _2_, cavity of inferior turbinal;
_3_, cavum oris; _4_, _4_, genio-glossi; _5_, _5_, genio-hyoidei;
_6_, hyo-glossus; _7_, upper, _7′_, lower fourth cheek tooth. Line
to facial artery crosses zygomaticus.
]
The =floor= of the mouth in its anterior part is free and is formed by
the body of the mandible, covered by mucous membrane. The remainder is
concealed by the attached portion of the tongue, with the exception of a
narrow space on each side of the latter. About opposite the canine tooth
on each side is a papilla, the =caruncula sublingualis=, through which
the duct of the submaxillary gland opens. Just behind these papillæ is a
median fold of mucous membrane which passes to the under surface of the
tongue, constituting the =frenum linguæ=. On either side are the
sublingual crests, which extend from the frenum to the level of the
fourth cheek tooth. The crest presents numerous small papillæ, through
which open the ducts from the subjacent sublingual gland.[79] Behind the
last tooth a vertical fold of the mucous membrane passes from upper to
lower jaw. This is termed the plica pterygomandibularis: it contains a
ligament of like name.
The =isthmus faucium= is the orifice of communication between the mouth
and the pharynx. It is bounded above by the soft palate, below by the
root of the tongue, and laterally by the anterior pillars of the soft
palate. It is long, relatively small, and not very dilatable in the
horse, and is closed by the soft palate under normal conditions, except
during deglutition.
THE TONGUE
The =tongue= (Lingua) is situated on the floor of the mouth, between the
rami of the mandible, and is supported mainly in a sort of sling formed
by the mylo-hyoid muscles. Its posterior portion, the =root= (Radix
linguæ), is attached to the hyoid bone, soft palate, and pharynx. Only
the upper surface of this part is free, and slopes downward and
backward. The middle portion, the =body= (Corpus linguæ), has three free
surfaces. The upper surface or =dorsum= (Dorsum linguæ) is rounded. The
lateral surfaces are nearly flat for the most part, but anteriorly
become rounded and narrower. The lower surface is attached to the
mandible. The =apex= or tip (Apex linguæ) is free, spatula-shaped, and
presents superior and inferior surfaces and a rounded border.
[Illustration:
FIG. 241.—TONGUE OF HORSE, DORSAL ASPECT.
]
=Structure.=—The tongue consists of: (1) The mucous membrane; (2) the
glands; (3) the muscles.
The =mucous membrane= (Tunica mucosa linguæ) adheres intimately to the
subjacent tissue, except on the lower part of the lateral surfaces of
the body and the under surface of the tip. It varies considerably in
thickness. On the dorsum it is very thick and dense. Underneath this
portion there is a dense fibrous cord, which extends medially a distance
of five or six inches forward from the vallate papillæ. On the sides and
under surface of the tongue the membrane is much thinner and smooth, and
can more readily be dissected off the muscular tissue. From the under
surface of the free part of the tongue a fold of the mucous membrane
passes to the floor of the mouth, forming the =frenum linguæ=. This
contains the anterior edges of the genio-glossi muscles. Posteriorly a
fold passes on each side from the edge of the dorsum to join the soft
palate, forming the anterior pillars of the latter. A central
glosso-epiglottic fold (Plica glossoepiglottica) passes from the root to
the base of the epiglottis. The mucous membrane presents numerous
=papillæ=, which are of four kinds—filiform, fungiform, vallate, and
foliate. The =filiform papillæ= (Papillæ filiformes) are fine, pointed
projections. They cover the upper surface of the body and tip, to which
they give a distinct pile. The =fungiform papillæ= (Papillæ fungiformes)
are rounded at the free end, which is supported by a neck. They occur
principally on the lateral part of the tongue, but are also found
scattered over the dorsum and upper surface of the free portion. The
=vallate papillæ= (Papillæ vallatæ) are usually two or three in number.
The two constant ones have a diameter of about 7 mm., and are found on
the posterior part of the dorsum, one on each side of the median plane,
about an inch (ca. 3 cm.) apart. The third, when present, is behind
these, is centrally situated, and is always smaller. Rarely a fourth may
be seen. They are rounded, broader at their exposed than at their
attached surfaces, and are situated in a cup-shaped cavity. The =foliate
papillæ= (Papillæ foliatæ) are situated just in front of the anterior
pillars of the soft palate, where they form a rounded eminence about an
inch (ca. 2 to 3 cm.) in length, marked by transverse fissures. The last
three varieties are covered with microscopic secondary papillæ and are
furnished with taste buds. The mucous membrane of the root of the tongue
presents numerous folds and depressions. Into the latter open the ducts
from the =lingual glands= (Glandulæ linguales), which constitute a thick
layer in the loose submucous tissue. Mucous glands are found also on the
dorsum and sides of the tongue. In the submucosa of the root is found
also a large quantity of lymph follicles (Folliculi tonsillares) and
diffuse lymphoid tissue.
[Illustration:
FIG. 242.—MUSCLES OF TONGUE, HYOID BONE, PHARYNX, ETC., OF HORSE.
_T. p._, Tensor palati; _L. p._, levator palati; _Pt. p._,
pterygo-pharyngeus; _P. p._, palato-pharyngeus; _S. p._,
stylo-pharyngeus; _Th. p._, thyro-pharyngeus; _C. p._,
crico-pharyngeus; _Th. h._, thyro-hyoideus; _Hyo. gl._, hyo-glossus;
_G. p._, guttural pouch; _F. p._, foliate papilla; _A. v._, facial
artery and vein. The concealed parts of the hyoid bone are indicated
by dotted line.
]
The =muscular tissue= may be divided into intrinsic and extrinsic. The
intrinsic musculature consists, not of distinct muscles, but rather of
systems of fibers which run longitudinally, vertically, and
transversely, blending with the extrinsic muscles, which are now to be
described.
1. =Stylo-glossus.=—This is a long, thin muscle, which lies on the
lateral part of the tongue. It arises by a thin tendon from the outer
surface of the great cornu of the hyoid bone, near the articulation with
the small cornu. It terminates near the tip of the tongue by blending
with its fellow of the opposite side and with the intrinsic musculature.
The action is to retract the tongue. Unilateral contraction would also
draw the tongue toward the side of the muscle acting.
[Illustration:
FIG. 243.—MUSCLES OF TONGUE, PHARYNX, LARYNX, ETC., DEEP DISSECTION.
_T. p._, Tensor palati; _L. p._, levator palati, concealed part
indicated by dotted line; _Pt. p._, pterygo-pharyngeus; _P. p._,
palato-pharyngeus; _St. p._, stylo-pharyngeus; _C. a._,
crico-arytenoideus post.; _C. th._, crico-thyroideus; _Th. c._,
thyroid cartilage (wing); _Th. h._, thyro-hyoideus; _K. h._,
kerato-hyoideus; _Th. c._, thyroid cornu; _S. c._, small cornu; _L.
p._, lingual process; _F. p._, foliate papilla; _Fu. p._, fungiform
papillæ. Part of great cornu is removed and indicated by dotted
line.
]
2. =Hyo-glossus.=—This is a wide, flat muscle, somewhat thicker than the
preceding. It lies on the lateral part of the root and body of the
tongue, partly under cover of the preceding muscle. Its deep face is
related to the genio-glossus. It arises from the lateral aspect of the
hyoid bone, from the lingual process to the oral extremity of the great
cornu, and from the thyroid cornu. The fibers pass obliquely forward and
upward, and for the most part turn toward the median plane of the dorsum
of the tongue. Its action is to retract and depress the tongue.
(It is usually possible to recognize in this muscle three portions,
which would correspond to the baseo-, kerato-, and chondro-glossus of
human anatomy.)
3. =Genio-glossus.=—This is a fan-shaped muscle, which lies parallel to
the median plane of the tongue. It is separated from the muscle of the
opposite side by a quantity of fat and connective tissue. It arises from
the inner surface of the ramus of the mandible near the symphysis. From
the tendon the fibers pass in a radiating manner, some toward the tip,
others toward the dorsum, and others toward the root of the tongue; some
fibers pass from the posterior end of the tendon to the body and small
cornu of the hyoid bone. The muscle as a whole is a depressor of the
tongue, and especially of its middle portion; when both muscles act, a
median groove is formed on the dorsum. The posterior fibers protrude the
tongue, the middle fibers depress the tongue, and the anterior fibers
retract the tip of the tongue.
=Vessels and Nerves.=—The arteries of the tongue are the lingual and
sublingual branches of the external maxillary artery. The sensory nerves
are the lingual and glosso-pharyngeal, and the muscles are innervated by
the hypoglossal nerve.
THE TEETH
The teeth are hard white or yellowish-white structures, implanted in the
alveoli of the bones of the jaws—premaxilla, maxilla, and mandible.
Morphologically they are large calcified papillæ. Functionally they are
organs of prehension and mastication, and may serve as weapons of
offense and defense. They are classified according to form and position
as follows:
1. =The incisor teeth= (Dentes incisivi) are situated in front and are
implanted in the premaxilla and mandible.
2. =The canine teeth= (Dentes canini) are situated a little further
back, at or near the premaxillary suture in the upper jaw; in the lower
jaw they are nearer the incisors.
3. =The cheek teeth= (Dentes premolares et molares), the remaining
teeth, occupy the sides of the dental arch. The space between the
incisors and cheek teeth is termed the interdental or interalveolar
space. It is customary to divide the cheek teeth into an anterior
series, termed =premolars=, which appear as temporary, deciduous, or
milk teeth, and are replaced by permanent successors, and a posterior
series, the =molars=, which appear only as permanent teeth without
deciduous predecessors.
As the teeth of the two sides of the jaws are alike in number and
character (in normal cases), the complete dentition may be briefly
indicated by a =dental formula= such as the following:
( 2 1 2 3 )
2 ( I - C - P - M - ) = 32.
( 2 1 2 3 )
In this formula the letters indicate the kinds of teeth, and the figures
above and below the lines give the number of teeth of one side in the
upper and lower jaw respectively in man.
The individual teeth of each group are designated numerically, the
starting-point being the middle line; thus the incisor on either side of
the middle line is the first incisor, and may be conveniently indicated
by the notation I^1. The temporary or deciduous teeth may be designated
in a similar manner, prefixing D (for deciduous) to the letter
indicating the kind of tooth. In addition to the above systematic method
of notation other terms have received the sanction of popular usage.
Thus the first incisors are commonly called “pinchers,” or “nippers”;
the second, intermediate; and the third, corner teeth. The canines, when
highly developed, may be termed tusks or fangs. The vestigial and
inconstant first premolar of the horse is popularly termed the “wolf
tooth.”
Each tooth presents for description a portion coated with enamel, termed
the =crown= (Corona dentis), and a portion covered with cement, termed
the =root= (Radix dentis). The line of union of these parts is the neck
(Collum dentis).[80] In many teeth the neck is distinct and is embraced
by the gum, _e. g._, the teeth of the dog and the temporary incisors of
the horse. In other teeth no constriction is seen, as in the permanent
incisors of the horse. Between these extremes may be noted the molars of
the horse, in which the neck is seen only in advanced age.
The =surface= of a tooth directed toward the lips is termed =labial=;
toward the cheek, =buccal=; and toward the tongue, =lingual= (Facies
labialis, buccalis, lingualis). The surface opposed to a neighboring
tooth of the same dental arch is termed the =contact surface= (Facies
contactus). The grinding or =masticatory= or “table” surface (Facies
masticatoria) is that which comes in contact with a tooth or teeth of
the opposite jaw.
=Structure.=—Teeth are composed of four tissues, which are considered
here from within outward. The =pulp= (Pulpa dentis) is a soft gelatinous
tissue, which occupies a space in the central part of the tooth termed
the =pulp cavity= (Cavum dentis). The pulp is well supplied with
blood-vessels and nerves. It occupies a relatively large space in young
growing teeth, but later the dentine deposited on its surface gradually
encroaches on it until, in advanced age, the cavity is obliterated or
much reduced. The =dentine= (Substantia eburnea) forms the bulk of most
teeth, covering the surface of the pulp. It is very hard, and is
yellowish-white in color. The =enamel= (Substantia adamantina)
constitutes a layer of varying thickness covering the dentine of the
crown of the tooth. It is easily distinguished by its clear bluish-white
appearance and its extreme density. The =cement= (Substantia ossea) is
always the outermost tooth substance. In simple teeth it forms usually a
thin layer on the surface of the dentine of the root only, but in
complex teeth it exists in considerable quantity, tending to fill in the
spaces between the enamel folds of the crown also. Its structure is
practically the same as that of bone without Haversian canals, and even
these occur where the cement forms a very thick layer. The embedded part
of the tooth is attached to the alveolus by a vascular layer of
connective tissue, the =alveolar periosteum= (Periosteum alveolare),
which constitutes the periosteum at once of tooth and alveolus.
The =blood-supply= to the pulp is derived from the alveolar or dental
branches of the internal artery; the =nerve-supply= comes from branches
of the trigeminus.
THE TEETH OF THE HORSE
THE PERMANENT TEETH
The formula of the permanent teeth of the horse is:
( 3 1 3 or 4 3 )
2 ( I - C - P —————— M - ) = 40 or 42
( 3 1 3 3 )
[Illustration:
FIG. 244.—UPPER TEETH OF HORSE, ABOUT FOUR AND ONE-HALF YEARS OLD.
_I^1_, _I^2_, _I^3_, Incisors; _C_, canine; _P^1_, _P^2_, _P^3_,
_P^4_, premolars; _M^1_, _M^2_, _M^3_, molars.
]
[Illustration:
FIG. 245.—LOWER TEETH OF HORSE, FOUR YEARS OF AGE.
_I^1_, _I^2_, First and second permanent incisors; _Di^3_, third
deciduous incisor. The cheek teeth are numbered according to popular
usage.
]
In the mare the canines usually are very small and do not erupt,
reducing the number to 36 or 38.[81]
=Incisor Teeth.=—These are twelve in number. The six in each jaw are
placed close together, so that their labial edges form almost a
semicircle. They have the peculiarity (not found in existing mammals
other than the equidæ) of presenting, instead of the simple cap of
enamel on the crown, a deep invagination, the =infundibulum=, which
becomes partly filled up with cement. Hence as the tooth wears the table
surface has a central ring of enamel surrounding this cavity in addition
to the peripheral enamel. The cavity becomes darkened by deposits from
the food, and is commonly termed the “cup” or “mark.” Each tooth is
curved so that the labial surface is convex and the roots converge. The
average length of the incisors at five or six years of age is about two
and a half to three inches (ca. 7 cm.). They taper regularly from crown
to root, without any constriction, and in such a manner that in young
horses the exposed crown is broad transversely; toward the middle, the
two diameters of a cross-section are about equal; near the root the
antero-posterior diameter is considerably greater than the transverse.
[Illustration:
FIG. 246.—LOWER INCISOR AND CANINE TEETH OF HORSE, FIVE YEARS OLD.
]
[Illustration:
FIG. 247.—UPPER INCISOR AND CANINE TEETH OF HORSE, FIVE YEARS OLD.
_I^1_, _I^2_, _I^3_, Incisors; _C_, canine.
]
This fact is of value in the determination of age by the teeth, since
the table surface at different ages represents a series of such
cross-sections. As the exposed crown wears down the embedded part
(reserve crown) pushes up out of the alveolus, so that the tables of the
first and second lower incisors are at first oval, with the long
diameter transverse; later—at about fourteen years usually for the first
lower incisors—the tables are triangular, with the base at the labial
edge. At the same time the infundibulum or cup becomes smaller,
approaches the lingual border, and finally disappears; it remains longer
on the upper incisors, as it is deeper in them. Another marked feature
in old age is the progressive approach to a horizontal direction as seen
in profile; at the same time the teeth become parallel and finally
convergent.
=Canine Teeth.=—These are four in number in the male; in the mare they
are usually absent or rudimentary.[82] They interrupt the interdental
space, dividing it into two unequal parts. The upper canine is situated
at the junction of the premaxilla and the maxilla; the lower canine is
placed nearer the corner incisor. The canines are simple teeth, smaller
than the incisors, and are curved with the concavity directed backward.
The crown is compressed, convex, and smooth externally; concave with a
median ridge internally; its edges are sharp, and the apex is pointed in
the unworn tooth. The root is round and the pulp cavity is large,
persisting to advanced age.
[Illustration:
FIG. 248.—LONGITUDINAL SECTION OF PERMANENT INCISOR TOOTH OF HORSE,
ABOUT NATURAL SIZE.
]
[Illustration:
FIG. 249.—INCISOR TOOTH OF HORSE, LINGUAL ASPECT. (After
Ellenberger-Baum, Anat. für Künstler.)
]
[Illustration:
FIG. 250.—CANINE AND INCISOR TEETH OF HORSE.
The bone has been removed to show the embedded parts of the teeth.
(After Ellenberger-Baum, Anat. für Künstler.)
]
=Cheek Teeth= (Premolars and Molars).[83]—The constant number of these
is twenty-four—twelve in each jaw. Quite commonly, however, the number
is increased by the presence in the upper jaw of the so-called wolf
tooth. This tooth is usually situated just in front of the first
well-developed tooth; it is a much reduced vestige, not often more than
one-half or three-fourths of an inch (ca. 1 to 2 cm.) in length. (It is
interesting as being the remnant of a tooth which was well developed in
the Eocene ancestors of the horse.) It may erupt during the first six
months, and is often shed about the same time as the milk-tooth behind
it, but may remain indefinitely. The occurrence of a similar tooth in
the lower jaw—which rarely erupts—increases the dental formula to 44,
which is considered the typical number for mammals. They may be regarded
as belonging to the permanent set, having no predecessors. The cheek
teeth are very large, prismatic in form, and quadrilateral in
cross-section, except the first and last of the series, which are
triangular. The crown is remarkably long, most of it being embedded in
the bone or situated in the maxillary sinus in the young horse. As the
exposed part wears down the embedded part pushes up to replace it, so
that a functional crown of about four-fifths of an inch (ca. 2 cm.) is
maintained. The root begins to grow at four or five years of age, and is
complete at twelve to fourteen, although the deposition of cement may
continue indefinitely.
[Illustration:
FIG. 251.—SKULL OF ADULT HORSE SCULPTURED TO EMBEDDED PARTS OF TEETH.
The bone has been removed to show the embedded parts of the teeth
_I^1_, _I^2_, _I^3_, Incisors; _C_, canines. The cheek teeth are
numbered.
]
The =upper= or =maxillary teeth= are embedded in the alveolar processes
of the maxilla. The exposed parts of the crowns are normally in close
contact, forming a continuous row which is slightly curved, with the
convexity toward the cheek. The embedded parts diverge in the manner
shown in the annexed figures (Figs. 251, 253). Thus the long axis of the
first is directed upward and a little forward, that of the second is
almost vertical, while in the remainder it is curved backward in an
increasing degree. The average =length= at six years of age is about
three to three and a half inches (ca. 7 to 9 cm.). The =buccal= (or
outer) =surface= presents a central ridge running lengthwise, and
separating two grooves; the first tooth has, in addition, a less
prominent ridge in front of the primary one. The =lingual= (or inner)
=surface= is marked by a wide, rounded ridge, the accessory pillar or
column, which separates two very shallow grooves. The =masticatory= or
=table surface= presents two infundibula, an anterior and a posterior.
It slopes obliquely downward and outward, so that the outer edge is
prominent and sharp. The first and last teeth have three roots, the
remainder four or three.
The position of the embedded crowns and roots of the last four varies at
different ages and in different subjects. Two factors in this variation
may be noted. All these teeth are developed in the maxillary sinus close
to the orbital fossa. As growth proceeds the teeth move forward, so that
commonly only the last three, but sometimes also the third, remain
(except as to their free crowns) in the sinus. The second cause of
variation is the fact that the anterior limit of the maxillary sinus may
be at the extremity of the facial ridge, or more than an inch beyond it.
In the latter case the third tooth projects into the sinus.[84]
[Illustration:
FIG. 252.—CROSS-SECTIONS OF CHEEK TEETH OF HORSE.
Buccal (outer) surfaces face to left. _A_, Upper tooth, _B_, lower
tooth; _I_, anterior, _I′_, posterior infundibulum, both almost
filled up with cement.
]
The =structure= is quite complex. Two infundibula run vertically through
the entire length of the crown; these become filled with cement. There
are five main divisions of the pulp-cavity and five enamel folds, four
of which are arranged symmetrically, while the fifth is an outgrowth
from the inner side of the antero-internal fold. On the exposed crown of
the unworn tooth the enamel folds form rounded ridges covered with a
thin layer of cement. After the tooth comes into wear the enamel on the
masticatory surface stands out in the form of sharp prominent ridges.
Progressive cementation of the periphery of the tooth takes place, thus
leveling up the irregularities of surface to a considerable extent.
The =lower= or =mandibular cheek teeth= are implanted in the rami of the
mandible, forming two straight rows which diverge behind. The space
between the rows is considerably less than that separating the upper
teeth, especially in the middle of the series. The length of the lower
teeth is about the same as that of the upper set. Their direction is
also similar, but the embedded portions diverge even more, with the
exception of the first and second. The long axis of the first is
vertical; the remainder project downward and backward in a gradually
increasing obliquity. The =buccal= (outer) =surface= has a longitudinal
furrow; the last molar has a secondary, shallower furrow in addition.
The =lingual= (inner) =surface= is uneven, but the grooves are not
regular; there are usually three on the first and last tooth. The
=masticatory= or =table surface= is oblique, sloping upward and inward
in correspondence with the opposing tooth; thus the inner edge is
prominent. The first five have two roots, while the sixth commonly has
three. The width of the lower molars is a little more than half that of
the upper. There are two infundibula, which are open along the inner
face of the tooth until closed by cement. The pulp-cavity has two
principal divisions, and four or three secondary diverticula. The enamel
folds correspond, forming a pattern even more complicated than on the
upper teeth.
[Illustration:
FIG. 253.—SKULL OF TWO-YEAR-OLD COLT, SCULPTURED TO SHOW THE EMBEDDED
PARTS OF THE TEETH.
Both permanent and temporary cheek teeth are shown. The upper first
premolar (“wolf tooth”) is present, but not visible; the lower one
is indicated by the arrow. Temporary chief premolars are numbered
_1_, _2_, _3_; permanent premolars and molars are designated by
Roman numerals; _Dc._, upper temporary canine; _C_, lower permanent
canine, which was not ready to erupt; _Di 2_, _Di 3_, second and
third temporary incisors; _I 1_, first permanent incisor, not quite
ready to erupt.
]
THE TEMPORARY TEETH
The =deciduous=, temporary, or “milk” =teeth= (Dentes decidui) are
smaller and fewer than those of the permanent set. The formula is:
( 3 0 3 )
2 ( Di - Dc - Dp - ) = 24.
( 3 0 3 )
The =deciduous incisors= are much smaller than the permanent ones. They
have a distinct =neck= at the junction of the crown and root. The
=crown= is short, white in color, and its labial surface is smooth. The
=infundibulum= is shallow. The =root= is flattened; it undergoes
absorption as the permanent tooth develops behind it.
The =deciduous canines= are quite vestigial. They occur in both sexes as
slender spiculæ about a quarter of an inch in length, but do not erupt.
The lower one develops close to the corner incisor. They are not usually
included in the formula, as they are never functional.
The =deciduous cheek teeth= differ from the permanent set chiefly in
that they have much shorter crowns than the latter. The roots form
early, so that a distinct neck occurs.
The subjoined table indicates the average periods of the eruption of the
teeth:
TEETH ERUPTION
A. _Deciduous_:
1st incisor (Di 1) Birth or first week.
2nd „ (Di 2) 4–6 weeks.
3rd „ (Di 3) 6–9 months.
Canine (Dc )
1st premolar (Dp 2) Birth or first two weeks.
2nd „ (Dp 3) „
3rd „ (Dp 4) „
B. _Permanent_:
1st incisor (I 1) 2½ years.
2nd „ (I 2) 3½ years.
3rd „ (I 3) 4½ years.
Canine. (C ) 4–5 years.
1st premolar (or wolf tooth) (P 1) 5–6 months.
2nd „ (P 2) 2½ years.
3rd „ (P 3) 3 years.
4th „ (P 4) 4 years.
1st molar (M 1) 10–12 months.
2nd „ (M 2) 2 years.
3rd „ (M 3) 3½–4 years.
(The periods given for P 3 and 4 refer to the upper teeth; the lower
ones may erupt about six months earlier.)
THE SALIVARY GLANDS
This term is usually restricted to the three pairs of large glands
situated on the sides of the face and the adjacent part of the neck—the
parotid, submaxillary, and sublingual. Their ducts open into the mouth.
The =parotid gland= (Glandula parotis) (Fig. 172)—so named from its
proximity to the ear—is the largest of the salivary glands in the horse.
It is situated chiefly in the space between the ramus of the mandible
and the wing of the atlas. It is somewhat triangular in shape, the apex
partially embracing the base of the external ear. Its length is about
eight to ten inches (ca. 20 to 25 cm.), and its average thickness nearly
an inch (ca. 2 cm.). Its average weight is about seven ounces (ca. 200
to 225 g.).
It presents for description two surfaces, two borders, a base, and an
apex. The =external= (or superficial) =surface= is covered by the
parotid fascia, the panniculus, and the parotido-auricularis muscle. It
is crossed obliquely by the jugular vein, which is embedded in the gland
tissue to a varying extent. It is also related to the great auricular
vein, the cervical branch of the facial nerve, and branches of the
second cervical nerve. The =internal= (or deep) =surface= is very
uneven, and has numerous important relations. Some of these are: the
guttural pouch, and the great cornu of the hyoid bone; the masseter,
stylo-maxillaris, digastricus, and occipito-hyoideus muscles; the
tendons of the mastoido-humeralis and sterno-cephalicus (which separate
the parotid from the underlying submaxillary gland); the external
carotid artery and some of its branches; the facial nerve; the
pharyngeal lymph glands. The =anterior= (or facial) =border= is closely
attached to the ramus of the mandible and the masseter muscle; it
overlaps the latter to a varying extent. (In some cases there is a
well-marked triangular facial process, which covers the
temporo-mandibular joint, the facial nerve, and the transverse facial
vessels.) The =posterior= (or cervical) =border= is somewhat concave,
and is loosely attached to the underlying muscles. The =base= or
=ventral border= is related to the external maxillary vein. The =apex=
is attached to the base of the external ear, which it partially
embraces.
The gland has a yellowish-gray color and is distinctly lobulated. It is
inclosed in a capsule formed by the parotid fascia. The =parotid duct=
(Ductus parotideus Stenonis) is formed at the lower part of the gland,
near the facial edge, by the union of three or four radicles. It leaves
the gland about an inch (ca. 2 to 3 cm.) above the external maxillary
vein, crosses the tendon of the sterno-cephalicus, and gains the inner
face of the pterygoideus internus. It then runs forward in the
submaxillary space below the external maxillary vein and winds around
the lower border of the mandible behind the vein, passes upward between
the vein and the masseter muscle for about two inches (ca. 5 cm.), turns
forward underneath the facial vessels, and perforates the cheek
obliquely opposite the third upper cheek tooth. Before piercing the
cheek it is somewhat dilated, but its termination is small, and is
surrounded by a circular mucous fold (Papilla salivalis).
=Blood-supply.=—Branches of the carotid and maxillary arteries.
=Nerve-supply.=—Trigeminal, facial, and sympathetic nerves.
The =submaxillary gland= (Glandula submaxillaris) is much smaller than
the parotid. It is long, narrow, and curved, the dorsal edge being
concave. It extends from the fossa below the wing of the atlas to the
body of the hyoid bone, so that it is covered partly by the parotid
gland, partly by the lower jaw. Its length is about eight to ten inches
(ca. 20 to 25 cm.), its width an inch to an inch and a half (ca. 2.5 to
3 cm.), and its thickness about half an inch (ca. 1 cm.). It weighs
about one and a half to two ounces (ca. 45 to 60 g.). It is often
divisible into two parts.
It presents for description two surfaces, two borders, and two
extremities. The =external surface= is covered by the parotid gland, the
stylo-maxillaris, digastricus, and pterygoideus internus muscles. The
tendon of the sterno-cephalicus crosses this surface, and is a useful
guide in separating the parotid gland from it. The =internal surface= is
related chiefly to the flexor muscles of the head; the guttural pouch;
the larynx; the division of the carotid artery; and the tenth, eleventh,
and sympathetic nerves. The =superior border= is concave and thin. It is
related to the guttural pouch and the duct of the gland. The =inferior
border= is convex and thicker. It is related to the thyroid gland and
the external maxillary vein. The =posterior extremity= is loosely
attached in the fossa atlantis. The =anterior extremity= lies at the
side of the root of the tongue, and is crossed externally by the
external maxillary artery.
The =submaxillary duct= (Ductus submaxillaris Whartoni) is formed by the
union of small radicles which emerge along the concave edge. It runs
forward along this border, and, after leaving the anterior extremity,
crosses the intermediate tendon of the digastricus, passes between the
hyo-glossus and mylo-hyoideus, and gains the inner surface of the
sublingual gland. Its terminal part lies on the body of the mandible,
under the mucous membrane, which it pierces opposite the canine tooth.
The orifice is at the end of a flattened papilla (Caruncula
sublingualis).
=Blood-supply.=—Occipital, external carotid, and external maxillary
arteries.
=Nerve-supply.=—Chorda tympani and sympathetic nerves.
The =sublingual gland= (Glandula sublingualis) is situated beneath the
mucous membrane of the mouth, between the body of the tongue and the
ramus of the mandible. It extends from the symphysis to the third or
fourth lower cheek tooth. Its length is about five or six inches (ca. 12
to 15 cm.) and its weight about half an ounce (ca. 15 to 16 g.).
It is flattened laterally, and has a thin =upper border= which causes an
elevation of the mucous membrane of the floor of the mouth, termed the
=sublingual crest= (Plica sublingualis). The =external surface= is
related to the mylo-hyoideus muscle, and the =internal surface= to the
genio-glossus and stylo-glossus, the submaxillary duct, and branches of
the lingual nerve. The =inferior border= is related to the genio-hyoid
muscle.
The =sublingual ducts= (Ductus sublinguales minores), about thirty in
number, are small, short, and twisted; they open on small papillæ on the
sublingual crest.
=Blood-supply.=—Sublingual artery.
=Nerve-supply.=—Trigeminal and sympathetic nerves.
THE PHARYNX
The pharynx is a musculo-membranous sac which belongs to the digestive
and respiratory tracts in common. It is funnel-shaped, the base joining
the mouth and nasal cavity, while the apex is continued by the
œsophagus. Its long axis is directed obliquely downward and backward,
and has a length of about six inches (ca. 15 cm.).
The pharynx is attached by its muscles to the palate, pterygoid, and
hyoid bones, and to the cricoid and thyroid cartilages of the larynx.
Its principal =relations= are: dorsally, the base of the cranium and the
guttural pouches; ventrally, the larynx; laterally, the internal
pterygoid muscle, the great cornu of the hyoid bone, the internal and
external maxillary arteries, the glosso-pharyngeal, superior laryngeal,
and hypoglossal nerves, the submaxillary salivary gland, and the
pharyngeal lymph glands.
It presents =seven openings=. The =posterior nares= (Choanæ) communicate
dorsally with the nasal chambers. The pharyngeal orifices (Ostia
pharyngea) of the two =Eustachian tubes= are situated on the lateral
wall behind the nares and a little below the level of the inferior nasal
meatus. They are slit-like openings, slightly oblique downward and
backward, and are a little more than an inch (ca. 3 cm.) in length. They
are bounded internally by a valvular flap formed by the expanded
extremity of the cartilaginous Eustachian tube. The =isthmus faucium= is
situated below and in front. It is closed by the soft palate except
during swallowing. The =laryngeal orifice= (Aditus laryngis) occupies
the greater part of the ventral wall or floor of the pharynx. Behind
this is the =œsophageal opening=.
The wall of the pharynx comprises from without inward: the muscles, the
pharyngeal aponeurosis, and the mucous membrane.
The =muscles= (Figs. 243, 244) are covered by the pharyngeal fascia,
which is attached to the base of the skull, the great cornu of the hyoid
bone, and the thyroid cartilage of the larynx. They are as follows:
1. The =stylo-pharyngeus= arises from the inner surface of the dorsal
third of the great cornu of the hyoid bone, passes downward and inward,
and enters the wall of the pharynx by passing between the
pterygo-pharyngeus and palato-pharyngeus. Its fibers radiate, many
passing forward, others inward beneath the hyo-pharyngeus. It raises and
dilates the pharynx to receive the bolus in swallowing.
[Illustration:
FIG. 254.—POSTERIOR PART OF A SAGITTAL SECTION OF HEAD OF HORSE, CUT
ABOUT 1 CM. TO THE LEFT OF THE MEDIAN PLANE.
_1_, Posterior nares; _2_, pharyngeal orifice of Eustachian tube; _3_,
aditus laryngis; _4_, entrance to œsophagus; _5_, posterior pillar
of soft palate; _5′_, junction of _5_ with its fellow over entrance
to œsophagus; _6_, epiglottis; _7_, body of thyroid cartilage; _8_,
arytenoid cartilage; _9_, _9_, cricoid cartilage; _10_, true vocal
cord; _11_, false vocal cord; _12_, lateral ventricle of larynx;
_13_, crico-arytenoideus post. s. dorsalis; _14_, œsophagus; _15_,
external carotid artery; _16_, hypoglossal nerve; _17_,
glosso-pharyngeal nerve; _18_, great cornu of hyoid bone; _19_,
Eustachian tube; _20_, body of hyoid bone; _21_, hyoideus
transversus; _22_, ridges of hard palate; _22′_, soft palate; _23_,
septum between frontal sinuses; _24_, olfactory mucous membrane;
_25_, sphenoidal sinus; _26_, basilar part of occipital bone; _26′_,
supraoccipital; _27_, body of sphenoid bone; _28_, pituitary body;
_29_, chiasma opticum; _30_, corpora quadrigemina; _31_, thalamus;
_32_, arachnoid; _33_, odontoid ligament; _34_, posterior auricular
muscles.
]
2. The =palato-pharyngeus= arises by means of the aponeurosis of the
soft palate from the palate and pterygoid bones. Its fibers pass
backward on the lateral wall of the pharynx, and are inserted in part
into the upper edge of the thyroid cartilage, in part turn inward to end
at the median fibrous raphé. Its action is to shorten the pharynx, and
to draw the larynx and œsophagus toward the root of the tongue in
swallowing.
3. The =pterygo-pharyngeus= is flat and triangular. It lies on the
anterior part of the lateral wall of the pharynx. It arises from the
pterygoid bone above the preceding muscle—from which it is not
distinctly separated—crosses the levator palati, and is inserted into
the median raphé. Its action is similar to the preceding.
4. The =hyo-pharyngeus= may consist of two portions:
(_a_) The =kerato-pharyngeus= is a small and inconstant muscle which
arises from the inner surface of the great cornu of the hyoid bone near
its lower end. It passes upward and backward, turns inward toward the
raphé, and spreads out under the next muscle.
(_b_) The =chondro-pharyngeus=, broad and fleshy, arises from the
thyroid cornu of the hyoid bone and by a thin fasciculus from the wing
of the thyroid cartilage and ends at the median raphé.
5. The =thyro-pharyngeus= arises from the lateral surface of the wing of
the thyroid cartilage. Its fibers pass forward and inward to the median
raphé.
6. The =crico-pharyngeus= arises from the cricoid cartilage and ends at
the raphé. The fibers are directed upward, forward, and inward; they
blend behind with the longitudinal fibers of the œsophagus.
The last three muscles are constrictors of the pharynx.
The =pharyngeal aponeurosis= is attached to the base of the cranium. It
is well developed on the inner face of the palato-pharyngeus muscle and
forms a median raphé (Raphé pharyngis) dorsally, which is wide in its
posterior part.
The =mucous membrane= of the pharynx is continuous with that of the
several cavities which open into it. It is thin and closely adherent to
the base of the skull in the vicinity of the posterior nares, where the
muscular wall is absent. Behind the Eustachian openings is a median
cul-de-sac, the =pharyngeal recess=. The recess is somewhat variable,
but is usually about an inch in depth and will admit the end of the
finger. In the ass and mule it is much deeper. Here also the muscular
wall is absent and the mucous membrane lies against the guttural
pouches. From the Eustachian opening a fold of the mucous membrane
(Plica salpingo-pharyngea) passes toward but does not reach the
laryngeal opening. Below, a horizontal fold, the =posterior pillar of
the soft palate= (Arcus pharyngopalatinus), passes along the lateral
wall and unites with its fellow over the entrance to the œsophagus. The
upper part of the cavity (the naso-pharynx) is lined with a ciliated
epithelium, while the lower part (oro-pharynx) has a stratified squamous
epithelium. The communication between the two is oval and is bounded by
the free edge of the soft palate and its posterior pillars; it is termed
the =pharyngeal isthmus=. On either side of the laryngeal opening is a
narrow deep depression, the =pyriform sinus= (Recessus piriformis).
The submucous tissue contains numerous mucous glands (Glandulæ
pharyngeæ). In the young subject the lymph follicles are numerous and
form a collection dorsally and between the Eustachian openings, known as
the pharyngeal tonsil.
=Blood-supply.=—External carotid, external maxillary, and
thyro-laryngeal arteries.
=Nerve-supply.=—Glosso-pharyngeal, vagus, and sympathetic nerves.
THE ŒSOPHAGUS
The œsophagus is a musculo-membranous tube, about 50 to 60 inches (ca.
125 to 150 cm.) in length, which extends from the pharynx to the
stomach. It begins in the median plane above the cricoid cartilage of
the larynx. In its course it shows several changes of direction. At the
level of the fourth cervical vertebra it inclines to the left side of
the trachea, and continues this relation to the level of the third
thoracic vertebra. Here it again gains the dorsal surface of the
trachea, and passing backward, crosses the left bronchus, being here
almost in the median plane. It continues in the mediastinum between the
lungs backward, upward, and a little to the left, to reach the hiatus
œsophageus of the diaphragm. Passing through this it terminates at once
at the cardiac orifice of the stomach, at the level of the fourteenth
thoracic vertebra, a little to the left of the median plane, and about
four or five inches (ca. 10 to 12 cm.) ventral to the vertebral column.
Viewed with reference to the frontal plane, its course is downward and
backward till it enters the thorax and passes upward to gain the dorsal
face of the trachea. For a short distance (_i. e._, to the root of the
lung) its direction is almost horizontal; behind this it passes somewhat
upward to its termination. The =cervical part= of the tube is about four
to six inches (10 to 15 cm.) longer than the =thoracic part=, while the
so-called abdominal part is about an inch (2 to 3 cm.) long.[85]
[Illustration:
FIG. 255.—CROSS-SECTION OF HEAD OF HORSE.
The section passes through the temporo-mandibular articulation, but is
slightly oblique. _1_, Corpus callosum; _2_, lateral ventricle of
brain; _3_, caudate nucleus; _4_, internal capsule; _5_, lenticular
nucleus; _6_, optic chiasma; _7_, middle cerebral artery; _8_,
sphenoidal sinuses; _9_, cavernous sinus; _10_, Eustachian tube,
inner lamina; _11_, _11_, guttural pouches; _12_, soft palate; _13_,
epiglottis; _14_, hyo-epiglottic muscle; _15_, thyro-hyoid muscle.
]
The principal =relations= of the œsophagus at its origin are: to the
cricoid cartilage below; to the guttural pouches and the ventral
straight muscles above; and to the carotid arteries laterally. In the
middle of the neck the relations are: to the left longus colli muscle
above; to the trachea internally; to the left carotid artery, vagus,
sympathetic, and recurrent nerves externally. At its entrance into the
thorax it has the trachea on its inner side; the first rib, the roots of
the brachial plexus of nerves and the inferior cervical ganglion
externally. After gaining the upper surface of the trachea, it has the
aorta on its left and the vena azygos and right vagus nerve on its right
side. In its course through the posterior mediastinum the œsophageal
trunks of the vagus nerves lie above and below it, and the œsophageal
artery is dorsal to it.
=Structure.=—The wall is composed of four coats: (1) A fibrous sheath;
(2) the muscular coat; (3) a submucous layer; (4) the mucous membrane.
The =muscular coat= is of the striped variety as far as the base of the
heart, where it rapidly changes to the unstriped type. In addition to
this change, the muscular coat becomes much thicker and firmer, while
the lumen is diminished.[86] The outer fibers are arranged
longitudinally, beginning in two bundles attached in the interval
between the arytenoid and cricoid cartilages. The inner fibers run in
two spiral strata to the terminal part of the tube, where the
arrangement is an outer longitudinal and an inner circular layer.[87]
The =mucous membrane= is pale, and is covered with squamous stratified
epithelium. It is loosely attached to the muscular coat by an abundant
submucosa, and lies in longitudinal folds which obliterate the lumen
except during deglutition.
=Blood-supply.=—Carotid, broncho-œsophageal, and gastric arteries.
=Nerve-supply.=—Vagus, glosso-pharyngeal, and sympathetic nerves.
THE ABDOMINAL CAVITY
The abdominal cavity (Cavum abdominis) is the largest of the body
cavities. It is separated from the thoracic cavity by the diaphragm and
is continuous behind with the pelvic cavity.
It is ovoid in form but somewhat compressed laterally. Its long axis
extends obliquely from the center of the pelvic inlet to the sternal
part of the diaphragm. Its dorso-ventral diameter is greatest at the
first lumbar vertebra, while its greatest transverse diameter is a
little nearer the pelvis.
The =dorsal wall= or roof is formed by the lumbar vertebræ, the lumbar
muscles, and the lumbar part of the diaphragm.
The =lateral walls= are formed by the oblique and transverse abdominal
muscles, the abdominal tunic, the anterior parts of the ilia, the
cartilages of the asternal ribs, and the parts of the posterior ribs
which are below the attachment of the diaphragm.
The =ventral wall= or floor consists of the two recti, the aponeuroses
of the oblique and transverse muscles, the abdominal tunic, and the
xiphoid cartilage.
The =anterior wall= is formed by the diaphragm, which is very deeply
concave, thus greatly increasing the size of the abdomen at the expense
of the thorax.
It should be noted that the diaphragm also concurs practically in the
formation of a considerable part of the lateral walls, since its
costal portion even during ordinary inspiration lies directly on the
ribs over a width of four or five inches (ca. 10 to 12 cm.); in
expiration this area of contact would be about twice as wide,
including about all of the fleshy rim. This fact is of clinical
importance, with reference to auscultation and percussion, and
penetrating wounds. The cupola of the diaphragm extends as far forward
as a plane through the sixth intercostal space to the right of the
heart.
There is no wall between the abdominal and pelvic cavities. The line of
demarcation here is the =terminal line= (Linea terminalis) or brim of
the pelvis; it is formed by the base of the sacrum, the ilio-pectineal
lines, and the anterior borders of the pubic bones.
The muscular walls are lined by a layer of fascia, distinguished in
different parts as: (1) the diaphragmatic fascia; (2) the transversalis
fascia; (3) the iliac fascia; (4) the deep layer of the lumbo-dorsal
fascia.
The subperitoneal or extraperitoneal connective tissue (Tela subserosa)
unites the fascia and peritoneum. It is composed of areolar tissue, more
or less loaded with fat according to the condition of the subject,
except over the diaphragm. It sends laminæ into the various peritoneal
folds.
The peritoneum, the serous membrane which lines the cavity, will be
described later.
The abdominal walls are pierced in the adult by =five apertures=. These
are: the three openings in the diaphragm which transmit the aorta,
posterior vena cava, and the œsophagus; the inguinal canals, which
contain the spermatic cord or the round ligament (in female carnivora).
In the fœtus there is the umbilical opening also.
The cavity contains the greater part of the digestive and urinary
organs, part of the internal generative organs, numerous nerves,
blood-vessels, lymph vessels and glands, ductless glands (spleen and
adrenal bodies), and certain fœtal remains.
For topographic purposes the abdomen is divided into nine regions by
imaginary planes.[88] Two of these planes are sagittal, and two are
transverse. The sagittal planes cut the middles of the inguinal
(Poupart’s) ligaments; the transverse planes pass through the last
thoracic and fifth lumbar vertebræ, or the lower end of the fifteenth
rib and the external angle of the ilium respectively. The transverse
planes divide the abdomen into three zones, one behind the other, viz.,
=epigastric=, =mesogastric=, and =hypogastric=: these are subdivided by
the sagittal planes as indicated in the subjoined table.
Left parachondriac Xiphoid Right parachondriac
Left lumbar Umbilical Right lumbar
Left iliac Prepubic Right iliac.
Other useful regional terms are: sublumbar, diaphragmatic, inguinal. The
first two require no explanation. The inguinal regions (right and left)
lie in front of the inguinal (Poupart’s) ligament. The flank is that
part of the lateral wall which is formed only of soft structures. The
depression on its upper part is termed the paralumbar fossa.
THE PERITONEUM[89]
The peritoneum is the thin serous membrane which lines the abdominal and
(in part) the pelvic cavity, and covers to a greater or less extent the
viscera contained therein. In the male it is a completely closed sac,
but in the female there are two small openings in it; these are the
abdominal orifices of the Fallopian tubes, which at their other ends
communicate with the uterus, and so indirectly with the exterior. The
peritoneal cavity is only a potential one, since its opposing walls are
normally separated only by the thin film of serous fluid (secreted by
the membrane) which acts as a lubricant.
The free surface of the membrane has a glistening appearance and is very
smooth. This is due to the fact that this surface is formed by a layer
of flat endothelial cells, and is moistened by the peritoneal fluid.
Friction is thus reduced to a minimum during the movements of the
viscera. The outer surface of the peritoneum is related to the
subperitoneal tissue, which attaches it to the abdominal wall or the
viscera.
In order to understand the general disposition of the peritoneum, we may
imagine the abdominal cavity to be empty and lined by a simple layer of
peritoneum, termed the =parietal layer= (Lamina parietalis). We may
regard the organs as beginning to develop in the subperitoneal tissue,
enlarging, and migrating into the cavity to a varying extent. In doing
so they carry the peritoneum before them, producing introversion of the
simple sac, and forming folds which connect them with the wall or with
each other. The viscera thus receive a more or less complete covering of
peritoneum, termed the =visceral layer= (Lamina visceralis). The
connecting folds are termed =omenta=, =mesenteries=, =ligaments=, etc.
They contain a varying quantity of connective tissue, fat and lymph
glands, and furnish a path for the vessels and nerves of the viscera.
Some contain unstriped muscular tissue. An omentum is a fold which
passes from the stomach to other viscera. There are three of these,
namely: (1) the =small= or =gastro-hepatic omentum= (Omentum minus),
which passes from the lesser curvature of the stomach to the liver; (2)
the =gastro-splenic omentum= (Ligamentum gastrolienale), which extends
from the greater curvature of the stomach to the spleen; (3) the =great
omentum= (Omentum majus), which passes from the greater curvature of the
stomach and from the spleen to the terminal part of the great colon and
the origin of the small colon. It does not pass directly from one organ
to the other, but forms an extensive loose sac (Figs. 278, 279). A
=mesentery= (Mesenterium) is a fold which attaches the intestine to the
dorsal wall of the abdomen. There are two mesenteries, namely: (1) the
=great mesentery= which connects the greater part of the small intestine
with the dorsal abdominal wall; (2) the =colic mesentery=, which
attaches the small colon to the dorsal abdominal wall. =Ligaments= are
folds which pass between viscera other than parts of the digestive tube,
or connect them with the abdominal wall. The term is also applied to
folds which attach parts of the digestive tract to the abdominal wall,
but do not contain their blood-vessels and nerves. In some cases (_e.
g._, the lateral and coronary ligaments of the liver) they are
strengthened by fibrous tissue; in other cases (_e. g._, the broad
ligaments of the uterus) they contain also unstriped muscular tissue.
THE PELVIC CAVITY
The pelvis is the posterior part of the trunk. It incloses the pelvic
cavity (Cavum pelvis), which communicates in front with the abdominal
cavity, the line of demarcation being the pelvic brim or terminal line.
The =dorsal wall= or roof is formed by the sacrum and first three
coccygeal vertebræ. The =lateral walls= are formed by the parts of the
ilia behind the ilio-pectineal lines and the sacro-sciatic ligaments.
The =ventral wall= or floor is formed by the pubic and ischial bones.
The boundary of the =outlet= is formed by the third coccygeal vertebra
dorsally, the ischial arch ventrally, and the posterior edges of the
sacro-sciatic ligaments and the semimembranosus muscles laterally. The
outlet is closed by the perineal fascia; this consists of superficial
and deep layers, which are attached around the margin of the outlet and
centrally to the organs at the outlet—the anus and its muscles, the
vulva (in the female), and the root of the penis (in the male).
The cavity contains the rectum, parts of the internal generative and
urinary organs, some fœtal remnants, muscles, vessels, and nerves. It is
lined by the fascia pelvis, and in part by the peritoneum.
The =pelvic peritoneum= is continuous in front with that of the abdomen.
It lines the cavity as far back as the third or fourth sacral vertebra
in the horse, where it is reflected on to the viscera, and from one
organ to another. We may therefore distinguish an anterior, peritoneal,
and a posterior, retroperitoneal part of the cavity. Along the
mid-dorsal line it forms a continuation of the colic mesentery, the
=mesorectum=, which attaches the first or peritoneal part of the rectum
to the roof. In animals in fair condition a considerable quantity of
subperitoneal and retroperitoneal fat is found on the walls and in the
various interstices.
[Illustration:
FIG. 256.—DIAGRAM OF SAGITTAL SECTION OF MALE PELVIS TO SHOW
DISPOSITION OF PERITONEUM.
_a_, Pouch between rectum and roof of cavity, continuous laterally
with _b_, recto-genital pouch; _c_, vesico-genital pouch; _d_, pouch
below bladder and its lateral ligaments. The lateral line of
reflection of the peritoneum is dotted. The area of rectum covered
by peritoneum varies widely. When the rectum is empty, the
reflection dorsally may be at the posterior end of the sacrum; when
the rectum is very full, the reflection may occur a short distance
behind the promontory.
]
[Illustration:
FIG. 257.—SCHEMATIC CROSS-SECTIONS TO SHOW ARRANGEMENT OF PELVIC
PERITONEUM OF HORSE: A, IN MALE; B, IN FEMALE.
_A_: _a_, _b_, Recto-genital pouch, _c_, _c_, vesico-genital pouch;
_d_, _d_, pouch below bladder and its lateral ligaments; _1_,
mesorectum; _2_, _2_, urogenital fold; _3_, _3_, lateral, _4_,
median ligaments of bladder; _v. d._, vas deferens; _u. m._, uterus
masculinus. _B_: _a_, _b_, recto-genital pouch; _c_, _c_,
vesico-genital pouch; _d_, _d_, pouch below bladder and its lateral
ligaments; _1_, mesorectum; _2_, _2_, broad ligaments of uterus;
_3_, _3_, lateral, _4_, median ligaments of bladder.
]
In the male the general disposition of the peritoneum here is as
follows. If traced along the dorsal wall, it is reflected at the third
or fourth sacral vertebra on to the rectum, forming the visceral
peritoneum for the first part of that tube. Laterally it is reflected in
a similar fashion. If the rectum be raised, it will be seen that the
peritoneum passes from its ventral surface and forms a transverse fold
which lies on the dorsal surface of the bladder (Fig. 272). This is the
=urogenital fold= (Plica urogenitalis). Its concave free edge passes on
either side into the inguinal canal. The ventral layer of this fold is
reflected on to the dorsal surface of the bladder near its neck. Thus
there is formed a pouch between the rectum and bladder—the
=recto-vesical pouch= (Excavatio recto-vesicalis), which is partially
subdivided by the urogenital fold into recto-genital and vesico-genital
cavities. The fold contains the vasa deferentia, part of the vesiculæ
seminales, and the uterus masculinus (a fœtal remnant). The space on
either side of the rectum is occupied by coils of the small colon and
the pelvic flexure of the great colon usually. If the bladder is now
raised, it is seen that the peritoneum passes from its ventral surface
on to the pelvic floor, forming a median fold, the so-called =middle
ligament= (Plica umbilicalis media). It also forms on each side a
lateral fold, the =lateral ligament= (Plica umbilicalis lateralis),
which contains in its edge the so-called =round ligament= (Ligamentum
teres)—the partially occluded umbilical artery, which is a large vessel
in the fœtus.
[Illustration:
FIG. 258.—STOMACH OF HORSE, PARIETAL SURFACE, WITH FIRST PART OF
DUODENUM.
Fixed _in situ_ when full but not distended. The larger branches of
the anterior gastric artery with two satellite veins are shown.
]
In the female the arrangement is modified by the presence of the uterus;
the urogenital fold is very large, so as to inclose the uterus and a
small part of the vagina. It forms two extensive folds, the =broad
ligaments of the uterus= (Ligamenta lata uteri), which attach that organ
to the sides of the pelvic cavity and the lumbar part of the abdominal
wall (Fig. 271). It thus divides the recto-vesical pouch completely into
dorsal and ventral compartments—the =recto-genital pouch= (Excavatio
recto-uterina), and the =vesico-genital= pouch (Excavatio
vesico-uterina).
Further details will be given in the description of the pelvic viscera.
THE STOMACH
The stomach (Ventriculus) is the large dilatation of the alimentary
canal between the œsophagus and the small intestine. It is a sharply
curved, U-shaped sac, the right branch being, however, much shorter than
the left one. The convexity is directed ventrally. When moderately
distended, there is often a slight constriction which indicates the
division into right and left sacs. It is relatively small, and is
situated in the dorsal part of the abdominal cavity behind the diaphragm
and liver, mainly to the left of the median plane.
[Illustration:
FIG. 259.—STOMACH OF HORSE, VISCERAL SURFACE, WITH FIRST PART OF
DUODENUM.
Fixed _in situ_ when full but not distended. The posterior gastric
artery and its larger branches with two satellite veins are shown.
]
It presents for description two surfaces, two curvatures, and two
extremities. The =parietal surface= (Facies parietalis) is convex and is
directed forward, upward, and toward the left; it lies against the
diaphragm and liver. The =visceral surface= (Facies visceralis), also
convex, faces in the opposite direction; it is related to the terminal
part of the large colon, the pancreas, the small colon, and the small
intestine. The =lesser curvature= (Curvatura minor) is very short,
extending from the termination of the œsophagus to the junction with the
small intestine. When the stomach is _in situ_, its walls are here in
contact, and the cardia and pylorus close together. The =greater
curvature= (Curvatura major) is very extensive. From the cardia it is
first directed upward and curves over the left extremity; it then
descends, passes to the right, crosses the median plane, and curves
upward to end at the pylorus. Its left portion is related to the spleen,
while its ventral portion rests on the left divisions of the great
colon. The =left extremity= or =saccus cæcus= is a rounded cul-de-sac
which lies under the upper ends of the fourteenth, fifteenth, and
sixteenth ribs and the diaphragm.[90] It is related to the pancreas
behind and the base of the spleen externally. The =right= or =pyloric
extremity= is much smaller and is continuous with the duodenum, the
junction being indicated by a marked constriction. It lies on the liver,
a little to the right of the median plane, and a little lower than the
cardiac opening. About two or three inches (ca. 5 to 8 cm.) from the
pylorus there is a constriction which marks off the =antrum pylori= from
the rest of the right sac. The =œsophageal orifice= or =cardia= is
situated at the left extremity of the lesser curvature, but about eight
to ten inches (ca. 20 to 25 cm.) from the left extremity. The œsophagus
joins the stomach very obliquely. The opening is closed by the sphincter
cardiæ and numerous folds of mucous membrane. The =pyloric orifice=
communicates with the duodenum. Its position is indicated externally by
a distinct constriction. Internally it presents a circular ridge
produced by a ring of muscular tissue—the =sphincter pylori=.
The stomach is held in position mainly by the pressure of the
surrounding viscera and by the œsophagus. The following peritoneal folds
connect it with the adjacent parts:
1. The =gastro-phrenic ligament= (Lig. gastrophrenicum) connects the
great curvature, from the cardia to the left extremity, with the crura
of the diaphragm. This leaves a narrow area uncovered with peritoneum,
and here the stomach is attached to the diaphragm by loose connective
tissue.
2. The =small= or =gastro-hepatic omentum= (Omentum minus) connects the
lesser curvature and the first part of the duodenum with the liver below
the œsophageal notch and the portal fissure.
3. The =gastro-splenic omentum= (Lig. gastrolienale) passes from the
left part of the great curvature to the hilus of the spleen.
4. The =great= or =gastro-colic omentum= (Omentum majus) connects the
ventral part of the great curvature and the first curve of the duodenum
with the terminal part of the great colon and the initial part of the
small colon.
5. The =gastro-pancreatic fold= (Plica gastro-pancreatica) extends from
the left sac above the cardia to the duodenum. It is attached dorsally
to the liver and vena cava, ventrally to the pancreas.
[Illustration:
FIG. 260.—EVERTED STOMACH OF HORSE FROM WHICH THE MUCOUS MEMBRANE HAS
BEEN REMOVED.
_O_, Œsophagus; _D_, duodenum; _b_, circular layer; _c′_, internal
oblique fibers; _c″_, loop around cardia; _c‴_, transition of
internal to external oblique fibers; _d_, fibers connecting the two
branches of the cardiac loop; _p_, antral sphincter; _p′_, pyloric
sphincter. (Ellenberger-Baum, Anat. d. Haustiere.)
]
The stomach of the equidæ is relatively small, its capacity varying from
two to four gallons (ca. 8 to 15 liters).
The size, form, and position of the stomach are subject to
considerable variation. When the stomach is nearly empty the saccus
cæcus contains only gas and is strongly contracted; the middle portion
(physiological fundus) contains the ingesta and preserves its rounded
character, while the pyloric portion is contracted. When distended the
middle portion settles down some four or five inches, pushing back
coils of the small colon and small intestine which may lie between the
great curvature and the large colon, and also pushing to the left or
right the left dorsal part of the great colon; the spleen, small
colon, and small intestines are pushed back by the distention of the
left sac.
=Structure.=—The wall is composed of four coats—serous, muscular,
submucous, and mucous.
The =serous coat= (Tunica serosa) covers the greater part of the organ
and is closely adherent to the muscular coat except at the curvatures.
It partially bridges over the lesser curvature, and covers here elastic
tissue which assists in retaining the bent form of the stomach. The
peritoneal folds have been described.
The =muscular coat= consists of three incomplete layers, an external of
longitudinal, a middle of circular, and an internal of oblique fibers.
The layer of =longitudinal fibers= (Stratum longitudinale) is very thin
and exists only along the curvatures and at the antrum. At the lesser
curvature it is continuous with the longitudinal fibers of the
œsophagus. On the antrum pylori it forms a well developed complete
layer. The layer of =circular fibers= (Stratum circulare) exists only on
the right sac. At the pyloric orifice it forms a thick ring—the =pyloric
sphincter=. Another ring, the antral sphincter, is found at the left end
of the antrum pylori. The =oblique fibers= (Fibræ obliquæ) are arranged
in two layers; the external stratum covers the left sac and is a
continuation (in part) of the longitudinal fibers of the œsophagus; the
internal stratum is found also on the left sac, and exchanges fibers
with the circular and external oblique layers. It forms a remarkable
loop around the cardiac orifice, constituting a powerful =cardiac
sphincter= (Sphincter cardiæ).
[Illustration:
FIG. 261.—FRONTAL SECTION OF STOMACH AND FIRST PART OF DUODENUM OF
HORSE.
_C_, Cardiac orifice. Photograph of specimen fixed _in situ_.
]
The =submucous coat= is a layer of loose connective tissue which
connects the muscular and mucous coats; in it the vessels and nerves
ramify before entering the mucosa.
The =mucous coat= is clearly divided into two parts. That which lines
the left sac resembles the œsophageal mucous membrane, and is termed
=œsophageal= or =cuticular=. It is white in color, destitute of glands,
and covered with a thick, squamous, stratified epithelium. At the
cardiac orifice it presents numerous folds which occlude the
opening.[91] It terminates abruptly at an elevated, denticulated,
sinuous line, termed the =cuticular ridge= (Margo plicatus). Below and
to the right of this line the mucous membrane has a totally different
character, being soft and velvety to the touch, and covered by a mucoid
secretion. It is glandular, and three zones may be recognized, although
no sharp line of demarcation exists. A narrow zone next to the cuticular
ridge has a yellowish-gray color, and contains short tubular =cardiac
glands= (Cardiac gland region). Next to this is a large area which has a
mottled reddish-brown color, and contains =fundus glands= (fundus gland
region). This part of the mucous membrane is thick and very vascular,
and corresponds to the fundus of the stomach in man and the dog. The
remainder of the mucous membrane has a reddish-gray color and contains
branched, tubular, =pyloric glands= (pyloric gland region); it
corresponds to the pyloric portion of man and the dog.
The folding of the stomach wall at the lesser curvature produces a
prominent ridge which projects into the cavity of the stomach. Circular
ridges occur at the antral and pyloric sphincters.
=Blood-vessels and Nerves.=—The stomach receives blood from all the
branches of the cœliac artery. The gastric veins drain into the portal
vein. The nerves are derived from the vagus and sympathetic nerves.
[Illustration:
FIG. 262.—DIAGRAM OF ZONES OF MUCOUS MEMBRANE OF STOMACH OF HORSE.
]
THE SMALL INTESTINE
The =small intestine= (Intestinum tenue) is the tube which connects the
stomach with the large intestine. It begins at the pylorus and
terminates at the lesser curvature of the cæcum. Its average length is
about seventy feet (ca. 22 meters). When distended its diameter varies
from two to four inches (5 to 10 cm.). Its capacity is about twelve
gallons (40 to 50 liters).
It is clearly divisible into a =fixed= and a =mesenteric= or floating
portion. The fixed portion is termed the duodenum, while the mesenteric
portion (Intestinum tenue mesenteriale) is arbitrarily divided into
parts termed the jejunum and ileum.[92]
The =duodenum= is about three to four feet (ca. 1 to 1.25 m.) long. Its
shape is somewhat like a horseshoe, the convexity being directed toward
the right. The =first part= is directed to the right and forms an
ᔕ-shaped curve. The convexity of the first part of the curve is dorsal,
of the second ventral. It lies on the middle and right lobes of the
liver, and presents two dilatations (Ampullæ) with a constriction
between them. The duodenal angle or head of the pancreas lies in the
concavity of the second curve, and here, five to six inches (ca. 12 to
15 cm.) from the pylorus, the pancreatic duct and the bile-duct pierce
the bowel wall. The =second part= passes upward and backward on the
right lobe of the liver and, on reaching the right kidney and the base
of the cæcum, it curves toward the median plane, opposite the last rib.
The =third part= passes almost transversely from right to left behind
the base of the cæcum, crosses the median plane under the third and
fourth lumbar vertebræ, and turns forward to become continuous with the
jejunum under the left kidney. The sacculations of the first part have a
diameter of three to four inches (ca. 7.5 to 10 cm.).
It is attached by a short peritoneal fold termed the =mesoduodenum=.
This fixes the first part of the duodenum closely to the liver and the
right dorsal part of the colon; the remainder is somewhat less closely
attached by it to the cæcum and right kidney, the sublumbar muscles, and
(more closely) to the terminal part of the great colon and the first
part of the small colon.[93]
[Illustration:
FIG. 263.—TOPOGRAPHY OF VISCERA OF HORSE, LEFT VIEW.
_1.R._, First thoracic vertebra; _1.L._, first lumbar vertebra;
_2.K._, second sacral spine; _S._, scapula; _A._, humerus; _St._,
sternum; _B._, ilium; _O._, femur; _L._, lung in complete
expiration; _l._, dotted line indicating contour of lung in
inspiration; _H_, pericardium; _Z_, costal part of diaphragm; _Z′_,
tendinous center of diaphragm; _l.N._, left kidney; _l.v.C._, left
ventral colon; _v.Q._, sternal flexure of colon; _d.Q._,
diaphragmatic flexure of colon; _D._, small intestine; _M._, small
colon; _M′_, rectum; _a_, coccygeus muscle; _b_, retractor ani; _c_,
_c_, sphincter ani externus; _d_, constrictor vulvæ; _e_,
sacro-coccygeus inferior; _f_, anterior gluteal artery; _g_,
internal pudic artery; _h_, abdominal wall in section. (After
Ellenberger, in Leisering’s Atlas, reduced.)
]
The =jejunum= and =ileum= together (Jejuno-ileum) constitute the
mesenteric or floating portion of the small intestine. No distinct point
exists at which to make the demarcation. With the exception of the last
two or three feet, the mesenteric part of the intestine varies so much
in position that only a general statement can be made. It lies in
numerous coils (Ansæ) mingled with those of the small colon, chiefly in
the dorsal part of the left half of the abdomen, from the visceral
surface of the stomach to the pelvis. It may insinuate itself between
the left portions of the colon and the abdominal wall; also between the
ventral portions of the colon, reaching the floor of the abdomen. The
terminal part of the intestine (ileum) ascends almost vertically, a
little to the right of the median plane, to open into the cæcum at the
lesser curvature of its base. The average diameter of the jejuno-ileum
is about two and a half to three inches (ca. 6 to 7 cm.). In the cadaver
one finds most of the tube presenting irregular constricted and dilated
parts. The last three or four feet (ca. 1 meter) are usually tightly
contracted, resembling somewhat the terminal part of the œsophagus. This
part may be termed the ileum.
The mesenteric part is connected with the dorsal abdominal wall by the
=great mesentery=. This is a wide fan-shaped fold, consisting of two
layers of peritoneum, between which the vessels and nerves reach the
bowel; it also contains the mesenteric lymph glands and some fat. The
visceral border of the mesentery contains the intestine, while the
parietal border or =root= (Radix mesenterii) is attached to a small area
around the great mesenteric trunk under the first and second lumbar
vertebræ. The root is thick, as it contains a large number of vessels
and nerves placed close together. The mesentery is short at first, but
soon reaches a length of one and a half to two feet (ca. 50
cm.)—sufficient to allow coils of the intestine to reach the abdominal
floor, the pelvic cavity, or even to descend into the scrotum through
the inguinal canal. Near its termination the intestine (ileum) leaves
the border of the mesentery, so that the latter has a free edge which
passes to the cæcum.
=Structure.=—The wall consists of four coats—serous, muscular,
submucous, and mucous, enumerated from without inward.
The =serous coat= is complete except at the mesenteric edge, where the
vessels and nerves reach the bowel.
The =muscular coat= consists of an outer longitudinal and an inner
circular layer, the latter being the thicker. In the last few feet of
the intestine the muscular coat is very thick, and being usually firmly
contracted in the dead subject, gives the impression that this part of
the bowel is of smaller caliber; such, however, is not the case during
life.
[Illustration:
FIG. 264.—DIAGRAM OF SECTION OF DIVERTICULUM DUODENI OF HORSE.
Solid line indicates mucous membrane.
]
The =submucous coat= is a layer of areolar tissue in which the vessels
and nerves ramify. It contains also the duodenal glands and the bases of
the solitary glands and Peyer’s patches.
The =mucous membrane= is soft and velvety. It has a grayish or
yellowish-red color and is very vascular. About five or six inches from
the pylorus it forms a pouch, the =diverticulum duodeni=, in which the
pancreatic and hepatic ducts open. On a small papilla opposite this is
the termination of the accessory pancreatic duct. At the ileo-cæcal
opening the mucous membrane projects slightly into the cavity of the
cæcum, forming the =ileo-cæcal valve=. The free surface is thickly beset
with villi, small projections of the mucous membrane which can be seen
well by placing a piece of the membrane in water. They are relatively
short and thick and have a distinct neck in the horse. Each contains a
central lymph vessel (lacteal), and around this a plexus of capillaries,
lymphoid tissue, and unstriped muscle-fibers. They are important agents
in absorption from the contents of the intestine. The epithelium is
columnar, with many goblet cells. Underneath the basement membrane is a
layer of unstriped muscle-fibers, the =muscularis mucosæ=.
The glands of the small intestine are of three kinds:
1. The =intestinal glands= (Glandulæ intestinales Lieberkuehni) are
found throughout. They are simple tubular glands which open between the
villi.
2. The =duodenal glands= (Glandulæ duodenales Brunneri) are found in the
first twenty feet (ca. 6 meters) of the bowel. They are racemose glands,
and are situated in the submucosa, so that their ducts perforate the
muscularis mucosæ and the mucous membrane.
3. The =lymph follicles= (Noduli lymphatici) are found either scattered
or in groups. In the former case they are termed =solitary glands=
(Noduli lymphatici solitarii), in the latter =Peyer’s patches= (Noduli
lymphatici aggregati). The solitary glands are about the size of a
millet-seed or a small sago grain. Peyer’s patches are situated chiefly
along the surface opposite to the mesenteric attachment and begin about
three or four feet from the pylorus. They number one to two hundred, and
are usually one to two inches (2 to 5 cm.) long and a quarter of an inch
to one-half inch (ca. 2 to 14 mm.) wide. Larger ones occur in the
terminal part, where one patch may have a length of seven to fifteen
inches (ca. 17 to 38 cm.) and a width of half an inch to one inch (ca. 5
to 25 mm.) in young horses (Ellenberger). They undergo atrophy in old
subjects.
[Illustration:
FIG. 265.—PEYER’S PATCHES OF SMALL INTESTINE OF HORSE.
]
=Vessels and Nerves.=—The =arteries= of the small intestine come from
the cœliac and anterior mesenteric arteries. The =veins= go to the
portal vein. The =lymph vessels= are numerous and go to the mesenteric
lymph glands. The =nerves= are derived from the vagus and sympathetic
through the solar plexus.
THE LARGE INTESTINE
The large intestine (Intestinum crassum) extends from the termination of
the ileum to the anus. It is about twenty-five feet (ca. 7.5 to 8 in.)
in length. It differs from the small intestine in its greater size, in
being sacculated, for the most part, possessing longitudinal bands, and
having a more fixed position. It is divided into cæcum, great colon,
small colon, and rectum.
THE CÆCUM
The =cæcum= (Intestinum cæcum) is a great cul-de-sac intercalated
between the small intestine and the colon. It has a remarkable size,
shape, and position in the horse. Its length is three to four feet (ca.
1 to 1.25 m.), and its capacity about seven to eight gallons (ca. 25 to
30 liters). It is conical in form, and is curved somewhat like a
reversed comma. It is situated almost entirely to the right of the
median plane, extending from the right iliac and sublumbar regions to
the abdominal floor behind the xiphoid cartilage. Both extremities are
blind, and the two orifices are placed close together on the concave
curvature. It presents for description a base, a body, and an apex.
The =base= (Saccus cæcus) extends from about the thirteenth intercostal
space backward almost to the pelvic inlet. Its greater curvature is
dorsal, its lesser ventral; connected with the latter are the
termination of the ileum and the origin of the colon. The =body= (Corpus
cæci) extends downward and forward from the base and rests largely on
the ventral wall of the abdomen. Its lesser curvature is about parallel
with the costal arch and about five to six inches (10 to 15 cm.) below
it. The =apex= (Apex cæci) lies usually on the abdominal floor about a
hand’s length behind the xiphoid cartilage.
The base is attached dorsally by connective tissue and peritoneum on the
ventral surface of the pancreas and right kidney, the psoas muscles, and
the iliac fascia; internally, it is attached to the terminal part of the
great colon, and ventrally to the origin of the great colon. The body is
attached dorsally to the first part of the colon by the cæco-colic fold.
The apex is free, and consequently may vary in position.
[Illustration:
FIG. 266.—DIAGRAM OF CÆCUM AND LARGE COLON OF HORSE.
]
The cæcum has four =longitudinal bands= (Tæniæ), situated on the dorsal,
ventral, right, and left surfaces; these cause four rows of
=sacculations= (Haustra). The ventral band is entirely exposed or free
(Tænia libera); the dorsal band is free on the apex. The cæcal arteries
are placed on the other two. The right or parietal surface of the cæcum
is related chiefly to the right abdominal wall, the diaphragm, duodenum,
and liver. The left or visceral surface lies against the left divisions
of the colon, the root of the great mesentery, and the small intestine.
The =ileo-cæcal orifice= (Ostium ileocæcale) is situated in the lesser
curvature of the base, about four or five inches (ca. 10 to 12 cm.) to
the right of the median plane and about opposite the lower end of the
last rib. The end of the ileum is partially telescoped into the cæcum,
so that the orifice is surrounded by a fold of mucous membrane, forming
the =ileo-cæcal valve= (Valvula ileocæcalis). The peritoneum and
longitudinal muscle-fibers do not take part in its formation.
The =cæco-colic orifice= (Ostium cæcocolicum) is placed above and
external to the preceding one; the interval between them is only about
two inches (ca. 5 cm.), and they are separated by a distinct ridge which
projects into the interior of the cæcum. The orifice is slit-like and is
small in relation to the size of the cæcum and colon. It has a =valvular
fold= (Valvula cæcocolica) at its lower margin and a =muscular ring=
(Sphincter cæci). Large crescentic or semilunar folds (Plicæ cæci)
project into the cavity of the bowel, and between these are large
pouches (Cellulæ cæci).
[Illustration:
FIG. 267.—TOPOGRAPHY OF VISCERA OF HORSE, RIGHT VIEW.
_1 R._, First thoracic vertebra; _1 L._, first lumbar vertebra; _2
K._, second sacral spine; _S._, scapula; _A._, humerus; _St._,
sternum; _B._, ilium; _O._, femur; _L._, right lung; _H._,
pericardium; _Z._, diaphragm (pars costalis); _r.v.C._, right
ventral colon; _v.Q._, sternal flexure of colon; _d.Q._,
diaphragmatic flexure of colon; _C._, body of cæcum; _C′._, base of
cæcum; _C″._, apex of cæcum; _D._, small intestine; _F._, pelvic
flexure of colon; _M._, rectum; _a._, abdominal wall in section;
_b_, duodenum; _c_, coccygeus muscle; _d_, retractor ani; _e_, _e′_,
sphincter ani externus; _f_, anterior gluteal artery; _g_, internal
pudic artery; _h_, xiphoid cartilage. (After Ellenberger, in
Leisering’s Atlas.)
]
=Vessels and Nerves.=—The cæcal arteries come from the great mesenteric
artery. The veins go to the portal vein. The nerves are derived from the
great mesenteric plexus of the sympathetic.
THE GREAT COLON
[Illustration:
FIG. 268.—ILEO-CÆCAL ORIFICE OF HORSE.
_a_, Mucous membrane of cæcum; _b_, ileum; _c_. ileo-cæcal orifice;
_d_, fold of mucous membrane. (After P. Schumann.)
]
The =great colon= (Colon crassum) begins at the cæco-colic orifice, and
terminates by joining the small colon behind the saccus cæcus of the
stomach. It is ten to twelve feet (ca. 3 to 3.7 m.) long, and its
average diameter (exclusive of its narrowest part) is about eight to ten
inches (ca. 20 to 25 cm.). Its capacity is more than double that of the
cæcum. When removed from the abdomen, it consists of two parallel
portions, which are connected by peritoneum and partially by areolar
tissue also. _In situ_, it is folded so that it consists of four parts,
which are designated according to their position or numerically. The
three bent connecting parts are termed the flexures. The first, =right
ventral part= (Colon ventrale dextrum), begins at the cæco-colic orifice
about opposite the middle of the last rib, passes downward and forward
along the right costal arch, and reaches the floor of the abdomen. Over
the xiphoid cartilage it bends sharply to the left and backward, forming
the =sternal flexure= (Flexura diaphragmatica ventralis). The second,
=left ventral part= (Colon ventrale sinistrum), passes backward on the
left part of the abdominal floor, and, on reaching the pelvic inlet,
bends sharply dorsally and forward, forming the =pelvic flexure=
(Flexura pelvina). This is continued by the third, =left dorsal part=
(Colon dorsale sinistrum), which passes forward above the left ventral
portion. On reaching the stomach, diaphragm, and left lobe of the liver,
it turns to the right, forming the =diaphragmatic= or =gastro-hepatic
flexure= (Flexura diaphragmatica dorsalis). The fourth or =right dorsal
part= (Colon dorsale dextrum) passes backward above the first portion,
and on reaching the inner or left surface of the base of the cæcum it
turns upward and to the left behind the left sac of the stomach; here it
becomes constricted, and joins the small colon below the left kidney.
[Illustration:
FIG. 269.—ABDOMINAL VISCERA OF HORSE, VENTRAL VIEW.
The ventral wall and part of the lateral walls of the abdomen are
removed. _C_, Cæcum; _r.v.C._, right ventral part of colon; _v.Q._,
sternal flexure of colon; _l.v.C._, left ventral part of colon;
_d.Q._, diaphragmatic flexure of colon; _D_, small intestine; _M_,
small colon; _a_, ventral free band of cæcum; _b_, inner band of
cæcum; _c_, lateral band of ventral part of colon; _d_, ventral band
of ventral part of colon; _e_, point of elbow; _f_, anterior end of
sternal region; _g_, xiphoid cartilage; _h_, teats. (After
Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
The =caliber= of the great colon varies greatly at different points. At
its origin it is only about two to three inches (ca. 5 to 7.5 cm.) in
diameter. This soon increases to about eight to ten inches (ca. 20 to 25
cm.) for the ventral portions. Beyond the pelvic flexure the diameter is
reduced to about three or four inches (ca. 8 to 9 cm.). Near the
diaphragmatic flexure the caliber rapidly increases, and reaches its
maximum in the last division, where it may be about twenty inches (50
cm.) in its widest part. This is succeeded by a somewhat funnel-shaped
terminal contraction.
[Illustration:
FIG. 270.—TOPOGRAPHY OF VISCERA OF HORSE, RIGHT SIDE, DEEPER VIEW.
_1.R._, First thoracic vertebra; _1.L._, first lumbar vertebra; _2.
K._, second sacral spine; _S_, scapula; _A_, humerus; _B_, ilium;
_O._, femur; _Sch._, pubis; _Si._, ischium; _St._, sternum; _L._,
right lobe of liver; _r.N._, right kidney; _C._, body, _C′._, base,
_C″._, apex of cæcum; _r.v.C._, right ventral colon; _v.Q._, sternal
flexure of colon; _d.Q._, diaphragmatic flexure of colon; _r.d.C._,
right dorsal colon; _F._, pelvic flexure of colon; _D._, small
intestine; _H._, urinary bladder; _M._, rectum; _a_, left ventricle;
_a′_, right ventricle; _b_, _b′_, right coronary artery; _c_, left
atrium; _c′_, right atrium; _d_, small (left) coronary vein; _e_,
vena azygos; _f_, anterior vena cava; _g_, posterior vena cava; _h_,
sinus venosus; _i_, right phrenic nerve; _k_, right vagus, with its
dorsal (_k′_) and ventral (_k″_) divisions; _l_, aorta; _m_,
œsophagus; _n_, trachea; _o_, diaphragm (median section); _p_, right
lateral ligament of liver; _q_, duodenum; _r_, dotted line
indicating position in median section of diaphragm in inspiratory
phase; _s_, recto-coccygeus; _t_, suspensory ligament of rectum;
_u_, sphincter ani; _v_, vesicula seminalis; _w_, prostate; _x_,
bulbo-urethral (Cowper’s) gland; _y_, urethra; _z_, abdominal wall;
_z′_, xiphoid cartilage. (After Ellenberger, in Leisering’s Atlas,
reduced.)
]
The first part of the great colon is attached to the lesser curvature of
the cæcum by two layers of peritoneum which form the =cæco-colic fold=.
The ventral parts of the colon are similarly connected to the dorsal
parts of the same side by the mesocolon. The right portions are united
also by areolar tissue and muscular fibers, the surface of contact being
about four or five inches (ca. 10 to 12 cm.) wide; the left portions are
attached to each other by a peritoneal fold wide enough to allow them to
be drawn apart five or six inches (ca. 12 to 15 cm.) near the pelvic
flexure. The terminal part of the colon is attached by peritoneum and
areolar tissue to the ventral surface of the pancreas dorsally and to
the base of the cæcum externally. It is connected indirectly with the
diaphragm and liver by means of a fold derived from the right lateral
ligament of the liver.
The =relations= are complex, but the more important facts are as
follows: The ventral portions (first and second) have extensive contact
with the abdominal wall ventrally and laterally. On the right side the
colon is almost entirely excluded from contact with the flank by the
cæcum; on the left side it has no contact with the upper part of the
flank, being excluded here by coils of the small colon and small
intestine. Dorsally the chief relations are to the stomach, duodenum,
liver, pancreas, small colon, small intestine, aorta, vena cava, and
portal vein. Since there are no transverse attachments of the right and
left portions, and the latter have no attachment to the wall, they are
subject to considerable displacement.[94] The pelvic flexure is variable
in position, but usually it is directed to the right across the pelvic
inlet.
[Illustration:
FIG. 271.—TOPOGRAPHY OF VISCERA OF HORSE, LEFT DEEP VIEW.
_1R._, First thoracic vertebra; _1L._, first lumbar vertebra; _2K._,
second sacral spine; _S._, scapula; _A._, humerus; _B._, ilium;
_F._, femur; _Sch._, pubis; _Si._, ischium; _L._, liver (left lobe);
_Ma._, stomach, the posterior contour of which is indicated by
dotted line _x_; _Mi._, spleen; _l.N._, left kidney, concealed part
indicated by dotted line; _M._, small colon; _D._, small intestine,
parts of which have been removed; _l. d. C._, left dorsal colon;
_l.v.C._, left ventral colon; _v.Q._, sternal flexure; _d.Q._,
diaphragmatic flexure; _O._, left ovary; _U._, cornu uteri; _L.1._,
broad ligament; _M′._, rectum; _V._, vagina; _H._, bladder; _a_,
left ventricle; _a′_, right ventricle; _b_, left coronary artery
with descending (_b′_) and circumflex (_b″_) branches; _c_, left
auricle; _d_, pulmonary artery (cut); _e_, aorta; _f_, ligamentum
arteriosum; _g_, brachiocephalic trunk (anterior aorta); _h_,
trachea; _i_, œsophagus; _k_, left phrenic nerve; _l_, diaphragm in
median section; _m_, Fallopian tube; _n_, bursa ovarica; _o_,
urethra; _p_, cut edge of broad ligament; _q_, line of reflection of
pelvic peritoneum; _r_, recto-coccygeus; _s_, so-called suspensory
ligament of rectum; _t_, sphincter ani internus; _u_,
sacro-coccygeus inferior; _v_, abdominal wall in section; _w_,
xiphoid cartilage. (After Ellenberger, in Leisering’s Atlas.)
]
The ventral portions of the colon have four longitudinal =muscular
bands= (Tæniæ) which produce four rows of sacculations (Haustra). On the
first part the external and internal bands are free; the dorsal band is
covered by the adhesion to the overlying dorsal division, while the
ventral band is largely covered by the adhesion to the cæcum. On the
left ventral part the external and ventral bands are free; of the two
dorsal bands, the inner one is concealed by the mesocolon, the outer one
is chiefly free. The pelvic flexure has a band on its lesser curvature,
which is continued on to the third part, concealed by the peritoneal
attachment; these parts are practically non-sacculated. Near the
diaphragmatic flexure two other bands appear, so that the flexure has
three bands; two of these are dorsal and free, the third is ventral and
concealed. The last part has three bands, of which the inner and outer
ones are free, the ventral one covered.
THE SMALL COLON
The =small colon= (Colon tenue) begins at the termination of the great
colon, behind the saccus cæcus of the stomach and below the left kidney,
and is continued by the rectum at the pelvic inlet. Its length is about
ten to twelve feet (ca. 3.5 m.), and its diameter about three to four
inches (ca. 7.5 to 10 cm.).
[Illustration:
FIG. 272.—PELVIC INLET AND POSTERIOR PART OF ABDOMINAL WALL OF HORSE,
VIEWED FROM THE FRONT.
The left inguinal canal is partially opened. The peritoneum is
retained except over a part of the left cremaster muscle. The
sublumbar region is greatly foreshortened in this view. _a_, _a′_,
Kidneys; _a″_, adrenal; _b._, ureter; _c_, renal artery; _d_, aorta;
_e_, cœliac artery (cut); _f_, anterior mesenteric artery (cut);
_g_, posterior mesenteric artery; _h_, circumflex iliac artery; _i_,
external iliac artery; _k_, internal iliac artery; _l_, spermatic
artery in peritoneal fold (plica vasculosa), _m_; _n_, vas deferens,
inclosed in urogenital fold, _o_; _p_, urinary bladder; _q_, round
ligament of bladder; _r_, middle ligament of bladder; _s_, rectum;
_t_, margin of vaginal ring; _u_, posterior abdominal artery; _v_,
external pudic artery; _w_, rectus abdominis muscle; _x_,
transversus and obliquus internus abdominis; _y_, _y′_, cremaster
externus; _z_, posterior vena cava (cut). (After Ellenberger-Baum,
Top. Anat. d. Pferdes.)
]
Its coils lie in the space between the stomach and the pelvic inlet,
dorsal to the left portions of the great colon. They are mingled with
those of the small intestine, from which they are easily distinguished
by the tæniæ and sacculation.
It is attached to the sublumbar region by the =colic mesentery=, and to
the termination of the duodenum by a short peritoneal fold (Lig.
duodeno-colicum). The great omentum is also attached to the origin of
the bowel. The colic mesentery is narrow at its origin, but soon reaches
a width of about three feet (ca. 80 to 90 cm.). Its parietal border is
attached along a line extending from the ventral surface of the left
kidney to the sacral promontory; it is continuous in front with the root
of the great mesentery, and behind with the mesorectum.
There are two =tæniæ= and two rows of sacculations. Of the tæniæ, one is
free, the other concealed by the mesentery. When the bowel is hardened
_in situ_ its lumen between the pouches is reduced to a narrow slit.
THE RECTUM
The =rectum= (Intestinum rectum) is the terminal part of the bowel; it
extends from the pelvic inlet to the anus.[95] Its length is about one
foot (ca. 30 cm.). Its direction may be straight or oblique. The first
or =peritoneal part= of the rectum is like the small colon, and is
attached by a continuation of the colic mesentery termed the
=mesorectum=. The second or =retroperitoneal part= forms a flask-shaped
dilatation termed the =ampulla recti=; it is attached to the surrounding
structures by connective tissue and muscular bands.
The first part of the rectum is related to the small colon and the
pelvic flexure of the great colon. It is frequently deflected to the
left by the latter. The second part of the rectum is related dorsally
and laterally to the pelvic wall. Ventrally the relations differ in the
two sexes. In the male they are the bladder, the terminal parts of the
vasa deferentia, the vesiculæ seminales, the prostate, the
bulbo-urethral (Cowper’s) glands, and the urethra. In the female they
are the uterus, vagina, and vulva.[96]
=Structure of the Large Intestine.=—The =serous coat= covers the
different parts in varying degrees. It does not cover (_a_) the opposed
surfaces of the cæcum and colon which are between the layers of the
cæco-colic fold and mesocolon; (_b_) the areas of attachment of the
cæcum and colon to the pancreas, right kidney, and sublumbar region;
(_c_) the second part of the rectum.
The =muscular coat= consists of longitudinal and circular fibers. The
bulk of the former is in the bands already described. Some of the
circular fibers pass from one part of the colon to another, where they
are attached to each other, forming the fibræ transversæ coli. The
muscular coat of the second part of the rectum presents special
features. The longitudinal layer of fibers is very thick and consists of
large bundles, loosely united. A large band, the =recto-coccygeus=, is
detached from it on either side, and passes upward and backward to be
inserted into the fourth and fifth coccygeal vertebræ.
The =submucous tissue= is abundant in the wall of the rectum, so that
the mucous membrane is loosely attached to the muscular coat, and forms
numerous folds when the bowel is empty.
The =mucous membrane= of the large intestine is thicker and darker in
color than that of the small intestine. It forms large crescentic or
semilunar folds corresponding to the external constrictions. It has no
villi, Brunner’s glands, or Peyer’s patches. The =intestinal glands= (of
Lieberkühn) are large and numerous. =Solitary glands= are also numerous,
especially at the apex of the cæcum and in the left dorsal part of the
colon.
=Blood-supply.=—Greater and lesser mesenteric and internal pudic
arteries. The veins go to the portal vein.
=Nerve-supply.=—Mesenteric plexus of the sympathetic nerves.
The =anus= is the terminal orifice of the alimentary canal. It is
situated below the root of the tail, where it forms a round projection,
with a central depression when contracted. It is covered externally by
an integument which is thin, hairless, and provided with numerous
sebaceous and sweat glands. The mucous lining is pale, glandless, and
covered with a thick, squamous, stratified epithelium.
There are three muscles of the anus.
1. The =sphincter ani internus= is merely a terminal thickening of the
circular coat of the bowel.
2. The =sphincter ani externus= is a broad band of striped muscle-fibers
outside the internal sphincter. Some fibers are attached to the
coccygeal fascia above, others to the perineal fascia below. Its action
is to close the anus.
3. The =retractor ani= (M. levator ani) is a flat muscle which lies
between the rectum and the sacro-sciatic ligament. It arises from the
superior ischiatic spine and the sacro-sciatic ligament, and ends under
the external sphincter. Its action is to reduce the partial prolapse
which the anus undergoes during defecation.
The suspensory ligament of the anus is a band of unstriped muscle which
arises from the first coccygeal vertebra, passes downward over the
retractor, and unites with its fellow below the anus. In the male it is
largely continued by the retractor penis muscle; in the female it blends
with the constrictor vulvæ. It may act as an accessory sphincter of the
anus.
=Blood-supply.=—Internal pudic artery.
=Nerve-supply.=—Hæmorrhoidal and perineal nerves (for the sphincter ani
externus and retractor ani).
THE PANCREAS
The =pancreas= is situated transversely on the dorsal wall of the
abdomen, the greater part being to the right of the median plane. Its
central part lies under the sixteenth and seventeenth thoracic vertebræ.
When fresh it has a reddish cream color, but if left in the unpreserved
cadaver it rapidly decomposes and becomes dark. It resembles the
salivary glands in appearance, but is softer, and its lobules are more
loosely united. Its average weight is about twelve ounces (ca. 350 g.).
When hardened in situ its shape is very irregular. It is triangular in
outline, and presents for description two surfaces, three borders, and
three angles.[97]
The =dorsal surface= faces upward and forward. It is partially covered
by peritoneum. It is related chiefly to the ventral surface of the right
kidney and adrenal, the posterior vena cava, the portal vein, the cœliac
artery and its divisions, the gastro-phrenic ligament and the saccus
cæcus of the stomach, the right and caudate lobes of the liver, and the
gastro-pancreatic fold. There are grooves for the divisions of the
cœliac artery, and a large one for the splenic vein.
The =ventral surface= looks downward and backward; it is in general
concave. It presents two impressions, separated by an oblique ridge. The
smaller of these (Impressio cæcalis) lies to the right, and is caused by
the pressure of the base of the cæcum; the larger one (Impressio colica)
indicates the area of contact with the terminal part of the great colon
and its junction with the small colon. It has usually no peritoneal
covering except over a small area at the anterior angle.
The =right border= is nearly straight; it is related to the second part
of the duodenum and the caudate lobe of the liver.
The =left border= is slightly concave, and is related to the first part
of the duodenum, the left sac of the stomach, and the splenic vessels.
The =posterior border= presents a deep notch to the right of the median
plane for the portal vein, which passes through the gland very
obliquely. There is a thin bridge of gland tissue dorsal to the vein,
thus forming the =portal ring= (Annulus portarum). The root of the great
mesentery is in contact with the border just to the left of the median
plane.
The =anterior= or =duodenal angle= (Caput pancreatis) is attached to the
concavity of the second curve of the duodenum, and the adjacent part of
the right lobe of the liver. The ducts leave at this extremity.
The =left= or =splenic angle= (Cauda pancreatis) corresponds to the tail
of the pancreas in man. It is in contact with the base of the spleen,
the left kidney and adrenal body, and the saccus cæcus of the stomach.
[Illustration:
FIG. 273.—PANCREAS OF HORSE WITH CHIEF RELATIONS, VENTRAL VIEW.
The pancreatic duct and its two chief radicles are indicated by dotted
lines, since they are in the substance of the gland.
]
The =right angle= is rounded, and lies on the ventral surface of the
right kidney and adrenal body.
The pancreas is attached dorsally by connective tissue to the kidneys
and adrenal bodies, the gastro-phrenic ligament and the suspensory
ligament of the spleen, the posterior vena cava, the portal fissure, and
the gastro-pancreatic fold. The ventral surface is mainly attached by
areolar tissue to the base of the cæcum and the terminal part of the
great colon.
There are almost invariably two =ducts=. The large one is termed the
=pancreatic duct= (Ductus pancreaticus [Wirsungi]). It is formed by the
union of two radicles which come from the right and left extremities,
and passes through the duodenal angle to end at the duodenal
diverticulum alongside of the bile-duct. The duct is nearly half an inch
(ca. 1 cm.) wide, and is very thin-walled. It is situated in the
substance of the gland near its dorsal surface; none of it is free. The
=accessory pancreatic duct= (Ductus pancreaticus accessorius
[Santorini]) arises either from the chief duct or its left radicle, and
ends on a papilla in the duodenum opposite the chief duct.
=Structure.=—The pancreas belongs to the class of tubulo-alveolar
glands, the alveoli being long, like those of the duodenal glands; in
other respects it resembles the serous salivary glands very closely. It
has no proper capsule and the lobules are rather loosely united.
=Vessels and Nerves.=—The arteries of the pancreas come from the
branches of the cœliac and anterior mesenteric arteries. The nerves are
derived from the cœliac and mesenteric plexuses of the sympathetic.
THE LIVER
The =liver= (Hepar) is the largest gland in the body. It is situated
obliquely on the abdominal surface of the diaphragm. Its highest point
is at the level of the right kidney, its lowest on the left side,
usually about three or four inches (ca. 8 to 10 cm.) from the abdominal
floor, opposite the lower end of the seventh or eighth rib. The greater
part of it lies to the right of the median plane.
It is red-brown in color and is rather friable. Its average weight is
about ten to twelve pounds (ca. 5 kg.). When in the body, or if hardened
_in situ_, it is strongly curved and accurately adapted to the abdominal
surface of the diaphragm. When removed in the soft state, it flattens
out into a cake-like form quite different from its natural
configuration. It presents for description two surfaces and a
circumference, which may be divided into four borders.
The =parietal surface= (Facies diaphragmatica) is strongly convex, and
lies against the diaphragm. It faces chiefly upward and forward. It
presents, just to the right of the median plane, a sagittal groove for
the posterior vena cava (Fossa venæ cavæ). The vein is partially
embedded in the substance of the gland, and receives the hepatic veins.
The =visceral surface= (Facies visceralis) faces in general downward and
backward; it is concave and irregular, being moulded on the organs which
lie against it. It presents, a little to the right of the median plane,
the =portal fissure= (Porta hepatis). Through this the portal vein,
hepatic artery, and hepatic plexus of nerves enter, and the hepatic duct
and lymph vessels leave the liver. The portal or hepatic lymph glands
are also found here. The pancreas is attached at and to the right of the
fissure, and the gastro-hepatic omentum to the left of it. Above the
fissure is a ridge which represents the caudate lobe (Lobus caudatus
Spigelii), and is continued to the right by the pointed caudate process
(Processus caudatus). Further to the left there is a large depression
(Impressio gastrica) for the stomach. To the right of this may be seen a
groove passing to the right and dorsally; this is the duodenal
impression (Impressio duodenalis). Ventral to these is a large
depression for the great colon (Impressio colica). Dorsal to this is a
smaller depression for the blind end of the base of the cæcum.[98] Coils
of the small intestine may also lie on this surface, and the apex of the
spleen may reach to it when the stomach is empty.
The =dorsal border= (Margo obtusus) is thick for the most part. It
presents from right to left: (1) a depression for the right kidney
(Impressio renalis); (2) a notch, which is the dorsal end of the fossa
venæ cavæ; (3) a deep notch (Impressio œsophagea) which is mainly
occupied by the thick margin of the œsophageal opening of the diaphragm.
The =ventral border= is thin, and is marked by two deep =interlobar
fissures= or =incisures= (Incisuræ interlobares), which partially divide
the organ into three principal =lobes=—=right=, =middle=, and =left=.
The right lobe is the largest, except in old subjects, in which it is
frequently much atrophied. The middle lobe is the smallest. It is marked
by several small fissures, and by the =umbilical fissure= (Incisura
umbilicalis); the latter contains the umbilical vein in the fœtus, which
is transformed into the round ligament after birth.
The =right border= is thin and long. It is nearly vertical, and extends
backward to about the middle of the sixteenth rib.
The =left border= is thin and short. It extends backward to a point
opposite the lower part of the ninth or tenth rib. The ventral and
lateral borders together constitute the margo acutus.
[Illustration:
FIG. 274.—LIVER OF YOUNG HORSE, HARDENED _in situ_, PARIETAL SURFACE.
]
The liver is held in position largely by the pressure of the other
viscera and by its close application to the diaphragm. It has six
ligaments.
1. The =coronary ligament= (Lig. coronarium hepatis) attaches it closely
to the diaphragm. It consists of two laminæ. The right one is attached
to the right of the fossa venæ cavæ; the left one begins to the left of
the vena cava and passes upward and outward, becoming continuous with
the left lateral ligament at the left margin of the œsophageal notch; it
detaches a middle fold which extends to the notch and is continuous with
the small omentum. The two laminæ unite below the vena cava to form the
next ligament.
2. The =falciform ligament= (Lig. falciforme hepatis) is a crescentic
fold which attaches the middle lobe to the sternal part of the diaphragm
and to the abdominal floor for a variable distance. In its concave free
edge is found.
3. The =round ligament= (Lig. teres hepatis), a fibrous cord which
extends from the umbilical fissure to the umbilicus; it is the vestige
of the umbilical vein, which in the fœtus carries the blood from the
placenta to the liver.
4. The =right lateral ligament= (Lig. triangulare dextrum) is a wide
fold which attaches the dorsal border of the right lobe to the costal
part of the diaphragm.
[Illustration:
FIG. 275.—LIVER OF HORSE, VISCERAL SURFACE.
Specimen from middle-aged subject, hardened _in situ_.
]
5. The =left lateral ligament= (Lig. triangulare sinistrum) attaches the
dorsal edge of the left lobe to the tendinous center of the diaphragm.
6. The =hepato-renal= or =caudate ligament= (Lig. hepatorenale) attaches
the caudate process to the right kidney and the base of the cæcum. The
gastro-hepatic omentum and the mesoduodenum have been described.
As stated above, the liver is divided by fissures into three principal
lobes—right, middle, and left. The right lobe is the largest in the
young subject and is irregularly quadrilateral in form. On its dorsal
part is the caudate lobe, which ends in a pointed process directed
outward, and assists in forming the cavity for the right kidney. The
middle lobe is normally much the smallest. The left lobe is oval in
outline and thickest centrally. In old or middle-aged subjects it often
exceeds the right one in size. In some cases the atrophy of the right
lobe is so extreme that the middle lobe may exceed it in size.[99]
The =hepatic duct= (Ductus hepaticus) is formed at the ventral part of
the portal fissure by the union of right and left chief lobar ducts. It
is two or three inches (ca. 5 to 8 cm.) long and about half an inch (ca.
1 to 1.5 cm.) wide. It passes between the two layers of the lesser
omentum, and pierces the wall of the duodenum about five or six inches
(ca. 12 to 15 cm.) from the pylorus, alongside of the pancreatic duct.
The ducts pass obliquely through the wall of the duodenum for about half
an inch (ca. 1 cm.) before opening into the diverticulum duodeni. The
arrangement forms an effective valve, which prevents regurgitation from
the intestine. There is no gall-bladder.
[Illustration:
FIG. 276.—LIVER OF NEW-BORN FOAL, HARDENED _in situ_. VISCERAL
SURFACE.
The differences, when compared with the organ in the adult, are very
striking.
]
=Structure.=—The liver is covered by an outer serous, and an inner
fibrous coat. The =serous coat= covers the gland except at the
attachment of the pancreas and at the portal fossa; it is reflected from
it to form the ligaments and the lesser omentum. The =fibrous capsule=
is in general thin; it sends laminæ into the ligaments, and also
delicate strands into the gland substance. At the portal fissure it is
abundant and surrounds the vessels and ducts, which it accompanies in
the portal canals of the gland substance.
The gland substance is composed of the parenchyma and the interstitial
tissue. The =parenchyma= is made up of lobules, 1 to 2 mm. in diameter,
which are held together by a small amount of interlobular connective
tissue. On account of the very small amount of the latter, the
lobulation of the horse’s liver is not usually at all distinct to the
naked eye; for the same reason the organ is also quite friable.[100]
=Vessels and Nerves.=—The =portal vein= enters at the portal fissure. It
conveys blood from the digestive tract and the spleen, which contains
various products of digestion and numerous white blood-cells. The
=hepatic artery= also enters at the portal fissure; it may be termed the
nutrient vessel. All the blood is returned from the liver to the
posterior vena cava by the hepatic veins. The portal vein and the
hepatic artery both divide into interlobular branches, which run
together in the portal canals of the interlobular tissue. The branches
of the portal vein (Venæ interlobulares) give off intralobular branches
which form plexuses of capillaries in the lobules and give rise to a
central vein (Vena centralis). The branches of the hepatic artery (Rami
arteriosi interlobulares) are of relatively small size. They supply
mainly (if not exclusively) the interlobular tissue, the capsule, and
the walls of the vessels and ducts. The =hepatic veins=[101] (Venæ
hepaticæ) empty into the vena cava as it lies in the fossa of the gland.
Their ultimate radicles are the central lobular veins, which emerge from
the bases of the lobules and join the sublobular veins (Venæ
sublobulares); the latter unite to form the hepatic veins. The largest
hepatic veins, three or four in number, join the posterior vena cava
just before it leaves the liver to pass through the diaphragm.
The nerve-supply comes from the =hepatic plexus=, composed of branches
from the vagus and sympathetic nerves.
THE SPLEEN
The =spleen= (Lien) is the largest of the ductless glands.[102] It is
situated chiefly in the left parachondrium, in close relation to the
left part of the great curvature of the stomach, to which its long axis
corresponds. Its size and weight vary greatly in different subjects, and
also in the same subject under different conditions, depending chiefly
on the great variability of the amount of blood contained in it. The
average weight is about 35 ounces (ca. 1 kg.), its length about 20
inches (ca. 50 cm.), and its greatest width about 8 to 10 inches (ca. 20
to 25 cm.). It is usually bluish-red or somewhat purple in color. In the
natural state it is soft and yielding, but not friable.
The weight appears to vary ordinarily from about one to eight pounds,
although in large horses the latter figure even may be exceeded
without any apparent evidence of disease. There does not seem to be
any constant relation to the body-weight. For example, the spleen of a
colt about ten months old weighed three and a half pounds, while it
often weighs less than two pounds in horses weighing 1000 to 1200
pounds. The chief variation in outline consists of increase of width,
especially of the dorsal part.
It extends obliquely in a curved direction from the left crus of the
diaphragm and the saccus cæcus of the stomach to the ventral third of
the ninth or tenth rib. It presents for description two surfaces, two
borders, and two extremities.
The =parietal= or =external surface= (Facies parietalis) is convex, and
lies chiefly against the diaphragm, but is in direct contact with the
upper parts of the last two ribs and to a small extent with the flank at
the lumbo-costal angle.
The =visceral= or =internal surface= (Facies visceralis) is in general
concave. It is divided into two unequal portions by a longitudinal
ridge; on this is a groove, the =hilus=, in which the vessels and nerves
are situated. The area in front of the ridge (Facies gastrica) is
moulded on the great curvature of the stomach; it is about two inches
(ca. 5 cm.) wide. The area behind the ridge (Facies intestinalis) is
much more extensive; it is related chiefly to the small colon, the small
intestine, and the great omentum. It may be marked by one or two
fissures.
[Illustration:
FIG. 277.—SPLEEN OF HORSE, HARDENED _in situ_. VISCERAL SURFACE.
The area marked intestinal impression is related to the first coil of
the small colon.
]
The =anterior border= (Margo anterior) is concave and thin.
The =posterior border= (Margo posterior) is convex and thin.
The =base= or =dorsal extremity= is beveled, and fits into the interval
between the left kidney and the left crus of the diaphragm and the psoas
major. When hardened _in situ_, it shows an impression (Facies renalis)
where it lies against the kidney. The left extremity of the pancreas
touches it also. The anterior basal angle fits in between the saccus
cæcus of the stomach and the left kidney; the posterior basal angle
usually lies against the flank just behind the last rib.
The =apex= or =ventral extremity= is small; it lies—when the stomach is
not full—between the left lobe of the liver and the left dorsal portion
of the colon; when the stomach is full, the spleen is pushed further
back and loses contact with the liver.
The spleen is attached by two peritoneal folds, the suspensory ligament
and the gastro-splenic omentum. The =suspensory ligament= (Lig.
suspensorium lienis) attaches the base to the left crus of the diaphragm
and the left kidney; it contains a quantity of elastic tissue. The part
which passes to the diaphragm is the ligamentum phrenico-lienale, and
blends with the gastro-phrenic ligament; the part which goes to the
kidney is termed the ligamentum renolienale. The =gastro-splenic
omentum= (Lig. gastrolienale) passes from the hilus to the left part of
the great curvature of the stomach. It is narrow above, where it joins
the suspensory ligament; below it becomes much wider and is continuous
with the great omentum.
Small globular or lenticular masses of splenic tissue may be found in
the gastro-splenic omentum. They are termed =accessory spleens=
(Lienes accessoriæ).
=Structure.=—The spleen has an almost complete =serous coat=. Subjacent
to this and intimately united with it is a =capsule= of fibrous tissue
(Tunica albuginea), which contains many elastic fibers and some
unstriped muscular tissue. Numerous =trabeculæ= (Trabeculæ lienis) are
given off from the deep face of the capsule and ramify in the substance
of the organ to form a supporting network. In the interstices of this
framework is the =spleen pulp= (Pulpa lienis), a dark red, soft, grumous
material. This is supported by a delicate adenoid =reticulum=, and
contains numerous leukocytes, the large splenic cells, red
blood-corpuscles, and pigment. The pulp is richly supplied with blood.
The branches of the splenic artery enter at the hilus and pass along the
trabeculæ. The arteries which enter the pulp have a sheath of lymphoid
tissue, which collects on the vessel wall at certain points, forming
small =lymph nodules=, the so-called Malpighian corpuscles (Noduli
lymphatici lienales). These are visible to the naked eye as white spots,
about as large as the head of a pin. The blood passes into cavernous
spaces lined by endothelium which is continuous with the cells of the
reticulum of the pulp. From these the veins arise. The splenic vein runs
in the hilus in company with the artery and nerves, and joins the
posterior gastric vein to form a large radicle of the portal vein.
=Blood-supply.=—Splenic artery.
=Nerve-supply.=—Splenic plexus.
THE PERITONEUM
The general disposition of the peritoneum has been described, and other
facts in regard to it were mentioned in the description of the viscera.
It is now desirable to study it as a continuous whole.[103] (Figs. 256,
257, 278, 279.)
We may consider the peritoneum as consisting of two sacs—a greater and a
lesser. The =greater sac= lines the greater part of the abdominal
cavity, and covers most of the viscera which have a peritoneal
investment. The =lesser sac= is an introversion or recess of the greater
sac, formed during the development of the viscera. The two sacs
communicate by a relatively narrow passage, termed the =epiploic
foramen= of Winslow (Foramen epiploicum). This opening is situated on
the visceral surface of the liver above the portal fissure. It can be
entered by passing the finger along the caudate lobe of the liver toward
its root. Its dorsal (or anterior) wall is formed by the caudate lobe
and the posterior vena cava. Its ventral (or posterior) wall consists of
the pancreas, the gastro-pancreatic fold, and the portal vein. The walls
are normally in contact, and the passage merely a potential one. It is
usually about four inches (ca. 10 cm.) in length. It is narrowest at the
right extremity, where it is about an inch (ca. 2.5 to 3 cm.) wide.[104]
If the finger is passed into the foramen from right to left, it enters
the cavity of the lesser sac. If now an opening is made in the great
omentum and the other hand introduced through it, the fingers of the two
hands touch each other over the lesser curvature of the stomach. The
formation and boundaries of the lesser sac should now be examined by
spreading out the great omentum. It will be found that the latter now
incloses a considerable cavity behind the stomach; this is termed the
=omental cavity= (Bursa omentalis). Passing forward over the lesser
curvature of the stomach, we enter another space, the =vestibule= of the
omental cavity (Vestibulum bursæ omentalis). This space is closed on the
left by the gastro-phrenic ligament, below and on the right by the
lesser omentum, and dorsally by the gastro-pancreatic fold, which is
attached to the dorsal border of the liver and to the posterior vena
cava. Above the œsophageal notch the fingers can be passed around the
border of the liver and the vena cava till the coronary ligament is
encountered. Thus the vestibule is closed except (1) on the right, where
it communicates with the cavity of the greater sac by the epiploic
foramen; and (2) behind, where it communicates with the cavity of the
omentum.
[Illustration:
FIG. 278.—DIAGRAM OF GENERAL ARRANGEMENT OF PERITONEUM (OF MARE) IN
SAGITTAL TRACING.
_a_, Pouch between rectum and roof of pelvis, continuous with _b_,
recto-genital pouch; _c_, vesico-genital pouch; _d_, pouch below
bladder and its lateral ligaments; _f_, lesser omentum; _Int._,
small intestine. The arrow points to the epiploic foramen (of
Winslow).
]
The general arrangement of the great omentum has already been indicated.
We may now trace its line of attachment, which would correspond to the
mouth of the sac. Beginning at the ventral part of the great curvature
of the stomach, the line passes to the ventral face of the pylorus, then
crosses obliquely the first part of the duodenum to the point where the
pancreas is adherent to it. Here it passes to the anterior face of the
terminal transverse part of the great colon, runs along this
transversely (from right to left), and continues for some ten or twelve
inches (ca. 25 to 30 cm.) on the small colon. It then forms an acute
angle, passes inward and forward along the small colon to the dorsal
part of the hilus of the spleen, where it blends with the suspensory
ligament of the latter, and forms a recess (Recessus lienalis) behind
the saccus cæcus of the stomach. It now passes along the hilus of the
spleen, and is continued to the great curvature of the stomach by the
gastro-splenic omentum. It is convenient to regard the spleen as being
intercalated in the left part of the great omentum; on this basis the
gastro-splenic omentum would be that part of the great omentum which
connects the hilus of the spleen with the great curvature of the
stomach. The great omentum is relatively small in the horse, and is
usually not visible when the abdomen is opened. It is generally folded
up in the space between the visceral surface of the stomach and the
intestine.[105]
The lesser sac furnishes the peritoneal covering for: (1) the visceral
surface of the stomach and a small area of the first curve of the
duodenum; (2) a large part of the dorsal surface of the pancreas and
portal vein; (3) a small part of the visceral surface of the liver
above the attachment of the lesser omentum and the portal fossa; (4)
the posterior vena cava, from the level of the epiploic foramen [of
Winslow] to its passage through the diaphragm (in so far as it is not
embedded); (5) the part of the parietal surface of the liver between
the right and middle divisions of the coronary ligament; (6) the
corresponding part of the diaphragm, and the right part of the right
crus of the same; (7) part of the anterior surface of the terminal
part of the great colon, and the origin of the small colon; (8) the
left extremity of the pancreas (inconstant); (9) the spleen.
We may now trace the peritoneum in a longitudinal direction, beginning
in front. It is reflected from the ventral abdominal wall and the
diaphragm upon the liver, forming the ligaments and serous coat of the
gland. It leaves the visceral surface of the liver as lesser omentum,
and the crura of the diaphragm as the gastro-phrenic ligament, reaches
the saccus cæcus and lesser curvature of the stomach and the first curve
of the duodenum, covers these organs, and is continued by the great
omentum.
[Illustration:
FIG. 279.—DIAGRAM OF ABDOMINAL PERITONEUM IN FRONTAL (HORIZONTAL)
TRACING.
_D_, Duodenum. The arrow indicates the epiploic foramen (of Winslow).
By an oversight the leader line to the great omentum is omitted, and
the coronary ligament of the liver is erroneously marked lesser
omentum; the latter extends from liver to stomach, but is not
marked.
]
On the left it passes from the left crus of the diaphragm and the left
kidney to form the suspensory ligament of the spleen, clothes that
organ, and leaves it to be continued by the great omentum.
On the right it passes from the right crus of the diaphragm and the
dorsal border of the liver to the concave border of the duodenum,
forming the gastro-pancreatic fold (second part of the mesoduodenum),
and covering part of the dorsal surface of the pancreas. From the margin
of the pancreas, the right kidney, and a small area of the sublumbar
region behind the latter, it passes on to the base of the cæcum and the
terminal part of the great colon. From these it passes on the right to
the duodenum, forming the third part of the mesoduodenum. On the left it
clothes part of the ventral surface and the outer border of the left
kidney, from which it passes to the base of the spleen, forming the
ventral layer of the suspensory ligament of the latter. Behind the
terminal part of the great colon it is reflected around the great
mesenteric artery to form the great mesentery. Behind this it is
reflected almost transversely from the roof of the cavity and from the
origin of the small colon on to the duodenum, forming the terminal part
of the mesoduodenum. The line of origin of the colic mesentery begins on
the inner part of the ventral surface of the left kidney, and extends to
the sacral promontory, where the mesorectum begins. At the termination
of the latter the peritoneum is reflected from the rectum on the dorsal
and lateral walls of the pelvic cavity. Below the rectum it forms the
urogenital fold, and passes on to the dorsal surface of the bladder,
covers its anterior part, and is reflected on to the body-wall laterally
and ventrally, forming the lateral and middle ligaments of the bladder.
In the female the broad ligaments of the uterus replace the urogenital
fold, with which they are homologous.
In the new-born foal certain folds are specially large. The falciform
ligament of the liver extends to the umbilical opening, and contains in
its free edge the large umbilical vein. The bladder—at this time an
abdominal organ—has a ventral median fold, which connects it and the
urachus with the abdominal floor. This is flanked on either side by a
fold which also extends to the umbilicus, and contains the large
umbilical artery.
DIGESTIVE SYSTEM OF THE OX
THE MOUTH
The cavity of the mouth is shorter and wider than that of the horse, and
the vestibule is more capacious.
[Illustration:
FIG. 280.—ANTERIOR PART OF LOWER JAW OF OX.
_60_, Tip of tongue. (After Ellenberger-Baum, Anat. für Künstler.)
]
The =lips= are thick, wide, and comparatively immobile. The middle part
of the upper lip and the surface between the nostrils is bare, and is
termed the muzzle (Planum nasolabiale). It is smooth, and (in health) is
kept cool and moist by a clear fluid secreted by a layer of subcutaneous
glands (Glandulæ nasolabiales) about half an inch (ca. 1.5 cm.) thick.
It shows irregular lines, mapping out small polygonal areas on which the
orifices of the gland-ducts are visible. A narrow bare strip also exists
along the edge of the lower lip. The remainder of the integument is
provided with ordinary and tactile hairs. The free edge and the lining
membrane present verrucose, horny papillæ. The labial glands form
compact masses near the angles of the mouth.
The =cheeks= are more capacious than in the horse. The mucous membrane
presents large conical pointed =papillæ=, which are directed toward the
fauces and are covered with a horny epithelium. The largest of these
have a length of about half an inch (ca. 1 to 1.5 cm.) and are situated
around the angle of the mouth and parallel with the cheek teeth. The
orifice of the parotid duct is opposite the fifth upper cheek tooth. (In
the sheep and goat it is opposite the fourth tooth.) The =buccal= or
=molar glands= are very well developed, and are arranged in three parts.
The dorsal row extends from the maxillary tuberosity to the angle of the
mouth. Its lobules are of a light yellow color. The ventral part
consists of a compact brownish mass which reaches from the angle of the
mouth a short distance under the masseter muscle. The middle part
consists of loosely arranged yellow lobules.
[Illustration:
FIG. 281.—SAGITTAL SECTION OF HEAD OF COW, CUT A LITTLE TO THE RIGHT
OF THE MEDIAN PLANE.
_1_, Cerebral hemisphere; _2_, corpus striatum; _3_, hippocampus; _4_,
olfactory bulb; _5_, corpora quadrigemina; _6_, optic nerve; _7_,
pons; _8_, medulla oblongata; _9_, spinal cord; _10_, pituitary
body; _11_, sphenoid sinus; _12_, lateral mass of ethmoid; _13_,
ventral straight muscles; _14_, pharyngeal (retropharyngeal) lymph
gland; _15_, longus colli; _16_, soft palate; _17_, vallate papillæ;
_18_, tonsillar sinus; _19_, conical papillæ of cheek; _20_,
hyo-epiglotticus muscle; _21_, epiglottis; _22_, hyo-glossus muscle;
_C1_, _C2_, atlas, axis. Subject was hardened with mouth open.
]
A linear series of large papillæ exists on the floor of the mouth on
each side of the frenum linguæ. Near these are found the openings of the
small ducts of the sublingual gland. The papilla on which the
submaxillary duct opens is wide, hard, and has a serrated edge.
The =hard palate= is wide, and is usually more or less pigmented. The
body of the premaxilla is covered with a thick layer of dense connective
tissue, which has a thick, horny epithelial covering—forming the
so-called dental plate or pad. The palatine ridges extend from this
backward about two-thirds of the length of the hard palate. They are
nearly straight, and, for the most part, are serrated on the free edge.
A median furrow extends between the ridges. The posterior third of the
palate is smooth. Between the dental plate and the first ridge is the
triangular papilla incisiva; on either side of this is a deep furrow, in
which is the oral opening of the =naso-palatine canal=. This canal is
two inches or more (ca. 5 to 6 cm.) in length and opens on the floor of
the nasal cavity; it also communicates by a slit-like opening with the
organ of Jacobson.
[Illustration:
FIG. 282.—CROSS-SECTION OF HEAD OF OX.
The section passes through the internal canthi. _L.a._, Lingual
arteries. The arrow indicates the communication between the
maxillary and palatine sinuses.
]
The =soft palate= is somewhat shorter than that of the horse, but is
long enough to close the isthmus of the fauces. The posterior pillars do
not extend to the entrance of the œsophagus. The azygos muscle is much
better developed than in the horse. The fibrous aponeurosis is for the
most part replaced by muscular tissue.
The =isthmus faucium= is wide and dilatable. On either side, behind the
anterior pillar of the soft palate, is a deep depression, the =sinus
tonsillaris=; external to this is the compact bean-shaped tonsil, which
is about one to one and a half inches (ca. 3 to 4 cm.) in length. The
tonsil does not project into the fauces, but outward instead: hence it
does not occupy the tonsillar sinus, and is not visible internally, as
is the case in most animals.
[Illustration:
FIG. 283.—TONGUE OF OX, DORSAL ASPECT.
Pharynx, soft palate, and origin of œsophagus are cut dorsally and
reflected.
]
THE TONGUE
The tongue of the ox is often variably pigmented. The root and body are
wider than that of the horse, but the free part is more pointed. The
posterior part of the dorsum forms a remarkable elliptical prominence,
which is sharply defined in front. The filiform papillæ in front of this
prominence are large and horny, with sharp points directed backward.
They impart to the tongue its rasp-like roughness. The papillæ on the
prominence are large, broad and horny; some have a blunt conical form,
others are rounded or flattened. Behind the prominence, the papillæ are
long and soft, _i. e._, not horny. The fungiform papillæ are numerous
and distinct; they are scattered more generally over the dorsum and
edges of the free part. The vallate papillæ are about twenty or thirty
in number; they are smaller than those of the horse, and are irregularly
distributed on either side of the posterior part of the prominence of
the dorsum. The foliate papillæ and the lingual fibrous cord are absent.
The muscles are well developed; the hyo-glossus arises by additional
portions from the great and middle cornua of the hyoid bone. The tongue
is highly protractile and is the chief organ of prehension.
THE TEETH
The dental formula of the ox is:
( 0 0 3 3 )
2 ( I - C - P - M - ) = 32
( 4 0 3 3 )
The =incisors= are absent from the upper jaw. There are eight incisors
in the lower jaw, arranged in a somewhat fan-like manner. They are
simple teeth, without infundibulum. The crown is white, short, and
shovel-shaped. The root is rounded, and is embedded in the jaw in such a
manner as to allow a considerable degree of movement. There is a
distinct =neck=. In addition to the simple numerical designation, the
following terms are commonly applied to the individual teeth: pinchers
or central, first intermediate, second intermediate, and corner
incisors. It is probable that the latter are much modified canines. The
incisors of the ox do not advance out of the alveoli, as is the case in
the horse; in old age, however, the gum retracts so that the roots are
partly exposed and may come into wear.[106]
[Illustration:
FIG. 284.—INCISOR TEETH OF OX, LINGUAL ASPECT.
_C.s._, Caruncula sublingualis.
]
[Illustration:
FIG. 285.—INCISOR TOOTH OF OX.
_24′_, Lingual surface of crown; _24″_, masticatory surface. The crown
is clearly marked off from the rounded root by a neck. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =deciduous incisors= differ from the permanent set chiefly in being
much smaller. The crowns are narrower and diverge more.
The =canines= are absent (unless the fourth incisors be considered to
represent them).
[Illustration:
FIG. 286.—SKULL OF OX TWO YEARS OF AGE, SCULPTURED TO SHOW THE
EMBEDDED PARTS OF THE TEETH.
_11–4_, Permanent incisor teeth, the third and fourth not erupted;
_Di.3, 4_, third and fourth deciduous incisors; _P1–3_, upper
permanent premolars, only first erupted; _Dp.2, 3_, deciduous
premolars; _M1–3_, molars.
]
The =cheek teeth= (Fig. 286) resemble those of the horse in number and
general arrangement. They are, however, smaller, and also differ in the
fact that they progressively increase in size from before backward. This
feature is so marked that the first tooth is quite small, and the space
occupied by the first three (_i. e._, the premolars) is only about
one-half of that required for the posterior three (_i. e._, the true
molars). The enamel folds stand out even more prominently in relief on
the masticatory surface than in the horse. The occurrence of wolf-teeth
is rare.
The formula of the deciduous teeth is:
( 0 0 3 )
2 ( Di — Dc — Dp — ) = 20
( 4 0 3 )
TABLE OF AVERAGE PERIODS OF ERUPTION OF THE TEETH
IN THE OX
│
TEETH │ ERUPTION
│
_A._ _Temporary:_ │
First incisor (Di 1) │Birth to 3 weeks.
Second incisor (Di 2) │ „
Third incisor (Di 3) │ „
Fourth incisor (Di 4) │ „
──────────────────────────────┼──────────────────
First cheek tooth (Dp 1) │Birth to 3 weeks.
──────────────────────────────┼──────────────────
Second cheek tooth (Dp 2)│Birth to few days.
Third cheek tooth (Dp 3) │ „
──────────────────────────────┼──────────────────
│
_B._ _Permanent:_ │
First incisor (I1) │1½ to 2 years.
Second incisor (I2) │2 to 2½ years.
Third incisor (I3) │3 years.
Fourth incisor (I4) │3½ to 4 years.
First cheek tooth (P1) │2 to 2½ years.
Second cheek tooth (P2) │1½ to 2½ years.
Third cheek tooth (P3) │2½ to 3 years.
Fourth cheek tooth (M1) │5 to 6 months.
Fifth cheek tooth (M2) │1 to 1½ years.
Sixth cheek tooth (M3). │2 to 2½ years.
The eruption of the permanent teeth is subject to great variation. The
above figures are the average of observations of improved breeds under
favorable conditions.
THE SALIVARY GLANDS
The =parotid gland= is smaller than that of the horse, and is light
red-brown in color. It has somewhat the form of a very narrow long
triangle, and lies chiefly on the posterior part of the masseter muscle.
The thick wide upper end partly covers a large subparotid lymph gland.
The small lower end is bent forward and fits into the angle of union of
the jugular and external maxillary veins; it lies on the submaxillary
gland. The parotid duct leaves the lower part of the deep face; in its
course it resembles that of the horse, but it pierces the cheek opposite
the fifth upper cheek tooth.
The =submaxillary gland= is very large, and is pale yellow in color. It
is covered to a small extent by the parotid. Its general form resembles
that of the horse, but its lower (or anterior) end is large and rounded,
and is separated by a small interval only from the gland of the other
side. This part can be distinctly felt in the living animal, and is
related externally to a large submaxillary lymph gland. The duct leaves
the middle of the superficial face of the gland, crosses the
stylo-hyoideus and the intermediate tendon of the digastricus, and is
then disposed as in the horse.
The =sublingual gland= consists of two parts. The dorsal part (Glandula
sublingualis parvicanalaris) is long, thin, and pale yellow in color. It
extends from the anterior pillar of the soft palate about to the
symphysis of the jaw. It has numerous small tortuous ducts (Ductus
sublinguales minores), which open between the papillæ under the side of
the tongue. The ventral part is shorter and thicker, and is salmon pink
in color. It has a single duct (Ductus sublingualis major), which either
opens alongside of or joins the submaxillary duct.
THE PHARYNX
The pharynx is short and wide. The vault (Fornix pharyngis) is divided
into two cul-de-sacs by a median fold of mucous membrane (Septum nasi
membranaceum), which is a continuation of that of the septum nasi; on
the outer wall of each is the relatively small opening of the Eustachian
tube, which is covered by a simple fold of mucous membrane. The
posterior nares are small. The entrance to the œsophagus is large.
[Illustration:
FIG. 287.—SALIVARY GLANDS OF OX.
_a_, Parotid gland; _b_, submaxillary gland; _c_, inferior, _d_,
middle, and _e_, superior buccal glands; _f_, labial glands; _g_,
buccinator nerve; _h_, buccinator vein; _1_, masseter (cut); _2_,
ramus of mandible; _3_, zygomaticus muscle; _4_, conical papillæ of
lip; _5_, buccinator muscle. (After Ellenberger, in Leisering’s
Atlas.)
]
On the dorsal wall of the pharynx are two large pharyngeal lymph
glands, which, when enlarged, cause difficulty in swallowing and
breathing (Fig. 281).
THE ŒSOPHAGUS
This is much shorter, wider, and more dilatable than that of the horse.
Its average diameter (when moderately inflated) is about two inches (ca.
5 cm.), and its length in a large animal is about three to three and a
half feet (ca. 90 to 100 cm.). The wall is relatively thin, and the
muscular tissue is striped throughout. The latter consists of two strata
of spiral fibers, except near the stomach, where they are longitudinal
and circular. Fibers are continued into the wall of the stomach for some
distance. There are submucous glands in the first part of the tube.
There is no terminal dilatation, and no part in the abdominal cavity.
A very large mediastinal lymph gland lies above the posterior part of
the œsophagus and may, if enlarged, obstruct it (Fig. 289).
THE ABDOMINAL CAVITY
The abdominal cavity of the ox is very capacious, both absolutely and
relatively, as compared with that of the horse. This is due to several
factors. The lumbar portion of the spine is about one-fourth longer than
that of the horse. The transverse diameter between the last ribs is
greater. The costal attachment of the diaphragm is almost vertical in
direction from the lower part of the ninth rib to the extreme upper part
of the thirteenth; in fact, the attachment to the last rib is not
constant. Thus the abdomen is increased at the expense of the thorax,
and the last three or four ribs enter more largely into the formation of
the abdominal wall than in the horse. The flank is also much more
extensive. The ilia, on the other hand, do not extend forward beyond a
transverse plane through the middle of the last lumbar vertebra. The
epigastric and mesogastric regions would be separated by a plane through
the lower end of the tenth pair of ribs, or through the last thoracic
vertebra. The chief differential features in the arrangement of the
peritoneum will be described with the viscera.
THE PELVIC CAVITY
The pelvic cavity is relatively long and narrow. The inlet is more
oblique than that of the horse; it is elliptical in outline, and the
transverse diameter is smaller than that of the horse. The anterior
(pubic) part of the floor is about horizontal, but the posterior
(ischial) part slopes upward and backward to a marked degree; this part
is also deeply concave transversely. The roof is concave in both
directions. The peritoneum extends backward as far as the first
coccygeal vertebra, so that the retroperitoneal part of the cavity is
short.
THE STOMACH
=General Arrangement.=—The stomach of the ox is very large, and occupies
nearly three-fourths of the abdominal cavity. It fills all of the left
half of the cavity (with the exception of the small space occupied by
the spleen) and extends considerably over the median plane into the
right half.
It is compound, being composed of four divisions, viz., =rumen=,
=reticulum=, =omasum=, and =abomasum=.[107] The division is clearly
indicated externally by furrows or constrictions. The first three
divisions may be regarded as proventriculi or œsophageal sacculations,
the fourth being the stomach proper (in the narrower sense of the term).
The œsophagus opens into the stomach on a sort of dome formed by the
rumen and reticulum, and is continued through the latter by the
œsophageal groove. From the ventral end of the latter a groove traverses
the ventral wall of the omasum, thus giving a direct path to the
abomasum for finely divided or fluid food. The abomasum joins the small
intestine.
=Capacity.=—The capacity of the stomach varies greatly, depending on the
age and size of the animal. In cattle of medium size it holds 30 to 40
gallons, in large animals 40 to 60, in small 25 to 35. The relative
sizes of the four parts vary with age. In the new-born calf the rumen
and reticulum together are about half as large as the abomasum; in ten
or twelve weeks this ratio is reversed. During this period the omasum
appears to be contracted and functionless. At four months the rumen and
reticulum together are about four times as large as the omasum and
abomasum together. At about one and one-half years the omasum equals (or
nearly so) the abomasum in capacity. The four divisions have now reached
their definitive relative capacities, the rumen constituting about 80
per cent., the reticulum 5 per cent., the omasum 7 or 8 per cent., and
the abomasum 8 or 7 per cent. of the total amount.
EXTERIOR AND RELATIONS
[Illustration:
FIG. 288.—PROJECTION OF VISCERA OF COW ON BODY-WALL, LEFT SIDE.
_Oes._, Œsophagus; _Ret._, reticulum; _b.s._, anterior blind sac;
_b.s.′_, _b.s.″_, posterior blind sacs of rumen; _O_, ovary. The
left kidney, concealed by the dorsal sac of the rumen, is indicated
by dotted line. The median line of the diaphragm is dotted.
]
The =rumen= occupies almost all of the left half of the abdominal
cavity, and extends considerably over the median plane ventrally and in
its middle. It is somewhat compressed laterally, and may be described as
having two surfaces, two curvatures or borders, and two extremities. The
=parietal= (or left) =surface= (Facies parietalis) is convex and is
related to the diaphragm, spleen, and the left wall of the abdomen. It
extends from the lower part of the seventh intercostal space almost to
the pelvis. The =visceral= (or right) =surface= (Facies visceralis) is
somewhat irregular, and is related chiefly to the omasum and abomasum,
the intestine, the liver, pancreas, kidneys, the uterus in the female,
and the posterior aorta and vena cava. The =dorsal curvature= (Curvatura
dorsalis) is convex, following the curve formed by the diaphragm and
sublumbar muscles. It is firmly attached to the left portion of the
crura of the diaphragm and the sublumbar muscles by peritoneum and
connective tissue. The =ventral curvature= is also convex and lies on
the floor of the abdomen. The surfaces are marked by the right and left
=longitudinal furrows= (Sulci longitudinales), which indicate externally
the division of the rumen into dorsal and ventral sacs.[108] The
=reticular= (or anterior) =extremity= (Extremitas reticularis) is
divided ventrally by a transverse groove (Sulcus ruminis cranialis) into
two sacs. The dorsal sac is the longer of the two, and curves ventrally
over the round, blind end of the ventral sac. The former only is
continuous with the reticulum, a ventral groove (Sulcus
rumino-reticularis) being the only external line of demarcation.
Dorsally no natural separation exists, the rumen and reticulum together
forming a dome-like vestibule (Atrium ventriculi) on which the œsophagus
terminates. The =pelvic= (or posterior) =extremity= (Extremitas pelvina)
extends nearly to the pubis, and is related to the intestine and
bladder, and the uterus in the cow. It is divided into =dorsal= and
=ventral blind sacs= (Saccus cæcus caudalis dorsalis, ventralis) by a
deep transverse groove (Sulcus ruminis caudalis) in which the
longitudinal furrows terminate. The blind sacs are marked off from the
remainder of the rumen by the =dorsal= and =ventral coronary grooves=
(Sulcus coronarius dorsalis, ventralis).
The left longitudinal groove (Sulcus longitudinalis sinister) begins
at the anterior transverse groove, passes somewhat dorsally and
backward and divides into two grooves. The ventral one is the chief
groove and passes backward to terminate in the angle of union of the
posterior blind sacs. The dorsal (accessory) groove curves dorsally
and then backward to terminate in the dorsal coronary sulcus. On the
right surface there are two longitudinal grooves. The dorsal one is
the chief sulcus (Sulcus longitudinalis dexter). It extends in a
curved direction (the convexity being dorsal) and is continuous with
the left longitudinal groove by means of the grooves between the
dorsal and ventral blind sacs at each end. The ventral groove (Sulcus
accessorius) curves somewhat ventrally and backward to rejoin the
chief sulcus between the posterior blind sacs.
The =reticulum= is the smallest of the four divisions in the ox. It is
also the most anterior, and lies on the concave surface of the
diaphragm, so that the median plane divides it into two nearly equal
portions. It is somewhat pyriform, but much compressed from before
backward. The =parietal= or =phrenic surface= (Facies diaphragmatica) is
convex and lies against the diaphragm and liver.[109] The =ruminal= (or
posterior) =surface= (Facies ruminalis) is flattened by the pressure of
the other three compartments; it ends dorsally by joining the wall of
the rumen, the concave line of junction forming, in the interior of the
stomach, the lower margin of the large rumino-reticular orifice. The
=omasal= (or right) =surface= is narrow and concave, and is connected
with the omasum. The =dorsal curvature= by its left portion joins the
rumen to form the atrium, and by its right portion touches the liver.
The =ventral curvature= lies on the sternal portion of the diaphragm,
opposite the sixth and seventh ribs. The =right extremity= forms a
rounded cul-de-sac, which is in contact with the liver, omasum, and
abomasum.
The =omasum= (Fig. 294) is ellipsoidal in form and somewhat compressed
laterally. It is very clearly marked off from the other divisions. It is
situated almost entirely to the right of the median plane, opposite the
seventh to the eleventh ribs. The =parietal= (right) =surface= (Facies
dextra) lies against the diaphragm, liver, and lateral wall of the
abdomen. The contact with the latter extends over a small area only
(ventral part of seventh to ninth intercostal spaces). The =visceral=
(left) =surface= (Facies sinistra) is in contact with the rumen and
reticulum. The =dorsal= (greater) =curvature= is convex, and is related
to the diaphragm, liver, and vena cava. The =ventral= (lesser)
=curvature= is concave, and rests on the abomasum chiefly, the junction
with the latter appearing as a constriction near the middle of the
curvature; at its anterior part there is a =neck= (Collum omasi) which
is the connection with the reticulum.
The =abomasum= (Fig. 294) is an elongated pyriform or flask-shaped sac,
which lies for the most part on the abdominal floor, to the right of the
ventral sac of the rumen. Its narrow posterior part is strongly curved,
the concavity being dorsal. The =parietal= (right) =surface= lies
against the abdominal wall from the seventh to the twelfth intercostal
space. The =visceral= (left) =surface= is related chiefly to the ventral
sac of the rumen. The =dorsal= (lesser) =curvature= is concave, and is
in contact with the omasum; the junction of the two sacs is indicated by
a constriction about four or five inches (ca. 10 to 12 cm.) from the
anterior extremity of the abomasum. The =ventral= (greater) =curvature=
is convex, and rests on the abdominal wall from the xiphoid cartilage to
the ventral part of the last (right) intercostal space. The =anterior
extremity= forms a rounded blind sac which lies against the reticulum.
The =posterior= (or pyloric) =extremity= is much smaller and bends
upward and forward to join the duodenum. About six to eight inches (ca.
15 to 20 cm.) from the pylorus is a constriction which marks off the
pyloric portion from the fundus.
The rumen is attached by peritoneum and connective tissue to the crura
of the diaphragm and left psoas muscles, from the hiatus œsophageus
backward to about the third or fourth lumbar vertebra.
The lesser omentum attaches the right face of the omasum and the pyloric
portion of the abomasum to the visceral surface of the liver.
A small area of the anterior part of the right face of the rumen is
adherent to the adjacent surface of the abomasum. The greater part of
the ventral curvature of the omasum is attached by connective tissue to
the dorsal face of the abomasum.
(Adhesion of the reticulum to the diaphragm is frequently present, but
is pathological; the same is true in regard to adhesion to the liver.)
INTERIOR
The cavity of the rumen is partially divided into dorsal and ventral
sacs by the =pillars=; these are folds of the wall, strengthened by
additional muscular fibers, and correspond with the grooves on the
outside. The two most extensive ones project like shelves into the
anterior and posterior ends of the cavity forming the blind sacs at
either extremity; they are termed the =chief pillars=. The =anterior
chief pillar= (Pila cranialis) projects obliquely backward and upward
from the ventral wall, and has a thick concave free edge which is
opposite to the tenth and eleventh ribs. Its width from the middle of
the free edge to its anterior border is about eight to ten inches (ca.
20 to 25 cm.). It is continued on either side by the relatively narrow
=longitudinal pillars=, which connect it with the posterior pillar. The
=posterior pillar= (Pila caudalis) is more nearly horizontal than the
anterior one, and separates the large dorsal and ventral posterior blind
sacs. Its concave free border is about a hand’s breadth in front of a
transverse plane through the external angles of the ilia. From it are
detached three =accessory pillars= on either side; of these, two pass
around the blind sacs to meet the corresponding pillars of the opposite
side. They thus mark off the posterior blind sacs from the general
cavity, and are termed the =coronary pillars=. It will be noticed that
the ventral coronary pillar is complete, while the dorsal one is not.
The other accessory pillars join the right and left longitudinal
pillars. The =right longitudinal pillar= is in part double; its ventral
division fades out about the middle of the surface, while the dorsal one
joins the posterior chief pillar. The distance between the middles of
the anterior and posterior pillars is =only= about sixteen to eighteen
inches (ca. 40 to 45 cm.) in a cow of medium size. In this space the
dorsal and ventral sacs communicate freely.
The anterior =dorsal blind sac= of the rumen is separated from the
reticulum by an almost vertical fold formed by the apposition of the
walls of the two compartments. This =rumino-reticular fold= (Pila
rumino-reticularis) is opposite to the seventh rib and intercostal
space. Its free upper edge is concave and forms the lower and outer
margin of the large, oval =rumino-reticular orifice= (Ostium
ruminoreticulare). The inner margin of the fold if continued would end
about at the cardia, but there is in this region no demarcation between
rumen and reticulum; hence it is termed the =atrium ventriculi= or
=vestibule=.
If the rumino-reticular fold and an imaginary completion of it be
taken as the boundary between the rumen and reticulum, it will be seen
that the cardia belongs to the latter. The outer border of the
rumino-reticular fold ends above and behind the cardia, the inner one
just behind the œsophageal groove and about four to five inches lower
down. Undoubtedly food or water swallowed with a moderate degree of
force passes first into the rumen. Foreign bodies (which are commonly
swallowed by cattle) are, however, found in the reticulum.
The =cardiac orifice= is opposite the seventh rib, a little to the left
of the median plane and about four inches (ca. 10 cm.) below the spine;
it is not funnel-shaped.
The =mucous membrane= of the rumen is brown in color, except on the
margins of the pillars, where it is pale. It is for the most part
thickly studded with large papillæ, many of which are nearly half an
inch (ca. 1 cm.) long. The edges of the chief pillars and a large part
of the wall of the middle of the dorsal sac are, however, not
papillated. The papillary arrangement is most marked in the blind sacs.
The papillæ vary much in size and form; the largest are foliate, many
are narrow or filiform, and others are conical or club-shaped. The
mucous membrane on the inner wall of the atrium is finely wrinkled and
non-papillated, while above and externally it is papillated. The
papillary arrangement also extends over the edge of the rumino-reticular
fold an inch or two (ca. 2 to 5 cm.).
[Illustration:
FIG. 289.—THORACIC AND ANTERIOR ABDOMINAL VISCERA OF OX, DEEP
DISSECTION.
Most of the rumen has been removed and the left wall of the reticulum
cut away. _A._, Left pulmonary artery; _B._, left bronchus; _V. V.
V._, pulmonary veins; _b. b._, bronchial lymph glands; _L.g._,
posterior mediastinal lymph gland; _D._, termination of duodenum;
_F._, rumino-reticular fold.
]
The =œsophageal groove= (Sulcus œsophageus) is a semicanal which begins
at the cardia and passes downward (ventrally) on the right wall of the
reticulum to end at the reticulo-omasal orifice. It is about six or
seven inches (ca. 15 to 18 cm.) in length. Its axial direction is
practically vertical, but it is twisted in a spiral fashion; thus its
thickened edges or lips project first backward, then to the left, and
finally forward. The twist involves chiefly the left lip, and the
relative positions of the lips is reversed at the ventral end.
The mucous membrane on the lips of the œsophageal groove is brown and
wrinkled, like that of the atrium; in the bottom of the groove it is
pale, like that of the œsophagus, marked by longitudinal folds, and
presents pointed horny papillæ on the lower part.
The =reticulo-omasal orifice= (Ostium reticulo-omasicum) is situated in
the right wall of the reticulum about five or six inches above the
bottom of the latter. It is rounded, and is limited below and laterally
by the junction of the lips of the œsophageal groove.
In the reticulum the mucous membrane is raised into folds about half an
inch high, which inclose four-, five-, or six-sided spaces (Cellulæ
reticuli); this peculiar arrangement suggested the scientific name, and
also the popular term “honeycomb.” These cells are subdivided by smaller
folds, and the bottoms are studded with pointed horny papillæ. The cells
grow smaller and gradually disappear near the œsophageal groove and the
edge of the rumino-reticular fold; an inch or two from the latter the
mucous membrane has the papillary arrangement of the rumen. At the
reticulo-omasal orifice there are peculiar horny papillæ, which are
curved and resemble the claws of a small bird.
[Illustration:
FIG. 290.—RETICULUM OF OX, FROM PHOTOGRAPH.
The specimen was cut along the greater curvature and laid open by
reflecting the anterior wall. _C_, is the cardia. The arrow points
to the reticulo-omasal orifice. The spiral twist of the œsophageal
groove was of necessity partly undone by reflecting the wall; its
lips are drawn apart, showing some of the peculiar birdclaw-like
papillæ in the lower part.
]
The cavity of the omasum is occupied to a considerable extent by about a
hundred longitudinal folds, the =laminæ= (Laminæ omasi), which spring
from the dorsal and lateral walls. The largest of these—a dozen or more
in number—have a convex attached edge, and a ventral, free, slightly
concave edge which reaches to within a short distance of the ventral
wall of the sac. If these are drawn apart or a cross-section is made, it
will be seen that there is a second order of shorter laminæ, and a third
order still shorter; finally, there is a series of very low folds or
lines. The food is pressed into thin layers in the narrow spaces between
the laminæ (Recessus interlaminares), and reduced to a fine state of
division by being ground down by the numerous rounded horny papillæ
which stud the surfaces of the folds. The ventral wall of the omasum
forms a groove (Sulcus omasi), which connects the reticulo-omasal
opening with the omaso-abomasal opening; it is about three or four
inches (ca. 8 to 10 cm.) long, and is directed backward and a little
downward and to the right. It is free from leaves, but marked usually by
slight folds and small papillæ; it forms a direct path from the
reticulum to the abomasum for fluid and finely divided food. In the neck
of the omasum there are thick folds, and a number of the peculiar
papillæ already mentioned as occurring in the lower part of the
œsophageal groove. The =omaso-abomasal orifice= (Ostium
omaso-abomasicum) is oval, and is about four inches (ca. 10 cm.) long.
It is bounded in front by a thick muscular pillar which fades out above
on the lateral walls of the omasum. Laterally there are two folds
(Valvulæ terminales), which probably prevent regurgitation of the
contents of the abomasum.
The cavity of the abomasum is divided by a constriction into two areas.
The first of these (fundus gland region) is lined with a soft glandular
mucous membrane, which forms about a dozen large, slightly spiral folds
(Plicæ spirales). The second part (pyloric region) is much narrower and
resembles in appearance the corresponding region of the horse’s stomach.
A small cardiac gland zone surrounds the omaso-abomasal orifice. The
pyloric orifice is small and round.
[Illustration:
FIG. 291.—MUSCULATURE OF ŒSOPHAGEAL GROOVE AND ADJACENT PART OF
STOMACH OF OX, SEEN FROM WITHIN AFTER REMOVAL OF MUCOUS MEMBRANE.
_a_, Œsophagus; _b_, inner muscular layer of atrium; _d_,
reticulo-omasal orifice; _e_, _e′_, muscle of lips of groove; _g_,
lower end of muscle of larger lip, which curves around the
reticulo-omasal orifice in part and spreads out in the inner
muscular layer of the reticulum in part; _h_, lower end of muscle of
smaller lip which in part curves around the reticulo-omasal orifice
and is in part continuous with the inner muscular layer of the
omasal groove and the omasum; _i_, inner muscular layer of
reticulum. (Ellenberger-Baum, Anat. d. Haustiere.)
]
=Structure.=—The =serous coat= invests all of the free surface of the
stomach. The surface of the rumen which is attached to the dorsal
abdominal wall is of course uncovered, as well as the adjacent area to
which the spleen is attached. The furrows are bridged over by the
peritoneum and superficial muscle-fibers, and contain fat and (in most
cases) branches of the gastric arteries. The =lesser omentum= passes
from the visceral surface of the liver to the right (parietal) face of
the omasum and the pyloric portion of the abomasum. There is a fold
between the ventral curvature of the omasum and the dorsal curvature of
the abomasum. The =great omentum= is formed by the peritoneum leaving
the stomach along the left longitudinal and posterior transverse furrows
and the right surface of the rumen below the longitudinal furrow, also
the ventral curvature of the abomasum. Its superficial (ventral) part is
attached on the right to the duodenum, while the deep (dorsal) part
blends with the mesentery. It conceals the greater part of the intestine
on the right side, with the exception of the duodenum, and covers the
ventral sac of the rumen almost entirely. It is not lace-like, as in the
horse, and contains a large amount of fat in animals in good condition.
The =epiploic foramen= (of Winslow) is almost sagittal in direction.
The =muscular coat of the rumen= consists of an external longitudinal,
and a thicker internal circular layer. The latter forms the bulk of the
chief pillars, where it is about one-half to one inch (ca. 1 to 2 cm.)
thick. Scattered bundles of striped muscle-fibers radiate from the
cardia in the wall of the atrium.
The =muscular coat of the reticulum= consists of two chief layers which
begin and end at the œsophageal groove; they pass in a circular or
oblique fashion around the sac, the fibers of the two layers crossing
each other at an acute angle. The walls of the cells contain a central
muscular layer. The lips of the œsophageal groove contain a thick layer
of longitudinal fibers, which are largely continuous at or cross each
other below the reticulo-omasal orifice. The bottom of the groove has
two layers of oblique, unstriped muscle-fibers, with a variable outer
layer of striped muscle continuous with that of the œsophagus.
The =muscular coat of the omasum= consists of a thin external
longitudinal layer and a thick internal circular layer. At the omasal
groove there is an additional inner layer of longitudinal fibers. The
laminæ contain three muscular strata—a central layer of vertical fibers,
flanked on either side by a layer of longitudinal fibers, which are
continuous at the attached border with the muscularis mucosæ.
[Illustration:
FIG. 292.—STOMACH OF NEW-BORN CALF, RIGHT VIEW.
The rumen is raised.
]
The =muscular coat of the abomasum= consists of longitudinal and
circular layers; the latter forms a well-developed pyloric sphincter.
The =mucous membrane= of the first three divisions is destitute of
glands, and is covered with a thick, stratified, squamous epithelium;
the superficial part of the latter is horny, and is shed in large
patches in the rumen and omasum. The =corium= (Tunica propria) is
papillated. The mucous membrane of the abomasum is glandular, and
corresponds to that of the right sac of the stomach of the horse. The
short fundus glands occur in that part which presents the large folds,
while the long pyloric glands are found in the remainder, except about
the omaso-abomasal orifice, where cardiac glands occur. The mucosa of
the fundus gland region is very thin as compared with that of the horse.
There is a round prominence on the pyloric valve.
THE INTESTINE
The intestine of the ox lies almost entirely to the right of the median
plane, chiefly in contact with the right face of the rumen. It is
attached to the sublumbar region by a common mesentery.
The =small intestine= has an average length of about 130 feet (ca. 40
m.) and a diameter of about two inches (ca. 5 to 6 cm.).
The =duodenum= is about three or four feet (ca. 1 m.) in length. It
passes forward to the visceral surface of the liver; here it forms,
ventral to the right kidney, an =S=-shaped curve. Thence it runs
backward almost to the external angle of the ilium, where it turns on
itself, passes forward alongside of the terminal part of the colon, and
joins the mesenteric part (jejunum) under the right kidney. It is
attached to the liver by the lesser omentum, to the abomasum by the
great omentum, and to the terminal part of the colon. The =bile-duct=
opens in the ventral part of the =S=-shaped curve, about two feet (ca.
60 cm.) from the pylorus. The =pancreatic duct= opens about a foot (ca.
30 cm.) further back.
The remainder of the small intestine is arranged in numerous very close
coils, in contact chiefly with the right face of the ventral sac of the
rumen, forming a sort of festoon at the edge of the mesentery. It is not
subject to much variation in position, but a few coils may find their
way behind the blind sacs of the rumen to the left side.
[Illustration:
FIG. 293.—PEYER’S PATCHES OF SMALL INTESTINE OF OX (about ⅓ natural
size).
]
The orifices of the pancreatic duct and the bile-duct are on papillæ, no
diverticulum being present. There are permanent transverse folds of the
mucous membrane (Plicæ circulares). Duodenal glands (of Brunner) occur
in the first fifteen feet or more (4 to 5 m.), intestinal glands
throughout. Peyer’s patches are larger and more distinct than in the
horse, and vary greatly in size and number; in adult cattle there are
eighteen to forty; in calves, twenty to fifty-eight. They usually have
the form of narrow bands. Close to the ileo-cæcal valve there is always
a patch, and in most cases there is also a patch on the cæcal side of
the valve.
The =large intestine= is much smaller in caliber than that of the horse,
has no bands, and is not sacculated. Most of it is situated between the
layers of the common mesentery.
The =cæcum= is about 20 to 30 inches (ca. 50 to 60 cm.) long, 4 to 5
inches (ca. 10 to 12 cm.) wide, and has a capacity of about 2½ gallons
(ca. 9 to 10 liters). It begins opposite the lower part of the eleventh
rib, and extends upward and backward against the right flank; its
rounded blind end is free, and lies near or in the pelvic inlet.
[Illustration:
FIG. 294.—PROJECTION OF VISCERA OF BULL ON BODY-WALL, RIGHT SIDE.
_P._, Pylorus; _G.b._, gall-bladder; _R.K._, right kidney; _L.K._,
left kidney; _P._, (above duodenum) pancreas; _Bl._, urinary
bladder; _V.s._, vesicula seminalis; _B.g._, bulbo-urethral
(Cowper’s) gland. Costal attachment and median line of diaphragm are
indicated by dotted lines.
]
[Illustration:
FIG. 295.—LIVER OF OX, PARIETAL SURFACE; HARDENED _in situ_.
]
The =colon= is about 35 feet (ca. 10 m.) long; its diameter is at first
about the same as that of the cæcum, but diminishes to about two inches
(ca. 5 cm.). Its capacity is about 6 to 8 gallons (ca. 25 to 30 liters).
With the exception of its first and terminal parts, it is arranged in
double elliptical coils between the layers of the mesentery; the
adjacent parts are therefore alternately centripetal and centrifugal
(Gyri centripetales et centrifugales). The first part (Ansa proximalis)
is marked off from the cæcum only by the ileo-cæcal opening; it forms an
=S=-shaped curve and is continued by the spiral part (Ansa spiralis).
The coils of this are attached to each other by connective tissue, and
are best seen from the inner side. The bowel gradually diminishes in
caliber, and the terminal part (Ansa distalis) leaves the spiral mass,
passes forward to the great mesenteric artery and turns backward between
the duodenum and the initial sigmoid part. From the ventral surface of
the right kidney it passes backward, forms an =S=-shaped curve near the
pelvic inlet, and joins the rectum; this part is attached to the
sublumbar muscles by a short mesentery, and is also attached to the
dorsal part of the duodenum.
The =rectum= is somewhat shorter than that of the horse, and is usually
covered with peritoneum as far back as the first coccygeal vertebra. The
retroperitoneal part is surrounded by a quantity of fat. The anus is not
prominent.
[Illustration:
FIG. 296.—LIVER OF OX, LEFT MARGINAL VIEW; HARDENED _in situ_.
]
The =serous coat= is of course absent on the adherent surfaces of the
spiral part of the colon. There is a large amount of fat in the
mesentery. The =longitudinal muscular coat= is evenly distributed,
consequently there is no sacculation of the bowel. There is a valvular
mucous fold at the ileo-cæcal orifice. A Peyer’s patch occurs in the
beginning of the cæcum and one in the first part of the colon.
THE LIVER
The liver lies almost entirely to the right of the median plane. Its
long axis is directed obliquely downward and forward, about parallel
with the median plane, and corresponds to the curvature of the right
portion of the diaphragm. It is less extensive, but thicker than that of
the horse. Its average weight is about 10 to 12 pounds (ca. 4.5 to 5.5
kg.).
In small subjects the weight (according to Schmaltz) varies from 6½ to
10 pounds (ca. 3 to 4.5 kg.), in large subjects from 11 to 13 pounds
(ca. 5 to 6 kg.). According to Schneider, the average weight is about
13 pounds (ca. 6 kg.)—a little over 1 per cent. of the live weight and
about 2 per cent. of the dressed carcass.
When hardened _in situ_, its configuration adapts it accurately to the
structures with which it is in contact.
The =parietal surface= is convex and is for the most part applied to the
right part of the diaphragm, but a small part of it is in direct contact
with the last two ribs and with the flank at the lumbo-costal angle. It
faces upward, forward, and to the right.
The curvature of the parietal surface is not regular. It is marked,
except in its ventral part, by a blunt oblique ridge which corresponds
to the basal border of the right lung. This prominence divides the
surface into two areas. Of these, the external one is directed
outward, is only slightly convex, and often shows impressions of the
last three ribs. The inner area presents a depression produced by the
right crus of the diaphragm, and otherwise is regularly convex and
adapted to the tendinous center and sternal portion of the diaphragm.
The falciform ligament is attached to the surface from the œsophageal
notch to the umbilical fissure.
[Illustration:
FIG. 297.—LIVER OF YOUNG OX, VISCERAL SURFACE; HARDENED _in situ_.
]
The =visceral surface= is concave and very irregular; it presents
impressions of the chief organs which are in contact with it—the omasum
and reticulum. It is also related to the pancreas and duodenum.
The following markings are quite distinct on the visceral surface of
well hardened specimens: (1) The omasal impression (Impressio omasica)
is a deep central cavity below the portal fissure. (2) The reticular
impression (Impressio reticularis) is a smaller marginal depression
below the œsophageal notch and the inner part of the preceding, from
which it is separated by a rounded ridge. (3) The abomasal impression
(Impressio abomasica), present only in the calf, is produced by the
anterior part of the abomasum. It lies along the ventral part of the
surface, and is separated by ridges from the preceding impressions. It
disappears as the omasum and reticulum increase in size and displace
the abomasum from contact with the liver. (4) Shallow grooves for the
=S=-shaped portion of the duodenum (Impressio duodenalis) may be found
above and external to the portal fissure. (5) The fossa of the
gall-bladder (Fossa vesicæ felleæ) is distinct when that organ is
full. In the calf the omasal impression is small, and the abomasal one
large in correspondence with the relative sizes of these two sacs.
The =portal fissure= is a well defined rounded depression, situated
dorsal to the omasal impression. It contains, besides the vessels and
duct, several large hepatic lymph glands. Above and external to it a
part of the pancreas is attached.
[Illustration:
FIG. 298.—LINE DRAWING OF LIVER OF OX, VISCERAL SURFACE OF SOFT
SPECIMEN.
_L.g._, Hepatic lymph glands at portal fissure.
]
The =dorsal border= is short and thick; it extends backward a short
distance beyond the upper part of the last rib. It presents the large,
thick, quadrilateral =caudate lobe=, and a deep depression for the right
kidney and adrenal.
The =ventral border= is short and thin and has no interlobar incisures.
The =right= (or external) =border= is marked by a small umbilical
fissure, in which the ligamentum teres is attached in the young subject.
The =left border= presents the œsophageal notch below its middle. Above
this it is practically median in position, and lodges the posterior vena
cava, which is partially embedded in the gland. Below the notch the
border extends an inch or two (ca. 2.5 to 5 cm.) to the left of the
median plane opposite the ventral third of the sixth rib.
There is no left lateral ligament. The falciform ligament is usually
present, but the ligamentum teres is found only in young subjects. The
lesser omentum leaves the liver along a line extending from the
œsophageal notch to the portal fissure. The only distinct lobe in the
adult is the caudate (Processus caudatus).
[Illustration:
FIG. 299.—PANCREAS OF OX, GASTRO-INTESTINAL SURFACE, WITH RELATED
ORGANS.
The position of some of the larger lymph glands (_l.g._) is indicated
by dotted line; also the intraglandular course of the pancreatic
duct. Probe is passed through epiploic foramen (of Winslow).
]
A =gall-bladder= (Vesica fellea) is present. This is a pear-shaped sac,
four to six inches (ca. 10 to 15 cm.) long, which lies partly on the
visceral surface of the liver (to which it is attached), but largely on
the abdominal wall at the lower part of the eleventh or twelfth
intercostal space. It may be regarded as a diverticulum of the
bile-duct, enlarged to form a reservoir for the bile. Its neck is
continued by the =cystic duct= (Ductus cysticus), which joins the
hepatic duct at an acute angle just outside of the portal fissure, to
form with it the bile-duct (Ductus choledochus). The latter is short and
enters the second bend of the =S=-shaped curve of the duodenum, _i. e._,
about two feet (ca. 60 cm.) from the pylorus. Several small ducts
(Ductus hepato-cystici) open directly into the gall-bladder.
In the new-born calf the liver is relatively much larger than in the
adult. The visceral surface presents, below the portal fissure, a
large rounded eminence, which is caused by the presence in the
underlying gland substance of a large venous sinus into which the
umbilical and portal veins empty. A large vessel, the =ductus
venosus=, leads from this sinus directly to the posterior vena cava.
Just external to this elevation is a small but distinct lobe about two
inches long (Processus papillaris?). The umbilical fissure is deep and
partially divides the gland into two chief lobes.
THE PANCREAS
The pancreas of the ox is irregularly quadrilateral in form, and lies
almost entirely to the right of the median plane. Its weight is about
the same as that of the horse. Its dorsal surface is related to the
crura of the diaphragm, the cœliac and anterior mesenteric arteries, and
the liver. It is attached to the liver at and external to the portal
fissure, and to the crura of the diaphragm. Between these adhesions it
is free and forms the ventral wall of the epiploic foramen (of Winslow).
On the right side it extends backward beyond the caudate lobe of the
liver between the layers of the mesoduodenum; here it is in contact with
the upper part of the flank at the lumbo-costal angle, and is related
above to the right kidney and by its ventro-lateral border to the
ventral part of the duodenum. The gastro-intestinal or ventral surface
is in contact with the dorsal curvature of the rumen and the intestine.
The portal vein passes through the gland. The left extremity is small;
the right or posterior is wide and thin and is often divided into two
branches. The duct leaves the posterior part of the ventro-lateral (or
right) border and enters the duodenum about twelve inches (ca. 30 cm.)
further back than the bile-duct.
[Illustration:
FIG. 300.—SPLEEN OF OX; VISCERAL SURFACE.
]
THE SPLEEN
The spleen has an elongated, elliptical outline, both extremities being
thin, rounded, and similar in size.
Its average weight is about 30 ounces (ca. 800 to 900 gm.), or about ⅙
per cent. of the body-weight. Its length is about 16 to 20 inches (ca.
40 to 50 cm.), its width about 5 to 6 inches (ca. 12 to 15 cm.), and in
the middle its thickness is about an inch (ca. 2 to 3 cm.).
The =dorsal extremity= lies under the upper ends of the last two ribs;
the =ventral extremity= is usually opposite the seventh or eighth rib,
about a handbreadth above its junction with the cartilage. The =parietal
surface= is convex, and is related to the diaphragm. The =visceral
surface= is concave, and is related chiefly to the left face of the
rumen, but also usually to a narrow adjacent area of the reticulum. The
dorsal part is attached to the left crus of the diaphragm and the left
surface of the rumen by peritoneum and connective tissue; the ventral
part is free. The hilus is situated on the dorsal third of the visceral
surface, near the anterior border.
About one-half of the visceral surface of the spleen is attached
directly to the rumen and is not covered by peritoneum; the line of
reflection of the latter crosses the surface obliquely, from the upper
part of the posterior border to the anterior border a little below the
middle. Similarly there is a narrow uncovered area on the upper part
of the parietal surface along the anterior border. The hilus is not a
groove, but a simple depression. When hardened _in situ_, the organ is
seen to be somewhat twisted, so that the upper part of the parietal
surface faces upward and forward, while below it is directed outward.
DIGESTIVE SYSTEM OF THE SHEEP
The =lips= are thin and mobile; the upper one is marked by a very
distinct philtrum, and otherwise is not bare.
The anterior part of the =hard palate= is prominent and smooth; on the
posterior part of this area there are two narrow depressions in the form
of a =V=, at the deep anterior ends of which the naso-palatine ducts
open. The ridges of the palate are irregular and their edges are smooth.
The posterior third or rather more of the palate is not ridged and
presents numerous orifices of ducts of the palatine glands. The mucous
membrane is often more or less pigmented.
The mucous membrane of the =cheeks= is covered with large papillæ, many
of which are long and sharp-pointed, while others are short and blunt.
There is also a series of conical papillæ on the floor of the mouth
under the lateral part of the tongue.
The =tongue= resembles that of the ox in form, but the tip is
comparatively smooth; the papillæ here are very numerous, but short and
blunt. This difference is in conformity with the dissimilarity in the
mode of prehension. The prominence of the dorsum is commonly not so
pronounced nor so sharply marked off in front as in the ox. The root is
smooth. The mucous membrane of the dorsum is often pigmented in spots.
The dental formula is the same as that of the ox. The =incisor teeth=
form a narrow and strongly curved arch. The crowns are long and narrow;
their labial surfaces are strongly convex and end at a sharp edge which
is used in cropping the grass. The roots are more firmly embedded than
in the ox.
The =cheek teeth= resemble those of the ox. There is a thinner layer of
cement, which is usually black.
The average periods of eruption of the teeth are indicated in the
subjoined table.
TEETH TEMPORARY PERMANENT
I_{1}. At birth or first 1 to 1½ years
week
I_{2} First or second week 1½ to 2 years
I_{3} Second or third week 2½ to 3 years
I_{4} Third or fourth week 3½ to 4 years
──────────────────────────────────────────────────────────────
P_{1} 2 to 6 weeks. 1½ to 2 years
P_{2} „ „
P_{3} „ „
──────────────────────────────────────────────────────────────
M_{1} 3 months (lower), 5 months (upper)
M_{2} 9 to 12 months
M_{3} 1½ to 2 years
[Illustration:
FIG. 301.—STOMACH OF SHEEP, LEFT VIEW.
From photograph of specimen hardened _in situ_. The reticulum is
somewhat contracted. Arrow points to posterior furrow between blind
sacs.
]
[Illustration:
FIG. 302.—STOMACH OF SHEEP, RIGHT VIEW.
From photograph of specimen hardened _in situ_. Dotted line indicates
position of spleen.
]
The =salivary glands= resemble those of the ox in general, but the
parotid duct crosses the surface of the masseter muscle, and opens
opposite the third or fourth cheek tooth.
The =tonsil= is bean-shaped and about half an inch (ca. 12 mm.) in
length. It does not project into the fauces. The mucous membrane of the
latter presents two deep and very narrow tonsillar sinuses on either
side.
[Illustration:
FIG. 303.—CROSS-SECTION OF SHEEP, THROUGH NINTH THORACIC VERTEBRA,
ANTERIOR VIEW.
_1_, Cardiac orifice; _2_, œsophageal groove; _3_, rumino-reticular
orifice; _4_, rumino-reticular fold; _5_, dorsal sac of rumen; _6_,
body of ninth thoracic vertebra; _7_, vena hemiazygos; _8_, aorta;
_9_, posterior mediastinal lymph gland; _10_, _10_, crura of
diaphragm; _11_, posterior vena cava; _12_, portal vein; _R.l._,
right lung; _L.l._, left lung; _S_, spleen (cut very obliquely);
_L_, liver; _R_, reticulum (posterior wall). Arrow points to
reticulo-omasal orifice.
]
The fornix of the =pharynx= presents a median plicated fold which is a
continuation of the septum nasi. The pharyngeal orifice of the
Eustachian tube has the form of a crescentic slit, placed about on a
level with the inferior nasal meatus. There are two large lymph glands
and a number of hæmolymph glands above the pharynx.
The =œsophagus= has a lumen of about an inch when moderately distended;
otherwise it resembles that of the ox.
[Illustration:
FIG. 304.—ABDOMINAL VISCERA OF SHEEP, SUPERFICIAL VENTRAL VIEW.
]
The =stomach= is like that of the ox in its general arrangement. Its
average capacity is about four gallons (ca. 15 liters). The =cardiac
opening= is opposite the middle of the eighth intercostal space; it is
just to the left of the median plane and about two to three inches (ca.
5 to 7 cm.) below the vertebral column. The ventral sac of the =rumen=
is relatively larger and extends further to the right of the median
plane than in the ox. There are no coronary pillars in the dorsal sac,
but its upper part is papillated. The papillæ of the rumen are
relatively =large= and somewhat tongue-like; the largest are about a
fourth of an inch (ca. 6 mm.) in length. The =reticulum= is relatively
larger than in the ox. Its ventral part curves more backward and less to
the right than in the ox. The parietal surface extends forward as far as
the sixth rib or intercostal space, and is related to the diaphragm and
liver. The fundus lies on the sternal part of the diaphragm and in
contact with the abomasum. The =œsophageal groove= is disposed much like
that of the ox, and is about four to five inches (ca. 8 to 10 cm.) long.
The =omasum= is much smaller than the reticulum, its capacity being only
about one pint. It is oval and compressed laterally. It is situated
almost entirely to the right of the median plane, opposite to the ninth
and tenth ribs, higher than in the ox, and has no contact with the
abdominal wall. It is related on the right to the liver and
gall-bladder, on the left to the rumen, and below to the abomasum. The
laminæ are less numerous than in the ox; in the neck which connects the
omasum with the reticulum they have the form of low thick ridges, and
bear long, pointed, horny papillæ. The =abomasum= is relatively larger
and longer than in the ox. Its capacity is about twice that of the
reticulum and averages about two quarts (ca. 1.75 to 2 liters). The
blind anterior end lies almost centrally in the xiphoid region, in
relation to the liver and reticulum. Its body extends backward a little
below and almost parallel with the right costal arch. The pylorus is
opposite the ventral end of the eleventh or twelfth intercostal space.
The cells of the reticulum are much shallower than in the ox. At the
reticulo-omasal opening and on the adjacent part of the laminæ of the
omasum are large, pointed, horny papillæ. The number of laminæ is less
than in the ox.
The general arrangement of the =intestine= is like that of the ox. The
=small intestine= is about 80 feet (ca. 24 to 25 m.) long; its average
diameter is about an inch (ca. 2 to 3 cm.), the caliber increasing in
its terminal part, where a very extensive Peyer’s patch is found. The
=cæcum= is about 10 to 12 inches (ca. 25 to 30 cm.) long, 2 inches (ca.
5 cm.) wide, and has a capacity of about a quart (ca. 1 liter). The
=colon= is about 15 feet (ca. 4 to 5 m.) long. Its caliber is at first
about the same as that of the cæcum, but diminishes to about the width
of the small intestine.
[Illustration:
FIG. 305.—LIVER OF SHEEP, VISCERAL SURFACE; HARDENED _in situ_.
]
The =liver= weighs about 20 to 25 ounces (ca. 550 to 700 gm.). It lies
entirely to the right of the median plane. The parietal surface is
related almost exclusively to the right part of the diaphragm. The
visceral surface presents extensive reticular and abomasal impressions,
and a small omasal impression internal to the portal fissure. The
umbilical fissure is deep and partially divides the gland into two chief
lobes. The caudate lobe is prismatic and blunt-pointed. The neck of the
gall-bladder is long. The bile-duct joins the pancreatic duct to form a
=common duct= (Ductus choledochus communis) which opens into the
duodenum about one foot (ca. 30 cm.) from the pylorus.
The =pancreas= is arranged as in the ox. Its duct unites with the
bile-duct.
The =spleen= (Fig. 301) is somewhat triangular, with the angles rounded
off. It weighs about three or four ounces (ca. 100 grams). Its length is
about five inches (ca. 12 to 13 cm.) and its greatest width about four
inches (ca. 10 cm.). The parietal surface is convex and is related to
the diaphragm, to which rather more than the anterior third is adherent.
The visceral surface is concave and its anterior half is attached to the
dorsal curvature of the rumen. The dorsal end or base is attached to the
left crus of the diaphragm under the last two or three ribs. The hilus
is at the posterior basal angle. The ventral end is narrower and thinner
than the base; it is situated opposite the ninth and tenth ribs above
their middles.
[Illustration:
FIG. 306.—LIVER OF SHEEP, PARIETAL SURFACE; HARDENED _in situ_.
]
DIGESTIVE SYSTEM OF THE PIG
THE MOUTH
The =rima oris= is extensive, the angles of the mouth being situated far
back. The =upper lip= is thick and short, and is blended with the snout;
the =lower lip= is small and pointed. The labial glands are few and
small.
The mucous membrane of the =cheeks= is smooth. The =buccal glands= are
compactly arranged in two rows opposite the cheek teeth. The =parotid
duct= opens opposite the fourth or fifth cheek tooth.
The =hard palate= is long and narrow; it is marked by a median furrow,
on each side of which are twenty or more ridges. On its anterior part
there is a triangular incisive papilla, at which the naso-palatine ducts
open.
The =soft palate= is very thick. Its direction almost continues that of
the hard palate, _i. e._, it is nearly horizontal. It extends to the
middle of the oral surface of the epiglottis.[110] It has a median
prolongation termed the =uvula=. The oral surface presents a median
furrow, on either side of which is an oval raised area, marked by
numerous crypts; these elevations are the =tonsils=. Tonsillar tissue
also occurs in the lateral walls of the fauces.
[Illustration:
FIG. 307.—TONGUE OF PIG.
_1_, Apex; _2_, dorsum; _3_, root; _a_, orifices of ducts of lingual
glands; _b_, papillæ of root; _c_, vallate papilla (not really so
distinct as in figure); _d_, foliate papilla; _e_, fungiform
papillæ; _f_, epiglottis (pulled back); _g_, median
glosso-epiglottic fold. (Ellenberger-Baum, Anat. _d_. Haustiere.)
]
The =tongue= is long and narrow and the apex is thin. Two or three
vallate papillæ are present. The fungiform papillæ are small and are
most numerous laterally. The filiform papillæ are soft and very small.
On the root there are soft, long, pointed papillæ, directed backward.
Foliate papillæ are also present.
There is a well-marked median glosso-epiglottic fold, on either side of
which is a depression (Vallecula epiglottica). The frenum linguæ is
double.
The =dental formula= of the pig is:
( 3 1 4 3 )
2 ( I - C - P - M - ) = 44
( 3 1 4 3 )
The formula for the temporary teeth is:
( 3 1 4 )
2 ( Di - Dc - Dp - ) = 32
( 3 1 4 )
The =upper incisors= are small; they are separated from each other by
spaces, and from the canines by a larger interval. The first incisors
are the largest, are convergent, and have no distinct neck. The second
are narrower and somewhat smaller. The third (corner) incisors are much
smaller, are flattened laterally, and have three small eminences on the
crown.
The =lower incisors= are almost horizontal and are convergent and close
together. The first and second are about equal in size, prismatic, and
deeply implanted in the jaw. The labial surface is slightly convex, the
lingual concave and marked near its extremity by a ridge. The third
incisor is much smaller and has a short narrow crown and a distinct
neck.
[Illustration:
FIG. 308.—SKULL OF PIG ABOUT A YEAR AND A HALF OLD, SCULPTURED TO SHOW
THE EMBEDDED PARTS OF THE TEETH.
_I1–3_, Incisors; _C_, canines; _P1–4_, premolars; _M1–3_, molars.
]
The =canine teeth= or tusks of the male are greatly developed and
project out of the mouth. The upper canine of the boar may be about
three or four inches (ca. 8 to 10 cm.) long. The crown is conical and is
curved somewhat backward and outward; the embedded part is curved and
has a large pulp cavity.[111] The lower canine may reach a length of
eight inches or more (ca. 20 cm.); the crown is prismatic and is curved
backward and outward in front of the upper one, so that the friction
between the two keeps a sharp edge on the lower tooth. In the sow they
are much smaller.
[Illustration:
FIG. 309.—SUPERFICIAL GLANDS OF HEAD OF PIG.
_a_, Parotid gland; _a′_, _a″_, cervical and submaxillary angles of
_a_; _b_, _c_, ventral and dorsal buccal glands; _d_, labial glands;
_e_, masseter muscle; _f_, _f′_, lymph glands; _g_, dotted line
indicating outline of submaxillary gland, which is concealed.
(Ellenberger-Baum, Anat. d. Haustiere.)
]
The average periods of =eruption= of the teeth are given in the
subjoined table.
TOOTH│ ERUPTION │ CHANGE
│ │
I_{1}│2 to 4 weeks │12 months
I_{2}│upper 2 to 3 months│
│lower 1½ to 2 month│16 to 20 months
I_{3}│Before birth │8 to 10 months
C │Before birth │9 to 10 months
P_{1}│5 months │
─────┼───────────────────┼───────────────────
P_{2}│5 to 7 weeks │12 to 15 months
P_{3}│upper 4 to 8 days │ „
│lower 2 to 4 weeks.│
P_{4}│upper 4 to 8 days │ „
│lower 2 to 4 weeks │
─────┼───────────────────┼───────────────────
M_{1}│4 to 6 months │
M_{2}│8 to 12 months │
M_{3}│18 to 20 months │
The =cheek teeth= increase in size from before backward. They have (with
certain exceptions noted below) complex tuberculate crowns; the term
bunodont is applied to this condition, as distinguished from the
selenodont structure in horses and cattle, in which there are prominent
ridges of enamel. They are short-crowned teeth with a distinct neck and
root. The first tooth in each jaw is small, simple, and appears only
once; in the lower jaw it is near the canine, in the upper near the
second cheek tooth. The next two teeth are larger, laterally compressed,
and sectorial. The fourth tooth below is larger, but otherwise like the
preceding ones, while the upper one is much wider and is tuberculate.
[Illustration:
FIG. 310.—DISSECTION OF MOUTH AND PHARYNGEAL REGION OF PIG.
_1_, Hard palate; _2_, tongue showing distinctly fungiform papillæ;
_3_, foliate papilla; _4_, lymph nodules of soft palate; _5_,
stylo-glossus muscle, out of which a portion has been cut; _6_,
hyo-glossus; _7_, genio-glossus; _8_, genio-hyoideus; _9_,
mylo-hyoideus (reflected); _10_, stylo-hyoideus; _11_, great cornu
of hyoid bone; _12_, tensor palati; _13_, levator palati; _14_,
pterygo- et palato-pharyngeus; _15_, stylo-pharyngeus; _16_,
chondro-pharyngeus; _17_, sterno- et omo-hyoideus; _18_,
retropharyngeal lymph glands; _a_, bulla ossea; _b_, paramastoid
process. (Ellenberger-Baum, Anat. d. Haustiere.)
]
The =parotid gland= is large and triradiate. It extends very little on
to the masseter muscle and its upper angle does not quite reach the base
of the ear. It is pale in color, and is embedded in fat in animals in
good condition. On its deep face are several large subparotid lymph
glands, some of which are only partially covered by the parotid. The
=duct= arises on the deep face, has a course similar to that of the ox,
and perforates the cheek opposite the fourth or fifth upper cheek tooth.
Small accessory glands (Glandulæ parotideæ accessoriæ) may be found
along the course of the duct.
The =submaxillary gland= is small, reddish in color, and oval in
outline; it is covered by the parotid. Its superficial face is convex,
and is marked by rounded prominences. From its deep face a narrow
process extends forward about two or three inches (ca. 5 to 7.5 cm.)
beneath the mylo-hyoideus muscle along with the duct. The latter opens
near the frenum linguæ, but there is no papilla.
[Illustration:
FIG. 311.—SAGITTAL SECTION OF PHARYNGEAL REGION OF PIG, PARTLY
SCHEMATIC.
_1_, Palate bone; _2_, sphenoid bone; _2′_, sphenoidal sinus; _2″_
occipital bone; _3_, epiglottis; _4_, arytenoid cartilage; _5_,
thyroid cartilage; _6_, root of tongue; _7_, mouth cavity; _8_,
isthmus faucium; _9_, hard palate; _10_, septum nasi; _11_, ventral
muscles of head; _a_, soft palate; _a′_, free edge of _a_; _b_,
dorsal wall of pharynx; _c_, fornix of pharynx; _d_, cavity of
larynx; _e_, _g_, naso-pharynx; _f_, oro-pharynx; _h_, posterior
pillar of soft palate; _i_, dotted line indicating lateral boundary
between nasal cavity and pharynx; _k_, aditus laryngis; _l_,
entrance to œsophagus; _m_, Eustachian orifice; _n_, pharyngeal
recess; _o_, posterior naris. (After Ellenberger, in Leisering’s
Atlas.)
]
[Illustration:
FIG. 312.—STOMACH OF PIG, PARIETAL SURFACE.
The organ contained a rather small amount of ingesta and hence is
somewhat contracted.
]
[Illustration:
FIG. 313.—STOMACH OF PIG, VISCERAL SURFACE.
Organ was fixed _in situ_ and is somewhat contracted.
]
The =sublingual gland= has an arrangement similar to that of the ox. The
posterior part (Glandula sublingualis grandicanalaris) is reddish-yellow
in color, and is about two inches (ca. 5 cm.) long, and half an inch
wide; its posterior end is in relation to the submaxillary gland and its
duct. The anterior part is much larger, being two or three inches (ca. 5
to 7 cm.) long and about twice the width and thickness of the posterior
part. All or most of the ducts from the posterior part unite to form the
=ductus sublingualis major=, which opens near the ductus submaxillaris.
Eight or ten =ductus sublinguales minores= convey the secretion from the
anterior part through the floor of the mouth.
[Illustration:
FIG. 314.—DIAGRAM OF ZONES OF MUCOUS MEMBRANE OF STOMACH OF PIG.
]
[Illustration:
FIG. 315.—VISCERAL SURFACE OF STOMACH OF PIG, FROM WHICH THE SEROUS
COAT HAS BEEN REMOVED.
]
[Illustration:
FIG. 316.—EVERTED STOMACH OF PIG, FROM WHICH THE MUCOUS MEMBRANE HAS
BEEN REMOVED.
_O_, Œsophagus; _D_, duodenum; _Di_, diverticulum; _a_, _a′_, _a″_,
_a‴_, longitudinal fibers; _b_, circular fibers; _c_, external
oblique fibers; _c′_, internal oblique fibers; _c″_, cardiac loop;
_d_, fibers which connect branches of cardiac loop; _f_, fold at
entrance to diverticulum; _p_, pyloric sphincter; _p′_, pyloric
prominence. (Ellenberger-Baum, Anat. d. Haustiere.)
]
THE PHARYNX
The =pharynx= presents in its posterior part a median cul-de-sac about
an inch and a half (ca. 3 to 4 cm.) long, which is situated between the
ventral straight muscles of the head and the origin of the œsophagus.
Its lower margin is formed by the junction of the posterior pillars of
the soft palate, which contain muscular tissue derived from the
palatinus and palato-pharyngeus. The vault of the pharynx (Fornix
pharyngis) is divided by a median fold of mucous membrane which is a
direct continuation of the septum nasi. On either side of this is an
infundibulum in which the Eustachian tube opens.
THE ŒSOPHAGUS
The =œsophagus= is short and nearly straight. It has (according to
Rubeli) a potential caliber of nearly 3 inches (ca. 7 cm.) at either
end, and about 1⁷⁄₁₀ inches (ca. 4.2 cm.) in its middle part.[112] The
muscular coat, except near the cardia, is striated. There are mucous
glands in the submucosa to about the middle of the tube.
[Illustration:
FIG. 317.—ABDOMINAL VISCERA OF YOUNG PIG, VENTRAL ASPECT.
The stomach was very large in this subject.
]
[Illustration:
FIG. 318.—DIAGRAM OF CÆCUM AND COLON OF PIG.
Coils of colon have been pulled apart somewhat.
]
[Illustration:
FIG. 319.—SOLITARY NODULES FROM LARGE INTESTINE OF PIG.
(Ellenberger-Baum, Anat. d. Haustiere.)
]
[Illustration:
FIG. 320.—ILEO-CÆCAL OPENING AND ADJACENT PART OF CÆCUM AND COLON OF
PIG.
_a_, Mucous membrane of colon; _b_, mucous membrane of cæcum; _c_,
Peyer’s patch; _d_, ileo-cæcal opening; _e_, end of ileum; _f_,
folds (frenula) of ileum. (After P. Schumann.)
]
THE STOMACH
The =stomach= is large and pyriform. Its average capacity is about 1½ to
2 gallons (ca. 5.7 to 8 liters). When full it extends backward to the
last left intercostal space laterally and the umbilicus ventrally. The
left portion is large and rounded, while the right portion (Pars
pylorica) is small, and bends sharply upward to join the small
intestine. The parietal surface is related to the liver, gall-bladder,
and diaphragm. The visceral surface is related to the intestine, the
mesentery, and the pancreas. The great curvature is related to the
diaphragm, spleen, and abdominal floor. The pyloric end lies on the
right lateral lobe of the liver. The left extremity presents a flattened
conical blind pouch, the =diverticulum ventriculi=, the apex of which
projects backward. The œsophagus joins the stomach very obliquely,
almost in the median plane, and about three or four inches (ca. 8 to 10
cm.) below the twelfth thoracic vertebra. The cardiac opening is
slit-like and is bounded above and to the left by a fold which contains
a thickening of the internal oblique layer of the muscular coat. The
opening into the diverticulum is situated above and a little to the left
of the cardia; it is transversely oval, and is bounded (except
externally) by a thick fold which contains spirally arranged muscular
fibers. The mucous membrane may be divided into four regions. Over a
quadrilateral area around the cardia (about one inch on the right and
two or three inches on the left side of the orifice) it is œsophageal in
character, and presents a number of folds. A sharp line of demarcation
separates this from the rest of the mucous membrane, which is soft and
glandular. The second or cardiac gland region is pale gray in color and
thin (ca. 0.5 to 1 mm.); it extends about to the middle of the stomach.
The third or fundus gland region is readily distinguished by its
thickness (ca. 3 mm.) and its brownish-red mottled appearance.[113] The
fourth or pyloric region is pale, thinner than the preceding, and
presents a number of irregular folds. At the pylorus there is a
remarkable ridge which projects from the wall of the lesser curvature
and diminishes considerably the size of the orifice. It is about an inch
and a half (ca. 3 to 4 cm.) long and nearly half an inch (ca. 1 cm.)
high. Sometimes it is grooved; in other cases it has the form of a
rounded eminence attached by a pedicle to the wall. Fibers from the
circular muscular coat extend into it.
[Illustration:
FIG. 321.—LIVER OF PIG, SOFT SPECIMEN SKETCHED WITH LOBES DRAWN APART.
]
THE INTESTINE
The =small intestine= is 50 to 65 feet (ca. 15 to 20 m.) long. The
mesentery of about the first two feet (ca. 60 cm.) is two to two and a
half inches (ca. 5 to 6 cm.) long; this part may be termed duodenum. The
remainder (Jejuno-ileum) has a mesentery about six to eight inches (ca.
15 to 20 cm.) long, which is thick and contains a quantity of fat, and
numerous large lymph glands at its root; the root is attached in the
sublumbar region behind the stomach and blends here with the mesentery
of the large intestine. The small intestine is arranged in close coils
and lies mainly on the left side and floor of the abdomen, from the
stomach to the pelvis; some coils, however, lie against the right flank.
The opening of the =bile-duct= is about one or two inches (ca. 2.5 to 5
cm.) from the pylorus, and that of the =pancreatic duct= about four or
five inches (ca. 10 to 15 cm.) beyond it. =Peyer’s patches= and
=solitary glands= are numerous and very distinct; the patches are
usually band-like and prominent; the solitary glands form projecting
nodules marked by crypts.
[Illustration:
FIG. 322.—LIVER OF PIG, VISCERAL SURFACE.
Photograph of specimen hardened _in situ_.
]
The =large intestine= is about 15 feet (ca. 4 to 5 meters) in length,
and is for the most part much wider than the small intestine; it is
connected by a mesentery with the dorsal abdominal wall between the
kidneys. The =cæcum= is cylindrical, about 8 to 12 inches (ca. 20 to 30
cm.) long, and 3 to 4 inches (ca. 8 to 10 cm.) wide. It lies against the
upper part of the right flank, its blind end reaching to within about
two inches (ca. 5 cm.) of the pelvic inlet. The ileum joins the cæcum
obliquely and projects somewhat into its lumen. The =colon= has at first
about the same caliber as the cæcum, but becomes gradually smaller. Most
of it is arranged in three close, double spiral coils in the mesentery,
in relation chiefly to the right flank externally, and to the small
intestine behind and to the left. On emerging from this spiral
labyrinth, it passes forward to the stomach and pancreas and then turns
backward; this terminal part is narrow, median in position, and closely
attached by a short mesentery to the sublumbar region. The =rectum= is
usually surrounded by a quantity of fat. The cæcum has three
longitudinal muscular bands and three rows of sacculations, which are
continued a short distance on the colon. The spiral colon has two bands
and two series of sacculations, which, however, gradually disappear in
the centrifugal part.
THE LIVER
[Illustration:
FIG. 323.—LIVER OF PIG, PARIETAL SURFACE.
Photograph of specimen hardened _in situ_.
]
The liver is relatively large, its average weight being about 4 to 4½
pounds (ca. 2 kg.). It is thick and very strongly curved.[114] It is
divided by three deep interlobar incisures into four principal
=lobes=—=right lateral=, =right central=, =left central=, =left
lateral=; the last of these is usually considerably the largest. On the
upper part of the right lateral lobe is the =caudate lobe= and its
process. That part of the right central lobe which lies below the portal
fissure and to the left of the gall-bladder and cystic duct is
homologous with the quadrate lobe of man. The parietal surface is
extremely convex, its most anterior part reaching to a plane through the
lower part of the sixth or seventh intercostal space. The visceral
surface is deeply concave; most of it is related to the stomach, for
which there is a correspondingly large and deep gastric impression.
There is a duodenal impression on the upper part of the right lateral
lobe, but no renal impression, as the right kidney does not touch the
liver. The fossa for the gall-bladder is mainly on the right central
lobe, but also in part on the adjacent surface of the left central lobe.
The posterior vena cava enters the dorsal border of the caudate lobe and
soon becomes entirely embedded in the gland substance, emerging only at
its passage through the diaphragm. The œsophageal notch is large and is
occupied mainly by the large right crus of the diaphragm. The right
lateral border extends backward to the upper part of the twelfth
intercostal space or thirteenth rib. The left lateral border is opposite
the eighth rib and intercostal space. The ventral border extends
backward about as far as the umbilicus.
There are no lateral ligaments and the falciform ligament disappears
early.
The =gall-bladder= is attached in the fossa vesicæ felleæ on the right
central lobe, at a considerable distance from the ventral border. The
cystic duct joins the hepatic duct at an acute angle immediately after
the emergence of the latter from the portal fissure. The =bile-duct=
(Ductus choledochus) opens at the papilla duodeni about one or two
inches (ca. 2.5 to 5 cm.) from the pylorus.
[Illustration:
FIG. 324.—PROJECTION OF VISCERA OF PIG ON BODY-WALL, LEFT SIDE.
_D_, Costal line of diaphragm; _U_, ureter; _V. S._, vesicula
seminalis; _B. g._, bulbo-urethral gland; _P_, penis.
]
[Illustration:
FIG. 325.—PROJECTION OF VISCERA OF PIG ON BODY-WALL, RIGHT SIDE.
_D_, Costal attachment of diaphragm; _O_, ovary.
]
Owing to the large amount of interlobular tissue, the =lobules= are
mapped out sharply; they are polyhedral in form and are 1 to 2.5 mm. in
diameter. For the same reason the gland tissue is much less friable than
that of the other animals, from which it is easily distinguished.
THE PANCREAS
The =pancreas= is elongated, and is situated transversely on the dorsal
abdominal wall, with its right extremity on the ventral surface of the
right kidney, and the left end touching the dorsal end of the spleen and
the left kidney. The right portion has two lobes; the posterior lobe
bends around the great mesenteric artery and the portal vein; the
anterior one is pointed, extends downward and forward about in the
median plane, and is attached to the portal fissure and the duodenum.
The left portion is prismatic and rests mainly on the left sac of the
stomach, its left extremity being included between the left kidney and
the dorsal end of the spleen. The pancreatic =duct= passes from the
anterior lobe directly through the duodenal wall, opening about five or
six inches (ca. 12.5 to 15 cm.) from the pylorus. The interlobular
tissue usually contains a good deal of fat.
THE SPLEEN
The =spleen= is long and narrow. Its long axis is nearly dorso-ventral
in direction, and is slightly curved to conform to the left part of the
greater curvature of the stomach. The dorsal end lies under the
vertebral ends of the last three ribs. The ventral end is smaller,
reaches to the ventral abdominal wall, and lies against the left lobe of
the liver. The visceral surface has a longitudinal ridge on which the
hilus is situated; this divides the surface into nearly equal gastric
and intestinal areas. The spleen is attached so loosely to the stomach
that it may be regarded as being intercalated in the great omentum. In
large subjects it may reach a length of 15 to 18 inches (ca. 38 to 45
cm.) and a width of 3 to 4 inches (ca. 8 to 10 cm.).
DIGESTIVE SYSTEM OF THE DOG
THE MOUTH
The size and form of the mouth vary greatly in different breeds, the
cavity being in some long and narrow, in others short and wide. The
=rima oris= is very extensive, so that the labial commissure is opposite
the third or fourth cheek tooth. The =lips= are thin and mobile, and
present numerous tactile hairs. The upper lip has a small, central, bare
area which forms part of the muzzle, and is marked by a central groove,
the philtrum, or (as in the bulldog) a fissure, giving the appearance of
harelip. The lateral borders of the lower lip are flaccid and
denticulated. The mucous membrane is usually pigmented and forms
distinct frena labiorum. The labial glands are small and scanty.
[Illustration:
FIG. 326.—TONGUE OF DOG. _a_, Tonsil; _b_, vallate papillæ; _c_,
foliate papilla; _d_, fungiform papillæ; _e_, median groove of
dorsum; _f_, epiglottis; _g_, soft papillæ of root; _h_, middle
glosso-epiglottic fold; _1_, tip; _2_, root. (Ellenberger-Baum,
Anat. d. Haustiere.)
]
The =cheeks= are loose and capacious, and their mucous lining is smooth
and more or less pigmented. The =parotid duct= opens usually opposite
the third upper cheek tooth. Near the last tooth are the openings of the
four or five ducts from the orbital gland.
The =hard palate= is widest between the fourth pair of cheek teeth. It
has eight to ten curved ridges on either side of the raphé. Behind the
first pair of incisor teeth is the triangular incisive papilla, at which
the naso-palatine ducts open. The mucous membrane is usually pigmented.
The =soft palate= is thick except at its margins. In the resting state
of the parts it comes in contact with the oral surface of the
epiglottis. Between its anterior and posterior pillars on either side is
a marked tonsillar sinus, in which an elongated =tonsil= is situated;
this is reddish in color, about an inch long, and projects somewhat into
the fauces between two folds of mucous membrane.
The =tongue= is wide, thin, and very mobile. It is not pigmented, but
has a bright red color. The upper surface is marked by a median groove
(Sulcus medianus linguæ), and is thickly beset with short, pointed,
filiform papillæ, the free ends of which are directed backward. On the
root the papillæ are long and soft; similar papillæ occur on the lateral
walls of the isthmus faucium. The fungiform papillæ are small, and are
scattered over the dorsum and sides of the tongue, but are absent on the
root. There are usually two or three vallate papillæ on either side.
Small foliate papillæ are also present. In the inferior part of the tip
of the tongue is the =lyssa=, a fusiform cord, composed of fibrous
tissue, muscular tissue, and fat. In large dogs it is about two inches
(ca. 4 to 5 cm.) long.
[Illustration:
FIG. 327.—SKULL OF ADULT ST. BERNARD DOG, SCULPTURED TO SHOW THE
EMBEDDED PARTS OF THE TEETH.
_I1–3_, Incisors; _C_, canines; _P1–4_, premolars; _M1–3_, molars.
]
THE TEETH
The formula for the permanent teeth is:
( 3 1 4 2 )
2 ( I - C - P - M - ) = 42
( 3 1 4 3 )
All of the teeth have short crowns and distinct necks; they erupt
rapidly. The crowns are white, being destitute of cement.
The =incisors= are placed almost vertically and close together in the
jaw-bones. They do not correspond to an opposing tooth, but rather to
parts of two teeth of the other jaw. The crowns are trituberculate, the
central projection being the largest. They increase in size from the
first to the third. The labial surface is convex, the lingual slightly
concave, and marked off from the neck by a =V=-shaped ridge, the
cingulum. The roots are flattened transversely. The lower incisors are
smaller than the upper ones. One or two supernumerary teeth may be
present.
[Illustration:
FIG. 328.—BASE OF SKULL OF COCKER SPANIEL.
_I1–3_, Incisors; _C_, canine; _P1–4_, premolars; _M1–2_, molars. Note
the crowding of the canines and premolars on account of the
shortness of the jaw.
]
The =canine teeth= are large, conical, and curved. The upper canine is
separated from the corner incisor by an interval into which the lower
canine is received when the jaws are closed.[115] The lower canine is
close to the corner incisor. The root is about an inch (ca. 2 to 3 cm.)
long and is flattened laterally.
The =cheek teeth= are typically ⁶⁄₇, but in brachycephalic breeds they
are commonly reduced to ⁵⁄₇, and in extreme cases even to ⅘. The
reduction occurs at either end or at both ends of the series.[116] The
first tooth appears only once. The fourth tooth of the upper row and the
fifth of the lower row are much larger than the rest, and termed
=sectorial= or =carnassial= teeth. From these the teeth diminish in size
both forward and backward. The upper and lower teeth do not correspond,
but rather dovetail. The teeth behind the sectorial ones are
tuberculate, _i. e._, have rounded eminences on the masticatory surface.
The others are all sectorial in character, _i. e._, have sharp-edged,
pointed projections, the middle one being the most prominent. The
premolars are laterally compressed, and are separated by intervals from
the canines and from each other, except in the brachycephalic breeds.
The upper molars have wide, somewhat quadrangular crowns, and three
roots. The crown of the upper fourth premolar (Dens sectorius) is
divided into two pointed lobes and has an antero-internal tubercle; it
has three roots. The crown of the first lower molar (Dens sectorius) is
compressed laterally and has two pointed, sharp-edged lobes, behind
which are one or two tubercles; it has two roots.
[Illustration:
FIG. 329.—DISSECTION OF HEAD OF DOG, SHOWING SALIVARY GLANDS, ETC.
_a_, Ocular muscles; _b_, pterygoideus internus (cut); _c_,
stylo-glossus; _d_, digastricus (cut); _e_, genio-glossus; _f_,
genio-hyoideus; _g_, hyo-glossus; _h_, thyro-pharyngeus; _i_,
crico-pharyngeus; _k_, thyro-hyoideus; _l_, zygomatic process of
temporal (sawn off); _1_, parotid gland; _2_, submaxillary gland;
_3_, posterior part of sublingual gland; _3′_, anterior part of
same; _4_, submaxillary duct; _5_, ductus sublingualis major; _6_,
palatine glands; _7_, orbital or zygomatic gland; _8_, ducts of _7_;
_9_, lacrimal gland. (Ducts colored red.) (After Ellenberger, in
Leisering’s Atlas.)
]
The average periods of eruption are given below.
Tooth Eruption │ Change
│
I_{1} 4 to 5 weeks │4 to 5 months
I_{2} 4 to 5 weeks │ „
I_{3} 4 weeks │ „
C 3 to 4 weeks │4 to 5 months
P_{1} 4 to 5 months│5 to 6 months
P_{2} 4 to 5 weeks │ „
P_{3} 3 to 4 weeks │ „
P_{4} 3 to 4 weeks │ „
M_{1} 4 months │
upper 5 to 6 │
M_{2} months │
lower 4 ½ to │
5 months │
M_{3} 6 to 7 months│
THE SALIVARY GLANDS
The =parotid gland= is small. Its upper part is wide and is divided into
two lobes by a deep notch into which the base of the ear is received.
The lower end is small and overlaps the submaxillary gland. The =duct=
leaves the gland at its anterior border, crosses the masseter muscle,
and opens into the mouth opposite the third upper cheek tooth. Small
accessory glands (Glandulæ parotidæ accessoriæ) are sometimes found
along the course of the duct.
The =submaxillary gland= is usually larger than the parotid. In large
dogs it is about two inches (ca. 5 cm.) long and an inch or more (ca. 3
cm.) wide. It is rounded in outline and of a pale yellow color. Its
upper part is covered by the parotid, but it is otherwise superficial,
and is palpable in the angle of junction of the jugular and external
maxillary veins. The =duct= leaves the deep face of the gland, passes
along the surface of the digastricus and stylo-glossus, and opens into
the mouth near the frenum linguæ on a very indistinct papilla.
[Illustration:
FIG. 330.—SAGITTAL SECTION OF PHARYNGEAL AND LARYNGEAL REGIONS OF DOG.
_1_, Œsophagus; _2_, larynx; _3_, mouth cavity; _4_, epiglottis; _5_,
arytenoid cartilage; _6_, soft palate; _6″_, position of soft palate
when raised; _7_, vomer; _8_, base of cranium; _9_, root of tongue;
_a_, _a′_, _a″_, pharynx; _b_, fornix of pharynx; _c_, posterior
wall of pharynx; _d_, floor of pharynx; _e_, pharyngeal surface of
soft palate; _f_, origin of œsophagus; _g_, vestibule of larynx;
_h_, isthmus faucium; _i_, Eustachian opening; _k_, posterior naris.
(After Ellenberger, in Leisering’s Atlas.)
]
The =sublingual gland= is divided into two parts. The posterior part
(Glandula sublingualis grandicanalaris) lies on the digastricus muscle
in intimate relation with the submaxillary gland, but clearly separable
from it after removal of the common fibrous capsule. It has a pointed
anterior process. The =duct= (Ductus sublingualis major) accompanies the
submaxillary duct, and usually opens beside it, but in some cases joins
it. The anterior part (Glandula sublingualis parvicanalaris) is long and
narrow; it lies on the stylo-glossus muscle. It has a number (8 to 12)
of small ducts (Ductus sublinguales minores), some of which open
directly into the mouth, while others join the large duct.
The =orbital= or =zygomatic gland= (Glandula zygomatica) represents the
superior molar glands of herbivora. It is prismatic and is situated in
the orbital region, between the zygomatic arch and the internal
pterygoid muscle, in contact with the periorbita. It has four or five
=ducts= (Ductus zygomatici) which open near the last upper cheek tooth;
one of them (canal of Nuck) is almost as large as the parotid duct; the
others are small.
THE PHARYNX
The fornix is narrow. The orifices of the Eustachian tubes are small and
slit-like; the end of the tube causes a rounded projection of the mucous
membrane (Torus tubarius). The œsophageal opening is relatively small
and is encircled by a fold of the mucous membrane. The hyo-pharyngeus
muscle is clearly divided into a kerato-pharyngeus and a
chondro-pharyngeus.
THE ŒSOPHAGUS
The =œsophagus= is relatively wide and dilatable except at its origin.
The constriction at its origin is termed the =isthmus œsophagi=. The
cardiac end is slightly dilated; it joins the stomach under the tenth or
eleventh thoracic vertebra, slightly to the left of the median plane.
The muscular tissue is striated and consists mainly of two layers of
spiral fibers which cross each other; near the cardia, however, the
fibers are longitudinal and circular. There are mucous glands and lymph
glands in the submucosa throughout.
[Illustration:
FIG. 331.—STOMACH OF DOG. PARIETAL SURFACE.
Organ fixed _in situ_ when well filled.
]
THE STOMACH
The =stomach= is relatively large. Its capacity in a dog weighing about
40 pounds is about six to seven pints.
Colin estimates the average capacity at about 3 liters (ca. 6½ pints),
with a range between 0.6 and 8 liters (ca. 1⅓ to 17½ pints). Neumayer
gives the capacity as 100 to 250 c.c. per kilogram of body-weight (ca.
2.7 ounces per pound). The average capacity of the human stomach is
estimated at 35 to 40 ounces—only about one-half of that of a dog of
medium size.
When full it is irregularly pyriform. The left or cardiac part (Corpus
ventriculi) is large and rounded, while the right or pyloric part (Pars
pylorica) is small and cylindrical. When empty, or nearly so, the left
sac is strongly contracted; the pyloric part is not materially affected
by variations in the amount of ingesta.
The parietal surface of the full stomach is very extensive, strongly
convex, and faces partly forward, but largely to the left. It is related
to the liver, the left part of the diaphragm, and the left and ventral
abdominal wall as far back as a transverse section through the second or
third lumbar vertebra.
The visceral surface is much less extensive and is considerably
flattened; it faces chiefly to the right, and is related to the
intestine, pancreas, and left kidney.
The upper part of the lesser curvature is nearly straight and vertical,
but the lower part forms a deep, narrow angle, due to the fact that the
pyloric part is directed sharply forward and upward.
The greater curvature is nearly four times as long as the lesser
curvature. In the full stomach it extends considerably behind the left
costal arch (having carried the spleen backward); ventrally, it lies on
the abdominal wall, almost midway from the xiphoid cartilage to the
pubis.
[Illustration:
FIG. 332.—STOMACH OF DOG, VISCERAL SURFACE.
Organ fixed _in situ_ when well filled.
]
The left extremity or fundus is large and rounded; it is the most dorsal
part of the organ, and lies under the dorsal ends of the eleventh and
twelfth ribs.
The pyloric extremity is small and is directed forward and somewhat
upward; it lies usually about an inch or two (ca. 3.5 to 5 cm.) below
the cardia, a little to the right of the median plane. It is related to
the portal fissure of the liver and to the pancreas.
[Illustration:
FIG. 333.—EVERTED STOMACH OF DOG FROM WHICH THE MUCOUS MEMBRANE IS
REMOVED.
_O_, Œsophagus; _D_, duodenum; _b_, circular fibers; _c′_, internal
oblique fibers; _c″_, cardiac loop; _c‴_, transition of internal to
external oblique fibers; _d_, fibers uniting branches of cardiac
loop; _p_, pyloric sphincter; _p′_, antral sphincter.
(Ellenberger-Baum, Anat. d. Haustiere.)
]
[Illustration:
FIG. 334.—DIAGRAM OF ZONES OF MUCOUS MEMBRANE OF STOMACH OF DOG.
]
The cardia is situated about two to three inches (ca. 5 to 7 cm.) from
the left extremity, and is oval; it lies a little to the left of the
median plane, below the tenth or eleventh thoracic vertebra.
When empty, or nearly so, the stomach is separated from the ventral
abdominal wall by the liver and small intestine, and the greater
curvature extends back to the eleventh or twelfth rib. In this state
there is not rarely a marked constriction between the right and left
portions.
The longitudinal muscular fibers are found on the curvatures and on the
pyloric part. The oblique fibers are arranged in two layers: the
external layer is a continuation of the longitudinal fibers of the
œsophagus onto the body and fundus. The circular layer covers the whole
stomach except the fundus, and forms a pyloric sphincter and an antral
sphincter. The internal oblique layer is arranged as in the horse, and
forms a similar loop-like, cardiac sphincter.
Three regions of the mucous membrane exist. Cardiac glands are found in
a very narrow pale zone around the cardiac opening, and also scattered
along the lesser curvature. The fundus gland region has a thick,
reddish-brown mucous membrane, which lines about two-thirds of the
organ. The pyloric mucous membrane is thinner and pale; in the dead
subject it is often stained by regurgitated bile.
[Illustration:
FIG. 335.—ABDOMINAL VISCERA OF DOG.
Superficial ventral view after removal of the great omentum. From
photograph of formalin-hardened subject.
]
THE INTESTINE
The intestine is short—about five or six times the length of the body.
The =small intestine= has an average length of about thirteen feet (ca.
4 meters). It occupies most of the abdominal cavity behind the liver and
stomach. The duodenum begins at the portal fissure and passes backward
and upward, at first on the visceral surface of the liver, then in
contact with the right flank. Near the pelvis it turns inward and
sharply forward, passes along the inner border of the left kidney, and
joins the jejunum to the left of the root of the mesentery. The
mesoduodenum is given off from the common mesentery; it is a relatively
wide fold, except at the terminal part. Here there are two short folds,
one of which joins the mesocolon; the other passes on to the terminal
part of the colon. The first part of the mesoduodenum contains the right
branch of the pancreas. Its root is blended with the mesocolon to form a
common mesentery. The remainder of the small intestine forms numerous
coils, and is attached by a wide mesentery to the sublumbar region. The
=pancreatic= and =bile-ducts= open into the duodenum about two or three
inches (ca. 5 to 8 cm.) from the pylorus; the =accessory pancreatic
duct= opens an inch or two (ca. 2.5 to 5 cm.) further back. The mucous
membrane has very long villi. The duodenal (Brunner’s) glands occur only
near the pylorus. Peyer’s patches are numerous (about twenty in young
subjects), and begin in the duodenum. They are usually elliptical in
outline, but the last one is band-like, reaches to the end of the ileum
and is four to sixteen inches (ca. 10 to 40 cm.) long in young dogs
(Ellenberger). There is an ileo-cæcal valve.[117] The muscular coat is
relatively thick.
[Illustration:
FIG. 336.—DEEP DISSECTION OF ABDOMINAL VISCERA OF DOG (FEMALE).
_BL_, Bladder; _B_, body; _C_, _C′_, cornua of uterus; _O_, _O′_,
ovaries; _L. K._, left kidney. The concealed part of the colon is
indicated by dotted lines. (From photograph of formalin-hardened
subject.)
]
The =large intestine= is two to two and a half feet (ca. 60 to 75 cm.)
long. Its caliber is about the same as that of the small intestine, and
it has neither longitudinal bands nor sacculations.
The =cæcum= is about three or four inches (ca. 8 to 10 cm.) long, and is
twisted in a spiral fashion. The twist is maintained by the peritoneum,
which attaches it to the ileum. It is situated usually against the
middle of the upper part of the right flank, below the duodenum and the
right branch of the pancreas.[118]
The =colon= is attached to the sublumbar region by a mesentery, the
mesocolon. It presents three parts, which correspond to the ascending,
transverse, and descending colon of man. The first or right part (Colon
ascendens) is very short. It begins at the junction of the ileum and
cæcum, and passes forward along the inner surface of the duodenum and
the right branch of the pancreas till it reaches the pyloric part of the
stomach; here it turns inward and crosses the median plane, forming the
transverse part (Colon transversum). The third or left part (Colon
descendens) passes backward in the sublumbar region along the inner
border or ventral surface of the left kidney; then inclines toward the
median plane and joins the rectum.[119] The caliber of the colon is
about the same throughout. It has no bands nor sacculations.
[Illustration:
FIG. 337.—CÆCUM OF DOG.
_1_, Ileum; _2_, cæcum; _3_, colon. (From Leisering’s Atlas.)
]
[Illustration:
FIG. 338.—TERMINATION OF ILEUM OF DOG.
_a_, Colon; _b_, cæcum; _c_, ileum; _d_, ileo-cæcal opening; _e_,
circular depression around end of ileum. (After P. Schumann.)
]
The mucous membrane of the cæcum contains numerous solitary glands; they
are found also in the first part of the colon.
The =rectum= is almost completely covered with peritoneum, the line of
peritoneal reflection being under the second or third coccygeal
vertebra. At the junction of the rectum and anus the mucous membrane has
a stratified, squamous epithelium, and contains the =anal glands=. A
small opening on either side leads into two lateral =anal sacs= (Sinus
paranales); these are usually about the size of a hazelnut, and contain
a dirty gray, fatty substance, which has a peculiar and very unpleasant
odor. The skin which lines these pouches contains coil glands. Further
back the skin contains large sebaceous glands and peculiar =circumanal
glands=.
The retractor ani muscle is extensive. It arises from the shaft of the
ilium, the pubis, and the symphysis pelvis, and passes upward and
backward to end on the first coccygeal vertebræ and the sphincter ani
externus. The retractors, together with the coccygei, form a sort of
pelvic diaphragm, analogous to that of man.
THE LIVER
The liver is relatively large, weighing usually about 5 per cent. of the
body-weight. It is divided into six or seven =lobes= by fissures which
converge at the portal fissure. When the gland is examined in the soft
condition, all the lobes are visible on the visceral surface, but
usually only four on the parietal surface.
The =left lateral lobe= is the largest, and is oval in outline. The
=left central lobe= is much smaller and is prismatic. The =right central
lobe= is second in size, and presents a somewhat tongue-shaped quadrate
lobe, marked off by the deep fissure in which the gall-bladder lies. The
=right lateral lobe= is third in size, and is oval in outline. On its
visceral surface is the large =caudate lobe=; this consists of two
parts—on the right, the caudate process; on the left, the papillary
process or lobe, both often being subdivided by fissures.
[Illustration:
FIG. 339.—LIVER OF DOG.
Soft specimen sketched with lobes drawn apart.
]
[Illustration:
FIG. 340.—LIVER OF DOG, VISCERAL SURFACE; HARDENED _in situ_.
Left central lobe, gall-bladder, and great part of right central lobe
not visible.
]
When hardened _in situ_ (with the stomach full), the gland presents the
following characters:
The visceral surface is marked by a somewhat oblique ridge
(corresponding to the lesser curvature of the stomach), which separates
two deep cavities. The depression to the left of the ridge is occupied
by the body and fundus of the stomach. The depression on the right is
smaller, and is occupied by the pyloric part of the stomach, the origin
of the duodenum, and the right branch of the pancreas. The gall-bladder
is not visible.
When the stomach is empty and contracted, the visceral surface of the
liver is strikingly different. There is then a shallow impression for
the left part of the stomach on the left lobe, and a large convex
area, related to the small intestine and a mass of omentum. The
pyloric and duodenal impressions are not much changed. The
gall-bladder is visible.
The portal fissure is very deep and might well be termed a fossa. It is
bounded on the right (externally) by the caudate process, on the left
(internally) by the papillary process or lobe, which is directed
ventrally. The hepatic artery enters at the dorsal end and the portal
vein centrally, while the bile-duct leaves at the ventral part. The left
central lobe is not visible, and the right central one is largely
concealed.
The parietal surface is extremely convex, being adapted to the diaphragm
and the adjacent part of the ventral wall of the abdomen. On it all the
lobes except the papillary are completely or partially visible. The
gall-bladder is visible in the fissure between the quadrate and chief
portions of the right central lobe.
The dorsal border presents a renal impression on its right portion. The
posterior vena cava passes downward and forward at first in a deep
groove on the caudate lobe, then largely embedded in the parietal
surface of the right lateral lobe; it receives two large hepatic veins
just before piercing the diaphragm.
The œsophageal notch is large, and is occupied on the right by the thick
margin of the hiatus œsophageus. The left border is opposite to the
ninth and tenth ribs; it is thin and is marked by numerous indentations.
The caudate process extends usually a little beyond the last right rib,
between the right kidney and the right branch of the pancreas. The
ventral border lies on the ventral abdominal wall a variable distance
behind the xiphoid cartilage.
[Illustration:
FIG. 341.—SPLEEN OF DOG, VISCERAL SURFACE.
_a_, _a_, Ridge; _b_, ventral end; _c_, dorsal end. (After
Ellenberger, in Leisering’s Atlas.)
]
The =gall-bladder= lies in the fossa vesicæ felleæ, between the two
parts of the right central lobe; it does not reach to the ventral border
of the liver. The cystic duct joins the hepatic duct at the lower part
of the portal fissure, forming with it the bile duct (Ductus
choledochus); the latter passes to the right and opens into the
duodenum, about two or three inches (ca. 5 to 8 cm.) from the pylorus.
Of the ligaments, the coronary and right lateral are well developed, but
the left lateral and falciform are small.
THE PANCREAS
The =pancreas= is =V=-shaped, consisting of two long narrow branches,
which meet at an acute angle above the pylorus. The =right branch=
extends backward above the first part of the duodenum, below the caudate
lobe of the liver and the right kidney, and ends usually a short
distance behind the latter. The =left branch= passes inward and backward
on the visceral surface of the stomach, and ends under the left kidney.
There are two =ducts=: the larger one unites with the bile duct, while
the smaller one enters the duodenum an inch or two (ca. 3 to 5 cm.)
further back.
THE SPLEEN
[Illustration:
FIG. 342.—PROJECTION OF VISCERA OF DOG, (MALE) ON BODY-WALL, LEFT
SIDE.
_A_, _C_, _D_, Apical, cardiac, and diaphragmatic lobes of lung; _P_,
pericardium; _Pr_, prostate. Costal attachment and median line of
diaphragm are dotted.
]
[Illustration:
FIG. 343.—PROJECTION OF VISCERA OF DOG (FEMALE) ON BODY-WALL, RIGHT
SIDE.
_A_, _C_, _D_, Apical, cardiac, and diaphragmatic lobes of right lung;
_P._, pericardium; _L. K._, right kidney; _Pan._, right branch of
pancreas; _O_, ovary; _U_, cornu of uterus. Costal attachment and
median line of diaphragm are dotted; also posterior contour of
stomach.
]
The =spleen= is bright red in color in the fresh state. It is somewhat
falciform, long, and narrow; the ventral part is the widest. Its
position varies in accordance with the fullness of the stomach. When
that organ is moderately full the long axis of the spleen corresponds to
the direction of the last rib. Its parietal surface is convex and lies
largely against the left flank. The visceral surface is concave in its
length, and is marked by a longitudinal ridge, on which the vessels and
nerves are situated. The dorsal end lies against the left kidney and
left crus of the diaphragm. The ventral end is a little further back,
and reaches to the ventral wall of the abdomen. It is so loosely
attached by the great omentum as to be regarded as an appendage of the
latter.
THE RESPIRATORY SYSTEM
The organs of respiration (Apparatus respiratorius) comprise the =nasal
cavity=,[120] the =pharynx=, the =larynx=, the =trachea=, the =bronchi=,
and the =lungs=. The lungs are the central organs in which the exchange
of gases between the blood and the air takes place; the other parts of
the system are passages by which the air passes to and from the lungs.
The nasal cavity opens externally at the nostrils, and communicates
behind with the pharynx through the posterior nares (Choanæ); it
contains the peripheral part of the olfactory apparatus, which mediates
the sense of smell. The pharynx is a common passage for the air and
food—a remnant of the primitive embryonic arrangement; it has been
described as a part of the digestive tube. The larynx is a complex
valvular apparatus which regulates the volume of air passing through the
tract; it is also the chief organ of voice. The trachea, and the bronchi
formed by its bifurcation, are permanently open conducting tubes. The
thorax, the pleural sacs which it contains, and the muscles which
increase or diminish the size of the cavity are also parts of the
system. The bones, joints, and muscles of the thorax have already been
described.
For topographic reasons two ductless glands, the =thyroid= and the
=thymus=, are usually described in this section, although they are in no
sense a part of the respiratory system.
RESPIRATORY SYSTEM OF THE HORSE
THE NASAL CAVITY
The =nasal cavity= (Cavum nasi), the first segment of the respiratory
tract, is a long, somewhat cylindrical passage, inclosed by all the
facial bones except the mandible and hyoid. It is separated from the
mouth ventrally by the palate. It opens externally at the nostrils, and
communicates posteriorly with the pharynx through the posterior nares.
The =nostrils= or =anterior nares= (Nares) are somewhat oval in outline,
and are placed obliquely, so that they are closer together below than
above. They are bounded by two =alæ= or =wings= (Alæ nasi), which meet
above and below, forming the =commissures=. The outer ala is concave;
the inner one is convex above, concave below. The upper commissure is
narrow, the lower one wide and rounded. If the finger is passed into the
nostril at the upper commissure, it enters the so-called =false
nostril=, which leads backward to a blind cutaneous pouch. This
cul-de-sac, the =diverticulum nasi=, extends backward to the angle of
junction of the nasal bone and the nasal process of the premaxilla. The
posterior part of the diverticulum is blind, but the false nostril
communicates below and internally with the vestibule of the nasal
cavity. The external opening of the =naso-lacrimal duct= is seen when
the nostril is dilated; it is situated on the floor of the vestibule,
perforating the skin close to its junction with the mucous membrane,
about two inches (ca. 5 cm.) from the lower commissure. (It is not rare
to find one or two accessory orifices further back.)
=Structure.=—The =skin= around the nostrils presents long tactile hairs
as well as the ordinary ones. It is continued around the alæ and lines
the vestibule. In the posterior part of the diverticulum the skin is
thin and usually black, and is covered with exceedingly fine hairs; it
is provided with numerous sebaceous glands. The inner wing is supported
by the =alar cartilage= (Cartilago alaris), which is shaped somewhat
like a comma, the convex margin being direct medially. The cartilages
are attached by fibrous tissue to the extremity of the septal cartilage.
Each consists of an upper, quadrilateral curved plate, the =lamina=, and
a narrow =cornu= which curves downward and outward, supporting the inner
wing and the lower commissure, but not entering into the formation of
the outer wing. The lamina causes the projection of the upper part of
the internal wing, from which the thick =alar fold= (Plica alaris)
passes backward along the external wall of the nasal cavity to cover the
cartilaginous prolongation of the inferior turbinal bone. This fold
separates the true from the false nostril. The extremity of the cornu
usually causes a slight projection of the skin a short distance behind
and below the lower commissure.
[Illustration:
FIG. 344.—NOSTRILS OF HORSE.
_a_, Diverticulum nasi (shown as if distended); _b_, philtrum; _c_,
false nostril; _d_, true nostril; _e′_, prominence caused by lamina
of alar cartilage; _e″_, prominence over cornu of same; _f_,
external wing of nostril; _g_, internal wing; _h_, lower commissure;
_i_, orifice of naso-lacrimal duct. (Ellenberger-Baum, Anat. d.
Haustiere.)
]
[Illustration:
FIG. 345.—CROSS-SECTION OF NARIAL REGION OF HORSE.
_1_, Nasal bone; _2_, tendon of levator labii superioris proprius;
_3_, external nasal nerve; _4_, nasal diverticulum; _5_, outer wall
of _4_; _6_, dilatator naris inferior; _7_, levator nasolabialis +
dilatator naris lateralis; _8_, maxilla and premaxilla; _9_,
naso-lacrimal duct; _10_, _11_, chief branches of superior labial
nerve, with superior labial artery at their inner side; _12_, nasal
cavity; _13_, superior turbinal fold; _14_, inferior turbinal fold,
inclosing cartilaginous prolongation of inferior turbinal bone;
_15_, venous plexus; _16_, septum nasi; _16′_, parietal cartilage;
_17_, vomero-nasal organ (of Jacobson); _18_, venous plexus of
palate; _19_, buccinator; _20_, skin; _23_, anterior nasal nerve;
_24_, palatine process of premaxilla. (After Ellenberger-Baum, Top.
Anat. d. Pferdes.)
]
The muscles of the nostrils have been described.
=Blood-supply.=—Palato-labial, superior labial, and lateral nasal
arteries.
=Nerve-supply.=—Trigeminal and facial nerves.
The nasal cavity is divided into two symmetrical halves by the median
=septum nasi=. The osseous part of the septum (Septum osseum) is formed
behind by the perpendicular plate of the ethmoid and below by the vomer.
A few ridges on the former correspond to the ethmoidal meatuses. The
major part of it, however, is formed by the =septal cartilage=
(Cartilago septi nasi). The surfaces of the cartilage are marked by
faint grooves for the vessels and nerves which course over it. The
=dorsal border= is attached along the frontal and nasal sutures, and
extends beyond the apices of the nasal bones about two inches (ca. 5
cm.). From this border a thin, narrow plate, the =parietal cartilage=
(Cartilago parietalis) curves outward for a short distance on either
side. Near the nostrils these plates are somewhat wider, partially
making good the defect in the bony roof of the cavity in this situation.
The =ventral border= is thick and rounded; it lies chiefly in the groove
of the vomer, but anteriorly it occupies the space between the
premaxillary bones. The =posterior border= is continuous with the
perpendicular plate of the ethmoid bone.[121] The alar cartilages are
attached to the anterior extremity by fibrous tissue in such a manner as
to allow very free movement—in fact, an actual joint may be found. The
ventral part of the cartilage is about half an inch (ca. 1 cm.), the
middle part about one-tenth of an inch (ca. 2.5 mm.), and the dorsal
part about a quarter to a third of an inch (ca. 6 to 8 mm.) in
thickness.
[Illustration:
FIG. 346.—NASAL CARTILAGES OF HORSE, DORSAL VIEW. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The two =turbinal bones= (Conchæ nasales) project from the lateral wall,
and divide the outer part of the cavity into three =meatuses=—superior,
middle, and inferior.
The =superior meatus= (Meatus nasi dorsalis) is a narrow passage,
bounded dorsally by the roof of the cavity, and ventrally by the
superior turbinal bone; its posterior end is closed by the junction of
the inner plate of the frontal bone with the cribriform plate and
lateral mass of the ethmoid. It transmits air to the upper part of the
olfactory region.
[Illustration:
FIG. 347.—NASAL CAVITY OF HORSE, SAGITTAL SECTION WITH SEPTUM REMOVED.
_1_, Superior turbinal fold; _2_, alar fold, containing cartilaginous
prolongation of inferior turbinal; _3_, arrow pointing to
naso-maxillary fissure; _4_, cranial cavity; _5_, sphenoidal sinus;
_6_, hamulus of pterygoid bone. The olfactory mucous membrane is
shaded. Dotted lines indicate anterior limit of uncoiled parts of
turbinal bones, which inclose parts of frontal and maxillary
sinuses.
]
The =middle meatus= (Meatus nasi medius) is between the two turbinal
bones. It is somewhat larger than the superior meatus, and does not
extend back so far; it ends near the great ethmoturbinal and the
ethmoidal meatuses. In its posterior part is found the extremely narrow,
slit-like interval by which the maxillary sinus communicates with the
nasal cavity—the =naso-maxillary fissure= (Aditus naso-maxillaris). The
fissure is not visible from the nasal side, being concealed by the
overhanging superior turbinal. A fine flexible probe, passed outward and
somewhat backward between the turbinal bones, enters the maxillary
sinus; if introduced a little further in the same direction, it usually
passes through the orifice of communication between the maxillary and
the frontal sinus and enters the latter. A small part of the fissure
usually brings the anterior division of the maxillary sinus into
communication with the nasal cavity. The spaces inclosed by the coiled
portions of the turbinals also open into the middle meatus. This passage
may be characterized as the sinus-meatus, but it also conducts air to
the olfactory region.
[Illustration:
FIG. 348.—CROSS-SECTION OF HEAD OF HORSE. THE SECTION PASSES THROUGH
THE INTERNAL CANTHI.
_1_, Mylo-hyoideus; _2_, stylo-glossus; _3_, hyo-glossus; _4_,
genio-glossus; _5_, lingual process of hyoid bone. An arrow points
to the naso-maxillary fissure.
]
The =inferior meatus= (Meatus nasi ventralis) is situated between the
inferior turbinal and the floor of the cavity. It is much larger than
the other two, and is the direct passage between the nostrils and the
pharynx.
The =common meatus= (Meatus nasi communis) is situated between the
septum and the turbinals, and is continuous externally with the other
meatuses. It is very narrow dorsally, but widens ventrally.
The lateral masses of the ethmoid bone project forward into the
posterior part (fundus) of the nasal cavity (Fig. 347). Between the
ethmoturbinals of which each mass is composed there are three principal
and numerous small passages, the =ethmoidal meatuses= (Meatus
ethmoidales).
The =posterior nares= (Choanæ) are two elliptical orifices by which the
nasal cavity and pharynx communicate. They are in the same plane as the
floor of the nasal cavity, and are separated from each other by the
vomer. They are, taken together, about two inches (ca. 5 cm.) wide and
three to four inches (ca. 8 to 10 cm.) long.
The =nasal mucous membrane= (Membrana mucosa nasi) is thick, highly
vascular, and is, in general, firmly attached to the underlying
periosteum and perichondrium. It is continuous in front with the skin
which lines the nostrils, and behind with the mucous membrane of the
pharynx. It is also continuous at the naso-maxillary fissure with the
very thin and only slightly vascular mucous membrane which lines the
sinuses. In the anterior part of the cavity it forms prominent thick
folds on the lateral wall, which extend from the turbinal bones to the
nostril. There are usually two =superior turbinal folds= which unite
anteriorly. The upper one incloses a thin plate of cartilage which is
continuous with the superior turbinal bone. The =inferior turbinal fold=
is curved, and incloses an ᔕ-shaped cartilaginous plate which prolongs
the inferior turbinal bone; this fold is continuous with the alar fold
of the nostril, and forms with it the upper margin of the entrance from
the true nostril to the nasal cavity. Below this there is a rounded
ridge produced by the nasal process of the premaxilla. The mucous
membrane of the greater part of the cavity (Regio respiratoria) is red
in color, and is covered with a stratified ciliated epithelium. It
contains numerous acinous =nasal glands= (Glandulæ nasales). The
submucosa contains rich venous plexuses which form in certain situations
a sort of cavernous tissue (Plexus cavernosus), composed of several
strata of freely anastomosing veins, between which there are unstriped
muscle-fibers. This arrangement is most marked in the turbinal folds, on
the lower part of the inferior turbinal bone, and the lower part of the
septum. On the posterior part of the lateral masses of the ethmoid and
the adjacent part of the superior turbinal and the septum (Regio
olfactoria) the mucous membrane is brownish-yellow in color and thicker;
it contains the olfactory nerve-endings in a special non-ciliated
epithelium. In it are numerous =olfactory glands= (Glandulæ olfactoriæ);
these are long, tubular, and often branched.
The =vomero-nasal organ= of Jacobson (Organon vomeronasale) is situated
on the floor of the nasal cavity, on either side of the ventral border
of the septum (Fig. 345.) It consists of a tubular cartilage lined with
mucous membrane, to which fibers of the olfactory nerve may be traced.
Its anterior part communicates with the nasal cavity by a slit-like
orifice.
The =paranasal sinuses= are described in the Osteology.
THE LARYNX
The =larynx= is a short tube which connects the pharynx and trachea. It
is a complex valvular apparatus, which regulates the volume of air in
respiration, prevents aspiration of foreign bodies, and is the chief
organ of voice.
It is situated partly between the internal pterygoid muscles, partly in
the neck between the parotid glands.[122] Its long axis is practically
horizontal when the head and neck are extended (Fig. 254).
It is related dorsally to the pharynx and the origin of the œsophagus.
Ventrally it is covered by the skin, fascia, and sterno-hyoid and
omo-hyoid muscles. Laterally it is related to the parotid and
submaxillary glands and to the internal pterygoid, stylo-maxillaris,
digastricus, stylo-hyoid, and pharyngeal constrictor muscles.
It is attached to the body and thyroid cornua of the hyoid bone, and
thus indirectly to the base of the cranium.
Its cavity communicates anteriorly with the pharynx and (potentially)
with the mouth; posteriorly, with the trachea.
The wall of the larynx consists of a framework of cartilages, connected
by joints and ligaments or membranes, and moved by extrinsic and
intrinsic muscles. The cavity is lined with mucous membrane.
CARTILAGES OF THE LARYNX
There are three single cartilages and one pair; the single cartilages
are the cricoid, thyroid, and epiglottis; the arytenoid cartilages are
paired.
[Illustration:
FIG. 349.—LARYNGEAL CARTILAGES OF HORSE, RIGHT VIEW.
]
The =cricoid cartilage= (Cartilago cricoidea) is shaped like a signet
ring. The dorsal part is a broad, thick, quadrilateral plate termed the
=lamina=; the outer (dorsal) surface of this is marked by a median ridge
separating two shallow cavities, which give attachment to the posterior
crico-arytenoid muscles. On either side of these depressions are two
articular facets. The =anterior facets= (Facies articulares arytænoideæ)
are placed at the anterior border, are oval and convex, and articulate
with the arytenoid cartilages. The =posterior facets= (Facies
articulares thyreoideæ) are situated on the front of a ridge, a short
distance from the posterior border; they are concave, and articulate
with the posterior cornua of the thyroid cartilage. The ventral and
lateral parts of the ring are formed by a curved band, called the arch
(Arcus), which is narrowest below. The lateral surfaces of the arch are
grooved for the crico-thyroid muscle. The anterior border of the lamina
is thick and slightly concave; the posterior border is thin and
irregularly notched. The anterior border of the arch is concave
ventrally and gives attachment to the crico-thyroid membrane; laterally
it is thicker and gives attachment to the crico-arytenoideus lateralis
muscle. The posterior border is attached to the first ring of the
trachea by an elastic membrane. The inner surface is smooth and is
covered with mucous membrane.
[Illustration:
FIG. 350.—CRICOID CARTILAGE OF HORSE, LEFT LATERAL VIEW.
]
The =thyroid cartilage= (Cartilago thyreoidea) consists of a median
thickened portion, termed the body, and two lateral laminæ or wings. The
=body= forms ventrally a slight prominence (Prominentia laryngea), which
can be felt, but is not visible in the living subject; it supports the
base of the epiglottis, which is attached to it by an elastic ligament.
The =wings= or =laminæ= spring from the body on either side and form a
large part of the lateral wall of the larynx. Each is a rhomboid plate,
presenting a slightly convex outer surface, which is divided into two
areas by an oblique line (Linea obliqua), on which the thyro-hyoid and
thyro-pharyngeus muscles meet. The superior (dorsal) border is nearly
straight; it gives attachment to the pharyngeal fascia and the
palato-pharyngeus muscle, and bears a cornu at each end. The =anterior
cornu= (Cornu orale) is attached to the thyroid cornu of the hyoid bone;
below it is a notch, which is converted into a foramen (Foramen
thyreoideum) by a fibrous band, and transmits the superior laryngeal
nerve to the interior of the larynx. The =posterior cornu= (Cornu
caudale) articulates with the cricoid cartilage. The inferior (ventral)
border is fused with the body in front; behind, it diverges from its
fellow to inclose a triangular space (Incisura thyreoidea caudalis),
which is occupied by the crico-thyroid membrane. The anterior border is
slightly convex, and is attached to the hyoid bone by the thyro-hyoid
membrane. The posterior border overlaps the arch of the cricoid
cartilage, and gives attachment to the crico-thyroid muscle. The inner
surface is concave, and is covered by mucous membrane to a small extent.
[Illustration:
FIG. 351.—THYROID CARTILAGE OF HORSE, VENTRAL VIEW.
]
The =epiglottis= (Cartilago epiglottica) is situated above the body of
the thyroid cartilage and curves toward the root of the tongue. It is
shaped somewhat like a pointed ovate leaf, and presents two surfaces,
two borders, a base, and an apex. The =oral= (or anterior) =surface= is
concave in its length, convex transversely; the =pharyngeal= (or
posterior) =surface= has the reverse configuration. The =borders= are
thin, denticulated, and somewhat everted. The =base= is thick, and is
attached to the dorsal surface of the body of the thyroid cartilage by
elastic tissue. From each side of it a cartilaginous bar projects
backward; these processes correspond to the cuneiform cartilages of man.
The =apex= is pointed and curved ventrally. Nearly all of the epiglottis
is covered with mucous membrane. It lies sometimes in front of,
sometimes behind, the soft palate.
[Illustration:
FIG. 352.—EPIGLOTTIS OF HORSE, RIGHT LATERAL VIEW.
]
The =arytenoid cartilages= (Cartilagines arytenoideæ) are situated on
either side, in front of the cricoid, and partly between the alæ of the
thyroid cartilage. They are somewhat pyramidal in form, and may be
described as having two surfaces, two borders, a base, and an apex. The
=internal surface= is concavo-convex, smooth, and covered by mucous
membrane. The =external surface= is divided by a ridge into two areas:
the lower flat area faces outward, and is covered by the thyro-arytenoid
and lateral crico-arytenoid muscles; the upper concave area faces
chiefly forward, and is covered by the transverse arytenoid muscle. The
=anterior border= is convex, and at the base of the cartilage forms a
projection termed the =vocal process= (Processus vocalis); it is so
named because it gives attachment to the vocal or thyro-arytenoid
ligament, which forms the basis of the true vocal cord. The =posterior
border= is straight, and extends from the vocal process to the facet on
the base. The =dorsal border= forms a deep notch with the apex. The
=base= is concave and faces chiefly backward; it presents an oval,
concave facet for articulation with the anterior border of the lamina of
the cricoid cartilage. The external angle of the base forms a strong
eminence termed the =muscular process= (Processus muscularis), which
gives attachment to the crico-arytenoid muscles. The internal angle is
attached to its fellow by the transverse arytenoid ligament. The =apex=
(Cartilago corniculata) curves upward and backward, forming with its
fellow the pitcher-shaped lip, from which the cartilages derive their
name.
[Illustration:
FIG. 353.—LEFT ARYTENOID CARTILAGE OF HORSE, INNER VIEW.
]
The cricoid and thyroid cartilages, and the greater part of the
arytenoid cartilages, consist of hyaline cartilage. The apices and vocal
processes of the arytenoid cartilages and the epiglottis (including the
cuneiform processes) consist of elastic cartilage; they show no tendency
toward ossification at any age. The thyroid and cricoid cartilages
regularly undergo considerable ossification; the process begins in the
body of the thyroid, and often involves the greater part of the
cartilage.
JOINTS, LIGAMENTS, AND MEMBRANES OF THE LARYNX
The =crico-thyroid joints= (Articulationes crico-thyreoideæ) are
diarthroses formed by the apposition of the convex facets on the ends of
the posterior cornua of the thyroid cartilage with corresponding facets
on the sides of the cricoid cartilage. The =capsule= is thin, but is
strengthened by accessory bands dorsally, externally, and internally.
The movements are chiefly rotation around a transverse axis passing
through the centers of the two joints.
The =crico-arytenoid joints= (Articulationes crico-arytænoidea) are also
diarthrodial. They are formed by the apposition of the convex facets on
the anterior border of the cricoid cartilages with the concave facets on
the bases of the arytenoid cartilages. Each has a very thin, loose
=capsule=, strengthened by accessory bundles dorsally and internally.
The movements are gliding and rotation. In the former the arytenoid
cartilage glides inward or outward; in the latter it rotates around a
longitudinal axis, so that the vocal process swings outward or inward.
The =thyro-hyoid joints= (Articulationes hyo-thyreoideæ) are formed by
the anterior cornua of the thyroid cartilage and the extremities of the
thyroid cornua of the hyoid bone. They permit rotation around a
transverse axis passing through the two joints.
The =crico-thyroid membrane= (Ligamentum crico-thyreoideum) occupies the
thyroid notch and extends backward to the arch of the cricoid cartilage.
It is triangular in form, and is attached by its base to the anterior
border of the arch of the cricoid cartilage, while its borders are
attached to the margins of the thyroid notch. It is strong, tightly
stretched, and composed largely of elastic tissue. It is reinforced
ventrally by longitudinal fibers, dorsally by fibers which stretch
across the thyroid notch.
The =thyro-hyoid membrane= (Membrana hyo-thyreoidea) connects the
anterior border of the thyroid cartilage with the body and thyroid
cornua of the hyoid bone.
The =hyo-epiglottic ligament= (Ligamentum hyo-epiglotticum) attaches the
lower part of the oral surface of the epiglottis to the body of the
hyoid bone. It forms an elastic sheath for the hyo-epiglottic muscle.
Ventrally it blends with the thyro-hyoid membrane, and dorsally it is
not well defined.
The =thyro-epiglottic ligament= (Ligamentum thyreo-epiglotticum) is
strong and thick; it is composed chiefly of elastic tissue. It connects
the base of the epiglottis with the body and the adjacent inner surface
of the laminæ of the thyroid cartilage. Other fibers attach the
cuneiform processes somewhat loosely to the thyroid laminæ.
The =transverse arytenoid ligament= (Ligamentum arytænoideum
transversum) is a slender band which connects the inner angles of the
bases of the arytenoid cartilages.
The =vocal= (or inferior thyro-arytenoid) =ligament= (Ligamentum vocale)
forms the basis of the true vocal cord (Fig. 254). It is elastic and is
attached ventrally to the body of the thyroid cartilage and the
crico-thyroid membrane close to its fellow of the opposite side, and
ends dorsally on the processus vocalis of the arytenoid cartilage.
The =ventricular= (or superior thyro-arytenoid) =ligament= (Ligamentum
ventriculare) is included in the false vocal cord. It consists of
loosely arranged bundles which arise chiefly from the cuneiform process
and end on the outer surface of the processus vocalis and adjacent part
of the arytenoid cartilage.
The =crico-tracheal membrane= (Ligamentum crico-tracheale) connects the
cricoid cartilage with the first ring of the trachea.
MUSCLES OF THE LARYNX
A. EXTRINSIC MUSCLES
The =sterno-thyro-hyoideus= is described on p. 226.
The =thyro-hyoideus= (M. hyo-thyreoideus) is a flat, quadrilateral
muscle, which lies on the outer surface of the thyroid lamina and the
lateral part of the thyro-hyoid membrane. It arises from the thyroid
cornu of the hyoid bone, and ends on the oblique line on the lamina of
the thyroid cartilage. Its action is to draw the larynx toward the root
of the tongue.
The =hyo-epiglotticus= (M. hyo-epiglotticus) is a feeble muscle which
occupies a median position above the central part of the thyro-hyoid
membrane, inclosed by an elastic sheath, the hyo-epiglottic ligament. It
arises from the body of the hyoid bone by two branches which unite and
are inserted into the front of the base of the epiglottis. Its action is
to draw the epiglottis toward the root of the tongue.
[Illustration:
FIG. 354.—LARYNGEAL MUSCLES OF HORSE, SEEN FROM LEFT SIDE AFTER
REMOVAL OF MAJOR PART OF LAMINA OF THYROID CARTILAGE.
_a_, Kerato-hyoideus; _b_, thyro-hyoideus; _c_, crico-thyroideus; _d_,
sterno-thyroideus; _e_, ventricularis; _f_, vocalis; _g_,
crico-arytenoideus lateralis; _h_, crico-arytenoideus post. _s_,
dorsalis; _i_, arytenoideus transversus; _1_, lingual process; _2_,
small cornu; _3_, thyroid cornu, of hyoid bone; _4_, thyroid
cartilage; _5_, cricoid cartilage; _6_, epiglottis; _7_, apex of
arytenoid cartilage; _8_, trachea; _9_, muscular process of
arytenoid; _10_, lateral lobe of thyroid gland; _10′_, isthmus of
thyroid gland; _11_, laryngeal saccule. (Ellenberger-Baum, Anat. d.
Haustiere.)
]
B. INTRINSIC MUSCLES
The =crico-thyroideus= (M. crico-thyreoideus) is a short muscle which
fills the groove on the lateral surface of the cricoid cartilage; its
fibers are directed dorsally and somewhat forward. It arises on the
lower half of the lateral surface and posterior edge of the cricoid
cartilage, and is inserted into the posterior border and adjacent part
of the surfaces of the lamina of the thyroid cartilage. Its action is to
draw the thyroid cartilage and the ventral part of the cricoid cartilage
together. In this action the cricoid cartilage is probably rotated,
carrying the bases of the arytenoid cartilages with it and thus tensing
the vocal cords.
The =crico-arytenoideus dorsalis s. posterior= (M. crico-arytænoideus
dorsalis) is a strong, somewhat fan-shaped muscle, which, with its
fellow, covers the dorsal surface of the lamina of the cricoid
cartilage. It is partially divisible into two layers. It has a broad
origin on half of the lamina of the cricoid cartilage, and its fibers
converge to be inserted into the processus muscularis of the arytenoid
cartilage. Its action is to dilate the rima glottidis by rotating the
arytenoid cartilage so as to carry the vocal process and cord outward.
The =crico-arytenoideus lateralis= (M. crico-arytænoideus lateralis)
lies on the inner face of the thyroid lamina. It arises from the
anterior border of the lateral part of the arch of the cricoid
cartilage. The fibers pass in a dorsal direction and converge on the
processus muscularis of the arytenoid cartilage. It closes the rima
glottidis by rotating the arytenoid cartilage inward.
The =arytenoideus transversus= (M. arytænoideus transversus) is an
unpaired muscle which stretches across the concave dorsal surface of the
arytenoid cartilages. Its fibers are attached on either side to the
processus muscularis and the ridge which extends forward from it. The
right and left parts of the muscle meet at a fibrous raphé which is
connected with the transverse arytenoid ligament. Filters of the
thyro-arytenoideus muscle overlap its anterior part. It narrows the rima
by drawing the arytenoid cartilages together.
[Illustration:
FIG. 355.—ADITUS LARYNGIS OF HORSE, EXPOSED BY OPENING PHARYNX AND
BEGINNING OF ŒSOPHAGUS ALONG MEDIAN DORSAL LINE.
_1_, False vocal cord; _2_, lateral ventricle; _3_, true vocal cords;
_4_, rima glottidis.
]
The =thyro-arytenoideus= (Mm. ventricularis et vocalis) is situated in
the lateral wall of the larynx, covered by the lamina of the thyroid
cartilage. It consists of two parts, between which the mucous membrane
of the lateral ventricle pouches to form the saccule. The =anterior
part= (M. ventricularis) arises from the anterior part of the
crico-thyroid membrane and the ventral border of the thyroid lamina. Its
fibers pass upward and backward to end partly on the processus
muscularis, partly on the arytenoideus transversus, meeting its fellow.
The =posterior part= (M. vocalis) has a more extensive origin on the
crico-thyroid membrane. Its direction corresponds with that of the true
vocal cord. It is inserted into the outer surface of the arytenoid
cartilage below the processus muscularis. The muscle closes the rima and
slackens the vocal cords. With the arytenoideus transversus and
crico-arytenoideus lateralis it forms a sphincter which closes the
entrance to the larynx.
CAVITY OF THE LARYNX
The =cavity= of the larynx (Cavum laryngis) is smaller than one would
expect from its external appearance. On looking into it through the
pharyngeal end two folds are seen projecting from its lateral walls.
These are termed the =vocal cords=, and they divide the cavity into two
portions.
The =aditus laryngis=, or pharyngeal aperture, is a large, oblique, oval
opening, which faces forward and upward into the ventral part of the
pharynx. It is bounded in front by the epiglottis, behind by the
arytenoid cartilages, and laterally by the aryteno-epiglottic folds of
mucous membrane (Plicæ aryepiglotticæ), which stretch between the edges
of the epiglottis and the arytenoid cartilages.
[Illustration:
FIG. 356.—SECTION OF LARYNX OF HORSE.
The plane of the section is parallel with the vocal cords.
]
The =vestibule= of the larynx (Vestibulum laryngis) is that part of the
cavity which extends from the aditus to the vocal cords. On its lateral
walls are the =false vocal cords= (Plicæ ventriculares), each of which
consists of a fold of mucous membrane covering the anterior part of the
thyro-arytenoid ligament and the cuneiform process. Between the false
and true vocal cord there is a pocket-like depression termed the
=lateral ventricle= of the larynx (Ventriculus lateralis laryngis). This
is the entrance to the =laryngeal saccule= (Appendix ventriculi
laryngis), a cul-de-sac of the mucous membrane which is about one inch
(ca. 2 to 3 cm.) long and extends upward and backward on the inner
surface of the thyroid lamina. There is a small =middle ventricle=
(Ventriculus laryngis medianus) at the base of the epiglottis.
The middle, narrow part of the cavity is termed the =glottis= or =rima
glottidis=.[123] It is bounded on either side by the true vocal cord and
the inner surface of the arytenoid cartilage. The =true vocal cords=
(Labia vocales) are situated behind the false cords and the lateral
ventricles. They extend from the angle between the body and laminæ of
the thyroid cartilage to the vocal processes of the arytenoid
cartilages. They are prismatic in cross-section, and their free edges
look forward and somewhat upward. The mucous membrane of the cord (Plica
vocalis) is very thin and smooth, and is intimately attached to the
underlying ligament. In ordinary breathing the rima is somewhat
lanceolate in form; when dilated, it is diamond-shaped, the widest part
being between the vocal processes. The narrow part of the glottis
between the vocal cords is termed the glottis vocalis (Pars
intermembranacea), while the wider part between the arytenoid cartilages
is the glottis respiratoria (Pars intercartilaginea).
The =posterior compartment= of the laryngeal cavity is directly
continuous with the trachea. It is inclosed by the cricoid cartilage and
the crico-thyroid membrane. It is oval in form, the transverse diameter
being an inch and a half to two inches (ca. 4 to 5 cm.), and the
dorso-ventral diameter two to two and a half inches (ca. 5 to 6 cm.).
The =mucous membrane= which lines the larynx (Tunica mucosa laryngis) is
reflected around the margin of the aditus to become continuous with that
of the pharynx, and behind it is continuous with that which lines the
trachea. It is closely attached to the pharyngeal surface of the
epiglottis, but elsewhere in the aditus and vestibule it is loosely
attached by submucous tissue which contains many elastic fibers.[124] It
is thin and very closely adherent over the vocal cords and the inner
surfaces of the arytenoid cartilages. The epithelium is of the
stratified squamous type from the aditus to the glottis, beyond which it
is columnar ciliated in character. There are numerous =mucous glands=
(Glandulæ laryngeæ), except over the glottis and the pharyngeal surface
of the epiglottis, in which situations they are scanty.
=Blood-supply.=—Thyro-laryngeal artery.
=Nerve-supply.=—Superior laryngeal and recurrent laryngeal nerves (from
the vagus).
THE TRACHEA
The =trachea= extends from the larynx to the roots of the lungs, where
it divides into the right and left bronchi. It is kept permanently open
by a series of about fifty to fifty-five incomplete cartilaginous rings
embedded in its wall. It occupies a median position, except near its
termination, where it is pushed a little to the right by the arch of the
aorta. It is approximately cylindrical, but its cervical portion is for
the most part depressed dorso-ventrally by contact with the longus colli
muscle, so that the dorsal surface is flattened. The average caliber is
about two to two and one-half inches (ca. 5 to 6 cm.), but in the
greater part of the neck the transverse diameter is greater and the
dorso-ventral smaller. It is inclosed by a fascia propria.
In its =cervical part= the trachea is related dorsally to the œsophagus
for a short distance, but chiefly to the longus colli muscle. Laterally
it is related to the thyroid gland, the carotid artery, the jugular
vein, the vagus, sympathetic, and recurrent laryngeal nerves, and the
tracheal lymph ducts and cervical lymph glands. The œsophagus lies on
its left face from the third cervical vertebra backward. The
sterno-cephalicus muscles cross it very obliquely, passing from the
ventral surface forward over its sides, and diverging to reach the
angles of the jaw. The omo-hyoidei also cross it very obliquely, passing
over the lateral surfaces of the tube, and converging ventrally to the
body of the hyoid bone. The sterno-thyrohyoideus lies on the ventral
surface.[125] The scaleni lie on either side near the entrance to the
thorax.
The =thoracic part= of the trachea passes backward between the pleural
sacs and divides into the two bronchi over the left atrium of the heart.
It is related dorsally to the longus colli for a short distance, and
beyond this to the œsophagus. Its left face is crossed by the aortic
arch, the left brachial artery, and the thoracic duct. Its right face is
crossed by the vena azygos, the dorso-cervical and vertebral vessels,
and the right vagus nerve. Ventrally it is related to the anterior vena
cava, the brachiocephalic and common carotid trunks, and the left
recurrent nerve.
[Illustration:
FIG. 357.—CROSS-SECTION OF VENTRAL PART OF NECK OF HORSE.
The section is cut at right angles to the long axis of the neck,
passing through the junction of the second and third cervical
vertebræ. _S.c._, Spinal cord; _S.v._, spinal vein; _V.v._, _V.a._,
vertebral vein and artery; _T.p._, transverse process (tip); _F_,
intervertebral fibro-cartilage; _T_, atlantal tendon common to
mastoido-humeralis, splenius, and lower part of trachelo-mastoideus;
_M_, digitation of mastoido-humeralis inserted by _T_.
]
The =bifurcation= of the trachea (Bifurcatio tracheæ) is situated
opposite to the fifth intercostal space, and about five or six inches
(ca. 12 to 15 cm.) below the seventh and eighth thoracic vertebræ.
The trachea is composed of—(1) A fibro-elastic membrane in which are
embedded (2) the cartilaginous rings; (3) a muscular layer; (4) the
mucous membrane. The =elastic membrane= is intimately attached to the
perichondrium of the rings. In the intervals between the latter it
constitutes the annular ligaments (Ligamenta annularia). The =rings= of
the trachea (Cartilagines tracheales) are composed of hyaline cartilage.
They are incomplete dorsally, and when their free ends are drawn apart,
resemble somewhat the letter C. In the cervical part the thin wide free
ends overlap, while in the thoracic part they do not meet; here the
deficiency is made up by thin plates of variable size and form, embedded
in a membrana transversa. Ventrally the rings are about one-half inch
(ca. 1 to 1.2 cm.) wide and much thicker than dorsally. The first ring
is attached to the cricoid cartilage by the crico-tracheal membrane, and
is usually fused dorsally with the second ring. Various irregularities,
such as partial bifurcation or partial or complete fusion with an
adjacent ring, are common. The arrangement in the terminal part is very
irregular. The =muscular layer= (Musculus trachealis) consists of
unstriped fibers which stretch across the dorsal part of the tube. It is
separated from the ends of the rings and the membrana transversa by a
quantity of areolar tissue. When it contracts the caliber of the tube is
diminished. The =mucous membrane= is pale, normally, and presents
numerous fine longitudinal folds, in which are bundles of elastic
fibers. The epithelium is stratified columnar ciliated. Numerous tubular
=mucous glands= (Glandulæ tracheales) are present.
=Blood-supply.=—Common carotid arteries.
=Nerve-supply.=—Vagus and sympathetic nerves.
THE BRONCHI
The two =bronchi=, right and left (Bronchus dexter, sinister), are
formed by the bifurcation of the trachea. Each passes backward and
outward to the hilus of the corresponding lung. The right bronchus is a
little wider and less oblique in direction than the left. They are
related ventrally to the divisions of the pulmonary artery, and dorsally
to the branches of the bronchial artery and the bronchial lymph glands.
Their structure is similar to that of the trachea.
THE THORACIC CAVITY
The =thoracic cavity= (Cavum thoracis) is the second in point of size of
the body cavities. In form it is somewhat like a truncated cone, much
compressed laterally in its anterior part, and with the base cut off
very obliquely.
The =dorsal wall= or =roof= is formed by the thoracic vertebræ and the
ligaments and muscles connected with them.
The =lateral walls= are formed by the ribs and the intercostal muscles.
The =ventral wall= or =floor= is formed by the sternum, the cartilages
of the sternal ribs, and the muscles in connection therewith. It is
about one-half as long as the dorsal wall.
The =posterior wall=, formed by the diaphragm, is very oblique and is
strongly convex.
The =anterior aperture= or =inlet= (Apertura thoracis cranialis) is
relatively small, and of narrow, oval form. It is bounded dorsally by
the first thoracic vertebra and laterally by the first pair of ribs. It
is occupied by the longus colli muscles, the trachea, œsophagus,
vessels, nerves, and the prepectoral lymph glands.
The cavity is lined by the =endothoracic fascia= and by the =pleuræ=.
A longitudinal =septum=, termed the =mediastinum= (Septum mediastinale),
extends from the dorsal wall to the ventral and posterior walls, and
subdivides the cavity into two lateral chambers which contain the lungs.
Each of these chambers is lined by a serous membrane called the pleura,
and is called a =pleural cavity= (Cavum pleuræ). The mediastinum is, for
the most part, not median in position; this is largely due to the fact
that the largest organ contained in it, the heart, is placed more on the
left side; consequently the right pleural cavity and lung are larger
than the left. Practically all the organs in the thorax are in the
mediastinal space with the exception of the lungs, the posterior vena
cava, and the right phrenic nerve. The part in which the heart and the
pericardium are situated, together with that above it, is usually called
the middle mediastinal space; the parts before and behind this are
termed the anterior and posterior mediastinal spaces respectively.
THE PLEURÆ
The =pleuræ= are two serous sacs which line the pleural cavities and are
reflected at the roots of the lungs to invest those organs. We,
therefore, distinguish =parietal= and =visceral= parts of the pleuræ.
[Illustration:
FIG. 358.—CROSS-SECTION OF THE THORAX OF NEW-BORN FOAL.
_Tr._, Trachea; _S_, left brachial artery; _B_, brachiocephalic
artery; _l.g._, lymph gland. Pleura indicated by red line.
]
The =parietal pleura= (Pleura parietalis) lines the cavity in which each
lung is situated (Cavum pleuræ). On the lateral thoracic wall it is
adherent to the ribs and intercostal muscles and is termed the =costal
pleura= (Pleura costalis). Behind it is closely attached to the
diaphragm, forming the =diaphragmatic pleura= (Pleura diaphragmatica).
The part which is in apposition with the opposite sac or covers the
mediastinal organs is termed the =mediastinal pleura= (Pleura
mediastinalis); where this layer is adherent to the pericardium, it is
distinguished as =pericardiac pleura= (Pleura pericardiaca).[126]
The pleura is reflected at the root of the lung, which it covers,
constituting the =visceral= or =pulmonary pleura= (Pleura pulmonalis).
Behind the root of the lung a considerable triangular area is not
covered by the pleura, the two lungs being attached to each other by
connective tissue in this situation.
The =ligament of the lung= (Lig. pulmonale) is a fold formed by the
reflection of the pleura from the mediastinum and the diaphragm to the
lung, behind the triangular area of adhesion just mentioned. It is seen
when the base of the lung is drawn outward. It contains elastic tissue,
especially in its posterior part.
[Illustration:
FIG. 359.—CROSS-SECTION OF THORAX OF NEW-BORN FOAL.
_A_, Aorta; _Br._, bronchi; _P.A._, pulmonary arteries; _l_, lymph
gland; _R.A._, right atrium; _L.A._; left atrium; _R.V._, right
ventricle; _L.V._, left ventricle of heart.
]
The right pleura forms a special =sagittal fold= (Plica venæ cavæ) about
a handbreadth to the right of the median plane, which incloses the
posterior vena cava in its upper edge and gives off a small accessory
fold for the right phrenic nerve. The fold arises from the thoracic
floor and from the diaphragm below the foramen venæ cavæ, and intervenes
between the mediastinal lobe and the body of the right lung. It is
delicate and lace-like.
The posterior mediastinum is very delicate below the œsophagus, and
usually appears fenestrated; when these apertures are present, the two
pleural cavities communicate with each other.[127]
The pleural sacs contain a serous fluid, the =liquor pleuræ=; in health
there is only a sufficient amount to moisten the surface, but it
accumulates rapidly after death.
[Illustration:
FIG. 360.—CROSS-SECTION OF THORAX OF NEW-BORN FOAL. Ribs are numbered.
]
THE LUNGS
The =lungs= (Pulmones) occupy much the greater part of the thoracic
cavity. They are accurately adapted to the walls of the cavity and the
other organs contained therein. The two lungs are not alike in form or
size, the right one being considerably larger than the left; the
difference is chiefly in width, in conformity with the projection of the
heart to the left.
The lung is soft, spongy, and highly elastic. It crepitates when pressed
between the finger and thumb, and floats in water. When the thoracic
cavity of the unpreserved subject is opened, the lung collapses
immediately to about one-third of its original size, and loses its
proper form; this is due to its highly elastic character and the fact
that the tension of the lung tissue caused by the air pressure in its
cavities has been relieved by the external air pressure.[128]
The =color= varies according to the amount of blood contained in the
lung. During life the lung has a pink color, but in subjects which have
been bled for dissection it is light gray or faintly tinged with red. In
unbled subjects it is dark red; the depth of color varies, and is often
locally accentuated by gravitation of blood to the most dependent parts
(hypostasis).
The =fœtal lung=, since it contains no air and has a relatively small
blood-supply, differs from that of an animal which has breathed in the
following respects: (1) It is much smaller; (2) it is firmer and does
not crepitate; (3) it sinks in water; (4) it is pale gray in color.
In =form= the lungs are like casts of the pleural cavities in which they
are situated. When well hardened _in situ_, their surfaces present
impressions and elevations corresponding exactly to the structures with
which they are in contact. Each lung presents two surfaces, two borders,
a base, and an apex.
[Illustration:
FIG. 361.—LEFT LUNG OF HORSE, COSTAL SURFACE. Specimen hardened _in
situ_.
]
The =costal= (or external) =surface= (Facies costalis) is convex, and
lies against the lateral thoracic wall, to which it is accurately
adapted.
The =mediastinal= (or internal) =surface= (Facies mediastinalis) is less
extensive than the costal surface. It is molded on the mediastinum and
its contents. It presents a large cavity adapted to the pericardium and
heart; this is termed the =cardiac impression= (Impressio cardiaca), and
is larger and deeper on the left lung than on the right. Above and
behind this is the =hilus=, at which the bronchus, vessels, and nerves
enter the lungs. The bronchial lymph glands are also found here. Behind
this the two lungs are adherent to each other over a triangular area.
Above this is a groove for the œsophagus (Sulcus œsophageus), which is
deepest on the left lung. A groove for the aorta (Sulcus aortæ) curves
upward and backward over the hilus, and passes backward near the dorsal
border of the lung; the curved part of the groove for the aortic arch is
absent on the right lung, on which there is a groove for the vena
azygos. Anteriorly there are grooves for the trachea, the anterior
aorta, the anterior vena cava, and other vessels.
[Illustration:
FIG. 362.—LEFT LUNG OF HORSE, MEDIASTINAL AND DIAPHRAGMATIC SURFACES.
Organ hardened _in situ_. (Venous impression for common
dorso-cervico-vertebral stem.)
]
[Illustration:
FIG. 363.—RIGHT LUNG OF HORSE, MEDIASTINAL AND DIAPHRAGMATIC SURFACES.
Organ hardened _in situ_. _c_, _d_, Grooves for superior cervical and
dorsal veins. Arrows indicate canal for posterior vena cava between
mediastinal lobe and main part of lung.
]
The =dorsal= (or superior) =border= (Margo obtusus) is long, thick, and
rounded; it lies in the groove alongside of the bodies of the thoracic
vertebræ.
The =ventral= (or inferior) =border= (Margo acutus) is thin and short.
It presents, opposite to the heart, the =cardiac notch= (Incisura
cardiaca). On the left lung this notch is opposite to the third, fourth,
and fifth ribs, so that a considerable area of the pericardium here lies
in direct contact with the chest-wall. On the right lung the notch is
less extensive, and is an intercostal space further forward.
The =base= of the lung (Basis pulmonis) is oval in outline; its surface
(Facies diaphragmatica) is deeply concave in adaptation to the thoracic
surface of the diaphragm. Laterally and posteriorly it is limited by a
thin =basal border= which fits into the narrow recess (Sinus
phrenico-costalis) between the diaphragm and the chest-wall. The
position of this border, of course, varies during respiration. In the
deepest inspiration it may reach the bottom of this recess; in ordinary
inspiration it lies about four or five inches (ca. 10 to 12 cm.) from
the costal arch, to which it is nearly parallel; in ordinary expiration
it lies about twice as far from the costal arch.
The =apex= of the lung (Apex pulmonis) is prismatic, narrow, and
flattened transversely. It is partially marked off from the rest of the
lung by the cardiac notch. It curves downward, and is related internally
to the anterior mediastinum and behind to the anterior part of the
pericardium.
In the horse the lungs are not divided into distinct =lobes= by deep
fissures, as in most mammals. In the case of the left lung there is no
lobation, but the right lung presents a =mediastinal lobe=, separated
from the body of the lung by a fissure which forms in its dorsal part a
canal for the posterior vena cava and the right phrenic nerve, inclosed
in a special fold of the right pleura.[129]
The =root= of the lung (Radix pulmonis) is composed of the structures
which enter or leave the lung at the hilus on the mediastinal surface.
These are: (1) The =bronchus=; (2) the =pulmonary artery=; (3) the
=pulmonary veins=; (4) the =bronchial artery=; (5) the =pulmonary
nerves=; (6) the =lymph vessels=, which open into the bronchial lymph
glands. The bronchus is situated dorsally, with the bronchial artery on
its upper surface and the pulmonary artery immediately below it. The
pulmonary veins lie chiefly below and behind the artery.
The =lobulation= of the lungs is not very evident on account of the
small amount of interlobular tissue. The lobules appear on the surface
or on sections as irregular polygonal areas of different sizes.[130]
=Bronchial Branches.=—Each bronchus at its entrance into the lung gives
off a branch to the apex of the lung. It is then continued backward as
the main stem bronchus, parallel with the dorsal border of the lung,
giving off branches (Rami bronchiales) in monopodic fashion; these
branch similarly and reach all parts of the lung. The right bronchus
gives off a special branch to the mediastinal lobe.
The arrangement of the larger bronchi is not the same in the two
lungs. The right bronchus, after detaching the apical branch, gives
off a large ventral branch which shortly bifurcates. One of the
divisions passes ventrally into the part of the lung behind the
cardiac notch (homologue of cardiac lobe), while the other passes
downward and backward into the lower part of the base. The stem
bronchus then gives off the branch to the mediastinal lobe, and
divides, about six inches from the hilus of the lung, into two nearly
equal branches; the dorsal branch is a direct continuation of the
stem, the ventral one passes into the middle part of the base. The
left bronchus, after a short course, divides into two nearly equal
branches. The dorsal branch may be regarded as the continuation of the
stem; it passes backward parallel with the dorsal border of the lung,
giving off a ventral branch much further back than in the right lung.
The ventral division of the stem bronchus divides, after a very short
course, into two branches; the anterior one passes ventrally into the
homologue of the cardiac lobe, while the posterior one passes downward
and backward into the base of the lung.
The =structure= of the larger bronchial tubes is, in general, similar to
that of the trachea. Their walls contain irregular plates of cartilage
instead of rings. There is a continuous layer of unstriped muscle,
composed of circularly arranged bundles. The mucous membrane presents
numerous longitudinal folds; it contains many elastic fibers, mucous
glands, and lymph nodules, and is lined by ciliated columnar epithelium.
As the tubes diminish in size the coats become thinner and the
cartilages smaller; in tubes about 1 mm. in diameter the cartilages and
mucous glands are absent.
By repeated branching the =interlobular bronchi= are formed, and from
these arise the =lobular bronchioles=. The latter enter a lobule and
branch within it, forming the =respiratory bronchioles=; these give off
the =alveolar ducts=, the walls of which are pouched out to form
hemispherical diverticula, the =alveoli= or =air-cells=.
A =lobule= of the lung, the unit of lung structure, is made up of a
lobular bronchiole with its branches, and their air-cells, blood- and
lymph vessels, and nerves. Between the lobules is the =interlobular
tissue=, which forms the supporting framework of the lung.
=Vessels of the Lungs.=—The branches of the =pulmonary artery= carry
venous blood to the lungs. They accompany the bronchi, and form rich
capillary plexuses on the walls of the alveoli. Here the blood is
arterialized, and is returned to the heart by the =pulmonary veins=. The
=bronchial arteries= are relatively small vessels which carry arterial
blood for the nutrition of the lungs. The branches of these arteries
accompany the bronchial ramifications as far as the alveolar ducts, but
do not extend to the alveoli. The œsophageal artery also supplies
pulmonary branches (in the horse) which reach the lung by way of the
ligament of the latter. These branches vary much in size, and ramify
chiefly in the subpleural tissue of the basal part of the lung.[131] The
=lymph vessels= are numerous, and are arranged in two sets. The
superficial set forms close networks in and under the pleura, while the
deep set accompanies the bronchi and pulmonary vessels. All converge to
the root of the lung and enter the =bronchial lymph glands=.
=Nerve-supply.=—The pulmonary nerves come from the vagus and sympathetic
nerves. They enter at the hilus and supply branches to the bronchial
arteries and the air-tubes.
THE THYROID GLAND
The =thyroid gland= (Glandula thyreoidea) is a very vascular ductless
gland, situated on the trachea close to the larynx. It is red brown in
color, and consists of two =lateral lobes= and a connecting =isthmus=
(Fig. 354).
The =lateral lobes= are situated on either side of the first and second
or second and third rings of the trachea, to which they are loosely
attached. Each is about the size of a walnut, and has a convex
superficial face which is related to the parotid gland and the omo-hyoid
muscle, and a slightly concave, deep face, applied to the trachea.
The =isthmus= in the adult horse is usually very rudimentary. It may
occur as a very narrow glandular band which connects the posterior
extremities of the lateral lobes, extending across the ventral surface
of the trachea, but it is frequently only a small strand of connective
tissue, and sometimes is entirely absent. It may be represented by a
small tail-like process of one lobe.
The lateral lobes vary in size and position, and are often dissimilar
on the two sides. The anterior extremity is the larger; it is rounded
and usually lies about a finger’s breadth behind the larynx, but may
be in contact with it. The posterior extremity is often produced to
form a narrow tail-like process, which is continuous with the isthmus
when one is present. In the ass and mule the isthmus is usually well
developed. There is sometimes a narrow band of thyroid tissue which
extends forward from the isthmus for a variable distance; this is
termed the pyramidal lobe. The position of the lateral lobe is
indicated approximately by the junction of the external maxillary and
jugular veins.
=Structure.=—The gland is enveloped by a thin, fibrous =capsule=, from
which =trabeculæ= pass into the gland, dividing it into =lobules=. The
lobules consist of non-communicating =alveoli= or =follicles= of varying
form and size. The alveoli are lined by cubical epithelium, and contain
a viscid colloid substance.
=Blood-supply.=—The arteries are relatively very large; there are
usually two thyroid arteries, which arise from the carotid and enter
each extremity of the gland.
=Nerve-supply.=—The nerves are derived from the sympathetic system.
Nodules of thyroid tissue of variable size, sometimes as large as a pea,
may be found near the anterior extremity of the lateral lobes, on the
course of the anterior thyroid artery or on the trachea, even at a
considerable distance from the thyroid region. They are termed
=accessory thyroids= (Glandulæ thyreoidæ accessoriæ).
The =parathyroids= are small glandular bodies found in the thyroid
region. They are paler and not so dense as the thyroid tissue, but often
cannot be differentiated by their naked-eye appearance. In the horse
there is usually only one on each side in the connective tissue over the
anterior extremity of the lateral lobe of the thyroid. They resemble in
structure embryonic thyroid tissue.
THE THYMUS GLAND
The =thymus= is a ductless gland which has a close resemblance to the
lymphoid tissues. It is well developed only in late fœtal life and for a
few months after birth. After this it undergoes rapid atrophy, fatty
infiltration, and amyloid degeneration, so that in the adult it is
represented by a thin remnant in the lower part of the anterior
mediastinum or has entirely disappeared. In the new-born foal it is of a
grayish-pink color, and consists of two =lateral lobes= (Fig. 358). The
greater part of the gland is situated in the anterior mediastinum, but
the two lobes are continued into the neck by a chain of lobules which
lie along the course of the carotid artery, extending sometimes as far
as the thyroid gland.[132]
=Structure.=—The thymus is inclosed in a thin, connective-tissue
=capsule=, and consists of secondary =lobules= (Lobuli thymi), of
varying shape and size, held together by areolar tissue and fat, and all
attached to a cord of adenoid tissue termed the =tractus centralis=.
These lobules are subdivided into polyhedral primary lobules, which are
composed of lymphoid tissue, and present a dark vascular =cortex=, and a
lighter =medulla= that contains Hassal’s corpuscles.
=Blood-supply.=—Internal thoracic and carotid arteries.
=Nerve-supply.=—Sympathetic and vagus nerve.
RESPIRATORY SYSTEM OF THE OX
THE NASAL CAVITY
The =nostrils=, situated on either side of the muzzle, are relatively
small, and are much less dilatable than those of the horse. The alæ are
thick and firm. The superior commissure is narrow. There is no false
nostril or diverticulum nasi. The skin is smooth, bare, and moist, and
there is no clear line of demarcation between it and the nasal mucosa.
The opening of the naso-lacrimal duct is not visible, as it is on the
outer wall of the nostril, and is concealed by the cartilaginous
prolongation of the inferior turbinal. There are two =parietal= or
=lateral cartilages= on either side, united by fibrous tissue. The
dorsal cartilages are thin laminæ which curve outward and downward from
the dorsal margin of the septal cartilage; they are prolongations of the
nasal bones, and carry the alar cartilages on their anterior
extremities. The ventral pair are lateral continuations of the basal
lamellæ of the inferior turbinals. They lie along the nasal processes of
the premaxillæ; anteriorly, they become thicker, turn a little upward,
and each blends with the cartilaginous prolongation of the upper coil of
the inferior turbinal. The =alar cartilages= are of peculiar form. The
lamina is oblong, and curves outward and downward from the anterior
extremity of the dorsal parietal cartilage, with which it is connected.
The cornu springs from the outer part of the lamina and curves outward
and upward into the outer wing of the nostril; it carries on its
extremity a small transverse bar, thus having some resemblance to the
fluke of an anchor.
The =nasal cavity= is short, wide anteriorly, narrow behind. It is not
completely divided by the septum, which in its posterior third is
separated from the floor of the cavity by an interval that increases
from before backward. The middle meatus is very narrow, and divides
posteriorly into two branches; the upper division leads to the ethmoidal
meatuses, and communicates with the frontal sinus and the cavity of the
superior turbinal. Anterior to the division are communications with the
upper cavity of the ventral turbinal and the maxillary sinus. The main
facts in regard to the sinuses were stated in the osteology.
[Illustration:
FIG. 364.—MUZZLE OF OX.
_49_, Naso-labial region; _45_, lower lip. (After Ellenberger-Baum,
Anat. für Künstler.)
]
THE LARYNX
The =larynx= is more compact than in the horse, and presents numerous
differential features. The =cricoid cartilage= is compressed laterally.
The lamina is not distinctly marked off from the arch; it slopes
downward and backward and has a large median ridge. The =thyroid
cartilage= is complete ventrally, _i. e._, the laminæ are united
throughout to form a long plate which is notched in front and behind;
the laryngeal prominence is small and is situated posteriorly. The
height and thickness of the cartilage increase from before backward. The
posterior cornua are about an inch long, and form syndesmoses with the
cricoid cartilage; the short anterior cornua unite similarly with the
hyoid bone. The =epiglottis= is oval in outline and its apex is rounded;
its base rests on the thyro-hyoid membrane, to which it is rather
loosely attached. The cuneiform cartilages are absent. The =arytenoid
cartilages= present only slight differences. The muscular process is
well developed, and the vocal process is narrow and long. The =vocal
cords= project very little from the wall, so that the rima glottidis is
wide; the vocal ligament is attached ventrally to the crico-thyroid
membrane; it has the form of a half tube, open behind. The =lateral
ventricles= are extremely shallow, and the saccules are absent. The
thyro-arytenoideus muscle is not divided; it is fan-shaped, thick, and
narrow dorsally; ventrally, it is attached to the base of the
epiglottis, the angle of the union of the thyroid laminæ, and the
crico-thyroid membrane. The hyo-epiglotticus muscle is large and bifid.
THE TRACHEA
The caliber of the trachea is relatively small, its width being about an
inch and a half (ca. 4 cm.) and its height one and a half to two inches
(ca. 4 to 5 cm.). The rings are smaller, and number about fifty. In the
neck their free ends are separated by a varying interval, so that the
tube is flattened and membranous dorsally. In the thorax the ends are in
apposition, so that they form a ridge dorsally. The trachea is adherent
to the right lung from the second rib backward. The bifurcation is
opposite the fourth intercostal space.
[Illustration:
FIG. 365.—SAGITTAL SECTION OF HEAD OF COW.
_1_, Cerebral hemisphere; _2_, lateral ventricle; _3_, thalamus; _4_,
corpora quadrigemina; _5_, optic chiasma; _6_, pituitary body; _7_,
pons; _8_, medulla oblongata; _9_, cerebellum; _10_, spinal cord;
_11_, ventral straight muscles; _12_, pharyngeal lymph gland; _13_,
arytenoid cartilage; _14_, epiglottis; _15_, cricoid cartilage;
_16_, vocal cord; _17_, palatine sinus; _18_, soft palate; _19_,
Eustachian opening; _C_{1}_, _C_{2}_, _C_{3}_, first, second, and
third cervical vertebræ; _B.o._, basioccipital; _Sp._, presphenoid.
]
THE BRONCHI
There are three chief bronchi. The bronchus for the apical and the
anterior cardiac lobe of the right lung is detached from the trachea at
a considerable distance anterior to the bifurcation.
THE THORACIC CAVITY AND PLEURA
The thoracic cavity is relatively small; it is especially short
dorsally, and is diminished laterally by the mode of attachment of the
diaphragm to the ribs (_vide_ Myology). The endothoracic fascia is
better developed than in the horse, and is distinctly elastic. The
pleura is also thick, and there are no perforations of the mediastinum.
The pleural sacs are more unequal in extent than in the horse, and the
ventral part of the mediastinum is further to the left; in front of the
pericardium it lies for the most part on the left wall of the chest.
[Illustration:
FIG. 366.—CROSS-SECTION OF THORAX OF SHEEP, PASSING THROUGH MIDDLE OF
FIFTH PAIR OF RIBS, POSTERIOR VIEW.
_1_, _1′_, Lungs; _2_, _2′_, bronchi; _3_, _3′_, pulmonary arteries;
_4_, thoracic aorta; _5_, œsophagus; _6_, lymph gland; _7_, vena
hemiazygos; _8_, posterior vena cava; _9_, large pulmonary vein;
_10_, left atrium, _11_, vena hemiazygos; _12_, left ventricle;
_13_, right ventricle; _14_, sternum; _15_, internal thoracic
vessels; _16_, sixth thoracic vertebra.
]
THE LUNGS
The difference in size between the two lungs is greater than in the
horse, the right lung weighing about half as much again as the left one.
The average weight of the lungs is about 7½ pounds (ca. 3 to 4 kg.);
they form about ¹⁄₁₇₀ of the body-weight.
[Illustration:
FIG. 367.—RIGHT LUNG OF OX, COSTAL SURFACE.
Organ hardened _in situ_.
]
[Illustration:
FIG. 368.—RIGHT LUNG OF OX, MEDIASTINAL ASPECT.
Hardened _in situ_. _1_, Left bronchus; _2_, pulmonary veins; _3_,
pulmonary artery.
]
They are divided into lobes by deep =fissures= (Incisuræ interlobares).
The =left lung= is divided into =three lobes=, named from before
backward =apical=, =cardiac=, and =diaphragmatic=. The =right lung= has
=four= or =five lobes=; the =apical lobe= is much larger than that of
the left lung, and occupies the space in front of the pericardium,
pushing the mediastinum against the left wall;[133] the =mediastinal
lobe= resembles that of the horse, while the =cardiac lobe= is often
divided by a fissure into two parts. The apical lobe of the right lung
receives a special bronchus from the trachea opposite the third rib. The
right lung is adherent to the trachea from the second rib backward.
[Illustration:
FIG. 369.—LUNGS AND HEART OF SHEEP, VENTRAL VIEW.
Specimen hardened _in situ_. Space between heart and lungs was
occupied by pericardium and fat.
]
The interlobar fissures begin at the ventral margin of the lung and
pass toward the root. Those of the left lung lie opposite to the
fourth and sixth ribs. The diaphragmatic lobe is the largest, and has
the form of a three-sided pyramid with its base resting on the
diaphragm. The cardiac lobe is prismatic and forms the posterior
margin of the cardiac notch; its long axis corresponds to the fifth
rib. The apical lobe of the left lung is small and pointed; its
ventral margin lies on the pulmonary artery and the anterior aorta;
below this the space in front of the heart is occupied by the apical
lobe of the right lung. The cardiac lobe of the right lung is much
larger than that of the left lung, and covers the right face of the
pericardium, so that the latter has no contact with the lateral wall
of the thorax.
The =lobulation= is very distinct on account of the extremely large
amount of interlobular tissue.
In the =sheep= the costal attachment of the diaphragm resembles that of
the horse, and the basal part of the lung corresponds thereto. The
lobation of the lungs resembles that of the ox, but the lobulation is
very indistinct. The pleural sacs extend under the first lumbar
vertebra.
THE THYROID GLAND
The lobes of the thyroid gland are more extensive and paler in color
than in the horse; they extend further forward, overlapping the
crico-pharyngeus muscle to a small extent, and come in contact dorsally
with the œsophagus. They are flattened, and have an irregular, lobulated
surface. In the young subject the isthmus is well developed, being about
half an inch (ca. 1 to 1.5 cm.) in width.
Accessory thyroids may be found, and parathyroids also occur near the
posterior extremity or inner surface of the lateral lobes of the
thyroid.
[Illustration:
FIG. 370.—RIGHT LUNG OF SHEEP, MEDIASTINAL ASPECT.
Hardened _in situ_. _B_, Bronchus; _P.a._, pulmonary artery; _P.v._,
pulmonary vein; _V.c._, posterior vena cava; _L.g._, bronchial lymph
gland.
]
THE THYMUS GLAND
The thymus is pale and distinctly lobulated. It is much larger in the
calf than in the foal, weighing at five or six weeks about 15 to 25
ounces (ca. 425 to 600 grams). The cervical part is specially large,
thick, and compact; it extends to the thyroid gland. It undergoes
atrophy slowly and remnants of the thoracic part often remain even in
advanced age.
RESPIRATORY SYSTEM OF THE PIG
THE NASAL CAVITY
The =nostrils= are small, and are situated on the flat anterior surface
of the =rostrum= or snout (Rostrum suis). The latter is a short
cylindrical projection, with which the upper lip is fused, and is
circumscribed by a prominent circular margin. The skin on the snout is
thin and highly sensitive; it presents small pores, and scattered over
it are fine short hairs. In the snout between the nostrils is the =os
rostri=, which is to be regarded as a special development of the
extremity of the septum nasi in adaptation to the habit of rooting. A
plate of cartilage, representing the lamina of the alar cartilage of the
horse, curves outward and downward from the upper part of the os rostri
and a pointed bar of cartilage curves upward from the lower part of the
bone in the outer wing of the nostril. The notch between the nasal bone
and the premaxilla is closed in by parietal cartilages which resemble
those of the ox.
The =nasal cavity= is long and narrow. It is divided behind by a
horizontal plate into an upper olfactory part, which leads to the
ethmoidal meatuses, and a lower respiratory part, which is a direct
continuation of the inferior meatus. The posterior part of the septum is
membranous.
The =turbinal bones= resemble in general those of the ox. The =superior
meatus= is exceedingly small. The =middle meatus= is a deep fissure
between the two turbinals: it divides posteriorly into two branches; one
of these extends upward and backward between the lateral mass of the
ethmoid bone and the superior turbinal; the other widens and joins the
inferior meatus. The opening between the maxillary sinus and the middle
meatus lies in a plane through the last cheek teeth. The middle meatus
is continuous with the space inclosed by the dorsal part of the inferior
turbinal and with the cavity of the superior turbinal. The dorsal
division of the middle meatus presents several openings into the frontal
sinus. The =inferior meatus= is relatively roomy; it communicates with
the space inclosed by the ventral coil of the inferior turbinal. The
opening of the naso-lacrimal duct is found in the posterior part of the
inferior meatus. The naso-palatine duct and the vomero-nasal organ (of
Jacobson) resemble those of the ox.
THE LARYNX
The larynx is remarkable for its great length and mobility. The
cartilages are more loosely attached to each other than in the other
animals. The =cricoid cartilage= is thick and compressed laterally; its
lamina is long and narrow; its arch is directed obliquely downward and
backward. The =thyroid cartilage= is very long; its laminæ are united
ventrally and form a median ridge. The anterior cornua being absent,
there are no joints formed with the hyoid bone. The posterior cornua are
broad, bent inward, and articulate with the cricoid cartilage. The
=epiglottis= is relatively very large, and is more closely attached to
the hyoid bone than to the rest of the larynx. The middle part of its
base is turned forward, and rests on the thyro-hyoid membrane; it is
closely connected with the body of the hyoid bone by the hyo-epiglottic
ligament and the strong hyo-epiglottic muscle.[134] The apex of the
=arytenoid cartilage= is very large, and is divided into two parts at
its extremity; the inner part is fused with that of the opposite
cartilage. There is a small =interarytenoid cartilage= in the transverse
ligament. The =rima glottidis= is very narrow. The =vocal cords= are
directed obliquely downward and backward; and each is pierced by a long,
slit-like opening, which leads into the large laryngeal saccule. The
thyro-arytenoid or vocal ligament is similarly divided into a larger
anterior and a smaller posterior part. There is a middle ventricle near
the base of the epiglottis. The thyro-arytenoid muscle is very strong
and is undivided. The arytenoideus is very small. The crico-thyroid
consists of two strata; the superficial layer corresponds to the muscle
of the other animals; the deep part consists of transverse fibers.
TRACHEA AND BRONCHI
The trachea is circular in cross-section, and contains thirty or more
rings which almost meet dorsally. A special bronchus is detached for the
apical lobe of the right lung, as in the ox.
THE LUNGS (Figs. 324, 325)
The =right lung= has =four= or =five lobes=, according to whether the
apical is subdivided or not. The =left lung= resembles that of the ox in
form and lobation. The lobulation is distinct, but the interlobular
septa are thinner than in the ox.
[Illustration:
FIG. 371.—RIGHT LUNG OF PIG, MEDIASTINAL ASPECT.
Hardened _in situ_. _B_, Left bronchus; _V._, pulmonary veins; _A._,
pulmonary artery; _l_, lymph glands.
]
THE THYROID GLAND
The two lobes of the thyroid are long and flattened; they are situated
close together, on the ventral surface of the trachea, extending as far
forward as the cricoid cartilage. The gland is dark red in color.
THE THYMUS
The thymus is very large, extending to the larynx or even to the
submaxillary space in young subjects.
RESPIRATORY SYSTEM OF THE DOG
THE NASAL CAVITY
The =nostrils= are situated on the muzzle, with which the upper lip
blends. They are shaped somewhat like a comma, with the broad part next
to the septum and the narrow part directed backward and outward. The
skin around the nostrils is bare, usually black, and in health moist and
cool. The muzzle is marked by a median furrow (philtrum) or a deep
fissure in some breeds. The cartilaginous framework is formed
essentially by the septal cartilage and the parietal cartilages which
proceed from it. The septal cartilage projects beyond the premaxilla,
and is much thickened at its extremity; it gives off from its upper and
lower margins the two parietal cartilages, which curve laterally and
toward each other. A grooved plate extends outward from the septal
cartilage in the floor of the nostril, and another lamina supports the
alar fold of the inferior turbinal bone.
The length of the =nasal cavity= varies greatly in different breeds,
corresponding, of course, to the length of the face. The cavity is
roomy, but is very largely occupied by the turbinals and the lateral
masses of the ethmoid bone. The =middle meatus= is short and narrow, and
divides posteriorly into two branches; the upper branch leads to the
ethmoidal meatuses; the lower branch joins the inferior meatus. The
=inferior meatus= is very small in its middle part, owing to the great
development here of the inferior turbinal. The posterior part of the
nasal cavity is divided by a horizontal plate, the lamina transversalis,
into an upper olfactory part and a lower respiratory part. The sinuses
have been described (_vide_ Osteology).
[Illustration:
FIG. 372.—NASAL CARTILAGES OF DOG.
_a_, Upper parietal cartilage; _b_, lower parietal cartilage; _c_,
alar cartilage. (After Ellenberger, in Leisering’s Atlas.)
]
THE LARYNX
The larynx is relatively short. The lamina of the =cricoid cartilage= is
wide; the arch is grooved laterally. The laminæ of the =thyroid
cartilage= are high, but short; they unite ventrally to form the body,
on which there is anteriorly a marked prominence, and posteriorly a deep
notch. The oblique line on the outer surface of the lamina is prominent.
There is a rounded notch (Fissura thyreoidea) below the short anterior
cornua for the passage of the superior laryngeal nerve. The posterior
cornu is strong, and has a rounded surface for articulation with the
cricoid cartilage. The =arytenoid cartilages= are relatively small, and
have between them a small =interarytenoid cartilage=. The =epiglottis=
is quadrilateral; its lower part or stalk is narrow, fitting into the
angle of the thyroid cartilage. The =cuneiform cartilages= are large and
somewhat crescent-shaped; they are not blended with the epiglottis.
[Illustration:
FIG. 373.—SAGITTAL SECTION OF NASAL REGION OF DOG.
_1_, Skin; _2_, parietal cartilage; _3_, floor of nasal cavity; _4_,
lamina transversalis; _5_, mucous membrane of hard palate; _6_,
upper lip; _7_, frontal bone; _8_, frontal sinus; _9_, cranial plate
of frontal bone; _10_, cranial cavity; _11_, dotted line indicating
anterior limit of olfactory region; _a_, superior turbinal; _b_,
inferior turbinal; _b′_, _b″_, inferior turbinal fold; _c_, _e_,
ethmoturbinals; _d_, cribriform plate of ethmoid; _f_, superior
meatus; _g_, middle meatus; _h_, inferior meatus; _i_,
naso-pharyngeal meatus. (After Ellenberger, in Leisering’s Atlas.)
]
The =false vocal cords= extend from the cuneiform cartilages to the
thyroid. The =true vocal cords= are large and prominent. The entrance to
the large lateral ventricle and saccule is a long slit parallel with the
anterior margin of the true vocal cord.
The crico-thyroid muscle is thick. The hyo-epiglotticus is well
developed, and is double at its hyoid attachment. The anterior part of
the thyro-arytenoideus arises on the cuneiform cartilage. Hence Lesbre
has suggested the name cuneo-arytenoideus for it.
THE TRACHEA AND BRONCHI
The trachea is very slightly flattened dorsally. It contains forty to
forty-five =U=-shaped rings; the ends of the rings do not meet dorsally,
so that here the wall of the trachea is membranous and is composed of a
layer of transverse smooth muscle-fibers outside of the rings, the
fibrous membrane, and the mucous membrane.
The stem bronchi diverge at an obtuse angle, and each divides into two
branches before entering the lung. The anterior branch goes to the
apical and cardiac lobes, the posterior one to the diaphragmatic lobe,
supplying also the mediastinal lobe of the right lung. The anterior
branch of the left bronchus crosses under the pulmonary artery.
THE LUNGS
The lungs (Figs. 342, 343) differ in shape from those of the horse and
ox in conformity with the shape of the thorax, which is relatively very
wide in the dog; the lateral thoracic walls are strongly curved, and the
costal surface of the lungs is correspondingly convex. There is no
cardiac notch on the left lung, although a small part of the pericardium
is not covered by the lung at the lowest part of the fifth and sixth
intercostal spaces. On the right side the cardiac notch is opposite the
fourth and fifth intercostal spaces. Each lung is divided by deep
fissures into =three lobes=—=apical=, =cardiac=, and =diaphragmatic=;
the right lung has in addition a =mediastinal lobe=. The apical lobe of
the right lung is considerably larger than that of the left. The latter
is often more or less fused with the cardiac lobe. Variable accessory
lobes may be found. On account of the small amount of interlobular
tissue the lobulation is not distinct.
THE THYROID GLAND
The =lateral lobes= of the thyroid gland are long and narrow, and have a
flattened, ellipsoidal form; they are placed on the lateral surfaces of
the trachea near the larynx. The extremities are small, the posterior
one often being pointed. The =isthmus= is inconstant and variable; in
large dogs it usually has the form of a glandular band which may be
nearly half an inch (ca. 1 cm.) wide; in small dogs it is usually
absent.
=Accessory thyroids= are frequently present; three or four may be found
on either side, as well as a median one near the hyoid bone.
The =parathyroids=, about the size of millet or hemp seed, are four in
number usually. Two are placed on the deep face of the thyroid lobes;
the others are placed laterally near the anterior extremity of the
thyroid.
THE THYMUS
The thymus is relatively small, and is situated almost entirely in the
thorax. The left lobe is much larger than the right, and extends back as
far as the sixth rib at the time of its greatest size. According to Baum
the gland increases in size during the first two weeks after birth, and
atrophies rapidly in the next two or three months. Traces of it are
present at two or three years of age, and may be found even in old
subjects.
THE UROGENITAL SYSTEM
This system (Apparatus urogenitalis) includes two groups of organs, the
urinary and the genital. The =urinary organs= elaborate and remove the
chief excretory fluid, the urine. The =genital organs= serve for the
formation, development, and expulsion of the products of the
reproductive glands. In the higher vertebrates the two apparatus are
independent except at the terminal part, which constitutes a urogenital
tract, and includes the vulva in the female and the greater part of the
urethra in the male.
THE URINARY ORGANS
The =urinary organs= (Organa uropoiëtica) are the kidneys, ureters,
bladder, and urethra. The =kidneys= are the glands which secrete the
urine; they are red-brown in color, and are situated against the dorsal
wall of the abdomen, being in most animals almost symmetrically placed
on either side of the spine. The =ureters= are tubes which convey the
urine to the =bladder=. The latter is an ovoid or pyriform sac, situated
on the pelvic floor when empty or nearly so; it is a reservoir for the
urine. The urine accumulates in the bladder until that organ is full,
and is then expelled through the =urethra=.
[Illustration:
FIG. 374.—GENERAL DORSAL VIEW OF URINARY ORGANS OF HORSE.
_1_, Right kidney; _1′_, left kidney; _2_, _2′_, adrenal bodies; _3_,
_3′_, ureters; _4_, urinary bladder; _4′_, anterior end of bladder
with cicatricial remnant of urachus; _4″_, urethra; _5_, aorta; _6_,
_6_, renal arteries; _7_, _7_, external iliac arteries; _8_, _8_,
internal iliac arteries; _9_, _9_, umbilical arteries. (After
Leisering’s Atlas.)
]
THE URINARY ORGANS OF THE HORSE
THE KIDNEYS
Each kidney (Ren) presents two surfaces, two borders, and two
extremities or poles, but they differ so much in form and position as to
require a separate description of each in these respects.[135]
The =right kidney= (Ren dexter) in outline resembles the heart on a
playing card, or an equilateral triangle with the angles rounded off. It
lies ventral to the upper parts of the last two or three ribs and the
tip of the first lumbar transverse process. The =dorsal= (or superior)
=surface= (Facies dorsalis) is strongly convex; it is related chiefly to
the diaphragm, but also to a small extent posteriorly to the psoas
muscles. In well hardened specimens, especially those from thin
subjects, impressions of the last two ribs and the tip of the first
lumbar transverse process are usually visible. The =ventral= (or
inferior) =surface= (Facies ventralis) is in general slightly concave,
and is related to the liver, pancreas, cæcum, and right adrenal; it
either has no peritoneal covering, or only a narrow area externally is
so covered. The =internal border= (Margo medialis) is convex and
rounded; it is related to the right adrenal and the posterior vena cava.
It presents about its middle a deep notch, the =hilus= (Hilus renalis);
this is bounded by rounded margins, and leads into a space termed the
=renal sinus= (Sinus renalis). The vessels and nerves reach the kidney
at the hilus, and the sinus contains the pelvis or dilated origin of the
ureter. The =external border= (Margo lateralis) is rounded, and is
thinner than the internal one. It consists of two parts, anterior and
posterior, which meet at an external angle; the anterior part fits into
the renal impression of the liver. The duodenum curves around the
external border. The =anterior extremity= (Extremitas cranialis), thick
and rounded, lies in the renal impression of the liver. The =posterior
extremity= (Extremitas caudalis) is thinner and narrower.
[Illustration:
FIG. 375.—DIAGRAM OF POSITION AND DORSAL RELATIONS OF KIDNEYS OF
HORSE.
Areas of direct relations are inclosed by continuous lines; parts of
skeleton which overlie the kidneys but are not in contact with them
are indicated by dotted lines. _L.I_-_III_, lumbar transverse
processes.
]
[Illustration:
FIG. 376.—KIDNEYS AND ADRENALS OF HORSE, DORSAL VIEW.
Hardened _in situ_. Impression of seventeenth rib on right kidney is
indicated by small cross.
]
[Illustration:
FIG. 377.—KIDNEYS AND ADRENALS OF HORSE, VENTRAL VIEW.
Hardened _in situ_. Left renal vein (not marked) is seen curving round
posterior end of left adrenal.
]
The =left kidney= (Ren sinister) is bean-shaped. It is considerably
longer and narrower than the right one, and is situated nearer the
median plane and further back, so that the hilus of the left kidney is
about opposite to the posterior extremity of the right one. It lies
usually under the upper part of the last rib and the first two or three
lumbar transverse processes. The =dorsal surface= is convex, and is
related to the left crus of the diaphragm, the psoas muscles, and the
base of the spleen. The =ventral surface= is convex and irregular; the
greater part of it is covered by the peritoneum. It is in relation with
the origin of the small colon, the terminal part of the duodenum, the
left adrenal, and the left extremity of the pancreas. The =internal
border= is longer, straighter, and thicker than that of the rightkidney.
It is related to the posterior aorta, the adrenal, and the ureter. The
=external border= is related chiefly to the base of the spleen. The
=anterior extremity= extends almost to the saccus cæcus of the stomach;
it is related to the left end of the pancreas, and the splenic vessels.
The =posterior extremity= is usually larger than the anterior one.
The form of the left kidney is variable. In some cases its outline is
similar to that of the right kidney, but its ventral surface is convex
and is often marked by several furrows which diverge from the hilus.
In well hardened specimens the three areas of the dorsal surface are
often distinct. The psoas area is flat, parallel with the inner
border, and widens behind. The diaphragmatic area is small and convex;
it is crescentic and is confined to the anterior pole. The splenic
area, convex and external, is often so extensive and distinct as
really to constitute a third surface.
=Fixation.=—The kidneys are held in position chiefly by the pressure of
adjacent organs and by the renal fascia. The latter is a special
development of the subperitoneal tissue, which splits into two layers to
inclose the kidney, together with the perirenal fat or capsula adiposa.
On account of its relations with the liver, pancreas, and the base of
the cæcum, the right kidney is much more strongly attached than the left
one. It is, therefore, not surprising that the latter varies somewhat in
position; its posterior pole may be found ventral to the third or fourth
lumbar transverse process. The position of the right kidney seems to be
very constant, excluding its movements during respiration.
[Illustration:
FIG. 378.—FRONTAL (HORIZONTAL) SECTION OF KIDNEY OF HORSE.
The renal vein is removed. A large accessory renal artery entered the
posterior pole. Sections of arteries in limiting layer between
cortical and medullary substance are white in figure.
]
=Weight and Size.=—The right kidney is usually one or two ounces heavier
than the left. The average weight of the right kidney is about 23 to 24
ounces (ca. 700 gm.); that of the left, about 22 to 23 ounces (ca. 670
gm.). The relation of the weight of both kidneys to the body-weight is
about 1 ∶ 300–350.
Chauveau gives as an average 750 grams for the right kidney, and 710
grams for the left. Ellenberger and Baum (24 cases) give the right
kidney as varying between 430 and 840 grams; and the left between 425
and 780; this is an average of 635 grams (about 22½ ounces) for the
right kidney, and 602.5 grams (about 21½ ounces) for the left. They
give the relation of the weight of both kidneys to the body-weight as
1 ∶ 255–344. In a Percheron mare weighing about 2000 pounds the right
kidney weighed 4 pounds 3 ounces, and the left one 4 pounds. In a
horse of medium size the right kidney is about six inches (ca. 15 cm.)
in length, about the same in width, and about two inches (ca. 5 cm.)
thick. The left kidney is about seven inches (ca. 18 cm.) long, four
to five inches (ca. 10 to 12 cm.) wide, and two to two and a half
inches (ca. 5 to 6 cm.) thick.
=Structure.=—The surface of the kidney is covered by a thin but strong
=fibrous capsule= (Tunica fibrosa), which is in general easily stripped
off the healthy kidney. It is continued along the hilus and lines the
renal sinus. Sections through the kidney show it to consist of an
external cortical substance and an internal medullary substance.[136]
The =cortical substance= (Substantia corticalis) is red brown in color
and has a granular appearance. It is dotted over with minute dark
points; these are the =renal= (or Malpighian) =corpuscles= (Corpuscula
renis), each consisting of the dilated origin of a uriniferous tubule
(Capsula glomeruli), with an invaginated tuft of capillaries
(Glomerulus) inclosed by it. The =medullary substance= (Substantia
medullaris) is more resistant and presents a distinct radial striation.
Its central part is pale, but its periphery, the =intermediate zone=, is
of a deep red color; in the latter are seen, at fairly regular
intervals, sections of the relatively large arciform vessels, which are
taken to represent the demarcation between the primitive lobes.[137]
Between the vessels the medulla is prolonged somewhat toward the
periphery, forming the bases of the =renal= (or Malpighian) =pyramids=.
These are not very pronounced in the kidney of the horse, especially as
the gland is not papillated. Between the bases of the pyramids processes
of the cortex dip in toward the sinus, forming the =renal columns=.[138]
The inner central part of the medulla forms a concave ridge or crest
which projects into the pelvis of the kidney; the crest is marked by
numerous small openings at which the renal tubules terminate.
[Illustration:
FIG. 379.—TRANSVERSE SECTION OF RIGHT KIDNEY OF HORSE THROUGH THE
HILUS.
Posterior portion of organ hardened _in situ_. Note curvature of
dorsal surface.
]
Examination with a pocket lens shows that the cortex is imperfectly
divided into =lobules= (Lobuli corticales). Each lobule consists of an
axial =radiate part= (Pars radiata), surrounded by a =convoluted part=
(Pars convoluta). The former (formerly termed pyramids of Ferrein)
appear as ray-like prolongations from the bases of the pyramids (hence
also termed medullary rays), and consist largely of narrow, straight or
slightly flexuous, tubules (limbs of the loops of Henle). The convoluted
part (formerly termed the labyrinth) is granular in appearance, and
consists largely of the renal corpuscles and convoluted tubules.
The =pelvis= of the kidney (Pelvis renalis) is the dilated origin of the
excretory duct. It lies in the sinus of the kidney, and it is
funnel-shaped, but flattened dorso-ventrally. The =renal crest=[139]
(Papilla communis) projects into the outer part of the pelvis in the
form of a horizontal ridge with a concave free edge. The tubules of the
middle part of the medullary substance open on this crest into the
pelvis. The tubules from each end of the kidney do not open into the
pelvis proper (Recessus medius), but into two long, narrow diverticula
(Recessus terminales), which proceed from it toward the poles of the
kidney. The wall of the pelvis consists of three layers. The external
=fibrous coat= or adventitia is continuous with the supporting tissue of
the kidney. The =muscular coat= consists of longitudinal and circular
fibers. The =mucous coat= does not cover the renal crest, nor is it
continued into the diverticula of the pelvis. It has a yellowish tinge,
and presents numerous folds. It contains glands (Glandulæ pelvis
renalis) which secrete the thick mucus always found in the pelvis.
[Illustration:
FIG. 380.—DIAGRAMMATIC SCHEME OF URINIFEROUS TUBULES AND BLOOD-VESSELS
OF KIDNEY.
Drawn in part from the descriptions of Golubew (Böhm, Davidoff, and
Huber).
]
=Renal Tubules=—The parenchyma or proper substance of the kidney is
composed of the small =renal= or =uriniferous tubules= (Tubuli
renales), which are very close together and have a complicated course.
Each tubule begins in a thin-walled, spherical dilatation or
=capsule=, which is invaginated to receive a tuft of looped
capillaries termed a =glomerulus=; these two structures constitute a
=renal= (or Malpighian) =corpuscle=; the corpuscles are visible as
minute red or dark spots in the convoluted part of the cortex.
Succeeding this is a short narrow neck, beyond which the tubule
becomes wide and convoluted, forming the proximal convoluted tubule,
and enters the radiate portion of the cortex. It then gradually
narrows and enters the intermediate zone; becoming very narrow and
nearly straight, it descends for a variable distance into the
medullary substance, turns sharply upon itself, and returns to the
cortex, forming thus the loop of Henle, with its descending and
ascending limbs. In the convoluted part of the cortex, it widens and
becomes tortuous, constituting the distal convoluted tubule. The
tubule then narrows, enters a medullary ray, and opens with other
tubules into a straight collecting tubule; this passes axially through
a pyramid, and unites with other collecting tubules to form the
relatively large papillary ducts, which open into the renal pelvis.
=Stroma.=—The interstitial tissue forms a reticulum throughout which
supports the tubules and blood-vessels. It is very scanty in the
cortex, much more abundant in the medulla, in which it increases in
amount toward the pelvis.
=Blood-supply.=—The kidneys receive a large amount of blood through the
=renal arteries=. Branches of these enter at the hilus and on the
ventral surface of the gland, and reach the intermediate zone, where
they form anastomotic arches (Arteriæ arciformes). From these arciform
arteries branches pass into the cortex and medulla. The cortical
branches (Arteriæ interlobulares) have in general a radial course
between the cortical lobules, and give off short lateral branches, each
of which ends as the =afferent vessel= (Vas afferens) of a renal
corpuscle. The blood is carried from the glomerulus by a smaller
=efferent vessel=, which breaks up immediately into capillaries which
form networks around the tubules. The medullary branches descend in the
pyramids, forming in them bundles of straight twigs (Arteriolæ rectæ).
The =veins= correspond in general to the arteries. In the superficial
part of the cortex the veins form star-like figures (Venæ stellatæ) by
the convergence of several small radicles to a common trunk.
=Lymph Vessels.=—These may be divided into two sets, capsular or
superficial, and parenchymatous or deep.
=Nerve-supply.=—The nerves are derived from the renal plexus of the
sympathetic, and form a plexus around the vessels.
THE URETERS
The =ureters= are the narrow part of the excretory ducts of the kidneys.
Each begins at the renal pelvis and terminates at the bladder. It is
about ⅓ to ¼ inch (ca. 6 to 8 mm.) in diameter, and its average length
is about 28 inches (ca. 70 cm.). The =abdominal part= (Pars abdominalis)
of each ureter emerges ventrally from the hilus of the kidney, and
curves backward and inward toward the lateral face of the posterior vena
cava (right side) or the posterior aorta (left side). They then pass
almost straight backward in the subperitoneal tissue on the surface of
the psoas minor, cross the external iliac vessels, and enter the pelvic
cavity. The =pelvic part= (Pars pelvina) passes backward and a little
downward on the lateral wall of the pelvic cavity, turns inward, and
pierces the dorsal wall of the bladder near the neck.
In the male the pelvic part enters the urogenital fold and crosses the
vas deferens. In the female the ureter is situated in the greater part
of its course in the dorsal part of the broad ligament of the uterus.
The wall of the ureter is composed of three coats. The outer =fibrous
coat= (Tunica adventitia) is composed of loose fibrous tissue. The
=muscular coat= (Tunica muscularis) consists of inner and outer layers
of longitudinal fibers, with a stratum of circular fibers between them.
The =mucous membrane= (Tunica mucosa) is covered with transitional
epithelium; glands (Glandulæ mucosæ ureteris) resembling those of the
renal pelvis occur in the first three or four inches of the ureter.
THE URINARY BLADDER
The =urinary bladder= (Vesica urinaria) (Figs. 270, 271, 272) differs in
form, size, and position according to the amount of its contents. When
empty and contracted, it is a dense, pyriform mass, about the size of a
fist, lies on the ventral wall of the pelvic cavity, and does not reach
to the inlet. When moderately filled, it is ovoid in form, and extends a
variable distance along the ventral abdominal wall. Its physiological
capacity varies greatly, but may be estimated approximately at about
three or four quarts.
The anterior rounded blind end is termed the =vertex=;[140] on its
middle is a mass of cicatricial tissue (Centrum verticis), a vestige of
the urachus, which in the fœtus forms a tubular connection between the
bladder and the allantois. The =body= or middle part (Corpus vesicæ) is
rounded, and is somewhat flattened dorso-ventrally, except when
distended. It presents two surfaces, dorsal and ventral, the former
being the more strongly convex, especially in its posterior part in
front of the entrance of the ureters.[141] The posterior narrow
extremity, the =neck= (Collum vesicæ), joins the urethra.
The =relations= of the bladder vary according to the degree of fullness
of the organ, and also differ in important respects in the two sexes.
The ventral surface lies on the ventral wall of the pelvis, and extends
forward on the abdominal wall as the bladder fills. The dorsal surface
in the male is related to the rectum, the urogenital fold, the terminal
parts of the vasa deferentia, the vesiculæ seminales, and the prostate;
in the female it is in contact, instead, with the body of the uterus and
the vagina. The vertex of the full bladder is related to coils of the
small intestine and small colon, and to the pelvic flexure of the large
colon.
=Fixation.=—Displacement of the bladder is limited chiefly by three
peritoneal folds, termed the middle and lateral ligaments (Figs. 257,
272). The =middle ligament= (Plica umbilicalis media) is a median
triangular fold, formed by the reflection of the peritoneum from the
ventral surface of the bladder on to the ventral wall of the pelvis and
abdomen. In the new-born animal it is extensive and reaches to the
umbilicus; in the adult it is usually much reduced in length relatively.
It contains elastic and muscular fibers in its posterior part. The
=lateral ligaments= (Plicæ umbilicales laterales) stretch from the
lateral aspects of the bladder to the lateral pelvic walls. Each
contains in its free edge a round, firm band, the =round= or =umbilical
ligament= (Lig. umbilicale s. teres); this is the remnant of the large
fœtal umbilical artery, the lumen of which in the adult is very small.
The retroperitoneal part of the bladder is attached to the surrounding
parts by loose connective tissue, in which there is a quantity of fat.
It is evident that the posterior part of the bladder has a definite
fixed position, while its anterior part is movable.
=Structure.=—The wall of the bladder consists of a partial peritoneal
investment, the muscular coat, and the mucous lining.
The =serous coat= (Tunica serosa) covers the greater part of the dorsal
surface, from which it is reflected in the male to form the urogenital
fold; in the female it passes on to the vagina, forming the
vesico-genital pouch. Ventrally the peritoneum covers only the anterior
half or less of the bladder, and is reflected posteriorly on to the
pelvic floor.
The =muscular coat= (Tunica muscularis) is relatively thin when the
bladder is full. It is unstriped, pale, and not clearly divided into
layers, but has rather a plexiform arrangement. Longitudinal fibers
occur on the dorsal and ventral surfaces, but laterally they become
oblique and decussate with each other. A distinctly circular arrangement
is found at the neck, where the fibers form a =sphincter= (Annulus
urethralis).
The =mucous coat= (Tunica mucosa) is pale and thin. It is in general
attached by a highly elastic submucosa to the muscular coat, and forms
numerous folds when the organ is empty and contracted. It is modified
dorsally in the vicinity of the neck over a triangular area, termed the
=trigonum vesicæ=; the angles of this space lie at the orifices of the
two ureters and the urethra, which are close together. Here the mucous
membrane is closely attached and does not form folds. From each
=ureteral orifice= (Orificium ureteris) a fold of mucous membrane (Plica
ureterica) passes backward and inward, uniting with its fellow to form a
median crest (Crista urethralis) in the first part of the urethra. The
ureteral orifices are a little more than one inch (ca. 3 cm.) apart. The
terminal part of the ureter, after piercing the muscular coat of the
bladder, passes for a distance of about an inch (ca. 2 to 3 cm.) between
the muscular and mucous coats before piercing the latter; this
arrangement constitutes a valve which prevents absolutely the return of
the urine from the bladder into the ureter. The =internal urethral
orifice= (Orificium urethæ internum) lies at the apex of the trigonum,
and is about an inch and a half (ca. 4 cm.) behind the ureteral
orifices. The mucous membrane is covered with transitional epithelium
like that of the ureter and renal pelvis. It contains lymph nodules.
=Blood-supply.=—This is derived chiefly from the vesico-prostatic branch
of the =internal pudic artery=. It is also supplied by small twigs from
the =obturator= and =umbilical arteries=. The =veins= terminate chiefly
in the =internal pudic veins=. They form plexuses posteriorly.
=Lymph Vessels.=—These form plexuses on both surfaces of the muscular
coat. They go to the internal iliac and lumbar glands.
=Nerves.=—The nerves are derived from the =pelvic plexus= (sympathetic
and ventral branches of third and fourth sacral nerves). They form a
plexus in the submucosa which presents microscopic ganglia.
In the fœtus and new-born animal the bladder is situated chiefly in
the abdomen. It is long, narrow, and fusiform. Its abdominal end lies
at the umbilicus, through which it is continued by the urachus to the
extra-embryonic part of the allantois. As the pelvis increases in size
and the large intestine grows, the bladder retracts into the pelvis
and changes its form.
The urethra will be described with the genital organs.
THE ADRENAL BODIES
The =adrenal bodies= or =suprarenal glands= (Glandulæ suprarenales)[142]
are two small, flattened organs, which lie in contact with the anterior
part of the inner border of the kidneys (Figs. 376, 377). They are
ductless.
In the horse they are red-brown in color, about three and a half to four
inches (ca. 9 to 10 cm.) long, one to one and a half inches (ca. 3 to 4
cm.) wide, and about half an inch or more (ca. 1 to 5 cm.) in thickness.
The weight varies from one to two ounces (ca. 28 to 56 gm.).
The =right adrenal= is related internally to the posterior vena cava, to
which it is adherent. Its anterior part curves dorsally around the inner
border of the right kidney. Its posterior part is flattened and is
related ventrally to the pancreas and cæcum, dorsally, to the right
renal vessels. The anterior extremity is concealed in the renal
impression of the liver; the posterior is related to the ureter.
The =left adrenal= is a little shorter than the right one, and its
extremities are rounded; it is usually curved, so that its internal
border partly embraces the anterior mesenteric artery. Its dorsal
surface is related to the kidney, the renal artery, the aorta, and the
left cœliaco-mesenteric ganglion. The ventral surface is in relation
with the left extremity of the pancreas and the root of the great
mesentery. The posterior extremity often curves inward behind the
anterior mesenteric artery; it is related behind to the left renal vein.
When hardened _in situ_ the adrenals present several features not
evident in the soft organs. The anterior part of the right adrenal is
twisted upward and outward over the inner margin of the kidney, so
that this part is prismatic and has three surfaces; of these, the
concave outer one is applied to the kidney, the dorsal one is related
to the right crus of the diaphragm and the liver, and the inner one is
in contact with the posterior vena cava. The anterior mesenteric
artery is nearly always more or less enlarged as a result of verminous
arteritis, and the form and degree of curvature of the left adrenal
seem to vary in conformity with the condition of the artery.
=Structure.=—The =fibrous capsule= adheres intimately to the surface of
the organ. It contains elastic fibers, and in its deep part unstriped
muscle-fibers. From it trabeculæ pass radially into the substance,
blending with the fine supporting reticulum. The =parenchyma= consists
of a cortical and a medullary portion. The =cortical substance=
(Substantia corticalis) is red-brown in color, and is clearly
distinguishable from the yellow =medullary substance= (Substantia
medullaris). A large =central vein= (Vena centralis) is visible on
cross-sections.
The cells of the cortex are arranged in chains of one or two rows. In
the peripheral portion the cells are of high cylindrical shape, and
the chains form connecting loops; Günther has proposed the name zona
arcuata for this part, instead of the usual term zona glomerularis.
More deeply the chains are distinctly palisade-like, and this region
is called the zona fasciculata. Next to the medulla is the zona
reticularis, in which the chains form a network. The cells in these
two zones are polygonal and contain a brown pigment.
The cells of the medulla are arranged in irregular groups or form
sheaths around the veins. They react to chromic salts by assuming a
yellow or yellow-brown color, and are termed chromaffin cells; they
share this peculiarity with certain cells of the sympathetic ganglia
and paraganglia, with which they are probably related genetically. The
alkaloid adrenalin appears to be formed in the medullary cells.
=Vessels and Nerves.=—The adrenals receive a relatively large
blood-supply through the =adrenal arteries= (Aa. suprarenales), which
arise from the renal arteries or from the aorta directly. The =veins=
terminate in the posterior vena cava and the left renal vein. The =lymph
vessels= go to the renal lymph glands. The numerous =nerves= are derived
from the sympathetic system through the solar and renal plexuses. The
fibers form a rich interlacement, especially in the medullary substance.
Ganglion cells are found chiefly in the medulla, but also occur in the
deeper part of the cortex.
[Illustration:
FIG. 381.—ADRENAL BODY OF HORSE; HORIZONTAL SECTION, REDUCED.
_1_, Capsule; _2_, _2′_, cortical substance; _3_, medullary substance;
_4_, blood-vessel in section. (From Leisering’s Atlas, reduced.)
]
URINARY ORGANS OF THE OX
The =kidneys= are superficially divided into polygonal lobes by fissures
of variable depth. The lobes vary in size, and are commonly about twenty
to twenty-five in number. The fissures are filled with fat.
The =right kidney= has an elongated elliptical outline, and is flattened
dorso-ventrally. It lies ventral to the last rib and the first two or
three lumbar transverse processes. The dorsal surface is rounded, and is
in contact chiefly with the sublumbar muscles. The ventral surface is
less convex, and is related to the liver, pancreas, duodenum, and
terminal part of the colon. The hilus is situated on the anterior part
of this surface near the inner border. The internal border is nearly
straight, and lies parallel with the posterior vena cava. The external
border is convex. The anterior extremity occupies the renal impression
of the liver, and is capped by the adrenal body.
The =left kidney= occupies a remarkable position, and when hardened _in
situ_, differs strongly in form from the right one. When the rumen is
full, it pushes the kidney backward and across the median plane, so that
it is situated on the right side, behind and at a lower level than the
right kidney. It then lies usually under the third, fourth, and fifth
lumbar vertebræ. When the rumen is not full, the left kidney may lie
partly to the left of the median plane. It has three surfaces. The
dorsal surface is convex, and presents on its antero-external part the
hilus, which opens outward. The ventral surface is related to the
intestine. The third face is often more or less flattened by contact
with the rumen, and may be termed the ruminal surface. The anterior
extremity is small, the posterior large and rounded.
[Illustration:
FIG. 382.—RIGHT KIDNEY OF OX, VENTRAL FACE.
Organ hardened _in situ_. Fat has been removed from fissures between
lobes.
]
The preceding statements refer to the adult subject, and are based on
investigations made on living subjects, and studies of frozen sections
and material hardened _in situ_. In the young calf the kidneys are
almost symmetrically placed, but as the rumen grows it pushes the left
kidney to the right and backward _pari passu_. It also usually causes
a rotation of the kidney, so that the primary dorsal surface comes to
lie almost in a sagittal plane. Further, the gland is bent so that the
hilus is largely closed up and faces outward (to the right). In very
fat subjects the three-sided appearance of the kidney may be absent,
and about one-third or more may remain to the left of the median
plane, even where the rumen is pretty well filled.
[Illustration:
FIG. 383.—FRONTAL SECTION OF KIDNEY OF OX.
_L_, Lobes of cortex; _P_, papillæ; _C_, calyx major; _c′_, calyces
minores.
]
The kidneys are embedded in a large amount of perirenal fat. The weight
of a kidney is about 20 to 25 ounces (ca. 570 to 700 gm.), the left one
being usually an ounce or more the heavier. The two form about ¼ per
cent. of the body-weight.
The right kidney measures about 8 to 10 inches (ca. 20 to 25 cm.) in
length, 4 to 5 inches (ca. 10 to 12 cm.) in width, and 2½ to 3 inches
(ca. 7 cm.) in thickness. The left kidney is one or two inches (ca. 2
to 5 cm.) shorter, but its posterior part is much thicker than the
right one.
=Structure.=—The hilus is equivalent to the hilus and sinus of the
kidney of the horse; in the right kidney it is an extensive elliptical
cavity, in the left, a deep fissure. The pelvis is absent. The ureter
begins at the junction of two wide, thin-walled tubes, the =calyces
majores=; the anterior calyx is usually the larger. Each calyx major
gives off a number of branches, and these divide into several
funnel-shaped =calyces minores=, each of which embraces a renal papilla.
The space not occupied by the calyces and vessels is filled with fat.
On section through the kidney the =renal pyramids= are easily made out.
The blunt apex of each pyramid, the =papilla renalis=, projects into a
calyx minor. On each papilla are small orifices (Foramina papillaria) by
which the terminal renal tubules (Ductus papillares) open into the
calyx. The renal columns are much more distinct than in the horse.
At the hilus the renal artery is dorsal, the vein in the middle, and the
ureter ventral; a quantity of fat surrounds these structures in the
hilus.
The kidneys of the =sheep= are bean-shaped and smooth, without any
superficial lobation. The soft organ is regularly elliptical in form,
with convex dorsal and ventral surfaces and rounded extremities; its
length is about 2½ to 3 inches (ca. 5 to 8 cm.), its width about 1½ to 2
inches (ca. 4 to 5 cm.), and its thickness a little more than 1 inch
(ca. 3 cm.). In position they resemble those of the ox, except that the
right one is usually a little further back, and lies under the first
three lumbar transverse processes. The average weight of each is about
four ounces. The hilus is in the middle of the inner border. There is a
renal crest or common papilla formed by the fusion of twelve to sixteen
pyramids.
[Illustration:
FIG. 384.—KIDNEY OF SHEEP, VENTRAL VIEW.
_V.V._, Branches of renal vein.
]
[Illustration:
FIG. 385.—KIDNEY OF SHEEP, HORIZONTAL SECTION.
_1_, Cortical substance; _2_, medullary substance; _3_, renal crest;
_4_, renal pelvis; _5_, ureter. (From Leisering’s Atlas, reduced.)
]
When the rumen is full, the left kidney (which is attached by a short
mesentery) usually lies entirely to the right of the median plane,
under the third, fourth, and fifth lumbar transverse processes. The
primitive dorsal surface has become ventro-medial, and is somewhat
flattened by contact with the rumen.
The =ureters= are, in general, like those of the horse, except in regard
to the first part of the left one, which has a peculiar course, in
conformity with the remarkable position of the kidney. It begins at the
ventral part of the hilus (which faces toward the right), curves upward
and inward over the outer aspect of the kidney to its dorsal surface,
crosses the median plane, and runs backward on the left side.
The =bladder= is longer and narrower than that of the horse, and extends
further forward on the abdominal floor. The peritoneal coat extends
backward further than in the horse.
THE ADRENAL BODIES
The =right adrenal= lies against the inner part of the anterior pole of
the right kidney. When hardened _in situ_ it is pyramidal in form. Its
inner surface is flattened and is in contact with the right crus of the
diaphragm. The outer surface is convex and lies in the renal impression
of the liver. The ventral surface is grooved for the posterior vena
cava; on this surface a relatively large vein emerges near the apex. The
base is concave and rests obliquely against the anterior pole of the
kidney. The apex fits into the angle between the posterior vena cava and
the dorsal border of the liver.
The =left adrenal= lies on the inner face of the posterior vena cava
just behind the anterior mesenteric artery, and is therefore practically
median in position. It is flattened, and irregularly triangular or
heart-shaped in outline. Its left face is related to the dorsal sac of
the rumen. Its right face is related to the vena cava, and presents a
large emergent vein. The posterior border or base is deeply notched.
[Illustration:
FIG. 386.—LEFT ADRENAL OF OX, VENTRAL VIEW: HARDENED _in situ_.
]
[Illustration:
FIG. 387.—RIGHT ADRENAL OF OX, VENTRAL VIEW: HARDENED _in situ_.
]
It is interesting to note that the left adrenal does not migrate with
the kidney, but retains its primitive position; it lies usually about
two inches (ca. 5 cm.) in front of a transverse plane through the
anterior pole of the left kidney.
The adrenals of the =sheep= are both bean-shaped. The right one lies
along the anterior part of the inner border of the kidney, at the angle
of the junction of the right renal vein and the posterior vena cava. It
is a little over an inch (ca. 3 cm.) long, and about an inch (ca. 12 to
15 mm.) wide. The left adrenal is longer, flatter, and somewhat bent. It
lies across the left renal vein, to which it is attached, but is not in
contact with the kidney.
[Illustration:
FIG. 388.—KIDNEYS OF PIG _in situ_, VENTRAL VIEW.
_C.a._, Hepatic artery; _M.a._, gastro-splenic artery.
]
[Illustration:
FIG. 389.—FRONTAL SECTION OF KIDNEY OF PIG.
]
URINARY ORGANS OF THE PIG
The =kidneys= are smooth and bean-shaped; they are more flattened
dorso-ventrally, more elongated, and smaller at the extremities than
those of the dog. The length is about twice the width. They are usually
almost symmetrically placed on either side of the first four lumbar
vertebræ. (Variations in position are not rare, and involve the left
kidney oftener than the right. The former has been found near the pelvic
inlet.) The external border lies against the flank parallel with the
edge of the longissimus muscle. The posterior extremity usually lies
about midway between the last rib and the external angle of the ilium.
The anterior extremity of the right kidney usually extends as far
forward as the last rib, but has no contact with the liver.
The weight of the kidney of a medium-sized pig is about seven to nine
ounces (200 to 250 grams). The ratio of their combined weight to that of
the body is about 1 ∶ 150–200.
=Structure.=—The hilus is about in the middle of the inner border. The
pelvis is funnel-shaped, and divides into two calyces majores, which
pass in a curve forward and backward respectively, and give off some
eight to twelve short calyces minores; each of the latter contains a
papilla. Some papillæ are narrow and conical, and correspond to a single
pyramid; others are wide and flattened, and result from the fusion of
two or more pyramids; some project directly through the wall of the
pelvis without the formation of a calyx. The renal pyramids are
distinct, but it is apparent that some are compound, _i. e._, formed by
fusion of primitively separate pyramids. The renal artery enters the
ventral part of the hilus, and the ureter leaves it dorsally.
The only special feature in regard to the =ureter= is that it is at
first relatively wide and gradually diminishes in caliber.
The =bladder= is relatively very large; when full, it lies chiefly in
the abdominal cavity. It is almost completely covered with peritoneum.
URINARY ORGANS OF THE DOG
The =kidneys= are relatively large, forming about ¹⁄₁₅₀ to ¹⁄₂₀₀ of the
body-weight; the weight of the kidney of a medium-sized dog is about two
ounces (ca. 50 to 60 grams). They are both bean-shaped, thick
dorso-ventrally, with a rounded ventral surface and a less convex dorsal
surface; the surfaces are smooth.
The =right kidney= (Fig. 343) is not subject to much variation in
position; it is situated usually under the last rib and the first three
lumbar transverse processes. Its anterior part lies in the deep renal
impression of the liver; its posterior part is related to the sublumbar
muscles dorsally, and the pancreas and duodenum ventrally.
The =left kidney= (Fig. 342) is subject to some variation in position;
this is due to the fact that it is loosely attached by the peritoneum,
and is affected by the degree of fullness of the stomach. When the
stomach is nearly empty, the kidney usually lies under the transverse
processes of the second, third, and fourth lumbar vertebræ, so that its
anterior pole is opposite to the hilus of the right kidney. As the
stomach fills it pushes the left kidney backward, so that the anterior
pole of the latter may be opposite the posterior pole of the right
kidney. The dorsal surface is related to the sublumbar muscles. The
ventral surface is in contact with the terminal part of the colon (Colon
descendens). The external border is related to the spleen and the flank.
The anterior extremity touches the stomach and the left extremity of the
pancreas.
The external border of the left kidney has considerable contact with
the flank, and hence it may be palpated more or less distinctly in the
living animal about half-way between the last rib and the crest of the
ilium.
=Structure.=—The hilus is in the middle of the inner border and is,
relatively wide. Cortex, limiting zone, and medulla are clearly defined.
On frontal sections it is seen that the medullary substance forms a
horizontal renal crest like that of the horse, but with the important
difference that curved ridges proceed dorsally and ventrally from the
crest somewhat like buttresses. Sections above or below the renal crest
often cut these ridges in such a manner as to give the appearance of
conical papillæ, and thus tend strongly to produce a false impression.
The pelvis is adapted to this arrangement of the medullary substance. It
incloses a central cavity into which the renal crest projects, and is
prolonged outward between the ridges, forming cavities for the latter,
thus simulating the appearance of calyces which do not exist.
The =ureters= present no special features.
The =bladder= is abdominal in position, the neck lying at the anterior
border of the pubic bones. It is relatively large, and when full, the
vertex may reach to the umbilicus. It has a practically complete
peritoneal coat.
THE ADRENALS
The =right adrenal= lies between the anterior part of the inner border
of the kidney and the posterior vena cava. It is somewhat prismatic, and
is pointed at either end.
The =left adrenal= lies along the posterior aorta, from the renal vein
forward, but is not in contact with the kidney. It is elongated and
flattened dorso-ventrally. (There is a furrow on the ventral surface for
the vein which crosses it; the part in front of this furrow is discoid,
and may be taken for the entire organ in a fat subject.)
The cortex is pale yellow in color, the medulla dark brown.
THE MALE GENITAL ORGANS
The male =genital organs= (Organa genitalia masculina) are: (1) The two
=testicles=, the essential reproductive glands, with their coverings and
appendages; (2) the =vasa deferentia=, the ducts of the testicles; (3)
the =vesiculæ seminales=; (4) the =prostate=, a musculo-glandular organ;
(5) the two =bulbo-urethral= (or Cowper’s) =glands=; (6) the male
=urethra=, a canal which transmits the generative and urinary
secretions; (7) the =penis=, the male copulatory organ. The vesiculæ
seminales, the prostate, and the bulbo-urethral glands discharge their
secretions into the urethra, where they mix with the seminal fluid
secreted by the testicles; hence they are often termed the accessory
sexual glands.
MALE GENITAL ORGANS OF THE HORSE
THE TESTICLES
The =testicles= (Testes) are situated in the inguinal region, inclosed
in a diverticulum of the abdomen termed the scrotum. Their long axes are
nearly longitudinal. They are ovoid in form, but considerably compressed
from side to side. Each presents two surfaces, two borders, and two
extremities. The =internal= and =external surfaces= (Facies medialis,
lateralis) are convex and smooth. The =free= or ventral =border= (Margo
liber) is convex in both directions. The =attached= or dorsal =border=
(Margo epididymidis) is nearly straight, and is the one by which the
gland is suspended in the scrotum by the spermatic cord; the epididymis
is attached to this border and overlies it externally. The =anterior=
and =posterior extremities= (Extremitas capitata, caudalis) are rounded.
At the anterior extremity there is often a sessile or pedunculated sac
which contains a clear fluid; this is the =appendix testis= or hydatid
of Morgagni, from which a thread-like process extends backward toward
the vas deferens. It is regarded as a remnant of the Müllerian duct of
the embryo.
A testicle of average size of an adult stallion is about four or five
inches (ca. 10 to 12 cm.) long, two and a half inches (ca. 6 to 7 cm.)
high, and one and a half to two inches (ca. 4 to 5 cm.) wide; it weighs
about ten and one-half ounces (ca. 300 grams). They vary much in size in
different subjects, and are commonly of unequal size, the left one being
more often the larger.
The =epididymis= is adherent to the attached border of the testicle, and
overlaps somewhat the external surface. Its anterior enlarged end is
termed the =head= or globus major (Caput epididymidis), and its
posterior, slightly enlarged end is the tail or globus minor (Cauda
epididymidis); while the intermediate narrow part is the =body= (Corpus
epididymidis). The head is closely connected with the testicle by the
efferent ducts of the latter, by connective tissue, and by the serous
membrane. The body is less closely attached by the serous covering,
which forms externally a pocket beneath the epididymis termed the
=digital fossa= (Sinus epididymidis). The tail is firmly attached to the
posterior extremity of the testicle by a short ligament (Lig.
epididymidis), formed by a thick fold of the tunica vaginalis, which
contains smooth muscle-fibers; it is continued by the vas deferens.
=Structure of the Testicle and Epididymis.= The greater part of the
surface of the testicle is covered by a serous membrane, the =tunica
vaginalis propria=, which is the visceral layer of the serous envelop of
the cord and testicle; this is reflected from the attached border of the
gland, leaving an uncovered area at which the vessels and nerves in the
spermatic cord reach the testicle. Beneath this serous covering is the
=tunica albuginea=, a strong capsule composed of dense white inelastic
fibrous tissue and unstriped muscle-fibers. From the deep surface of
this tunic delicate membranous =septa= (Septula testis) pass into the
gland, dividing it into pyramidal spaces, the bases of which are
peripheral. At the anterior part of the attached border of the testicle
connective tissue and smooth muscle-fibers pass into the substance of
the gland, forming the =mediastinum testis=; from this the septa
radiate. The mediastinum contains a network of fine canals, the =rete
testis=; it is traversed by blood-vessels, which radiate on the septa to
the deep face of the tunica albuginea, forming a delicate network—the
so-called tunica vasculosa. The spaces imperfectly marked off by the
septa contain the =parenchyma testis=, which consists of =seminiferous
tubules= (Tubuli seminiferi), supported by loose intertubular connective
tissue. The tubules are collected into small masses or =lobules= (Lobuli
testis). They are at first very tortuous (Tubuli contorti); toward the
apex of the lobule they unite with other tubules, forming larger
straight tubules (Tubuli recti); these pass into the mediastinum testis,
where they form the =rete testis=. From the latter a number (ca. 15 to
20) of larger =efferent tubules= (Vasa efferentia) pierce the albuginea
and enter the head of the epididymis.
[Illustration:
FIG. 390.—INGUINAL REGION OF STALLION, WITH TESTICLES EXPOSED.
_a_, _a′_, Testicles; _b_, scrotum, opened and reflected; _c_, tunica
vaginalis communis, opened and reflected; _d_, ligament of
epididymis; _e_, tunica vaginalis propria (mesorchium); _f_, vas
deferens; _g_, _g′_, tail of epididymis; _h_, body of same; _i_,
head of same; _k_, digital fossa or sinus epididymidis; _l_,
spermatic vessels showing through tunica vaginalis propria; _m_,
spermatic artery; _n_, prepuce; _n′_, raphé; _o_, preputial orifice.
(After Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
The =epididymis= is covered by the tunica vaginalis propria and a thin
albuginea. Its head consists of =lobules= (Lobuli epididymidis), each of
which consists of a coiled tubule or =conus vasculosus=, which succeeds
a vas efferens. By the union of these tubules is formed a single tube,
the =duct of the epididymis= (Ductus epididymidis), which, by its
complex coils, forms the body and tail of the epididymis and terminates
in the vas deferens. The tubules and the coils of the duct of the
epididymis are held together by connective tissue and unstriped
muscle-fibers. The tubules and duct are lined with ciliated epithelium,
and the duct has a muscular coat which consists of longitudinal and
circular fibers.
=Vessels and Nerves.=—The testicle is richly supplied with blood by the
=spermatic artery=, a branch of the posterior aorta. The artery descends
in the anterior part of the spermatic cord, and is very tortuous near
the testicle; on reaching the attached border of the gland it passes
backward in a flexuous manner, giving branches to the testicle and
epididymis, turns around the posterior extremity, and runs forward on
the free border to the anterior extremity. It is partially embedded in
the tunica albuginea, and detaches lateral branches which ascend in a
tortuous fashion on each surface of the testicle; these give off small
branches which enter the gland on the septa.
[Illustration:
FIG. 391.—RIGHT TESTICLE AND SPERMATIC CORD OF HORSE, INCLOSED IN
TUNICA VAGINALIS.
_c_, Tunica vaginalis communis; _g_, prominence caused by tail of
epididymis; _p_, cremaster externus muscle. (After Ellenberger-Baum,
Top. Anat. d. Pferdes.)
]
[Illustration:
FIG. 392.—RIGHT TESTICLE AND SPERMATIC CORD OF HORSE, EXPOSED.
_a′_, External surface of testicle; _c_, tunica vaginalis, cut and
reflected; _d_, ligament of epididymis; _e_, mesorchium; _g_, tail,
_h_, body, _i_, head of epididymis; _k_, digital fossa or sinus
epididymidis; _l_, spermatic vessels showing through tunica
vaginalis propria; _m_, end of spermatic artery. Dotted line
indicates position of vas deferens on other side of mesorchium.
(After Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
The =spermatic veins= on leaving the testicle, form the =pampiniform
plexus= around the artery in the spermatic cord. The vein which issues
from this plexus usually joins the posterior vena cava on the right
side, the left renal vein on the left side.
The =nerves=, derived from the renal and posterior mesenteric plexuses,
form the =spermatic plexus= around the vessels.
THE SCROTUM
The =scrotum=, in which the testicles and the lower parts of the
spermatic cords are situated, is somewhat globular in form, but is
commonly asymmetrical, since one testicle—more often the left—is the
larger and more dependent. It varies in form and appearance in the same
subject, according to the condition of its subcutaneous muscular tissue.
The latter contracts on exposure to cold, so that the scrotum is drawn
up and becomes thicker and wrinkled; when relaxed under the influence of
heat or fatigue, or from debility, it becomes smooth and pendulous, with
a constriction or neck superiorly. It consists of layers which
correspond with those of the abdominal wall; considered from without
inward these are:
(1) The =skin=, which is thin, elastic, usually black in color, and
smooth and oily to the touch. It presents scattered short fine hairs,
and is abundantly supplied with very large sebaceous and sweat glands.
It is marked centrally by a longitudinal furrow, in which is a line, the
=raphé scroti=; this is continued forward on the prepuce and behind on
the perineum.
(2) The =dartos= (Tunica dartos) is reddish in color and is closely
adherent to the skin except superiorly. It consists of fibro-elastic
tissue and unstriped muscle. Along the raphé it forms a median
partition, the =septum scroti=, which divides the scrotum into two
pouches. Dorsally the septum divides into two layers which diverge on
either side of the penis to join the abdominal tunic. At the bottom of
the scrotum fibers connect the dartos closely with the tunica vaginalis
and the tail of the epididymis, constituting the =scrotal
ligament=.[143] Elsewhere the dartos is loosely connected with the
underlying tunic by areolar tissue which contains no fat.
(3) The scrotal =fascia=, which is apparently derived from the oblique
abdominal muscles.
It has been customary to describe three layers of fascia, in
conformity with the accounts given in text-books of human anatomy.
These are: (1) the intercolumnar or spermatic fascia, derived from the
margin of the external inguinal ring; (2) the cremasteric fascia,
derived from the internal oblique muscle; (3) the infundibuliform
fascia, derived from the fascia transversalis. The first two cannot be
distinguished by dissection and the third is (in the scrotum) fused
with the parietal peritoneum of the tunica vaginalis.
(4) =The parietal layer of the tunica vaginalis.=—This is a fibro-serous
sac which is continuous with the parietal peritoneum of the abdomen at
the internal inguinal ring. It is thin above, but is thick in its
scrotal part, where it is strengthened by fibrous tissue (Lamina
fibrosa) derived from the transversalis fascia. It will be described
further under the caption tunica vaginalis.[144]
THE VAS DEFERENS
This tube (Ductus deferens) extends from the tail of the epididymis to
the ejaculatory duct. It passes upward in the inguinal canal, inclosed
in a fold detached from the inner surface of the mesorchium, near the
posterior (attached) border of the latter. At the vaginal ring it
separates from the other constituents of the spermatic cord, and turns
backward and inward into the pelvic cavity (Fig. 272). For some distance
it lies in the free edge of the urogenital fold, by which it is attached
to the lower part of the lateral wall of the pelvis. In its further
course (over the dorsal surface of the bladder) it leaves the edge of
the fold and inclines inward between its layers, coming in contact with
the inner face of the vesicula seminalis. Over the neck of the bladder
the two vasa lie very close together, flanked laterally by the necks of
the vesiculæ seminales, and having the uterus masculinus between them.
They then disappear under the isthmus of the prostate, and are continued
through the wall of the urethra by the =ejaculatory ducts=. The latter
are formed in the urethral wall by the union of the vas deferens with
the duct (or neck) of the corresponding vesicula seminalis; they are
thin-walled tubes, about 2 to 3 mm. long and 6 to 7 mm. wide, which open
into the urethra on either side of the colliculus seminalis. In about 15
per cent. of subjects the vas deferens and duct of the seminal vesicle
do not unite, but open side by side into the urethra. From its origin
until it reaches the dorsal surface of the bladder the vas deferens has
a uniform diameter of about a quarter of an inch (ca. 6 mm.). It then
forms a fusiform dilatation, the =ampulla ductus deferentis= (Fig. 394);
this part is about six to eight inches (ca. 15 to 20 cm.) long, and in
its largest part nearly an inch (ca. 2 cm.) in diameter in the stallion;
in geldings the dilatation is usually not very pronounced. Beyond the
ampulla the duct abruptly contracts.
=Structure.=—The wall of the vas deferens is thick and the lumen
relatively small, so that the tube has a firm and cord-like character.
It is covered with peritoneum, except in the last few inches of its
course. The loose =adventitia= contains numerous vessels and nerves. The
thick =muscular coat= consists of longitudinal and circular layers. The
=mucous membrane= has an epithelium of short columnar cells. In the
posterior part of the tube, and especially in the ampulla, there are
numerous tubulo-alveolar glands.
=Blood-supply.=—Spermatic and umbilical arteries.
=Nerve-supply.=—Spermatic and pelvic plexuses.
THE SPERMATIC CORD
The =spermatic cord= (Funiculus spermaticus) consists of the structures
carried down by the testicle in its migration through the inguinal canal
from the abdominal cavity to the scrotum. It begins at the internal
inguinal ring, where its constituent parts come together, extends
obliquely downward through the inguinal canal, passes over the side of
the penis, and ends at the attached border of the testicle. It consists
of the following structures:
(1) The =spermatic artery=.
(2) The =spermatic veins=, which form the pampiniform plexus around the
artery.
(3) The =lymphatics=, which accompany the veins.
(4) Sympathetic =nerves=, which run with the artery.
(5) The =vas deferens=.
(6) The =internal cremaster muscle=, which consists of bundles of
unstriped muscular tissue.
(7) The =visceral layer= of the =tunica vaginalis= or =mesorchium=.
The first four of these constituents are gathered into a rounded mass
which forms the anterior part of the cord; they are united by connective
tissue, interspersed with which are bundles of the cremaster internus.
The vas deferens is situated posteriorly, inclosed in a special fold
detached from the inner surface of the mesorchium; hence it is not
visible externally.
The term spermatic cord is to a certain extent misleading as applied
to most animals, while in man the structure is distinctly cord-like.
In the horse, when the tunica vaginalis is slit open and the “cord”
stretched out, the latter is seen to have the form of a wide sheet,
the mesorchium, which has a thick, rounded anterior edge, the
so-called “vascular part” of the cord. The posterior edge of the
mesorchium is continuous with the parietal layer of the tunic; its
inner surface presents posteriorly the deferential fold (Plica ductus
deferentis). Between the two layers of the mesorchium are bundles of
unstriped muscle (cremaster internus) and small vessels.
THE TUNICA VAGINALIS
The =tunica vaginalis= is a somewhat pyriform serous sac which extends
from the internal inguinal ring through the inguinal canal to the bottom
of the scrotum. Like the abdominal peritoneum, of which it is an
evagination, it consists of two layers—parietal and visceral. The
=parietal layer=, or =tunica vaginalis communis= (s. reflexa), lines the
scrotum below; its narrow, tubular part lies in the inguinal canal and
is directly continuous with the parietal peritoneum of the abdomen at
the internal inguinal ring. The =cavity= of the tunica vaginalis (Cavum
vaginale) is a diverticulum of the general peritoneal cavity, with which
it communicates through the =vaginal ring= (Annulus vaginalis). It
contains normally a small quantity of serous fluid. The parietal layer
is reflected from the posterior wall of the inguinal canal around the
structures of the cord, forming the =mesorchium=, a fold analogous to
the mesentery of the intestine. The =visceral layer=, or =tunica
vaginalis propria=, covers the spermatic cord, testicle, and epididymis.
The =external cremaster muscle= (M. cremaster externus) lies on the
outer and posterior part of the tunic, to the scrotal part of which it
is attached.
Confusion has arisen from the use of the term internal abdominal or
inguinal ring in two senses. The term is used to designate the upper
or abdominal opening of the inguinal canal, but it is also applied to
the upper opening of the cavity of the tunica vaginalis. It should
only be applied to the abdominal opening of the canal, the
=subperitoneal ring=. The =peritoneal ring= at which the cavity of the
tunica vaginalis opens into the general peritoneal sac is
distinguished by the name =vaginal ring=. It is placed about four or
five inches (ca. 10 to 12 cm.) from the linea alba, and about two or
three inches (ca. 6 to 8 cm.) in front of the ilio-pectineal eminence.
In stallions it will usually admit the end of the finger readily, but
it may be abnormally large and allow a loop of bowel to enter the
cavity of the tunica vaginalis. In the gelding it is smaller and
sometimes partially occluded. In man the cavity is almost always
obliterated early, except in its scrotal portion, thus abolishing the
vaginal ring.
[Illustration:
FIG. 393.—DIAGRAM OF CROSS-SECTION OF SPERMATIC CORD AND TUNICA
VAGINALIS; LATTER REPRESENTED AS DISTENDED.
]
DESCENT OF THE TESTICLES
During early fœtal life the testicle is situated against the dorsal wall
of the abdominal cavity, in contact with the ventral surface of the
corresponding kidney. As growth proceeds it gradually migrates from this
primitive position, and finally passes down the inguinal canal into the
scrotum. Previous to its descent through the abdominal wall the testicle
is suspended by a fold of peritoneum, termed the =mesorchium=. This fold
contains the vessels and nerves of the testicle in its anterior border.
In its posterior edge is the elongated tail of the epididymis, and two
cords of fibrous tissue and unstriped muscle. One of these cords is
short and connects the tail of the epididymis with the testicle; later
it becomes shorter, and is termed the ligament of the epididymis. The
other cord, the =gubernaculum testis=, extends from the tail of the
epididymis to the subperitoneal tissue in the vicinity of the future
vaginal ring. The =deferential fold= (Plica ductus deferentis) is given
off from the inner face of the mesorchium, and joins the urogenital fold
posteriorly. The body of the epididymis at this time lies in the edge of
an oblique fold formed by the outer layer of the mesorchium. After the
middle of fœtal life, a pouch or diverticulum of the peritoneum, the
=processus vaginalis=, grows downward through the inguinal canal,
carrying with it cremaster fibers derived from the internal oblique
muscle and a layer from the transversalis fascia. It is accompanied by
an inguinal extension of the gubernaculum testis. The latter blends
below with the subcutaneous tissue which later becomes the dartos. The
tail of the epididymis first enters the processus vaginalis, followed by
the testicle with its mesorchium, which descends within this
diverticulum of the peritoneum until it reaches the scrotum. The vas
deferens and its fold descend synchronously with the epididymis and
testicle.
The mechanical factors concerned in the migration of the testicle are
matters on which much uncertainty still exists. That the gubernaculum
exerts sufficient traction to guide the epididymis and testicle to the
inguinal canal seems plausible. The internal inguinal ring may
constitute a locus minoris resistentiæ in the abdominal wall,
especially after the descent of the processus vaginalis. Progressive
shortening of the gubernaculum was formerly considered to be the chief
cause of the descent through the abdominal wall. Increase in the
intra-abdominal pressure is probably an important factor.
In the foal the descent of the testicles is often complete at birth, but
it frequently happens that one testicle or both may be retained in the
inguinal canal or in the abdomen for some months. In other cases the
testicle may return into the canal or abdomen, since in the young foal
the vaginal ring is large and the testicle small and soft, and not yet
closely anchored by the scrotal ligament. In rare cases the descent may
be completed as late as the fourth year (personal observation).
Indefinite retention of one testicle or both in the abdominal cavity
or inguinal canal is not rare in horses; this condition is termed
cryptorchism. Abdominal retention is the more usual form of
cryptorchism in adult horses, inguinal retention being usually
temporary. The retained testicle is usually, but not always, small,
thin, soft, and flabby, and is non-spermiogenic. The processus
vaginalis and the inguinal part of the gubernaculum are usually
present, but may be rudimentary. The ligament of the epididymis and
the corresponding part of the mesorechium are often so long that the
tail of the epididymis may be several inches distant from the
testicle. The abdominal part of the gubernaculum may be 8 to 10 inches
(ca. 20 to 25 cm.) long, and the ligament of the epididymis much
elongated (10 to 15 cm. in length according to Vennerholm); thus the
testicle may have a wide range. The vaginal ring is sometimes closed.
In many mammals the testicles normally remain in the abdominal cavity;
such animals are termed testiconda, and include the elephant, some
insectivora, hyrax, sloths, ant-eaters, armadillos, and cetacea. In
others the testicles descend periodically during the period of œstrum,
and then return into the abdomen, or they may be extruded and
retracted voluntarily; this is true of most rodents, many insectivora
(moles, shrews, hedgehog), and bats.
THE VESICULAE SEMINALES
The =vesiculæ seminales= (Fig. 394) are two elongated and somewhat
pyriform sacs, which lie on either side of the posterior part of the
dorsal surface of the bladder. They are partly inclosed in the
urogenital fold, and are related to the rectum dorsally. Their long axes
are parallel with the vas deferentia and converge posteriorly. Each
consists of a rounded blind end, the =fundus=, a middle, slightly
narrower part, the =body=, and a posterior constricted part, the =neck=
or =duct=.
In the stallion they are about six to eight inches (ca. 15 to 20 cm.)
long, and their greatest diameter is about two inches (ca. 5 cm.); in
the gelding they are usually much smaller.[145]
The vesiculæ are, for the most part, retroperitoneal, but the fundus
extends forward into the urogenital fold and hence has a serous
covering. The =neck= or =duct= (Ductus excretorius) dips under the
prostate, and usually unites with the end of the vas deferens to form
the =ejaculatory duct=.
[Illustration:
FIG. 394.—INTERNAL GENITAL ORGANS OF STALLION, DORSAL VIEW.
On left side urethral muscle has been removed over bulbo-urethral
gland. Cornua of uterus masculinus are indicated in urogenital fold.
]
=Structure.=—The wall, exclusive of the partial serous coat, consists of
a fibrous =adventitia=, a middle =muscular coat=, and a =mucous lining=.
The muscular coat is thickest at the fundus, and consists of two planes
of longitudinal fibers with a circular layer between them. The mucous
membrane is thin, and is arranged in numerous folds which form a
network; the spaces so inclosed present the openings of tubulo-alveolar
glands. The epithelium is columnar. The =blood-supply= is derived from
the =internal pudic artery=.
THE PROSTATE
The =prostate= (Prostata) is a musculo-glandular organ which lies on the
neck of the bladder and the beginning of the urethra, beneath the
rectum. It consists of two lateral lobes and a connecting isthmus.
The =lateral lobes=, right and left (Lobus dexter et sinister), are
somewhat prismatic in form, and are directed forward, outward, and
somewhat upward. The antero-internal surface of each lobe is concave and
partly embraces the corresponding vesicula seminalis. The dorsal surface
is concave and is in relation with the rectum. The ventral surface is
convex and lies on the obturator internus muscle and fat. The apex is
pointed and lies near the posterior end of the superior ischiatic spine.
The =isthmus= is a thin, transverse band, about four-fifths of an inch
(ca. 2 cm.) wide. It lies over the junction of the bladder with the
urethra, the uterus masculinus, the terminal parts of the vasa
deferentia, and the necks of the vesiculæ seminales. Dorsally it is
partly covered by transverse fibers of the urethral (Wilson’s) muscle.
=Structure.=—The prostate is inclosed in a fibro-muscular =capsule=,
which sends thick, somewhat radially arranged =trabeculæ= into the gland
substance, dividing it into spheroidal or ovoid =lobules=. The lobules
contain a central space in which the prostatic secretion (Succus
prostaticus) collects. The walls of these spaces are pouched out to form
tubular diverticula, and the latter present saccular dilatations. These
cavities are all lined by cubical epithelium. There are 15 to 20
=prostatic ducts= (Ductus prostatici) on either side, which perforate
the urethra and open lateral to the colliculus seminalis. The
=blood-supply= is derived from the =internal pudic artery=.
The surface of the prostate is commonly tuberculate in old subjects,
and amyloid bodies and calcareous concretions may be found in it.
THE UTERUS MASCULINUS
The =uterus masculinus= or =prostatic utricle= is a rudimentary
structure of variable size and form, situated centrally on the posterior
part of the dorsal surface of the bladder. When well developed, it
consists of a median flattened tube, some three or four inches (ca. 7.5
to 10 cm.) long, and about half an inch (ca. 1 to 1.5 cm.) wide, the
anterior part of which lies in the urogenital fold and gives off two
slender processes or cornua; the latter curve forward and outward in the
fold a variable distance, being sometimes traceable as far as the
anterior end of the ampulla of the vas deferens. The posterior extremity
of the tube passes under the isthmus of the prostate, and opens into the
urethra on the summit of the colliculus or joins an ejaculatory duct. It
has a muscular coat and a mucous lining. In many cases it consists
merely of a very small central tubule with a blind anterior end, or a
band, not at all sharply marked off from the adjacent tissue; in other
cases it cannot be recognized. It is interesting chiefly as being a
remnant of the ducts of Müller and the homologue of the uterus and
vagina.
THE BULBO-URETHRAL GLANDS
The =bulbo-urethral= (or Cowper’s) =glands= (Glandulæ bulbourethrales)
are two in number, and are situated on either side of the pelvic part of
the urethra close to the ischial arch (Fig. 452). They are covered by
the urethral (Wilson’s) muscle. They are ovoid in form, somewhat
depressed dorso-ventrally, and their long axes are directed obliquely
forward and outward. In the stallion they may measure about two inches
(ca. 5 cm.) in length, and an inch or more (ca. 3 cm.) in width. In the
gelding they are about the size of an average hazel nut.
=Structure.=—They resemble the prostate in general structure, but the
interstitial tissue is much less abundant, especially in regard to its
muscular elements. In the peripheral part there are striped
muscle-fibers. Each gland has six to eight =excretory ducts= (Ductus
excretorii) which open into the urethra on a series of small papillæ
behind the prostatic ducts and close to the median plane. The
=blood-supply= comes from the =internal pudic artery=.
THE PENIS
The =penis=, the male organ of copulation, is composed essentially of
erectile tissue, and incloses the extrapelvic part of the urethra. It
extends from the ischial arch forward between the thighs on to the
umbilical region of the abdominal wall. It is supported by the fascia
penis and the skin, and its prescrotal portion is situated in a
cutaneous pouch, the prepuce or sheath. It is cylindrical in form, but
much compressed laterally in the greater part of its extent.
[Illustration:
FIG. 395.—PENIS OF HORSE, LATERAL VIEW.
]
In the quiescent state it is about 20 inches (ca. 50 cm.) long; of
this, about 6 to 8 inches (ca. 15 to 20 cm.) is free in the prepuce.
In erection it increases 50 per cent. or more in length.
It may be divided into a root, a body, and a terminal enlargement, the
glans.
The =root= (Radix penis) is attached to the lateral parts of the ischial
arch by two =crura=, which converge and unite below the arch (Fig. 452).
The urethra passes over the ischial arch between the crura, and curves
forward to become incorporated with the penis.
The =body= (Corpus penis) begins at the junction of the crura and
constitutes the bulk of the organ. At its origin it is attached to the
symphysis ischii by two strong flat bands, the =suspensory ligaments= of
the penis (Ligamenta suspensoria penis), which blend with the tendon of
origin of the graciles muscles (Figs. 451, 456). This part of the penis
is flattened laterally for the most part, but becomes rounded and
smaller anteriorly. It presents four surfaces. The =dorsal surface= or
=dorsum penis=, is narrow and rounded; on it are the dorsal arteries and
nerves of the penis and a rich venous plexus. The =ventral= or =urethral
surface= (Facies urethralis) is rounded, and along it runs the urethra,
embedded in the deep =urethral groove= of the corpus cavernosum. The
=lateral surfaces= are high and flattened, except anteriorly, where they
are lower and rounded.
The =glans penis= is the enlarged free end of the organ. It is marked
off from the body by a faintly marked =neck= (Collum glandis). In front
of this is a prominent circular ridge, the =corona glandis=, which is
notched below. The base of the glans is rounded and extends further
backward dorsally than ventrally; it is marked in its lower part by a
deep depression, the =fossa glandis=, in which the urethra protrudes for
about an inch (ca. 2.5 cm.) as a free tube, the =urethral process=
(Processus urethræ), covered by a thin integument. The urethra is thus
surrounded by a circular fossa, which opens superiorly into the
=urethral sinus=, a bilocular diverticulum lined by thin black skin.
This diverticulum is filled sometimes with a caseous mass of sebaceous
matter and epithelial débris.
=Structure.=—The penis consists essentially of two erectile bodies, the
corpus cavernosum penis and the corpus spongiosum.
The =corpus cavernosum penis= forms the greater part of the bulk of the
penis except at its free extremity. It arises from each side of the
ischial arch by a =crus=, which is embedded in the ischio-cavernosus
muscle. Below the ischial arch the crura fuse completely to form the
laterally compressed body of the corpus cavernosum; this presents
ventrally the =urethral groove= (Sulcus urethralis), which contains the
urethra and corpus spongiosum. Anteriorly, the corpus cavernosum divides
into three processes, a long central one, which is capped by the glans
penis, and two short blunt lateral ones. The corpus cavernosum is
inclosed by the =tunica albuginea=, a thick capsule of fibrous tissue
which contains many elastic fibers and some unstriped muscle. Externally
the fibers are chiefly longitudinal; internally they are mainly circular
and are looser in arrangement. Numerous =trabeculæ= pass inward from the
tunic and form a sponge-like framework in the interior of the corpus
cavernosum, which is thus divided into numerous spaces (Cavernæ). These
spaces may be regarded as greatly enlarged capillaries; they contain
blood, are lined with flat endothelial cells, and are directly
continuous with the veins of the penis. Their walls are composed very
largely of unstriped muscle. Erection is produced by distention of these
spaces with blood; at other times the spaces are mere slits.
[Illustration:
FIG. 396.—CROSS-SECTION OF BODY OF PENIS OF HORSE.
]
In man there are two distinct corpora cavernosa, separated by a
complete septum penis, except in the middle part of the organ, where
the septum is composed of vertical trabeculæ, between which are
slit-like intervals; through the latter the blood-spaces of the two
corpora cavernosa communicate. In the horse no distinct septum exists
except near the root, but in the proximal and distal parts of the
corpus cavernosum there are vertical trabeculæ.
The =corpus spongiosum= or =corpus cavernosum urethræ= forms a tube
around the urethra, and is much enlarged at its free end to form the
bulk of the glans penis; throughout the remainder of its course it is
practically uniform in size, and does not form any very distinct bulb
(Bulbus urethræ) at its origin, as in man and many animals. The glans
has been described in part; it should be noted that the corpus
spongiosum extends backward dorsally a distance of about four inches
(ca. 10 cm.) on the middle process of the corpus cavernosum penis,
forming the processus dorsalis glandis. The urethral process is covered
by a thin layer of corpus spongiosum.
In structure the corpus spongiosum has a general resemblance to the
corpus cavernosum, but the trabeculæ are finer and more elastic. In the
glans the trabeculæ are highly elastic, and the spaces are large and
very extensible; the latter are continuous at the extremity of the
processus dorsalis with large veins on the dorsum penis. There is a
partial septum glandis. The skin covering the glans is thin, destitute
of glands, and richly supplied with nerves and special nerve-endings.
=Vessels and Nerves.=—The penis is supplied with blood by three
=arteries=, viz., the =internal pudic=, =obturator=, and =external
pudic=. The =veins= form a rich plexus on the dorsum and sides of the
penis, which is drained by the =external pudic= and =obturator veins=;
from the root the blood is carried by the =internal pudic veins=. The
=lymphatics= run with the veins and go to the inguinal and lumbar
glands. The =nerves= are derived chiefly from the =pudic nerves= and the
=pelvic plexus= of the sympathetic.
MUSCLES OF THE PENIS (Figs. 183, 451, 452, 456)
1. The =ischio-cavernosus= (or erector penis) is a short but strong
paired muscle, which arises from the tuber ischii and the adjacent part
of the sacro-sciatic ligament, and is inserted on the crus and adjacent
part of the body of the penis. It is somewhat fusiform, incloses the
crus as in a sheath, and is situated in a deep depression in the
semimembranosus muscle. It pulls the penis against the pelvis, and
assists in producing and maintaining erection by compressing the dorsal
veins of the penis. Its blood-supply is derived from the obturator
artery, and the nerve-supply from the pudic nerve.
2. The =retractor penis= is an unstriped muscle which arises on the
ventral surface of the first two or three coccygeal vertebræ. It divides
into two flat bands, half an inch or more (ca. 1.5 cm.) in width, which
pass downward over the sides of the rectum to meet below the anus. Here
there is a decussation of fibers, thus forming a sort of suspensory
apparatus for the posterior part of the rectum and the anus. From the
decussation the muscle passes for a short distance between superficial
and deep layers of the bulbo-cavernosus, and then along the ventral
surface of the penis, to which it is loosely attached. Near the glans
penis it splits up into bundles which pass through the bulbo-cavernosus
and are attached to the tunica albuginea. Below the anus the muscle is
attached to the sphincter ani externus. On the penis the two muscles are
intimately united to each other. Their action is to withdraw the penis
into the sheath after erection or protrusion. The proximal part would
draw the anus upward and forward and support it during defecation.
THE PREPUCE
The =prepuce= (Præputium), popularly called the “sheath,” is a double
invagination of the skin which contains and covers the free or
prescrotal portion of the penis when not erect. It consists of two
parts, external and internal. The external part or sheath extends from
the scrotum forward close to the umbilicus, where the external layer is
reflected ventrally and laterally, forming the thick margin of the
=preputial orifice= (Ostium præputiale); dorsally it is directly
continuous with the integument of the abdominal wall. It is marked by a
median =raphé præputii=, a continuation of the scrotal raphé. At the
lower margin of the preputial orifice there are often in the stallion
two papillæ, which are rudimentary teats or nipples. The internal layer
=passes= backward from the preputial orifice a distance of about six to
eight inches (ca. 15 to 20 cm.), lining the cavity of the external
prepuce, and is then reflected forward until it approaches the orifice,
where it is again reflected backward. It thus forms within the cavity of
the sheath a secondary tubular invagination, the prepuce proper, in
which the anterior part of the penis lies. This tubular cavity is closed
behind by the reflection of the internal layer on to the penis to form
the penile layer of the prepuce. Its orifice is surrounded by a thick
margin, the =preputial ring= (Annulus præputialis), which is connected
ventrally with the outer part of the sheath by the =preputial frenum=
(Frenulum præputii).
The arrangement differs from that found in man in the fact that the
inner part of the prepuce as described above is equivalent to the
entire human prepuce. This part, the prepuce proper, is well seen on
sagittal sections, and can be demonstrated by pulling the penis,
inclosed in this prepuce, out of the cavity of the sheath; the
arrangement of the free part of the penis and prepuce is then like
that in man. (In paraphimosis the penis is strangulated by the
preputial ring.)
[Illustration:
FIG. 397.—SAGITTAL SECTION OF PREPUCE AND PART OF PENIS OF HORSE.
_P_, Internal part of prepuce or prepuce proper; _P′_, external part
of prepuce or sheath; _c.p._, preputial cavity; _F.g._, fossa
glandis; _D_, diverticulum of fossa glandis; _p.u._, processus
urethræ.
]
=Structure.=—The =external skin= of the prepuce resembles that of the
scrotum. The =inner layers= of skin are hairless, variable in color, and
often irregularly pigmented; they form irregular folds, and are supplied
with numerous large sebaceous glands and coil glands, which reach their
greatest size at the preputial ring. Beyond this the glands are absent,
and the skin resembles a non-glandular mucous membrane. The secretion of
the =preputial glands= (Glandulæ præputiales), together with desquamated
epithelial cells, forms the fatty =smegma præputii=, which has a strong
unpleasant odor, and often accumulates in considerable amount. Beneath
the skin is a large amount of loose connective tissue, except over the
glans penis, where the skin is closely attached to the tunic of the
corpus spongiosum. The external part of the prepuce is strengthened by a
layer of elastic tissue, derived from the abdominal tunic, and termed
the suspensory ligament.
=Vessels and Nerves.=—The =arteries= are branches of the =external pudic
artery=, and the =veins= go chiefly to the =external pudic vein=. The
=lymphatics= go to the superficial inguinal and lumbar lymph glands. The
=nerves= are derived from the =pudic=, =ilio-hypogastric=, and
=ilio-inguinal= nerves.
THE MALE URETHRA
The =urethra= of the male (Urethra masculina) is the long mucous tube
which extends from the bladder to the glans penis. It passes backward on
the floor of the pelvis, turns around the ischial arch, forming an acute
angle, and passes forward inclosed in the corpus spongiosum. It may,
therefore, be divided into two segments, pelvic and extrapelvic.
The =pelvic part= (Pars pelvina) is four or five inches (ca. 10 to 12
cm.) long. At its origin it is not distinguishable from the neck of the
bladder in size or structure; in fact no line of demarcation exists
between the two. Behind the prostate the tube dilates to a potential
width of two inches or more (ca. 5 to 6 cm.). Near the ischial arch,
between the bulbo-urethral (Cowper’s) glands, it contracts again,
forming the =isthmus urethræ=. It is related dorsally to the rectum and
the prostate, ventrally to the internal obturator muscles, and laterally
to the bulbo-urethral glands. It is inclosed, except at its origin, by
the urethral (Wilson’s) muscle. Beneath this is a rich venous plexus,
forming a sort of erectile tissue.[146]
[Illustration:
FIG. 398.—PELVIC URETHRA AND POSTERIOR PART OF BLADDER OF HORSE SLIT
VENTRALLY AND LAID OPEN.
_e.d._, Ejaculatory ducts.
]
The =extrapelvic part= (Pars cavernosa) passes between the two crura of
the penis and runs along the groove on the ventral surface of the corpus
cavernosum penis, inclosed by the corpus spongiosum and the
bulbo-cavernosus muscle. It passes through the glans penis and projects
forward about an inch in the fossa glandis as a free tube, the
=processus urethræ=; this part is covered by a delicate integument,
under which there is a thin layer of erectile tissue.
The lumen of the tube is largely obliterated in the inactive condition
of the parts. When moderately distended its dimensions in a horse of
medium size are as follows: At its origin the diameter is about half
an inch (1 to 1.5 cm.). The pelvic dilatation at its widest part
measures one and a half to two inches (ca. 3.5 to 5 cm.) transversely,
and about an inch (2 to 3 cm.) vertically; it is elliptical in
cross-section when fully distended. The isthmus at the ischial arch is
a little smaller than the initial part. Beyond this the lumen is about
one-half to three-fourths of an inch (ca. 1.5 cm.) in diameter, and is
fairly uniform to the glans penis. Here there is a slight fusiform
dilatation (Fossa navicularis), beyond which the tube contracts.
The opening from the bladder into the urethra is termed the =internal
urethral orifice= (Orificium urethræ internum); it is closed except
during urination. The terminal opening is the =external urethral
orifice= (Orificium urethræ externum) or meatus urinarius. The two
orifices of the =ejaculatory ducts= are situated dorsally on either side
of the colliculus seminalis, about two inches (ca. 5 cm.) behind the
internal urethral orifice; they are slit-like and close together. The
small orifice of the uterus masculinus is placed centrally on the
colliculus; it is inconstant. The orifices of the =prostatic ducts= are
on two groups of small papillæ, placed lateral to the openings of the
ejaculatory ducts. The =ducts= of the =bulbo-urethral= (Cowper’s)
=glands= open on two lateral series of small papillæ, about an inch (ca.
2.5 cm.) further back and close to the median line. The small orifices
of the =urethral glands= are situated laterally in the wide pelvic
portion.
=Structure.=—The =mucous membrane= contains an unusually large amount of
fine elastic fibers, and in its pelvic part there are alveolar =glands=
(Glandulæ urethrales). The epithelium is at first like that of the
bladder, then becomes cylindrical, and in the terminal part is
stratified squamous. In the dorsal wall the membrane forms a median
ridge, the =urethral crest= (Crista urethralis); this terminates about
two inches from the internal urethral orifice in a rounded elevation,
the =colliculus seminalis=, on the sides of which the ejaculatory ducts
open.
At the origin of the urethra there is a layer of circular =unstriped
muscle-fibers= outside of the mucous coat. Beyond this the latter is
inclosed by a layer of =erectile tissue=, composed of plexuses of veins
supported by trabeculæ of elastic and smooth muscular tissue. This is
continued by the corpus spongiosum. Outside of the erectile tissue there
is a continuation of the intrinsic unstriped muscular coat, consisting
of external and internal longitudinal strata, with a layer of circular
fibers between them.
Except at its origin and termination the urethra is provided with a
continuous layer of striped muscle, placed outside of the erectile
tissue. This is described as consisting of two parts or muscles.
(1) The =urethral= (or Wilson’s) =muscle= (M. urethralis) consists of
dorsal and ventral layers of transverse fibers on the wide pelvic part
of the urethra, and covers the bulbo-urethral (Cowper’s) glands. It is a
compressor of the pelvic part of the urethra and the bulbo-urethral
glands. By its forcible contraction it plays an important rôle in the
ejaculation of the seminal fluid, and also in evacuating the last of the
urine in micturition.[147]
(2) The =bulbo-cavernosus muscle= (or accelerator urinæ) is the
continuation of the urethral muscle on the extrapelvic part of the
urethra; it extends from the ischial arch to the glans penis. At the
root of the penis it is the thickest, and forms a complete layer of
circular fibers which inclose the corpus spongiosum and the urethra.
Beyond this it diminishes very gradually in thickness, and consists of
fibers which arise on a median ventral raphé and curve around the corpus
spongiosum to end on the tunica albuginea of the corpus cavernosum. Its
action is to empty the extrapelvic part of the urethra.
The =ischio-urethral muscles= (Fig. 452) are small bands which arise
on the ischial arch and crura of the penis and pass forward to become
lost on the ventral layer of the urethral muscle. They may assist in
erection of the penis by exerting pressure on the dorsal veins.
MALE GENITAL ORGANS OF THE OX
The =scrotum= is situated somewhat further forward than in the horse. It
is long, pendulous, and has a well-marked neck. The skin here is usually
flesh-colored, but in some breeds is more or less pigmented; it is
sparsely covered with short hairs. Just in front of it are four
(sometimes only two) rudimentary teats.
The =testicles= are relatively larger than those of the horse, and have
an elongated, oval outline. The long axis is vertical. The inner surface
is somewhat flattened.
A testicle of an adult bull measures on the average about four or five
inches (10 to 12 cm.) in length, exclusive of the epididymis; with the
latter the length is about six inches (15 cm.). The width is about two
and a half to three inches (ca. 6 to 8 cm.), and the antero-posterior
diameter about the same. The weight is about nine or ten ounces (ca.
250 to 300 grams).
[Illustration:
FIG. 399.—GENERAL VIEW OF GENITAL ORGANS OF BULL.
]
The tunica albuginea is thin. The parenchyma is yellowish in color. The
mediastinum testis descends from the anterior part of the upper
extremity deeply into the gland as an axial strand about 5 mm. in
thickness. The vasa efferentia leave at the upper end of the
mediastinum.
The =epididymis= is very closely attached to the testicle. The head is
long; it curves over the upper extremity and nearly half-way down the
anterior border of the testicle. The body is very narrow, and lies along
the outer part of the posterior border of the testicle, to which it is
attached by a narrow peritoneal fold. The tail is large and is closely
attached to the lower extremity of the testicle.
The =spermatic cord= and the =tunica vaginalis= are much longer than in
the horse; the extra-inguinal part of the cord is about eight to ten
inches (20 to 25 cm.) in length. The =cremaster externus= is well
developed, and almost completely incloses the tunic to the nook of the
scrotum; it does not extend so far down as in the horse, but is inserted
about at the level of the upper pole of the testicle. The =vaginal ring=
is relatively very small, and is about four inches (ca. 10 cm.) from the
linea alba. The cremaster internus is feeble.
[Illustration:
FIG. 400.—INTERNAL GENITAL ORGANS OF BULL; DORSAL VIEW.
The right vesicula is sectioned frontally. The dotted line indicates
the backward extension of the peritoneum.
]
The spermatic cords emerge through the outer angles of the external
inguinal rings, and curve downward and inward to the neck of the
scrotum. The external rings are about four inches (ca. 10 cm.) long,
and are two and a half to three inches (6 to 8 cm.) apart. In animals
in good condition there is a large mass of fat above the neck of the
scrotum, between the spermatic cords. The mesorchium extends to the
bottom of the tunica vaginalis forming a narrow fold (ca. 1 cm. wide)
which attaches the epididymis to the posterior part of the tunic.
The inguinal canal presents several special features in the bull. The
internal ring is very long. Its anterior border, formed by the edge of
the internal oblique, is decidedly concave and is tendinous in its
inner part. The long axis of the external ring is directed outward,
forward, and downward. The spermatic cord lies in its outer part, the
external pudic vessels in its middle. A muscular band about an inch
wide, detached from the internal oblique muscle, crosses the outer
side of the vaginal ring.
The =vas deferens= is small in caliber. The urogenital fold is narrow,
so that the vasa are closer together in it than in the horse. On
reaching the posterior part of the bladder they are in apposition for a
distance of about four inches (10 cm.), flanked and overlapped by the
vesiculæ seminales. They form ampullæ about four or five inches (10 to
12 cm.) long and half an inch (1.2 to 1.5 cm.) wide, the mucous lining
of which is plicated. They then pass under the body of the prostate and
unite with the ducts of the vesiculæ seminales to form the ejaculatory
ducts. The latter have slit-like openings on either side of the
colliculus seminalis.
The =vesiculæ seminales= are not bladder-like sacs, as in the horse, but
are compact glandular organs with a lobulated surface. In the adult they
measure about four or five inches (ca. 10 to 12 cm.) in length, two
inches (5 cm.) in width in their largest part, and an inch or more (ca.
3 cm.) in thickness. The dorsal surface of each faces upward and inward
and is partially covered with peritoneum. The ventral surface faces in
the opposite direction and is non-peritoneal. Each may be regarded as
consisting of a very thick-walled, sacculated tube, bent on itself in a
tortuous manner. This tube, if straightened out, would be about ten
inches (25 cm.) in length. They are commonly unsymmetrical in size and
shape. Short branches are often given off from the chief tube. The
excretory duct or neck joins the outer side of the vas deferens at an
acute angle to form the ejaculatory duct.
[Illustration:
FIG. 401.—ANTERIOR EXTREMITY OF PENIS OF BULL, LEFT VIEW. (After
Böhm.)
]
[Illustration:
FIG. 402.—CROSS-SECTION OF PELVIC URETHRA OF BULL.
_1_, Prostate gland (pars disseminata); _2_, urethra; _3_, urethral
muscle; _4_, aponeurosis. The lumen of the urethra is black.
]
The structure of the vesicula is masked by a thick capsule of fibrous
tissue and unstriped muscle, which maintains it in its bent condition
and also sends trabeculæ between the alveoli. There is a central canal
into which the secretion formed in the alveoli passes. The cavities
(central canal and alveoli) are lined with columnar epithelium. On
account of this structure the term glandulæ vesiculares is preferred
by some anatomists.
The =prostate= is pale yellow in color, and consists of two parts. The
=body= (Corpus prostatæ) is a mass which stretches across the dorsal
surface of the neck of the bladder and the origin of the urethra. It
measures about an inch and a half (ca. 3.5 to 4 cm.) transversely, and
about half an inch (ca. 1 to 1.5 cm.) in width and thickness. The =pars
disseminata= surrounds the pelvic part of the urethra; dorsally it forms
a layer about half an inch (ca. 10 to 12 mm.) thick, but ventrally it is
quite thin. It is concealed by the urethral (Wilson’s) muscle; hence it
often escapes notice, but is very evident on cross-section (fig. 402).
The =prostatic ducts= open into the urethra in rows between two folds of
the mucous membrane which proceed backward from the colliculus
seminalis.
The =uterus masculinus= appears to be absent frequently. Ellenberger
states that it opens between the ejaculatory ducts, while Martin says
that it usually has two orifices at the colliculus, but that it often
unites with the vasa deferentia.
The =bulbo-urethral= (Cowper’s) =glands= are somewhat smaller than in
the stallion. They are liable to escape notice, since they are covered
by a thick layer of dense fibrous tissue and also partially by the
bulbo-cavernosus muscle. Each has a single duct which opens into the
urethra under cover of a fold of the mucous membrane.
The =penis= is cylindrical, and is longer and of very much smaller
diameter than in the horse. Just behind the scrotum it forms an
=S=-shaped curve, the =sigmoid flexure=; thus about one foot is folded
up when the penis is fully retracted. The flexure is effaced during
erection. The =glans penis= is about three inches (ca. 8 cm.) in length.
It is flattened dorso-ventrally, and its extremity is pointed and
twisted. The =external urethral orifice= is situated at the end of a
groove formed by this twist; it is only large enough to admit a probe of
medium size. Even in the non-erect state the penis is remarkably dense
and firm. The =tunica albuginea= is very thick, and incloses the
urethra. In the first part, as far as the first curve, there is a thick
median =septum penis=. Beyond this there is a central axial rod of dense
fibrous tissue from which numerous strong trabeculæ radiate. The
erectile tissue is small in amount, so that the organ undergoes very
little enlargement in erection.
The length of the penis in the adult is about three feet (ca. 90 cm.).
The crura are flattened laterally. The suspensory ligaments are
attached to the ventral ridge on the symphysis. The body is somewhat
flattened dorso-ventrally beyond the first curve. The extremity of the
glans is unsymmetrical, the urethral orifice being situated
ventro-laterally. The glans contains little erectile tissue, and hence
undergoes little enlargement in erection.
The =bulbo-cavernosus muscle= presents several remarkable features. It
is for the greater part an inch or more (ca. 3 cm.) in thickness, but
its length is only six to eight inches (15 to 20 cm.). It is covered by
a strong aponeurosis, and is divided by a median raphé into two lateral
halves except at its origin. It diminishes in size from behind forward,
and its anterior extremity is pointed.
The =ischio-cavernosus muscle= resembles in general that of the horse,
but is flattened laterally. It is covered by a close aponeurosis.
The =retractor penis= muscle resembles that of the horse in origin. Its
two parts are about an inch (ca. 2 to 5 cm.) apart on the root of the
penis, where they lie in a groove on either side of the
bulbo-cavernosus. They then come close together and pass on either side
of the ventral curve of the sigmoid flexure. Further forward they lie
along the ventral aspect of the penis, and end about five or six inches
(ca. 12 to 15 cm.) behind the glans.
The =prepuce= is very long and narrow. Its orifice is about two inches
(ca. 5 cm.) behind the umbilicus; it is only large enough to admit a
finger readily, and is surrounded by long hairs. The cavity of the
sheath is about fifteen inches (35 to 40 cm.) long, and a little over an
inch (ca. 3 cm.) in diameter. The lining membrane forms longitudinal
folds; it is covered with squamous stratified epithelium, and has coiled
tubular glands. The penile layer is glandless, and is reddish in color.
It presents lymph nodules in its posterior part.
There are two pairs of =preputial muscles= which are derivatives of the
panniculus carnosus. The anterior pair, the =protractors= of the prepuce
(Mm. præputiales craniales), are two flat bands, two inches or more (5
to 6 cm.) in width, which arise close together in the xiphoid region,
about eight inches (20 cm.) in front of the preputial orifice. Traced
backward they diverge, leaving the umbilicus and an area about one and a
half inches wide free, and then unite behind the preputial orifice. They
draw the prepuce forward. The posterior pair, the =retractors= of the
prepuce (Mm. præputiales caudales), arise in the inguinal region and
converge on the anterior part of the prepuce. They draw the prepuce
backward.
These muscles are subject to a good deal of variation. The retractor
may be absent. Many fibers come in from the panniculus on either side,
dip under the protractor, and are inserted into the skin just behind
the preputial opening. The homologue of the protractor is present in
the cow.
The =urethra= in its pelvic part is about five inches (12 cm.) long, and
is of relatively small and uniform caliber. The =urethral= (Wilson’s)
=muscle= incloses the tube ventrally and laterally; it is very thick,
crescentic in cross-section, and is covered by an aponeurosis. Dorsally,
the aponeurosis is thick and the muscle absent. Inside of these the pars
disseminata of the prostate surrounds the urethra as far back as the
bulbo-urethral glands. The =colliculus seminalis= is short, but
prominent; from it the urethral crest extends forward to the trigonum
vesicæ. The extrapelvic part has an enlargement, the =bulb=, at its
origin; it then gradually diminishes in diameter, and is relatively very
small at its termination. Other features have been mentioned in
preceding paragraphs.
[Illustration:
FIG. 403.—ANTERIOR PART OF PENIS OF RAM.
_A_, Right side; _B_, left side. (After Böhm.)
]
In the ram the urethra lies in a groove on the ventral surface of the
corpus cavernosum. Its terminal part projects commonly 3 to 4 cm. beyond
the glans penis, forming a twisted processus urethræ.
MALE GENITAL ORGANS OF THE PIG
The =scrotum= is situated a short distance from the anus, and is not so
sharply defined from the surrounding parts as in the other animals.
The =testicles= are very large and are soft in texture. Their long axis
is almost vertical, the free border being posterior and the tail of the
epididymis dorsal. The mediastinum testis is well developed. The
epididymis is closely attached to the testicle and the tunica vaginalis;
the tail is specially large.
The =spermatic cord= is necessarily very long (20 to 25 cm. in a boar of
medium size). The =vas deferens= in its testicular part is flexuous, and
is closely attached to the tunica vaginalis; it forms no ampullæ. The
=cremaster externus= is well developed, and extends to about the middle
of the scrotal part of the tunic.
The =vesiculæ seminales= are exceedingly large, and extend into the
abdominal cavity. They are three-sided pyramidal masses, are in
apposition with each other medially, and cover the posterior part of the
bladder and the ureters, the vasa deferentia, the body of the prostate,
and the anterior part of the urethra. They are pale pink in color,
distinctly lobulated and glandular in structure, and contain large
alveoli, but no central cavity. There are two excretory ducts which open
into the urethra close to the vasa deferentia; the two ducts frequently
unite.
In the adult boar the vesiculæ are about five to six inches (ca. 12 to
15 cm.) long, two to three inches (ca. 5 to 8 cm.) wide, and one and a
half to two inches (ca. 4 to 5 cm.) thick; they weigh about 6 to 8
ounces each.
The =prostate= consists of two parts, as in the ox. The =body= is about
an inch (2.5 cm.) wide, and embraces the neck of the bladder and the
urethra at their junction dorsally and laterally. It is concealed by the
vesiculæ seminales. The =pars disseminata= forms a layer which surrounds
the pelvic part of the urethra, and is covered by the urethral muscle.
The uterus masculinus is small.
The =bulbo-urethral= (Cowper’s) =glands= are very large and dense. They
are somewhat cylindrical, and lie on either side of and upon the
posterior two-thirds of the pelvic urethra. In a large boar they are
about five inches (ca. 12 cm.) in length and an inch or more (ca. 2.5 to
3 cm.) in diameter. They are partially covered with a layer of striated
muscle (M. ischio-glandularis), and have a lobulated surface. Each gland
has a large excretory duct which leaves at the posterior extremity,
perforates the dorsal wall of the urethra at the ischial arch, and opens
in a cul-de-sac covered by a fold of mucous membrane.
[Illustration:
FIG. 404.—GENITAL ORGANS OF BOAR.
_a_, Testicle; _b_, epididymis; _c_, vas deferens; _d_, spermatic
artery; _e_, vesicula seminalis reflected to show the body of the
prostate, _f_; _e′_, excretory ducts of vesiculæ; _g_,
bulbo-urethral (Cowper’s) gland; _h_, urinary bladder; _i_, urethral
muscle; _k_, bulbo-cavernosus muscle; _l_, penis; _l′_, sigmoid
flexure of penis; _l″_, spiral anterior part of penis, exposed by
slitting open prepuce; _m_, orifice of preputial pouch; _n_,
retractor penis muscle. (Ellenberger-Baum, Anat. d. Haustiere.)
]
It is to be noted that these accessory glands are very small in
animals which have been castrated early.
The =penis= resembles in general that of the ox. The sigmoid flexure is,
however, prescrotal. The anterior portion has no glans, and is spirally
twisted, especially in erection. The =urethral orifice= is slit-like and
is situated ventro-laterally, close to the pointed extremity. The penis
in the adult boar measures about 18 to 20 inches (ca. 45 to 50 cm.) in
length. Its muscles resemble those of the bull; the bulbo-cavernosus is
very strong but short.
The =prepuce= has a narrow orifice, around which there are a number of
stiff hairs. The cavity is partially divided by a circular fold into a
posterior narrow portion and a much wider anterior portion. The lining
membrane of the posterior part is papillated, and is in close contact
with the penis. In the dorsal wall of the wide part there is a circular
opening which leads into a cul-de-sac, the =preputial diverticulum=.
This pouch is ovoid in form (when distended), and varies greatly in size
in different subjects. It extends for the most part backward over the
narrow part of the prepuce. Its cavity is partially divided by a narrow
median septum. It contains usually decomposing urine and macerated
epithelium, which have a characteristic and very unpleasant odor.
Concrements have been found in it.
Oehmke found that a cast of the pouch in a Yorkshire boar weighing
about 500 pounds measured 9 cm. in length, 12½ cm. in breadth, and 6
cm. in height. The opening into the prepuce will admit two fingers in
the adult, but is ordinarily closed by folds of the lining membrane.
The sac is much smaller in animals which were castrated young, and the
opening is vertical and further back; in them it is often empty or
contains only a little clear urine. The pouch is covered by a layer of
striped muscle which is mainly derived from the homologue of the
protractor of the prepuce of ruminants.
The =urethra= has a very long pelvic portion (ca. 15 to 18 cm. long in
the adult); it is inclosed (with the pars disseminata of the prostate)
by a thick =urethral muscle=. There is a distinct =bulb= at the root of
the penis. The penile part is of small caliber, and is surrounded by
erectile tissue which, however, does not extend to the extremity of the
penis.
MALE GENITAL ORGANS OF THE DOG
The =scrotum= is situated about half-way between the inguinal region and
the anus. The skin covering it is pigmented and is covered sparsely with
fine hairs. The raphé is not very distinct.
The =testicles= are relatively small, and have a round-oval form. The
long axis is oblique, and is directed upward and backward. The
mediastinum testis is central and is well developed. The epididymis is
large, and is closely attached along the outer part of the dorsal border
of the testicle.
The =spermatic cord= and the =tunica vaginalis= are long; they cross the
side of the penis very obliquely. The upper end of the tunic is
sometimes closed, so that there is then no vaginal ring. The vasa
deferentia have very narrow ampullæ.
The =vesiculæ seminales= are absent; hence there are no ejaculatory
ducts.
The =prostate= is relatively large; it is yellowish in color, dense in
structure, and lies at the anterior border of the pubis. It is globular,
and surrounds the neck of the bladder and the urethra at their junction.
A faint median furrow indicates a division into two lateral lobes. The
capsule and stroma contain a large amount of unstriped muscle. The ducts
are numerous. Lobules of prostatic tissue (pars disseminata) are also
found on the urethra further back. The gland is subject to much
variation in size, and is often enlarged, especially in old subjects.
The =uterus masculinus= is a very small saccule (Utriculus prostaticus),
often difficult to find.
The =bulbo-urethral= (Cowper’s) =glands= are absent.
The =penis= presents several special features. In its posterior part
there are two distinct corpora cavernosa, separated by a median septum
penis. In its anterior part there is a bone, the =os penis=, which in
large dogs reaches a length of four inches (ca. 10 cm.) or more. It is
regarded as a continuation forward of the corpus cavernosum. Ventrally
it is grooved for the urethra; dorsally it is convex, and anteriorly it
becomes smaller and has a curved fibrous prolongation. The =glans penis=
is very long, extending over the entire length of the os penis;
posteriorly it forms a rounded enlargement, the =bulbus glandis=;
anteriorly it is cylindrical, smaller, and pointed at the extremity.
Just in front of the bulbus glandis there is a thick circular layer of
glands, forming the =annulus glandularis= (Schmaltz). The two dorsal
veins arise from the bulbus glandis, pass backward on the dorsum penis,
and unite at the ischial arch. A small muscle (M. compressor venæ
dorsalis penis) arises from the tuber ischii on either side; the two
converge on the dorsum penis near the bulbus glandis. They compress the
dorsal veins, and may also tend to elevate the penis and thus assist in
copulation. The other muscles offer no features worthy of special
description.
The =prepuce= forms a complete sheath around the anterior part of the
penis. The outer layer is ordinary integument. The inner layer has the
character of a glandular mucous membrane; it is thin and reddish in
color. The penile layer is glandless. In the fundus of the præputial
cavity there are numerous lymph follicles. The protractor muscles arise
in the xiphoid region and decussate posteriorly around the extremity of
the penis.
[Illustration:
FIG. 405.—EXTERNAL GENITAL ORGANS OF MALE DOG, VENTRO-LATERAL VIEW OF
PREPARATION.
_1_, Scrotum; _1′_, tunica vaginalis; _2_, epididymis; _3_, vascular
part of spermatic cord; _4_, vas deferens; _5_, prepuce; _6_, glans
penis; _6′_, corpus cavernosum penis; _7_, bulbus glandis; _7′_,
contour of bulbus in erection; _8_, ischio-cavernosus muscle; _a_,
acetabulum; _b_, obturator foramen. (After Ellenberger, in
Leisering’s Atlas.)
]
[Illustration:
FIG. 406.—INTERNAL GENITAL ORGANS OF MALE DOG.
_1_, Urinary bladder; _2_, ureter; _3_, vas deferens; _4_, prostate;
_5_, urethral muscle; _6_, bulb of urethra; _a_, abdominal wall;
_b_, ilium; _c_, ischium. (After Ellenberger, in Leisering’s Atlas.)
]
The pelvic part of the =urethra= is relatively long. Its first part is
inclosed in the prostate.[148] At the ischial arch the urethra has a
well-developed bilobed =bulb=, formed by an enlargement here of the
corpus spongiosum. It is covered by the strong but short
bulbo-cavernosus muscle. The other erectile bodies have been described.
The =urethral= (Wilson’s) =muscle= is very strong; it encircles the
urethra and has a median raphé dorsally.
THE FEMALE GENITAL ORGANS
The =female genital organs= (Organa genitalia feminina) are: (1) The two
=ovaries=, the essential reproductive glands, in which the ova are
produced; (2) the =uterine= or =Fallopian tubes=, which convey the ova
to the uterus; (3) the =uterus=, in which the ovum develops; (4) the
=vagina=, a dilatable passage through which the fœtus is expelled from
the uterus; (5) the =vulva=, the terminal segment of the genital tract,
which serves also for the expulsion of the urine; (6) the =mammary
glands=, which are glands of the skin, but are so closely associated
functionally with the generative organs proper as to be described with
them.
GENITAL ORGANS OF THE MARE
THE OVARIES
[Illustration:
FIG. 407.—LATERAL VIEW OF GENITAL ORGANS AND ADJACENT STRUCTURES OF
MARE.
The removal of the other abdominal viscera has allowed the ovaries and
uterus to sink down, whereas they are normally in contact with the
roof of the cavity in the non-pregnant subject. _1_, Left ovary;
_2_, Fallopian tube; _3_, left cornu uteri; _4_, right cornu uteri;
_5_, corpus uteri; _5′_, portio vaginalis uteri, and _5″_, os uteri,
seen through window cut in vagina; _6_, broad ligament of uterus;
_6″_, round ligament; _7_, vagina; _8_, labia vulvæ; _9_, rima
vulvæ; _9′_ superior commissure, and _9′_, inferior commissure of
vulva; _10_, constrictor vulvæ; _11_, position of vestibular bulb;
_12_, ventral wall of abdomen; _13_, left kidney; _14_, left ureter;
_15_, urinary bladder; _16_, urethra; _17_, rectum; _18_, anus;
_19_, _19′_, unpaired and paired parts of sphincter ani externus;
_20_, retractor ani cut at disappearance under sphincter; _21_,
suspensory ligament of anus; _22_, longitudinal muscular layer of
rectum; _22′_, recto-coccygeus; _23_, constrictor vaginæ; _a_,
utero-ovarian artery, with ovarian (_a′_) and uterine (_a″_)
branches; _b_, uterine artery; _c_, umbilical artery; _d_, ischium;
_e_, pubis; _f_, ilium. (After Ellenberger, in Leisering’s Atlas.)
]
The =ovaries= (Ovaria) of the mare are bean-shaped, and are much smaller
than the testicles. Their size varies much in different subjects, and
they are normally larger in young than in old animals; one ovary is
often larger than the other. They are about three inches (ca. 7 to 8
cm.) long and an inch to an inch and a half (ca. 3 to 4 cm.) thick. The
weight is about two and a half to three ounces (ca. 70 to 80 grams).
Each presents for description two surfaces, two borders, and two
extremities or poles. The =surfaces= are termed internal and external
(Facies medialis, lateralis); they are both smooth and rounded.[149] The
=attached= or =mesovarial border= (Margo mesovaricus) is convex. It is
inclosed in a part of the broad ligament termed the mesovarium; the
vessels and nerves reach the gland at this border. The =free border=
(Margo liber) is marked by a notch which leads into a depression, the
=ovulation fossa=. The =tubal= or =anterior extremity= (Extremitas
tubaria) is rounded, and is related to the fimbriated end of the uterine
or Fallopian tube. The =uterine= or =posterior extremity= (Extremitas
uterina) is also round, and is connected with the horn of the uterus by
the ovarian ligament.
The ovaries are situated in the sublumbar region of the abdominal
cavity, about a handbreadth behind the corresponding kidney. They are in
contact with the lumbar wall of the abdomen, and are commonly about two
or three inches (ca. 5 to 7.5 cm.) from the median plane. The distance
from the ovaries to the vulvar orifice is about twenty inches (ca. 50
cm.) in a mare of medium size. The attached (mesovarial) border is
commonly directed toward the median plane, the free border laterally and
somewhat ventrally.
The position of the ovaries is not constant, but is subject to less
variation than might be expected from their mode of attachment. The
normal variations in the non-pregnant state are chiefly in a
transverse direction, and do not usually exceed two or three inches
(ca. 5 to 7 cm.). It is not at all rare to find the ovary deflected
medially, so that the external surface faces ventrally. In the
longitudinal direction little variation appears to occur. The right
ovary is usually about four or five inches (ca. 10 to 12 cm.), and the
left one about three or four inches (ca. 8 to 10 cm.), behind the
corresponding kidney. Thus they lie about in a transverse plane
tangent to the external angles of the ilia, i. e., through the fifth
lumbar vertebra. They may be about two inches (ca. 5 cm.) from the
extremity of the corresponding cornu of the uterus or in contact with
it. The right ovary commonly lies a little (ca. 2.5 cm.) further
forward than the left one. Except during pregnancy, they are normally
in contact with the lumbar abdominal wall, and do not hang down among
the adjacent viscera.
[Illustration:
FIG. 408.—RIGHT OVARY OF MARE, WITH ADJACENT STRUCTURES.
The extremity of the cornu uteri is opened. _1_, Ovary; _2_, Fallopian
tube, with its ostium abdominale (_2′_), fimbriæ (_2″_), and ostium
uterinum (_2‴_); _3_, cornu uteri, with its mucous lining (_3′_);
_4_, ovarian ligament; _4′_, mesosalpinx. (After Ellenberger, in
Leisering’s Atlas, reduced.)
]
The ovary is attached to the sublumbar region by the anterior part of
the broad ligament; this part of the ligament, the =mesovarium=, is
about three or four inches (ca. 8 to 10 cm.) wide, measured from the
ovary directly to the parietal attachment. The uterine or posterior
extremity of the ovary, is connected with the extremity of the cornu of
the uterus by the =ovarian ligament= (Ligamentum ovarii proprium); this
is a band of unstriped muscle inclosed between the layers of the broad
ligament.
=Structure.=—The greater part of the surface of the ovary has a covering
of peritoneum. The peritoneal investment is absent at the attached
border where the vessels and nerves enter; this area is termed the
=hilus=. The ovulation fossa is covered by a layer of columnar cells, a
remnant of the primitive =germinal epithelium=. The =stroma= of the
ovary (Stroma ovarii) is a network of connective tissue and unstriped
muscular fibers. In the deeper or medullary portion of the stroma (Zona
vasculosa) the meshes are largely occupied by the numerous
blood-vessels. In the peripheral or cortical portion (Zona
parenchymatosa) are numerous =ova= (Ovula) in various stages of
development. The immature ova are surrounded by follicle cells; those
more advanced in development are inclosed also by a condensation of the
stroma termed the =theca folliculi=; within the theca is a quantity of
fluid, the =liquor folliculi=. These constitute the =Graafian follicles=
(Folliculi oöphori), which enlarge as they mature, becoming visible to
the naked eye as vesicles with a diameter of a centimeter or more. When
fully developed, the follicles are superficially situated, and often
project slightly from the surface of the ovary. At intervals follicles
rupture and their contents escape. This process, which sets free the
ovum, is termed =ovulation=; it takes place in the mare only at the
ovulation fossa, and occurs during the periods of œstrum.
[Illustration:
FIG. 409.—SCHEMATIC REPRESENTATION OF CHANGES IN OVARY OF MARE FROM
FŒTAL TO ADULT STATE. (After Born.)
The changes affect chiefly the free border (upper in figure) and the
extent and form of the area covered by germinal epithelium (_4_).
_1_, Peritoneum (broad ligament); _2_, ligament of ovary; _3_,
fimbria of Fallopian tube; _4_, germinal epithelium; _5_, vessels,
which reach the ovary at the attached border (_6_). The latter
represents the hilus, while the deep depression at the free border
is the ovulation fossa. (Ellenberger, in Leisering’s Atlas.)
]
After rupture of a follicle its cavity is partly occupied by a
blood-clot, constituting what may be termed a =corpus rubrum=. By
proliferation and enlargement and fatty changes, the follicle cells
are transformed into lutein cells, forming a yellow mass known as a
=corpus luteum=. If impregnation takes place, the accompanying
increase in vascularity of the organs may cause the corpus luteum to
reach a large size; if impregnation does not occur, it is much
smaller, and is sooner replaced by scar tissue, the =corpus albicans=.
In the young foal the ovaries are large and oval in form. The free
border is convex and is covered by germinal epithelium, which extends
over part of the surfaces also. This area is distinguishable by its
dull gray appearance from the peritoneal surface, which has the usual
smooth glistening character. As growth proceeds the ovary gradually
becomes bent until it assumes its definitive curved shape. The
germinal epithelium is then limited to the ovulation fossa. The ovary
migrates somewhat during development from its primitive position,
which is the same as that of the testicle.
In old animals the ovaries commonly consist largely of fibrous tissue,
in which there are often cysts of various sizes. The ova, present in
enormous number at birth, have then been extruded, or destroyed by
phagocytic action or degeneration.
=Vessels and Nerves.=—The =arteries= of the ovary are derived from the
=ovarian artery=. The artery is relatively large and is flexuous; it
reaches the attached border of the ovary by passing between the layers
of the mesovarium. The veins are large and numerous. They form a plexus
somewhat like that of the spermatic cord. The =lymph vessels= pass to
the lumbar glands. The =nerves= are derived from the sympathetic system
through the renal and aortic plexuses. They accompany the arterial
branches.
THE UTERINE OR FALLOPIAN TUBES
The =uterine= or =Fallopian tubes= (Tubæ uterinæ) act as excretory ducts
of the ovaries, since they convey the ova from the reproductive glands
to the uterus. They are not, however, in direct continuity with the
glands, but rather partly in contiguity with, and partly attached to,
them.[150] They are two flexuous tubes, about ten to twelve inches (ca.
25 to 30 cm.) long, which extend from the extremities of the uterine
cornua to the ovaries. Each is inclosed in a peritoneal fold, derived
from the external layer of the broad ligament, and termed the
=mesosalpinx=. This largely covers the outer aspect of the ovary, and
forms with it and the broad ligament a pouch called the =bursa ovarica=.
The =uterine extremity= of the tube communicates with the cavity of the
cornu by a minute orifice, the =ostium uterinum=. The =ovarian= or
=fimbriated extremity= is expanded into a funnel-shaped =infundibulum=.
The margin of the latter is slit into irregular processes or =fimbriæ=,
some of which, the =fimbriæ ovaricæ=, are attached in the ovulation
fossa. In the center of the fimbriated extremity is a small opening, the
=ostium abdominale=, by which the tube communicates with the peritoneal
cavity. The tube appears normally to be applied to the ovary, so that
the extruded ova pass into it and are conveyed to the uterus.[151]
Pedunculated cysts, the hydatids of =Morgagni=, are often found on one
or more of the fimbriæ. In the mesosalpinx are blind flexuous tubules,
which constitute the =paroöphoron=, a remnant of the Wolffian body.
They are most evident in the young adult, and tend to disappear with
increasing age. Not uncommonly they give rise to cysts.
=Structure.=—The tube is covered externally by a =serous coat= formed by
the mesosalpinx. The serous membrane is continued on the fimbriæ, and
meets the mucous lining on them. The =fibrous coat= or adventitia is
continuous with the fibrous lamina of the broad ligament. The =muscular
coat= consists chiefly of circular fibers, although longitudinal fibers
occur externally. The =mucous coat= is thin and is much plicated. The
folds (Plicæ tubariæ) are chiefly longitudinal, but in the wide part of
the tube (Ampullæ tubæ) they are very complex, so that on cross-sections
the spaces between the folds may be mistaken for branched tubular
glands. The folds are continued on to the fimbriæ. The =epithelium= is a
single layer of columnar ciliated cells, the cilia producing a current
directed toward the uterus. At the fimbriated extremity this epithelium
passes gradually into the squamous type of the serous coat.
=Vessels and Nerves.=—The =arteries= are derived from the =utero-ovarian
artery=. The =veins= are satellites of the arteries. The =lymphatics=
pass with the ovarian vessels to the lumbar glands. The nerves have a
similar origin to those of the ovary.
THE UTERUS
The =uterus= is a hollow muscular organ, which receives the Fallopian
tubes anteriorly and opens into the vagina posteriorly. It is situated
chiefly in the abdominal cavity, but extends a short distance into the
pelvic cavity. It is attached to the lumbar wall of the abdomen and the
lateral walls of the pelvic cavity by two folds of peritoneum termed the
broad ligaments. It consists of two cornua or horns, the body, and the
neck.
The =cornua= or =horns= of the uterus (Cornua uteri) are situated
entirely in the abdomen. They appear to vary considerably in position;
commonly they are pressed up against the sublumbar muscles by the
intestine (left portions of large colon, small colon, and small
intestine). They are cylindrical, and are about ten inches (ca. 25 cm.)
in length. The anterior extremity of each forms a blunt point which
receives the Fallopian tube. Posteriorly they increase somewhat in
caliber, converge, and unite with the body. The =dorsal= (or attached)
=border= is slightly concave and is attached to the broad ligament. The
=ventral border= is convex and free.
[Illustration:
FIG. 410.—GENITAL ORGANS OF MARE, DORSAL VIEW.
The left cornu and adjacent part of the body of the uterus and the
vagina and vulva are opened up. _1_, Ovary; _2_, Fallopian tube,
with _2′_, its fimbriated end; _3_, cavity of corpus uteri; _4_,
cavity of left cornu; _5_, right cornu, with _5′_, its communication
with the body; _6_, portio vaginalis uteri; _6′_, os uteri; _7_,
broad ligament of uterus; _8_, ligament of ovary; _9_, vagina; _10_,
vulva; _10′_, glandulæ vestibulares majores; _10″_, glandulæ
vestibulares minores; _11_, transverse fold; _12_, external urethral
opening; _13_, _13′_, labia vulvæ; _14_, glans clitoridis; _14′_,
junction of crura to form corpus clitoridis indicated by dotted
lines; _15_, urinary bladder; _a_, utero-ovarian artery with ovarian
(_a′_) and uterine (_a″_) branches; _b_, uterine artery. (After
Ellenberger, in Leisering’s Atlas.)
]
When a soft uterus is distended, the cornua are strongly curved, but
this does not represent the natural form. When fixed _in situ_ the
horns are either slightly curved or nearly straight. The two horns are
commonly unsymmetrical in length and diameter in mares which have
borne young.
The =body= of the uterus (Corpus uteri) is situated partly in the
abdomen, partly in the pelvic cavity. It is cylindrical, but
considerably flattened dorso-ventrally, so that in cross-section it is
elliptical. Its average length is about six inches (15 cm.), and its
diameter, when moderately distended, about four inches (10 cm.). Its
=dorsal surface= (Facies rectalis) is related to the small colon and
rectum. Its =ventral surface= (Facies vesicalis) is in contact with the
bladder, and has inconstant relations with various parts of the
intestine. The term =fundus uteri= is applied to the anterior wide part
from which the cornua diverge.
The position of the body of the uterus is variable, especially in
regard to its anterior part. It is often pressed up against the
rectum, and may be deflected to either side—most frequently to the
left—by the pelvic flexure of the colon or coils of the small colon.
The =cervix= or =neck= of the uterus (Cervix uteri) is the constricted
posterior part which joins the vagina. Part of it (Portio vaginalis
uteri) projects into the cavity of the vagina; it is therefore not
visible externally, but may be felt through the vaginal wall. It is
about two inches (5 cm.) in length, and an inch and a half (3.5 to 4
cm.) in diameter.
=Attachments.=—The body and cornua are attached to the abdominal and
pelvic walls by two extensive peritoneal folds, the =broad ligaments=
(Ligamenta lata). These extend on either side from the sublumbar region
and the lateral pelvic walls to the dorsal border of the cornua and the
lateral margins of the body of the uterus. They contain the vessels and
nerves of the uterus and ovaries, connective tissue, and unstriped
muscular fibers. The ureters are situated along their parietal margins.
The outer layer of each forms a fold, the =round ligament= of the uterus
(Ligamentum teres uteri), which blends with the parietal peritoneum over
the internal inguinal ring; its anterior extremity is situated above the
extremity of the cornu and is rounded and free. It contains muscular
tissue, vessels, and nerves, and is the homologue of the gubernaculum
testis. The anterior part of the neck is continuous with the vagina, and
thus has a more fixed position than the rest of the organ.
=The cavity= of the uterus (Cavum uteri) is largely obliterated in the
non-pregnant state by the contraction of the wall and by folds of the
mucous lining. At the extremity of each cornu it communicates by a
minute opening with the Fallopian tube. The cavity of the neck is termed
the =cervical canal= (Canalis cervicis); it is closed ordinarily by
mucous folds and a plug of mucus. It opens into the vagina by the =os
uteri externum=, and into the body by the =os uteri internum=.
=Structure.=—The wall of the uterus consists of three coats—an external
serous, a middle muscular, and an internal mucous. The =serous coat=
(Perimetrium) is, for the most part, closely adherent to the muscular
coat. It is continuous with the broad ligaments. The =muscular coat=
consists essentially of two layers, a thin external stratum of
longitudinal fibers, and a thick layer of circular fibers. Between these
is a very vascular layer (Stratum vasculare) of connective tissue with
circular and oblique muscular fibers in it. The circular coat is very
thick in the neck, where it forms a =sphincter= half an inch or more
(ca. 1.5 cm.) in thickness. The =mucous membrane= rests directly on the
muscular coat. It is thick, and is covered by columnar epithelium. It
contains numerous long tubular =uterine glands= (Glandulæ uterinæ). It
is brownish-red in color, except in the neck, where it is pale.
=Vessels and Nerves.=—The chief =arteries= are the =uterine= and the
=uterine branch= of the =utero-ovarian=, which have a flexuous course in
the broad ligaments; there is also a branch from the =internal pudic=
artery. The =veins= form pampiniform plexuses and accompany the
arteries. The =lymphatics= are numerous and go to the internal iliac and
lumbar glands. The =nerves= are derived from the sympathetic through the
uterine and pelvic plexuses.
The foregoing statements refer to the non-gravid uterus. In the
pregnant state it undergoes important changes in size, position, and
structure. The increase in size affects chiefly the gravid cornu
(except in the case of twins) and the body. The cornu attains a length
of about two and a half to three feet (ca. 80 to 90 cm.), and a
corresponding diameter; in this process it extends much beyond the
ovary, and the broad ligament. The gravid uterus is entirely abdominal
in position, and extends along the ventral wall, chiefly to the left
of the median plane. It weighs about nine pounds (ca. 4 kg.),
according to Ellenberger. The broad ligaments increase greatly in size
and contain more muscular tissue. The vessels are greatly enlarged and
form new branches. The muscular coat, in spite of the increase in size
and number of the fibers, is somewhat thinner, except in the neck. The
mucous membrane is thicker and more vascular; the epithelium becomes
non-ciliated and stratified.
THE VAGINA
The =vagina= is the passage which extends horizontally through the
pelvic cavity from the neck of the uterus to the vulva. It is tubular,
is about six to eight inches (ca. 15 to 20 cm.) in length, and, when
slightly distended, about four or five inches (ca. 10 to 12 cm.) in
diameter. Its dilatability appears to be limited only by the pelvic
wall. There is no external line of demarcation between the vagina and
the uterus or the vulva.
It is related dorsally to the rectum, ventrally to the bladder and
urethra, and laterally to the pelvic wall. The recto-genital pouch of
the peritoneum extends between the vagina and rectum for a distance of
about two inches (5 cm.), and ventrally the vesico-genital pouch passes
backward somewhat less between the vagina and bladder. Thus most of the
vagina is retroperitoneal and is surrounded by a quantity of loose
connective tissue, a venous plexus, and a variable amount of fat.
=Structure.=—With the exception of the short peritoneal part, as
indicated above, the proper wall of the vagina is composed of muscular
and mucous coats. The =muscular coat= is composed of a thin layer of
longitudinal fibers, and a thicker layer of circular fibers; it contains
also many elastic fibers. The =mucous coat= is highly elastic, and is
covered with a stratified epithelium. It has no glands.
Under usual conditions the cavity is practically obliterated by
apposition of the walls, so that the lumen is a transverse slit; this
condition is pronounced when the ampulla of the rectum is full. The
anterior end of the vagina is largely occupied by the intravaginal part
of the neck of the uterus, so that the cavity is here reduced to an
annular recess termed the =fornix vaginæ=. The posterior part is
directly continuous with the vulva without any line of demarcation
except the valvular fold, which covers the external urethral orifice; in
very young subjects this fold is continued on either side, forming the
=hymen=, which narrows the entrance to the vagina (Introitus
vaginæ).[152]
=Vessels and Nerves.=—The blood-supply is derived from the branches of
the =internal pudic arteries=. The =veins= form a plexus which is
drained by the =internal pudic veins=. The =lymphatics= pass to the
internal iliac lymph glands. The =nerves= are derived from the
sympathetic through the pelvic plexus.
THE VULVA
The =vulva= or =urogenital sinus= is the terminal part of the genital
tract.[153] It is continuous in front with the vagina, and opens
externally at the vulvar cleft below the anus. There is no external line
of demarcation between the vagina and vulva. The tube is about five
inches (ca. 12 cm.) in length, measured from the external urethral
orifice to the inferior commissure; dorsally it is considerably shorter.
It is related dorsally to the rectum and anus, ventrally to the pelvic
floor, and laterally to the sacro-sciatic ligament, the semimembranosus
muscle, and the internal pudic artery. The external orifice or =vulvar
cleft= (Rima vulvæ) has the form of a vertical slit, about four to six
inches (ca. 10 to 15 cm.) high, and is margined by two prominent rounded
folds, the labia. The =labia= of the vulva (Labia vulvæ) meet above at
an acute angle, forming the =superior commissure= (Commissura dorsalis),
which is about two inches (ca. 5 cm.) below the anus. Below they unite
to form the thick rounded =inferior commissure= (Commissura ventralis),
which lies about two inches (ca. 5 cm.) behind and below the ischial
arch. When the labia are drawn apart, a rounded body, about an inch (ca.
2.5 cm.) wide, is seen in the inferior commissure; this is the =glans
clitoridis=, the homologue of the glans penis. Overlying it is a thin
fold, the =prepuce= of the clitoris (Præputium clitoridis). At the
anterior extremity of the ventral wall of the vulva, _i. e._, about four
or five inches (ca. 10 to 12 cm.) from the inferior commissure, is the
=external urethral orifice= or meatus urinarius (Orificium urethræ
externum). It readily admits the finger and is very dilatable. It is
covered by a fold of mucous membrane, the free edge of which is directed
backward.
=Structure.=—The =labia= are covered by thin, pigmented, smooth skin,
which is richly supplied with sebaceous and sweat glands. This is
continuous at a distance of about half an inch (ca. 1 to 1.5 cm.) from
the free edge with a thin glandless mucous membrane. Between these is a
layer of striped muscle, the =constrictor vulvæ=; this fuses above with
the sphincter ani, and embraces the clitoris below, spreading out
laterally at the inferior commissure. It constricts the vulvar orifice
and elevates the clitoris. The =constrictor vestibuli= muscle embraces
the vulva in front of the preceding; it is joined on either side by a
band of unstriped muscle which arises from the first and second
coccygeal vertebræ, and is homologous with the proximal part of the
retractor penis. It constricts the vulva. Under this muscle in the
lateral wall is a flattened, oval body, the =bulbus vestibuli= (Fig.
453); this is an erectile structure, homologous with the corpus
spongiosum urethræ of the male. It is about two and a half to three
inches (ca. 6 to 8 cm.) long, and an inch or more (ca. 3 cm.) wide. It
consists of a venous network inclosed in a fibrous capsule, and is
supplied with blood by a large branch of the internal pudic artery. The
=mucous membrane= of the vulva is reddish in color, and forms
longitudinal and transverse folds. It presents ventrally two linear
series of small papillæ which converge toward the inferior commissure;
these mark the orifices of the ducts of the =glandulæ vestibulares
minores=. On either side of the dorsal wall is a group of eight to ten
larger prominences on which the ducts of the =glandulæ vestibulares
majores= (of Bartholin) open.
Quite exceptionally there may be found on either side of the urethral
orifice the opening of the canals of Gartner (Ductus epoöphori
longitudinales).
The =clitoris= is the homologue of the penis. It arises from the ischial
arch by two crura, which unite to form a =body= as large as one’s little
finger. This projects backward into the inferior commissure of the
vulva, capped by a small rounded =glans=. The organ is composed of
erectile tissue similar to the corpus cavernosum penis. The
=ischio-cavernosus= (or erector clitoridis) is a very feeble muscle
which depresses the clitoris. The veins of the clitoris communicate by
an intermediate plexus on either side with the bulbus vestibuli.
THE FEMALE URETHRA
The female =urethra= (Urethra feminina) represents only that part of the
canal of the male which lies between the internal urethral orifice and
the openings of the ejaculatory ducts. Its length is about two inches (5
cm.), and its lumen is sufficient to admit of the introduction of the
finger; it is, however, capable of remarkable dilatation if sufficient
care and patience are exercised in the process. It lies centrally on the
pelvic floor, and is related and attached dorsally to the vagina.
=Structure.=—The intrinsic =muscular coat= consists of longitudinal and
circular layers of unstriped fibers. Between these is a layer of areolar
tissue which contains a rich =venous plexus=. The =mucous membrane= is
thrown into longitudinal folds when the canal is closed; it is highly
elastic, and is covered with stratified epithelium.
The =urethral muscle= (M. compressor urethræ) embraces the urethra and
is continued backward for some distance under the constrictor vestibuli.
It is covered by a fibro-elastic membrane.
THE MAMMARY GLANDS
The =mammary glands= (Glandulæ lactiferæ) are modified cutaneous glands
which are so closely associated functionally with the genital organs as
to be considered accessory to them.
In the mare they are two in number, and are placed on either side of the
median plane in the inguinal region. Each gland has the form of a short
cone, much compressed transversely, and having a flat inner surface. It
consists of the glandular mass or body of the gland (Corpus mammæ) and
the =teat= or =nipple= (Papilla mammæ). The base is related to the
abdominal wall, to which it is attached by areolar tissue, which
contains a venous plexus, the superficial inguinal lymph glands, and a
variable amount of fat. The apex is constituted by the teat, which is
also flattened transversely and varies in length from one to two inches
(ca. 2.5 to 5 cm.). Between the bases of the teats is the intermammary
groove. On the apex of each teat two or three small orifices are placed
close together; these are the openings of the lactiferous ducts.
=Structure.=—The =skin= over the glands is thin, pigmented, chiefly
hairless, and supplied with numerous large sebaceous and sweat glands.
Under this are two layers of =fascia= except on the teats. The
superficial fascia presents no special features. The deep fascia
consists of two laminæ detached from the abdominal tunic which descend
on either side of the median plane, forming a =septum= between the two
glands, and constituting their ligamentum suspensorium.
These laminæ are separated by a layer of areolar tissue, so that it is
possible to remove one gland if diseased by careful dissection between
the layers of the septum.
The =gland substance= or =parenchyma= is pinkish gray in color, and of
firmer consistence than the fat which is found around and within the
gland. It is inclosed by a fibro-elastic capsule which sends inward
numerous trabeculæ; these form the =interstitial tissue=, and divide the
gland into =lobes= and =lobules=. In the latter are the secretory
=tubules= and =alveoli=, which unite to form the larger =ducts=. Each
lobe has a duct, which opens at the base of the teat into a space called
the =lactiferous sinus= (Sinus lactiferus); this is lined with mucous
membrane, and from it two (or three) =lactiferous ducts= (Ductus
lactiferi) pass through the extremity of the nipple. These ducts are
lined with a non-glandular mucous membrane, which is covered with
stratified squamous epithelium. They are surrounded by unstriped
muscular tissue, the bulk of the fibers being arranged in a circular
manner to form a =sphincter=.
The size and form of the mammary glands are subject to much variation.
In the young subject, before pregnancy, they are small and contain
little gland tissue. During the latter part of gestation, and
especially during lactation, they increase greatly in size, and the
gland tissue is highly developed. After lactation the secretory
structures undergo marked involution, and the gland is much reduced in
size. The relative amounts of gland substance and interstitial tissue
vary greatly; in some cases a gland of considerable size contains
little secretory tissue and is consequently functionally deficient.
=Vessels and Nerves.=—The =arteries= are derived from the =external
pudic artery=, which enters the gland at the posterior part of its base.
The =veins= form a plexus on either side of the base of the gland, which
is drained by the =external pudic vein= chiefly. The =lymphatics= are
numerous and pass chiefly to the superficial inguinal (or supramammary)
lymph glands. The =nerves= are derived from the =inguinal nerves= and
the =posterior mesenteric plexus= of the sympathetic system.
GENITAL ORGANS OF THE COW
The =ovaries= of the cow are much smaller than those of the mare,
measuring usually about one to one and a half inches (ca. 3 to 4 cm.) in
length, and a little less than an inch (ca. 2 cm.) in thickness in their
largest part. They are oval in form, pointed at the uterine end, and
have no ovulation fossa. They are situated usually a little above the
middle of the lateral margin of the pelvic inlet in the non-pregnant
subject, but may be found a little further forward. They are thus about
16 to 18 inches (ca. 40 to 45 cm.) from the vulva in a cow of medium
size. The greater part of the surface of the gland is covered with
germinal epithelium, the peritoneal epithelium being limited to a narrow
zone along the attached border. Follicles of various sizes are often
seen projecting from the surface, as well as corpora lutea; a corpus
luteum verum has a pronounced yellow color, and may reach a width of
half an inch or more (ca. 1 to 1.5 cm.).
[Illustration:
FIG. 411.—OVARY OF COW.
_1_, Broad ligament of uterus; _2_, ligament of ovary; _3_, fimbria
ovarica; _4_, attachment of broad ligament; _5_, surface of ovary
covered with germinal epithelium; _6_, corpora lutea; _7_, Graafian
follicle. (From Leisering’s Atlas.)
]
[Illustration:
FIG. 412.—UTERUS OF COW, CONTRACTED, DORSAL VIEW.
_a_, Body of uterus; _b_, _b′_, horn of uterus; c, ovary; _d_, _d′_,
triangular folds connecting horns of uterus (Lig. intercornualia).
(After Zieger.)
]
The =Fallopian= or =uterine tubes= are long and less flexuous than in
the mare. The junction with the cornu of the uterus is not so abrupt as
in the mare, since the extremities of the horns are pointed. The uterine
orifice of the tube is rather large and funnel-shaped. The fimbriæ are
not so extensive as in the mare.
The =uterus= lies almost entirely within the abdominal cavity in the
adult. The =body= is only about one inch (ca. 2 to 3 cm.) in length,
although externally it appears to be much longer. This false impression
is due to the fact that the posterior parts of the cornua are united by
connective and muscular tissue and have a common peritoneal covering.
The =cornua= are, therefore, really longer than they appear externally.
They taper gradually toward the free end, so that the junction with the
Fallopian tubes is not abrupt, as in the mare. The free part of the horn
curves at first downward, forward, and outward, and then turns upward,
forming a spiral coil. The =cervix= is about four or five inches (ca. 8
to 10 cm.) long; its wall is remarkably dense, and may be nearly an inch
(ca. 2 cm.) in thickness. Its lumen, the =cervical canal=, is spiral,
and is ordinarily tightly closed and very difficult to dilate. The
=muscular coat= of the uterus is thicker than in the mare. It consists
of an external longitudinal layer and two circular strata. The inner
circular layer is about a fourth of an inch (ca. 6 mm.) thick in the
cervix. The other layers are continued in the vagina. The =mucous
membrane= of the horns and body presents as a characteristic feature the
=uterine cotyledons= (Cotyledones uterinæ). These are oval prominences,
about a hundred in number, which are either irregularly scattered over
the surface or arranged in rows of about a dozen.
In the non-gravid uterus they average about ½ to ¾ inch (ca. 15 to 18
mm.) in length, ⅓ inch (ca. 8 mm.) in width, and ⅛ inch (ca. 2 to 4
mm.) in thickness. During pregnancy they become greatly enlarged and
pedunculated. The larger ones then measure about 4 to 5 inches (10 to
12 cm.) in length, 1 to 1½ inches (3 to 4 cm.) in width, and 1 inch (2
to 2.5 cm.) in thickness. The deep face has a hilus at which the
vessels enter. The rest of the surface has a spongy appearance, due to
numerous crypts which receive the villi of the chorion.
The =uterine glands= are long and branched. The mucous membrane of the
cervix is pale and forms numerous folds. The latter are arranged in
several series which obliterate the lumen. At the external orifice (os
uteri) the folds (Plicæ palmatæ) form rounded prominences arranged
circularly, which project into the cavity of the vagina. There are no
glands in the cervix, but a thick mucus is secreted by goblet cells.
[Illustration:
FIG. 413.—UTERINE COTYLEDON OF COW.
The figure represents a cotyledon of medium size. (After Ellenberger,
in Leisering’s Atlas.)
]
[Illustration:
FIG. 414.—GENITAL ORGANS OF COW, DORSAL VIEW.
The right uterine cornu and the vagina and vulva are opened up: _1_,
Labium vulvæ; _2_, ventral commissure; _3_, glans clitoridis; _4_,
glandula vestibularis major, exposed by slit in mucous membrane;
_5_, opening of duct of preceding; _6_, suburethral diverticulum;
_7_, external urethral opening; _8_, openings of canals of Gartner;
_9_, os uteri; _10_, corpus uteri; _11_, cornu uteri; _12_,
cotyledons; _13_, Fallopian tube; _14_, ostium abdominale tubæ;
_15_, ovary (From Leisering’s Atlas, reduced.)
]
The =broad ligaments= are not attached in the sublumbar region as in the
mare, but to the upper part of the flanks, about a handbreadth below the
level of the external angle of the ilium. They contain a conspicuous
amount of unstriped muscle. The =round ligaments= are well developed,
and can be traced distinctly to the vicinity of the internal inguinal
ring.
The =vagina= is somewhat longer and more roomy than that of the mare;
its wall is also thicker. Its average length in the non-pregnant animal
is about eight inches (ca. 20 cm.); but in the pregnant cow the length
increases to twelve inches (30 cm.) or more. The recto-genital pouch of
peritoneum extends backward about five inches (ca. 12 cm.) on the dorsal
surface, while ventrally the serous coat only extends backward about two
inches (ca. 5 cm.).
This gives ample space dorsally for the incision of the fornix vaginæ
in oöphorectomy.
In the ventral wall of the vagina, between the muscular and mucous
coats, there are frequently present the two =canals of Gartner= (Ductus
epoöphori longitudinales). When well developed they may attain the
diameter of a goose quill, and may be traced forward to the anterior
part of the vagina or even further. They open posteriorly near the
external urethral orifice.
These tubes are remnants of the Wolffian ducts, and, like other fœtal
vestiges, are very variable. Röder states that the right canal was
absent in over 52 per cent., the left in only 22 per cent., of the
cows examined by him. In some cases they may be traced in the broad
ligaments for a variable distance toward the ovary. They are of
clinical interest in that cysts frequently form along their course.
[Illustration:
FIG. 415.—DIAGRAMMATIC SAGITTAL SECTION OF PART OF UROGENITAL TRACT OF
COW, SHOWING SUBURETHRAL DIVERTICULUM.
]
The =vulva= has thick wrinkled labia, and both commissures are acute;
the lower one is pointed, and has on it a number of long hairs; it lies
about two inches (5 cm.) behind, and about the same distance below, the
level of the ischial arch. The =glans clitoridis= is small; the =crura=
are about four inches (ca. 10 cm.) long and are flexuous. The =external
urethral orifice= or meatus urinarius is four or five inches (10 to 12
cm.) from the ventral commissure. Beneath it is a blind pouch, the
=suburethral diverticulum=, which is more than an inch (ca. 3 to 4 cm.)
long, and readily admits the end of a finger.
The form and position of this pouch should be carefully noted on
account of the difficulty it causes in catheterizing the bladder. If
the catheter is passed along the ventral wall of the vulva (as in the
mare), it will always enter the pouch instead of the urethra.
The =glandulæ vestibulares majores= (or glands of Bartholin) are
situated on the lateral walls of the vulva, under the constrictor vulvæ.
They are little over an inch (ca. 3 cm.) long and about half an inch
(ca. 1.5 cm.) in width. Each has a single duct which opens about an inch
and a half (ca. 3 to 4 cm.) lateral to and behind the external urethral
orifice.
The =urethra= of the cow is about four inches (10 cm.) in length; it is
narrower and much less dilatable than that of the mare. It is fused
dorsally with the wall of the vagina, while laterally and ventrally it
is covered by the constrictor vaginæ muscle.
The =mammary glands=, normally two in number, are popularly termed the
udder. They are very much larger than in the mare, and the body of each
is somewhat ellipsoidal in form, but flattened transversely. The =base=
(or dorsal surface) of each gland is slightly concave and slopes
obliquely downward and forward in adaptation to the abdominal wall, to
which it is adherent; posteriorly it is in relation to the large
supramammary lymph glands and a quantity of fat. The inner surface is
flat, and is separated from the other gland by a well-developed double
septum. The outer surface is convex. Four well-developed teats are
present; they average about three inches (ca. 7 to 8 cm.) in length. It
is customary to consider the udder to consist of four “quarters.” There
is no septum nor visible division between the two quarters of the same
side, but, on the other hand, injections of fluids of different colors
into the two teats of the gland demonstrate that the cavities drained by
them do not communicate.
[Illustration:
FIG. 416.—CROSS-SECTION OF MAMMARY GLANDS OF COW.
_a_, Body of gland; _b_, lactiferous sinus; _c_, cavity of teat; _d_,
duct of teat; _e_, intermammary groove; _f_, septum between glands;
_g_, supramammary fat.
]
The size and form of the glands vary greatly; in the highly
specialized dairy breeds (_e. g._, Holsteins) they often attain
enormous dimensions. The size of the udder is not a certain index of
its productivity, since some so-called “fleshy” udders contain a very
large amount of interstitial tissue and relatively little parenchyma.
Small accessory teats often occur posteriorly; commonly these are
rudimentary and imperforate (polythelia), but sometimes they drain a
small amount of gland substance (polymastia). Sanson described a case
in which there were seven teats, all giving milk.
Each teat has a single duct which widens superiorly and opens freely
into a roomy =lactiferous sinus= or milk cistern (Sinus lactiferus). The
=lactiferous duct= or teat canal is lined by a glandless mucous membrane
which is covered with stratified squamous epithelium; the lower part
(ca. 1 cm.) of the canal is narrow, and is closed by a =sphincter= of
unstriped muscle. The =mucous membrane= of the sinus forms numerous
folds which render the cavity multilocular.
=Vessels and Nerves.=—The blood-supply is derived from the =external
pudic arteries=. The =veins= form a circle at the base of the udder,
from which the blood is drained by three trunks, viz., the very large
=subcutaneous abdominal= (“milk vein”), the =external pudic=, and the
=perineal vein=. The =lymphatics= are numerous, and pass to the
supramammary glands chiefly. The nerves are derived from the =inguinal
nerves= and the =posterior mesenteric plexus= of the sympathetic.
GENITAL ORGANS OF THE SOW
[Illustration:
FIG. 417.—GENITAL ORGANS OF SOW, DORSAL VIEW. THE VAGINA AND CERVIX
UTERI ARE SLIT OPEN.
_1_, Labia vulvæ; _2_, glans clitoridis; _3_, vulva; _4_, external
urethral orifice; _5_, vagina; _5′_, cervix uteri; _6_, corpus
uteri; _7_, cornua uteri, one of which is opened at _7′_ to show
folds of mucous membrane; _8_, Fallopian tube; _8′_, abdominal
opening of tube; _9_, ovaries; _10_, ovarian bursa; _11_, broad
ligaments of uterus; _12_, urinary bladder. (From Leisering’s
Atlas.)
]
The =ovaries= are concealed in the bursa ovarii, owing to the large
extent of the mesosalpinx. They are more rounded than in the bitch, and
have a distinct hilus. They are situated usually as in the cow, but
their position is quite variable in animals which have borne young. The
surface commonly presents rounded prominences, so that sometimes the
gland has an irregular, mulberry-like aspect; this is due to the fact
that there is very little stroma and the larger Graafian follicles
project from the surface.
The =Fallopian= or =uterine tubes= are long (ca. 15 to 30 cm.), and less
flexuous than in the mare. The fimbriated extremity forms an ampulla and
has a large abdominal opening. The uterine end shades insensibly into
the small extremity of the cornu of the uterus.
The =uterus= presents several striking features. The =body= is only
about two inches (ca. 5 cm.) long. The =horns= are extremely long and
flexuous, and are freely movable, on account of the large extent of the
broad ligaments. The extremities of the horns taper to about the
diameter of the Fallopian tubes.[154] The =neck= is remarkable for its
length (ca. 15 to 20 cm.) and the fact that it is directly continued by
the vagina without forming any intravaginal projection (os uteri). It
can be distinguished by the transverse folds of its mucous membrane and
the thickness of its wall.
The changes in form and position of the uterus during pregnancy are
similar to those mentioned later in the case of the bitch.
The =vagina= is about four or five inches (ca. 10 to 12 cm.) long in a
sow of medium size. It is small in caliber, and has a thick muscular
coat which consists mainly of circular fibers. The mucous membrane is
plicated, and is intimately united with the muscular coat.
The =vulva= is relatively long. The inferior commissure is pointed and
dependent. The mucous lining is plicated. There is a small =suburethral
diverticulum=. The vestibular glands are small and variable in number.
The vestibular bulbs are little developed. The canals of Gartner may
sometimes be traced as far as the ovary, but are often difficult to
find.
The =clitoris= is long, flexuous, and pointed; beneath it is a
cul-de-sac.
The =urethra= is very long; its vulvar orifice is not concealed by a
valvular fold.
The =mammary glands= are usually ten or twelve in number, and are
arranged in two rows, as in the bitch. Each teat has commonly two
excretory ducts.
GENITAL ORGANS OF THE BITCH
The =ovaries= (Fig. 336) are small, elongated-oval in outline, and
flattened. Each ovary is situated close to or in contact with the
posterior pole of the corresponding kidney, and thus lies ventral to the
third or fourth lumbar vertebræ, or about half-way between the last rib
and the crest of the ilium. Each is concealed in a peritoneal pouch, the
=bursa ovarii=, which has a slit-like opening ventrally. The two folds
which form this pouch contain a quantity of fat and unstriped muscle.
They are continued to the cornu of the uterus, constituting the
=mesosalpinx= and the =ovarian ligament=. The surface of the ovary
presents prominences caused by projecting Graafian follicles. There is
no distinct hilus.
The =Fallopian= or =uterine tubes= are small and average two or three
inches (ca. 5 to 8 cm.) in length. Each passes at first forward and then
turns backward, having a straight or only slightly flexuous course. The
fimbriated extremity lies in the bursa ovarii, and has a rather large
opening. The uterine orifice is very small.
The =uterus= has a very short body and two long narrow horns. In a bitch
of medium size the body is about an inch (ca. 2 to 3 cm.) and the cornua
five or six inches (ca. 12 to 15 cm.) long. The horns are of uniform
diameter, are nearly straight, and lie entirely within the abdomen. They
diverge from the body in the form of a V toward each
kidney. Their posterior parts are united by the peritoneum. The neck is
very short and is fused dorsally with the vagina. It has a thick
muscular coat. The mucous membrane of the uterus has long uterine glands
and also short tubular crypts.
The =broad ligaments= contain fat and unstriped muscle. They are much
longer in the middle than at either end. The posterior part is attached
to the anterior part of the vagina. The =round ligaments= are very long,
extending through the inguinal canals, and traceable almost to the
vulva.
The horns of the gravid uterus present dilatations or =ampullæ=, which
contain the fœtuses, and are separated by constrictions. The gravid
uterus lies on the ventral abdominal wall, and toward the end of
gestation extends forward to the stomach and liver.
The =vagina= is relatively long. It is narrow anteriorly, and has no
distinct fornix. The muscular coat is thick and consists chiefly of
circular fibers. The mucous membrane forms longitudinal folds. The
canals of Gartner are usually absent.
[Illustration:
FIG. 418.—GENITAL ORGANS OF BITCH.
Vulva, vagina, and uterus (in part) are slit open. _a_, Ovarian bursa;
_b_, same opened to show the right ovary, _c_; _d_, _d_, horns of
uterus; _e_, _e′_, body of uterus; _f_, neck of uterus; _f′_, os
uteri; _g_, vagina; _h_, hymen; _i_, vulva; _k_, external urethral
orifice; _l_, urinary bladder; _m_, urethra; _n_, _n_, labia vulvæ;
_o_, fossa clitoridis; _p_, clitoris. (After Ellenberger, in
Leisering’s Atlas.)
]
The =vulva= has thick labia which form a pointed inferior commissure.
The mucous lining is smooth. On either side of the urethral orifice
there is a small depression. The glandulæ vestibulares majores are
absent, but the smaller glands are present, and their ducts open
ventrally on either side of a median ridge. The vestibular bulbs are
relatively large and join dorsally. The clitoris has a small pointed
glans, beneath which is a diverticulum. The corpus cavernosum is a
little more than an inch (ca. 3 to 4 cm.) long in a subject of medium
size, and is infiltrated with fat.
The =mammary glands= are usually ten in number, and are arranged in two
series extending from the posterior part of the pectoral region to the
inguinal region; they are, therefore, designated according to location
as =pectoral=, =abdominal=, and =inguinal=. The teats are short, and
present on their apices six to twelve small orifices of the excretory
ducts.
ANGIOLOGY: THE VASCULAR SYSTEM
=Angiology= is the description of the organs of circulation of the blood
and lymph—the heart and vessels. The =heart= is the central hollow
muscular organ which functions as a suction and force pump; the
differences in pressure caused by its contraction and relaxation
determine the circulation of the blood and lymph. It is situated in the
middle mediastinal space of the thorax, between the two lungs, and is
inclosed in a fibro-serous sac—the pericardium. The vessels are tubular
and run through almost all parts of the body. They are designated
according to their contents as =blood-= and =lymph vessels=.
The =blood-vascular system= consists of: (1) the =arteries=, which
convey blood from the heart to the tissues; (2) the =capillaries=,
microscopic tubes in the tissues which permit of the necessary
interchange between the blood and the tissues; (3) the =veins=, which
convey the blood back to the heart.
The blood-vessels are divided into the =pulmonary= and the =systemic=.
The =pulmonary artery= conveys the blood from the right ventricle of the
heart to the lungs, where it is arterialized, and is returned by the
=pulmonary veins= to the left atrium of the heart, and passes into the
left ventricle. The =systemic arteries= convey the blood from the left
ventricle all over the body, whence it is returned by the =venæ cavæ= to
the right atrium, and passes into the right ventricle.
It should be noted, however, that the lungs receive arterial blood
through the systemic bronchial arteries. This blood is returned in
part by the bronchial veins to the right atrium (indirectly), in part
by the pulmonary veins to the left atrium.
The term =portal system= is often applied to the portal vein and its
tributaries which come from the stomach, intestine, pancreas, and
spleen. The vein enters the liver, where it branches like an artery, so
that the blood in this subsidiary system passes through a second set of
capillaries before being conveyed to the heart by the hepatic veins and
the posterior vena cava.
The =arteries= (Arteriæ), as a rule, divide at an acute angle, giving
off finer and finer branches. In some cases branches come off at a right
angle, and others are recurrent, _i. e._, run in a direction opposite to
that of the parent stem. The intercommunication of branches of adjacent
arteries is termed =anastomosis=. Most commonly the connections are made
by a network of numerous fine branches (Plexus vasculosus). Relatively
large communicating branches (Rami communicantes) occur in certain
places; they may be transverse or in the form of arches. Wide-meshed
networks of vessels are termed =Retia vasculosa=. =Terminal= or =end
arteries= are such as form isolated networks, _i. e._, do not anastomose
with adjacent arteries. A =rete mirabile= is a network intercalated in
the course of an artery. A =collateral vessel= (Vas collaterale) is one
which pursues a course near and similar to that of a larger vessel.
The =veins= (Venæ) are in general arranged like the arteries, but are
usually of greater caliber. When a vein accompanies an artery, it is
termed a =vena comitans= or =satellite vein=; in many places two veins
accompany a single artery. The primitive venous trunks do not run with
the arteries, and most of the superficial veins (Venæ cutaneæ) pursue
independent courses. They anastomose even more freely than the arteries,
and large communicating branches are very common. The veins form very
rich plexuses (Plexus venosi) in many places. Some veins which are
without independent walls and are inclosed by dense membranes and run
usually in bony grooves are termed (venous) =sinuses=; examples of this
are the sinuses of the dura mater of the brain.
=Structure of Arteries.=—The wall consists of three coats. The =external
coat= (Tunica externa) consists chiefly of fibrous connective tissue. In
the deeper part are some elastic fibers, and in some arteries there are
also longitudinal unstriped muscle-fibers. The =middle coat= (Tunica
media) is composed of unstriped muscle and elastic tissue in
medium-sized arteries. In small vessels there is only the muscular
tissue, and in the largest trunks only elastic tissue. The =internal
coat= or =intima= (Tunica intima) consists of a layer of endothelial
cells, resting on an elastic membrane. The =sheath= (Vagina vasis) is a
condensation of the surrounding connective tissue, and is attached more
or less closely to the external coat.
=Structure of Veins.=—The walls of veins are similar in structure to
those of the arteries, but are very much thinner, so that veins collapse
more or less completely when empty, while arteries do not. The =middle
coat= is very thin and consists to a large extent of ordinary connective
tissue. The =intima= is also less elastic than in the arteries. In many
veins this coat forms semilunar =valves=, the free edges of which are
directed toward the heart. They are most numerous in the veins of the
skin and the deep veins of the extremities (except the foot), while in
most veins of the body cavities and viscera they are absent or occur
only where the veins open into larger ones or where two veins join.
The walls of the vessels are supplied with blood by numerous small
arteries, called =vasa vasorum=. These arise from branches of the artery
which they supply or from adjacent arteries, ramify in the external
coat, and enter the middle coat also.
The =nerves= of the vessels consist of both medullated and
non-medullated fibers. They form plexuses around the vessels, from which
fibers pass mainly to the muscular tissue of the middle coat.
BLOOD-VASCULAR SYSTEM OF THE HORSE
THE PERICARDIUM[155]
The =pericardium= is the fibro-serous sac which surrounds the heart, and
also the great vessels in connection with it to a greater or less
extent. Its form is in general similar to that of the heart. The
=fibrous layer= is relatively thin, but strong and inelastic. It is
attached dorsally to the large vessels at the base of the heart, and is
continued in part up to the longus colli muscle. Ventrally it is firmly
attached to the middle of the posterior half of the thoracic surface of
the sternum. The =serous layer= is a closed sac, surrounded by the
fibrous pericardium, and invaginated by the heart. It is smooth and
glistening, and contains a small amount of clear serous fluid, the
=liquor pericardii=. Like other serous membranes, it may be regarded as
consisting of two parts, parietal and visceral. The =parietal part=
lines the fibrous layer, to which it is closely attached. The =visceral
layer= covers the heart and parts of the great vessels, and is therefore
also termed the =epicardium=. The serous pericardium is composed of a
connective-tissue membrane, rich in elastic fibers, and covered on its
free surface by a layer of flat endothelial cells.
The pericardium is covered by the mediastinal pleura (Pleura
pericardica) and is crossed laterally by the phrenic nerves. Its lateral
surfaces are related chiefly to the lungs, but the lower part is in
partial contact with the chest-wall. On the left side the area of
contact is from the third to the fifth intercostal space inclusive. On
the right side the contact is smaller and is at the third and fourth
ribs. The anterior border of the base is opposite to the second
intercostal space, and the posterior border is opposite to the sixth rib
or space. The base is related to the great vessels, the trachea and its
bifurcation, the bronchial lymph glands, the œsophagus, and the vagus,
left recurrent, and cardiac nerves.
The two parts of the serous pericardium are, of course, continuous
with each other at the line of reflection on to the great vessels. The
latter are covered in varying degree by the visceral layer. The aorta
and pulmonary artery are inclosed in a complete common sheath as far
as the bifurcation of the latter. A pouch passes inward between the
pulmonary artery and the left auricle, and is connected with another
pouch which passes backward between the right auricle and the aorta,
thus forming the great transverse sinus of the pericardium. The
posterior vena cava is covered on the right and below for a distance
of an inch or a little more (ca. 3 cm.). The pulmonary veins receive
practically no serous covering. The epicardium is closely adherent to
the muscular tissue of the heart, but is attached to the vessels by
loose tissue and fat, and hence is easily dissected off them.
THE HEART
The =heart= (Cor) occupies the greater part of the middle mediastinal
space. Its shape is that of an irregular and somewhat flattened cone. It
is attached at its base by the great vessels, but is otherwise entirely
free in the pericardium. It presents two surfaces, two borders, a base,
and an apex for description.
[Illustration:
FIG. 419.—HEART OF HORSE, LEFT VIEW. HARDENED _in situ_.
The dotted line indicates the line of reflection of the serous
pericardium. The epicardium and subepicardial fat have not been
removed from the heart.
]
In =position= the heart is decidedly asymmetrical, about two-fifths
being to the right of the median plane and three-fifths to the left. The
long axis (from the middle of the base to the apex) is directed
downward, backward, and somewhat to the left. The =base= (Basis cordis)
is directed dorsally and lies a little above the middle of the
dorso-ventral diameter of the thorax. It is opposite to the ribs from
the third to the sixth inclusive. The =apex= (Apex cordis) lies above
the last segment of the sternum, and is separated by a very short
interval from the sternal part of the diaphragm. The =anterior border=
(Margo cranialis) is strongly convex and is directed obliquely downward
and backward; its lower part is parallel with the sternum. The
=posterior border= (Margo caudalis) is much shorter, nearly vertical,
and is opposite to the sixth rib or intercostal space. The =surfaces=,
=right= and =left= (Facies dextra, sinistra), are convex and are marked
by =grooves= which indicate the division of the heart into four
chambers, the two atria above and two ventricles below. The left surface
(covered by the pericardium) is in contact with the lower third of the
chest-wall from the third to the fifth intercostal space. On the right
side the cardiac notch of the lung is smaller and further forward, so
that the area of contact is at the third and fourth ribs.
[Illustration:
FIG. 420.—HEART OF HORSE, RIGHT VIEW. HARDENED _in situ_.
Line of reflection of serous pericardium dotted. Epicardium and
subepicardial fat have not been removed from heart. Left ventricle
is considerably contracted.
]
The =coronary= or =atrio-ventricular groove= (Sulcus coronarius)
indicates the division between the atria and the ventricles. It almost
completely encircles the heart, but is interrupted by the origin of the
pulmonary artery. The =longitudinal= or =interventricular grooves=,
right and left (Sulci longitudinales sinister et dexter), correspond to
the septum between the ventricles. The left groove is left-anterior in
position. It begins at the coronary groove behind the origin of the
pulmonary artery, and passes downward almost parallel to the posterior
border, but does not reach the apex. The right groove is right posterior
in position. It begins at the coronary groove below the termination of
the posterior vena cava and passes downward and a little backward,
ending about an inch and a half (ca. 3 to 4 cm.) above the apex. The
grooves are occupied by the coronary vessel and a variable quantity of
fat.
[Illustration:
FIG. 421.—BASE OF HEART OF HORSE WITH LARGE VESSELS, DORSAL VIEW.
SPECIMEN HARDENED _in situ_.
]
=Size and Weight.=—In horses of medium size the heart usually weighs
about seven or eight pounds (ca. 3.5 kg.), or about 0.7 per cent. of the
body-weight. There is, however, great range of variation in apparently
normal specimens.
The following measurements were obtained in medium-sized hearts in
diastole:
Sagittal diameter of base 25 cm.
Greatest width of base 18 to 20 cm.
Circumference at coronary groove 65 to 70 cm.
Distance between origin of pulmonary artery and apex 25 cm.
Distance between termination of posterior vena cava and apex 18 to 20 cm.
THE RIGHT ATRIUM
The =right atrium= (Atrium dextrum) or auricle forms the right-anterior
part of the base of the heart, and lies above the right ventricle. It
consists of a =sinus venosus=, into which the veins open, and an
=auricle= or auricular appendix. The latter is a conical diverticulum
which curves around the right and anterior surfaces of the aorta, its
blind end appearing on the left side in front of the origin of the
pulmonary artery.
[Illustration:
FIG. 422.—RIGHT SIDE OF HEART OF HORSE OPENED UP BY REMOVAL OF GREATER
PART OF RIGHT WALL. ORGAN HARDENED _in situ_.
The right ventricle was in diastole. _r_, Intervenous crest; _v_, _v_,
tricuspid valve; _p_, _p_, papillary muscles; _m_, _m_, moderator
bands. Arrow points into origin of pulmonary artery.
]
There are five chief openings in the right atrium. The =opening of the
anterior vena cava= (Ostium venæ cavæ cranialis) is in the upper and
fore part. The =opening of the posterior vena cava= (Ostium venæ cavæ
caudalis) is at the lower posterior part. Between the two the wall
pouches upward somewhat, forming what is sometimes termed the sinus
venosus or sac of Lower. In the anterior part of this the =vena azygos=
opens. The =coronary sinus= opens immediately below the posterior vena
cava; the orifice is provided with a small semilunar valve or valve of
Thebesius (Valvula sinus coronarii). The middle coronary vein has a
separate opening in some cases close to that of the coronary sinus. The
=atrio-ventricular opening= is in the lower part, and leads into the
right ventricle. In addition to the foregoing there are several small
orifices of the venæ cordis parvæ; these are concealed in the
depressions between the musculi pectinati.
The atrium is lined with a glistening membrane, the =endocardium=. Its
walls are smooth except on the right and in the auricle (or appendix),
where it is crossed in various directions by muscular ridges, the
=musculi pectinati=. Small bands extend across some of the spaces
inclosed by the musculi pectinati. The latter terminate above on a
curved crest, the =crista terminales=, which indicates the junction of
the primitive sinus venosus of the embryo with the atrium proper, and
corresponds with the sulcus terminalis externally. The openings of the
venæ cavæ are without valves. A ridge, the intervenous crest,[156]
projects downward and forward from the roof just in front of the opening
of the posterior vena cava; it tends to direct the flow of blood from
the anterior vena cava to the atrio-ventricular opening. The =fossa
ovalis= is an oval depression in the septal wall at the point of
entrance of the posterior vena cava, bounded internally by a thick
margin (Limbus fossæ ovalis). The fossa is the remains of an opening,
the =foramen ovale=, through which the two atria communicate in the
fœtus.
THE LEFT ATRIUM
The =left atrium= (Atrium sinistrum) or auricle forms the posterior part
of the base of the heart. It lies behind the pulmonary artery and the
aorta and above the left ventricle. The auricle (or appendix) extends
outward and forward on the left side, and its blind end is behind the
origin of the pulmonary artery. The =pulmonary veins=, usually seven or
eight in number, open into the atrium behind and on the right side. The
cavity of the atrium is smooth, with the exception of the auricle (or
appendix), in which the musculi pectinati are present. In some cases
there is a depression on the septal wall opposite the fossa ovalis,
bounded above by a fold which is the remnant of the valve of the foramen
ovale of the fœtus. The =atrio-ventricular opening= is situated below
and in front; it usually appears smaller than the right one on account
of the contraction of the left ventricle in the dead subject. The
apertures of small veins of the heart are found in the spaces inclosed
by the musculi pectinati.
The number and the arrangement of the pulmonary veins are variable.
They may be five to nine in number. The largest orifice is posterior.
Usually three veins of considerable size enter close together on the
right above the posterior vena cava, and three or four open close to
the ridge which projects from the roof at the base of the auricle
(appendix).
THE RIGHT VENTRICLE
The =right ventricle= (Ventriculus dexter) constitutes the
right-anterior part of the ventricular mass. It forms almost all of the
anterior border of the heart, but does not reach the apex, which is
formed entirely by the left ventricle. It extends from the third rib to
the fourth intercostal space on the left side, to the fifth rib and
space on the right side. It is somewhat triangular in outline, and is
semilunar in cross-section. Its base faces upward and a little to the
right and is connected largely with the right atrium, with which it
communicates through the atrio-ventricular orifice; but its left part
projects higher and forms the =conus arteriosus=, from which the
pulmonary artery arises. Its apex is two inches or more (ca. 5 to 6 cm.)
above the apex of the heart. On opening the cavity it is seen that the
two openings are separated by a thick rounded ridge (Crista
supraventricularis). The axis of the cavity, taken from this ridge to
the apex forms a spiral curve downward and to the right. The septal wall
is convex and faces obliquely forward and to the right.
[Illustration:
FIG. 423.—SECTION OF HEART OF HORSE.
Specimen hardened _in situ_ and cut nearly at right angles to the
ventricular septum. The left ventricle is contracted, but not _ad
maximum_. _V. a._, Segment of aortic valve.
]
The =right atrio-ventricular orifice= (Ostium venosum dextrum) is oval
and is situated opposite to the lower parts of the third and fourth
ribs. It is guarded by a =tricuspid valve= (Valvula tricuspidalis); of
the three large cusps of this valve, one is between the
atrio-ventricular opening and the conus arteriosus, one is septal, and
the third is on the right margin. Small intermediate cusps intervene
between the large ones. The peripheral edges of the cusps are attached
to the fibrous ring at the atrio-ventricular opening. The central edges
are irregular and hang down into the ventricle; they give attachment to
chordæ tendineæ. The auricular surfaces are smooth. The ventricular
surfaces are rough and furnish attachment to interlacing branches of the
chordæ tendineæ. The valves are folds of the endocardium, strengthened
by fibrous tissue and at the periphery by muscular fibers also. The
=chordæ tendineæ= are attached below to the three =musculi papillares=,
which project from the ventricular wall; superiorly they divide into
branches which are inserted into the ventricular surfaces and the free
edges of the valves. Each segment of the valve receives chordæ tendineæ
from two papillary muscles. Of the latter, two are on the septum and the
third and largest springs from the anterior wall.
The =pulmonary orifice= (Ostium arteriæ pulmonalis) is circular and is
situated at the summit of the conus arteriosus, opposite to the lower
part of the third intercostal space. It is guarded by the =pulmonary
valve=, composed of three semilunar cusps (Valvulæ semilunares arteriæ
pulmonalis); of these, one is internal, one external, and the third
posterior. The convex peripheral border of each cusp is attached to the
fibrous ring at the junction of the pulmonary artery and the conus
arteriosus. The central border is free and slightly concave. Each cusp
consists of a layer of endocardium on its ventricular surface, a
continuation of the inner coat of the artery on its arterial surface,
and an intermediate layer of fibrous tissue. The upper edge of the conus
arteriosus forms three arches with intermediate projecting angles or
horns, to all of which the cusps are attached; and the artery forms
opposite each cusp a pouch, the sinus of the pulmonary artery (or of
Valsalva).
[Illustration:
FIG. 424.—SECTION OF HEART OF HORSE. SPECIMEN HARDENED _in situ_.
The section is cut nearly at right angles to the ventricular septum,
and is viewed from the right and posteriorly.
]
The walls of the ventricle (except in the conus arteriosus) bear
muscular ridges and bands, termed =trabeculæ carneæ=. These are of three
kinds, viz., (1) ridges or columns in relief; (2) musculi papillares,
somewhat conical flattened projections, continuous at the base with the
wall and giving off the chordæ tendineæ to the tricuspid valve; (3)
moderator bands (Musculi transversi cordis) which extend from the septum
to the opposite wall. The latter are partly muscular, partly tendinous,
and vary in different subjects. The strongest one is usually about
midway between the base and apex and extends from the septum to the base
of the anterior musculus papillaris. It is considered that they tend to
prevent overdistention.
THE LEFT VENTRICLE
The =left ventricle= (Ventriculus sinister) forms the left posterior
part of the ventricular mass. It is more regularly conical than the
right ventricle and its wall is much thicker except at the apex. It
forms all of the posterior border of the ventricular part and the apex
of the heart. Its base is largely continuous with the left atrium, with
which it communicates through the left atrio-ventricular opening, but in
front it opens into the aorta. The cavity usually appears smaller than
that of the right ventricle in the dead subject, on account of the
greater contraction of its wall. It is almost circular in cross-section.
[Illustration:
FIG. 425.—THE BASES OF THE VENTRICLES OF THE HEART OF THE HORSE.
The atria have been removed and the aorta and pulmonary artery cut off
short. The left ventricle is contracted. _p.v._, Pulmonary valve;
_a.v._, aortic valve.
]
The =left atrio-ventricular orifice= (Ostium venosum sinistrum) is
opposite to the fifth rib and intercostal space. It is almost circular
and is guarded by the =bicuspid= or =mitral valve= (Valvula
bicuspidalis). The two segments of this valve are larger and thicker
than those of the right side of the heart. One is placed in front and
separates the atrio-ventricular and aortic openings. The other is placed
behind and laterally and is usually divided into two or three flaps.
The =aortic orifice= (Ostium aorticum) is directed upward and slightly
forward. It is situated opposite to the fourth rib. It is guarded by the
=aortic valve=, composed of three semilunar cusps (Valvulæ semilunares
aortæ); one cusp is anterior, the others right and left posterior. They
are similar to those of the pulmonary valve, but are much stronger. The
free edge of each contains a central nodule of fibrous tissue, the
corpus Arantii (Nodulus valvulæ semilunaris).
The =chordæ tendineæ= are fewer but larger than those of the right
ventricle.
There are two large =musculi papillares=, one on each side; they are
usually compound. The moderator bands are variable. Commonly two or
three larger ones (which are often branched) extend from the musculi
papillares to the septum. Smaller ones may be found in various places,
especially at the apex. The other trabeculæ are fewer and less prominent
than in the right ventricle.
The =interventricular septum= (Septum ventriculorum) is the
musculo-membranous partition which separates the cavities of the two
ventricles. It is placed obliquely. One surface is convex, faces forward
and to the right, and bulges into the right ventricle. The other
surface, which faces into the left ventricle, is concave and looks
backward and to the left. The greater part of the septum is thick and
muscular (Septum musculare), but the upper part is thin and membranous
(Septum membranaceum). The latter intervenes between the left ventricle,
on the one hand, and the right ventricle and atrium on the other.
STRUCTURE OF THE HEART
The heart-wall consists mainly of peculiar striped muscle, the
myocardium, which is covered externally by the visceral part of the
serous pericardium or epicardium, and is lined by the endocardium.
The =epicardium= is in general closely attached to the muscular wall,
but is loosely attached over the coronary vessels and the associated
subepicardial fat. It consists of a layer of flat polygonal cells,
resting on a membrane of white and elastic fibers.
The =myocardium= consists of planes of fibers arranged in a somewhat
complicated manner. The muscular tissue of the atria is almost
completely separated from that of the ventricles by the fibrous rings
around the atrio-ventricular orifices.
In the atria the muscle bands fall naturally into two groups—superficial
and deep. The former are common to both atria, the latter special to
each. The =superficial= or =common fibers= for the most part begin and
end at the atrio-ventricular rings, but some enter the interatrial
septum. The =deep= or =special bundles= also form two sets. Looped
fibers pass over the atria from ring to ring, while annular or spiral
fibers surround the ends of the veins which open into the atria, the
auricles, and the fossa ovalis.
The muscular wall of the ventricles is much stronger than that of the
atria. That of the left ventricle is in general about three times as
thick as that of the right one, but is thin at the apex. The
=superficial fibers= are attached above to the atrio-ventricular fibrous
rings and pass in a spiral toward the apex. Here they bend upon
themselves and pass deeply upward to terminate in a papillary muscle of
the ventricle opposite to that in which they arose. The loops so formed
at the apex constitute a whorl, the =vortex cordis=. The =deep fibers=,
although they appear to be proper to each ventricle, have been shown by
MacCallum to be in reality almost all common to both. Their arrangement
is scroll-like. They begin on one side, curve around in the wall of that
ventricle, then pass in the septum to the opposite side, and curve
around the other ventricle. There is a layer of deep fibers which is
confined to the basal part of the left ventricle; it is attached to the
left atrio-ventricular ring.
Four =fibrous rings= (Annuli fibrosi) surround the orifices at the bases
of the ventricles. The atrio-ventricular rings separate the musculature
of the atria from that of the ventricles. Those which surround the
origins of the pulmonary artery and aorta are festooned in conformity
with the attached borders of the valves. The aortic ring contains on the
right side a plate of cartilage (Cartilago cordis), which frequently
becomes more or less calcified in old animals. Sometimes a smaller plate
is present on the left side.
The =endocardium= lines the cavities of the heart and is continuous with
the internal coat of the vessels which enter and leave the organ. Its
free surface is smooth and glistening and is formed by a layer of
endothelial cells. The latter rest on a thin layer of connective tissue,
which is connected with the myocardium by a subendocardial elastic
tissue containing vessels and nerves.
=Vessels and Nerves.=—The heart receives its blood-supply through the
two =coronary arteries= which arise from the aorta opposite to the
anterior and left cusps of the aortic valve. Most of the blood is
returned by the =coronary veins=, which open into the right atrium by
the coronary sinus.[157] A few small veins open directly into the right
atrium, and others are said to open into the left atrium and the
ventricles. The =lymph vessels= form a subepicardial network which
communicates through stomata with the cavity of the pericardium. There
is a less distinct subendocardial network. The vessels converge usually
to two trunks which accompany the blood-vessels in the atrio-ventricular
grooves and enter the glands at the bifurcation of the trachea. The
=nerves= are derived from the =vagus= and =sympathetic= through the
cardiac plexus.
THE ARTERIES
THE PULMONARY ARTERY
The =pulmonary artery= (A. pulmonalis) springs from the conus arteriosus
at the left side of the base of the right ventricle. It curves upward,
backward, and inward, and divides behind the arch of the aorta into
right and left branches. It is related in front to the right auricle
(appendix), behind to the left auricle (appendix), and internally to the
aorta. It is enveloped with the latter in a common sheath of the
visceral layer of the serous pericardium. Near the bifurcation it is
connected with the arch of the aorta by a fibrous band about half an
inch (ca. 1.2 cm.) in width; this is the =ligamentum arteriosum=, a
remnant of the large =ductus arteriosus=, which conducts most of the
blood from the pulmonary artery to the aorta in the fœtus. The artery is
bulbous at its origin, and forms three =sinuses= or pouches, which
correspond to the cusps of the semilunar valve. Beyond this it gradually
diminishes in caliber.
In a horse of medium size the artery is about seven inches (ca. 17 to
18 cm.) long. At the origin it is about two and a half inches (ca. 6
to 6.5 cm.) in width; at the bifurcation its caliber is about one and
a half inches (ca. 3.5 to 4 cm.). The wall is relatively thin,
especially at the origin.
The =right branch= (Ramus dexter) of the pulmonary artery is a little
longer and wider than the left one. It passes over the fore part of the
left atrium and below the bifurcation of the trachea to the hilus of the
right lung, and enters the latter below the right bronchus. In the lung
it passes to the outer and lower side of the stem bronchus and
accompanies it to the base of the organ. The branches correspond to the
ramification of the bronchi. The =left branch= (Ramus sinister) is very
short. It passes backward and enters the lung below the left bronchus.
Its branches within the lung are arranged like that of the right one.
THE SYSTEMIC ARTERIES
The =aorta= is the main systemic arterial trunk. It begins at the base
of the left ventricle and is practically median at its origin. It passes
upward and slightly forward between the pulmonary artery on the left and
right atrium on the right. It then curves sharply backward and upward
and inclines somewhat to the left, forming the =arch of the aorta=
(Arcus aortæ), and reaches the ventral surface of the spine at the
eighth or ninth thoracic vertebra. After passing backward along the
ventral aspect of the bodies of the vertebræ between the lungs it
traverses the hiatus aorticus and enters the abdominal cavity, where it
lies below the vertebral bodies and the psoas minor, just to the left of
the median plane. It divides under the fifth lumbar vertebra into the
two internal iliac or hypogastric arteries.
From the bifurcation a small vessel, the middle sacral artery (A.
sacralis media), sometimes passes backward on the pelvic surface of
the sacrum. It becomes lost in the periosteum or joins the coccygeal
artery, or in exceptional cases is traceable to the sphincter ani
externus.
The caliber of the aorta is greatest at its origin, which is termed the
=bulbus aortæ=. Here it forms three pouch-like dilatations, the =sinuses
of the aorta= (or of Valsalva). These correspond to the cusps of the
aortic valve, and the coronary arteries arise from the left posterior
and anterior sinuses. At the arch the diameter is about two inches (ca.
5 cm.), and beyond this it diminishes gradually in width.
[Illustration:
FIG. 426.—CARDIAC VESSELS OF HORSE, RIGHT SIDE.
Veins are black, arteries white.
]
It is convenient to divide the aorta into thoracic and abdominal parts.
The =thoracic aorta= (Aorta thoracica) lies within the pericardium to
the point of attachment of the ligamentum arteriosum, and is inclosed
with the pulmonary artery in a prolongation of the epicardium. Beyond
this it is between the two pleural sacs. It is crossed on the right by
the œsophagus and trachea, on the left by the left vagus nerve. The left
recurrent nerve winds around the concavity of the arch from left to
right, and the vena azygos and thoracic duct lie along the dorsal part
of its right face. The trachea causes it to deviate to the left; but
beyond this it becomes median. The =abdominal aorta= (Aorta abdominalis)
(Fig. 450) is related above to the lumbar vertebræ, the inferior common
ligament, and the left psoas minor muscle; in the hiatus aorticus it is
related to the cisterna chyli. On its right is the posterior vena cava,
and on its left the left kidney and ureter.
BRANCHES OF THE THORACIC AORTA
1. CORONARY ARTERIES
The two coronary arteries, right and left, are distributed almost
entirely to the heart, but send some small twigs to the origins of the
great vessels.
The =right coronary artery= (A. coronaria dextra) arises from the
anterior sinus of the aorta. It passes forward between the conus
arteriosus and the right auricle (appendix) to the coronary groove, in
which it curves around to the right and backward. It then descends in
the right ventricular groove almost to the apex of the heart.
[Illustration:
FIG. 427.—CARDIAC VESSELS OF HORSE, LEFT SIDE.
The dotted lines indicate part of the left coronary artery which is
concealed by the left auricle.
]
The =left coronary artery= (A. coronaria sinistra) arises from the left
posterior sinus of the aorta, passes to the left behind the origin of
the pulmonary artery, and divides into two branches. The =descending
branch= (Ramus descendens) passes down the left ventricular groove
toward the apex. The =circumflex branch= (Ramus circumflexus) runs
backward in the coronary groove, in which it winds around to the right
side.
2. COMMON BRACHIOCEPHALIC TRUNK OR ANTERIOR AORTA
The =common brachiocephalic trunk= or =anterior aorta= (Truncus
brachiocephalicus communis) is a very large vessel which arises from the
convexity of the arch of the aorta within the pericardium. It is
directed forward and upward. Its length in horses of medium size is
usually about two inches (ca. 5 to 6 cm.), but it is sometimes only half
an inch or less (ca. 1 cm.). It is crossed on the left by the left vagus
and cardiac nerves, and the left recurrent nerve runs between it and the
trachea. It divides opposite to the second intercostal space or third
rib into the brachiocephalic and left brachial arteries.
The =brachiocephalic artery= (A. brachiocephalica) is directed forward
and a little upward in the anterior mediastinum, beneath the trachea.
Opposite the first rib it gives off the bicarotid trunk and is continued
as the =right brachial artery=. The latter (A. subclavia dextra) turns
downward and bends around the anterior border of the first rib and the
insertion of the scalenus muscle above the brachial vein. Its course and
branches beyond this point will be described with the vessels of the
thoracic limb.
[Illustration:
FIG. 428.—TOPOGRAPHY OF THORACIC CAVITY OF HORSE, LEFT SIDE, AFTER
REMOVAL OF LEFT LUNG.
The ninth, fifteenth, and eighteenth ribs are retained. _a_,
Pericardium; _b_, thoracic aorta; _c_, brachiocephalic trunk; _d_,
_d″_, dorsal artery; _d′_, subcostal artery; _e_, _e′_, superior or
deep cervical artery; _f_, vertebral artery; _g_, _g′_, left
brachial artery; _h_, inferior cervical artery; _i_, internal
thoracic artery; _k_, common carotid artery; _l_, jugular vein; _m_,
brachial vein; _m′_, inferior cervical vein; _n_, anterior vena
cava; _o_, thoracic duct; _p_, œsophagus; _q_, costal part of
diaphragm; _q′_, tendinous center of same; _q″_, left crus of same;
_r_, anterior mediastinal lymph glands; _s_, trachea; _t_, bronchial
lymph glands; _u_, root of left lung; _v_, anterior mediastinum;
_v′_, posterior mediastinum; _w_, longus colli; _x_,
sterno-cephalicus; _y_, scalenus; _z_, transversalis costarum; _1_,
longissimus; _2_, splenius; _3_, spinalis et semispinalis; _4_,
_4′_, rhomboideus; _5_, left phrenic nerve; _6_, left vagus; _6′_,
_6″_, œsophageal continuations of vagi; _7_, dorsal branch of right
vagus; _8_, cardiac nerve; _9_, left recurrent nerve; _10_, cervical
trunk of sympathetic; _11_, first thoracic ganglion of sympathetic;
_12_, thoracic trunk of sympathetic; _13_, brachial plexus. (After
Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
The =left brachial artery= (A. subclavia sinistra) is longer than the
right one and rises to a higher level. It forms an almost semicircular
curve, the concavity being ventral. It is related internally to the
œsophagus, trachea, and thoracic duct, and the left vagus, phrenic, and
cardiac nerves cross under its origin. It emerges from the thorax like
the artery of the right side. There is thus a difference at first
between the trunks of opposite sides, but beyond this their course and
distribution are similar.
The brachial and brachiocephalic arteries within the thorax give off the
dorsal, superior cervical, vertebral, and internal thoracic arteries. At
the first rib they give off the external thoracic and inferior cervical
arteries.
1. The left =dorsal= or =dorso-intercostal artery= (A. costo-cervicalis)
passes dorsally across the left face of the trachea and œsophagus toward
the second intercostal space. The right artery arises usually by a
common trunk with the superior cervical, crosses the right face of the
trachea and has no contact with the œsophagus. Both detach small
branches to the trachea, lymph glands, and pleura, and divide on
reaching the longus colli into two branches. Of these the =subcostal
artery= (A. intercostalis suprema) is the smaller. It passes backward
under the costo-vertebral joints with the sympathetic trunk. It gives
off the second, third, and fourth intercostal arteries, and ends at the
fifth space, where it anastomoses with the first aortic intercostal
artery, or constitutes the fifth intercostal artery, or dips into the
longissimus muscle. It also gives off spinal branches and twigs to the
longus colli and the pleura. The other branch (A. transversa colli) is
the direct continuation of the trunk. It emerges through the upper end
of the second intercostal space, passes across the transversalis
costarum and longissimus toward the withers, and divides into several
diverging branches. An anterior branch passes upward and forward between
the splenius and complexus and anastomoses with branches of the superior
cervical artery; the others are directed upward under the serratus
magnus and rhomboideus to the withers, supplying the muscles and skin of
this region.
[Illustration:
FIG. 429.—TOPOGRAPHY OF THORACIC CAVITY OF HORSE, RIGHT VIEW.
The ninth, fifteenth, and eighteenth ribs are retained. _a_,
Pericardium; _b_, posterior vena cava; _c_, vena azygos; _c′_,
œsophageal vein; _d_, _e_, anterior vena cava; _f_, brachial vein;
_g_, inferior cervical vein; _h_, jugular vein; _i_, vertebral vein;
_k_, superior cervical vein; _l_, dorsal vein; _m_, trachea; _n_,
root of right lung; _o_, œsophagus; _p_, mediastinal lobe of right
lung; _q_, mediastinum; _r_, bronchial lymph glands; _s_,
mediastinal lymph glands; _t_, costal part of diaphragm; _t′_,
tendinous center of same; _u_, intercostal muscle; _v_, longus
colli; _w_, posterior deep pectoral muscle; _w′_, anterior deep
pectoral muscle; _x_, superficial pectoral muscle; _y_,
sterno-cephalicus; _z_, scalenus; _1_, _5_, right brachial artery;
_2_, dorso-cervical trunk; _2′_, superior or deep cervical artery;
_3_, dorsal artery (cut); _3′_, subcostal artery; _4_, internal
thoracic artery; _6_, external thoracic artery; _7_, inferior
cervical artery; _8_, bicarotid trunk; _10_, aorta; _11_, œsophageal
artery; _12_, thoracic duct; _13_, right phrenic nerve; _14_,
brachial plexus; _15_, right vagus; _15′_, _15″_, œsophageal
continuations of vagi; _16_, right recurrent nerve; _17_, cervical
trunk of sympathetic; _18_, thoracic trunk of sympathetic; _20_,
inferior cervical ganglion; _21_, first thoracic ganglion of
sympathetic; _22_, right cardiac nerve; _23_, longissimus; _24_,
transversalis costarum; _25_, spinalis; _26_, multifidus; _27_,
ligamentum nuchæ. (After Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
The left dorsal artery sometimes arises with the superior cervical by
a common trunk. On the right side there may be a common stem for the
dorsal, superior cervical, and vertebral arteries. Occasionally the
artery arises from the anterior aorta. Sometimes it emerges through
the third space. The subcostal may arise independently behind the
dorsal or from the superior cervical artery.
2. The =superior= or =deep cervical artery= (A. cervicalis profunda)
arises in front of the dorsal or by a common trunk with it. It crosses
the œsophagus (left side), the trachea (right side), and the longus
colli, and emerges from the thoracic cavity by passing through the space
behind the first costo-transverse articulation. In the thorax it gives
off a small branch (A. mediastini cranialis) to the mediastinum and the
pericardium; also the first intercostal artery (A. intercostalis prima),
a very small vessel which passes down in the first intercostal space.
After leaving the thorax the artery passes upward and forward on the
spinalis muscle and the lamellar part of the ligamentum nuchæ, covered
by the complexus. Its terminal branches anastomose with branches of the
occipital and vertebral arteries in the region of the axis. Numerous
collateral branches are detached to the extensor muscles of the head and
neck, the ligamentum nuchæ, and the skin, and anastomoses occur with the
dorsal artery above and the vertebral artery below.
The artery sometimes emerges through the second intercostal space.
[Illustration:
FIG. 430.—VERTEBRAL ARTERY OF HORSE. (After Schmaltz, Atlas d. Anat.
d. Pferdes.)
]
3. The =vertebral artery= (A. vertebralis) arises from the brachial (or
brachiocephalic) opposite the first intercostal space and passes upward
and forward. On the left side it crosses the œsophagus, on the right the
trachea. Emerging from the thorax it passes between the longus colli
internally and the scalenus externally, under the transverse process of
the seventh cervical vertebra, and continues along the neck through the
series of foramina transversaria, between which it is covered by the
intertransversales colli. Emerging from the foramen of the axis, it
crosses the capsule of the atlanto-axial joint, and joins the retrograde
branch of the occipital artery under cover of the great oblique muscle
of the head. At each intervertebral foramen a =spinal branch= (Ramus
spinalis) is given off which enters the vertebral canal and reinforces
the ventral spinal artery. It also gives off series of dorsal and
ventral =muscular branches= (Rami musculares). The dorsal branches are
the larger; they supply the deep extensor muscles of the head and neck,
and anastomose with the deep cervical and occipital arteries. The
ventral branches supply chiefly the scalenus, longus colli,
intertransversales, and rectus capitis anterior major. The artery is
accompanied by the vertebral vein and a sympathetic nerve-trunk.
In some cases the last cervical transverse process has a foramen
transversarium, through which the artery passes.
4. The =internal thoracic artery= (A. thoracica s. mammaria interna) is
a large vessel which arises from the ventral side of the brachial
opposite the first rib. It curves downward and backward, being at first
on the inner surface of the rib, and then crosses the lower part of the
first intercostal space and passes under the transversus thoracis
muscle. It runs backward under cover of that muscle over the
chondro-sternal joints to the eighth costal cartilage, where it divides
into asternal and anterior abdominal branches. At each intercostal space
two collateral branches are detached. The =intercostal branches= (Rami
intercostales) pass upward in the intercostal spaces and anastomose with
homonymous descending arteries. The lower branches detach small twigs to
the transversus thoracis, pleura, and pericardium, and pass out between
the costal cartilages as =perforating branches= (Rami perforantes) to
supply the pectoral muscles and skin, anastomosing with the external
thoracic artery. A very small pericardiaco-phrenic artery ascends in the
mediastinum on the left side, in the caval fold of pleura on the right
side; it supplies fine twigs to the pericardium and pleura and
accompanies the phrenic nerve to the diaphragm. In the young subject it
gives small branches (Aa. thymicæ) to the thymus gland. The =asternal
artery= (A. musculophrenica) passes along the ninth costal cartilage and
continues along the costal attachment of the transversus abdominis (Fig.
185). It gives off intercostal branches which anastomose with those
descending from the thoracic aorta, and twigs to the diaphragm and
transversus abdominis. The =anterior abdominal artery= (A. epigastrica
cranialis) is the direct continuation of the internal thoracic. It
passes between the ninth costal cartilage and the xiphoid cartilage,
runs backward on the abdominal surface of the rectus abdominis and then
becomes embedded in it (Fig. 466). It supplies the ventral wall of the
abdomen and anastomoses with the posterior abdominal artery.
5. The =external thoracic artery= (A. thoracica externa) is given off
from the ventral aspect of the brachial, usually at the inner surface or
anterior border of the first rib. It turns around the first rib below or
behind the brachial vein (when given off within the thorax) and passes
backward under the deep pectoral muscle; it is continued as a small
vessel in the panniculus carnosus, where it accompanies the external
thoracic (“spur”) vein. It sends branches to the pectoral muscles and
the axillary lymph glands.
This artery varies in origin and size. Not rarely it arises from the
internal thoracic or from the brachial outside of the thorax. In other
cases it arises by a common trunk with the inferior cervical. It may
be very small or even absent, in which case the perforating branches
of the internal thoracic compensate.
6. The =inferior cervical artery= (Truncus omo-cervicalis) arises
usually from the dorsal surface of the brachial opposite the first rib
or where that vessel winds around the rib. It is directed downward and a
little forward across the external surface of the jugular vein and the
deep face of the scalenus among the lymph glands at the thoracic inlet,
and divides into ascending and descending branches. The =ascending
branch= (A. cervicalis ascendens) passes upward and forward along the
external surface of the jugular vein, then turns sharply backward and
runs upward along the anterior border of the anterior deep pectoral
muscle, between the omo-hyoideus and mastoido-humeralis and in relation
to the prescapular lymph glands; it gives branches to these muscles and
the prepectoral and prescapular lymph glands. The =descending branch=
(A. transversa scapulæ) passes downward and outward across the surface
of the anterior deep pectoral and then runs in the groove between that
muscle and the mastoido-humeralis in company with the cephalic vein. It
supplies branches to these muscles and the skin of the breast.
THE COMMON CAROTID ARTERY
These two vessels (Arteriæ carotides communes) arise from the
brachiocephalic artery by a common trunk. This stem, the =truncus
bicaroticus= or =cephalic artery=, is detached from the inner face of
the brachiocephalic opposite the first rib and passes forward in the
median plane beneath the trachea. It is related ventrally to the
prepectoral lymph glands, the terminal parts of the jugular veins, and
the anterior vena cava, and laterally to the vagus and recurrent nerves.
It is commonly two or three inches (ca. 5 to 7 cm.) in length, but it
may vary between one and eight inches (ca. 2.5 to 20 cm.).
[Illustration:
FIG. 431.—VESSELS AND NERVES OF NECK OF HORSE.
_a_, Mastoido-humeralis; _b_, sterno-cephalicus; _c_, omo-hyoideus;
_d_, sterno-thyro-hyoideus; _e_, trachea; _f_, position of
cariniform cartilage; _g_, anterior superficial pectoral muscle;
_h_, scalenus; _i_, intertransversales; _k_, insertion of serratus
cervicis; _l_, origin of trapezius; _m_, rhomboideus; _n_, splenius;
_o_, complexus; _p_, _q_, trachelo-mastoideus; _p′_, _q′_, tendons
of same; _r_, longissimus; _s_, obliquus capitis posterior; _t_,
wing of atlas; _u_, parotid gland; _v_, supraspinatus; _w_, anterior
deep pectoral; _x_, spine of scapula; _y_, prescapular lymph glands;
_1_, external maxillary vein; _2_, _3_, jugular vein; _4_, carotid
artery, exposed by drawing jugular vein aside; _5_, _6_, ascending
and descending branches of inferior cervical artery; _7_, cephalic
vein; _8_, branches of superior or deep cervical artery; _9–14_,
ventral branches of second to seventh cervical nerves; _15_,
branches of dorsal divisions of cervical nerves. (Ellenberger-Baum,
Top. Anat. d. Pferdes.)
]
The =right common carotid artery= passes obliquely from the ventral face
of the trachea to its right side. In this position it runs upward and
forward and divides at the crico-pharyngeus muscle and under the
submaxillary gland into external carotid, internal carotid, and
occipital arteries. It is inclosed in a fibrous sheath, and is
accompanied dorsally by the vagus and sympathetic nerves, ventrally by
the recurrent nerve. At the last two cervical vertebræ it is in contact
superficially with the jugular vein, but further forward the
omo-hyoideus muscle intervenes between the artery and vein. Near its
termination the artery becomes more deeply placed and is related
externally to the submaxillary and parotid glands, internally to the
œsophagus. In some cases it is in contact ventrally with the thyroid
gland, especially when the latter is larger than usual.
The =left common carotid artery= differs from the right one in that it
is related deeply to the œsophagus, which separates it from the trachea
in the greater part of its course.
The collateral branches of the common carotids are in the main small.
They comprise:
1. =Muscular branches= (Rami musculares) of variable size, which go to
the ventral muscles of the neck and the skin.
2. =Œsophageal= and =tracheal branches= (Rami œsophagei et tracheales).
Small twigs go to the cervical lymph glands also.
3. The =parotid artery=. This comes off near the termination and enters
the ventral part of the parotid gland. It also supplies the subparotid
lymph glands, and sometimes sends a branch to the submaxillary gland. It
is inconstant.
4. The =thyro-laryngeal artery= (A. thyreoidea cranialis). This, the
largest collateral branch of the carotid, arises from the latter two or
three inches before it divides. It curves over the anterior end of the
thyroid gland, into which it sends several branches. It gives off a
=laryngeal branch= (A. laryngea), which sends twigs to the external
muscles of the larynx and the constrictors of the pharynx, passes
between the cricoid and thyroid cartilages, and supplies the internal
muscles and the mucous membrane of the larynx. A small =pharyngeal
branch= (A. pharyngea ascendens) runs upward and forward to the
crico-pharyngeus, and supplies twigs to the posterior part of the
pharynx and the origin of the œsophagus. Small innominate twigs are
given off to the trachea, the œsophagus, and the sterno-thyro-hyoideus
and omo-hyoideus muscles.
In some cases the thyroid and laryngeal arteries arise from the
carotid separately or by a short common stem. A laryngeal branch is
often detached from the carotid in front of the thyro-laryngeal and
enters the larynx with the superior laryngeal nerve. The pharyngeal
branch frequently comes directly from the carotid.
[Illustration:
FIG. 432.—CROSS-SECTION OF NECK OF HORSE, PASSING THROUGH FIFTH
CERVICAL VERTEBRA; ANTERIOR VIEW.
_a_, Branches of cervical nerves; _a′_, nuchal fat; _b_,
intertransversalis muscle; _c_, longissimus muscle; _d_, vertebral
artery; _e_, vertebral vein; _f_, vertebral nerve; _g_, spinal
accessory nerve (upper division); _h_, recurrent nerve; _i_,
vago-sympathetic trunk; _k_, tracheal lymph duct; _l_, body of fifth
cervical vertebra; _l′_, transverse process of same; _m_, carotid
artery; _n_, jugular vein; _o_, superior cervical artery; _o′_,
satellite vein of _o_; _p_, spinal cord; _q_, dura mater; _r_,
spinal vein; _s_, ligamentum nuchæ; _t_, rhomboideus muscle; _u_,
splenius; _v_, complexus; _w_, multifidus; _x_, serratus cervicis;
_y_, mastoido-humeralis; _z_, sterno-cephalicus; _1_, rectus capitis
ant. major; _2_, omo-hyoideus; _3_, panniculus; _4_,
sterno-thyro-hyoideus; _5_, longus colli; _6_, _7_,
trachelo-mastoideus; _8_, trapezius; _9_, spinalis; _10_, œsophagus;
_11_, trachea, with cartilaginous ring (_11′_), mucous membrane
(_11″_), and muscular layer (_11‴_). (After Ellenberger, in
Leisering’s Atlas.)
]
5. The =accessory thyroid artery= (A. thyreoidea caudalis) is an
inconstant vessel which arises from the carotid at a variable distance
behind the thyro-laryngeal—sometimes from the latter or from the parotid
artery. It sends branches into the posterior part of the thyroid gland
and detaches small tracheal and muscular twigs. In some cases it is
distributed chiefly or entirely to the adjacent muscles.
THE OCCIPITAL ARTERY
[Illustration:
FIG. 433.—DEEP DISSECTION OF NECK OF HORSE.
_a_, _a_, Ends of sterno-cephalicus; _b_, anterior part of
omo-hyoideus; _c_, sterno-thyro-hyoideus; _d_, trachea; _e_,
œsophagus; _f_, cariniform cartilage; _g_, rectus cap. ant. major;
_h_, stump of trachelo-mastoideus; _i_, intertransversales; _k_,
multifidus; _l_, _m_, scalenus; _n_, serratus cervicis; _o_, _o_,
stumps of splenius, _p_, longissimus, _q_, complexus (most of which
is removed); _r_, rhomboideus; _s_, trapezius; _t_, spinalis et
semispinalis; _u_, lamellar part of lig. nuchæ; _v_,
mastoido-humeralis; _w_, anterior deep pectoral; _x_, supraspinatus;
_y_, anterior superficial pectoral; _z_, scapular tuberosity; _1_,
_1_, articular processes of cervical vertebræ; _2_, _2_, transverse
processes of same; _3_, atlas; _3′_, axis; _4_, _4_, jugular vein
(remainder removed); _5_, common carotid artery, from which a piece
is removed to show the accompanying nerves; _6_, vago-sympathetic
trunk; _7_, _7_, tracheal and muscular branches of carotid artery;
_8_, recurrent nerve; _10_, left tracheal lymph duct; _11_, _12_,
ascending and descending branches of inferior cervical artery
(_13_); _14_, cephalic vein; _15–20_, ventral branches of second to
seventh cervical nerves; _21_, roots of phrenic nerve; _22_,
thoracic or pectoral nerves; _22′_, nerve to serratus magnus; _23_,
musculo-cutaneous nerve; _24_, median nerve; _25_, ulnar nerve;
_26_, radial nerve; _27_, axillary nerve; _28_, dorsal branches of
cervical nerves; _28′_, accessory nerve (cut); _29_, superior or
deep cervical artery; _30_, muscular branch of vertebral artery;
_31_, posterior (anastomotic) branch of occipital artery; _32_,
vertebral artery; _33_, muscular branches of occipital artery; _34_,
obliquus capitis post.; _35_, obi. cap. ant.; _36_, twig from dorsal
branch of third cervical nerve. (After Ellenberger-Baum, Top. Anat.
des Pferdes.)
]
The =occipital artery= (A. occipitalis) is the second in size of the
terminals of the carotid. It arises usually just in front of the
internal carotid, but in some cases with that artery by a common trunk
of variable length. It pursues a somewhat flexuous course to the fossa
atlantis, where it divides into anterior and posterior branches. It is
related superficially to the submaxillary gland and the
mastoido-humeralis, and deeply to the guttural pouch and the rectus
capitis anterior major.[158] The internal carotid artery, the inferior
cerebral vein, and the accessory, vagus, and sympathetic nerves cross
its deep face. It gives twigs to the submaxillary gland, the anterior
straight muscles, the guttural pouch and the adjacent lymph glands, and
two named collateral branches. The =condyloid= or =prevertebral artery=
(A. condyloidea) is a small vessel which passes upward and forward on
the guttural pouch, and divides into muscular and meningeal branches.
The latter enter the cranium through the foramen lacerum and hypoglossal
foramen and are distributed to the dura mater. This artery is very
variable in its origin. The =posterior meningeal= or =mastoid artery=
(A. meningea caudalis) is a much larger vessel which runs upward and
forward between the small oblique muscle and the paramastoid process,
passes through the mastoid foramen into the parieto-temporal canal,
enters the cranial cavity, and is distributed to the dura mater.
[Illustration:
FIG. 434.—VESSELS AND NERVES OF BASE OF BRAIN OF HORSE.
_13_, Cerebro-spinal artery; _14_, middle spinal artery; _15_, basilar
artery; _16_, posterior cerebellar artery; _17_, anterior cerebellar
artery; _18_, internal auditory artery; _19_, posterior cerebral
artery; _20_, deep cerebral artery; _21_, stump of internal carotid
artery; _22_, anterior choroid artery; _23_, anterior meningeal
artery; _24_, middle cerebral artery; _25_, artery of corpus
callosum; _26_, anterior communicating artery; _1_, _1′_, _1″_,
olfactory tracts; _1‴_, olfactory peduncle; _2–12_, cranial nerves;
_a_, olfactory bulb; _b_, trigonum olfactorium; _c_, lamina
perforata anterior; _d_, fossa transversa; _e_, pyriform lobe; _f_,
cerebral peduncle; _g_, tractus transversus; _h_, corpus mammillare;
_i_, tuber cinereum; _k_, lateral fissure (of Sylvius); _l_,
presylvian fissure; _m_, pons; _o_, pyramid; _p_, facial eminence;
_q_, corpus restiforme; _r_, cerebellum; _s_, middle peduncle of
cerebellum. (After Ellenberger Baum, Top. Anat. d. Pferdes.)
]
The =posterior= or =retrograde branch= (Ramus descendens) of the
occipital passes up through the foramen transversarium of the atlas and
joins the vertebral artery. It gives branches to the great oblique
muscle of the head, which covers it.
The =anterior= or =occipital branch= (Ramus occipitalis) passes through
the alar (antero-external) foramen of the atlas and supplies the muscles
and skin of the poll, anastomosing with the deep cervical artery and its
fellow of the opposite side. In the alar furrow it gives off the
=cerebrospinal artery=, which enters the spinal canal through the
intervertebral (antero-internal) foramen of the atlas, perforates the
dura mater, and divides into cerebral and spinal branches. The =cerebral
branch= unites with that of the opposite side to form the =basilar
artery=, and the =spinal branch= similarly forms by union with its
fellow the =middle spinal artery=.
The =basilar artery= (A. basilaris cerebri) passes forward in the median
groove on the ventral surface of the medulla and pons and divides into
the two posterior cerebral arteries. The collateral branches of the
basilar are:
1. Medullary branches (Rami medullares), ten or twelve in number,
distributed to the medulla oblongata.
2. Posterior cerebellar arteries (Aa. cerebelli caudales) which pass
outward around the medulla behind the pons to the cerebellum, to which
they are distributed after giving twigs to the medulla and pons.
3. The small auditory artery (A. auditiva interna) accompanies the
eighth nerve to the internal ear. It often arises from the posterior
cerebellar.
4. Anterior cerebellar arteries (Aa. cerebelli nasales). These are very
variable in number and origin. There are often two or three on either
side and they frequently arise from the posterior cerebrals. They pass
outward in front of the pons and supply the anterior part of the
cerebellum.
The =posterior cerebral arteries= (Aa. communicantes caudales) diverge
at an acute angle and join the posterior communicating branches of the
internal carotid arteries on the inferior surface of the cerebral
peduncles. They are connected by a transverse branch and by a network of
fine twigs which form often a rete mirabile.
THE INTERNAL CAROTID ARTERY (Figs. 434, 436, 437)
This artery (A. carotis interna) is somewhat smaller than the occipital.
It usually arises just behind that artery, crosses its deep face, and
runs upward and forward on the guttural pouch to the foramen lacerum. It
is closely related to the vagus nerve and the superior cervical ganglion
of the sympathetic nerve, fibers from which accompany it. It is crossed
externally by the ninth and twelfth cranial nerves and the pharyngeal
branch of the vagus. It passes through the inferior petrosal sinus and
enters the cavernous sinus, within which it forms an =S=-shaped curve.
It is connected with the opposite artery by a transverse branch (A.
intercarotica), which lies behind the pituitary body in the
intercavernous sinus. A branch (A. caroticobasilaris) sometimes connects
it with the basilar artery. It then perforates the dura mater, gives off
the posterior communicating branch, and passes forward and divides at
the side of the optic chiasma into anterior and middle cerebral
arteries.
The =posterior communicating artery= (A. communicans posterior) turns
backward and joins the posterior cerebral. It gives off the =deep
cerebral artery= (A. cerebri profunda) which winds around the cerebral
peduncle and is distributed chiefly to the mid-brain. A smaller
collateral branch is the anterior choroid artery (A. chorioidea nasalis)
which passes along the optic tract and is distributed in the choroid
plexus of the lateral ventricle.
The =anterior cerebral artery= (A. cerebri anterior) unites with the
corresponding branch of the opposite artery above the optic chiasma.
From this junction proceeds the =artery of the corpus callosum= (A.
corporis callosi), which turns around the genu of the corpus callosum,
enters the great longitudinal fissure, divides into two branches, and is
distributed to the inner aspect of the cerebral hemispheres. A small
=anterior meningeal= branch (A. meningea nasalis) of the anterior
cerebral is distributed to the anterior part of the dura, and assists in
forming a network in the ethmoidal fossa (Rete ethmoidale), anastomosing
with the ethmoidal branch of the ophthalmic artery.
The =middle cerebral artery= (A. cerebri media) passes outward in the
lateral fissure (of Sylvius) and divides into branches on the outer
surface of the hemisphere.
The =arterial circle of Willis= (Circulus arteriosus) (Fig. 434) is
formed at the interpeduncular space of the base of the brain by the
union of the anterior cerebral arteries in front, by the diverging
posterior cerebral arteries behind, and is completed laterally by the
junction of the latter with the posterior communicating arteries and by
the internal carotid. It is irregularly polygonal in outline.
The cerebral arteries are very variable in arrangement, and the
foregoing account is a brief statement of the more usual disposition
of the larger vessels. The internal carotid artery often arises with
the occipital by a common trunk of variable length.
THE EXTERNAL CAROTID ARTERY (Figs. 436, 437)
This artery (A. carotis externa) by its size and direction constitutes
the continuation of the common carotid. It passes forward on the lateral
wall of the pharynx at the lower border of the guttural pouch, covered
by the submaxillary gland and the stylo-maxillaris, digastricus, and
stylo-hyoideus muscles. It then emerges between the stylo-hyoideus and
the great cornu of the hyoid bone, passes upward on the latter parallel
with the posterior border of the lower jaw, and terminates about two
inches (ca. 5 cm.) below the temporo-maxillary articulation by dividing
into superficial temporal and internal maxillary branches. It is crossed
deeply near its origin by the superior laryngeal and pharyngeal branches
of the vagus nerve. Just before its emergence its superficial face is
crossed by the hypoglossal nerve, and the glosso-pharyngeal nerve passes
over its inner surface at the ventral border of the great cornu. The
chief collateral branches are the masseteric, external maxillary, and
posterior auricular. It also furnishes variable branches to the
submaxillary and parotid glands, the guttural pouch, and the pharyngeal
lymph glands, as well as twigs to some adjacent muscles.
1. The =inferior masseteric= or maxillo-muscular artery (A. masseterica
inferior) is given off from the external carotid at its emergence from
beneath the stylo-hyoideus. It passes downward and slightly forward
under cover of the parotid gland and over the tendon of insertion of the
sterno-cephalicus to the posterior border of the mandible and appears on
the masseter muscle, into which it plunges after a short course on its
surface. It gives branches also to the internal pterygoid and
stylo-maxillaris muscles and the parotid gland.
2. The =external maxillary=, =facial=, or =submaxillary artery= (A.
maxillaris externa)[159] arises from the external carotid on the inner
surface of the posterior belly of the digastricus (Fig. 436). It runs
downward and forward on the lateral wall of the pharynx across the deep
face of the stylo-hyoideus toward the great cornu of the hyoid bone,
accompanied by the glosso-pharyngeal nerve in front and the hypoglossal
nerve behind. After giving off the lingual artery at the posterior
border of the great cornu, it inclines more ventrally on the inner
surface of the internal pterygoid muscle, crosses over the hyo-glossus
muscle, the hypoglossal nerve, the submaxillary duct, and the
intermediate tendon of the digastricus, and turns forward in the
submaxillary space. Here it lies on the lower part of the internal
pterygoid muscle, and is related internally to the submaxillary lymph
glands, above to the anterior belly of the digastricus, and below to the
homonymous vein. At the anterior border of the masseter it turns around
the lower border of the jaw and runs upward on the face in front of that
muscle.[160] At the turn the artery is in front, the vein in the middle,
and the parotid duct posterior. The artery and vein pass upward along
the anterior border of the masseter, under cover of the facial
panniculus and the zygomaticus, and are crossed superficially by
branches of the facial nerve and deeply by the parotid duct. The artery
terminates over the levator labii superioris proprius by dividing into
the dorsal nasal and the angular artery of the eye. The chief branches
of the external maxillary are as follows:
(1) The =pharyngeal artery= (A. palatina ascendens) arises usually
behind the stylo-pharyngeus, passes between that muscle and the great
cornu, and runs forward on the lateral wall of the pharynx under the
elastic pharyngeal fascia. It is distributed to the soft palate,
pharynx, and tonsil.
[Illustration:
FIG. 435.—SUPERFICIAL DISSECTION OF HEAD OF HORSE. MOST OF THE
PANNICULUS IS REMOVED.
_a_, Dilatator naris superior; _b_, levator labii superioris proprius;
_c_, levator nasolabialis; _d_, dilatator naris lateralis; _e_,
buccinator; _f_, zygomaticus; _g_, depressor labii inferioris; _h_,
stump of retractor anguli oris; _i_, masseter; _k_, _k_, scutularis;
_l_, scutulo-auriculares superficiales; _m_, zygomatico-auricularis;
_n_, parotido-auricularis; _o_, stylo-maxillaris; _p_,
sterno-cephalicus; _p′_, tendon of _p_; _q_, omo-hyoideus; _r_,
splenius; _s_, tendon of splenius and trachelo-mastoideus; _t_,
corrugator supercilii; _u_, orbicularis oris; _v_, parotid gland;
_w_, zygomatic arch; _x_, scutiform cartilage; _y_, upper commissure
of nostril; _1_, facial nerve; _2_, superior buccal nerve; _3_,
inferior buccal nerve; _4_, transverse facial nerve; _5_, cervical
branch of facial nerve; _6_, posterior auricular branch of second
cervical nerve; _7_, cutaneous cervical branch of same; _8_,
infratrochlear nerve; _9_, frontal nerve; _10_, lacrimal nerve;
_10′_, end of auriculo-palpebral nerve; _11_, inferior masseteric
artery and vein; _12_, transverse facial artery and vein; _13_,
facial artery; _14_, inferior labial artery; _15_, superior labial
artery; _16_, lateral nasal artery; _17_, dorsal nasal artery; _18_,
angular artery of the eye; _19_, posterior auricular artery; _20_,
_21_, jugular vein; _22_, external maxillary vein; _23_, great
auricular vein; _24_, parotid duct; _24′_, origin of same. (After
Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
(2) The =lingual artery= (A. lingualis) is a large branch which diverges
from the parent trunk at an acute angle, runs along the ventral border
of the great cornu of the hyoid bone, and dips under the hyo-glossus
muscle. It then passes across the kerato-hyoideus, turns inward under
the intercornual joint of the hyoid bone, and runs forward in the tongue
between the hyo-glossus and genio-glossus. This part (A. profunda
linguæ) is flexuous and is accompanied by branches of the hypoglossal
and lingual nerves. It is the chief artery of the tongue, and
anastomoses with the opposite artery and the sublingual.
(3) The =sublingual artery= (A. sublingualis) is a smaller vessel which
arises at the anterior extremity of the submaxillary gland (Fig. 436).
It passes forward on the anterior belly of the digastricus between the
ramus of the mandible and the mylo-hyoideus, perforates the latter, runs
along the lower border of the sublingual gland, and ramifies in the
mucous membrane of the anterior part of the floor of the mouth. It
detaches branches to the muscles and skin in the submaxillary space, the
submaxillary lymph glands, and the sublingual gland. It also gives off
the small =submental artery=, which runs forward superficially toward
the lower lip, supplying twigs to the skin and the mylo-hyoideus.
[Illustration:
FIG. 436.—PAROTID, MASSETERIC, AND LINGUAL REGIONS OF HORSE: DEEP
DISSECTION, THIRD LAYER.
_a_, Mylo-hyoideus, anterior part, reflected; _b_, genio-hyoideus;
_c_, genio-glossus; _d_, sublingual gland; _e_, ramus of mandible,
the greater part of which is removed; _e′_, stump of masseter; _f_,
maxillary tuberosity; _g_, great cornu of hyoid bone; _h_, wing of
atlas; _i_, intermediate tendon of digastricus; _i′_, anterior
belly, _i″_, posterior belly of digastricus; _k_, posterior part of
mylo-hyoideus; _l_, hyo-glossus; _m_, pterygoideus internus (cut);
_n_, stylo-hyoideus; _o_, stylo-maxillaris (cut); _p_,
crico-pharyngeus; _q_, obliquus capitis ant.; _r_, tendon of
trachelo-mastoideus; _s_, rectus cap. ant. major; _t_,
mastoido-humeralis (cut); _u_, sterno-cephalicus (cut); _v_,
sterno-thyroideus (cut); _w_, sterno-hyoideus (cut); _x_,
omo-hyoideus; _y_, obliquus cap. post.; _z_, splenius (cut); _1–4_,
upper cheek teeth; _4′_, last cheek tooth; _5_, stump of facial
nerve; _6_, stump of buccinator nerve; _7_, lingual nerve; _7′_,
superficial branch, _7″_, deep branch of lingual nerve; _8_, stumps
of inferior alveolar artery, vein and nerve; _9_, mylo-hyoid nerve
(cut); _10_, glosso-pharyngeal nerve; _11_, hypoglossal nerve; _12_,
superior laryngeal nerve; _13_, ventral branch of first cervical
nerve; _14_, vagus and sympathetic; _15_, dorsal branch of spinal
accessory nerve; _16_, ventral branch of same; _17_, inferior
cerebral vein; _18_, submaxillary duct; _19_, common carotid artery;
_20_, parotid branch; _21_, thyro-laryngeal artery; _22_, pharyngeal
artery; _23_, laryngeal artery; _24_, internal carotid artery; _25_,
occipital artery; _26_, external carotid artery; _27–31_, external
maxillary artery; _28_, posterior palatine artery; _29_, lingual
artery; _30_, sublingual artery; _32_, internal maxillary artery;
_33_, internal maxillary vein (origin); _34_, remnant of parotid
gland; _35_, thyroid gland; _36_, jugular vein; _37_, pharyngeal
lymph glands. (After Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
In some cases the sublingual artery arises from the lingual and the
submental from the external maxillary. Sometimes the sublingual
remains on the external face of the mylo-hyoideus—thus resembling the
submental of man—and the sublingual gland is supplied by a special
branch of the lingual.
Not uncommonly a considerable branch, given off in the submaxillary
space, turns round the lower border of the jaw and enters the middle
of the lower part of the masseter muscle. In some cases this artery is
of large size and its pulsation can be felt. It is accompanied by a
vein.
(4) The =inferior labial artery= (A. labialis inferior) arises from the
facial a little before it reaches the depressor labii inferioris (Fig.
435). It passes forward, dips under the depressor muscle, and continues
to the lower lip. It supplies branches to the muscles and skin in this
region, to the inferior buccal glands, the mucous membrane of the cheek,
and the lower lip, anastomosing with the mental artery and the
corresponding vessels of the opposite side. It detaches a branch (A.
anguli oris) to the angle of the mouth, which anastomoses with the
superior labial.
(5) The =superior labial artery= (A. labialis superior) arises from the
facial in front of the facial crest (Fig. 435). It passes forward under
the dilatator naris lateralis and levator nasolabialis to the upper lip,
gives twigs to the upper part of the cheek and the lateral nasal region,
and ramifies in the upper lip, anastomosing with the opposite artery and
the palato-labial.
(6) The =lateral nasal artery= (A. lateralis nasi) arises usually a
little above the preceding one, and runs forward parallel with it and
under the levator nasolabialis to the nostril (Fig. 435). It supplies
branches to the lateral nasal region and the nostril.
The vessel is often double. It may arise from the superior labial at
the point of bifurcation of the facial or with the dorsal nasal from
the infraorbital artery (as in the ox). In some cases it gives off a
dorsal nasal branch.
(7) The =dorsal nasal artery= (A. dorsalis nasi) arises on the levator
labii superioris proprius and passes forward under the levator
nasolabialis to the dorsum nasi (Fig. 435).
(8) The =angular artery of the eye= (A. angularis oculi) runs toward the
internal canthus of the eye, where it anastomoses with the orbital
branch (Ramus malaris) of the infraorbital artery (Fig. 435).
In addition to the preceding, unnamed branches are supplied to the
submaxillary salivary gland and the submaxillary lymph glands.
3. The =posterior auricular artery= (A. auricularis posterior) arises at
an acute angle from the external carotid just above the origin of the
masseteric. It passes upward under cover of the parotid gland, to which
it gives branches, and divides into several branches which supply the
skin and muscles of the external ear (Fig. 435). The =posterior branch=
passes to the posterior part of the base of the ear, where it divides
into two branches; of these, one (Ramus intermedius) passes up the
convex surface of the external ear to the apex, while the other (Ramus
medialis) winds around to the anterior (inner) border, and forms an arch
with the intermediate branch. The =external branch= (Ramus lateralis)
passes up the posterior (external) border of the ear and forms an arch
with the intermediate branch. The =deep branch= (A. auricularis
profunda) enters the interval between the external auditory canal and
mastoid process, and passes through an opening into the interior of the
external ear and ramifies in the skin which lines it. It gives off the
=stylo-mastoid artery=, which passes through the stylo-mastoid foramen
into the tympanum, forms an arch around the membrana tympani, and
supplies the middle ear and its muscles.
THE SUPERFICIAL TEMPORAL ARTERY
This artery (A. temporalis superficialis) is much the smaller of the two
terminal branches of the external carotid. It passes upward behind the
posterior border of the ramus of the mandible under cover of the parotid
gland, and divides below the level of the condyle into the anterior
auricular and transverse facial arteries. It is crossed superficially by
the facial nerve.
The =anterior auricular artery= (A. auricularis anterior) passes upward
behind the temporo-mandibular articulation under cover of the parotid
gland, crosses the zygomatic arch, and reaches the temporalis muscle. It
is crossed deeply at its origin by the superficial temporal nerve and is
accompanied by a satellite vein and the auriculo-palpebral branch of the
facial nerve. It is distributed to the skin and the temporal and
anterior auricular muscles, and sends a branch through the conchal
cartilage to the skin which lines it. Collateral twigs are detached to
the parotid gland, and an anterior branch anastomoses with the
supraorbital artery. A branch sometimes passes into the parieto-temporal
canal and anastomoses with the posterior meningeal (mastoid) artery.
The =transverse facial artery= (A. transversa faciei) is larger than the
preceding. It turns around the neck below the condyle of the mandible
and emerges from beneath the parotid gland (Fig. 435). It then passes
forward a short distance on the masseter about half an inch below the
zygomatic arch and plunges into the muscle, in which it commonly divides
into two chief branches. It is accompanied by a vein and a branch of the
superficial temporal nerve. It supplies the masseter and the skin of
this region, and anastomoses with the external maxillary and posterior
deep temporal arteries.
[Illustration:
FIG. 437.—DEEP DISSECTION OF HEAD OF HORSE.
The left ramus of the mandible and structures connected with it have
been removed. _a_, _a_, Stumps of stylo-glossus; _b_, genio-glossus;
_c_, genio-hyoideus; _d_, omo-hyoideus; _e_, kerato-hyoideus; _f_,
thyro-hyoideus; _g_, thyro-pharyngeus; _h_, crico-thyroideus; _i_,
sterno-thyroideus; _k_, thyroid gland; _m_, crico-pharyngeus; _n_,
palatinus and palato-pharyngeus; _o_, pterygoideus externus; _p_,
tensor palati; _q_, levator palati; _r_, temporalis; _s_, rectus
cap. ant. major; _t_, obliquus cap. ant.; _u_, guttural pouch; _v_,
great cornu of hyoid bone, posterior extremity of which is removed
and indicated by dotted line; _w_, position of small cornu, dotted
line; _x_, thyroid cornu; _y_, tongue; _z_, anterior pillar of soft
palate; _1_, superficial temporal nerve; _2_, chorda tympani; _3_,
stump of inferior alveolar nerve; _4_, _4_, lingual nerve,
intermediate part removed; _5_, deep temporal nerve; _6_, masseteric
nerve; _7_, buccinator nerve; _8_, great palatine nerve; _9_,
infraorbital nerve; _10_, sphenopalatine and posterior nasal nerves;
_11_, spinal accessory nerve; _12_, vagus; _13_, pharyngeal branch
of vagus; _14_, superior laryngeal nerve; _15_, vago-sympathetic
trunk; _16_, sympathetic, with superior cervical ganglion a little
further back; _17_, glosso-pharyngeal nerve; _18_, pharyngeal and
_19_, lingual branches of glosso-pharyngeal; _20_, hypoglossal
nerve; _21_, left recurrent nerve; _22_, common carotid artery;
_23_, parotid branch; _24_, thyro-laryngeal artery; _24′_, laryngeal
artery; _25_, occipital artery; _26_, internal carotid artery; _27_,
external carotid artery; _28_, _30_, external maxillary artery;
_29_, pharyngeal artery; _31_, lingual artery; _32_, internal
maxillary artery; _33_, stump of inferior alveolar artery; _34_,
middle meningeal artery; _35_, deep temporal artery; _36_,
buccinator artery; _37_, palatine artery; _38_, end of internal
maxillary artery; _39_, right external maxillary artery; _40_,
satellite vein of _39_; _41_, right parotid duct; _42_, submaxillary
lymph glands; _43_, pharyngeal lymph glands; _44_, trachea; _45_,
wing of atlas; _46_, dotted line indicating outline of submaxillary
gland; _47_, lacrimal gland. (After Ellenberger-Baum, Top. Anat. d.
Pferdes.)
]
The pulse may usually be felt in this artery as it passes below the
articulation of the jaw.
THE INTERNAL MAXILLARY ARTERY (Figs. 437, 438, 439)
This artery (A. maxillaris interna) is much the larger of the two
terminal branches of the external carotid. It begins at the inner side
of the posterior border of the mandible about two inches (ca. 5 cm.)
below the articulation of the jaw and ends in the anterior part of the
pterygo-palatine fossa. On account of its complex course and the large
number of branches given off it is convenient to divide it into three
parts.
The =first part= is much the longest, forms an =S=-shaped curve, and is
in great part in contact with the guttural pouch. It passes upward and
forward on the inner surface of the mandible a distance of about an inch
(ca. 2 to 3 cm.) and is related here to the vein, which is ventral. It
then turns inward below the external pterygoid muscle and the inferior
maxillary nerve, passes between that muscle and the tensor palati, and
runs forward to enter the alar (pterygoid) foramen. This part gives off
the following branches:
1. The =inferior alveolar= or =dental artery= (A. alveolaris mandibulæ
s. inferior) passes downward and forward with the homonymous vein and
nerve, being at first between the external and internal pterygoid
muscles, then between the latter and the ramus of the mandible. It
enters the mandibular foramen, passes downward and forward in the
mandibular canal, and terminates at the mental foramen by dividing into
mental and incisor branches. The =mental branch= (A. mentalis) emerges
through the mental foramen and anastomoses in the lower lip with the
opposite artery and the inferior labial. The =incisor branch= continues
forward in the bone, supplies twigs to the canine and incisor teeth, and
anastomoses with its fellow of the opposite side. Collateral branches
are detached to the pterygoid and mylo-hyoid muscles, and within the
bone to the teeth, alveolar periosteum, the gums, and the spongy
substance of the mandible.
2. The =pterygoid arteries=, two or three in number, are distributed to
the pterygoid and tensor and levator palati muscles.
3. The =tympanic artery= is a very small vessel which passes along the
Eustachian tube to the petro-tympanic fissure (of Glaser) and enters the
middle ear.
[Illustration:
FIG. 438.—RIGHT EYE OF HORSE.
_a_, Remnants of periorbita; _b_, levator palpebræ superioris; _c_,
obliquus oculi inferior; _d_, rectus oculi inferior; _e_, rectus
oculi externus; _f_, rectus oculi superior; _g_, sclera; _g′_,
cornea; _h_, lacrimal gland; _i_, frontal nerve; _k_, frontal
artery; _l_, branch of lacrimal nerve to gland; _m_, lacrimal
artery; _n_, zygomatic nerve; _o_, branch of ophthalmic artery; _p_,
branch of oculomotor nerve to obliquus oculi inferior; _q_,
maxillary nerve; _r_, infraorbital nerve; _s_, posterior nasal
nerve; _t_, great palatine nerve; _u_, small palatine nerve; _v_,
internal maxillary artery; _w_, buccinator artery (cut); _x_,
infraorbital artery; _x′_, malar artery; _y_, sphenopalatine artery;
_z_, great palatine artery; _z′_, small palatine (or staphyline)
artery; _1_, posterior deep temporal artery; _2_, _3_, stumps of
orbital margin; _4_, facial crest; _5_, temporal fossa; _6_, foramen
lacerum orbitale; _7_, anterior end of alar canal; _8_, posterior
opening of same. (After Ellenberger, in Leisering’s Atlas.)
]
4. The =middle meningeal artery= (A. meningea media) arises beneath the
buccinator nerve where the internal maxillary turns forward. It passes
backward across the temporal wing of the sphenoid to the antero-external
part (foramen spinosum) of the foramen lacerum. Entering the cranium, it
divides into branches which course in the grooves on the temporal and
parietal bones and supply the dura mater. It anastomoses with the
posterior meningeal.
The size of this artery is variable, and is in inverse ratio to that
of the posterior meningeal.
5. The =posterior deep temporal artery= (A. temporalis profunda
aboralis) arises from the internal maxillary just before the latter
enters the canal of the pterygoid process. It passes upward and backward
in the temporal fossa on the deep face of the temporalis muscle, in
which it ramifies. It sends a branch outward to the masseter, and
anastomoses with the superficial temporal and middle meningeal arteries.
In some cases the tympanic and middle meningeal arise from this
artery.
The =second part= lies in the alar canal and is about an inch (ca. 2 to
3 cm.) in length. It gives off two branches—the anterior deep temporal
and the ophthalmic.
1. The =anterior deep temporal artery= (A. temporalis profunda oralis)
emerges from the canal through the temporal or small alar foramen, and
passes upward in the anterior part of the temporal fossa on the deep
face of the temporalis muscle, in which it is chiefly distributed. It
gives twigs to the orbital fat and the skin of the frontal region.
[Illustration:
FIG. 439.—LEFT EYE OF HORSE, DEEPER DISSECTION.
The outer plate of bone has been removed behind the pterygoid crest to
expose the vessels and nerves. _a_, _a_, Remnants of periorbita;
_b_, stump of rectus oculi superior; _c_, obliquus oculi inferior;
_d_, rectus oculi inferior; _e_, rectus oculi lateralis; _e′_,
retractor oculi; _f_, rectus oculi internus; _g_, _g_, obliquus
oculi superior; _h_, eyeball; _i_, trochlear nerve; _k_, ophthalmic
nerve; _k′_, nasal nerve; _k″_, infratrochlear nerve; _k‴_,
ethmoidal nerve; _l_, optic nerve; _m_, frontal nerve; _n_, lacrimal
nerve; _o_, zygomatic nerve; _p_, nerve to obliquus inferior (from
oculomotor); _q_, maxillary nerve; _r_, infraorbital nerve; _s_,
sphenopalatine nerve; _t_, great palatine nerve; _u_, small palatine
nerve; _v_, internal maxillary artery; _w_, buccinator artery (cut
off); _x_, infraorbital artery; _x′_, malar artery; _y_,
sphenopalatine artery; _z_, great palatine artery; _z′_, small
palatine (or staphyline) artery; _1_, _2_, stumps of zygomatic arch;
_3_, stump of supraorbital process; _4_, facial crest; _5_, temporal
fossa; _6_, ophthalmic artery; _7_, muscular branch of _6_; _8_,
lacrimal artery (cut); _9_, frontal artery; _10_, anterior deep
temporal artery; _11_, ethmoidal artery. (After Ellenberger-Baum,
Top. Anat. d. Pferdes.)
]
2. The =ophthalmic artery= (A. ophthalmica externa) emerges from the
anterior opening of the alar canal, and enters the apex of the
periorbita or ocular sheath. Within this it forms a semicircular bend
under the rectus oculi superior and is continued by the ethmoidal
artery. Its branches are as follows:
(_a_) The =supraorbital= or =frontal artery= (A. supraorbitalis)[161] is
a small vessel which often arises from the anterior deep temporal or the
internal maxillary. It passes along the inner wall of the orbit in
company with the nerve of the same name to the supraorbital foramen,
through which it emerges. It is distributed to the orbicularis oculi,
the corrugator supercilii, and the skin of the supraorbital region.
(_b_) The =lacrimal artery= (A. lacrimalis) runs upward and forward
within the periorbita along the outer edge of the levator palpebræ
superioris to the lacrimal gland, in which it is chiefly distributed. It
also sends twigs to the upper eyelid.
(_c_) =Muscular branches= (Rami musculares) supply the orbital muscles,
the periorbita, the third eyelid, and the conjunctiva.
(_d_) =Ciliary branches= (Aa. ciliares), two sets of very slender
arteries, arise from the ophthalmic direct and from the muscular
branches. The anterior ciliary arteries (Aa. ciliares anteriores) pierce
the sclera in front of the equator and ramify chiefly in the ciliary
body and the iris. The posterior ciliary arteries (Aa. ciliares
posteriores) pierce the posterior part of the sclera; most of them
ramify in the choroid coat as the short ciliary arteries, but two of
larger size, the long ciliary arteries, run forward, one on each side,
between the sclera and choroid to the periphery of the iris. Here they
divide into branches which anastomose and form a circle (Circulus iridis
major). From this secondary branches are detached which form a second
circle around the pupil (Circulus iridis minor).
[Illustration:
FIG. 440.—SAGITTAL SECTION OF HEAD OF HORSE, CUT A LITTLE TO THE RIGHT
OF THE MEDIAN PLANE.
_1_, Skin; _2_, nasal bone; _3_, frontal bone; _4_, parietal bone;
_4′_, tentorium osseum; _5_, occipital bone; _6_, sphenoid bone;
_7_, hard palate; _8_, premaxilla; _9_, mandible; _10_, hyoid bone;
_11_, septum between frontal sinuses; _12_, alar cartilage; _13_,
dilatator naris transversus; _14_, septum nasi with venous plexuses;
_15_, palato-labial artery; _16_, _16′_, upper and lower septal
branches of _15_; _17_, septal branch of sphenopalatine artery and
satellite vein; _18_, septal branch of ethmoidal artery; _19_,
sphenoidal sinus; _20_, guttural pouch; _21_, pharynx; _22_,
pharyngeal orifice of Eustachian tube; _23_, posterior naris; _24_,
soft palate; _25_, palatinus muscle; _26_, pharyngeal muscles; _27_,
œsophagus; _28_, dotted line indicating position of posterior pillar
of soft palate; _29_, lamina; _29′_, arch of cricoid cartilage;
_30_, arytenoideus transversus muscle; _31_, epiglottis; _32_, body
of thyroid cartilage; _33_, vocal process and cord; _34_, arytenoid
cartilage; _35_, lateral ventricle of larynx; _36_, trachea; _37_,
ventral straight muscles of head; _38_, longus colli; _39_, atlas;
_40_, axis; _41_, lig. nuchæ; _42_, dorsal spinal muscles; _43_,
muscles of external ear; _44_, omo- and sterno-hyoideus; _45_,
tongue; _46_, mylo-hyoideus; _47_, genio-hyoideus; _48_,
genio-glossus; _49_, longitudinalis inferior; _50_, longitud.
superior; _51_, hyo-epiglotticus; _52_, chin and mentalis muscle;
_53_, venous plexus of hard palate; _54_, corpus callosum; _55_,
septum pellucidum; _56_, fornix; _57_, thalamus; _58_, pineal body;
_59_, corpora quadrigemina; _60_, cerebral peduncle; _61_, corpus
mammillare; _62_, pituitary body; _63_, chiasma opticum; _64_,
intercarotid artery; _65_, medulla oblongata; _66_, interventricular
foramen; _67_, infundibulum; _68_, third ventricle; _69_, cerebral
aqueduct; _70_, anterior medullary velum; _71_, fourth ventricle;
_72_, posterior medullary velum; _73_, basilar artery; _74_, spinal
cord; _75_, ethmoidal nerve; _76_, septal branch of posterior nasal
nerve; _76′_, branch of same to organ of Jacobson; _77_, olfactory
nerve to organ of Jacobson; _78_, nasal branches of palatine artery.
(After Ellenberger, in Leisering’s Atlas.)
]
(_e_) The =central artery of the retina= (Arteria centralis retinæ) is a
small vessel which arises from the ophthalmic or from a posterior
ciliary artery. It pierces the optic nerve a short distance behind the
sclera and runs in its center to the lamina cribrosa, where it breaks up
in thirty to forty fine branches. These appear in the fundus of the eye
at the margin of the optic papilla and radiate in the posterior part of
the retina.
(_f_) The =ethmoidal artery= (A. ethmoidalis) is the continuation of the
ophthalmic. It enters the cranial cavity through the ethmoidal foramen,
passes inward on the cribriform plate, and divides into meningeal and
nasal branches. The former ramify in the anterior part of the dura mater
and anastomose with branches of the artery of the corpus callosum. The
nasal branch passes through the cribriform plate, gives branches to the
mucous membrane of the lateral mass of the ethmoid and the adjacent part
of the septum nasi, and runs forward on the superior turbinal.
The =third part= passes forward in the pterygo-palatine fossa,
accompanied by branches of the maxillary nerve. On reaching the
posterior palatine foramen it is continued by the palatine artery. Its
branches are as follows:
(1) The =buccinator artery= (A. buccinatoria) arises from the lower
aspect of the internal maxillary shortly after its emergence (Fig. 437).
It turns around the maxillary tuberosity, accompanied by the buccinator
nerve, and under the masseter muscle, enters the cheek, and runs forward
in it. It supplies branches to the cheek, the superior buccal glands,
and the masseter and pterygoid muscles. Near its origin it gives off a
branch to the orbital fat behind the periorbita.
(2) The =infraorbital= or =superior dental artery= (A. infraorbitalis)
arises from the upper aspect of the internal maxillary a little in front
of the preceding vessel. It passes upward and forward to the maxillary
foramen, runs in the infraorbital canal in company with the nerve of the
same name, and is continued forward within the jaw to the incisor teeth.
It gives branches to the teeth and gums, and detaches a branch through
the infraorbital foramen which anastomoses with the lateral nasal and
superior labial. About midway between its origin and the maxillary
foramen it gives off the =malar= or =orbital branch= (Ramus malaris),
which passes along the floor of the orbit to end in the lower lid and
anastomose with the angularis oculi. It gives twigs to the inferior
oblique muscle and the lacrimal sac.
The infraorbital artery is usually small at its emergence upon the
face, but in some cases it is rather large and may partially replace
the superior labial and lateral nasal arteries.
(3) The =staphyline= or =small palatine artery= (A. palatina minor) is a
small vessel which passes forward in the groove at the inner side of the
maxillary tuberosity to the soft palate. In the groove it is accompanied
by the nerve of the same name and the palatine vein.
(4) The =sphenopalatine artery= (A. sphenopalatina) arises in the
extreme anterior part of the pterygo-palatine fossa and passes into the
nasal cavity, where it divides into internal and external branches. The
internal branch is distributed to the mucous membrane of the septum
nasi; the external one goes to the inferior turbinal, the inferior
meatus, the posterior nares, and the maxillary and frontal sinuses. It
may arise from the infraorbital.
(5) The =palatine= or =palato-labial artery= (A. palatina major) is the
direct continuation of the internal maxillary. It passes through the
palatine canal to the roof of the mouth, accompanied by the palatine
nerve, and runs forward in the palatine groove, where it is joined by
the vein. A little behind the plane of the corner incisor teeth it
curves inward over a bar of cartilage to the foramen incisivum, where it
unites with its fellow of the opposite side. The single artery thus
formed passes up through the foramen and divides under the transverse
dilator of the nostril into two branches. These ramify in the upper lip
and anastomose with the lateral nasal and superior labial arteries. In
its course in the roof of the mouth the palatine artery gives off
branches to the hard and soft palate and the gums, and others which pass
through the accessory palatine foramina to be distributed in the mucous
membrane of the lower part of the nasal cavity. Commonly two branches,
right and left, are detached from the convexity of the arch formed by
the union of the two arteries; these run forward in the anterior part of
the hard palate.
ARTERIES OF THE THORACIC LIMB
THE BRACHIAL ARTERY
The =brachial artery=, after turning around the lower border of the
scalenus at the first rib, passes backward and a little downward across
the origin of the coraco-brachialis and the insertion of the
subscapularis muscle at the inner side of the shoulder joint. At the
posterior border of the subscapularis it gives off the subscapular
artery, and turns downward on the inner surface of the arm. In its
course in the arm it inclines a little forward, crosses the humerus very
obliquely, and divides at the antero-internal aspect of the distal third
of the shaft of the bone into the anterior and posterior radial
arteries.[162]
It is related internally to the serratus magnus and the posterior deep
pectoral muscles, and the cubital lymph glands. Externally it lies on
the subscapularis, the brachialis, the insertion of the teres major and
latissimus dorsi, and the inner head of the triceps. The
coraco-brachialis muscle lies along the front of the artery, which,
however, overlaps the muscle distally. The vein crosses the inner face
of the artery and runs down behind it, accompanied part way by the ulnar
and radial nerves. The musculo-cutaneous and median nerves form a loop
around the artery close to its origin, and the latter nerve then passes
down in front of the artery. The chief branches are as follows:
1. The =suprascapular artery= (A. thoracico-acromialis) is a small and
somewhat flexuous vessel, which arises near the anterior border of the
subscapularis, runs upward, and dips in between that muscle and the
supraspinatus. It gives branches to these muscles, the anterior deep
pectoral, and the mastoido-humeralis. A branch passes in front of the
coraco-brachialis to the shoulder joint and the proximal end of the
humerus.
This vessel may be double, or be represented by one or more branches
of the inferior cervical artery.
2. The =subscapular artery= (A. subscapularis) is a very large vessel
which arises at the posterior border of the subscapularis muscle. It
passes upward in the interstice between that muscle and the teres major
on the inner surface of the long head of the triceps, turns around the
posterior border of the scapula below the posterior angle, and ends in
the infraspinatus and deltoid. Besides collaterals (Rami musculares) to
the subscapularis, teres major, triceps, and tensor fasciæ antibrachii
it gives off the following named branches:
(_a_) The =thoracico-dorsal= (A. thoracicodorsalis) is a long artery
which is usually given off about an inch from the origin of the
subscapular, crosses the inner face of the teres major, and runs upward
and backward on the latissimus dorsi. It gives branches to these
muscles, the abdominal panniculus and the axillary lymph glands.
(_b_) The =posterior circumflex artery= (A. circumflexa humeri
posterior) arises a little above the preceding vessel and passes outward
behind the shoulder joint between the long and external heads of the
triceps with the axillary (or circumflex) nerve. It gives branches to
these muscles, the joint capsule, and the muscles and skin of the outer
side of the shoulder, anastomosing with the anterior circumflex artery.
(_c_) The =circumflex artery of the scapula= (A. circumflexa scapulæ)
arises about two or three inches (ca. 5 to 7.5 cm.) above the shoulder
joint, passes forward to the posterior border of the scapula, and
divides into two branches. The outer one runs forward on the external
surface of the scapula below the spine and gives branches to the
supraspinatus, infraspinatus, and teres minor. The inner branch passes
forward in a similar fashion on the costal surface of the scapula and
supplies branches to the subscapularis.
[Illustration:
FIG. 441.—DISSECTION OF SHOULDER AND ARM OF HORSE, INNER SURFACE.
_A_, Brachial artery; _B_, subscapular artery; _C_, thoracico-dorsal
artery; _D_, deep brachial artery; _E_, ulnar artery; _F_, anterior
radial artery; _G_, posterior radial (or median) artery; _H_,
brachial vein; _I_, external thoracic (or “spur”) vein; _J_,
brachial vein; _K_, _K_, _K_, posterior radial veins; _L_, cephalic
vein; _L′_, communicating vein; _M_, brachialis muscle; _N_,
internal epicondyle of humerus; _O_, prescapular lymph glands; _P_,
position of axillary lymph glands; _Q_, position of cubital lymph
glands; _1_, suprascapular nerve; _2_, subscapular nerves; _3_,
thoraco-dorsal nerve; _4_, musculo-cutaneous nerve; _4′_, cutaneous
branch of musculo-cutaneous nerve; _5_, median nerve; _6_, axillary
nerve; _7_, ulnar nerve; _8_, radial nerve; _9_, thoracic nerves.
(After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 442.—DISSECTION OF RIGHT FOREARM AND CARPUS OF HORSE, INTERNAL
SURFACE.
_C.b._, Coraco-brachialis muscle; _E.m._, internal epicondyle of
humerus; _R_, subcutaneous surface of radius. (After Schmaltz, Atlas
d. Anat. d. Pferdes.)
]
3. The =anterior circumflex= (or prehumeral) =artery= (A. circumflexa
humeri anterior) arises usually at the upper border of the teres major.
It passes forward and outward between the two parts of the
coraco-brachialis or between the latter and the humerus. It gives
branches to the coraco-brachialis and deep pectoral and ends in the
upper part of the biceps and in the mastoido-humeralis. It anastomoses
with the posterior circumflex.
Not rarely it arises below the middle of the humerus and passes upward
between the biceps and coraco-brachialis. In these cases a small
branch for the coraco-brachialis is usually given off at the usual
point of origin of the anterior circumflex.
4. The =deep brachial artery= (A. profunda brachii) is a large but short
trunk which arises usually about the middle of the humerus. It passes
backward and divides into several branches which supply the triceps,
tensor fasciæ antibrachii, anconeus, and brachialis. A branch runs in
the musculo-spiral groove with the radial nerve to the front of the
elbow joint and anastomoses with the anterior radial. A slender branch
passes down along the external border of the extensor carpi and supplies
cutaneous twigs. Anastomoses occur with the ulnar and recurrent
interosseous arteries.
The point of origin is inconstant and it is not uncommon to find two
arteries instead. Often a large branch for the posterior deep pectoral
muscle is detached close to the origin or arises from the brachial
directly.
5. =Muscular branches= (Rami musculares) are distributed to the teres
major, deep pectoral, coraco-brachialis, and biceps. The largest and
least variable of these supplies the lower part of the biceps.
6. The =ulnar artery= (A. collateralis ulnaris superior) arises a little
below the nutrient foramen of the humerus and passes downward and
backward along the lower edge of the internal head of the triceps under
cover of the brachial vein and the tensor fascia antibrachii. It gives
branches to these muscles, the posterior superficial pectoral, the
cubital lymph glands, panniculus, and skin. At the internal epicondyle
of the humerus it is joined by the ulnar nerve and turns downward under
the ulnar head of the flexor carpi medius. It continues with the vein
and nerve under the deep fascia of the forearm between the ulnar and
humeral heads of the perforans, and in the distal half of the region
between the external and middle flexors of the carpus. It unites just
above the carpus (under cover of the flexor carpi externus) with a
branch of the radial artery, with which it forms the supracarpal arch.
It detaches small collaterals to the muscles along which it passes and
terminal twigs to the outer surface of the carpus.
7. The =nutrient artery of the humerus= (A. nutritia humeri) is a short
vessel which enters the nutrient foramen of the humerus. It often arises
from the ulnar.
8. The =anterior radial artery= (A. collateralis radialis inferior)
passes downward and a little outward on the anterior face of the humerus
under cover of the biceps and brachialis to the front of the elbow
joint, where it is joined by the radial nerve. It then descends on the
anterior surface of the radius under cover of the anterior extensor of
the digit to the carpus, where it concurs in the formation of the rete
carpi dorsale, anastomosing with the posterior radial and interosseous
arteries. It supplies branches to the elbow joint, the biceps,
brachialis, and the extensors of the carpus and digit. A cutaneous
branch emerges between the distal end of the biceps and the brachialis.
THE POSTERIOR RADIAL ARTERY
The =posterior radial= or =median artery= (A. mediana) is the direct
continuation of the brachial. It passes downward and slightly backward,
at first on the inner surface of the humerus, and then over the capsule
and internal lateral ligament of the elbow joint, under cover of the
posterior superficial pectoral muscle.[163] Below the elbow it dips
under the flexor carpi internus and passes down the inner part of the
posterior surface of the radius. In the distal part of the forearm it
inclines backward and is separated from the radius by the reinforcing
band (Caput tendineum) of the superficial flexor of the digit and is
continued by the large metacarpal artery.
It is accompanied by the median nerve, which lies in front of the artery
at its origin, then crosses over it obliquely at the elbow joint and
becomes posterior. In the arm the brachial vein lies behind and partly
upon the artery; lower down there are usually two satellite veins,
anterior and posterior. The chief collateral branches are as follows:
[Illustration:
FIG. 443.—DISSECTION OF LEFT FOREARM OF HORSE, EXTERNAL SURFACE.
(After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
1. =Articular branches= for the elbow joint.
2. =Muscular branches= to the flexors of the carpus and digit. The
largest of these arise at the proximal third of the forearm.
[Illustration:
FIG. 444.—DEEP DISSECTION OF RIGHT CARPUS OF HORSE, POSTERIOR VIEW.
_1_, Radial carpal bone; _2_, accessory carpal bone; _3_, second
carpal bone. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 445.—CROSS-SECTION OF RIGHT CARPUS OF HORSE.
The soft structures are cut at the level of the radio-carpal
articulation, exposing the proximal row of carpal bones. _Cr_,
Radial carpal bone; _Ci_, intermediate carpal bone; _Cu_, ulnar
carpal bone; _Ca_, accessory carpal bone. (After Schmaltz, Atlas d.
Anat. d. Pferdes.)
]
3. The =common interosseous artery= (A. interossea communis) is a vessel
of considerable size which arises at the level of the interosseous
space, through which it passes. Before entering the space it gives off a
small branch, the volar interosseous (A. interossea volaris), which
descends to the radial head of the perforans. In the space it supplies
the nutrient arteries of the radius and ulna. Emerging from the space it
gives off branches to the flexor carpi externus, a small =recurrent
branch= (A. interossea recurrens) which passes upward on the outer
surface of the ulna and anastomoses with the deep brachial and ulnar
arteries, and is continued as the =dorsal interosseous artery=. This
vessel (A. interossea dorsalis) passes down between the anterior and
lateral extensors of the digit and concurs with the anterior radial in
forming a network on the anterior surface of the carpus, the =rete carpi
dorsale=. From the latter arise two small vessels, the =internal= and
=external dorsal metacarpal arteries= (A. metacarpea dorsalis medialis,
lateralis), which run distally in the grooves between the large and
small metacarpal bones and anastomose with the volar metacarpal
arteries.
4. The =artery of the rete carpi volare= (A. retis carpi volaris) is a
small vessel which arises at the distal third of the forearm and passes
downward to the posterior surface of the carpus, where it concurs with
branches of the volar metacarpal arteries in forming the rete carpi
volare.
5. The =external volar metacarpal artery= (A. metacarpea volaris
lateralis) is a small vessel which arises just above the carpus under
cover of the flexor carpi medius and anastomoses with the ulnar artery,
forming the supracarpal arch. From the latter a branch descends with the
outer branch of the median nerve, inclines outward toward the posterior
border of the accessory carpal bone, and arrives at the head of the
external metacarpal bone. Here it is connected with the internal volar
metacarpal artery, usually by two transverse branches, thus forming the
=deep volar= or =subcarpal arch= (Arcus volaris profundus). One of these
branches lies between the subcarpal check ligament and the suspensory
ligament; the other (not always present) lies beneath the latter on the
large metacarpal bone. A small branch descends to the fetlock with the
external metacarpal nerve. Below the arch the artery pursues a flexuous
course downward on the posterior face of the large metacarpal bone
alongside of the external small metacarpal and under cover of the
suspensory ligament. At the distal third of the metacarpus it commonly
unites with the corresponding vessel of the inner side to form a short
trunk which passes backward through the angle of divergence of the
branches of the suspensory ligament and joins the external digital or
the common digital artery.
[Illustration:
FIG. 446.—CROSS-SECTION OF MIDDLE OF RIGHT METACARPUS OF HORSE.
_a_, Common digital (or large metacarpal) artery; _b_, internal
metacarpal vein; _c_, internal metacarpal nerve; _d_, external
metacarpal nerve; _e_, branch of external volar metacarpal artery;
_f_, external metacarpal vein; _g_, _g_, _g_, deep volar or
interosseous metacarpal arteries; _h_, tendon of anterior extensor;
_i_, tendon of lateral extensor; _k_, anastomotic branch connecting
metacarpal nerves; _l_, deep flexor tendon; _m_, check ligament;
_n_, superficial flexor tendon; _o_, suspensory ligament; _p_, large
metacarpal bone; _q_, _q_, small metacarpal bones; _r_, skin (After
Ellenberger, in Leisering’s Atlas.)
]
6. The =internal volar= or =small metacarpal artery= (A. metacarpea
volaris medialis) is given off from the posterior radial at an acute
angle, usually a little above the external one or by a common trunk with
it. It passes down the inner side of the carpus behind the tendon of the
flexor carpi internus and embedded in the posterior annular ligament.
Arriving at the proximal end of the inner metacarpal bone it becomes
more deeply placed and is connected with the external volar artery by
one or two transverse branches as stated above. It then pursues a
flexuous course downward alongside of the inner small metacarpal bone,
like the corresponding external artery, with which it commonly unites as
described above. It is larger than the external artery and supplies the
nutrient artery to the large metacarpal bone.
The foregoing account describes the most common arrangement of the
dorsal and volar metacarpal arteries. Variations in their origin and
connections are common, but have no great surgical importance.
Collateral branches are omitted for the same reason. In some cases the
internal volar metacarpal is connected with the common digital or
large metacarpal artery a little below the carpus by a branch passing
obliquely across the inner border of the deep flexor tendon; this
forms a superficial volar arch.
THE COMMON DIGITAL ARTERY
[Illustration:
FIG. 447.—DISSECTION OF RIGHT CARPUS, METACARPUS, AND DIGIT OF HORSE,
INNER VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =common digital= or =large metacarpal artery=[164] is the direct
continuation of the posterior radial. It descends in the carpal canal
along the inner side of the flexor tendons in company with the inner
branch of the median nerve and a satellite vein. Continuing down the
limb it preserves this relation to the tendons to the distal third of
the metacarpus, where it inclines toward the middle line of the limb
behind the suspensory ligament, and divides into the internal and
external digital arteries. In the metacarpus the artery is related to
the vein in front and the artery behind, and is covered by the fascia
and skin. It furnishes collateral branches to the suspensory ligament,
the flexor tendons, and the skin.
THE DIGITAL ARTERIES
The =internal= and =external digital arteries= (A. digitalis medialis,
lateralis) are formed by the bifurcation of the common digital at the
distal third of the metacarpus. They diverge, pass down over the outer
surface of the corresponding sesamoid at the fetlock, and descend
parallel with the borders of the deep flexor tendon to the volar grooves
and foramina of the third phalanx. Entering the latter the two arteries
unite in the semilunar canal and form the =terminal arch= (Arcus
terminalis), from which numerous branches pass through the bone to the
wall surface and ramify in the matrix of the wall and sole of the hoof.
A number of branches emerge through the foramina at the lower border,
where they anastomose with each other in arciform fashion. These
branches were named by Spooner the inferior communicating arteries, and
the anastomotic arch formed by them is termed the circumflex artery of
the third phalanx (Chauveau) or the artery of the lower border of the
third phalanx (Leisering).
Each artery is accompanied by a vein and by the digital nerves. Above
the fetlock the artery is most deeply placed and is covered by the vein;
the nerve is behind the vein. At the fetlock the artery has become
superficial and is related to the vein in front and the posterior branch
of the nerve behind. The anterior branch of the nerve crosses over the
artery obliquely to the lateral aspect of the first phalanx. The vessels
and nerves are crossed obliquely by a small tendinous band, the ligament
of the ergot, which begins in the fibrous basis of the ergot at the back
of the fetlock and extends downward and forward to end in the fascia at
the side of the pastern joint.
In addition to branches to the joints, tendons and synovial sheath,
ergot, and skin, the digital arteries give off:
1. The =artery of the first phalanx= or perpendicular artery (A.
phalangis primæ), a short trunk which arises at a right angle about the
middle of the first phalanx, and divides into dorsal and volar branches
(Rami dorsales et volares). The dorsal (anterior) branch passes between
the first phalanx and the extensor tendon and ramifies on the front of
the digit, anastomosing with its fellow. The volar (posterior) branch
dips in between the flexor tendons and the inferior sesamoidean
ligaments and anastomoses with the opposite artery.
2. The =artery of the plantar cushion= (A. toricæ phalangis tertiæ)
arises at the proximal border of the lateral cartilage and passes
backward and downward to ramify in the plantar cushion and the matrix of
the heels and frog.
3. The =dorsal artery of the second phalanx= (Ramus dorsalis phalangis
secundæ) arises a little above the navicular bone, and passes forward
under cover of the lateral cartilage and the extensor tendon to the
front of the second phalanx, where it anastomoses with the opposite
vessel. It gives branches to the skin, the tendon, the coffin joint, and
the coronary matrix of the hoof.
4. The =volar artery of the second phalanx= (Ramus volaris phalangis
secundæ) is smaller than the preceding, opposite to which it arises. It
passes above the proximal border of the third sesamoid and unites with
the opposite artery.
The arteries of the second phalanx form what is termed by Chauveau the
=coronary circle=. The dorsal (anterior) part of the circle gives off
commonly an artery (A. coronalis phalangis tertiæ) near either side of
the extensor tendon, which divides into two branches. The central
branch unites with that of the opposite side, while the other joins a
branch of the artery of the plantar cushion. In this way is formed the
=circumflex artery of the coronary cushion=, an anastomotic arch which
lies on the extensor tendon at the coronet. In some cases descending
branches of the arteries of the first phalanx concur in the formation
of the arch.
5. The =dorsal artery of the third phalanx= or preplantar artery (A.
dorsalis phalangis tertiæ) arises at the deep face of the wing of the
third phalanx, passes outward through the notch or foramen there, and
runs forward in the groove on the wall surface. It gives off ascending
and descending branches, which ramify in the matrix of the wall of the
hoof, anastomosing above with the circumflex artery of the coronary
cushion and below with the circumflex artery of the third phalanx.
Before passing through the wing it detaches a retrograde branch to the
plantar cushion, and after emerging one which ramifies on the outer
aspect of the lateral cartilage.
The terminal part of the digital artery after giving off the preceding
vessel is sometimes termed the plantar.
BRANCHES OF THE THORACIC AORTA
In addition to the coronary arteries and the common brachiocephalic
trunk (which have been described), the thoracic part of the aorta gives
off branches to the thoracic walls and viscera and to the spinal cord
and its membranes. The =visceral branches= (Rami viscerales) are the
bronchial and œsophageal, which arise by a broncho-œsophageal trunk. The
=parietal branches= (Rami parietales) are the intercostal and phrenic
arteries.
1. The =broncho-œsophageal= (Truncus broncho-œsophageus) is a short,
usually bulbous, trunk which arises at the sixth thoracic vertebra from
the aorta or in common with the first aortic intercostal arteries. It
passes (under cover of the vena azygos) down the right face of the aorta
toward the bifurcation of the trachea and divides into bronchial and
œsophageal branches.
(_a_) The =bronchial artery= (A. bronchialis) crosses the left face of
the œsophagus to the bifurcation of the trachea, where it divides into
right and left branches. Each enters the hilus of the corresponding lung
above the bronchus, which it accompanies in its ramification. It
supplies the lung tissue and also detaches twigs to the bronchial lymph
glands and the mediastinum.
(_b_) The =œsophageal artery= (A. œsophagea) (Fig. 429) is a small
vessel which passes backward above the œsophagus in the posterior
mediastinum and anastomoses with the œsophageal branch of the gastric
artery. It detaches twigs to the œsophagus and the mediastinal lymph
glands and pleura, and also gives off two branches which pass between
the layers of the ligaments of the lungs and ramify in the subpleural
tissue. Very commonly there is another artery which runs backward
ventral to the œsophagus.
In some cases there is no broncho-œsophageal trunk, the bronchial and
œsophageal arising separately. In other cases the second aortic
intercostal arises in common with them also.
2. The =intercostal arteries= (Aa. intercostales) (Figs. 428, 429)
number eighteen pairs. The first arises from the deep cervical artery,
the next three from the subcostal branch of the dorsal artery, and the
remainder from the aorta. The aortic intercostals arise from the dorsal
face of the aorta in pairs close together; the fifth and sixth usually
spring from a common stem. Each passes across the body of a vertebra to
the corresponding intercostal space, detaches twigs to the vertebræ and
the pleura, and divides into dorsal and ventral branches. The =dorsal
branch= (Ramus dorsalis) gives off a spinal branch (Ramus spinalis)
which passes through the intervertebral foramen, gives twigs to the
membranes of the spinal cord, perforates the dura, and reinforces the
ventral spinal artery. A muscular branch passes to the muscles and skin
of the back. The =ventral branch= (Ramus ventralis) is much the larger.
It passes downward, at first almost in the middle of the intercostal
space between the intercostal muscles, then gains the posterior border
of the rib and is subpleural. Each is accompanied by a vein and nerve,
the artery being in the middle and the vein in front. At the lower part
of the space it unites with a ventral intercostal branch of the internal
thoracic or the asternal artery. It supplies the intercostal muscles,
the ribs and the pleura, and gives off perforating branches which pass
out to the serratus magnus, the abdominal muscles, and the skin.
3. The =phrenic arteries= (Aa. phrenicæ) are two or three small vessels
which arise at the hiatus aorticus from the ventral aspect of the aorta,
often by a common trunk. They supply the crura of the diaphragm. In some
cases they arise in common with an intercostal artery.
BRANCHES OF THE ABDOMINAL AORTA
The collateral branches of the abdominal part of the aorta are
distributed chiefly to the walls and contents of the abdominal cavity,
but some branches are supplied to the spinal cord and its membranes, and
others extend into the pelvis and to the scrotum. The =visceral
branches= are the cœliac, anterior mesenteric, renal, posterior
mesenteric, and the spermatic or utero-ovarian. The =parietal branches=
are the lumbar arteries.
[Illustration:
FIG. 448.—PLAN OF BRANCHES OF CŒLIAC ARTERY OF HORSE.
_1_, Cœliac artery; _2_, gastric artery; _3_, hepatic artery; _4_,
splenic artery; _5_, posterior gastric artery; _6_, anterior gastric
artery; _7_, œsophageal branch; _8_, gastro-duodenal artery; _9_,
pancreatico-duodenal artery; _10_, right gastro-epiploic artery;
_11_, pyloric artery; _12_, left gastro-epiploic artery; _13_, short
gastric branches of splenic.
]
I. The =cœliac artery= or =axis= (A. cœliaca) is an unpaired vessel,
usually half an inch or less (ca. 1 cm.) in length, which arises from
the ventral aspect of the aorta at its emergence from the hiatus
aorticus. It divides on the dorsal surface of the pancreas into three
branches—the gastric, hepatic, and splenic.
1. The =gastric artery= (A. gastrica sinistra) passes downward and
forward in the gastro-phrenic ligament, gives off œsophageal and
pancreatic branches, and divides above and behind the cardia into
anterior and posterior branches.
(_a_) The =anterior branch= (Ramus cranialis) crosses the lesser
curvature just to the right of the cardia and ramifies on the parietal
surface of the stomach. The branches pursue a flexuous course toward the
greater curvature and anastomose with the short gastric arteries and the
gastric branch of the hepatic artery.
(_b_) The =posterior branch= (Ramus caudalis) is distributed in a
similar fashion on the visceral surface.
(_c_) The =œsophageal branch= (Ramus œsophageus) passes through the
hiatus œsophageus into the thoracic cavity above the œsophagus and
anastomoses with the œsophageal branch of the broncho-œsophageal artery.
[Illustration:
FIG. 449.—PLAN OF CHIEF BRANCHES OF ANTERIOR MESENTERIC ARTERY OF
HORSE.
_1_, Stump of anterior mesenteric artery; _2_, stumps of arteries of
small intestine; _3_, external cæcal artery, _4_, internal cæcal
artery; _5_, ileal artery; _6_, ventral colic artery; _7_, dorsal
colic artery; _8_, middle colic or first artery of small colon.
]
The gastric artery often arises by a common trunk with the splenic.
The two terminal branches may arise separately, or the anterior from
the splenic and the posterior from the hepatic. The œsophageal branch
often arises from the splenic or the posterior gastric.
[Illustration:
FIG. 450.—DISSECTION OF SUBLUMBAR REGION, PELVIC INLET, AND INNER
SURFACE OF THIGH OF HORSE.
_Blood-vessels_: _1_, Aorta; _2_, posterior vena cava; _3_, hepatic;
_4_, gastric; _5_, splenic; _6_, _7_, renal; _8_, anterior
mesenteric; _9_, arteries of small intestine; _10_, ileo-cæco-colic;
_11_, dorsal colic; _12_, artery of small colon; _13_, posterior
mesenteric; _14_, external iliac; _15_, internal iliac; _16_,
circumflex iliac; _17_, _19_, anterior and posterior branches of
_16_; _18_, anastomosis with intercostals; 20, spermatic; _21_,
cremasteric; _22_, lateral sacral; _23_, internal pudic; _24_,
umbilical; _25_, femoral; _26_, deep femoral; _27_, anterior
femoral; _28_, branch to gracilis; _29_, saphenous.
_Lymph vessels and glands_: _a_, Lymph vessels; _b_, lumbar glands;
_c_, internal iliac glands; _d_, external iliac glands; _e_,
precrural glands; _f_, deep inguinal glands (position indicated by
dotted line).
_Nerves and ganglia_: _1_, _2_, Left and right cœliaco-mesenteric
ganglia; _3_, posterior mesenteric ganglion; _4_, connection between
_1_ and _2_; _5_, connection between hepatic and splenic nerves;
_6_, _7_, connections between anterior and posterior mesenteric
ganglia; _8_, splanchnic nerve; _9_, lumbar trunk of sympathetic;
_10_, pelvic branches of posterior mesenteric ganglion; _11_,
internal spermatic nerve; _12_, last thoracic nerve; _13_,
ilio-hypogastric nerve; _14_, anastomosis between _13_ and _15_,
ilio-inguinal nerve; _16_, _17_, cutaneous and muscular branches of
_15_; _18_, _19_, muscular and scrotal branches of external
spermatic nerve; _20_, external cutaneous nerve of thigh; _21_,
femoral nerve; _22_, saphenous nerve; _23_, branch of _22_ to
sartorius.
_A_, Cut surface of obliquus abdominis externus; _B_, cut surface of
obliquus abdominis internus; _C_, depression due to disappearance of
fat in interval between outer border of psoas major and iliacus;
_D_, thick part of iliac fascia which extends from tendon of psoas
minor to external angle of ilium; _E_, superficial fascia of flank;
_F_, internal inguinal ring; _G_, external inguinal ring; _H_,
patella; _I_, femoral canal; _J_, semimembranosus; _K_, suspensory
ligaments of penis; _L_, cross-section of penis; _M_, stump of
spermatic cord; _N_, ilio-psoas; _O_, tensor fasciæ latæ; _P_, _P_,
extremities of external angle of ilium; _Q_, remains of iliac
fascia; _R_, ilio-lumbar ligament or deep layer of lumbo-dorsal
fascia; _S_, line of attachment of gastro-pancreatic fold; _T_,
tendon of right crus of diaphragm; _U_, right crus; _V_, aorta at
hiatus aorticus; _W_, left crus of diaphragm. The position of the
kidneys is indicated by dotted lines. (After Schmaltz, Atlas d.
Anat. d. Pferdes)
]
2. The =hepatic artery= (A. hepatica) is larger than the gastric. It
passes forward to the right and ventrally on the dorsal surface of the
pancreas, covered by the gastro-pancreatic fold, crossing obliquely
under the vena cava, and reaches the inner border of the portal vein. It
divides into three or four branches which enter the portal fissure of
the liver and ramify within the gland with the portal vein and the
hepatic duct. It gives off the following collateral branches:
(_a_) =Pancreatic branches= (Aa. pancreaticæ) are given off as the
artery crosses the pancreas, in which it is partly embedded.
(_b_) The =pyloric artery= (A. gastrica dextra) arises above the first
curve of the duodenum. It descends to the pylorus, sending branches to
the first part of the duodenum and the pylorus, and anastomoses with the
gastric and right gastro-epiploic arteries. It may arise from the
gastro-duodenal.
(_c_) The =gastro-duodenal artery= (A. gastroduodenalis) passes to the
second curve of the duodenum and divides into the right gastro-epiploic
and the pancreatico-duodenal. The =right gastro-epiploic artery= (A.
gastroepiploica dextra) crosses over the posterior surface of the
duodenum and enters the great omentum, in which it runs to the left,
parallel with the greater curvature of the stomach. It gives branches to
the latter and to the omentum and forms an anastomotic arch with the
left gastro-epiploic artery. The =pancreatico-duodenal artery= (A.
pancreaticoduodenalis) divides into pancreatic and duodenal branches.
The former (Ramus pancreaticus) supplies the middle part of the pancreas
and is often replaced by a number of variable twigs. The duodenal branch
(Ramus duodenalis) passes to the right along the lesser curvature of the
duodenum and anastomoses with the first branch of the anterior
mesenteric artery.
3. The =splenic artery= (A. lienalis) is the largest branch of the
cœliac. It passes to the left (with the large satellite vein) on the
left extremity of the pancreas and across the saccus cæcus of the
stomach. Entering the suspensory ligament of the spleen, it runs in the
hilus of the spleen to the apex, beyond which it is continued as the
left gastro-epiploic. It gives off the following branches:
(_a_) =Pancreatic branches= (Rami pancreatici) to the left extremity of
the pancreas.
(_b_) =Splenic branches= (Rami lienales), which plunge into the
substance of the spleen.
(_c_) =Gastric branches= (Aa. gastricæ breves), which pass in the
gastro-splenic omentum to the greater curvature of the stomach, where
they bifurcate and anastomose with the gastric arteries.
(_d_) The =left gastro-epiploic artery= (A. gastroepiploica sinistra) is
the continuation of the splenic artery. It passes to the right in the
great omentum, parallel with the greater curvature of the stomach, and
anastomoses with the right gastro-epiploic. It gives off branches to the
greater curvature of the stomach, and twigs to the omentum.
II. The =anterior= or =great mesenteric artery= (A. mesenterica
cranialis) arises from the ventral face of the aorta at the first lumbar
vertebra. It is a large unpaired trunk, about an inch (ca. 2 to 3 cm.)
in length, which passes ventrally between the vena cava and the left
adrenal into the root of the great mesentery, when it divides into three
branches—left, right, and anterior.[165]
1. The =left branch= gives off at once about fifteen to twenty =arteries
of the small intestine= (Aa. intestinales).[166] These come off close
together and pass in divergent fashion between the layers of the great
mesentery, each dividing into two branches which anastomose with
adjacent branches to form a series of arches. In the anterior part of
the series secondary arches are formed by the union of branches given
off from the primary set of arches. From the convex side of these arches
terminal branches pass to the wall of the small intestine, in which they
ramify and form a vascular network. They are accompanied by satellite
veins and by nerves and lymph vessels. The first artery anastomoses with
the pancreatico-duodenal, and the last with the ileal branch of the
great mesenteric artery. Branches are supplied to the mesenteric lymph
glands.
2. The =right branch= (A. ileo-cæco-colica) might be regarded as the
continuation of the trunk. It runs downward and a little forward and to
the right and gives off the ileal, the two cæcal, and the ventral colic
arteries.
(1) The =ileal= or =ileo-cæcal artery= (A. ilea) passes in retrograde
fashion along the terminal part of the ileum and unites with the last
branch of the left division.
(2) The =external= or =inferior cæcal artery= (Ramus cæcalis lateralis)
passes between the cæcum and the origin of the colon and runs on the
external muscular band of the cæcum to the apex, where it anastomoses
with the internal artery. Besides numerous collaterals to the cæcum, it
gives off the artery of the arch, which passes along the lesser
curvature of the base of the cæcum and runs on the outer face of the
origin of the great colon.
(3) The =internal= or =superior cæcal artery= (Ramus cæcalis medialis)
passes along the inner band to the apex of the cæcum, where it
anastomoses with the external cæcal artery.
(4) The =ventral=, =right=, or =direct colic artery= (A. colica
ventralis) runs along the opposed surfaces of the ventral (first and
second) parts of the great colon to the pelvic flexure, where it unites
with the dorsal colic artery. It supplies the ventral parts of the great
colon and sends a branch to the base of the cæcum.
3. The =anterior branch= divides after a very short course into the
dorsal and middle colic arteries.
(1) The =dorsal=, =left=, or =retrograde colic artery= (A. colica
dorsalis) is a large vessel which passes along the dorsal (fourth and
third) parts of the great colon to the pelvic flexure, where it joins
the ventral colic artery.
(2) The =middle colic artery= or =first artery of the small colon= (A.
colica media) is a much smaller vessel which passes to the origin of the
small colon, enters the colic mesentery, and forms an arch by joining
the first branch of the posterior mesenteric artery close to the lesser
curvature of the bowel. It sends an anastomotic branch to the dorsal
colic artery.
III. The =renal arteries= (Aa. renales), right and left, are relatively
large vessels which arise from the aorta near the anterior mesenteric.
The =right artery= is the longer of the two. It crosses over the dorsal
surface of the vena cava to the right and somewhat forward. At the hilus
it divides into several (five to eight) branches; some of these enter
the gland at the hilus, while others pass to the ventral surface and
enter there. The =left artery= is short and usually arises a little
further back; it passes directly outward to the kidney and is then
disposed like the right one. Small collateral branches are supplied to
the ureters and the adrenals. The latter also receive small vessels
directly from the aorta. The distribution within the kidney has been
described.
Variations in the renal arteries are frequent. Two or more arteries
may occur on one or both sides. Accessory arteries are more common on
the left side and usually enter the posterior pole of the gland. They
may arise from the aorta, the external iliac, or the circumflex iliac
artery.
IV. The =posterior= or =small mesenteric artery= (A. mesenterica
caudalis) is an unpaired vessel which arises from the ventral face of
the aorta at the fourth lumbar vertebra, _i. e._, about five or six
inches (ca. 12 to 15 cm.) behind the origin of the anterior mesenteric
artery. It is much smaller than the latter and supplies the greater part
of the small colon and rectum. It descends in the colic mesentery and
divides into two branches. The anterior branch (A. colica sinistra)
gives off three or four arteries which divide and form anastomotic
arches close to the bowel. The first arch is formed by union with the
middle colic branch of the anterior mesenteric. The posterior branch or
anterior hæmorrhoidal artery (A. hæmorrhoidalis cranialis) passes
backward in the upper part of the mesentery and the mesorectum and
terminates near the anus by anastomosing with the internal pudic artery.
Three or four of its anterior collateral branches form arches.
V. The =spermatic arteries= (Aa. spermaticæ internæ), right and left,
are long slender arteries which arise from the aorta near the posterior
mesenteric and supply the testicle and epididymis. Each passes backward
in a narrow fold of peritoneum (Plica vasculosa) to the internal
inguinal ring and descends through the inguinal canal to the scrotum. In
the canal and scrotum it pursues a very flexuous course in the anterior
border of the spermatic cord, surrounded by the pampiniform plexus of
veins, and associated closely with the spermatic nerves and lymphatics
and unstriped muscle-fibers. It passes between the epididymis and
testicle, runs in flexuous fashion along the attached border of the
latter, turns around the posterior pole, and runs forward on the free
border to the anterior pole. The largest branches arise from its ventral
part, pass tortuously up either side of the gland embedded in the tunica
albuginea, and give off fine branches to the gland substance. Small
collateral branches are detached to the ureter and the spermatic cord.
The =utero-ovarian arteries= in the female correspond to the preceding
vessels, but are much shorter. Each is placed in the anterior part of
the broad ligament of the uterus and divides into ovarian and uterine
branches. The =ovarian branch= (A. ovarica) pursues a flexuous course to
the ovary, which it supplies. The =uterine branch= (A. uterina
cranialis) passes to the concave border of the cornu of the uterus,
which it supplies, anastomosing with the uterine artery.
VI. The =lumbar arteries= (Aa. lumbales) are in series with the
intercostal arteries and have a similar origin and distribution. There
are usually six pairs of lumbar arteries, of which five arise from the
aorta and the sixth from the internal iliac or the lateral sacral at the
junction of the last lumbar vertebra and the sacrum. Each passes across
the body of a lumbar vertebra to the intertransverse space, gives
branches to the sublumbar muscles, and divides into dorsal and ventral
branches. The =dorsal branch= (Ramus dorsalis), the larger of the two,
passes upward to ramify in the extensor muscles of the spine and the
skin of the loins; it gives off a =spinal branch= (Ramus spinalis) which
comports itself like the corresponding branch of an aortic intercostal
artery. The =ventral branch= (Ramus ventralis) runs outward in the
intertransverse space, passes between the transversus and obliquus
internus abdominis, gives branches to these muscles, and ends in the
obliquus externus, the panniculus, and the skin of the flank.
[Illustration:
FIG. 451.—DISSECTION OF PELVIS, THIGH, AND UPPER PART OF LEG OF HORSE,
INTERNAL VIEW.
_L_, Lumbar vessels; _V.c._, posterior vena cava; _A_, aorta
(termination); _C_, sympathetic trunk; _1_, internal iliac artery,
_2_, lateral sacral artery; _3_, middle coccygeal artery; _4_,
lateral coccygeal artery; _5_, umbilical artery (cut off); _6_,
internal pudic artery; _6′_, vesico-prostatic artery; _7_, obturator
artery; _8_, a. profunda penis (from left obturator); _9_, posterior
gluteal (or ischiatic) vessels; _10_, external iliac artery; _11_,
_11′_, deep femoral artery; _12_, prepubic artery; _13_, branch of
deep femoral artery; _14_, great sciatic nerve; _15_, posterior
gluteal nerve; _16_ (above), internal pudic nerve; _16_ (below near
pelvic outlet), suburethral venous plexus; _17_, sacro-coccygeus
inferior; _18_, coccygeus; _19_, recto-coccygeus; _20_, retractor
ani; _21_, _21′_, two heads of obturator internus; _22_, symphysis
pelvis; _23_, prepubic tendon; _24_, suspensory ligament of penis;
_25_, retractor penis muscle; _26_, bulbo-cavernosus muscle; _27_,
urethra (cross-section); _28_, crus penis (cross-section); _29_,
suspensory ligaments of anus (= upper part of retractor penis
muscle); _30_, anal lymph glands; _31_, tibial nerve. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
THE INTERNAL ILIAC ARTERY
The =internal iliac= or =hypogastric arteries= (Aa. hypogastricæ) result
from the bifurcation of the aorta under the fifth or sixth lumbar
vertebra. They diverge at an angle of about 60 degrees, and each passes
backward under the wing of the sacrum, then inclines downward on the
pelvic surface of the shaft of the ilium, and divides a little above the
psoas tubercle into iliaco-femoral and obturator arteries. The chief
branches are as follows:
[Illustration:
FIG. 452.—DISSECTION OF PERINEUM OF HORSE (MALE).
_1_, Bulbo-urethral (Cowper’s) gland; _2_, transversus perinei muscle
(?); _3_, ischio-urethral muscle; _4_, retractor penis muscle; _5_,
bulbo-cavernosus muscle. (After Schmaltz, Atlas d. Anat. d.
Pferdes.)
]
1. The last pair of =lumbar arteries= pass up through the foramina at
the junction of the last lumbar vertebra and the sacrum.
2. The =internal pudic artery= (A. pudenda interna) arises near the
origin of the internal iliac. It passes backward and somewhat downward,
at first along the iliac head of the obturator internus, then above the
superior ischiatic spine on the inner surface of the sacro-sciatic
ligament, perforates the latter and runs for a variable distance in its
substance or on its external face. It then re-enters the pelvic cavity,
passes backward on the retractor ani to the ischial arch, and divides
into the perineal and the artery of the bulb in the male, perineal and
artery of the clitoris in the female. It is accompanied by the internal
pudic nerve. Its chief branches are as follows:
(1) The =umbilical artery= is given off from the internal pudic about an
inch (ca. 2 to 3 cm.) from the origin of that vessel. It is a very large
artery in the fœtus, in which it curves downward and forward at the side
of the bladder in the edge of the umbilical fold of peritoneum, passes
through the umbilical opening, becomes a component of the umbilical cord
and ramifies in the fœtal placenta. After birth it extends only to the
vertex of the bladder and is much reduced. Its lumen is almost
obliterated and its wall is very thick, giving the vessel a cord-like
character, hence it is commonly termed the round ligament of the
bladder.[167] It gives off small =vesical branches= (Aa. vesicates
craniales) to the bladder, and twigs to the prostate and vasa deferens
in the male. In the mare a small branch runs forward along the ureter
into the broad ligament of the uterus.
[Illustration:
FIG. 453.—DISSECTION OF PERINEUM OF MARE.
_1_, Sacro-coccygeus superior; _2_, sacro-coccygeus lateralis; _3_,
intertransversales; _4_, sacro-coccygeus inferior; _5_,
recto-coceygeus; _6_, sphincter ani externus; _6′_, branch
connecting sphincter ani with constrictor vulvæ; _7_, vestibular
bulb; _8_, tuber ischii; _9_, sacro-sciatic ligament. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
(2) The =middle hæmorrhoidal= or =vesico-prostatic artery= (A.
hæmorrhoidalis media) in the male arises usually near the prostate and
runs backward lateral to the rectum. It supplies branches to the rectum,
bladder, urethra, and accessory genital glands. In the female the
homologous vessel is much larger and gives off the =posterior uterine
artery= (A. uterina caudalis). This runs forward on the side of the
vagina, to which it gives branches, and ramifies on the body of the
uterus, anastomosing with the anterior and middle uterine arteries. (In
some cases this artery arises from the internal iliac or the umbilical.)
(3) The =perineal artery= (A. perinei) is relatively small in the male.
It passes upward at the side of the anus, which it supplies, and gives
twigs to the bulbo-cavernosus muscle and the skin of the perineum. In
the female it is large and is distributed to the anus and vulva, and
gives a large branch to the vestibular bulb.
(4) The =artery of the bulb= (A. bulbi urethræ) may be regarded as the
direct continuation of the internal pudic in the male. It lies at the
side of the urethra above the ischial arch, dips under the
bulbo-cavernosus muscle, and ramifies in the corpus spongiosum. Before
doing so it gives off a small branch which turns around the ischial arch
to reach the dorsum penis, and anastomoses with the deep branch of the
obturator.
(4_a_) The =artery of the clitoris= (A. clitoridis) is the homologue in
the female of the preceding vessel, but is much smaller. It passes to
the ventral surface of the vulva with the internal pudic nerve, supplies
the clitoris, and gives twigs to the vulva.
[Illustration:
FIG. 454.-CROSS-SECTION OF TAIL OF HORSE.
_1_, Dorso-lateral coccygeal vessels and nerve; _2_, ventro-lateral
coccygeal artery and nerve; _3_, middle coccygeal artery; _4_,
sacro-coccygeus superior; _4′_, sacro-coccygeus lateralis; _5_,
_5′_, intertransversales; _6_, sacro-coccygeus inferior; _7_,
recto-coccygeus; _8_, coccygeal fascia; _9_, fibro-cartilage between
fourth and fifth coccygeal vertebra. The veins are black.
]
3. The =lateral sacral artery= (A. sacralis lateralis) arises at the
lumbo-sacral articulation (Fig. 451). It passes backward under the wing
of the sacrum, then along the pelvic surface of the bone below the
inferior sacral foramina and the nerves emerging from them, and is
continued by the lateral coccygeal artery. The branches are as follows:
(1) =Spinal branches= (Rami spinales) enter the vertebral canal through
the foramen between the last lumbar vertebra and the sacrum and through
the ventral sacral foramina. They give off branches to the spinal cord
and its membranes which reinforce the ventral spinal artery, and others
which emerge through the dorsal sacral foramina and supply the muscles
and skin of the croup.
(2) The =middle coccygeal artery= (A. coccygea) is an unpaired vessel
which arises from the right or left lateral sacral or from a lateral
coccygeal artery. It passes backward on the pelvic surface of the sacrum
to the median line and continues in that position along the tail between
the depressor muscles, supplying these and the skin.
[Illustration:
FIG. 455.—DISSECTION OF PELVIS, THIGH, AND LEG OF HORSE, EXTERNAL
VIEW.
_1_, Dorsal branches of last intercostal and first three lumbar
nerves; _2_, cutaneous branch of fourth lumbar nerve; _3_, ventral
branches of last intercostal nerve: _4_, branches of
ilio-hypogastric nerve; _5_, superficial branch of ilio-inguinal
nerve; _6_, great sciatic nerve; _7_, _8_, nerves to biceps femoris
(from posterior gluteal nerve); _9_, nerve to semitendinosus (from
same); _10_, posterior cutaneous nerve of thigh; _11_, internal
pudic nerve; _12_, anterior gluteal vessels and nerves; _13_,
posterior gluteal (or ischiatic) vessels; _14_, branches of
obturator vessels; _15_, proximal muscular branches of great sciatic
nerve to biceps femoris, semitendinosus, and semimembranosus; _16_,
nerve to tensor fasciæ latæ (from anterior gluteal nerve); _17_,
gluteus profundus; _18_, stump of gluteus medius; _19_, gemellus;
_20_, trochanter major; _21_, stump of biceps femoris; _22_,
sacro-coccygeus superior; _22′_, sacro-coccygeus lateralis; _23_,
coccygeus; _24_, sacro-coccygeus inferior; _25_, line of fusion of
aponeuroses of internal and external oblique muscles of abdomen;
_25′_, aponeurosis of external oblique muscle (lamina iliaca); _26_,
branches of iliaco-femoral vessels; _27_, ilio-lumbar vessels; _28_,
ilio-lumbar ligament or deep layer of lumbo-dorsal fascia; _29_,
external angle of ilium; _30_, internal angle of ilium; _31_,
lateral sacro-iliac ligament; _32_, sacro-sciatic ligament. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
(3) The =posterior gluteal= or =ischiatic artery= (A. glutea caudalis)
emerges through the upper part of the sacro-sciatic ligament and runs
backward and downward on the latter under cover of the biceps femoris
(Fig. 455). It gives branches to that muscle and to the semitendinosus
and semimembranosus, and anastomoses with the obturator, deep femoral,
and posterior femoral arteries.
(4) The =lateral coccygeal artery= (A. caudalis lateralis ventralis)
continues the direction of the lateral sacral, but is much smaller than
the preceding vessel. It passes back between the depressor and
intertransversales muscles of the tail and divides into two branches
which supply twigs to the muscles and skin.
4. The =ilio-lumbar artery= (A. iliolumbalis) arises at a right angle
from the internal iliac and runs outward behind the sacro-iliac joint,
crossing the ventral surface of the ilium under cover of the iliacus
muscle. It gives branches to the ilio-psoas and longissimus, and
terminates by turning around the external border of the ilium a little
behind the external angle, giving branches to the gluteus medius and
tensor fasciæ latæ (Fig. 455).
[Illustration:
FIG. 456.—DEEP DISSECTION OF VENTRAL WALL OF PELVIS OF HORSE (MALE).
_1_, External pudic artery and small satellite vein; _2_, anastomosis
between external pudic and internal circumflex veins; _3_, accessory
ligament; _4_, round ligament; _5_, transverse ligament; _6_, head
of femur; _7_, obturator externus (stumps); _8_, inner margin of
obturator foramen; _9_, origin of gracilis; _10_, origin of
adductor; _11_, bulbo-cavernosus; _12_, retractor penis; _13_,
suspensory ligament of penis. (After Schmaltz, Atlas d. Anat. d.
Pferdes.)
]
5. The =anterior gluteal artery= (A. glutea cranialis) is the largest
branch of the internal iliac. It arises usually opposite to the
preceding vessel and passes outward through the great sacro-sciatic
foramen, dividing into several branches as it emerges; these enter the
gluteal muscles (Fig. 455).
6. The =iliaco-femoral= or =external circumflex artery= (A. cireumflexa
femoris lateralis) passes downward and outward across and beneath the
shaft of the ilium, under cover of the iliacus muscle, and dips in
between the rectus femoris and vastus externus. It is accompanied by two
satellite veins. It gives collateral branches to the ilio-psoas, the
glutei, and the tensor fasciæ latæ, supplies the nutrient artery of the
ilium, and terminates in the quadriceps femoris (Fig. 455).
7. The =obturator artery= (A. obturatoria), the inner terminal branch of
the internal iliac, passes downward and backward on the pelvic surface
of the shaft of the ilium along the ventral border of the iliac head of
the obturator internus, accompanied by the satellite vein and nerve,
which lie in front of the artery (Fig. 451). On reaching the anterior
border of the obturator foramen it dips under the obturator internus and
passes obliquely through the foramen. In this part of its course it
gives off a vesical branch and twigs to the obturator internus and the
hip joint. After its emergence from the pelvic cavity it runs backward
on the ventral face of the ischium, passes through the semimembranosus
and, in the male, enters the crus penis, forming the arteria profunda
penis. It anastomoses with the internal pudic, and usually with the
external pudic by a branch which runs forward on the dorsum penis. Large
collateral branches are detached to the adductors of the thigh, the
biceps femoris and semitendinosus, forming anastomoses with the deep
femoral and posterior femoral arteries. In the female the terminal part
is small and enters the root of the clitoris.
ARTERIES OF THE PELVIC LIMB
The main arterial trunk of each pelvic limb descends as far as the lower
border of the popliteus muscle, where it divides into the anterior and
posterior tibial arteries. The different parts of the trunk receive
special names which correspond to the several regions through which it
passes. In the abdomen it is termed the =external iliac artery=, in the
proximal two-thirds of the thigh it is called the =femoral artery=,
while below this it is termed the =popliteal artery=.
THE EXTERNAL ILIAC ARTERY (Figs. 450, 451)
The =external iliac artery= (A. iliaca externa) arises from the aorta
under the fifth lumbar vertebra, usually just in front of the origin of
the internal iliac. It descends at the side of the pelvic inlet along
the tendon of the psoas minor, crosses the insertion of that muscle, and
reaches the level of the anterior border of the pubis, where it becomes
the femoral artery. It is covered by the peritoneum and fascia, and is
related behind to the corresponding vein. Its branches are as follows:
1. The =circumflex iliac artery= (A. circumflexa ilium profunda) arises
from the external iliac at its origin or from the aorta directly. It
passes across the iliac fascia toward the external angle of the ilium,
near which it divides into two branches. The artery lies between the
fascia and the peritoneum and is accompanied by two veins and the
external cutaneous nerve of the thigh. The =anterior branch= gives twigs
to the iliacus and psoas muscles, and passes downward and forward in the
flank between the obliquus internus and transversus abdominis, in which
it ramifies. The =posterior branch= perforates the abdominal wall and
runs downward on the inner face of the tensor fasciæ latæ to the fold of
the flank, supplying branches to that muscle, the panniculus, the
precrural lymph glands, and the skin.
2. The =cremasteric artery= (A. spermatica externa) is a very small
vessel which arises in a variable manner. It springs most often from the
external iliac near its origin, but may come from the circumflex iliac,
the aorta between the external and internal iliac, or the latter vessel.
It accompanies the cremaster muscle to the inguinal canal, supplies
twigs to that muscle, the tunica vaginalis, and other constituents of
the spermatic cord (Fig. 450).
2_a_. The =middle uterine artery= (A. uterina media) of the female is
regarded as the homologue of the preceding vessel. It has a similar
origin, but is a much larger artery, which passes between the layers of
the broad ligament and reaches the horn of the uterus close to its
junction with the body. It is distributed to both, and anastomoses with
the anterior and posterior uterine arteries.
THE FEMORAL ARTERY (Figs. 450, 451)
The =femoral artery= is the main arterial trunk of the thigh. It begins
at the level of the anterior border of the pubis, from which it is
separated by the femoral vein. It descends almost vertically in the
femoral canal behind the sartorius muscle, covered at first by the
internal femoral fascia and lower down by the gracilis. After passing
over the insertion of the pectineus, it perforates the adductor muscle,
crosses in the vascular groove of the posterior surface of the femur,
and is continued between the two heads of the gastrocnemius as the
popliteal artery. It is related at its origin to the sartorius in front,
the femoral vein behind (which separates it from the pectineus), and the
iliacus externally. Lower down it is related superficially to the deep
inguinal lymph glands, and deeply to the vastus internus, while the
saphenous nerve is in front of it, and the vein passes to its external
face. The chief branches are as follows:
[Illustration:
FIG. 457.—DISSECTION OF INGUINAL REGION AND INNER SURFACE OF THIGH OF
HORSE.
_1_, External pudic artery; _2_, anterior branches of _1_; _3_,
posterior branches of _1_; _4_, transverse anastomosis between
external pudic veins; _4′_, venous plexus of dorsum penis; _5_,
femoral artery; _6_, saphenous nerve; _7_, anterior border of
external inguinal ring; _8_, obliquus abdominis internus; _9_,
posterior border of external inguinal ring; _10_, tunica vaginalis;
_11_, vas deferens; _12_, cremaster muscle; _13_, prepuce; _14_,
glans penis; _15_, external urethral orifice; _16_, posterior
branches of circumflex iliac vessels; _17_, saphenous vessels; _18_,
fold of flank; _19_, penis (cut); _A_, superficial inguinal lymph
glands; _B_, precrural lymph glands; _C_, deep inguinal lymph
glands. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
1. The =prepubic artery= (Truncus pudendo-epigastricus) arises from the
femoral artery at its origin, usually by a common trunk with the deep
femoral. It passes forward and a little inward and downward across the
edge of the inguinal ligament, and then runs on the abdominal surface of
the ligament to the inner part of the internal inguinal ring, where it
divides over the upper border of the internal oblique muscle into the
posterior abdominal and external pudic arteries.
(1) The =posterior abdominal artery= (A. epigastrica caudalis) passes
along the external border of the rectus abdominis and anastomoses in the
umbilical region with the anterior abdominal artery (Figs. 272). It
supplies branches to the rectus and obliquus internus muscles.
(2) The =external pudic artery= (A. pudenda externa) descends on the
inguinal ligament through the inner part of the inguinal canal and
emerges at the inner angle of the external ring. In the male it divides
into the =subcutaneous abdominal artery= and the =dorsal artery of the
penis=. The former runs forward a short distance from the linea alba,
and gives branches to the superficial inguinal lymph glands, the sheath,
and the scrotum. The latter passes to the dorsum penis and ends at the
glans as the arteria glandis. It gives off collateral branches (Rami
profundi penis) to the corpus cavernosum, one of which usually passes
backward and anastomoses with a branch of the obturator artery. Branches
are also supplied to the superficial inguinal lymph glands, the prepuce,
and the scrotum. In the female the =mammary artery= takes the place of
the dorsal artery of the penis; it plunges into the base of the mammary
gland.
2. The =deep femoral artery= (A. profunda femoris) arises either by a
common trunk with the prepubic or a little distal to it (Fig. 451). It
passes backward and downward across the inner face of the femoral vein,
then below the pubis in the space between the hip joint and the
pectineus muscle. On reaching the obturator externus it inclines more
ventrally and outward, passes out between the internal border of the
femur and the quadratus femoris, and ramifies in the biceps femoris and
semitendinosus. It supplies large collateral branches to the adductor
muscles and twigs to the deep inguinal lymph glands and the hip joint.
3. The =anterior femoral artery= (A. femoralis cranialis) arises a
little distal to the preceding vessel from the opposite side of the
femoral trunk. It passes forward, outward, and a little downward across
the deep face of the sartorius, and dips in between the rectus femoris
and vastus internus (Fig. 451). It is related externally to the
ilio-psoas and the femoral nerve.
In some cases this artery is replaced by a large branch of the
external circumflex, which passes between the ilio-psoas and rectus
femoris and enters the interstice between the latter muscle and the
vastus internus.
4. Innominate =muscular branches= (Rami musculares) of variable size and
arrangement are given off to the muscles of this vicinity.
5. The =saphenous artery= (A. saphena) is a small vessel which arises
from the femoral about its middle or from a muscular branch, and emerges
between the sartorius and gracilis or through the latter to the inner
surface of the thigh (Fig. 457). It is joined by the large saphenous
vein and the saphenous nerve and passes down superficially on the fore
part of the gracilis, continues on the deep fascia of the leg, and
divides above the hock into two branches, which accompany the radicles
of the vein. It gives off cutaneous twigs and anastomoses with the
recurrent tibial artery.
In some cases this anastomosis does not occur. The artery may be
larger and directly continuous with the internal tarsal artery.
6. The =articular branch= (A. genu suprema) is a slender artery which
arises from the femoral just before it passes through the adductor. It
descends along the posterior border of the vastus internus to the inner
surface of the stifle joint, where it ramifies.
7. The =nutrient artery of the femur= (A. nutritia femoris) is given off
at the middle of the femur and enters the nutrient foramen.
8. The =posterior femoral= or =femoro-popliteal artery= (A. femoris
caudalis) is a large vessel which arises from the posterior face of the
femoral just before the trunk passes between the two heads of the
gastrocnemius (Fig. 455). It is very short and divides into two
branches. The ascending branch passes upward and outward between the
adductor (in front) and the semimembranosus (behind), and enters the
biceps femoris, in which it ramifies. The descending branch passes
downward and backward on the external head of the gastrocnemius, then
curves upward between the biceps femoris and semitendinosus (crossed
externally by the tibial nerve) and divides into branches to these
muscles. A branch is detached from the convexity of the curve which
passes down between the heads of the gastrocnemius, gives branches to
that muscle and the flexor perforans, and is continued by a slender
artery which accompanies the tibial nerve and unites with the recurrent
tibial artery. A branch ascends alongside of the sciatic nerve between
the biceps and semitendinosus and anastomoses with a descending branch
of the obturator.
THE POPLITEAL ARTERY
This artery (A. poplitea) is the direct continuation of the femoral. It
lies between the two heads of the gastrocnemius, at first on the
posterior face of the femur, then on the femoro-tibial joint capsule. It
then passes down through the popliteal notch under cover of the
popliteus, inclines outward, and divides near the upper part of the
interosseous space into anterior and posterior tibial arteries. The
satellite vein lies along its inner side. Collateral branches are
supplied to the stifle joint and the gastrocnemius and popliteus.
POSTERIOR TIBIAL ARTERY
The =posterior tibial artery= (A. tibialis posterior) is much the
smaller of the two terminals of the popliteal. It lies at first between
the tibia and the popliteus, then between that muscle and the deep and
inner heads of the deep flexor. Lower down it descends along the tendon
of the inner head, becomes superficial in the distal third of the leg,
and passes behind the tendon. At the level of the tuber calcis it forms
an ᔕ-shaped curve, runs downward along the deep flexor tendon
accompanied by the plantar nerves, and divides at the lower part of the
hock into internal and external plantar arteries. The collateral
branches are as follows:
1. The =nutrient artery of the tibia= (A. nutritia tibiæ).
2. =Muscular branches= (Rami musculares) to the popliteus and deep
flexor.
3. The =external tarsal artery= (A. tarsea lateralis) arises at the
distal end of the leg and is distributed to the outer surface of the
hock. It gives off a small recurrent branch which ascends along the
external border of the gastrocnemius tendon and anastomoses with a
branch of the posterior femoral artery.
4. The =recurrent tibial artery= (A. tibialis recurrens) is given off
from the second part of the curve, ascends in relation to the tibial
nerve, and anastomoses with the descending branch of the posterior
femoral and with the saphenous artery.
5. Small branches (internal calcaneal) to the inner aspect of the hock.
6. The =plantar arteries=, internal and external (A. plantaris medialis,
lateralis), are the small terminals of the posterior tibial. They
descend along the sides of the tarsal sheath of the deep flexor with the
plantar nerves to the proximal part of the metatarsus, where they unite
with the perforating tarsal artery to form the =plantar arch= (Arcus
plantaris). Four =plantar metatarsal arteries= proceed from this arch.
The two slender =superficial plantar metatarsal arteries= (A. metatarsea
plantaris superficialis medialis, lateralis) descend on either side of
the deep flexor tendon with the plantar nerves and unite with the great
metatarsal or with the corresponding digital artery. The two =deep= or
=interosseous plantar metatarsal arteries= (A. metatarsea plantaris
profundus medialis, lateralis) descend between the suspensory ligament
and the corresponding small metatarsal bone and unite near the fetlock
with the great metatarsal. The inner artery is the larger of the two and
usually appears to be the continuation of the perforating tarsal. It
supplies the nutrient artery of the large metatarsal bone. In other
cases it is the direct continuation of the internal plantar artery, the
external artery only uniting with the perforating tarsal.
[Illustration:
FIG. 458.—DISSECTION OF LEG AND HOCK OF HORSE, INNER VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
ANTERIOR TIBIAL ARTERY
[Illustration:
FIG. 459.—DEEP DISSECTION OF RIGHT STIFLE, LEG, AND HOCK OF HORSE,
POSTERIOR VIEW.
The hock is flexed at a right angle, and the tuber calcis is sawn off.
The tibial nerve is drawn inward to show its muscular branches.
Branches of tibial nerve: _1_, _2_, to gastrocnemius; _3_, _4_, to
superficial flexor; _5_, to popliteus; _6_, to flexor longus or
accessorius; _7_, to deep flexor. (After Schmaltz, Atlas d. Anat. d.
Pferdes.)
]
[Illustration:
FIG. 460.—SUPERFICIAL DISSECTION OF RIGHT STIFLE, LEG, AND HOCK OF
HORSE, FRONT VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =anterior tibial artery= (A. tibialis anterior) is much the larger
of the two terminal branches of the popliteal. It passes forward through
the upper part of the interosseous space and descends with two satellite
veins on the outer part, of the front of the tibia, under cover of the
tibialis anterior. At the lower part of the leg it deviates to the outer
border of the tendon of this muscle, passes on to the capsule of the
hock joint, gives off the perforating tarsal artery, and is continued
asthe great metatarsal artery. It gives off =muscular branches= to the
dorso-lateral group of muscles of the leg and =articular branches= to
the hock. The =peroneal= branch (A. peronea) is a variable vessel which
descends along the fibula under the lateral extensor; it gives off
muscular branches and one which perforates the fascia and divides into
ascending and descending cutaneous twigs.
The =perforating tarsal artery= (A. tarsea perforans) is given off under
cover of the outer tendon of the peroneus tertius. It passes backward
through the vascular canal of the tarsus with a satellite vein and
unites on the upper part of the suspensory ligament with the plantar
arteries (or only with the external plantar) to form the plantar arch.
In well-injected specimens it is seen that there is a fine arterial
network (Rete tarsi dorsale) on the flexor surface of the hock, which is
formed by twigs from the anterior tibial and lateral tarsal arteries.
From it proceed two very slender =dorsal metatarsal arteries=. The inner
one descends in the furrow between the inner small and large metatarsal
bones, and anastomoses usually in the proximal part of the metatarsus
with the internal superficial plantar metatarsal, uniting sometimes with
the deep plantar metatarsal. The external vessel passes down under the
periosteum on the anterior face of the large metatarsal bone and becomes
lost or joins the large metatarsal artery.
Sometimes the anterior tibial artery passes undivided through the
tarsus, gives off the internal deep plantar metatarsal, and is
continued as a very large internal superficial plantar metatarsal
along the deep flexor tendon, thus resembling the arrangement in the
fore limb.
In a few cases the perforating tarsal is a large vessel, directly
continuing the anterior tibial, and is continued by a large internal
deep plantar metatarsal. The great metatarsal is then small. Other
variations are common.
THE GREAT METATARSAL ARTERY
This artery (A. metatarsea dorsalis lateralis) is the direct
continuation of the anterior tibial. It passes downward and outward
under the extensor brevis and the tendon of the lateral extensor, at
first on the joint capsule and then in the oblique vascular groove on
the upper part of the large metatarsal bone. It then descends in the
groove formed by the apposition of the large and external small
metatarsals, inclines inward between the two, and divides on the lower
part of the posterior face of the large metatarsal bone into the
internal and external digital arteries. It is not usually accompanied by
a vein. Beyond this the arterial arrangement is the same as in the
thoracic limb.
THE VEINS[168]
PULMONARY VEINS
The terminal =pulmonary veins= (Vv. pulmonales), usually seven or eight
in number, return the aërated blood from the lungs and open into the
left atrium of the heart. They are destitute of valves. Their
tributaries arise in the capillary plexuses in the lobules of the lungs,
and unite to form larger and larger trunks which accompany the branches
of the bronchi and pulmonary arteries. A very large vein is formed by
the union at an acute angle of a trunk from each lung, where the latter
are adherent to each other.
SYSTEMIC VEINS
THE VEINS OF THE HEART (Figs. 426, 427)
The =coronary sinus= (Sinus coronarius) is a very short bulbous trunk
which receives most of the blood from the wall of the heart. It is
situated just below the termination of the posterior vena cava and is
covered in part by a thin layer of ventricular muscle-fibers. It opens
into the right atrium just below the posterior vena cava. It is formed
by the union of two tributaries. The =great cardiac= or =left coronary
vein= (V. cordis magna) begins at the left side of the apex of the
heart, ascends in the left longitudinal groove and turns backward in the
coronary groove, in which it winds around the posterior border of the
heart to the right side and joins the coronary sinus. The =middle
cardiac= or =right coronary vein= (V. cordis media) begins on the right
side of the apex, ascends in the right longitudinal groove and joins the
coronary sinus, or opens separately into the atrium just in front of the
orifice of the left vein, so that a common trunk (coronary sinus) does
not then exist.
The =small cardiac veins= (Vv. cordis minores), three to five in number,
are small vessels which return some blood from the right ventricle and
atrium; they open into the latter near the coronary groove in spaces
between the musculi pectinati.
THE ANTERIOR VENA CAVA (Fig. 429)
The =anterior vena cava= (V. cava cranialis) returns to the heart the
blood from the head, neck, thoracic limbs, and the greater part of the
thoracic wall. It is formed at the ventral part of the thoracic inlet by
the confluence of the two jugular and two brachial veins. Its origin is
attached to the first pair of ribs. It passes backward in the anterior
mediastinum, at first median and ventral to the common carotid trunk,
then deviates to the right of the anterior aorta, and opens into the
right atrium opposite to the third rib. The demarcation between vein and
atrium is not very distinct. It contains no valves except at the mouths
of its radicles. Its length is about five to six inches (ca. 12 to 15
cm.) and its caliber about two inches (ca. 5 cm.) in a subject of medium
size. Its right face is crossed by the right phrenic nerve, and on the
left it is related to the anterior aorta and brachiocephalic artery. It
receives, in addition to small pericardial and mediastinal veins, the
following tributaries:
1. The =internal thoracic vein= (V. thoracica interna) is a satellite of
the artery of that name. It opens into the anterior vena cava at the
first rib.
2. The =vertebral vein= (V. vertebralis) corresponds to the homonymous
artery. On the right side it terminates either in front of the deep
cervical vein or by a short common trunk with it. On the left side it
almost always unites with the deep cervical and vertebral vein to form a
common trunk.
3. The =deep= or =superior cervical vein= (V. cervicalis profunda)
corresponds to the artery. On the right side it leaves the artery at the
first intercostal space, crosses the right face of the trachea and opens
into the vena cava; it may form a common trunk with the dorsal or
vertebral. On the left side there is nearly always a common trunk for
all three.
4. The =dorsal vein= (V. costo-cervicalis) corresponds to the artery. On
the right side it leaves the artery on entering the thorax, crosses the
right face of the trachea, and opens into the vena cava in front of the
deep cervical or by a common trunk with it. On the left side it almost
always joins the deep cervical and vertebral to form a short common
trunk which crosses the left face of the intrathoracic part of the
brachial artery opposite the second rib and opens into the anterior vena
cava.
THE VENA AZYGOS
The =vena azygos= (Fig. 429) is an unpaired vessel which arises at the
level of the first lumbar vertebra by radicles coming from the psoas and
the crura of the diaphragm; it is connected with the first lumbar vein.
It passes forward along the right side of the bodies of the thoracic
vertebræ, in contact usually with the thoracic duct, which separates the
vein from the aorta. At the seventh vertebra it leaves the spine, curves
downward and forward over the right side of the thoracic duct, trachea,
and œsophagus, and opens into the right atrium opposite the third
intercostal space. Its tributaries are:
1. The last fourteen =intercostal veins= (Vv. intercostales) of the
right side. On the left side the last four to seven intercostal veins
usually empty into the =vena hemiazygos=. This vessel runs on the left
side of the aorta from the fourteenth to the eleventh thoracic vertebra,
passes between the aorta and the spine, and joins the vena azygos. In
its absence its tributaries join the vena azygos.
2. The =œsophageal vein= (V. œsophagea), satellite of the œsophageal
artery, joins the vena azygos as it inclines downward.
3. The =bronchial vein= (Vena bronchialis) unites with the preceding to
form a short common trunk (Ellenberger-Baum), or empties into the great
coronary vein (Chauveau).[169]
VEINS OF THE HEAD AND NECK
JUGULAR VEINS
The =jugular veins= (Vv. jugulares), right and left (Fig. 431), arise
behind the posterior border of the lower jaw about two and a half inches
(ca. 6 to 7 cm.) below the temporo-maxillary articulation by the union
of the superficial temporal and internal maxillary veins. Each passes
downward and backward, at first embedded more or less in the parotid
gland, and continues in the jugular furrow to the thoracic inlet, where
it unites with its fellow and the two brachial veins to form the
anterior vena cava. In the neck it is covered by the skin, fascia, and
panniculus, and is superficial to the carotid artery, from which it is
separated in the anterior two-thirds of the region by the omo-hyoideus
muscle.[170] It contains valves at the mouths of its tributaries and has
several pairs of semilunar valves variably disposed along its course.
Its tributaries are as follows:
1. The =internal maxillary vein= (V. maxillaris interna) is larger than
the external maxillary. It may be considered to begin as the
continuation backward of the buccinator vein where the vessel crosses
the alveolar border of the mandible (about two inches (ca. 5 cm.) behind
the last molar tooth). It runs backward on the inner surface of the
ramus below the external pterygoid and covered by the internal pterygoid
muscle for a distance of about three inches (ca. 7 to 8 cm.), then
inclines a little downward and runs ventral to the artery for about an
inch (ca. 2 to 3 cm.). It crosses the external face of the artery at the
posterior border of the jaw, and is joined by the superficial temporal
vein to form the jugular. Its principal radicles are:
(1) The =dorsal lingual vein= (V. dorsalis linguæ), which is a satellite
of the lingual nerve.
(2) The =inferior alveolar= or =dental vein= (V. alveolaris mandibulæ),
a satellite of the corresponding artery. It often unites with the
preceding.
(3) =Pterygoid veins= (Rami pterygoidei).
(4) The =deep temporal vein= (V. temporalis profunda) is a large vessel
which receives tributaries from the temporalis muscle and emissaries
from the parieto-temporal canal. It is connected with the anterior
cerebral vein and usually with the meningeal veins by its frontal
branch. The latter drains chiefly the lacrimal gland and passes behind
the supraorbital process.
2. The =superficial temporal vein= (V. temporalis superficialis) is a
satellite of the corresponding artery. It is formed by the confluence of
the =anterior auricular= and =transverse facial veins=. The former
receives the =superior cerebral vein= (V. cerebralis dorsalis), which is
the emissary of the transverse sinus of the dura mater; it emerges from
the parieto-temporal canal behind the postglenoid process. The
=transverse facial vein= (V. transversa faciei) runs at first above the
artery of like name, then plunges deeply into the masseter and unites in
front with the facial vein. It is connected with the vena reflexa.
3. The =inferior masseteric= or =maxillo-muscular vein= (V. masseterica)
joins the jugular at the upper border of the sterno-cephalicus tendon.
It is a short trunk formed by the confluence at the posterior border of
the jaw of masseteric and pterygoid veins. The former is usually
connected by a large branch with the buccinator vein.
[Illustration:
FIG. 461.—SUPERFICIAL VESSELS AND NERVES OF HEAD AND ANTERIOR PART OF
NECK OF HORSE.
_a_, Masseter; _b_, parotid gland; _c_, parotido-auricularis; _1_,
masseteric artery; _2_, parotid branch; _3_, transverse facial
artery; _4_, facial artery; _5_, _6_, inferior labial artery; _7_,
superior labial artery; _8_, lateral nasal artery; _9_, infraorbital
artery; _10_, dorsal nasal artery; _11_, angular artery of eye;
_12_, _13_, jugular vein; _14_, great auricular vein; _15_,
masseteric vein; _16_, superficial temporal vein; _17_, transverse
facial vein; _17′_, deep temporal vein; _18_, external maxillary
vein; _19_, facial vein; _20_, labial vein; _21_, dorsal nasal vein;
_22_, lateral nasal vein; _23_, angular vein of eye; _24_, _25_,
facial nerve; _25′_, _25″_, superior and inferior buccal nerves;
_26_, transverse facial nerve; _27_, auriculo-palpebral nerve; _28_,
anterior auricular nerve; _29_, cervical branch of facial nerve;
_30_, ventral branch of second cervical nerve; _30′_, _30″_, _30‴_,
auricular and cutaneous branches of _30_; _31_, branches of dorsal
division of first and second cervical nerves; _32_, dorsal branch of
spinal accessory nerve. (After Leisering’s Atlas.)
]
4. The =great auricular vein= (V. auricularis magna) is a satellite of
the posterior auricular artery above, but joins the jugular a variable
distance below and behind the point of origin of the artery.
5. The =inferior cerebral vein= (V. cerebralis ventralis) is an emissary
of the cavernous sinus of the dura. It is a satellite of the internal
carotid artery, receives the =condyloid vein=, and joins the jugular
near the occipital vein or by a common trunk with it.
6. The =occipital vein= (V. occipitalis) arises in the fossa atlantis by
the union of muscular and cerebrospinal branches. The former comes from
the muscles of the poll and passes through the foramen transversarium.
The latter is connected with the occipital sinus of the dura mater and
emerges from the spinal canal by the intervertebral foramen.
7. The =external maxillary= or =facial vein= (V. maxillaris externa)
arises by radicles which correspond in general to the branches of the
artery of like name. It passes down over the cheek along the anterior
border of the masseter muscle behind the artery, crossing over the
parotid duct, which lies behind the vein lower down. Thus on the ramus
and as they turn around its lower border the artery is in front, the
vein in the middle, and the duct posterior. In the submaxillary space
the vein is ventral to the artery for some distance, then parts company
with the artery, runs straight backward along the lower border of the
parotid gland, and opens into the jugular vein at the posterior angle of
the gland.[171] The chief differences in the tributaries of the vein as
compared with the branches of the corresponding artery are as follows:
The =labial veins= (Vv. labiales) form a plexus in the submucous tissue
of the cheek from which two veins emerge. The upper one passes back and
joins the buccinator vein. The lower one (V. labialis communis) joins
the external maxillary vein.
Three veins connect with the external maxillary at the anterior border
of the masseter.
The upper one is the =transverse facial=, which unites close to the end
of the facial crest.
A little lower is the large valveless =vena reflexa= or =alveolar vein=.
This passes back under the upper part of the masseter on the maxilla,
turns around the tuber maxillare, perforates the periorbita, and joins
the ophthalmic vein. It is relatively small at each end, but presents
one or two large fusiform dilatations. It receives the following
tributaries: (_a_) The =palatine vein= (V. palatina major), which
separates from the palatine artery at the anterior palatine foramen and
passes in the groove between the tuber maxillare and the palate bone.
The palatine veins form a very rich plexus of valveless vessels in the
submucosa of the hard palate, which consists of several layers
anteriorly. (_b_) The =sphenopalatine vein= (V. sphenopalatina) forms a
rich plexus of valveless vessels on the turbinal bones and the septum
nasi. It is usually joined by the =infraorbital vein= (V.
infraorbitalis) to form a short common trunk.
[Illustration:
FIG. 462.—DISSECTION OF SUBMAXILLARY SPACE AND ADJACENT PART OF NECK
OF HORSE.
_a_, Ramus of mandible; _b_, sterno-cephalicus muscle; _c_, _c′_,
omo-hyoidei and sterno-hyoidei (portion removed on right side); _d_,
hyoid bone; _e_, anterior belly of digastricus; _f_, _g_,
mylo-hyoideus; _h_, submaxillary lymph glands (portion removed on
right side); _i_, parotid gland; _k_, submaxillary gland; _l_, chin;
_m_, stylo-maxillaris; _1_, parotid duct; _2_, facial vein; _3_,
facial artery; _4_, external maxillary vein; _5_, sublingual vein;
_6_, sublingual artery; _7_, ventral branch of first cervical nerve;
_8_, mylo-hyoid nerve. (After Ellenberger, in Leisering’s Atlas.)
]
The venous plexuses are remarkably developed in certain parts of the
nasal mucosa. On the septum a little below its middle and on the
turbinals the veins are in several layers. The olfactory region does
not share in this arrangement and the veins here are small and join
the ethmoidal vein.
(_c_) The =ophthalmic vein= (V. ophthalmica) is a short trunk, connected
in front with the vena reflexa and behind with the cavernous sinus
through the foramen lacerum orbitale. It receives veins which correspond
to the arterial branches.
The =buccinator vein= (V. buccinatoria) extends backward from the
external maxillary along the lower border of the depressor labii
inferioris and buccinator under cover of the masseter, passes between
the ramus of the mandible and the tuber maxillare and is continued as
the internal maxillary vein. It has a large fusiform dilatation and is
valveless. It receives a large common labial vein from the labial
plexus, and is usually connected with the masseteric vein.
[Illustration:
FIG. 463.—DEEPER VESSELS AND NERVES OF HEAD OF HORSE.
The parotid gland, most of the masseter muscle, and a portion of the
ramus of the mandible are removed. _a_, Remnant of masseter muscle;
_b_, internal pterygoid muscle; _c_, stylo-mandibularis; _d_, _d′_,
levator labii superioris proprius (portion removed); _e_,
periorbita; _1_, masseteric artery; _1′_, parotid branch; _2_, trunk
for anterior (_3_) and posterior (_4_) auricular arteries; _5_,
_5′_, superficial temporal artery; _5″_, transverse facial artery;
_6_, inferior alveolar (or dental) artery; _6′_, mental continuation
of _6_; _7_, buccinator artery; _8_, infraorbital artery; _9_, _11_,
jugular vein; _10_, external maxillary vein; _12_, inferior cerebral
vein; _13_, facial vein; _14_, angular vein of eye; _15_, dorsal
nasal vein; _16_, lateral nasal vein; _17_, superior labial vein;
_18_, _19_, inferior labial veins; _20_, labial plexus; _21_, _22_,
emergent veins of plexus; _23_, vena reflexa; _24_, trunk of
sphenopalatine and infraorbital veins; _25_, palatine vein; _26_,
great auricular vein; _27_, _28_, superficial temporal vein; _29_,
transverse facial vein; _30_, buccinator vein; _31_, dorsal lingual
vein; _32_, inferior alveolar or dental vein; _33_, pterygoid vein;
_34_, deep temporal vein; _35_, superior cerebral vein; _36_,
external nasal nerve; _37_, anterior nasal nerve; _38_, superior
labial nerve; _39_, masseteric nerve; _39′_, end branches of _39_;
_40_, buccinator nerve; _41_, pterygoid nerve; _41a_, inferior
alveolar or dental nerve; _41b_, mylo-hyoid nerve; _42_, posterior
auricular nerve; _43_, auricular branch of vagus; _44_, internal
auricular nerve; _45_, auriculo-palpebral nerve (cut); _46_,
digastric nerve. (After Leisering’s Atlas.)
]
The =lingual vein= (V. lingualis) is not a satellite of the artery. It
is formed at the side of the lingual process of the hyoid bone by the
confluence of several veins which come from the substance of the tongue.
One or two considerable vessels run partly in the substance of the
hyo-glossus, and another in the genio-hyoideus. The vein is at first
covered by the mylo-hyoideus, perforates that muscle, runs back along
the omo-hyoideus in relation to the submaxillary lymph glands, and joins
the external maxillary near the posterior border of the jaw. Near its
termination it receives the =sublingual vein=, or the latter may open
into the external maxillary directly.
8. The =thyroid vein= (V. thyreoidea) is a large vessel which joins the
jugular near the external maxillary vein. It receives anterior thyroid,
laryngeal, and pharyngeal radicles, and sometimes a posterior thyroid
vein.
9. =Muscular=, =tracheal=, and =œsophageal= veins.
10. The =cephalic vein= (Vena cephalica) enters the jugular near its
termination. It will be described with the veins of the thoracic limb.
11. The =inferior cervical vein= (V. cervicalis ascendens) accompanies
the artery. It may open into the brachial vein.
THE SINUSES OF THE DURA MATER
These (Sinus duræ matris) are blood-spaces between the meningeal and
periosteal layers of the dura mater and are lined with endothelium. In
many places the lumen is crossed by fibrous strands. They receive the
veins of the brain, communicate with the meningeal and diploic veins,
and with veins outside of the cranium; their connections with the latter
are by means of small =emissary veins= (Emissaria). They convey the
blood directly or indirectly to the jugular veins. Some are paired,
others unpaired. They may be divided into dorsal and basilar systems.
The =dorsal system= comprises the following:
The =superior longitudinal= or =sagittal sinus= (S. sagittalis superior)
is situated in the upper border of the falx cerebri along the internal
sagittal crest. It begins at the crista galli and ends at the tentorium
osseum by dividing into two transverse sinuses. It receives the superior
cerebral veins. Along each side are small pouches (Lacunæ laterales)
into which the veins open. The lumen of the sinus is traversed by
fibrous bands and is partially divided by a longitudinal septum.
[Illustration:
FIG. 464.—MEDIAN SECTION OF HEAD OF HORSE, UPPER PART WITH SEPTUM NASI
REMOVED.
_a_, Lateral mass of ethmoid bone; _b_, superior turbinal; _c_,
inferior turbinal; _d_, _d′_, turbinal folds; _e_, frontal sinus;
_f_, falx cerebri; _g_, tentorium cerebelli; _h_, medial surface of
hemisphere; _i_, cerebellum; _k_, occipital bone; _k′_, occipital
condyle; _k″_, paramastoid process; _l_, external auditory meatus;
_m_, temporal condyle; _n_, parieto-temporal canal; _1_, branches of
ethmoidal artery; _2_, _2′_, branches of sphenopalatine artery; _3_,
_3′_, branches of sphenopalatine vein; _4_, branches of ethmoidal
nerve; _5_, _5′_, branches of sphenopalatine nerve; _6_, artery of
corpus callosum; _7_, superior sagittal sinus; _8_, straight sinus;
_9_, vena magna cerebri; _10_, inferior sagittal sinus; _11_, _11′_,
transverse sinuses; _12_, superior petrosal sinus; _13_, superior
occipital sinus; _14_, superior cerebral vein; _15_, corpus
callosum; _16_, fornix. (After Ellenberger, in Leisering’s Atlas.)
]
The =transverse sinuses= (S. transversi), right and left, pass outward
in the transverse grooves of the parietal bones, enter the
parieto-temporal canals, and are continued by the superior cerebral
veins to the superficial temporal veins. The two sinuses are connected
by the sinus communicans.
The =inferior longitudinal= or =sagittal sinus= (S. sagittalis inferior)
runs backward on the upper surface of the corpus callosum along the
concave edge of the falx cerebri and joins the great cerebral vein (of
Galen) to form the straight sinus.
The =straight sinus= (S. rectus) passes upward and backward between the
cerebral hemispheres and in the tentorium cerebelli and joins the
superior sagittal sinus. The point of meeting is the confluence of the
sinuses (Confluens sinuum).
The =occipital sinuses= (S. occipitales) lie on either side of the
vermis cerebelli. They empty anteriorly into the sinus communicans and
communicate behind with the spinal veins.
The =superior petrosal sinuses= (S. petrosi superiores) pass in the
tentorium cerebelli to end in the transverse sinuses.
The =basilar system= consists of the following:
The =cavernous sinuses= (S. cavernosi) lie in the inner grooves of the
root of the temporal wings of the sphenoid bone at either side of the
sella turcica. The two are connected by a wide traverse branch (Sinus
intercavernosus) behind and below the posterior part of the pituitary
body. Each is continuous in front with the ophthalmic vein and below
with the inferior petrosal sinus. The third, sixth, and the ophthalmic
and maxillary divisions of the fifth nerve lie along the outer wall of
the sinus. The internal carotid artery traverses the sinus and is
connected with its fellow by a transverse branch which lies in the
corresponding part of the sinus. An oval opening in the floor
communicates with the inferior petrosal sinus and transmits the internal
carotid artery.
The sinus is not subdivided by strands of fibrous tissue as in man,
but a few delicate bands attach the artery to its wall.
The =inferior petrosal sinuses= (S. petrosi inferiores)[172] lie along
the borders of the basilar part of the occipital bone, inclosed in the
thick dura which closes the foramen lacerum. The anterior part extends
about half an inch (ca. 12 mm.) under the temporal wing of the sphenoid.
Here communications exist with veins in the pterygo-palatine fossa. The
posterior end is bulbous and lies in the condyloid fossa; it
communicates with the condyloid vein issuing from the hypoglossal
foramen and is drained by the inferior cerebral vein; it also receives
an emissary vein from the parieto-temporal canal. The roof of the sinus
is perforated by an oval opening at the carotid notch which opens into
the cavernous sinus and transmits the internal carotid artery; the
latter forms the first bend of its =S=-shaped curve in the petrosal and
the second in the cavernous sinus.
The =basilar plexus= (Plexus basilaris) is a venous plexus situated on
the upper surface of the basilar part of the occipital bone. It is
connected through the hypoglossal foramen with the inferior petrosal
sinus and communicates behind with the spinal veins.
THE VEINS OF THE CRANIUM
The =veins of the brain= (Venæ cerebri) do not in general accompany the
cerebral arteries. They have very thin walls, no muscular coat, and no
valves. They are arranged in two sets, superficial or cortical and deep
or central. The superficial veins are more numerous and larger than the
arteries. They lie on the surface of the brain in the pia mater and the
subarachnoid space.
The =superior cerebral veins= drain the upper and outer part of the
cerebral cortex. They receive veins from the medial surfaces of the
hemispheres and open into the superior sagittal sinus. Their terminal
parts are bulbous and their openings are directed obliquely forward, _i.
e._, contrary to the direction of the bloodstream in the sinus.
The =inferior cerebral veins= lie on the inferior and external aspect of
the hemispheres. They open into the inferior system of sinuses. The
=middle cerebral vein= runs in the lateral fissure (of Sylvius) and
opens into the cavernous sinus.
The =deep cerebral veins= issue from the central or ganglionic parts of
the brain at the transverse fissure. They converge to form the =great
cerebral vein= (of Galen) (V. magna cerebri). This passes upward and
backward behind the splenium of the corpus callosum and is continued as
the straight sinus to join the sagittal sinus.
The =superior cerebellar veins= ramify on the upper surface of the
cerebellum. They open into the superior system of sinuses and the great
cerebral vein. The =inferior cerebellar veins= are larger and go chiefly
to the basilar plexus. The veins of the medulla and pons end in the
inferior system of sinuses.
The =meningeal veins= (Venæ meningeæ) arise in capillary plexuses in the
superficial and deep faces of the dura mater. Some end in the sinuses of
the dura, others accompany the meningeal arteries.
The =diploic veins= (Venæ diploicæ) are anastomosing channels in the
spongy substance of the cranial bones. Their walls are thin, consisting
in many places only of the endothelium, and they have no valves. Some
open inward into venous sinuses, others into extracranial veins.
SPINAL VEINS
Two =longitudinal spinal veins= or =sinuses= (Sinus columnæ vertebralis)
extend along the floor of the vertebral canal, one on either side of the
superior common ligament. They are continuous in front with the basilar
plexus. They lie in the grooves on the bodies of the vertebræ and are
connected by a series of transverse anastomoses which pass between the
central part of the bodies of the vertebræ and the superior common
ligament or in channels in the bone. They receive veins from the spinal
cord, the dura mater, and the bodies of the vertebræ (Venæ basis
vertebræ). Through the intervertebral foramina efferent vessels connect
with the vertebral, intercostal, lumbar, and lateral sacral veins.
VEINS OF THE THORACIC LIMB
The =brachial vein= (V. brachialis) is a satellite of the extrathoracic
part of the brachial artery. It arises at the inner side of the distal
end of the shaft of the humerus and passes upward in the arm behind the
artery under cover of a layer of fascia and the posterior superficial
pectoral muscle. At the shoulder it is ventral to the artery, crosses
the anterior border of the first rib, and concurs with its fellow and
the two jugulars in the formation of the anterior vena cava. The roots
of the vein are somewhat variable, but most often four radial veins in
addition to a large oblique branch from the cephalic unite in its
formation. Its tributaries correspond in general to the branches of the
artery, but a few differences are worthy of notice. The
=thoracico-dorsal vein= joins the brachial directly or opens into the
deep brachial. The =external thoracic= or =“spur” vein= (V. thoracica
externa) is a large vessel which arises in the ventral wall of the
abdomen, passes forward (embedded more or less in the panniculus) along
the outer border of the posterior deep pectoral muscle, and joins the
brachial vein near the first rib. It often communicates with the
subscapular vein.
[Illustration:
FIG. 465.—SPINAL VESSELS OF HORSE.
The vertebral canal has been opened by sawing off the arches. The
nerve-roots are cut on one side and the spinal cord turned over to
right. _1_, Ventral or middle spinal artery; _2_, reinforcing
branches from vertebral, intercostal, or lumbar arteries (according
to region); _3_, longitudinal vertebral sinuses; _a_, ventral
surface of spinal cord; _b_, dura mater (cut); _c_, nerve-roots;
_d_, superior common ligament. (After Ellenberger, in Leisering’s
Atlas.)
]
The =cephalic vein= (V. cephalica) arises at the inner side of the
carpus as the continuation of the internal superficial metacarpal vein.
It runs upward on the deep fascia of the forearm at first in the furrow
between the flexor carpi internus and the radius. Toward the middle of
the forearm it inclines gradually forward on the inner surface of the
radius, accompanied by a cutaneous branch of the median nerve, and
arrives at the insertion of the biceps. Here it detaches a large branch
(Ramus communicans) which passes upward and backward over the inner
insertion of the biceps, the posterior radial artery, and the median
nerve, and joins the brachial vein. The vein to this point is often
termed the internal subcutaneous vein of the forearm (V. cephalica
antebrachii). It is continued (as the V. cephalica humeri) in the furrow
between the mastoido-humeralis and the anterior superficial pectoral
with a branch of the inferior cervical artery, crosses the deep face of
the cervical panniculus, and opens into the terminal part of the jugular
or the brachial vein. It receives an =accessory cephalic vein= (V.
cephalica accessoria), which arises from the carpal network, runs upward
along the inner border of the extensor carpi, turns along the lower
border of the brachialis, passes under the superficial tendon of the
biceps and joins the cephalic.
[Illustration:
FIG. 466.—DISSECTION OF PECTORAL REGION AND ANTERIOR PART OF ABDOMINAL
WALL OF HORSE.
_1_, Jugular vein; _2_, loose connective tissue of axillary space;
_3_, ascending branch of inferior cervical artery; _4_, descending
branch of same; _5_, cephalic vein; _6_, median nerve; _7_, ulnar
nerve; _8_, brachial artery; _9_, brachial vein; _10_, external
thoracic or “spur” vein; _11_, anterior abdominal artery and vein;
_12_, branches of sixth cervical nerve; _13_, cutaneous branch of
axillary nerve; _14_, cutaneous branch of musculo-cutaneous nerve;
_15_, cervical panniculus; _16_, sterno-cephalicus; _17_, scalenus;
_18_, mastoido-humeralis; _19_, anterior superficial pectoral; _20_,
posterior superficial pectoral; _21_, anterior deep pectoral; _22_,
posterior deep pectoral; _23_, abdominal panniculus; _24_, obliquus
abdominis externus; _25_, rectus abdominis; _26_, coraco-brachialis;
_27_, tensor fasciæ antibrachii; _a_, prescapular lymph glands; _b_,
prepectoral lymph glands; _c_, axillary lymph glands; _d_, cubital
lymph glands; _c.x._, xiphoid cartilage. (After Schmaltz, Atlas d.
Anat. d. Pferdes.)
]
The deep veins of the forearm are variable. Commonly two =posterior
radial veins= (Venæ medianoradiales) accompany the artery of like name,
one in front and one behind. A third vein arises by radicles emerging
from the proximal part of the deep flexor; it joins the posterior
satellite of the posterior radial artery or forms one of the roots of
the brachial vein. The =common interosseous vein= joins the posterior
satellite. The =anterior radial vein= (V. collateralis radialis) is a
satellite of the artery. The =ulnar vein= is usually double at its
proximal part, and communicates with the deep brachial vein.
There are three chief =metacarpal veins=. The =internal metacarpal vein=
(V. metacarpea volaris superficialis medialis) arises from the volar
venous arch above the fetlock. It is the largest vein of the region and
lies in front of the large metacarpal artery. It separates from the
artery at the proximal end of the metacarpus, passes upward on the inner
part of the posterior surface of the carpus, under cover of the
superficial layer of the posterior annular ligament, and is continued as
the cephalic vein. It communicates at its proximal part with the origin
of the posterior radial veins by a short but relatively large branch.
The =external metacarpal vein= (V. metacarpea volaris superficialis
lateralis) arises from the venous arch above the fetlock and passes
upward behind the external border of the suspensory ligament in front of
the external branch of the median nerve and accompanied by a small
artery. At the proximal end of the metacarpus it is connected with the
deep metacarpal vein by two transverse anastomoses which pass across the
suspensory ligament. It then passes upward as a satellite of the
external volar metacarpal artery and concurs in the origin of the ulnar
and posterior radial veins. The =deep metacarpal vein= (V. metacarpea
volaris profunda medialis) arises from the venous arch, passes forward
between the two branches of the suspensory ligament, and ascends on the
posterior surface of the large metacarpal bone. At the proximal end of
the latter it communicates with the other metacarpal veins, ascends with
the small metacarpal artery, and concurs in forming the radial veins.
The =venous arch= (Arcus venosus volaris), from which the metacarpal
veins arise, is situated above the sesamoids of the fetlock between the
suspensory ligament and the deep flexor tendon. It is formed by the
junction of the two digital veins.
The =digital veins=, internal and external (V. digitalis medialis,
lateralis), drain the venous plexuses of the foot. They arise at the
upper edge of the lateral cartilages and ascend in front of the
corresponding arteries.
It is convenient to recognize the following venous plexuses of the foot,
which, however, communicate very freely:
1. The =coronary plexus= encircles the upper part of the foot. It is
attached to the terminal part of the extensor tendon, the lateral
cartilages, and the bulbs of the plantar cushion.
2. The =dorsal= (or laminal) =plexus= covers the dorsal or wall surface
of the third phalanx in the deep layer of the matrix of the wall of the
hoof. It forms the circumflex vein of the third phalanx or vein of the
distal border of the third phalanx, which corresponds to the artery of
like name.
3. The =volar plexus= is in the deep layer of the matrix of the sole of
the hoof and on the deep surface of the lateral cartilages. It
communicates around the inferior border of the third phalanx with the
dorsal plexus and through the lateral cartilages with the coronary
plexus.
The deep vein of the third phalanx accompanies the terminal part of the
digital artery. It drains the =intraosseous plexus=.
THE POSTERIOR VENA CAVA (Figs. 270, 450)
The =posterior vena cava= (V. cava caudalis) returns almost all of the
blood from the abdomen, pelvis, and pelvic limbs. It is formed by the
confluence of the right and left common iliac veins at the fifth lumbar
vertebra, above the terminal part of the aorta and chiefly to the right
of the median plane.
The mode of origin is variable. In some cases there is a common trunk
formed by the union of the two internal iliac veins so that the
arrangement resembles the termination of the aorta. In other cases the
internal iliac vein does not exist.
It passes forward on the ventral face of the psoas minor to the right of
the abdominal aorta. At the last thoracic vertebra it separates from the
aorta and runs forward between the right crus of the diaphragm and the
pancreas till it reaches the liver. Here it inclines downward along the
inner border of the right lobe and the parietal surface of the liver,
largely embedded in the gland substance, and passes through the foramen
venæ cavæ of the diaphragm. It then runs forward and somewhat downward
between the mediastinal lobe and the main mass of the right lung at the
upper margin of a special fold of the right pleura, accompanied by the
right phrenic nerve, and opens into the posterior part of the right
atrium. It receives the following tributaries:
1. The =lumbar veins= (Vv. lumbales) correspond to the arteries. Five
pairs usually empty into the vena cava. Sometimes the corresponding
veins of opposite sides unite to form a common trunk. The first
communicate with the vena azygos.
2. The =spermatic veins= (Vv. spermaticæ internæ) (Fig. 450) accompany
the arteries of like name. In the spermatic cord they form the
pampiniform plexus about the artery and nerves. Their termination is
variable. The right one commonly joins the vena cava near the renal
vein, often by a common trunk with the left one. Frequently the left
vein joins the left renal, and sometimes the right one ends similarly.
2_a_. The =utero-ovarian veins= are much larger than the preceding and
are satellites of the arteries in the broad ligaments. The ovarian
branch is plexiform near the ovary. The uterine branches form a rich
plexus in the wall of the uterus. The trunk is very short.
3. The =renal veins= (Vv. renales), satellites of the arteries, are of
large caliber and thin-walled. The right vein passes inward and backward
on the ventral face of the kidney between the artery in front and the
ureter behind. It joins the vena cava above the right adrenal. The left
vein is somewhat longer. It passes inward at first like the right one,
then bends around the posterior end of the adrenal, crosses the origin
of the renal artery and opens into the vena cava a little further back
than the right one. They receive veins from the adrenals, but some
adrenal veins open directly into the vena cava.
4. The =hepatic veins= (Vv. hepaticæ) return the blood from the liver,
and open into the vena cava as it lies in the groove in the liver. Three
or four large vessels open into the vena cava just before it leaves the
liver, and numerous small ones discharge into its embedded part.
5. The =phrenic veins= (Vv. phrenicæ), two or three in number, return
the blood from the diaphragm. They are very large in comparison with the
arteries, and join the vena cava as it lies in the caval opening.
In some cases there is a small middle sacral vein (V. sacralis media),
a satellite of the artery. It opens into the angle of junction of the
common iliac veins or into one of the latter.
THE PORTAL VEIN
The =portal vein= (V. portæ) is a large trunk which returns the blood
carried to the viscera by the gastric, splenic, and mesenteric arteries.
Its peripheral tributaries correspond closely with the branches of the
arteries, but the terminal trunks do not. The vein is formed behind the
pancreas and below the posterior vena cava by the confluence of the
=anterior= and =posterior mesenteric= and =splenic veins=. It passes
forward, traverses the posterior part of the pancreas very obliquely,
inclines ventrally and a little to the right, and reaches the portal
fissure of the liver. Here it divides into three branches which enter
the liver and ramify in the substance of the gland like an artery,
terminating in the lobular capillaries. From the lobules the blood
passes into the hepatic veins and through these to the posterior vena
cava. Thus the blood which is distributed to the stomach, nearly the
entire intestinal tract, the pancreas, and the spleen, passes through
two sets of capillaries prior to its return to the heart, viz., the
capillaries of these viscera and of the liver.
1. The =anterior mesenteric vein= (V. mesenterica cranialis) is the
largest of the portal radicles. It is situated to the right of the
artery of like name, and its tributaries correspond in general to the
branches of the artery. Usually a single colic vein corresponds to the
two arteries of the right portions of the colon.
2. The =posterior mesenteric vein= (V. mesenterica caudalis) is the
smallest of the radicles of the portal. It accompanies the artery in the
colic mesentery and its rectal branches anastomose with those of the
internal pudic vein.
3. The =splenic vein= (V. lienalis) is the very large satellite of the
splenic artery. It is formed by the union of two radicles at the base of
the spleen. On leaving the hilus of the spleen it passes inward between
the anterior pole of the left kidney and the saccus cæcus of the stomach
and above the left end of the pancreas, receives commonly the =posterior
gastric vein= (V. gastrica caudalis), and unites with the anterior
mesenteric at the posterior border of the pancreas.
The collateral tributaries of the portal veins are as follows:
(1) =Pancreatic veins= (Rami pancreatici).
(2) The =gastro-duodenal vein= (V. gastroduodenalis) corresponds mainly
to the extrahepatic branches of the hepatic artery.
(3) The =anterior gastric vein= (V. gastrica cranialis) joins the portal
at the portal fissure.
THE COMMON ILIAC VEINS (Fig. 456)
These (V. iliacæ communes) are two very large but short trunks which
result from the union of the internal and external iliac veins of each
side at the sacro-iliac articulation. The left one is the longer and
crosses obliquely over the terminal part of the aorta. The chief
tributaries of each are as follows:
1. The last =lumbar vein=.
2. The =circumflex iliac veins= (Vv. circumflexæ ilium profundæ) are the
two satellites of each corresponding artery, on either side of which
they are placed. They may open directly into the posterior vena cava or
into the external iliac vein.
3. The =ilio-lumbar vein= (V. iliolumbalis) may open into the common
iliac, the external iliac, or the internal iliac vein.
THE INTERNAL ILIAC VEINS
The =internal iliac= or =hypogastric veins= (Vv. hypogastricæ), right
and left, are usually formed by the confluence of lateral sacral,
gluteal, and internal pudic veins. The obturator vein may open into them
also. They are short trunks and are smaller than the external iliac
veins. The tributaries correspond in general to the branches of the
three arteries of like names. The internal pudic veins receive affluents
from the venous plexuses of the prepuce and penis in the male; of the
mammary gland, vulva, vagina, and vestibular bulb in the female.
THE VEINS OF THE PELVIC LIMB
The =external iliac vein= (V. iliaca externa) (Figs. 450, 451) lies
behind the corresponding artery at the brim of the pelvis. It is the
upward continuation of the femoral vein, and unites at the sacro-iliac
joint with the internal iliac to form the common iliac vein. Its
tributaries are as follows:
1. The =obturator vein= (V. obturatoria) is a satellite of the artery
and usually opens into the external iliac at the insertion of the psoas
minor. Its radicles anastomose with those of the internal and external
pudic veins (Figs. 451, 455).
2. The =iliaco-femoral= or =external circumflex veins= (Vv. circumflexæ
femoris laterales) are the two satellites of the homonymous artery. They
open a little higher than the obturator.
The =femoral vein= (Figs. 450, 451) lies behind the artery in the upper
part of the thigh, external to it lower down. Its chief tributaries are:
1. A very large but short trunk formed by the union of the deep femoral
and the external pudic vein. The =deep femoral vein= (V. profunda
femoris) corresponds otherwise to the artery. The =external pudic vein=
(V. pudenda externa) arises chiefly from a rich plexus of large veins
situated above and along the sides of the penis and prepuce in the male,
the mammary glands in the female. It passes through a foramen in the
anterior part of the tendon of origin of the gracilis and runs outward
in the subpubic groove behind the pectineus to unite with the deep
femoral vein. The right and left veins are connected by a large
transverse anastomosis and each has a large connection with the
obturator vein. Each receives the =posterior abdominal vein= (V.
epigastrica caudalis) which accompanies the artery of like name. The
=subcutaneous abdominal vein= (V. abdominalis subcutanea) arises in the
skin and panniculus of the ventral abdominal wall, anastomoses with the
internal and external thoracic and deep abdominal veins, and joins the
external pudic or posterior abdominal vein.
A small vein accompanies the external pudic artery in the inguinal
canal.
2. The =anterior femoral vein= (V. femoris cranialis) accompanies the
artery.
3. The =saphenous vein= (V. saphena) (Figs. 451, 458, 460) arises at the
inner side of the flexion surface of the tarsus as the upward
continuation of the internal metatarsal vein. Its course is distinctly
visible. It ascends on the subcutaneous surface of the tibia and the
popliteus muscle, inclosed between layers of the deep fascia, inclines a
little backward to the proximal part of the leg, then deviates slightly
forward, runs upward on the gracilis, passes between that muscle and the
sartorius, and joins the femoral or the external pudic vein.[173] On the
upper part of the capsule of the hock joint it forms an arch with the
anterior tibial vein. The vein has numerous valves. The satellite artery
is relatively small and lies in front of the vein as far as the junction
with the recurrent tibial vein, which it accompanies on the leg. It
receives the =recurrent tibial vein= (V. recurrens tibialis)[174] at the
proximal fourth of the leg. This vessel arises at the inner surface of
the tarsus and forms an arch with the posterior tibial vein at the level
of the tuber calcis. It ascends in the furrow in front of the
gastrocnemius tendon, inclines forward at the proximal third of the leg,
and joins the saphenous vein at an acute angle. It has numerous valves.
A smaller vein from the anterior face of the metatarsus joins the
saphenous at the hock.
4. =Muscular branches= which correspond to the arteries.
5. The =posterior femoral= or =femoro-popliteal= vein (V. femoris
caudalis) is a satellite of the artery. It receives the =recurrent
tarsal= or =external saphenous vein= (V. tarsea recurrens), which arises
at the outer side of the hock, ascends on the deep fascia of the
external surface of the leg in front of the tendo Achillis, passes
between the biceps femoris and semitendinosus, and joins the posterior
femoral vein. It is connected with the recurrent tibial vein by a large
anastomotic branch which crosses in front of the tuber calcis. Usually a
branch from it ascends along the great sciatic nerve and anastomoses
with the obturator vein.
The =popliteal vein= (V. poplitea) lies along the inner side of the
artery (Fig. 459). It is formed by the confluence of anterior and
posterior tibial veins.
Two =anterior tibial veins= (Vv. tibiales anteriores) usually accompany
the artery of like name; the outer vein is much the larger. In other
cases there is a single large vein in the proximal part of the leg, two
lower down. They arise from a number of anastomosing radicles on the
front of the capsule of the hock joint, chiefly as the continuation of
the perforating tarsal vein. The origin of the chief vein is connected
with the saphenous by a large anastomotic branch.
The =posterior tibial vein= (V. tibialis posterior) is commonly double
(Fig. 458). It arises at the level of the tuber calcis, where it has a
communication with the recurrent tibial vein. It is a satellite of the
artery.
The =internal= or =great metatarsal vein= (V. metatarsea dorsalis
medialis) (Figs. 458, 460) arises from the venous arch above the
sesamoids at the fetlock, but is practically the upward continuation of
the internal digital vein. It ascends along the inner border of the deep
flexor tendon, then in the groove on the inner aspect of the proximal
part of the large metatarsal bone to the capsule of the hock joint, and
is continued by the saphenous vein.
The =external metatarsal vein= (V. metatarsea plantaris lateralis)
arises from the venous arch above the fetlock, but appears to be the
upward continuation of the external digital vein. It ascends along the
outer border of the deep flexor tendon in front of the plantar nerve,
and is connected with the deep metatarsal vein at the proximal part of
the metatarsus by a transverse branch. It then passes upward along the
deep flexor tendon in relation to the plantar nerves and the inner
tarsal artery and is continued by the recurrent tibial vein.
The =deep metatarsal vein= (V. metatarsea plantaris medialis) arises
from the plantar venous arch, passes forward between the branches of the
suspensory ligament, and ascends on the posterior face of the large
metatarsal bone. At the proximal end of the metatarsus it is connected
with the external metatarsal vein by a transverse branch. It then passes
(as the perforating tarsal vein) through the vascular canal of the
tarsus and forms the chief radicle of the anterior tibial vein.
The =plantar venous arch= (Arcus venosus plantaris) and the digital
veins are arranged like those of the thoracic limb.
The Lymphatic System
The =lymphatic system= (Systema lymphaticum) is subsidiary to the venous
part of the circulatory system, from which it arises in the embryo. It
consists of the lymph vessels and glands.
The =lymph vessels= (Vasa lymphatica) contain a colorless fluid, the
lymph, which contains numerous lymphocytes.[175] They resemble the veins
in structure but have thinner walls and are provided with more numerous
valves. The vessels are sacculated opposite the segments of the valves
and have a characteristic beaded appearance when distended. The
collecting lymph vessels do not usually form rich plexuses, as veins
often do, their branching is more limited and less tree-like than that
of the blood-vessels, and their caliber therefore increases less from
the periphery toward their termination. All of the lymph is ultimately
carried into the venous system by two trunks, the =thoracic duct= and
the =right lymphatic duct=. Almost all of the lymph passes through at
least one group of lymph glands before entering the blood-vascular
system.
The =lymph glands= or =nodes= (Lymphoglandulæ) are intercalated in the
course of the lymph vessels. They vary widely in size, some being
microscopic, others several inches in length. In form they may be
globular, ovoid and flattened, elongated, or irregular. In certain
situations they are aggregated into groups, and a knowledge of the
position of these and the territory drained into them is important. It
is convenient, when possible, to indicate their position with regard to
arteries on the course of which they are placed. In color they are
usually gray or yellowish-brown in the dead subject, pink or
reddish-brown during life, but this varies according to their position
and functional state. The bronchial glands are often blackened by
infiltration with carbon. The mesenteric glands are creamy or white
while the chyle is passing through, but pink at other times. Vessels
which carry lymph to a gland are called =afferent=; the =efferent=
vessels which convey it away are larger and fewer. Each gland has a
depression, the =hilus=, at which the blood-vessels enter and the
efferent lymph vessels emerge.
=Lymph nodules= or =follicles= (Noduli lymphatici) are minute masses of
lymphoid tissue which occur in certain mucous membranes. They may be
solitary, as in the solitary glands of the intestine, or aggregated into
masses or patches, as in the tonsils and the so-called Peyer’s patches.
The =lymph nodule= or =follicle= is the unit of structure of the lymph
gland. It consists essentially of an artery surrounded by a
=reticulum= of connective tissue, the meshes of which contain numerous
=lymphocytes=. Surrounding this is a rich plexus of lymph vessels,
forming the so-called =sinus=, inclosed in some cases by a fibrous
capsule. The gland consists of a mass of follicles, inclosed in a
fibrous =capsule=, from which =trabeculæ= pass in and unite the
follicles. Beneath the capsule is the =peripheral sinus=, which
consists of a very rich plexus of lymph vessels; to this the afferent
vessels pass at various points of the surface. In the =cortical
substance= the cells are in rounded masses, the cortical nodules,
while in the =medullary substance= they lie around the arteries,
forming the so-called medullary cords. The =medulla= is redder than
the cortex, since it is more vascular; it contains the =central lymph
sinuses=, which have a similar structure to the peripheral sinus.
The =hæmolymph glands= differ from the lymph glands in color and
structure. They are of a deep red color, which is due to the high
vascularity of the cortical substance. The peripheral sinuses especially
are greatly developed and contain numerous red blood-cells. There is no
clear division into cortical and medullary substance, and the trabeculæ
contain smooth muscle-cells. Some have afferent and efferent lymph
vessels and others do not. They resemble the spleen in some respects,
but their significance is not yet clear. They are numerous in the ox and
sheep, much fewer in the dog, and apparently are absent in the horse.
They occur along the course of the aorta, in the perineal fat, at the
portal fissure, and with the gastric and mesenteric lymph glands. In the
ox they are also found under the trapezius muscle, under the skin of the
upper part of the flank, and in other places less constantly.
The =tissue= or =lymph-spaces= are interstices of varying size between
cells or in the meshes of connective tissue. They contain a fluid
derived from the blood-plasma, which is usually called =lymph=. They are
drained by the veins and lymph vessels. The large serous sacs are often
included in this category.
The exact relationship between the lymphatic capillaries and the
tissue spaces is still a matter of controversy. It is held by some
that the lymph vessels are in direct communication with the tissue
spaces, while others maintain that the lymphatics are complete closed
tubes. Communication between the spaces and vessels is in general very
free. Mall has shown that granules injected into the hepatic artery
are returned by the lymphatics as well as by the veins, and
intramuscular injections will enter the lymph vessels of the tendon in
spite of the absence of lymphatics in muscle.
LYMPHATIC SYSTEM OF THE HORSE
THE THORACIC DUCT (Figs. 428, 429)
The =thoracic duct= (Ductus thoracicus) is the chief collecting trunk of
the lymphatic system. It begins as an elongated irregular dilatation,
the =cisterna= or =receptaculum chyli=, which is situated between the
right side of the aorta and the right crus of the diaphragm at the first
and second lumbar vertebræ. The duct enters the thorax through the
hiatus aorticus and runs forward on the right of the median plane
between the vena azygos and the aorta, covered by the pleura. At the
sixth or seventh thoracic vertebra it inclines somewhat ventrally,
crosses obliquely over the left face of the œsophagus, and passes
forward on the left side of the trachea to the inlet of the thorax. The
extrathoracic terminal part passes downward and forward a variable
distance (3 to 4 cm.) on the deep face of the left scalenus muscle,
bends inward and backward under the bicarotid trunk, and opens into the
upper part of the origin of the anterior vena cava just behind the angle
of junction of the jugular veins. The terminal bend is ampullate and
sometimes divides into two very short branches which open close
together.
Since the duct develops from a plexus of ducts in the embryo,
considerable variation from the more usual course occurs. There is
often a left duct which arises at the cisterna or at a variable point
from the right duct, runs across the left intercostal arteries
parallel to the latter, and unites with it over the base of the heart
or further forward. The two are connected by cross-branches. In some
cases the left duct is the larger, and there may indeed be none on the
right side. Other variations are common.
The chief tributaries of the thoracic duct are as follows:
1. The two =lumbar trunks= (Trunci lumbales) are formed by the
confluence of the efferent ducts of the lumbar glands, and commonly
unite with each other and with the posterior intestinal trunk before
opening into the cistern.
2. The =intestinal trunks= (Trunci intestinales), two or three in
number, receive the efferents of the lymph glands of the intestine,
stomach, liver, and spleen.[176]
In its course through the thorax the thoracic duct receives efferents
from the intercostal, mediastinal, and bronchial glands. At the thoracic
inlet it is joined by ducts from the prepectoral and right axillary
glands, and by the left tracheal duct. The duct is provided with several
pairs of valves; the best developed are at its termination.
THE RIGHT LYMPHATIC DUCT
This vessel (Ductus lymphaticus dexter)—when present—collects the lymph
from the right side of the head, neck, and thorax, and from the right
thoracic limb. It is most frequently absent, being represented by a
number of short ducts which terminate in the thoracic duct, the right
jugulo-brachial junction, or the origin of the anterior vena cava. When
present in its typical form, it results from the confluence of efferent
ducts from the right axillary and prepectoral lymph glands with the
right tracheal duct. It lies on the deep face of the scalenus muscle
above the terminal part of the right jugular vein. It is more or less
ampullate and usually opens into the anterior vena cava to the right of
the thoracic duct. It may be connected with the latter by considerable
anastomoses and may join it.
The duct is very variable in form and in regard to its afferents.
Often it is a very short, irregular, and bulbous trunk; in some cases
it is about an inch and a half (ca. 3 to 4 cm.) in length and receives
the tracheal duct at its terminal bend. The lymphatico-venous
connections here need further study.
THE LYMPH GLANDS AND VESSELS OF THE HEAD AND NECK
1. The =submaxillary lymph glands= (Lg. submaxillares) (Figs. 437, 462)
are arranged in two elongated groups in the submaxillary space along
each side of the omo-hyoid muscles. The two groups are in apposition in
front of the insertion of these muscles and diverge posteriorly in the
form of a =V=, extending backward about four or five inches (ca. 10 to
12 cm.). They are covered by the skin and a thin layer of fascia and
panniculus, and are therefore palpable. Anteriorly they are firmly
attached to the mylo-hyoidei, but otherwise they are rather movable in
the normal state. Each group is related externally to the external
maxillary artery and the anterior belly of the digastricus, below to the
external maxillary vein, and above to the lingual and sublingual veins.
They receive =afferent vessels= from the lips, nostrils, nasal region,
cheeks, the anterior part of the tongue, the jaws, the floor of the
mouth, and the greater part of the hard palate and nasal cavity. The
=efferent vessels= pass to the anterior cervical and pharyngeal glands.
The superficial lymph vessels of the face converge to twelve to
fifteen trunks which turn around the lower border of the jaw with the
facial vessels. Those of the lips form plexuses at the commissures.
The nasal mucous membrane is richly supplied with lymph vessels which
accompany the veins; posteriorly they communicate with the subdural
and subarachnoid spaces and send efferents to the pharyngeal and
anterior cervical glands.
2. The =pharyngeal lymph glands= (Figs. 436, 437, 569) may consist of
two groups. One lies on the lateral surface of the pharynx along the
course of the external carotid artery. These glands are related
externally to the stylo-maxillaris and digastricus and often to the
submaxillary gland also, above to the guttural pouch. Other glands (Lg.
retropharyngeales) are commonly found on the guttural pouch along the
course of the internal carotid artery. They lie below the artery and are
covered by the aponeurosis of the mastoido-humeralis and the cervical
end of the submaxillary gland.
They receive afferent vessels from the cranium, the posterior part of
the tongue, the soft palate, pharynx, guttural pouch, larynx, posterior
part of the nasal cavity, and efferents from the submaxillary glands.
3. The =anterior cervical lymph glands= (Lg. cervicales craniales) are
situated chiefly along the course of the common carotid artery in the
vicinity of the thyroid gland, under cover of the cervical angle of the
parotid gland. Some occur between the thyroid and the submaxillary
salivary gland, others above and partly upon the thyroid. They are
related deeply to the posterior part of the larynx, the trachea, the
thyroid gland, and the œsophagus; below to the external maxillary vein
and the outer border of the omo-hyoideus.[177]
These glands are variable. Often there are none in front of the
thyroid and the group may extend back a considerable distance along
the course of the carotid artery.
Their afferents are deep lymph vessels from the head, the pharynx,
larynx, guttural pouch, and thyroid gland, and efferents from the
submaxillary and pharyngeal glands. Their efferent vessels go to the
middle and posterior cervical glands.
4. The =middle cervical lymph glands= (Lg. cervicales mediæ) form an
inconstant group situated a little in front of the middle of the neck on
the trachea below the carotid artery. The group is usually small and in
some cases is absent, being replaced by a number of glands occurring at
intervals along the course of the carotid artery. In other subjects the
group consists of several glands of considerable size. They are
intercalated in the course of the tracheal lymph ducts.
5. The =posterior cervical= or =prepectoral lymph glands= (Lg.
cervicales caudales) form a large group below the trachea at the
entrance to the thorax (Fig. 466). They occupy the interstices between
the vessels and muscles and extend forward a variable distance on the
ventral aspect of the trachea. They are covered by the panniculus and
sterno-cephalicus. Their afferent vessels come from the head, neck,
thorax, and thoracic limb. They receive efferent ducts of the anterior
and middle cervical, prescapular, and axillary glands. Their efferents
go to the thoracic duct on the left, to the right lymphatic duct on the
right, or open directly into the vena cava.
6. The =prescapular= or =superficial cervical lymph glands= (Lg.
cervicales superficiales) lie on the anterior border of the anterior
deep pectoral muscle, in relation to the omo-hyoideus internally and the
mastoido-humeralis externally (Figs. 431, 441, 466). They are on the
course of the ascending branch of the inferior cervical artery. They
receive afferents from the neck, breast, shoulder, and arm. Their
efferents pass to the prepectoral glands.
The =tracheal ducts=, right and left (Ductus trachealis dexter,
sinister), are collecting trunks for the lymph of the head and neck.
They lie on the trachea in relation to the carotid arteries. The right
one goes to the prepectoral glands or to the right lymphatic duct, the
left one to the terminal part of the thoracic duct.
THE LYMPH GLANDS AND VESSELS OF THE THORAX
1. The =intercostal lymph glands= (Lg. intercostales) are small and are
situated at the sides of the bodies of the thoracic vertebræ, in series
corresponding to the intercostal spaces. They receive afferents from the
vertebral canal, the spinal muscles, the diaphragm, intercostal muscles,
and pleura. The efferent vessels go to the thoracic duct.
In the young subject these glands are more numerous than in the adult,
and there are also glands along the dorsal face of the thoracic aorta
which seem to disappear later.
2. The =anterior mediastinal lymph glands= (Lg. mediastinales craniales)
(Fig. 428) are numerous. Some are situated on the course of the brachial
arteries and their branches; on the right side they are related deeply
to the trachea, on the left to the œsophagus also. They are variable in
size and disposition and are continuous in front with the prepectoral
glands. Other glands lie along the ventral face of the trachea on the
anterior vena cava and the right atrium of the heart; these are
continuous behind with the bronchial glands. A few glands usually occur
along the dorsal surface of the trachea, and there is often one at the
angle of divergence of the brachiocephalic trunk. The afferent vessels
come chiefly from the pleura, the pericardium, the heart, the thymus or
its remains, the trachea, and the œsophagus. Their efferent vessels pass
to the prepectoral glands and the thoracic duct.
The glands along the ventral face of the trachea are frequently
enlarged and usually pigmented in dissecting-room subjects. The left
recurrent nerve lies above them on the ventral face of the trachea.
3. The =bronchial lymph glands= (Lg. bronchiales) are grouped around the
terminal part of the trachea and the bronchi. One group lies on the
upper surface of the bifurcation of the trachea and is continued a short
distance backward under the œsophagus (Fig. 428). Others lie below the
trachea and bronchi and also occupy the angle between the aortic arch
and the pulmonary artery, concealing the left recurrent nerve and often
covering the vagus in this part of its course. Small glands occur along
the chief bronchi in the substance of the lungs (Lg. pulmonales). They
receive the deep and most of the superficial lymph vessels of the lungs,
and the efferents from the posterior mediastinal glands. Their efferent
vessels go to the thoracic duct and the anterior mediastinal glands. The
deep lymph vessels of the lung arise in plexuses which surround the
terminal bronchi and accompany the bronchi to the root of the lung. The
superficial vessels form a rich network under the pleura; most of them
pass to the bronchial glands.
The bronchial glands are commonly pigmented except in young subjects
and are often enlarged and indurated.
4. The =posterior mediastinal lymph glands= (Lg. mediastinales caudales)
are usually small and are scattered along the posterior mediastinum
above the œsophagus. They receive afferent vessels from the œsophagus,
mediastinum, diaphragm, and liver. The efferents go to the bronchial and
anterior mediastinal lymph glands, partly to the thoracic duct directly.
Sometimes one or two small glands are situated in the acute angle
between the posterior vena cava and the diaphragm.
THE LYMPH GLANDS AND VESSELS OF THE ABDOMEN AND PELVIS
The =lymph glands of the abdomen= consist of two main groups, parietal
and visceral. The =parietal glands= lie in the subperitoneal or
subcutaneous tissue; they receive the lymph vessels from the abdominal
and pelvic walls, from parts of the viscera, and from the proximal lymph
glands of the pelvic limbs. The =visceral glands= lie on the walls of
the viscera or in the peritoneal folds which connect the organs with the
wall or with adjacent viscera. They receive all or most of the lymph
vessels from the organs with which they are connected.
The =parietal glands= comprise the following:
1. The =lumbar lymph glands= (Lg. lumbales) lie along the course of the
abdominal aorta and posterior vena cava (Fig. 450). Some are placed
along the lower surface and sides of the vessels, others above. A few
small glands may be found above the sublumbar muscles. The small nodes
which are situated at the hilus of the kidneys are often termed the
renal lymph glands. They receive afferent vessels from the lumbar wall
of the abdomen and the paired viscera (kidneys, adrenals, genital
organs), also the inguinal vessels and the efferents of the iliac
glands. Their efferents go to the thoracic duct, constituting the lumbar
trunks of origin of that vessel.
2. The =internal iliac lymph glands= (Lg. iliacæ internæ) are grouped
about the terminal part of the aorta and the origins of the iliac
arteries (Fig. 450). Their afferent vessels come chiefly from the
pelvis, pelvic viscera, and tail, and they receive efferent vessels of
the external iliac and deep inguinal glands.
3. The =external iliac lymph glands= (Lg. iliacæ externæ) form a group
on either side on the iliac fascia at the bifurcation of the circumflex
iliac artery (Fig. 450). Their afferent vessels come from the flank and
abdominal floor, the outer surface of the thigh, and the precrural
glands. The efferent vessels go to the lumbar and internal iliac glands.
4. The =sacral lymph glands= (Lg. sacrales) are small nodes situated
along the borders of the sacrum and on its pelvic surface. They receive
afferents from the roof of the pelvis and from the tail, and their
efferent vessels pass to the internal iliac glands.
5. The =superficial inguinal lymph glands= (Lg. inguinales
superficiales) lie on the abdominal tunic in front of the external
inguinal ring (Fig. 457). They form an elongated group along the course
of the subcutaneous abdominal artery, on either side of the penis in the
male, above the mammary glands in the female; in the latter they are
often termed =mammary=. Their afferents come from the inner surface of
the thigh, the abdominal floor, the sheath and scrotum in the male, and
the mammary glands in the female. The efferent vessels ascend through
the inguinal canal and go to the deep inguinal and lumbar glands.
6. The =ischiatic lymph gland= (Lg. ischiadica) is a small node which
may be found at the lesser sciatic notch. It receives lymph from the
adjacent parts and from the popliteal glands, and sends efferents to the
sacral and internal iliac glands.
The =visceral glands= include the following:
1. The =gastric lymph glands= (Lg. gastricæ) are situated along the
course of the gastric arteries. Several occur along the attachment of
the gastro-phrenic ligament. A group lies at the lesser curvature a
short distance below the cardia. There is another small group on the
visceral surface where the posterior gastric artery divides into its
primary branches. Two or three small nodes are usually found on the
ventral aspect of the pylorus. Other small glands are scattered along
the course of the gastro-epiploic and short gastric arteries in the
great and gastro-splenic omenta. The efferent vessels pass largely to
the cœliac radicle of the thoracic duct, but along the left part of the
great curvature they go to the splenic glands.
2. The =hepatic lymph glands= (Lg. hepaticæ) lie along the portal vein
and hepatic artery and in the lesser omentum. Their efferent vessels go
to the cœliac radicle of the cisterna chyli.
Many of the lymph vessels from the parietal surface of the liver pass
in the falciform and lateral ligaments to the diaphragm and anastomose
with its lymphatics. Some pass through the diaphragm with the vena
cava and go to the mediastinal glands.
The =pancreatic lymph vessels= follow the course of the blood-vessels
which supply the gland; most of them go to the splenic and hepatic
glands.
3. The =splenic lymph glands= (Lg. lienales) lie along the course of the
splenic blood-vessels. Their afferent vessels come from the subscapular
network of the spleen, from the greater curvature of the stomach, and
from the left part of the pancreas. The efferents pass to the cœliac
radicle of the thoracic duct.
4. The =mesenteric lymph glands= (Lg. mesentericæ) are situated in the
great mesentery near its root. They are numerous and hence lie close
together. They receive a very large number of afferent vessels (400 to
500) from the small intestine. They have several considerable efferents
which concur in the formation of the intestinal radicles of the cisterna
chyli.
The lymph vessels of the intestine form three sets of capillary
plexuses, viz., in the subserosa, submucosa, and mucosa. The lymph
follicles, solitary and aggregate, lie in the zone of the plexus of
the mucosa. The collecting vessels arise from the subserous plexus.
5. The =lymph glands of the cæcum= are numerous and are distributed
along the course of the cæcal blood-vessels. Their efferents enter into
the formation of an intestinal radicle of the cisterna chyli.
6. The =lymph glands of the great colon= are extremely numerous and are
placed close together along the colic blood-vessels. Their efferent
vessels are large and numerous. They converge to two large trunks which
concur with those of the cæcum and small intestine to form an intestinal
radicle of the cisterna chyli.
The intestinal radicles of the cisterna chyli are formed by the
confluence of efferents from the intestinal lymph glands. The anterior
trunk lies on the left side of the anterior mesenteric artery, passes
between that vessel and the cœliac artery, turns sharply backward
across the right renal vessels and opens into the cisterna. It is
formed by the union of the cœliac trunk with efferents from the glands
of the small intestine, cæcum and colon. It is about four inches (ca.
10 cm.) in length and is ampullate. The posterior trunk receives
vessels from the small intestine and small colon. It usually opens
into a trunk formed by the union of the right and left lumbar ducts.
It is usually ampullate at its termination (Franck). The arrangement
of these collecting trunks is, however, very variable.
7. The =lymph glands of the small colon= are situated in part on the
wall of the bowel along the attachment of the mesentery, in part between
the layers of the latter along the course of the blood-vessels. The
efferent vessels go to the lumbar glands and to the posterior intestinal
radicle of the thoracic duct.
The =lymph vessels of the rectum= pass chiefly to the lumbar and
internal iliac glands.
8. The =anal lymph glands= (Lg. anales) form a small group on either
side of the sphincter ani externus (Figs. 451, 453). They receive
afferents from the anus, perineum, and tail. Their efferents go to the
internal iliac glands.
THE LYMPH GLANDS AND VESSELS OF THE THORACIC LIMB
1. The =axillary lymph glands= (Lg. axillares), some ten to twelve in
number, are grouped on the inner face of the distal part of the teres
major and the tendon of the latissimus dorsi at the angle of junction of
the external thoracic and subscapular veins with the brachial (Fig.
466). Their efferents include most of the lymph vessels of the limb,
which come directly or as efferents from the cubital glands. They
receive also lymph vessels from the thoracic wall. The efferents
accompany the brachial blood-vessels and end in the prepectoral glands
and the thoracic and right lymphatic ducts.
2. The =cubital lymph glands= (Lg. cubitales), usually eight to ten in
number, form a discoid oval group at the inner side of the distal part
of the shaft of the humerus (Figs. 441, 446). They lie behind the biceps
muscle on the brachial vessels and median nerve and are covered by the
deep fascia and the posterior superficial pectoral muscle. They receive
as afferents most of the vessels from the limb below this point. Their
efferents pass chiefly to the axillary glands, but in part to the
prescapular glands also.
A number of superficial lymph vessels ascend with or near the
subcutaneous veins (cephalic and accessory cephalic) and join the
prescapular and prepectoral glands. Superficial vessels from the
chest-wall and shoulder run across the latter to the prescapular glands.
The superficial lymphatics of the pectoral region form a plexus which
drains into the prepectoral and prescapular glands by a number of
vessels which accompany the cephalic vein. The deep lymph vessels of the
pectoral region run with the external thoracic vein to the axillary
glands.
THE LYMPH GLANDS AND VESSELS OF THE PELVIC LIMB
1. The =precrural= or =subiliac lymph glands= (Lg. subiliacæ) are
situated in the fold of the groin on the anterior border of the tensor
fasciæ latæ, about midway between the point of the hip and the patella
(Figs. 450, 451, 457). They lie on the course of the posterior branch of
the circumflex iliac artery, and number usually about a dozen. They
receive superficial lymph vessels from the hip, thigh, and flank. Their
efferent vessels ascend with the posterior circumflex iliac vein, enter
the abdomen near the external angle of the ilium, and join the external
iliac lymph glands.
2. The =deep inguinal lymph glands= (Lg. inguinales profundæ) form a
large group situated in the upper part of the femoral canal between the
pectineus and sartorius muscles (Figs. 451, 457). They cover the femoral
vessels and are related superficially to the inguinal ligament. They
receive nearly all of the lymph vessels of the limb below them. Their
efferent vessels ascend to the internal iliac glands.
3. The =popliteal lymph glands= (Lg. popliteæ), usually four to six in
number, lie behind the origin of the gastrocnemius and between the
biceps femoris and semitendinosus at the division of the posterior
femoral artery into its primary branches (Fig. 455). They receive the
deep lymph vessels of the distal part of the limb. Their efferent
vessels chiefly follow the course of the femoral vessels to the deep
inguinal glands, but one or two ascend in company with a vein along the
great sciatic nerve and may enter a gland at the lesser sciatic notch.
From this a vessel accompanies the internal pudic vein and joins the
internal iliac glands.
Several superficial lymph vessels ascend with or near the internal
metatarsal and saphenous veins, enter the femoral canal, and end in
the deep inguinal glands.
THE FŒTAL CIRCULATION
The blood of the fœtus is oxygenated, receives nutrient matter, and
gives off waste matter by close contiguity with the maternal blood in
the placenta. The chief differences in the blood-vascular system as
compared with that which obtains after birth are correlated with this
interchange.
The =umbilical arteries=, right and left, are large vessels which arise
from the internal iliac arteries and pass downward and forward in the
umbilical folds of peritoneum on either side of the bladder to the
umbilicus. Here they are incorporated with the umbilical vein and the
urachus in the umbilical cord, ramify in the allantois, and end as the
capillaries of the fœtal placenta. They conduct the impure blood to the
placenta. After birth these vessels retract with the bladder to the
pelvic cavity; their lumen becomes greatly reduced and the wall
thickened so that they are cord-like and are termed the round ligaments
of the bladder.
The =umbilical vein= receives the oxygenated blood from the placenta.
Its radicles converge to form in the horse a single large trunk which
separates from the other constituents of the umbilical cord on entering
the abdomen and passes forward along the abdominal floor in the free
border of the falciform ligament of the liver. It enters the latter at
the umbilical fissure and joins the portal vein, so that the blood
conveyed by it passes through the capillaries of the liver before
entering the posterior vena cava.
In the ox and dog some of the blood in the umbilical vein is conveyed
directly to the vena cava by the =ductus venosus= (Arantii). This vessel
is given off within the liver from a venous sinus formed by the
confluence of the portal and umbilical veins and passes directly to the
posterior vena cava.
The =foramen ovale= is an opening in the septum between the atria, by
which the latter communicate with each other. It is guarded by a valve
(Valvula foraminis ovalis) which prevents the blood from passing from
the left atrium to the right. After birth the foramen soon closes, but
this part of the septum remains membranous, and there is a deep =fossa
ovalis= in the right atrium which indicates the position of the former
opening. In some cases the foramen persists to a variable extent in the
adult without apparent disturbance of the circulation.
The =pulmonary circulation= is very limited in the fœtus, and most of
the blood which enters the pulmonary artery passes through the =ductus
arteriosus= to the aorta. This vessel is larger than the divisions of
the pulmonary which go to the lungs and joins the left side of the
aortic arch. After birth the pulmonary circulation undergoes promptly an
enormous increase and the ductus is rapidly transformed into a fibrous
cord—the =ligamentum arteriosum=.
The only arterial blood in the fœtus is that carried by the umbilical
vein. This blood is mixed in the liver with the venous blood of the
portal vein, and after passing through the capillaries of the liver is
carried by the hepatic veins to the posterior vena cava. The latter
receives also the venous blood from the posterior part of the trunk and
the pelvic limbs. It is generally believed that the blood carried into
the right atrium by the posterior vena cava passes largely, if not
entirely, through the foramen ovale into the left atrium, while the
blood flowing into it through the anterior vena cava passes into the
right ventricle. On this basis the blood received by the left atrium
consists chiefly of mixed blood from the posterior vena cava, since the
small amount of blood conveyed by the pulmonary veins is venous. This
mixed blood passes into the left ventricle and is forced into the
systemic arteries. The venous blood from the anterior part of the body
and the thoracic limbs is conveyed by the anterior vena cava to the
right atrium, passes into the right ventricle, and is forced into the
pulmonary artery. A small amount is carried to the lungs, but the bulk
of it passes by the ductus arteriosus into the aorta behind the point of
origin of the brachiocephalic trunk (anterior aorta), and is carried to
the posterior part of the body, a large part passing by the umbilical
arteries to the placenta.
THE BLOOD-VASCULAR SYSTEM OF THE OX
THE PERICARDIUM AND HEART
The =pericardium= is attached by two fibrous bands (Ligamenta
sternopericardiaca) to the sternum opposite the facets for the sixth
costal cartilages; these ligaments, right and left, are embedded in the
mass of fat which separates the apex of the pericardium from the floor
of the thorax.
[Illustration:
FIG. 467.—HEART OF OX, LEFT VIEW.
]
The =heart= of the adult ox has an average weight of about 5½ to 6
pounds (ca. 2.5 to 2.7 kg.), or about 0.4 to 0.5 per cent. of the
body-weight. Its length from base to apex is relatively longer than that
of the horse and the base is smaller in both its diameters.
A shallow =intermediate groove= (Sulcus intermedius) extends from the
coronary groove down the left side of the posterior border, but does not
reach the apex. The amount of fat in and near the grooves is much
greater than in the horse.
The heart is situated more to the left of the median plane than in the
horse and is opposite to the third, fourth, and fifth ribs when it is
contracted. It has extensive contact with the lateral wall of the thorax
on the left side, but none on the right side, where a considerable
thickness of lung covers the pericardium.[178]
Two bones, the =ossa cordis=, develop in the aortic fibrous ring. The
right one is in apposition with the atrio-ventricular rings and is
irregularly triangular in form. Its left face is concave and gives
attachment to the right posterior cusp of the aortic valve. The right
surface is convex from before backward. The base is superior. The
posterior border bears two projections separated by a notch. It is
usually a little more than an inch (ca. 4 cm.) in length. The left bone
is smaller and is inconstant. Its concave right border gives attachment
to the left posterior cusp of the aortic valve. There is a large fleshy
moderator band in the right ventricle.
THE ARTERIES[179]
The great arterial trunks in the thorax resemble those of the horse in
general disposition.
The =left coronary artery= is much larger than the right one; it gives
off a branch which descends in the intermediate groove, and terminates
by running downward in the right longitudinal groove. The =right
artery=, after emerging from the interval between the right auricle and
the pulmonary artery, divides into branches which are distributed to the
wall of the right ventricle.
The =brachiocephalic trunk= (anterior aorta) is usually four or five
inches (ca. 10 to 12 cm.) in length.
The =brachial arteries= give off in the thorax the following branches:
1. A common trunk for the subcostal, dorsal, superior or deep cervical,
and vertebral arteries.
(1) The =subcostal artery= commonly arises separately, but may be given
off as in the horse. It supplies the first three intercostal arteries.
(2) The =dorsal artery= is relatively small. It usually ascends in front
of the first costo-vertebral joint and is distributed as in the horse.
(3) The =superior= or =deep cervical artery= may arise from a common
stem (Truncus vertebro-cervicalis) with the vertebral, or may constitute
a branch of that artery. It passes up between the first thoracic and
last cervical vertebræ or between the sixth and seventh cervical and is
distributed as in the horse.
(4) The =vertebral artery= passes along the neck as in the horse to the
intervertebral foramen between the second and third cervical vertebræ,
gives off a muscular branch, and enters the vertebral canal (Fig. 469).
It runs forward on the floor of the canal—connected with its fellow by
two or three transverse anastomoses—and divides in the atlas into two
branches. The smaller internal division (cerebrospinal artery) passes
forward to the floor of the cranium and concurs with the condyloid
artery and branches of the internal maxillary in the formation of a
large =rete mirabile=. The large external branch emerges through the
intervertebral foramen of the atlas and ramifies in the muscles of the
neck in that region, compensating for the smallness of the branches of
the occipital artery. It also sends a branch to the rete mirabile. The
collateral branches detached to the cervical muscles are large and
compensate for the small size of the deep cervical artery. The
collateral spinal branches of the vertebrals pass through the
intervertebral foramina, divide into anterior and posterior branches,
and form two longitudinal trunks which are connected by cross-branches
so as to form irregular polygonal figures.
2. The =internal thoracic artery=.
3. The =inferior cervical artery= corresponds usually to the ascending
branch of that vessel in the horse.
4. The =external thoracic artery= is large and usually gives off a
branch which is equivalent to the descending branch of the inferior
cervical artery of the horse.
THE COMMON CAROTID ARTERY
[Illustration:
FIG. 468.—SCHEMA OF CHIEF ARTERIES OF HEAD OF COW.
_1_, Common carotid artery; _2_, thyro-laryngeal; _3_, thyroid; _4_,
laryngeal; _5_, pharyngeal; _6_, occipital; _7_, condyloid; _8_,
middle meningeal; _9_, pharyngeal; _10_, external maxillary; _11_,
lingual; _12_, sublingual; _13_, superior labial; _14_, internal
maxillary; _15_, masseteric; _16_, inferior alveolar; _17_,
buccinator; _18_, great palatine; _19_, sphenopalatine; _20_,
posterior auricular; _21_, superficial temporal; _22_, posterior
meningeal; _23_, anterior auricular; _24_, artery to matrix of horn;
_25_, deep temporal; _26_, arteries to rete mirabile; _27_, frontal;
_28_, malar; _28′_, dorsal nasal continuation of malar; _29_,
infraorbital; _29′_, lateral nasal continuation of _29_.
]
The =carotid arteries= usually arise from a common trunk about two
inches (ca. 5 cm.) in length, but in exceptional cases are given off
separately from the brachiocephalic. Each pursues a course similar to
that of the horse and is accompanied by the small internal jugular vein,
but is separated from the external jugular vein by the omo-hyoid and
sterno-mastoid muscles. It divides at the digastricus into occipital,
external maxillary, and external carotid arteries. In addition to
tracheal, œsophageal, and muscular branches, it gives off the thyroid
and laryngeal arteries. The =thyroid artery= (A. thyreoidea cranialis)
bends around the anterior end of the thyroid gland, in which it
ramifies. The accessory thyroid artery is usually absent. The =laryngeal
artery= may arise with the thyroid.
1. The =occipital artery= is relatively small. It gives off:
(1) The =pharyngeal artery=, which, however, may arise from the external
carotid.
(2) Several branches to the muscles (chiefly the flexors) and to the
atlanto-occipital joint.
(3) The =condyloid artery= passes into the cranium through the anterior
foramen in the condyloid fossa, and joins the vertebral in the formation
of the rete mirabile about the pituitary gland. Before entering the
cranium it gives off a branch to the pharyngeal lymph glands, and the
middle meningeal artery; the latter passes through the foramen lacerum.
Another branch enters the temporal canal and gives twigs to the
temporalis muscle and the mucous membrane of the frontal sinus. A
muscular branch emerges from the intervertebral foramen of the atlas. A
diploic branch goes into the occipital condyle and squama, and emits
twigs to the occipital muscles.
[Illustration:
FIG. 469.—FLOOR OF CRANIUM AND ANTERIOR PART OF VERTEBRAL CANAL OF OX.
_1_, Vertebral artery; _2_, muscular branches of _1_; _3_, branches of
_1_ to the rete mirabile, _4_; _5_, branches of internal maxillary
artery to rete; _6_, branch of internal maxillary artery entering
cranium through foramen ovale; _7_, condyloid artery; _8_, emergent
artery from rete, distributed like internal carotid artery of horse;
_9_, _9′_, longitudinal vertebral sinuses; _a_, cribriform plate;
_b_, optic foramina; _c_, for. lacerum orbitale + rotundum; _d_,
foramen ovale; _e_, occipital condyle; _f_, _g_, _h_, first, second,
and third cervical vertebræ. (After Leisering’s Atlas.)
]
2. The =external maxillary artery= is smaller than that of the horse,
but pursues a similar course. The =lingual artery= is large, and often
arises separately from the common carotid; it gives off a branch to the
submaxillary gland, and the =sublingual artery=. After turning around
the jaw the facial gives off the two =labial arteries=. The =superior
labial= is large; it usually gives off a branch which runs forward
almost parallel with the lateral nasal. The =angular artery= is absent
or rudimentary, and the =lateral= and =dorsal nasal arteries= spring
from branches of the internal maxillary.
3. The =external carotid artery= passes upward between the
stylo-hyoideus and the great cornu of the hyoid bone, turns forward
across the external face of the latter, and divides into superficial
temporal and internal maxillary arteries. It gives off the following
collateral branches:
(1) Branches to the parotid and submaxillary glands.
(2) The =pharyngeal artery=, which, however, often arises from the
occipital.
(3) The =posterior auricular=, which resembles that of the horse and
sends a stylo-mastoid branch into the tympanum. It may arise from the
superficial temporal.
(4) The =masseteric artery= resembles that of the horse, but is smaller.
The =superficial temporal artery= is large and presents the following
special features: (1) Its transverse facial branch passes into the
central part of the masseter. (2) It gives off a branch which
corresponds to the posterior meningeal artery of the horse, enters the
temporal canal, and ramifies in the dura mater, giving off twigs to the
external ear, the temporal muscle, and the frontal sinus. (3) It usually
gives off the anterior auricular artery. (4) Branches are supplied to
the frontalis muscle and the eyelids, (5) A large branch passes around
the outer side of the base of the horn-core, supplies the matrix of the
horn, and anastomoses across the back of the frontal eminence with the
artery of the opposite side.
The =internal maxillary artery= is less curved than in the horse and is
entirely extraosseous, since the alar canal is absent. The principal
differential features in its branching are as follows:
(1) The =ophthalmic artery= forms a rete mirabile within the periorbita.
Its frontal branch enters the supraorbital canal and ramifies chiefly in
the frontal sinus.
(2) Several branches take the place of the internal carotid artery. One
of these enters the cranial cavity through the foramen ovale and several
small ones pass through the foramen which represents the foramen
rotundum and foramen lacerum orbitale of the horse. They concur with the
vertebral and condyloid arteries in the formation of an extensive =rete
mirabile= on the cranial floor around the sella turcica. From each side
of the rete an artery arises which is distributed in general like the
internal carotid of the horse.
(3) The =malar artery= is large; it arises by a common trunk with the
infraorbital and gives off the =dorsal nasal= and the =angular artery of
the eye=.
(4) The =infraorbital artery= is large and emerges from the infraorbital
foramen to form the =lateral nasal artery=.
(5) The =palatine artery= is smaller than in the horse and usually
arises by a common trunk with the sphenopalatine. It passes through the
palatine canal and along the palatine groove, enters the nasal cavity
through the incisive fissure, and does not go to the upper lip. It forms
a rete mirabile about the naso-palatine canal and terminates in the
mucous membrane of the anterior part of the nasal cavity.
ARTERIES OF THE THORACIC LIMB
The =brachial artery= pursues the same course in the arm as that of the
horse. At the elbow it becomes the median.[180] The chief differential
features in its branches are as follows:
1. The =subscapular artery= is almost as large as the continuation of
the brachial. The =posterior circumflex artery= sends branches backward
and downward into the triceps, taking the place in part of the deep
brachial artery. The =thoracico-dorsal artery= supplies branches to the
pectoral muscles and the triceps as well as the teres major and
latissimus dorsi; it may arise directly from the brachial.
2. The =deep brachial artery= is small.
3. The =superior collateral ulnar artery= is often double, and does not
extend to the carpus.
The =median artery= (posterior radial artery) descends along the inner
part of the posterior surface of the radius and divides near the middle
of the forearm into the radial and ulnar arteries. It gives off at the
upper third of the forearm the =common interosseous artery=, a large
vessel which anastomoses with the deep brachial, passes through the
proximal interosseous space, and descends (as the dorsal interosseous)
in the groove between the radius and ulna, and concurs in the formation
of the rete carpi dorsale. At the distal end of the forearm it sends a
branch through the distal interosseous space, which passes downward,
assists in forming the rete carpi volare, and is continued in the
metacarpus as the external deep volar metacarpal artery. This is a small
vessel which passes down under the outer border of the suspensory
ligament and assists in forming the deep volar arch near the fetlock.
[Illustration:
FIG. 470.—ARTERIES OF DISTAL PART OF RIGHT FORE LIMB OF OX, ANTERIOR
VIEW.
_a_, Interosseous artery; _b_, dorsal branch of radial artery; _c_,
rete carpi dorsale; _d_, dorsal metacarpal artery; _e_, dorsal
common digital artery; _f_, _f_, dorsal proper digital arteries.
]
[Illustration:
FIG. 471.—ARTERIES OF DISTAL PART OF RIGHT FORE LIMB OF OX, POSTERIOR
VIEW.
_g_, Ulnar artery; _h_, radial artery; _i_, volar branch of common
interosseous artery; _k_, _l_, _m_, deep volar metacarpal arteries;
_A.v._, volar arches; _n_, volar common digital artery; _o_, _o′_,
_p_, volar proper digital arteries.
]
The =radial artery= is smaller than the ulnar. It descends on the flexor
carpi internus, passes over the postero-internal surface of the carpus,
and is continued as the internal deep volar metacarpal. At the distal
end of the forearm and at the carpus it furnishes branches to the retia
carpi. Another branch (A. met. perforans proximalis) runs outward
between the suspensory ligament and the large metacarpal bone, passes
through the proximal foramen of the bone, and unites with the
interosseous artery; before passing through the foramen it detaches the
middle deep volar metacarpal artery (A. met. volaris prof. III.), which
descends on the posterior face of the metacarpal bone, receives an
anastomotic branch from the internal deep artery, and concurs in the
formation of the deep volar arch above the fetlock.
The =ulnar artery=, the larger of the two divisions of the median,
descends under cover of the flexor carpi internus without giving off any
large branches in the forearm. It passes through the carpal canal and
continues along the inner side of the deep flexor tendon as the =volar
common digital artery=. At the distal third of the metacarpus this
vessel is joined by a branch from the internal deep volar metacarpal
artery, forming the superficial volar arch. Near this another branch of
the common digital (or of the internal digital) passes around the outer
border of the flexor tendons to the posterior face of the metacarpal
bone and concurs with the deep volar metacarpal arteries in the
formation of the deep volar arch. A branch from the arch passes forward
through the inferior foramen of the metacarpal bone and joins the dorsal
metacarpal artery which descends from the rete carpi dorsale in the
anterior metacarpal groove.
The =volar common digital artery= (A. metacarpea volaris superficialis
III.) passes into the interdigital space and divides into two =volar
proper digital arteries=, which descend along the interdigital surfaces
of the chief digits and pass through the foramina at the upper part of
the interdigital surfaces of the third phalanges, enter the cavities in
these bones, and ramify in a manner similar to the corresponding vessels
in the horse. The volar common digital detaches a branch (A.
interdigitalis perforans) which passes forward through the upper part of
the interdigital space and anastomoses with the dorsal metacarpal
artery.
The volar proper digital arteries (or the common digital) give off, in
addition to other collaterals, branches which correspond to the
arteries of the plantar cushion of the horse. These pass to the bulbs
of the claws and anastomose with each other and with the inner and
outer digital arteries, forming an arch from which numerous branches
are distributed to the matrix of the hoofs.
The =dorsal metacarpal artery= (A. met. dorsalis III.) is a small vessel
which arises from the rete carpi dorsale, descends in the groove on the
anterior face of the metacarpal bone, and is joined by the inferior
perforating metacarpal artery from the deep volar arch to constitute the
dorsal common digital artery. This vessel (A. digitalis communis
dorsalis III.) divides into two =dorsal proper digital arteries=.
The =internal digital artery= (A. digiti III. medialis) is the
continuation of the internal deep volar metacarpal artery. It descends
on the inner side of the inner digit and terminates at the bulb of the
claw by anastomosing with the corresponding volar proper digital artery.
It gives off a branch to the rudimentary digit and forms a transverse
anastomosis behind the first phalanx with the volar common digital or
its inner division.
The =external digital artery= (A. digiti IV. lateralis) arises from the
deep volar arch, passes down on the outer side of the external digit and
is distributed like the inner one.
BRANCHES OF THE THORACIC AORTA
The =bronchial= and =œsophageal= arteries often arise separately.
Ten pairs of =intercostal arteries= usually arise from the aorta. The
other three come from the subcostal artery.
The two =phrenic arteries= are very variable in origin. They may come
from the aorta, the cœliac, left ruminal, or an intercostal or lumbar
artery.
BRANCHES OF THE ABDOMINAL AORTA
The =cœliac artery= is about four to five inches (ca. 10 to 12 cm.) in
length. It passes downward and curves forward between the rumen and
pancreas on the left and the right crus of the diaphragm and the
posterior vena cava on the right. It gives off five chief branches.
1. The =hepatic artery= arises from the convex side of the curve of the
cœliac artery as it crosses the posterior vena cava. It passes downward,
forward, and to the right above the portal vein to the portal fissure,
and gives off the following branches:
(1) Pancreatic branches.
(2) Dorsal and ventral branches to the liver. The ventral branch is the
larger; it gives off the right gastric artery, which runs in the lesser
omentum to supply the origin of the duodenum and the pylorus,
anastomosing with the dorsal branch of the omaso-abomasal artery.
(3) The cystic artery supplies the gall-bladder.
(4) The gastro-duodenal artery divides into right gastro-epiploic and
pancreatico-duodenal branches. The right gastro-epiploic artery
anastomoses with the left gastro-epiploic. The pancreatico-duodenal
artery anastomoses with the first intestinal branch of the anterior
mesenteric artery.
2. The =right ruminal artery= (A. ruminalis dextra) is the largest
branch, and usually arises by a short common trunk with the splenic. It
runs downward and backward on the right face of the dorsal sac of the
rumen to the posterior transverse fissure, in which it turns around to
the left and anastomoses with branches of the left ruminal artery. It
gives off a pancreatic branch, dorsal and ventral coronary arteries,
branches to the great omentum, and ramifies on both surfaces of the
rumen.
3. The =left ruminal artery= (A. ruminalis sinistra) runs downward on
the anterior part of the right face of the rumen, enters the anterior
furrow, in which it runs from right to left, and continues backward in
the left longitudinal groove, anastomosing with branches of the right
artery. It supplies chiefly the left face of the rumen, but not its
posterior part. It usually gives off near its origin the =reticular
artery= (A. reticularis); this rather small vessel passes forward on the
dorsal curvature of the rumen and turns downward in the rumino-reticular
groove, in the bottom of which it runs around ventrally to the right
side. It gives off a branch which passes to the left of the cardia and
along the lesser curvature of the reticulum to the neck of the omasum.
The reticular branches anastomose with the omaso-abomasal and left
ruminal arteries.
4. The =omaso-abomasal artery= (A. gastrica sinistra) appears as the
continuation of the cœliac. It passes forward and downward to the
greater curvature of the omasum and divides after a course of four or
five inches into two branches. The =dorsal branch= curves sharply
backward on the dorsal surface of the omasum, continues along the lesser
curvature of the abomasum, and anastomoses with the hepatic artery. It
supplies branches to the omasum and to the lesser curvature and pyloric
part of the abomasum. The =ventral branch= (A. gastroepiploica sinistra)
runs forward and downward over the anterior extremity of the omasum,
passes backward in the great omentum close to the ventral curvature of
the abomasum, and anastomoses with the right gastro-epiploic. A
considerable branch from it curves around in front of the neck of the
omasum to communicate with the reticular artery. Another branch runs
back across the left side of the omaso-abomasal junction, and a third
goes to the lesser (ventral) curvature of the omasum.
5. The =splenic artery= usually arises by a common trunk with the right
ruminal artery. It passes forward and to the left across the dorsal
curvature of the rumen and enters the hilus of the spleen.
The =anterior mesenteric artery= arises from the aorta just behind the
cœliac, and has about the same caliber as the latter. It passes downward
and a little to the right, and crosses the colon as it emerges from the
spiral to run backward. After detaching twigs to the pancreas it gives
off in succession the following branches:
1. A branch (A. colica media) passes to the colon as it emerges from the
spiral arrangement. This artery is comparable to the middle colic or
artery of the small colon of the horse; it runs backward along the
terminal part of the colon, which it supplies.
[Illustration:
FIG. 472.—GASTRIC ARTERIES OF OX, RIGHT VIEW (PARTLY SCHEMATIC).
_1_, Cœliac artery; _2_, right ruminal; _3_, splenic; _4_, reticular;
_5_, left ruminal; _6_, omaso-abomasal; _7_, dorsal branch of _6_;
_8_, ventral branch of _6_ (= left gastro-epiploic); _A_, dorsal sac
of rumen; _B_, ventral sac of rumen; _C_, _C_, posterior blind sacs;
_D_, œsophagus; _E_, reticulum; _F_, omasum; _G_, abomasum; _H_,
duodenum; _I_, right longitudinal furrow of rumen. By an oversight
the reticular artery is shown as arising from the omaso-abomasal.
]
[Illustration:
FIG. 473.—GASTRIC ARTERIES OF OX, LEFT VIEW (PARTLY SCHEMATIC).
_1_, Left ruminal artery; _2_, continuation of right ruminal artery;
_3_, reticular artery, which disappears into rumino-reticular
groove; _A_, dorsal sac of rumen; _B_, ventral sac of rumen; _C_,
_C_, posterior blind sacs; _D_, œsophagus; _E_, reticulum; F,
rumino-reticular groove; _G_, left longitudinal furrow of rumen.
]
2. The ileo-cæco-colic artery ramifies on the right face of the spiral
part of the colon. It gives off the ileo-cæcal artery, which divides
into ileal and cæcal arteries.
3. An artery (Ramus collateralis) runs in the mesentery in a curve along
the ventral border of the coils of the colon. (This vessel is absent in
the sheep.)
4. An artery which constitutes the direct continuation of the anterior
mesenteric pursues a course in the mesentery corresponding to the series
of mesenteric lymph glands.
[Illustration:
FIG. 474.—PLAN OF BRANCHES OF ANTERIOR MESENTERIC ARTERY OF OX.
_1_, Anterior mesenteric artery; _2_, middle colic artery; _3_,
ileo-cæco-colic artery; _4_, ramus collateralis; _5_, continuation
of anterior mesenteric artery, giving off branches to small
intestine; _6_, cæcal artery; _7_, colic branch of posterior
mesenteric artery; _A_, termination of duodenum.
]
The two preceding vessels are essentially the arteries of the small
intestine, which they supply with the exception of its initial and
terminal parts. The first gives off no considerable branches in its
course along the ventral border of the coils of the colon, but on
curving upward along the latter it anastomoses with the second artery
and detaches numerous branches to the small intestine which form series
of superposed anastomotic arches. It supplies, roughly speaking, about
one-third of the small intestine and terminates by joining the ileal
artery. The second artery gives off numerous branches which also form
arches and supply about the first two-thirds of the small intestine,
exclusive of the small part supplied by branches of the cœliac artery.
Both arteries give branches to the lymph glands.[181]
The =posterior mesenteric artery= arises from the aorta near its
termination. It is small and supplies branches to the terminal part of
the colon and to the rectum.
The =renal arteries= arise from the aorta close together. The right one
passes outward and forward across the dorsal face of the posterior vena
cava to the hilus of the kidney. The left one runs backward, but
necessarily varies in direction in conformity with the position of the
kidney (_q. v._).
The =spermatic arteries= resemble those of the horse.
The =utero-ovarian arteries= are small.
The five pairs of =lumbar arteries= derived from the aorta are
distributed much as in the horse. The sixth usually comes from the
internal iliac artery.
[Illustration:
FIG. 475.—PELVIC ARTERIES OF COW.
Part of the right wall of the uterus and vagina is removed and the
cervix uteri is shown in sagittal section. _a_, Aorta; _b_,
utero-ovarian artery; _b′_, ovarian, and _b″_, uterine branch of
_b_; _c_, external iliac artery; _d_, right internal iliac artery;
_e_, common trunk of umbilical artery (_e′_) and middle uterine
artery (_f_); _g_, ilio-lumbar artery; _h_, anterior gluteal
arteries; _i_, middle hæmorrhoidal artery; _k_, posterior uterine
artery; _l_, perineal artery; _m_, posterior gluteal artery; _n_,
obturator arteries; _o_, artery of clitoris; _p_, posterior
mesenteric artery; _r_, anterior hæmorrhoidal artery; _s_, middle
sacral artery; _1_, ovary; _2_, apparent body of uterus, really
apposed horns; _2′_, cornu; _3_, vagina; _4_, cervix uteri; _4′_,
vaginal part of uterus (os uteri); _5_, _5′_, broad ligaments, large
part of right one removed; _6_, urinary bladder; _7_, rectum; _8_,
sacrum; _9_, symphysis pelvis. (After Zieger.)
]
The =middle sacral artery= is a vessel about 5 mm. in diameter which
continues the aorta. It arises from the dorsal face of the aorta at the
angle of divergence of the internal iliacs, runs backward on the pelvic
surface of the sacrum a little to the left of the median line, and is
continued as the middle coccygeal artery. It gives off small collateral
branches to the spinal cord and the muscles of the tail and the =lateral
coccygeal arteries=. The latter may have a common trunk of origin, and
each divides into dorsal and ventral branches. The =middle coccygeal
artery= runs through the ventral (hæmal) arches of the coccygeal
vertebræ. The coccygeal arteries are connected at pretty regular
intervals by segmental anastomoses.
The =internal iliac arteries= are much longer than in the horse. Each
passes backward on the sacro-sciatic ligament and divides about the
middle of the pelvic wall into posterior gluteal and internal pudic
branches. The chief differences in its distribution are: (1) A large
trunk gives origin to the umbilical and middle uterine arteries. The
=umbilical artery= is usually largely obliterated and its terminal
branches receive their blood through anastomoses with the internal
pudic. It gives off near its origin two small vessels, the ureteral
artery (A. ureterica) and the deferential artery (A. deferentialis),
which accompany the ureter and the vas deferens respectively. The
=middle uterine artery= (A. uterina media) is very large. It is
distributed chiefly to the cornu of the uterus, and compensates for the
small size of the utero-ovarian artery. (2) The =ilio-lumbar= artery is
relatively small and is distributed chiefly to the sublumbar muscles. It
is sometimes replaced by branches of the circumflex iliac and gluteal
arteries. (3) The =anterior gluteal artery= is commonly represented by
several vessels. (4) The =obturator artery= is represented by several
small branches which supply the obturator and adductor muscles. (5) The
=iliaco-femoral= and =lateral sacral arteries= are absent. The absence
of the latter is compensated by the middle sacral and gluteal arteries.
(6) The =posterior gluteal= (or ischiatic) artery is large. It emerges
through the lesser sciatic notch and ramifies in the biceps femoris and
adjacent muscles. (7) The =internal pudic artery= (A. urethro-genitalis)
is the direct continuation of the internal iliac. It gives off branches
to the rectum, bladder, urethra, and genital organs. In the male it
supplies the accessory genital glands and divides into dorsal and deep
arteries of the penis; the a. dorsalis penis runs along the dorsum penis
to the glans and gives twigs to the prepuce; the a. profunda penis gives
off a perineal branch and enters the corpus cavernosum penis. In the
female it gives off a large posterior uterine artery, which supplies the
posterior part of the uterus and gives branches to the vagina and
bladder. It ends as the a. clitoridis, which supplies the clitoris and
adjacent parts.
ARTERIES OF THE PELVIC LIMB
The =external iliac artery= has the same course as in the horse. The
circumflex iliac artery is large. A branch from it emerges between the
abdominal and lumbar muscles near the external angle of the ilium and
ramifies like the terminals of the ilio-lumbar artery of the horse.
The =femoral= and =popliteal arteries= pursue a similar course to those
of the horse. The chief differences in their branches are as follows:
1. The =external pudic artery= is distributed chiefly to the scrotum in
the male. In the cow it is usually termed the =mammary= and is very
large, especially during lactation. Each divides at the base of the
mammary gland into two branches which are distributed to the anterior
and posterior parts (“quarters”) of the gland. A small branch
accompanies the subcutaneous abdominal vein to the xiphoid region.
2. The =deep femoral artery= gives off an obturator branch which passes
up through the obturator foramen to supply the obturator internus and
compensates otherwise for the absence of the obturator artery.
3. The =anterior femoral artery= is large. It often gives off the
=external circumflex artery= of the thigh, which perforates the proximal
end of the quadriceps, gives branches to that muscle, the iliacus,
glutei, and tensor fasciæ latæ.
4. The =saphenous artery= is large. It descends in front of the
homonymous vein to the postero-internal surface of the hock, where it
divides into two plantar branches. The =internal plantar artery= (A.
plantaris medialis) is the direct continuation of the saphenous. It
descends at first along the inner border of the superficial flexor
tendon and is continued as the =internal superficial plantar metatarsal
artery= along the inner side of the deep flexor tendon with the internal
plantar nerve. It anastomoses at the proximal end of the metatarsus with
the perforating metatarsal artery, assisting in the formation of the
proximal plantar arch. Near the fetlock it concurs with the perforating
branch of the dorsal metatarsal artery in the formation of the distal
plantar arch. Below this it is continued as the =internal digital
artery=. The =external plantar artery= (A. plantaris lateralis) is
small. It descends along the outer border of the deep flexor tendon with
the external plantar nerve, concurs with the perforating tarsal and the
internal plantar arteries in the formation of the proximal plantar arch,
and gives branches to the rete tarsi dorsale. Continuing downward along
the deep flexor tendon as the =external superficial plantar metatarsal
artery=, it assists in forming the distal plantar arch and becomes the
=external digital artery=.
[Illustration:
FIG. 476.—ARTERIES OF DISTAL PART OF RIGHT HIND LIMB OF OX, ANTERIOR
VIEW.
_a_, Anterior tibial artery; _b_, proximal perforating metatarsal
artery; _c_, dorsal metatarsal artery; _d_, dorsal common digital
artery; _e_, _e′_, dorsal proper digital arteries.
]
[Illustration:
FIG. 477.—ARTERIES OF DISTAL PART OF RIGHT HIND LIMB OF OX, POSTERIOR
VIEW.
_e_, Saphenous artery; _f_, _f′_, internal and external plantar
arteries; _g_, _g′_, internal and external superficial plantar
metatarsal arteries; _h_, deep plantar metatarsal artery; _i_, _j_,
internal and external plantar digital arteries; _k_, plantar common
digital artery; _l_, _l′_, internal and external plantar digital
arteries.
]
The =posterior tibial artery= is relatively small and is distributed
chiefly to the muscles on the posterior surface of the tibia. Lower down
it is replaced by the saphenous artery as described above.
The =anterior tibial artery= has the same course as in the horse. It is
continued down the groove on the front of the metatarsal bone as the
=dorsal metatarsal artery=. This is the chief artery of the region and
is accompanied by two veins. It detaches the proximal perforating
metatarsal artery, which passes through the proximal foramen of the
metatarsal bone and concurs with the superficial plantar arteries in
forming the proximal plantar arch. Near the distal end of the metatarsal
bone it gives off the distal perforating metatarsal artery which passes
back through the distal metatarsal foramen and assists in forming the
distal plantar arch. The two arches are connected by the small =deep
plantar metatarsal artery= which lies in the groove on the posterior
face of the large metatarsal bone.
The =dorsal common digital artery= is the direct continuation of the
dorsal metatarsal. It divides into two branches which unite in the
interdigital space with the corresponding branches of the plantar common
digital to form the proper digital arteries.
The =plantar common digital artery= descends from the distal plantar
arch, anastomoses in the interdigital space with the internal and
external digitals, and divides into two branches which join those of the
dorsal common digital artery as before mentioned.
The foregoing is a brief statement of the more common arrangement of the
vessels in the distal part of the limb, but minor variations are very
common.
THE VEINS[182]
The =vena hemiazygos= usually takes the place of the vena azygos. It
lies along the left side of the aorta and the bodies of the thoracic
vertebræ, turns down across the left face of the aorta and left
pulmonary artery, runs back over the left auricle and opens into the
great coronary vein or the right atrium. It receives the intercostal
veins.
Two =jugular veins= occur on either side. The =internal jugular vein=
(V. jugularis interna) is a relatively small vessel which accompanies
the carotid artery. It arises by occipital, laryngeal, and thyroid
radicles, receives tracheal, œsophageal, and muscular branches, and
joins the external jugular near its termination. It is sometimes absent,
but in some cases it appears, on the other hand, to be large enough to
interfere with venesection practised on the external jugular. The
=external jugular vein= (V. jugularis externa) is very large and
corresponds to the single jugular of the horse. It is separated from the
carotid artery in the greater part of its course by the
sterno-cephalicus and omo-hyoideus muscles.
The =inferior cerebral vein= usually does not unite with the occipital;
the latter is continued by the internal jugular vein.
The =orbital veins= form a network between the periorbita and the
muscles of the eyeball. This plexus communicates with the cavernous
sinus and with the superior cerebral vein. It is also drained by the
=frontal vein= which runs in the supraorbital canal and groove and joins
the angular vein of the eye.
The =dorsal nasal vein= is usually double.
The =superior labial vein= usually joins the infraorbital.
The =vena reflexa= is absent and the radicles which are received by it
in the horse go to the internal maxillary vein.
The =sublingual vein= is very large.
The =veins of the thoracic limb= differ chiefly in the distal part; the
special features are as follows:
The =dorsal digital veins= ascend on the front of the digits and are
connected with the other digital veins by transverse branches. They
unite near the fetlock to form the =dorsal metacarpal vein=. This runs
upward on the anterior face of the metacarpus and carpus, inclines to
the inner surface of the radius, and joins the accessory cephalic or the
cephalic vein.
The =volar digital veins= are larger than the dorsal. They lie on the
interdigital surfaces of the digits and unite in the interdigital space
to form a trunk which is a satellite of the volar common digital artery.
The =internal= and =external digital veins= lie in front of the
corresponding arteries. They are connected with the volar digital vein
by a large branch which passes between the flexor tendons and the first
phalanx. At the distal end of the metacarpus each inclines forward and
anastomoses with the volar common digital vein to form the volar venous
arch. The inner vein is continued as the internal volar metacarpal vein
along the inner border of the suspensory ligament, and becomes a
satellite of the radial artery in the forearm, while the outer one is
continued on the posterior face of the metacarpal bone by two irregular
veins, the external and middle volar metacarpals. The latter anastomose
freely with each other and with the inner vein. They unite below the
carpus or join the volar common digital vein.
The =accessory cephalic vein= is the upward continuation of the dorsal
metacarpal vein and is much larger than in the horse.
The =posterior vena cava= is partially embedded in the medial border of
the liver. Its abdominal part has a thicker wall than in the horse. Its
affluents correspond to the arteries of which they are satellites. The
=renal veins= are large and thick-walled; they run obliquely forward and
join the vena cava at an acute angle. The left one is much the longer.
Two =middle sacral= veins usually accompany the artery.
The =veins of the mammary glands= deserve special notice. They converge
to a venous circle at the base of the udder, which is drained chiefly by
two pairs of veins. The =subcutaneous abdominal vein= (anterior mammary
or “milk” vein) is very large in animals of the dairy breeds and its
course along the ventral wall of the abdomen is easily followed. It is
usually flexuous. It emerges at the anterior border of the udder about
two or three inches (ca. 5 to 8 cm.) from the linea alba, runs forward
(deviating a little outward), dips under the panniculus, passes through
a foramen in the abdominal wall about a handbreadth from the median
plane, and joins the internal thoracic vein. The =external pudic vein=
(middle mammary vein) is also of considerable size. It ascends in the
inguinal canal as a satellite of the artery and joins the external iliac
vein. The right and left veins are connected at the posterior border of
the base of the udder by a large transverse branch. From the latter
arises the =perineal vein= (posterior mammary vein), which runs medially
upward and backward to the perineum, turns around the ischial arch, and
joins the internal pudic vein. In the male these veins are relatively
small.
The deep veins of the thigh and leg resemble those of the horse, but
there is no recurrent tibial vein.
The =saphenous vein= is much smaller than in the horse.
The =recurrent tarsal vein= (external saphenous) is large. It is the
upward continuation of the external plantar metatarsal vein and
anastomoses with the anterior tibial and saphenous veins. It arises on
the outer face of the hock, ascends at first in front of the tendo
Achillis, then crosses the latter externally, passes up between the
biceps femoris and semitendinosus, and joins the posterior femoral vein.
There are three chief metatarsal veins. The great =dorsal metatarsal
vein= arises at the distal part of the metatarsus by the union of the
dorsal digital vein and a large branch from the venous arch above the
sesamoids. It ascends superficially between the long and lateral
extensor tendons and becomes the chief radicle of the anterior tibial
vein. The =internal plantar metatarsal vein= arises from the venous arch
above the fetlock, ascends along the inner border of the suspensory
ligament, passes through the vascular canal of the metatarsus and
centro-tarsal (as the perforating tarsal) and joins the anterior tibial
vein. The =external plantar metatarsal vein= is larger than the
preceding. It passes superficially over the outer face of the hock and
is continued by the recurrent tarsal vein.
The =digital veins= differ from those of the fore limb chiefly in that
the dorsal vein is large and the plantar absent or small.
The =portal vein= is formed usually by the confluence of two radicles,
gastric and mesenteric. It receives the right gastro-epiploic vein and
veins of the pancreas. The gastric vein is the largest affluent. It is
formed by the junction of three veins, the left of which receives the
splenic vein. The anterior mesenteric vein is also formed by the
confluence of three radicles; it usually receives the small posterior
mesenteric vein. The portal tributaries are in general satellites of the
corresponding arteries.
THE LYMPH VESSELS AND GLANDS
The =thoracic duct= arises from a small cisterna chyli and is very
variable. It is exceptional to find a single trunk throughout, as is
often the case in the horse. The duct is largely covered by fat and
small lymph glands. There are often two ducts, one on either side of the
aorta, which may join at a variable point or terminate close together at
the junctions of the jugular and brachial veins. In other cases the duct
is single for a variable distance, then bifurcates or divides into three
or four branches, which are often connected by plexiform anastomoses.
The efferent vessels from the intestine converge to a large trunk which
accompanies the anterior mesenteric artery and vein. It passes below the
pancreas and receives usually a large duct which is formed by efferent
vessels from the stomach, liver, and spleen; this duct sometimes opens
directly into the cisterna. The gastro-intestinal trunk receives the
collecting duct (truncus lumbalis) of the lumbar lymph vessels, forms a
bend around the right renal vessels, and joins the cisterna.
The =lymph glands= in the ox are in general less numerous but larger
than those of the horse, and in some situations a single large gland
occurs instead of a group of smaller ones, as found in the latter
animal.
The =submaxillary lymph glands= are usually two in number, right and
left; each is situated under the external maxillary vein between the
submaxillary salivary gland and the sterno-cephalicus muscle. Usually
one or two hæmolymph glands are near it. There is generally a small
gland on the deep face of the anterior part of the submaxillary salivary
gland, and small nodes may be found further forward in the submaxillary
space.
A large =subparotid lymph gland= lies on the postero-superior part of
the masseter muscle, partly under cover of the upper end of the parotid
gland. Several hæmolymph glands lie on its deep face.
The =pharyngeal lymph glands= number two or three on each side. Of
these, two large =suprapharyngeal glands= (Lg. retropharyngeales) are
situated about an inch apart between the dorsal wall of the pharynx and
the ventral straight muscles (Figs. 281, 365). These are two to three
inches long. Enlargement of them is likely to cause difficulty in
swallowing and in respiration. Behind these are several hæmolymph
glands. An =atlantal gland= is situated below the wing of the atlas on
the spinal accessory nerve. It is discoid, oval in outline, and may be
an inch and a half or more in length. It is partly covered by the upper
end of the submaxillary salivary gland.
A smaller lymph gland (parapharyngeal) is usually found along the lower
border of the carotid artery (_i. e._, ventral to the atlantal gland) on
the lateral wall of the pharynx and under cover of the submaxillary
salivary gland or at its posterior border.
Two or three small =anterior cervical lymph glands= commonly lie along
the carotid artery a little further back.
The =middle cervical lymph glands= comprise a series of small nodes
along the dorsal face of the trachea.
In the sheep and goat there is a lymph gland at the middle of the
neck, in the angle between the spinalis and complexus, covered by the
splenius. It receives vessels from the atlantal gland and sends
efferents to the prescapular gland.
The =prescapular= or =superficial cervical lymph gland= is situated at
the anterior border of the supraspinatus under cover of the
mastoido-humeralis and omo-transversarius. It is elongated and may be an
inch or more in width and four or five inches long. Two occur in
exceptional cases.
A chain of hæmolymph glands lies along the front of the shoulder,
covered above by the trapezius. Others are frequently found (in the
calf especially) on the surface of the omo-transversarius at the point
where it passes under the mastoido-humeralis (Forgeot).
[Illustration:
FIG. 478.—SUPERFICIAL LYMPH GLANDS OF COW PROJECTED ON SURFACE OF
BODY.
_1_, Submaxillary; _2_, subparotid; _3_, atlantal; _4_,
parapharyngeal; _5_, anterior cervical; _6_, middle cervical; _7_,
prescapular; _8_, precrural. (With use of fig. in Ellenberger-Baum,
Anat. f. Künstler.)
]
The =posterior cervical= or =prepectoral lymph glands= number commonly
three or four on each side. One or two are placed on the brachial
vessels, one below the brachial vein at the first rib, and one at the
junction of the common trunk of the external and subcutaneous thoracic
veins with the brachial.
The =intercostal lymph glands= are situated, as in the horse, at the
upper parts of the intercostal spaces. Associated with them are
hæmolymph glands.
The =sternal lymph glands= are situated along the course of the internal
thoracic artery at the lower part of the intercostal spaces. The largest
is close to the thoracic inlet. Several glands occur in the fat about
the apex of the pericardium.
4. Several =anterior mediastinal lymph glands= are placed along the
œsophagus and the trachea.[183] Hæmolymph glands occur here also.
Usually three large =bronchial lymph glands= are present (Fig. 289). One
is situated at the origin of each chief bronchus and the third is under
the trachea at the origin of the special bronchus of the apical lobe of
the right lung. Another may lie between the aorta and the left branch of
the pulmonary artery. These glands are often pigmented. Other small
nodes are situated on the bronchi within the lungs.
The =posterior mediastinal lymph glands= comprise two or three of large
size placed along the dorsal wall of the œsophagus. There may be a
single gland about eight inches (ca. 20 cm.) long, the anterior half of
which lies on the œsophagus (Fig. 289).[184] A small gland is situated
in the acute angle formed by the posterior vena cava and the diaphragm.
A single =axillary lymph gland= is situated on the distal part of the
teres major on the course of the vein from the latissimus dorsi.
The =lumbar lymph glands= form an irregular series scattered along the
abdominal aorta and posterior vena. A bean-shaped =renal lymph gland=
occurs at the hilus of each kidney. Hæmolymph glands occur along the
course of the aorta.
[Illustration:
FIG. 479.—INTESTINE OF OX, SPREAD OUT.
_Ca_, Cæcum; _C_, colon; _D_, duodenum; _H_, ileum; _J_, jejunum; _R_,
rectum; _m_, mesenteric lymph glands. (After Edelmann.)
]
The =internal iliac lymph glands= comprise a group of five or six at the
termination of the aorta and the origin of the vena cava. A discoid
gland, two inches or more in diameter, occurs near the side of the
pelvic inlet at the angle of divergence of the circumflex iliac artery
from the external iliac. A small gland is sometimes found at the origin
of the prepubic artery.
The =external iliac lymph glands= number commonly two on either side,
and are situated near the point of the hip in front of the anterior
branch of the circumflex iliac artery.
The =superficial inguinal lymph glands= are situated centrally below the
prepubic tendon and in the narrow space between the origins of the
graciles. In the male there are usually two or three on either side of
the penis behind the sigmoid flexure. In the cow they are
=supramammary=, _i. e._, are situated above the posterior margin of the
base of the udder; two large glands which are in apposition with each
other medially are constant, and above these there are often two smaller
glands.
An =ischiatic lymph gland=, which is discoid and usually about an inch
in diameter, is situated on the lower part of the sacro-sciatic ligament
near the lesser sciatic notch under cover of the biceps femoris.
An =anal lymph gland= is situated on the retractor ani on either side.
The =gastric lymph glands= are numerous and comprise: (1) a chain along
the course of the right ruminal artery and two or three in the left
groove of the rumen; (2) several on the reticulum above and below the
junction with the omasum; (3) a series along the course of the superior
omasal vessels and the lesser curvature of the abomasum; (4) an
extensive chain along the ventral face of the omasum and the great
curvature of the abomasum at the attachment of the great omentum.
Two or three large =hepatic= or =portal lymph glands= are found at the
upper part of the portal fissure of the liver.
No lymph glands occur at the hilus of the spleen. The efferent vessels
from the spleen appear to go to glands along the course of the cœliac
artery.
A large discoid =cœliac lymph gland= lies on the pancreas and the cœliac
artery, covering the latter as it gives off its primary branches.
The =mesenteric lymph glands= are large and numerous. They form a chain
in the lower part of the mesentery along the course of the great
mesenteric artery. They are chiefly elongated and narrow, and some have
a length of six to eight inches (15 to 20 cm.) or more. Sometimes
several unite and form a narrow band about two feet in length. A large
gland occurs at the origin of the spiral part of the colon, a group is
found near the anterior mesenteric trunk, and others are scattered along
the coils of the colon, which are best seen on the right side. A chain
of small lymph glands extends along the terminal part of the colon and
the dorsal face of the rectum.
The =precrural lymph gland= is situated on the aponeurosis of the
external oblique at the anterior border of the tensor fasciæ latæ a
short distance above the stifle. It is elongated like the prescapular
gland and may be six inches (ca. 15 cm.) long. Several subcutaneous
hæmolymph glands occur in this vicinity; others are situated further
forward on the flank not far from the last rib. There is usually a
round, flattened lymph gland about an inch in diameter on the upper part
of the quadriceps femoris under cover of the tensor fasciæ latæ, and one
or more small ones occur on the surface of the latter muscle.
No =deep inguinal lymph glands= are present.
A single =popliteal lymph gland= an inch or more in length is situated
somewhat lower down on the gastrocnemius than in the horse, behind the
tibial and peroneal nerves.
CIRCULATORY SYSTEM OF THE PIG
THE HEART
The =pericardium= is attached to the sternum from a point opposite to
the third rib as far as the xiphoid cartilage, and also to the sternal
part of the diaphragm.
The =heart= is small in proportion to the body-weight, especially in fat
animals. It is relatively short and wide. The apex is blunt and is
marked by a notch (Incisura apicis). Its long axis is more oblique, but
it is less asymmetrical with regard to the median plane, than in the
horse or ox. The lower border of the left auricle (appendix) is marked
by several notches and is situated at a lower level than the right one.
The right longitudinal groove is placed far back and there is no
posterior sulcus.
THE ARTERIES
The =pulmonary vessels= present no remarkable features.
The =aorta= resembles that of the horse and ox in its course and
relations, but the arch is more strongly curved. There is no common
brachiocephalic trunk (anterior aorta).
The =brachiocephalic artery= arises first from the aortic arch and
passes forward below the trachea to the first rib. Here it gives off the
=common carotid arteries=, and is continued around the first rib as the
right brachial.
The =superior cervical=, =vertebral=, and =dorsal arteries= usually
arise by a common trunk.
The =inferior cervical artery= is large; its ascending branch gives off
the =posterior thyroid artery= and =parotid branches=.
The =internal= and =external thoracic arteries= give branches to the
pectoral mammary glands; the external may be absent.
The =left brachial artery= arises from the aortic arch just above the
brachiocephalic. It curves forward and downward and turns around the
anterior border of the first rib. Its superior cervical, vertebral, and
dorsal branches usually arise separately.
The =carotid arteries= arise from the brachiocephalic close together or
by a very short common trunk. They terminate in occipital and internal
and external carotid divisions.
The =occipital artery= resembles that of the horse.
The =internal carotid artery= usually arises by a common trunk with the
occipital. After giving off a large meningeal branch it passes through
the foramen lacerum and forms with the opposite artery a rete mirabile
which resembles that of the ox, but is smaller and is not connected with
the vertebral and condyloid arteries.
The =external carotid artery= has the same course and termination as in
the horse. Its branches present the following special features: (1) The
=lingual artery= is relatively large and supplies the pharyngeal artery,
the sublingual, muscular branches, and branches to the soft palate,
submaxillary gland, and larynx. (2) The =external maxillary artery= is
small and is distributed chiefly to the submaxillary gland, the
pharyngeal lymph glands, the masseter and the panniculus. It does not
extend upon the lateral surface of the face. (3) The =posterior
auricular artery= is long and relatively large; it gives off the
posterior meningeal.
The =internal maxillary artery= pursues a flexuous course between the
ramus of the mandible and the pterygoid muscles. Its branches offer the
following special features: (1) The =inferior alveolar= (or dental) is
large; branches from it emerge through four or five mental foramina and
take the place of the inferior labial. (2) The =buccinator artery= is
also large and extends to the lips. (3) The =infraorbital artery=
extends to the snout and replaces the superior labial largely and the
lateral nasal in part. The malar branch compensates largely for the
absence of the lateral and dorsal nasal. (4) The =palatine artery= is
small.
The =intercostal arteries= number fourteen to sixteen in either side; of
these ten to twelve arise from the aorta, usually by short common
trunks. Frequently an intercostal artery is given off from that of an
adjacent space.
The =bronchial= and =œsophageal arteries= usually arise separately.
The =cœliac artery= is half an inch to an inch long. It supplies a
branch to the left crus of the diaphragm and divides into two primary
branches, gastro-hepatic and splenic. The =gastro-hepatic artery= is the
larger. It gives off pancreatic branches, the anterior gastric artery,
branches to the lesser curvature of the stomach, pyloric and
gastro-duodenal arteries. The latter divides into pancreatico-duodenal
and right gastro-epiploic. The anterior gastric usually supplies the
œsophageal artery. The continuing trunk (A. hepatica propria) gives off
a cystic branch and divides in the portal fissure into four branches
which supply the liver. The =splenic artery= gives off the posterior
gastric (usually), branches to the stomach above the cardia, twigs to
the pancreas, short gastric arteries to the left part of the great
curvature, and splenic branches, and is continued as the left
gastro-epiploic artery.
The posterior gastric may arise from the gastro-hepatic or in the
angle of divergence of the two primary divisions of the cœliac. The
œsophageal branch may come from the splenic.
[Illustration:
FIG. 480.—ARTERIES OF DISTAL PART OF RIGHT FORE LIMB OF PIG, ANTERIOR
VIEW.
_a_, Terminal part of volar interosseous artery; _b_, dorsal
interosseous artery; _c_, rete carpi dorsale; _d_, dorsal metacarpal
arteries; _e_, dorsal common digital arteries; _f_, dorsal proper
digital arteries.
]
[Illustration:
FIG. 481.—ARTERIES OF DISTAL PART OF RIGHT FORE LIMB OF PIG, POSTERIOR
VIEW.
_g_, Ulnar artery; _h_, superficial branch of radial artery; _i_,
collateral ulnar artery; _j_, volar interosseous artery; _h_, deep
branch of radial artery; _k_, deep volar metacarpal arteries; _l_,
superficial volar metacarpal arteries; _m_, volar common digital
artery; _n_, volar proper digital arteries.
]
The =anterior mesenteric artery= is long like that of the ox. It gives
twigs to the pancreas, the ilio-cæcal and two colic arteries, and is
continued in the mesentery as the artery of the small intestine. This
gives off numerous branches which form a series of arches along the
mesenteric lymph glands. From these is formed a rich network which gives
off innumerable fine branches placed close together. The colic arteries
enter the axis of the spiral coil of the colon and anastomose at its
apex. Their branches also form rich networks.
A =phrenico-abdominal artery= arises on either side a little in front of
the renals. It divides into branches which go to the costal part of the
diaphragm and the abdominal muscles.
The =renal= and =spermatic arteries= present no special characters.
The =posterior mesenteric artery= arises near the termination of the
aorta. It is small and is distributed like that of the ox.
Six pairs of =lumbar arteries= arise from the aorta. The seventh comes
from the middle sacral.
The terminal branches of the aorta resemble those of the ox.
The arteries of the shoulder, arm, and forearm resemble in general those
of the ox.
[Illustration:
FIG. 482.—ARTERIES OF DISTAL PART OF RIGHT HIND LIMB OF PIG, ANTERIOR
VIEW.
_a_, Anterior tibial artery, continued on tarsus as the dorsalis
pedis; _b_, perforating tarsal artery; _c_, dorsal metatarsal
arteries; _d_, common digital arteries; _e_, proper digital
arteries.
]
[Illustration:
FIG. 483.—ARTERIES OF DISTAL PART OF RIGHT HIND LIMB OF PIG, POSTERIOR
VIEW.
_f_, Saphenous artery, continued as internal tarsal artery; _g_,
external tarsal artery; _h_, internal plantar artery; _h′_, external
plantar artery; _i_, perforating tarsal artery; _j_, deep plantar
metatarsal arteries; _k_, common digital artery; _l_, proper digital
arteries.
]
The main facts as to the =metacarpal= and =digital arteries= are as
follows: The rete carpi dorsale is formed essentially by the terminals
of the interosseous artery of the forearm. It gives rise to three
=dorsal metacarpal arteries= which descend in the corresponding
interosseous spaces and unite with branches of the volar metacarpals to
form three =common digital arteries=. Each of these divides into two
=proper digital arteries=, which descend along the interdigital surfaces
of the digits. On the volar surface are two =volar arches=, superficial
and deep, from which three =superficial= and three =deep volar
metacarpal arteries= arise. The deep arteries unite near the distal end
of the space between the principal metacarpal bones to form a stem which
unites with the middle (third) superficial artery. The superficial
arteries unite to form an arch from which =proper digital arteries= are
given off to the axial aspect of the small digits, and a common digital
which supplies two =volar proper digital arteries= to each of the chief
digits.
The arteries of the hip, thigh, and leg are arranged much as in the ox.
A few special features may be noted.
The =ilio-lumbar artery= gives off a branch to the quadriceps femoris.
It may also supply the posterior abdominal artery, which otherwise
arises from the deep femoral.
The =deep femoral artery= is given off above the level of the pubis. The
posterior abdominal and external pudic arteries may arise from it by a
short common trunk or separately. The =external pudic= gives branches to
the prepuce but not to the penis. The =popliteal artery= gives off the
peroneal.
The =femoral artery= gives off a short trunk which divides into anterior
femoral and external circumflex arteries, the latter being much the
larger.
The =saphenous artery= is large. It descends on the inner surface of the
leg and hock and concurs with the perforating tarsal artery in forming
the proximal plantar arch.
The =posterior tibial artery= is small, being replaced distally by the
saphenous. It gives branches to the muscles on the posterior face of the
tibia and supplies the nutrient artery of that bone.
The =anterior tibial artery= is continued as the dorsalis pedis on the
flexion surface of the tarsus. This gives off the =perforating tarsal
artery=, which passes back through the vascular canal of the tarsus and
unites with the terminal branches of the saphenous to form the proximal
plantar arch.
The =metatarsal= and =digital arteries= resemble in arrangement the
corresponding vessels of the fore limb.
THE VEINS
The veins resemble in general those of the ox. Thus there is a
hemiazygos vein and two jugular veins, the internal one being relatively
larger than in the ox. A few differential features may be noted.
The =buccinator vein= resembles that of the horse, and unites with the
=vena reflexa= to form a short common trunk which joins the facial.
The =facial vein= resembles in general that of the horse. The =dorsal
nasal vein= is large, receives the veins from the snout, runs backward
in the groove of the nasal bone and joins the frontal vein; it is
connected with its fellow by a transverse branch, and anastomoses freely
with the malar and facial.
The veins of the distal parts of the limbs naturally present differences
which are correlated with those of the arteries.
THE LYMPH VESSELS AND GLANDS
The =thoracic duct= often divides near its termination into two branches
which unite to form an ampulla. The latter suddenly contracts and opens
into the terminal part of the left jugular vein.
The =submaxillary lymph glands= are situated in the space between the
omo-hyoid and internal pterygoid muscles in relation to the lower part
of the anterior border of the submaxillary salivary gland. There are
commonly two on each side, one large, the other small.
The =parotid lymph glands= (Fig. 309) are reddish-brown in color. There
are usually four of considerable size on either side. One is situated at
the upper part of the posterior border of the masseter, partly covered
by the parotid gland. Another large subparotid gland lies below the base
of the ear. Ventral to this are two smaller glands, one above and one
below the external jugular vein.
The =pharyngeal= (or retropharyngeal) =lymph glands= (Fig. 310) are
situated on the dorsal wall of the pharynx above the external carotid
artery and below and behind the paramastoid process. There are usually
two of considerable size on either side.
The =middle cervical lymph glands= form a group on the
mastoido-humeralis on the course of the external jugular vein.
The =prescapular lymph glands= are situated at the anterior border of
the anterior deep pectoral muscle undercover of the trapezius and
omo-transversarius.
The =prepectoral lymph glands= are reddish in color and usually three in
number. The largest is placed centrally under the trachea; the others
are situated on the brachial vessels as they turn around the first rib.
The =axillary lymph glands= are usually absent, but very small nodes may
be found near the insertion of the latissimus dorsi. Cubital glands are
not present.
[Illustration:
FIG. 484.—STOMACH AND PART OF INTESTINE OF PIG, SPREAD OUT.
_a_, Pyloric portion of stomach; _b_, duodenum; _c_, jejunum; _d_,
cæcum; _e_, _f_, colon; _g_, pancreas; _h_, epiploic foramen (of
Winslow); _i_, portal vein; _k_, hepatic lymph glands; _l_, gastric
lymph glands; _m_, œsophagus. (After Edelmann.)
]
The =thoracic lymph glands= comprise: (1) a gland of considerable size
on the first segment of the sternum; (2) about half a dozen reddish
glands along the upper face of the thoracic aorta; (3) several glands
along the lower face of the trachea; (4) the =bronchial lymph glands=;
one of these lies on the bifurcation of the trachea and another at the
apical bronchus of the right lung (Fig. 371).
The =lumbar lymph glands= are scattered along the abdominal aorta and
the vena cava. Those placed near the hilus of the kidney are often
designated =renal=.
The =internal iliac lymph glands= are rounded and relatively large. They
comprise: (1) three or four glands situated on and between the origin of
the circumflex iliac and the external and internal iliac arteries; (2) a
gland in the angle of divergence of the internal iliac arteries.
The =external iliac lymph glands= are small, two or three in number, and
lie in front of the circumflex iliac vessels near the point of the hip.
The visceral lymph glands of the abdomen comprise:
1. =Gastric lymph glands= on the lesser curvature of the stomach.
2. Several small =hepatic lymph glands= along the portal vein.
3. An elongated =splenic lymph gland= on the splenic vessels near the
dorsal end of the spleen.
4. A series of =mesenteric lymph glands= situated along the anastomotic
arches formed by the vessels of the small intestine.
5. Several =cæcal lymph glands= situated along the first part of the
cæcal vessels.
6. Two series of =colic lymph glands= which accompany the arteries of
the spiral part of the colon, and are exposed by separating the coils of
the bowel. Small glands are placed in the colic mesentery and above the
rectum.
7. The =anal lymph glands= are situated on either side on the retractor
ani.
A small =ischiatic lymph gland= is found on the sacro-sciatic ligament
near the lesser sciatic notch.
The =precrural lymph glands= are situated on the aponeurosis of the
external oblique below the external angle of the ilium.
The =superficial inguinal lymph glands= are situated behind the external
inguinal ring. No deep inguinal lymph glands are present.
The =popliteal lymph glands= are small normally and may escape notice.
A few nodules occur in front of the distal part of the tendo Achillis.
CIRCULATORY SYSTEM OF THE DOG
THE PERICARDIUM AND HEART
The =pericardium= is attached to the sternal part of the diaphragm by a
fibrous band, and is connected with the sternum only by the mediastinal
pleura.
The =heart= is almost globular in form, the apex being much blunter than
in the other animals, and marked by a notch. Its long axis is almost
parallel with the sternum and the apex (covered by the pericardium) is
directed against the sternal part of the diaphragm. Its weight averages
about 0.8 to 1 per cent. of the body-weight.[185]
The base extends forward to a transverse plane through the lower ends
of the third pair of ribs. The apex lies opposite the sixth costal
cartilage in expiration. On the right side the pericardium is in
direct contact with the chest-wall over a narrow triangular area (base
anterior) from the fourth to the sixth intercostal space inclusive. On
the left side the area of contact is smaller and is at the fourth,
fifth, and sixth cartilages.
The two coronary arteries may arise by a common trunk. Each divides into
circumflex and descending branches. The left artery is twice as large as
the right one.
The great coronary vein ascends in the left longitudinal groove to the
coronary groove, in which it winds around the posterior face of the
heart to the right side and opens into the right atrium below the
posterior vena cava. Near its termination it receives one or two veins
which ascend along the right longitudinal furrow. Several small veins
from the wall of the right ventricle open into the right atrium
separately or by a common trunk.
THE ARTERIES
There is no common brachiocephalic trunk (anterior aorta). Two large
vessels arise from the convexity of the aortic arch; these are the
=brachiocephalic= and =left brachial arteries=. The =brachiocephalic=
gives off the two =carotid arteries=, no common trunk being present. It
frequently also supplies the posterior thyroid artery. The intrathoracic
branches of the brachial arteries are as follows:
A common trunk gives off the =dorsal=, =subcostal=, and =superior
cervical arteries=. The dorsal artery passes out in front of the first
rib, and the superior cervical through the first intercostal space. The
latter is relatively small.
[Illustration:
FIG. 485.—ARTERIES OF THORACIC CAVITY AND PART OF NECK OF DOG.
_a_, Aortic arch; _a′_, thoracic aorta; _b_, brachiocephalic artery;
_c_, left brachial artery; _d_, _d_, common carotid arteries; _e_,
vertebral artery; _f_, dorsal artery; _g_, deep or superior cervical
artery (usually given off from a common trunk with _f_); _h_,
extrathoracic part of _f_; _i_, subcostal artery; _k_, inferior
cervical artery; _l_, descending branch of _k_; _m_, ascending
branch of _k_; _n_, internal scapular; _o_, acromial; _p_,
superficial cervical; _q_, _s_, extrathoracic part of left brachial;
_r_, external thoracic; _t_, internal thoracic; _t′_, asternal;
_t″_, anterior abdominal; _u_, perforating branch of _t_; _v_,
anterior mediastinal (thymic); _w_, ventral intercostals; _x_,
bronchial; _y_, œsophageal; _y′_, dorsal intercostals; _z_,
descending branch of left coronary artery; _z′_, circumflex branch
of same; _1_, œsophagus; _2_, trachea; _2′_, bronchi; _3_, first rib
(sawn off); _4_, right ventricle; _5_, left ventricle; _5′_, left
auricle; _5″_, pulmonary artery (cut off); _6_, diaphragm; _7_, _8_,
_9_, last three cervical vertebræ; _10_, thymus. (After Ellenberger,
in Leisering’s Atlas.)
]
The =vertebral artery= may arise either in front of or behind the trunk
above mentioned; in the latter case it crosses the inner face of the
trunk. It passes along the neck in typical fashion to the third cervical
vertebra and divides into three branches. The largest of these supplies
the muscles in this region, compensating for the absence of branches of
the superior cervical artery. The second passes between the second and
third cervical vertebræ into the vertebral canal and unites with the
opposite artery and a branch of the occipital artery to form the
basilar. The third branch is the small continuation of the parent trunk;
it passes to the wing of the atlas and anastomoses with the occipital.
The =inferior cervical artery= gives off the superficial cervical which
ascends in front of the supraspinatus.
The =internal thoracic artery= is large and sends perforating branches
to the pectoral mammary glands.
The =external thoracic artery= arises outside of the thorax and sends
branches to the mammary glands.
The =common carotid arteries=, left and right, arise in that order from
the brachiocephalic. In the neck the right one lies on the trachea, the
left on the œsophagus. Collateral branches are the posterior thyroid
(which may, however, arise from the right or left brachial or the
inferior cervical), pharyngeal, thyro-laryngeal muscular, tracheal, and
glandular (to the submaxillary gland). Each carotid divides under the
wing of the atlas into occipital and internal and external carotid
branches.
[Illustration:
FIG. 486.—SUPERFICIAL VESSELS OF HEAD OF DOG.
_1_, Facial artery; _2_, inferior labial artery; _3_, artery of angle
of mouth; _4_, superior labial artery; _5_, lateral nasal artery;
_6_, dorsal nasal artery; _7_, superficial temporal artery; _8_,
transverse facial artery; _9_, anterior auricular artery; _10_,
zygomatico-orbital artery; _11_, satellite vein of _10_; _12_, ant.
auricular vein; _13_, superficial temporal vein; _14_, internal
maxillary vein; _15_, post. auricular vein; _16_, _17_, external
jugular vein; _18_, external maxillary vein; _19_, _23_, facial
vein; _20_, inf. labial vein; _21_, buccinator vein; _22_, vena
reflexa; _24_, superior labial vein; _25_, vena angularis oculi;
_26_, dorsal nasal vein; _a_, concha; _b_, parotid gland; _c_,
submaxillary gland; _d_, submaxillary lymph glands; _e_,
mylo-hyoideus; _f_, digastricus; _g_, masseter; _h_, zygomaticus;
_i_, scutularis; _k_, temporalis; _l_, orbicularis oculi; _m_,
zygomatic arch; _n_, retractor anguli oris; _o_, buccinator.
(Ellenberger-Baum, Anat. d. Hundes.)
]
The =occipital artery= is small. It gives off =condyloid= and =posterior
meningeal= branches, passes up through the notch on the anterior margin
of the wing of the atlas, and is distributed to the muscles of this
region. Its =cerebrospinal= branch passes through the intervertebral
foramen, and unites in the vertebral canal with its fellow and a branch
from the vertebral artery to form the basilar. A retrograde branch
anastomoses with the vertebral as in the horse.
The =internal carotid artery=, also small, passes to the foramen lacerum
posterius, enters the carotid canal and forms a bend before entering the
cranium through the carotid foramen. It forms a plexus which is
connected by branches with the middle meningeal and ophthalmic arteries.
It then perforates the dura mater and enters into the formation of the
arterial circle (of Willis).
The =external carotid artery= is the direct continuation of the common
carotid. It passes along the lateral wall of the pharynx, emerges from
beneath the digastricus, and divides into superficial temporal and
internal maxillary arteries. It gives off the large flexuous =lingual
artery= which has a course similar to that of the horse. The =external
maxillary=, smaller than the lingual, passes along the upper border of
the digastricus, gives off the sublingual, gains the anterior border of
the masseter, and divides into superior and inferior labial and the
angularis oris. The last-named vessel passes forward on the cheek
between the labials to the angle of the mouth. The =sublingual artery=
passes at first along the upper border of the digastricus and continues
between the mylo-hyoideus and the ramus of the mandible. The =posterior
auricular artery= arises at the anterior border of the digastricus,
gives branches to the salivary glands and the adjacent muscles, and
ascends on the convex face of the concha. It divides into two branches
which return along the borders of the external ear.
The =superficial temporal artery=, after giving off the =anterior
auricular artery= and a small =transverse facial artery=, turns forward
under the temporal fascia toward the eye, and divides into upper and
lower branches which supply the frontal region and the eyelids. It also
supplies branches to the parotid gland and the masseter and temporalis
muscles.
The =internal maxillary artery= pursues a course similar to that of the
horse. The mental branches of the =inferior alveolar= (or dental)
=artery= are of considerable size and are distributed in the lower lip
and gums. Two or three =deep temporal arteries= are present. The
anterior one may arise from the buccinator; it gives off the middle
meningeal, which sends a branch to the carotid plexus. The =ophthalmic
artery= gives off a branch which enters the cranium through the foramen
lacerum orbitale and connects with the internal carotid; this is termed
the internal ophthalmic and gives off the arteria centralis retinæ. The
superficial branches of the =infraorbital artery= replace the dorsal and
lateral nasal arteries, and compensate for the small size of the
superior labial.
The =brachial artery= in its course in the arm presents no special
features. At the elbow it passes between the biceps and the pronator
teres, descends (as the median) under the flexor carpi radialis about a
third of the way down the forearm, and divides into radial and ulnar
arteries. Among its collateral branches are: (1) The =subscapular
artery=, which passes up between the subscapularis and teres major,
turns around the posterior angle of the scapula and terminates in the
supraspinatus, deltoid, trapezius, and mastoido-humeralis. In about half
the cases it gives off the =anterior circumflex=, which often arises
with the =posterior circumflex=. Its other branches resemble those of
the horse. (2) The =anterior circumflex artery= (in about half the
cases). (3) The =deep brachial= arises about a third of the way down the
arm. (4) The =bicipital artery= (for the biceps) is given off at the
lower part of the arm. (5) The =proximal collateral radial artery= (not
present in the horse) arises at the lower fourth of the arm, crosses
over the terminal part of the biceps, descends on the extensor carpi
radialis, and concurs with a branch of the volar interosseous in forming
the rete carpi dorsale. It often supplies the bicipital artery. (6) The
=anterior radial artery= (A. collateralis radialis distalis) is very
small. (7) The =common interosseous artery= is given off a little below
the elbow. It supplies branches to the flexor muscles and the =dorsal
interosseous artery=, which passes through the interosseous space, gives
branches to the extensor muscles, and by its terminal twigs concurs in
the formation of the rete carpi dorsale. The direct continuation of the
trunk is the =volar interosseous artery=, which descends under cover of
the pronator quadratus, gives off a branch to the rete carpi dorsale and
the =fifth volar metacarpal artery=, and terminates by joining the volar
branch of the radial artery to form the deep volar arch. (8) The =volar
antibrachial artery= (Ramus volaris antibrachii) arises below the
interosseous and descends at first under the flexor carpi radialis, then
between the heads of the deep flexor, and divides into ascending and
descending branches.
The =radial artery=, the smaller terminal of the brachial, descends
along the inner border of the radius, and divides near the carpus into
dorsal and volar branches. The =dorsal branch= assists in forming the
rete carpi dorsale. The larger =volar branch= descends behind the inner
border of the carpus and joins the end of the volar interosseous in
forming the =deep volar arch=. From this arch three =deep volar
metacarpal arteries= descend in the second, third, and fourth
intermetacarpal spaces and concur with the corresponding superficial
volar and the dorsal arteries to form the common digitals.
[Illustration:
FIG. 487.—VESSELS AND NERVES OF INNER SURFACE OF SHOULDER AND ARM OF
DOG.
_a_, _b_, Brachial artery; _c_, subscapular vessels; _d_,
thoracico-dorsal vessels; _e_, deep brachial vessels; _f_, superior
collateral ulnar vessels; _g_, brachial vein; _h_, _h″_, cephalic
vein; _h′_, mediano-radial vein; _i_, anterior thoracic nerves; _k_,
musculo-cutaneous nerve; _l_, median nerve; _m_, ulnar nerve; _n_,
radial nerve; _o_, thoracico-dorsal nerve; _1_, subscapularis
muscle; _2_, supraspinatus muscle; _3_, teres major; _4_, latissimus
dorsi; _5_, deep pectoral muscle; _6_, biceps brachii; _7_, long
head of triceps; _8_, tensor fasciæ antibrachii; _9_, internal head
of triceps; _10_, pronator teres. (Ellenberger-Baum, Anat. d.
Hundes.)
]
[Illustration:
FIG. 488.—ARTERIES OF FOREARM OF DOG, INNER VIEW.
_a_, Brachial; _a′_, median; _c_, common interosseous; _d_, volar
antibrachial; _e_, radial; _e′_, _e″_, dorsal and volar branches of
_e_; _f_, _f′_, cutaneous branches of _e_; _g_, ulnar; _1_, biceps
brachii; _2_, extensor carpi radialis; _3_, pronator teres; _4_,
deep digital flexor; _5_, radius; _6_, superficial digital flexor;
_7_, flexor carpi radialis; _8_, flexor carpi medius; _9_, humerus.
(Ellenberger-Baum, Anat. d. Hundes.)
]
The =ulnar artery= descends on the deep flexor of the digit, and sends a
connecting branch to the radial above the carpus. Near the middle of the
metacarpus it gives off the =first volar metacarpal artery= and divides
into the =second=, =third=, and =fourth superficial volar metacarpal
arteries=. The first volar artery unites with the corresponding dorsal
artery to form the =first common digital artery=, which supplies proper
digital arteries for the opposed surfaces of the first and second
digits. The superficial volar arteries descend in the spaces between the
other metacarpal bones, unite near the metacarpo-phalangeal joints with
the corresponding deep volar and dorsal metacarpal arteries to form
three =common digital arteries=. Each of the latter divides after a
short course into two =proper digital arteries=, which run along the
opposed surfaces of the second to the fifth digits. The external digital
artery of the fifth digit comes from the =superficial volar arch= formed
by the union of a branch of the volar interosseous with the fourth
superficial volar metacarpal artery.
[Illustration:
FIG. 489.—ARTERIES OF DISTAL PART OF RIGHT FORE LIMB OF DOG, ANTERIOR
VIEW.
_a_, Branch of volar interosseous artery; _b_, proximal collateral
radial artery (external branch); _c_, radial artery (dorsal branch);
_d_, rete carpi dorsale; _e_, deep dorsal metacarpal arteries; _f_,
superficial dorsal metacarpal arteries; _g_, common digital
arteries; _h_, proper digital arteries.
]
[Illustration:
FIG. 490.
_i_, Radial artery; _j_, ulnar artery; _k_, volar interosseous artery;
_l_, deep volar arch; _m_, external (fifth) volar metacarpal artery;
_n_, deep volar metacarpal arteries; _p_, superficial volar
metacarpal arteries; _o_, _q_, common digital arteries; _r_, proper
digital arteries.
]
The rete carpi dorsale gives off four =dorsal metacarpal arteries= which
descend in the intermetacarpal spaces and unite near the
metacarpo-phalangeal joints with the volar arteries to form the common
digitals.
The =thoracic aorta= supplies the last nine or ten pairs of intercostal
arteries, but no anterior phrenic arteries. It gives off two or more
œsophageal branches, in addition to the broncho-œsophageal, which arises
close to or with the sixth intercostal and ramifies in the usual manner.
The =abdominal aorta=, after giving off the external iliac arteries,
continues about half an inch to an inch (ca. 1 to 3 cm.) under the last
lumbar vertebræ, gives off the internal iliacs, and is continued by the
middle sacral artery. This small vessel runs backward under the sacrum
and coccygeal vertebræ and gives off branches in segmental fashion.
[Illustration:
FIG. 491.—END BRANCHES OF AORTA AND RADICLES OF POSTERIOR VENA CAVA OF
DOG.
_a_, Abdominal aorta; _b_, posterior mesenteric artery; _c_, lumbar
arteries; _d_, circumflex iliac artery; _e_, external iliac artery;
_f_, deep femoral artery; _g_, posterior abdominal artery; _h_,
external pudic artery; _a_, femoral artery; _i_, _i_, internal iliac
arteries; _k_, visceral branch of _i_; l, parietal branch of _i_;
_m_, ilio-lumbar artery; _n_, anterior gluteal artery; _o_, lateral
coccygeal artery, _p_, posterior gluteal artery; _q_, umbilical
artery; _r_, middle hæmorrhoidal artery; β, posterior hæmorrhoidal
artery; _s_, perineal artery; _t_, art. profunda penis; _n_, art.
bulbi urethræ, _v_, art. dorsalis penis; _w_, middle sacral artery,
_a′_, posterior vena cava; other veins are satellites of arteries
and correspondingly named; _1_, ilio-psoas muscle; _2_, tendon of
psoas minor; _3_, abdominal muscles; _4_, sartorius; _5_, rectus
femoris; _5′_, vastus internus; _6_, pectineus; _6′_, adductor; _7_,
gracilis; _8_, symphysis pelvis; _9_, ilium; _10_, pyriformis; _11_,
gluteus superficialis; _12_, obturator internus; _13_, penis; _14_,
lumbar vertebræ. (After Ellenberger, in Leisering’s Atlas.)
]
The =cœliac artery= gives off the hepatic artery and forms a short
=gastro-splenic= trunk. The hepatic artery gives off several hepatic
branches, and the pyloric or right gastric artery, which passes along
the lesser curvature of the stomach, anastomoses with the (left)
=gastric artery=, and is continued by the gastro-duodenal. This divides
near the pylorus into right gastro-epiploic and pancreatico-duodenal.
The (left) gastric artery passes to the lesser curvature of the stomach
and ramifies chiefly on the left part of the stomach, giving off a
branch which anastomoses with the pyloric branch of the hepatic. The
=splenic artery= gives off pancreatic branches, and reaches the lower
part of the spleen. It gives off the left gastro-epiploic, and a branch
which passes to the dorsal end of the spleen, which it supplies, besides
giving off twigs to the left extremity of the stomach.
The =anterior mesenteric artery= arises close behind the cœliac. It
gives off a common trunk for two colic arteries and the ileo-cæco-colic.
The former supply the transverse and the anterior part of the left or
descending colon, while the latter divides into branches for the ileum,
cæcum, and first part of the colon. The trunk is continued as the artery
of the small intestine, giving off fourteen to sixteen branches (Aa.
jejunales), which form a series of anastomotic arches in the mesentery
near the bowel.
Two =phrenico-abdominal arteries= (Aa. phrenicæ caudales) come off from
the aorta behind the anterior mesenteric, and divide into phrenic and
abdominal branches. Each phrenic artery diverges from its fellow in
descending on the abdominal surface of the corresponding crus of the
diaphragm to the sternal part. The inner branches anastomose with those
of the opposite artery, the outer branches with intercostal arteries
chiefly. The abdominal arteries give branches to the lumbar muscles, the
renal fat and capsules, and ramify in the oblique abdominal muscles.
The =renal= and =spermatic arteries= offer no special features.
The =utero-ovarian artery= divides near the ovary into three or four
branches which supply the ovary and uterus, anastomosing with the
uterine artery.
The =posterior mesenteric artery= is small. It divides into two branches
which supply the terminal part of the colon and the anterior part of the
rectum.
The =circumflex iliac artery= usually arises from the terminal part of
the aorta.
The =external iliac artery= usually gives off no collateral branches.
[Illustration:
FIG. 492.—ARTERIES OF PELVIC LIMB OF DOG, INTERNAL VIEW.
_a_, Abdominal aorta; _b_, femoral; _c_, _c′_, deep femoral; _d_,
posterior abdominal; _e_, external pudic; _f_, internal circumflex;
_g_, anterior femoral (accompanied by anterior branch of femoral
nerve); _h_, external circumflex; _i_, _k_, muscular branches; _l_,
articular branch; _m_, saphenous; _n_, _o_, plantar and dorsal
branches of saphenous; _q_, saphenous nerve; _r_, obturator nerve;
_1_, ilio-psoas; _2_, ilium; _3_, gracilis; _4_, semitendinosus;
_5_, adductor magnus; _6_, adductor longus; _7_, quadriceps femoris;
_8_, sartorius; _9_, semimembranosus; _10_, gastrocnemius; _11_,
tibialis anterior; _12_, tibia. (Ellenberger-Baum, Anat. d. Hundes.)
]
[Illustration:
FIG. 493.—ARTERIES OF DISTAL PART OF RIGHT HIND LIMB OF DOG, ANTERIOR
VIEW.
_a_, External branch of anterior tibial artery; _b_, anterior tibial
artery; _c_, saphenous artery (anterior branch); _d_, perforating
metatarsal artery; _e_, dorsal metatarsal arteries; _f_, deep dorsal
metatarsal arteries; _g_, superficial dorsal metatarsal arteries;
_h_, anastomoses between dorsal and plantar arteries; _i_, common
digital arteries; _j_, proper digital arteries.
]
[Illustration:
FIG. 494.—ARTERIES OF DISTAL PART OF RIGHT HIND LIMB OF DOG, POSTERIOR
VIEW.
_k_, Saphenous artery (posterior branch); _l_, _l′_, internal and
external plantar arteries; _m_, perforating metatarsal artery; _n_,
deep plantar metatarsal arteries; _o_, superficial plantar
metatarsal arteries; _p_, common digital artery; _q_, proper digital
arteries.
]
The =femoral artery= has the usual course. The deep femoral gives off
the posterior abdominal and external pudic arteries by a very short
common trunk or separately. In the female the external pudic divides
into anterior and posterior branches; the former runs forward, supplies
branches to the inguinal lymph glands, the mammary glands and skin, and
anastomoses with the mammary branch of the internal thoracic artery; the
posterior branch pursues a flexuous course between the thighs to the
vulva, where its terminal branches anastomose with the internal pudic
artery. The anterior femoral may arise by a short common trunk with the
external circumflex. The former, accompanied by the anterior branch of
the femoral nerve, dips in between the rectus femoris and vastus
internus. The external circumflex artery passes forward between the
sartorius internally and the rectus femoris and tensor fasciæ latæ
externally and supplies branches to these muscles and the glutei. In
addition to muscular branches of considerable size, an articular branch
(A. genu suprema) arises a little below the middle of the thigh and runs
downward and forward to the inner face of the stifle joint. The
=saphenous artery= is large. It arises from the inner surface of the
femoral a little below the middle of the femur, descends superficially
to the upper part of the leg and divides into two branches. The smaller
=anterior branch= (Ramus dorsalis) passes obliquely downward and forward
across the inner surface of the tibia to the flexion surface of the hock
and terminates in three =superficial dorsal metatarsal arteries=. The
=posterior branch= (Ramus plantaris) passes down on the inner face of
the gastrocnemius and the long digital flexor. It gives off a branch (A.
tarsea lateralis) which descends obliquely to the external surface of
the tarsus, and at the posterior face of the tarsus detaches the
=internal= and =external plantar arteries=; these descend on either side
of the deep flexor tendon and unite with the perforating metatarsal
artery to form the proximal plantar arch. The artery continues down the
middle of the plantar surface of the metatarsus and divides near the
metacarpo-phalangeal joints into three =superficial plantar metatarsal
arteries=. These vessels unite with three =deep plantar metatarsal
arteries= which descend from the proximal plantar arch and with branches
from the dorsal metatarsal arteries. From these anastomoses four digital
arteries result; of these, the central two have a common digital trunk.
The =popliteal= and =posterior femoral arteries= present nothing of
special interest.
The =posterior tibial artery= is small, being replaced largely by the
saphenous. It supplies twigs to the flexor muscles at the upper part of
the leg.
The =anterior tibial artery= descends on the anterior face of the tibia
and tarsus and is continued as the perforating metatarsal artery, which
passes through the upper part of the space between the second and third
metatarsal bones and concurs with the plantar branches of the saphenous
in the formation of the plantar arch. Besides muscular and articular
branches, the anterior tibial supplies the external or fifth dorsal
metatarsal artery for the outer side of the fifth digit. At the proximal
part of the metatarsus it gives off three =deep dorsal metatarsal
arteries= which descend in the intervals between the metatarsal bones
and concur with the superficial dorsal and the plantar arteries in the
formation of the =digital arteries=. The latter resemble in general
arrangement the corresponding arteries of the thoracic limb.
The =internal iliac artery= (Fig. 491) runs backward and a little
outward across the ilio-psoas, and on reaching the ilium divides into
parietal and visceral branches. The =parietal branch= is the larger. It
runs backward on the lateral wall of the pelvis, passes out through the
lesser sciatic notch, and breaks up into branches which supply the
muscles in this region like the posterior gluteal (or ischiatic) artery
of the horse. It gives off the following branches: (1) The =ilio-lumbar
artery= passes outward between the ilio-psoas and the shaft of the ilium
and ramifies in the gluteus medius, giving branches to the ilio-psoas
and tensor fasciæ latæ; it may arise from the internal iliac. (2) The
=anterior gluteal artery= passes out behind the posterior superior spine
of the ilium and supplies branches to the glutei. (3) =Muscular
branches= go to the obturator internus, coccygeus, and retractor ani.
(4) The =lateral coccygeal artery= (A. caudalis lateralis superficialis)
passes back at first on the outer face of the coccygeus and continues
beneath the skin along the side of the tail. The =visceral branch= or
=internal pudic artery= passes back below the parietal branch on the
lateral face of the rectum, retractor ani, and coccygeus. Its chief
collateral branches are: (1) The =umbilical artery=, which pursues a
flexuous course and supplies twigs to the bladder, ureter, and vas
deferens. In the bitch it gives off a large =uterine artery= which
ramifies chiefly in the body and neck of the uterus and the vagina and
anastomoses with the utero-ovarian. (2) The =middle hæmorrhoidal artery=
arises near the ischial arch, passes upward and forward on the lateral
surface of the rectum, gains its dorsal surface and anastomoses with the
posterior mesenteric; it supplies the rectum and the anus, together with
its muscles and glands. (3) A small =perineal artery= is detached to the
perineum. In the male the trunk turns around the ischial arch as the
=artery of the penis= (A. penis). This vessel, after giving off the
=deep artery of the penis= (A. profunda penis), which supplies the
=artery of the bulb= (A. bulbi urethræ) and enters the corpus
cavernosum, is continued as the =dorsal artery of the penis= (A.
dorsalis penis) along the dorsum penis. In the female the terminal
branches of the trunk go to the vulva, vestibular bulb, and clitoris.
THE VEINS
The arrangement of the veins is, of course, correlated in general with
the arterial system, but a few special features are worthy of mention.
The =anterior vena cava= is formed by the junction of short right and
=left brachiocephalic= (or subclavian) =veins=, and each of the latter
results from the confluence of =jugular= and =brachial veins=.
The =vena azygos= resembles that of the horse, and receives at the ninth
or tenth thoracic vertebra a =vena hemiazygos=.
Two =jugular veins= are present on each side. The =external jugular
vein= is formed by the union of external and internal maxillary veins at
the posterior border of the submaxillary gland. The two external
jugulars are commonly united by a transverse branch below the cricoid
cartilage. Each passes along the neck on the sterno-cephalicus, covered
only by the skin and panniculus, dips under the cleido-cervicalis, and
joins the internal jugular.
The =external maxillary vein= arises on the lateral nasal region by the
junction of the dorsal nasal vein with the angularis oculi. Near the
infraorbital foramen it receives the lateral nasal vein, and a little
lower the superior labial. In its course along the anterior border of
the masseter it receives the vena reflexa, which arises in the
pterygo-palatine fossa by the junction of infraorbital, sphenopalatine,
and palatine radicles, together with a branch from the cavernous sinus.
At the lower border of the mandible it is joined by the inferior labial
vein, which receives the buccinator vein. The lingual vein is connected
with its fellow by a superficial transverse branch at the insertion of
the sterno-hyoidei. The sublingual and submental veins terminate in a
variable manner, but often form a common trunk which joins the lingual.
The =internal maxillary vein= arises from the pterygoid plexus, formed
chiefly by dorsal lingual, inferior alveolar, deep temporal, pterygoid,
and meningeal tributaries. It receives the superior cerebral, auricular,
superficial temporal, transverse facial, and masseteric veins, and often
a trunk formed by the union of the inferior cerebral and occipital
veins.
The =internal jugular vein= results usually from the junction of
laryngeal and thyroid veins, but in some cases it is formed by the
confluence of the inferior cerebral and occipital veins.
The =brachial= and =radial veins= are satellites of the arteries.
The =ulnar vein= is usually double. It unites below the carpus with a
branch of the interosseous vein to form the superficial venous arch.
The =cephalic vein= accompanies the ulnar artery in the forearm and
joins the superficial venous arch below.
The =accessory cephalic vein= arises from the union of three dorsal
metatarsal veins. It joins the cephalic about the middle of the forearm.
There are three short =volar metacarpal veins= which open into the
superficial venous arch. They are formed above the metacarpo-phalangeal
joints by the junction of the =volar digital veins=, of which there are
two for each of the chief digits. The volar vein of the first digit
joins the superficial venous arch.
Each of the chief digits has two =dorsal digital veins=, while the first
digit has one.
The =posterior vena cava=, its collateral affluents, and common iliac
radicles present no special features of importance.
The =internal iliac vein= corresponds in regard to its tributaries with
the branches of the artery, except that it is not divided into dorsal
and ventral branches.
The =external iliac=, =femoral=, and =popliteal veins= with their
collateral tributaries are satellites of the arteries.
The =anterior tibial vein= is usually double, and the =posterior tibial
vein= is very small.
The =internal saphenous vein= is the upward continuation of the internal
plantar metatarsal vein. It communicates by a large branch with the
dorsal metatarsal vein, and ascends the leg as a satellite of the
saphenous artery and its plantar (posterior) branch. The =recurrent
tarsal= or =external saphenous vein= is larger. It is formed at the
lower part of the leg by the union of dorsal and external plantar
metatarsal veins, crosses the outer surface of the leg obliquely upward
and backward, ascends behind the gastrocnemius and joins the posterior
femoral vein.
The =metatarsal= and =digital veins= resemble in general the
corresponding vessels of the fore limb.
THE LYMPH VESSELS AND GLANDS
The =cisterna chyli= is large and fusiform. The =thoracic duct= may be
single throughout, but often divides anteriorly into two branches, which
may then unite and form a dilatation which receives the left tracheal
duct and the vessels from the fore limb. The primitive plexiform
arrangement persists in varying degree. The duct terminates in the left
brachiocephalic vein.
The =tracheal ducts= accompany the internal jugular veins. The right
duct opens into the right brachiocephalic vein.
The =submaxillary lymph glands= (Fig. 486) are commonly three in number
on each side. They are situated in the angle between the masseter and
the submaxillary salivary gland, in relation to the external maxillary
vein and covered only by the skin and panniculus. The number may be
reduced to two or one with a corresponding increase in size.
A small round =parotid= or =auricular lymph gland= is situated
superficially between the upper part of the posterior border of the
masseter and the parotid gland.
The =pharyngeal= (or retropharyngeal) =lymph glands=, one or two in
number on each side, lie on the pharynx chiefly under cover of the
submaxillary salivary gland.
The =prescapular= or =superficial cervical lymph glands= lie on the
serratus magnus at the anterior border of the supraspinatus, embedded in
a mass of fat. Usually two or three are present on each side, but there
may be only one. They are oval and are about an inch long in a dog of
medium size when two are present.
The =axillary lymph gland= lies in a mass of fat on the inner face of
the lower part of the teres major. It is discoid.
The =cubital lymph gland= is inconstant. It is situated on the deep face
of the long head of the triceps or on the latissimus dorsi.
The =mediastinal lymph glands= are small and quite variable in
arrangement. Usually one or two glands are found on the course of the
internal thoracic vessels at the second segment of the sternum.
The =bronchial lymph glands= are commonly four in number. The largest is
situated in the angle of divergence of the chief bronchi, two lie on the
origin of the right apical bronchus, and the fourth is between the
aortic arch and the anterior face of the left bronchus. They are
commonly pigmented.
The =lumbar lymph glands= are small.
The =mesenteric lymph glands= are represented chiefly by a long
flattened mass (formerly known as the pancreas Aselli) which lies in the
mesentery along the course of the anterior mesenteric artery and vein.
It is succeeded by three or four glands which lie along the portal vein
and appear to receive vessels from the stomach, spleen, liver, pancreas,
and great omentum. A few very small nodes occur along the colon.
The =iliac lymph glands= are relatively large and are situated at the
termination of the aorta and the origin of the iliac arteries. Commonly
four are present. Of these, the two largest lie on the psoas minor on
each side in relation to the aorta and vena cava respectively. The other
two are in the angle of divergence of the internal iliac arteries.
The =superficial inguinal lymph glands= are situated in the subcutaneous
fat behind the external inguinal ring. They are relatively large,
especially when there is only one on each side; two smaller ones may be
found instead.
The =popliteal lymph gland=—usually unique, but sometimes double—lies in
a pad of fat on the upper part of the gastrocnemius between the biceps
femoris and semitendinosus. It may project back so as to be superficial
and palpable.
NEUROLOGY
THE NERVOUS SYSTEM
The nervous system is a complex mechanism by which the organism is
brought into functional relation with its environment, and its various
parts are coördinated. For purposes of gross description it is divided
primarily into two parts, central and peripheral.
The =central nervous system= (Systema nervorum centrale) comprises (_a_)
the =spinal cord= (Medulla spinalis), and (_b_) the =brain=
(Encephalon).
The =peripheral nervous system= (Systema nervorum periphericum) includes
(_a_) the =cerebral= and =spinal nerves= with their =ganglia=, and (_b_)
the =sympathetic nervous system=.
The division into central and peripheral parts is quite arbitrary and
is employed purely as a matter of convenience of description. The
fibers of which the nerves are composed either arise or end within the
central system, and therefore constitute an integral part of the
latter. The structural and functional unit of the nervous system is
the =neurone=, which consists of the =cell-body=, usually termed the
=nerve-cell=, and all its =processes=. The processes arise as
outgrowths from the cell-body and conduct impulses to or from the
cell. They vary greatly in length, some being less than a millimeter
long, while others extend from a cell in the spinal cord to the distal
end of a limb. A nerve is composed of such processes, usually inclosed
in a protecting and insulating sheath, and united into bundles by
connective tissue. The neurones are embedded in a peculiar supporting
tissue termed =neuroglia=. This consists of a very intricate feltwork
of glia-fibers, many of which are connected with the small glia-cells
or astrocytes. In addition the nervous tissue is invested closely by a
vascular layer of connective tissue, the pia mater, from which
ingrowths extend into the nervous substance proper.[186]
To the naked eye the central nervous system appears to be composed
chiefly of two kinds of substance, white and gray. The =white matter=
(Substantia alba) is dead white in color and is soft in the natural
state. It consists largely of medullated nerve-fibers, packed closely
together and arranged more or less clearly in large or small bundles or
tracts (Funiculi, fasciculi). The =gray matter= (Substantia grisea) is
usually brownish-gray in color, often with a tinge of pink. It is softer
than the white substance and much more vascular. It is composed chiefly
of cell-bodies and non-medullated processes. In some situations it is
modified to form the =gelatinous substance= (Substantia gelatinosa),
which is pale yellowish-gray and jelly-like.
=Ganglia= are gray masses found on the dorsal roots of the spinal nerves
and on the course of many nerves. They are commonly ovoid in form and
are inclosed in a fibrous capsule. They are composed largely of the
cell-bodies of neurones, but have connected with and passing through
them nerve-fibers (processes) which extend peripherally and centrally.
In origin and function the spinal ganglia belong properly to the central
system, but it is customary to include them with the peripheral part in
gross anatomical descriptions.
=Nerves= are conducting trunks composed of bundles of parallel
nerve-fibers. They are enveloped in a fibro-elastic sheath, the
epineurium, which contains the blood and lymph vessels. They are
classified according to their central connections as =cranial= or
=cerebral=, =spinal=, and =sympathetic=. The groups of cells of which
the nerve-fibers are processes are termed the =nuclei of origin or
termination= of the nerves, according as the latter conduct impulses in
a peripheral or central direction. On the same basis the nerve-fibers
are designated =efferent= and =afferent= respectively. A bundle of
fibers which passes from one nerve-trunk to another is called an
=anastomotic branch= (Ramus anastomoticus). In some situations the
exchange of branches between adjacent nerves is so free as to constitute
a =nerve-plexus= (Plexus nervorum). The term =ramus communicans= is
properly restricted to branches which connect the ventral divisions of
the spinal nerves with adjacent ganglia or nerves of the sympathetic
system. The terminal twigs of the nerves are designated according to
their distribution as =muscular branches= (Rami musculares), =cutaneous
nerves= (Nervi cutanei), and =articular nerves= (Nervi articulares). The
muscular branches are motor in function, the cutaneous and articular
sensory, but all contain vasomotor fibers which control the caliber of
the blood-vessels.
THE MENINGES
The central organs of the nervous system are inclosed in three meninges
or membranes. From without inward these are: (1) the dura mater, (2) the
arachnoidea, and (3) the pia mater.
THE DURA MATER
The =dura mater= is a dense resistant membrane of white fibrous tissue;
in the fresh state it is bluish-white in color. On account of the
difference in its arrangement within the cranium from that in the spinal
canal it is customary to describe it as consisting of two parts,
cerebral and spinal; these portions are continuous with each other at
the foramen magnum.
The =cerebral dura mater= (Dura mater encephali) is adherent to the
interior of the cranium, and may be regarded as forming an internal
periosteum for the bones here as well as being an envelope of the brain.
Its outer surface is connected with the bony wall of the cranial cavity
by numerous fine fibrous strands and by blood-vessels; hence it appears
rough in many places when separated from the wall. The degree of
adhesion varies greatly at different points. It is most firmly attached
at the various projections, _e. g._, the internal sagittal crest, the
tentorium osseum, the petrosal crest; also at the base and the foramen
magnum. Before the sutures are closed the dura is connected with the
sutural ligaments and through them is continuous with the external
periosteum. The cranial nerves receive sheaths from the dura, which is
thus continuous without the cranium with the epineurium and periosteum.
Along the roof and sides (except as noted above) the adhesion is
relatively slight, and lymph-spaces are said to exist between the dura
and the bone. The internal surface of the dura is smooth and glistening,
since it is lined by endothelium and is moistened by a fluid resembling
lymph; it forms the outer boundary of the subdural space. In accordance
with its double function the dura is composed of two layers, which are,
however, intimately adherent to each other in most places in the adult.
The venous sinuses are channels between the two layers and are lined by
endothelium. They have been described with the other vessels.
Several folds or septa are given off from the inner surface of the dura;
these project into the cavity between the gross subdivisions of the
brain. These septa are: (1) the falx cerebri; (2) the tentorium
cerebelli; and (3) the diaphragma sellæ.
The =falx cerebri= is a sickle-shaped median partition which projects
downward in the great longitudinal fissure between the cerebral
hemispheres. It is attached above to the internal sagittal crest, in
front to the crista galli, and behind to the tentorium osseum. Its
superior border is convex and separates into two layers which inclose
the superior longitudinal sinus. Its lower border is concave and lies
over the corpus callosum. The falx is thick above, but much thinner
below, and in some places cribriform.
In the horse the posterior part of the falx cerebri does not extend to
the corpus callosum, and hence the hemispheres are here in contact and
adherent to each other over a small area. In the ox and pig the falx
does not descend so far as in the horse, while in the dog it
completely separates the hemispheres.
The =tentorium cerebelli= is a crescentic transverse fold which
separates the cerebellum from the posterior poles of the cerebral
hemispheres. It is attached above to the tentorium osseum and laterally
to the petrosal crests. Its lower border is thin, concave, and free; it
forms the upper and lateral boundaries of an opening (Incisura tentorii)
which incloses the mid-brain.
The =diaphragma sellæ= is a small circular fold which roofs over the
sella turcica and the pituitary body. It is perforated centrally by an
opening (Foramen diaphragmatis) for the infundibulum.
The falx cerebelli, a sickle-shaped fold which projects into the
median notch between the cerebellar hemispheres in man, is not present
in the domesticated animals. There is instead merely a slight
thickening of the dura.
The =spinal dura mater= (Dura mater spinalis) forms a tube around the
spinal cord from the foramen magnum to the second or third segment of
the sacrum. It is separated from the periosteum of the spinal canal by a
considerable =epidural space= (Cavum epidurale) which is occupied by
fatty connective tissue and veins. It is held in position chiefly by the
sheaths which it furnishes to the roots of the spinal nerves, and in its
anterior part by two ligaments; the latter connect it with the inferior
atlanto-occipital membrane and with the odontoid process. It is large in
proportion to its contents, but its diameter is not uniform. It is
largest in the atlas, small in the thoracic region, and becomes very
small in its terminal part, where it incloses the delicate filum
terminale of the spinal cord.
The =subdural space= (Cavum subdurale) is the cavity between the inner
surface of the dura mater and the arachnoidea. It is a mere capillary
space which contains just sufficient fluid to moisten its surfaces; this
fluid is usually regarded as lymph, which is replenished by filtration
through the walls of the blood-vessels. The space is in communication
with the lymph-paths of the nerve-sheaths.
THE ARACHNOIDEA
The =arachnoidea= is a very delicate and transparent membrane situated
between the dura and pia mater. Its outer surface forms the inner wall
of the subdural space and is covered by a layer of endothelium
continuous with that of the opposed surface of the dura mater. Between
it and the pia mater is the =subarachnoid space= (Cavum
subarachnoideale) which contains the cerebrospinal fluid. An inner
surface can scarcely be said to exist, since deeply the membrane becomes
a reticulum of fine fibers which traverse the subarachnoid space and are
attached to the pia mater. The arachnoidea furnishes sheaths to the
cerebral nerves from their superficial origins to a variable but usually
short distance beyond the emergence from the dursal sac. In the case of
the optic nerve this sheath extends to the eyeball.
The =arachnoidea of the brain= (Arachnoidea encephali), except in the
case of the great longitudinal and transverse fissures, does not dip
into the sulci on the surface of the brain. On the summits of the gyri
it is so closely attached to the pia mater that the two form practically
a single membrane. Its outer part bridges over the sulci, and here the
subarachnoid space is partially divided up by the loose arachnoid tissue
into intercommunicating cavities. In certain situations the arachnoidea
is separated from the pia by spaces of considerable depth and extent.
These enlargements of the subarachnoid space are termed =subarachnoid
cisterns= (Cisternæ subarachnoidales). In them the subarachnoid tissue
does not form a close network, but consists of a relatively small number
of long, thread-like strands which traverse the cavity.
The chief cisternæ are: (1) the cisterna magna, which is at the angle
formed between the posterior face of the cerebellum and the upper
surface of the medulla oblongata. It communicates with the fourth
ventricle through the foramen of Magendie (in man); and behind with
the wide subarachnoid space of the spinal cord; (2) the cisterna
pontis on the ventral surface of the pons; (3) the cisterna basalis,
which lies at the base of the cerebrum and is divided by the optic
chiasma into two parts (cisterna chiasmatis, cisterna
interpeduncularis); (4) the cisterna fossæ lateralis, situated at the
lower part of the lateral fissure (of Sylvius), and continuous with
the cisterna basalis.
Along the upper border of the falx cerebri the arachnoidea bears bulbous
excrescences, the =arachnoid granulations= or =Pacchionian bodies=.
These are inclosed in thin evaginations of the dura mater and project
into the sagittal sinus or the parasinoidal sinuses along either side of
it. In some cases they are sufficiently large to exert pressure on the
bone and produce in it depressions of variable depth.
The =spinal arachnoidea= (Arachnoidea spinalis) is directly continuous
with that of the brain at the foramen magnum. It forms a relatively wide
tube around the spinal cord, so that the latter (inclosed in the pia) is
surrounded by a very considerable quantity of cerebrospinal fluid. The
spinal subarachnoid space is traversed by fewer arachnoid trabeculæ than
is the case in the cranium. It is partially subdivided by three
imperfect septa. One of these, the septum dorsale, is median and dorsal.
The other two, the ligamenta denticulata, are lateral and will be
described with the pia mater.
PIA MATER
The =pia mater= is a delicate and very vascular membrane which invests
closely the surface of the brain and spinal cord and sends processes
into their substance. It also furnishes sheaths to the nerves, which
blend outside of the dural sac with the epineurium.
The =pia mater of the brain= (Pia mater encephali) follows accurately
all the inequalities of the surface, dipping into all the fissures and
sulci of the cerebrum, and into the larger fissures of the cerebellum.
Its external surface, which forms the inner boundary of the subarachnoid
space, is covered by a layer of endothelium. From its deep face numerous
trabeculæ are given off which penetrate into the substance of the brain
and cord, forming a path for the blood-vessels, and concurring with the
neuroglia in forming the supporting tissue of the nervous substance
proper. The larger blood-vessels of the brain lie within the
subarachnoid space, but the smaller vessels ramify in the pia, forming
rich plexuses. The twigs which penetrate into the gray matter are
inclosed in pial sheaths. They are end-arteries, _i. e._, constitute the
entire supply of the district which they enter and do not anastomose
with adjacent vessels.
Two important folds of the pia extend into the two great transverse
fissures of the brain; these processes overlie the third and fourth
ventricles and are known as the =telæ chorioideæ= of these cavities.
They constitute paths for the deeper vessels and their edges contain
vascular convolutions which are known as chorioid plexuses. They will
receive further consideration more appropriately later.
The =spinal pia mater= (Pia mater spinalis) is thicker and denser than
that of the brain. It has a strong outer layer of fibrous tissue, most
of the fibers of which are longitudinal. The inner layer is vascular and
adheres closely to the surface of the cord because it sends numerous
processes into it. It sends a fold into the median ventral fissure and
also helps to form the median dorsal septum of the cord. Along the
median ventral line it forms a band-like thickening, the linea
splendens, along which the ventral spinal artery runs. On each side the
pia mater gives off a strong longitudinal band, the =ligamentum
denticulatum=, which is connected externally with the dura mater. The
inner or pial border extends in a line between the dorsal and ventral
roots of the nerves. The outer or dural border is denticulated and to a
large extent free. The denticulations are attached to the dura between
the nerve-roots.
NERVOUS SYSTEM OF THE HORSE
THE SPINAL CORD
The =spinal cord= (Medulla spinalis) is the part of the central nervous
system which is situated in the vertebral canal. It extends from the
foramen magnum to about the middle of the sacrum.
In the horse its average length is about 76 to 78 inches (ca. 190 to 195
cm.), and its weight about 8½ to 9 ounces (ca. 240 to 255 grams).
It is approximately cylindrical, but more or less flattened
dorso-ventrally. There is no line of demarcation between it and the
medulla oblongata, but for practical purposes the division is usually
assumed to be at the posterior border of the foramen magnum. Its
posterior part tapers rapidly to a point, forming the =conus
medullaris=. This is prolonged for a short distance by the slender
=filum terminale=.
Forty-two pairs of spinal nerves are connected with the sides of the
spinal cord. They are classified as eight cervical, eighteen thoracic,
six lumbar, five sacral, and five coccygeal. According to the
attachments of these series of nerves the spinal cord is divided into
=cervical=, =thoracic=, =lumbar=, and =sacral= parts.
In a horse about 16½ hands high these parts measured 65 cm. (ca. 26
in.), 86 cm. (ca. 34.4 in.), 27 cm. (ca. 10.8 in.), and 15 cm. (ca. 6
in.) respectively (Dexler).
In the embryo these divisions correspond primitively to the regions of
the vertebral column, but later, through unequal growth of the cord and
spine, the correspondence between the two is not at all exact in the
anterior regions and is lost in the last two. The lumbar part of the
cord in the horse ends at the junction of the fifth and sixth lumbar
vertebræ, so that the roots of the last lumbar nerve must run backward
the length of the last lumbar vertebra to reach the intervertebral
foramen through which it emerges. The conus medullaris reaches only to
the anterior part of the sacral canal, so that the roots of the sacral
and coccygeal nerves extend backward in the spinal canal for a
considerable distance, forming a leash of bundles, in the center of
which lie the conus medullaris and the filum terminale. This arrangement
is expressively designated the =cauda equina=.
Each pair of spinal nerves is attached by its root-fibers to a certain
length of the cord, and the latter is, therefore, regarded as consisting
of as many =segments= as there are nerves. It is to be noted, however,
that there is no line of demarcation between the segments other than the
intervals between the root-fibers of adjacent nerves.
The segments are of different lengths; the longest are the third to
the sixth cervical, which measure 11, 10, 10, and 8.5 cm.
respectively. The spinal nerves are in general designated according to
the vertebræ behind which they emerge from the vertebral canal. In the
neck, however, there are eight pairs of nerves and only seven
vertebræ; here the first nerve emerges through the intervertebral
foramen of the atlas and the eighth between the last cervical and the
first thoracic vertebra.
In the greater part of the thoracic region the spinal cord is fairly
uniform in size, but there are two conspicuous wide enlargements which
involve the segments with which the nerves of the limbs are connected.
The =cervical enlargement= (Intumescentia cervicalis) begins gradually
in the fifth cervical vertebra and subsides in the second thoracic. Its
maximum transverse diameter is about an inch (ca. 25 mm.) and its
dorso-ventral nearly half an inch (ca. 12 mm.). The =lumbar enlargement=
(Intumescentia lumbalis) is situated in the fourth and fifth lumbar
vertebræ. It is a little narrower than the cervical enlargement, and its
dorso-ventral diameter is also slightly smaller. Behind this the cord
tapers rapidly to form the =conus medullaris=. The tip of the latter is
continued by a delicate glistening strand, the =filum terminale=, which
is composed largely of fibrous tissue continued from the pia mater,
covered by arachnoid.
[Illustration:
FIG. 495.—VENTRAL VIEW OF MEDULLA OBLONGATA AND FIRST AND SECOND
SEGMENTS OF SPINAL CORD OF HORSE; THE MEMBRANES ARE CUT AND
REFLECTED.
_1_, Lig. suspensorium arachnoideale; _2_, right cerebrospinal artery;
_3_, _5_, digitations of lig. denticulatum; _4_, free border of lig.
denticulatum; _6_, middle spinal artery; _7_, basilar artery; _8_,
pons; _9_, arachnoidea; _10_, dura mater; _11_, _12_, ventral
root-bundles of first and second segments of spinal cord; _VI._, N.
abducens; _IX_, _X_, glossopharyngeus and vagus; _XI_, accessory,
medullary part; _XI′_, accessory, spinal part; _a_, line between
medulla oblongata and spinal cord. (Dexler, in Ellenberger-Baum,
Anat. d. Haustiere.)
]
[Illustration:
FIG. 496.—CAUDA EQUINA.
_1_, Dura and arachnoidea divided and reflected; _2_, spinal cord;
_3_, nerve-roots. (From Leisering’s Atlas, reduced.)
]
The surface of the spinal cord is divided into two similar halves by a
=dorsal median groove= (Sulcus medianus dorsalis) and a =ventral median
fissure= (Fissura mediana ventralis). On either side of the former is
the =dorso-lateral groove= (Sulcus dorsalis lateralis) at which the
fibers of the dorsal nerve-roots enter the cord; it is faint except at
the enlargements, and is represented by two grooves in the first
cervical segment. The ventral root-fibers as they emerge from the cord
do not form a continuous series, but arise from a zone (Area radicularis
ventralis) 3 to 5 mm. in width a little lateral to the ventral median
fissure, and no groove is found here. In the greater part of the
cervical region and the anterior part of the thoracic region there is a
shallow =dorsal paramedian groove= (Sulcus intermedius dorsalis) a short
distance lateral to the median groove. These grooves indicate the
division of the white matter of the cord into columns to be described
later.
Examination of cross-sections of the spinal cord shows that it is a
bilaterally symmetrical structure, incompletely divided into right and
left halves by a ventral fissure and a dorsal septum. The =ventral
median fissure= (Fissura mediana ventralis) is narrow and penetrates
nearly to the middle of the dorso-ventral diameter of the cord. It is
occupied by a fold of pia mater. The =dorsal median septum= (Septum
medianum dorsale) is a partition which descends from the posterior
median groove to about the middle of the cord. It apparently consists of
condensed neuroglia with an admixture of pial tissue. The two halves of
the cord are connected by commissures of gray and white matter. The
=gray commissure= (Commissura grisea) is a transverse band of gray
matter at the ventral end of the dorsal septum. It is divided into
dorsal and ventral parts by the central canal of the cord. The =white
commissure= (Commissura alba) is a bridge of white matter which connects
the ventral columns of the cord over the dorsal end of the ventral
median fissure, and constitutes a conducting path from one side to the
other.
[Illustration:
FIG. 497.—CROSS-SECTION OF SPINAL CORD _in situ_, IN PART SCHEMATIC.
_1_, Dorsal column; _2_, lateral column; _3_, ventral column; _4_,
dorsal horn; _5_, ventral horn; _6_, gray commissure; _7_, white
commissure; _8_, central canal; _9_, dorsal septum; _10_, ventral
fissure; _11_, dorsal nerve-root; _12_, ventral nerve-root; _13_,
spinal ganglion; _14_, nerve; _15_, intervertebral foramen; _16_,
arch of vertebra; _17_, epidural space; _18_, dura mater
(represented a little too thick); _19_, ligamentum denticulatum;
_20_, _20_, longitudinal venous sinuses; _21_, middle spinal artery.
The subdural and subarachnoid spaces (black) are traversed by
delicate trabeculæ. The outer part of the arachnoid and the pia
mater are not shown.
]
The =central canal= of the cord (Canalis centralis), the spinal vestige
of the lumen of the embryonal neural tube, is a minute passage which
tunnels the gray commissure. It opens at its anterior end into the
posterior part of the fourth ventricle of the brain, and its terminal
part in the conus medullaris forms a slight dilatation, the ventriculus
terminalis. It is lined by epithelium and is surrounded by a layer of
modified neuroglia (Substantia grisea centralis).
The =gray matter= of the spinal cord as seen in cross-sections resembles
roughly a capital =H= the cross-bar of the letter being formed by the
gray commissure. Each lateral part is considered as consisting of
=dorsal= and =ventral gray columns= or =horns= (Columna grisea dorsalis,
ventralis). In the greater part of the cord the dorsal column or horn is
elongated and narrow and tapers to a point which extends almost to the
surface of the cord at the attachment of the dorsal root-fibers of the
spinal nerves. Its apex or tip consists of gray matter which is lighter
in color and less opaque than that of the rest of the horn and is termed
the =substantia gelatinosa= (Rolandi). The ventral column or horn is
short, thick and rounded, and is separated from the surface of the cord
by a thick layer of white matter, through which the fibers of the
ventral roots of the spinal nerves pass. From the middle of the cervical
region to the lumbar region there is a medial projection of gray matter
on the lower part of the dorsal column; this is the =nucleus dorsalis=
or Clarke’s column. In the anterior part of the cord there is an outward
projection of the gray matter at the base of the ventral horn; this is
termed the =lateral column= or =horn=. The demarcation between the gray
and white matter is in many places indistinct; this is especially the
case laterally, where processes of gray matter extend into the white
substance, producing what is known as the =formatio reticularis=.
Cross-sections of the spinal cord present the following gross regional
characters: (1) The cervical cord near the medulla is compressed
dorso-ventrally, its width is about 18 mm. and its greatest thickness
about 8 mm. It has dorsally a deep median sulcus and a distinct
dorso-lateral sulcus. Lateral grooves are also present. The dorsal
cornua are strongly everted. Each has an expanded head, which comes
very close to the surface of the cord, and has an extensive cap of
substantia gelatinosa. The neck is distinct. The ventral cornua are
short and blunt and diverge very little. The gray commissure is about
in the middle of the section and 2.5 mm. in length. According to
Dexler the column between the median and lateral grooves dorsally is
the funiculus cuneatus, the funiculus gracilis being very small and
not showing on the surface in this region. In the middle of the
cervical region the diameters are about 16 mm. and 10 mm.
respectively. The ventral surface is somewhat flattened. The dorsal
cornua have pointed ends and turn decidedly outward. The ventral
cornua are short and thick and are directed very slightly outward;
their ends are about 4 mm. from the ventral surface. The gray
commissure is just above the middle of the section and is about 2 mm.
long. The cervical enlargement measures about 25 mm. transversely and
12 mm. vertically. The dorsal cornua are smaller than the ventral and
have a large cap of substantia gelatinosa. The ventral cornua are
short and thick, curve strongly outward, and are about 4 mm. from the
ventral surface. Each bears a prominence on its inner side near the
base. The gray commissure is considerably above the middle of the
section and is about 4 mm. long. (2) In the middle of the thoracic
region the cross-section is biconvex, the ventral surface being the
more strongly curved. The transverse diameter is about 15 mm. and the
dorso-ventral about 10 mm. The gray columns are close together, the
gray commissure being only about 1 mm. in length, and lying
considerably above the middle of the section. The dorsal cornua are
short and have slightly enlarged ends. The ventral cornua have a
uniform diameter, turn very little outward, and end about 3 mm. from
the ventral surface. (3) The lumbar enlargement is much flattened,
especially dorsally. The transverse diameter is about 22 mm. and the
dorso-ventral 9 to 10 mm. The cornua are very large. The ventral
cornua are thick and rounded and turn sharply outward; they end about
2 mm. from the ventral surface. The dorsal cornua are smaller and
shorter and do not diverge so strongly. The gray commissure is about
in the middle of the section and is about 3 mm. long. In the third
lumbar vertebra the cord is about 3 mm. narrower and thicker, and both
surfaces are about equally convex. The dorsal cornua are smaller,
considerably everted, and constricted in the middle. The ventral
cornua are very short and do not turn outward. (4) In the first sacral
vertebra the cord is almost round and is 5 to 6 mm. in diameter; the
cornua are relatively very large and the commissure has the form of a
high intermediate mass.
The ventral horn contains large cells, the axones of which emerge as
the fibers of the ventral nerve-roots (Fila radicularia). The axones
of many cells cross to the opposite side in the white commissure and
pass out in a ventral root of that side, or enter the white matter and
pass forward and backward, associating various segments of the cord.
Some pass to the ventral horn of the opposite side at the same or at
different levels. Others pass to the periphery of the cord, join the
cerebellospinal fasciculus, and extend to the cerebellum. Scattered
through the gray matter are many smaller cells with axones which
pursue a short course and serve to connect different parts of the gray
matter.
The =white matter= of the spinal cord is divided into three pairs of
=columns=. The =dorsal columns= (Funiculi dorsales) lie on either side
of the dorsal median septum and extend outward to the dorso-lateral
groove and the dorsal gray column. The =ventral columns= (Funiculi
ventrales) are situated on either side between the median fissure and
the ventral gray columns. They are connected above the fissure by the
white commissure. The =lateral columns= (Funiculi laterales) lie
external to the gray columns on either side; their limits are indicated
superficially by the dorso-lateral groove and the emergence of the
ventral root-fibers. The paramedian groove (where present) indicates a
subdivision of the dorsal column into two fasciculi or tracts; the inner
of these is the =fasciculus gracilis= (Goll’s column); the outer, the
=fasciculus cuneatus= (Burdach’s column).
The amounts of gray and white matter vary greatly in different parts of
the cord both absolutely and relatively. In cross-section the absolute
areas of both are greatest in the enlargements. The relative area of
gray matter is smallest in the thoracic region (except at its anterior
end), and increases from the lumbar enlargement backward.
Investigations have shown that in man the columns of white matter are
subdivided into fasciculi or tracts, which constitute definite
conducting paths of greater or less length. Our knowledge of the
tracts in the domesticated animals is very limited, and it is quite
unsafe to make inferences from the arrangement in man. As evidence of
this it may be noted that the ventral cerebrospinal or direct
pyramidal tract of man cannot be recognized as such.
The dorsal white columns consist essentially of two sets of axones.
The afferent or sensory axones which come from the cells of the spinal
ganglia enter as the dorsal roots of the spinal nerves and divide into
two branches in the vicinity of the dorsal gray column. The anterior
(ascending) branches form the direct sensory path to the brain and
extend in the fasciculus cuneatus and fasciculus gracilis or
corresponding tracts to nuclei in the medulla oblongata. The posterior
(descending) branches extend backward for varying distances and give
off numerous collaterals to cells of the gray column, thus forming
part of the mechanism for the mediation of reflex action. Some
collaterals cross in the white commissure to the opposite side. Many
of these fibers are collected in the comma-shaped tract between the
fasciculus gracilis and cuneatus. The second set of axones arises from
the smaller cells of the gray column. They enter the white matter,
divide into anterior and posterior branches, forming the fasciculi
proprii or ground bundles of the cord. Some branches cross to the
opposite side. The function of this set of axones is chiefly to
associate various levels of the cord.
The lateral columns contain some axones of the dorsal nerve-roots,
which (in man) are grouped in the marginal tract of Lissauer, situated
just dorsal to the apex of the dorsal horn. The cerebellospinal
fasciculus (direct cerebellar tract of Flechsig) extends along the
periphery of the lateral column. It contains the axones of the cells
of the nucleus dorsalis (Clarke’s column), which proceed to the
medulla oblongata and enter the cerebellum by the restiform body. The
rubrospinal tract of Monakow appears to take the place of the lateral
cerebrospinal fasciculus or crossed pyramidal tract of man. It lies at
the inner side of the cerebellospinal fasciculus. Its fibers arise in
the nucleus ruber of the mid-brain, cross the median plane
(decussation of Forel), and pass backward in the tegmentum and medulla
oblongata to the lateral column of the cord. It is a path for motor
impulses coming from the cerebral cortex and the cerebellum. The
lateral fasciculus proprius or ground-bundle is deeply situated at the
side of the gray columns. The bulk of its fibers are axones of cells
of the posterior cornu which divide into anterior and posterior
branches. They are intersegmental paths which associate different
levels of the gray matter of the cord. The significance of the
remaining fibers is not yet known.
The ventral white columns do not contain a ventral cerebrospinal or
direct pyramidal tract, as in man. There is a small tract (Fasciculus
intracommissuralis ventralis) above the white commissure, which
separates it from the rest of the ventral column. It extends to the
middle of the thoracic region. It consists of intersegmental fibers,
and contains in the anterior part of the cervical cord in the sheep
and goat both crossed and direct pyramidal fibers. The descending
cerebellospinal fasciculus extends from the cerebellum to the lumbar
region. In the cervical region it occupies a semilunar area which
reaches almost to the surface ventro-laterally. Scattered fibers
belonging to it lie also in the medial part of the ventral column.
Posteriorly it diminishes in size and comes to occupy a position next
to the ventral median fissure, corresponding to the sulco-marginal
fasciculus of man (Dexler).
THE BRAIN
The =brain= or =encephalon= is the part of the central nervous system
that is situated in the cranial cavity. It is the enlarged and highly
modified cephalic part of the primitive neural tube. It conforms rather
closely in size and shape to the cavity in which it lies.
Its average weight without the dura mater is about 23 ounces (ca. 650
gm.), and forms about ⅐ of 1 per cent. of the body-weight.
It is desirable to examine the general external configuration of the
brain before studying its various parts in detail.[187]
When divested of its membranes and vessels (Figs. 499, 500), its ventral
surface or base presents the median =brain stem=, which is continuous
with the spinal cord without any natural line of demarcation; it divides
in front into two branches, the cerebral peduncles, each of which
disappears into the mass of the corresponding cerebral hemisphere. The
brain stem consists of three parts. The =medulla oblongata= is the
posterior part which extends forward as the direct continuation of the
spinal cord. The =pons= (Varolii) is a transversely elongated mass which
appears to turn up on either side into the cerebellum. The =cerebral
peduncles= extend forward from the pons and diverge to plunge into the
ventral part of the cerebral hemispheres. The area between them is the
=interpeduncular= space. It is largely covered by the =pituitary body=
or =hypophysis=, a yellowish-brown, discoid structure, which is
connected with the base of the cerebrum by a delicate tube called the
=infundibulum=.[188] On drawing the pituitary body gently aside, the
infundibulum is seen to be attached to a slight gray eminence, the
=tuber cinereum=. Behind this is the =mammillary body=, a well-marked
round prominence. The posterior part of the space is perforated by
numerous openings for the passage of small arteries, and hence is termed
the =locus perforatus posticus=. Two large bands of white matter, the
=optic tracts=, cross the anterior ends of the cerebral peduncles and
unite at the =optic chiasm= or =commissure=, forming the anterior
boundary of the interpeduncular space. Above and in front of the chiasm
the hemispheres are separated by the median =longitudinal fissure=. In
contact with the anterior extremity of each hemisphere is the =olfactory
bulb=, an oval enlargement adapted to the ethmoidal fossa of the
cranium. This appears as a gray swelling on a wide flat band, the
=olfactory peduncle=, which is continued behind by two divergent bands,
the =olfactory tracts= or =striæ=. The =internal tract= disappears after
a very short course on to the inner surface of the hemisphere. The
=external tract= is larger and longer; it runs backward, inclines at
first outward and then curves inward and disappears on the concealed or
tentorial surface of the hemispheres. It is separated from the lateral
cerebral gyri by a distinct groove (Sulcus rhinalis). Along the inner
side of the stria are two eminences. The anterior of these is the
=trigonum olfactorium=, a gray elevation situated in the angle of
divergence of the inner and outer striæ. Behind this is a depression,
the =fossa transversa=,[189] which is continued across the external
stria and sharply limits the second and much larger eminence, the
=pyriform lobe=.
The superficial origins of most of the cranial nerves are visible on the
base of the brain.
The =olfactory nerve-fibers= join the convex surface of the olfactory
lobe and give it a shaggy appearance in specimens which have been
removed intact—a difficult proceeding.
The =second= or =optic nerves= converge to the optic chiasm.
The =third= or =oculomotor nerve= arises from the inner part of the
cerebral peduncle.
The =fourth= or =trochlear nerve= may be seen emerging between the pons
and the hemisphere, but its connection with the brain is not visible.
The =fifth= or =trigeminal nerve= is connected with the lateral part of
the pons.
The =sixth= or =abducent nerve= arises just behind the pons and lateral
to the pyramid of the medulla.
The =seventh= or =facial= and the =eighth= or =auditory nerves= arise
close together just behind the pons proper on the extremity of the
corpus trapezoideum.
The =ninth= or =glosso-pharyngeal=, the =tenth= or =vagus=, and the
=eleventh= or =spinal accessory nerves= are connected by a linear series
of roots with the lateral aspect of the ventral surface of the medulla.
The spinal part of the accessory nerve comes forward along the edge of
the medulla to join its medullary root.
The =twelfth= or =hypoglossal nerve= arises from the posterior part of
the medulla along the lateral edge of the pyramid.
[Illustration:
FIG. 498.—BRAIN OF HORSE, DORSAL VIEW, ABOUT ⁵⁄₇ NATURAL SIZE.
_1_, Entomarginal fissure; _2_, marginal fissure; _3_, ectomarginal
fissure; _4_, suprasylvian fissure.
]
The parts that are visible when the brain is viewed from above are the
cerebral hemispheres, the cerebellum, and part of the medulla oblongata.
The =cerebral hemispheres= form an ovoid mass, and are separated from
each other by the median =longitudinal fissure=, in which the falx
cerebri is situated. Their surfaces are marked by thick folds, the =gyri
cerebri=, separated by =sulci=. The upturned ends of the =olfactory
bulbs= are seen in front of the frontal poles of the hemispheres. The
occipital poles of the hemispheres overlie the anterior part of the
cerebellum, from which they are separated by the =transverse fissure=
and the tentorium cerebelli contained in it. The =cerebellum= is a much
smaller rounded mass which conceals the greater part of the medulla
oblongata. Its surface is divided into a middle lobe, the =vermis=, and
two lateral =hemispheres=. It is marked by numerous gyri and narrow
sulci which have in general a transverse direction. The posterior third
of the =medulla oblongata= is not covered by the cerebellum.
The brain is developed from the expanded cephalic part of the neural
tube of the embryo. The process comprises a series of thickenings,
flexures, and unequal growth and expansion of various parts of the
tube. In the higher animals the result is that the tubular character
of the brain is not very evident, since the lumen comes to consist of
four irregular cavities, the ventricles, which are connected by narrow
passages. The tube is first subdivided by two constrictions into three
brain vesicles, termed respectively the hind-brain or rhombencephalon,
the mid-brain or mesencephalon, and the fore-brain or prosencephalon.
The hind-brain gives rise to three secondary segments and the
fore-brain to two. The annexed table indicates the origin of the
principal structures of the fully developed brain from the primitive
vesicles. It has become customary to describe the brain with reference
to its embryological relations.
TABLE INDICATING THE DERIVATION OF THE PRINCIPAL PARTS OF THE BRAIN
PRIMARY SEGMENTS.│ Secondary │ DERIVATIVES. │ CAVITIES.
│ SEGMENTS. │ │
Rhombencephalon │ │ │
(posterior │Myelencephalon │Medulla oblongata│Fourth ventricle
vesicle) │ │ │
„ │Metencephalon │Pons │ „
„ │ „ │Cerebellum │ „
│Isthmus │Anterior │
„ │ rhombencephali │ cerebellar │ „
│ │ peduncles │
„ │ „ │Anterior │ „
│ │ medullary velum│
Mesencephalon │ │Corpora │
(middle │Mesencephalon │ quadrigemina │Cerebral aqueduct
vesicle) │ │ │
„ │ „ │Cerebral │ „
│ │ peduncles │
Prosencephalon │ │{Optic thalami │Posterior part of
(anterior │Diencephalon │ } │ third ventricle
vesicle) │ │ │
„ │ „ │{Subthalamic │ „
│ │ tegmenta │
„ │ „ │{Pineal body │ „
│ │ │Anterior part of
│ │ │ third
│ │{Pituitary body │ ventricle.
„ │Telencephalon │ } │ Lateral
│ │ │ ventricles and
│ │ │ olfactory
│ │ │ continuations.
„ │ „ │{Optic nerves and│ „
│ │ retinæ │
„ │ „ │{Cerebral │ „
│ │ hemispheres │
„ │ „ │{Olfactory tracts│ „
│ │ and bulb │
THE RHOMBENCEPHALON
THE MEDULLA OBLONGATA
The =medulla oblongata= lies on the basilar part of the occipital bone.
It is quadrilateral in outline, but much wider in front than behind, and
compressed dorso-ventrally. Its length, measured from the root of the
first cervical nerve to the pons, is about two inches (ca. 5 cm.).
Its =ventral surface= is convex in the transverse direction. It is
marked by a =median fissure= (Fissura mediana ventralis) which is
continuous behind with the similar fissure of the spinal cord. The
posterior part of the fissure is faintly marked, but in front it becomes
deeper and ends in a small depression (Foramen cæcum) behind the central
part of a transverse band, the =corpus trapezoideum=. On either side of
the fissure is a rounded tract, the =pyramid= (Pyramis), which is
bounded externally by a faint lateral groove (Sulcus intermedius
ventralis). The pyramids join the pons in front; behind they become
narrower and disappear into the substance of the medulla, in which their
fibers intercross, forming the =decussation of the pyramids= (Decussatio
pyramidum).[190]
The superficial origin of the =sixth cranial nerve= (N. oculomotorius)
is just lateral to the anterior end of the pyramid. The =corpus
trapezoideum= is a transverse band which extends across the surface
immediately behind the pons. It is crossed by the pyramids, which cut
off a small central part. The lateral part extends out to the roots of
the seventh and eighth nerves on either side. Behind the outer part of
the corpus trapezoideum there is a variably developed rounded eminence,
the =tuberculum faciale=. The root-fibers of the twelfth or hypoglossal
nerve form an oblique linear series lateral to the posterior part of the
pyramid.
[Illustration:
FIG. 499.—BASE OF BRAIN OF HORSE, NATURAL SIZE.
]
The =dorsal surface= is largely concealed by the cerebellum and forms
the greater part of the floor of the fourth ventricle. The =dorsal
median fissure= (Fissura mediana dorsalis), the direct continuation of
the corresponding groove of the spinal cord, extends forward to about
the middle of the surface. Here the =restiform bodies=, which constitute
the lips of the fissure, diverge to form the lateral boundaries of a
triangular depression; this is the posterior part of the rhomboid fossa
or floor of the fourth ventricle of the brain. The dorso-lateral fissure
winds outward and forward to the lateral aspect of the medulla, where it
presents the roots of the =ninth=, =tenth=, and =eleventh cranial
nerves=. External to it is a distinct oval eminence on the anterior part
of the lateral column, termed the =tuberculum cinereum=. The central
canal of the cord is continued in the posterior part of the medulla,
inclines dorsally, and opens in the posterior angle of the fourth
ventricle. Hence it is customary to distinguish a closed and an open
part of the medulla. The dorsal aspect of the latter, which is concealed
at present, will be considered later in the description of the fourth
ventricle.
[Illustration:
FIG. 500.—LINE DRAWING OF BASE OF BRAIN OF HORSE. (KEY TO FIG. 499.)
]
The lateral surface is narrow behind, wider and rounded in front. From
it the root-fibers of the ninth, tenth, and eleventh cranial nerves
arise in a linear series, and alongside of it the spinal part of the
eleventh nerve passes forward to join the medullary root. Close
inspection reveals the presence of striæ which curve obliquely downward
and backward from the surface of the restiform body toward the
hypoglossal root-fibers; these are the =external arcuate fibers= (Fibræ
arcuatæ externæ). The recess between the lateral aspect of the medulla
and the cerebellum is occupied by an irregular mass of villous
projections of the pia mater, containing tufts of vessels; this is the
=chorioid plexus of the fourth ventricle=, and is the lateral edge of
the =tela chorioidea= of the ventricle. On raising the chorioid plexus
it is seen that the tela chorioidea is attached to the dorsal aspect of
the medulla, and reinforces here the wall of the fourth ventricle; also
that the restiform body terminates in front by entering the base of the
cerebellum, forming its posterior peduncle.
In the medulla the fiber tracts of the spinal cord either terminate in
the nuclei of the gray matter or undergo changes in their relative
position, and new tracts appear. The gray matter is highly modified
and forms masses which have no homologues in the cord. The central
canal of the closed part of the medulla is surrounded by a thicker
layer of gray matter than is the case in the spinal cord. As the
medulla opens out this gray matter is naturally spread in the floor of
the fourth ventricle. The dorsal horns of gray matter become wide,
spread apart, and are broken up to a great extent in the formatio
reticularis. Two elongated masses of cells appear above the central
gray matter; these are the =nucleus gracilis= and =nucleus cuneatus=,
and in them the fasciculi of like name gradually end. In front of
these are the =terminal nuclei= of the afferent or sensory cranial
nerves and of the sensory portions of the mixed nerves. The ventral
horns are succeeded by the nuclei of =origin= of the efferent or motor
cranial nerves and the motor root-fibers of the mixed nerves. Of the
twelve pairs of cranial nerves, the last eight are connected with
nuclei in the medulla and pons. The =posterior olivary nucleus=
(Nucleus olivaris caudalis) is a conspicuous gray mass which lies
above the pyramid on each side. On cross-sections it appears as a wavy
layer of gray matter which is folded on itself so as to inclose a mass
of white matter. It is about 2 cm. long in the horse, but is smaller
in circumference than in man and hence does not cause any very
distinct external enlargement (olivary eminence), as in the latter. It
is connected with the opposite side of the cerebellum by the
cerebello-olivary fibers. At its inner side are two small accessory
olivary nuclei. The =pyramidal tracts=, which are small in ungulates,
send most of their fibers across to the opposite side in the posterior
part of the medulla, forming the =pyramidal decussation=. Some fibers,
however, continue in the ventral column of the same side of the cord,
and others are connected with the nuclei of the motor nerve-roots.
From the nucleus gracilis and nucleus cuneatus fibers arise which are
traceable forward to the thalamus. These are the =internal arcuate
fibers= (Fibræ arcuatæ internæ), which curve across the median plane
below the central gray matter and form with those of the opposite side
the =decussation of the fillet= (Decussatio lemniscorum). Beyond the
decussation the fibers form an important longitudinal tract which
extends forward in the mid-brain. This is the =fillet= or =lemniscus=,
the chief continuation of the sensory conducting path from the dorsal
roots of the spinal nerves. The =external arcuate fibers=, some of
which were seen on the lateral aspect of the medulla, have a similar
origin. Part of them (Fibræ dorsales) pass directly to the dorsal
aspect of the restiform body of the same side; others (Fibræ
ventrales) cross to the opposite side, descend close to the ventral
fissure, and then curve upward and forward to the restiform body. The
decussation of the arcuate fibers forms the distinct median =raphé=
seen on cross-sections of the medulla anterior to the pyramidal
decussation. The restiform body, situated dorso-laterally, contains,
in addition to the arcuate fibers, the =cerebello-olivary fasciculus=
before mentioned, and the =cerebellospinal fasciculus= or direct
cerebellar tract. The =dorsal longitudinal fasciculus= corresponds to
the ventral ground-bundle of the spinal cord, displaced dorsally by
the decussation of the pyramids and fillet. In the posterior part of
the medulla it is not marked off from the fillet, along the dorsal
edge of which it lies. From the level of the hypoglossal nucleus
forward it is distinct and can be traced as a conspicuous tract in the
ventral margin of the gray matter of the floor of the fourth ventricle
and of the central gray matter of the mid-brain. Below the restiform
body and related externally to the external arcuate fibers, there is a
considerable bundle of longitudinal fibers, the =spinal root= (Tractus
spinalis) =of the fifth nerve=; internal to it is the terminal nucleus
of the sensory root of the nerve.
[Illustration:
FIG. 501.—BRAIN OF HORSE, LEFT LATERAL VIEW.
The larger arteries are shown. The nerve-roots are indicated by Roman
numerals. _P.c._, Chorioid plexus of fourth ventricle; _B.p._,
middle peduncle of cerebellum; _P_, pons; _H_, pituitary body;
_L.p._, pyriform lobe; _A.p._, trigonum olfactorium; _B.o._,
olfactory bulb; _S.r.a._, sulcus rhinalis anterior; _S.r.p._, sulcus
rhinalis posterior; _F.l._, lateral fissure (of Sylvius); _F.l.a._,
anterior branch of lateral fissure; _S.p._, presylvian fissure;
_S.p.n._, anterior presylvian fissure; _S.s._, suprasylvian fissure;
_S.e._, ectomarginal fissure.
]
THE PONS
[Illustration:
FIG. 502.—CROSS-SECTION OF MEDULLA OBLONGATA OF HORSE, PASSING THROUGH
FACIAL NUCLEUS.
_Cr_, Corpus restiforme; _D_, dorsal longitudinal fasciculus; _Fa_,
ascending part of facial nerve; _L_, fillet; _N7_, nucleus of facial
nerve; _N8_, triangular nucleus of vestibular root of eighth nerve;
_N8′_, spinal root of eighth nerve; _Py_, pyramid; _Ra_, raphé;
_R7_, radicular part of facial nerve; _R8_, vestibular root of
eighth nerve; _Sg_, substantia gelatinosa; _Ta_, posterior end of
tuberculum acusticum; _V_, spinal root of trigeminus.
(Ellenberger-Baum, Anat. d. Haustiere.)
]
[Illustration:
FIG. 503.—CROSS-SECTION OF MEDULLA OBLONGATA OF HORSE; SECTION PASSES
THROUGH MIDDLE OF CORPUS TRAPEZOIDEUM.
_Cr_, Corpus restiforme; _D_, dorsal longitudinal bundle; _Fa_,
ascending part of facial nerve; _Fa′_, emergent or descending part
of facial nerve; _R7_, root of facial nerve; _L_, fillet; _M_,
central white matter of cerebellum; _N6_, abducens nucleus; _N8_,
triangular nucleus; _N8′_, nucleus of Deiters; _N8″_, tuberculum
acusticum; _Oo_, anterior olive; _Py_, pyramid; _R6_, root of
abducens nerve; _R7_, root of facial nerve; _Rc_, cochlear nerve;
_Rv_, vestibular nerve; _Sg_, substantia gelatinosa; _T_, corpus
trapezoideum; _V_, spinal root of trigeminus. (Ellenberger-Baum,
Anat. d. Haustiere.)
]
The =pons= (Varolii) is that part of the brain stem which lies between
the medulla and the cerebral peduncles; it is marked off from these
ventrally by anterior and posterior grooves. Viewed from below it is
elongated transversely, convex in both directions, and presents a wide
shallow median groove (Sulcus basilaris), which lodges the basilar
artery. Laterally a large part of its mass curves upward and backward
into the base of the cerebellum, forming the =middle cerebellar
peduncle= (Brachium pontis). The superficial origin of the trigeminal
(fifth) nerve is at the lateral limit of the ventral surface. Transverse
striations indicate the course of its superficial (ventral) fibers which
connect the two sides of the cerebellum. The dorsal surface is blended
on either side with the overlying anterior peduncles of the cerebellum;
the central free portion forms the anterior part of the floor of the
fourth ventricle, and will be considered in the account of that cavity.
On cross-section the pons is seen to be composed of dorsal and ventral
parts. The =dorsal part= (Pars dorsalis pontis) consists superficially
of a layer of gray matter covered by the ependyma of the fourth
ventricle. Beneath this the median raphé of the medulla is continued
into the pons, dividing it into similar halves. In the anterior part
of the pons the fillet divides into an inner and outer part, the
=medial= and =lateral fillets= (Lemniscus medialis, lateralis); the
latter arches outward to reach the outer side of the anterior
cerebellar peduncle. The =dorsal longitudinal fasciculus= becomes
sharply defined into a round bundle which lies close to the raphé
under the gray matter of the floor of the fourth ventricle. In
cross-section the =formatio reticularis= forms a large area below the
superficial gray matter and the longitudinal bundles. Dorso-laterally
is the large rounded section of the =anterior cerebellar peduncle=.
Lower down is a large bundle, the =sensory root of the fifth nerve=.
In front of this is the =motor nucleus= of the same nerve, external to
which is its =motor root=. The =ventral part= of the pons (Pars
basilaris pontis) is composed of transverse and longitudinal fibers,
and a large amount of gray matter which is broken up into small masses
(Nuclei pontis) by the intersection of the fibers. The =transverse
fibers= are gathered laterally into a compact mass which turns upward
and backward and enters the central white matter of the cerebellum,
forming the =middle cerebellar peduncle=. Centrally the fibers are
arranged in bundles which intercross. The transverse fibers are
chiefly of two kinds. Some arise from the Purkinje cells of the
cerebellar cortex and pass either to the opposite side of the
cerebellum or turn at the raphé and run forward and backward in the
brain stem. Others are axones of cells of the nuclei pontis, and pass
to the hemispheres of the cerebellum. The corpus trapezoideum is
mainly the central continuation of the cochlear division of the
auditory nerve. Above it is the small =anterior olivary nucleus=
(Nucleus olivaris nasalis). The =longitudinal fibers= of the ventral
part of the pons consist chiefly of the =cerebrospinal= or =pyramidal
fasciculi=. These come from the ventral part (pes) of the cerebral
peduncles and are situated laterally, interspersed among the deep
transverse fibers in the anterior part of the pons. Toward the
posterior part the bundles incline toward the median plane and become
collected into a compact mass which appears superficially at the
posterior border. Many fibers come from the cerebral cortex and
terminate in the nuclei of the gray matter of the pons; they may be
designated =corticopontile fibers=.
THE CEREBELLUM
The =cerebellum= is situated in the posterior fossa of the cranium, and
is separated from the cerebral hemispheres by the transverse fissure and
the tentorium cerebelli which occupies it. It overlies the pons and the
greater part of the medulla, from which it is separated by the fourth
ventricle. Its average weight is about two ounces (ca. 60 gm.) or about
9 per cent. of the weight of the entire brain. Its shape is
approximately globular but very irregular. It is somewhat compressed
dorso-ventrally and its transverse diameter is the greatest.
The =anterior surface= faces upward and forward and is covered partially
by the tentorium cerebelli. The =posterior surface= is almost vertical.
The =ventral surface= or =base= lies over the fourth ventricle, and is
connected by three pairs of peduncles with the medulla, pons, and
mid-brain.
It is customary to recognize three gross divisions of the cerebellum,
viz., the median vermis and two lateral hemispheres. The =vermis=
(cerebelli) is curved in a circular manner so that its two extremities
are close together or even in contact on the ventral surface. The
anterior extremity is termed the =lingula=; it lies between the
cerebellar peduncles and gives attachment to the =anterior medullary
velum=, a thin lamina which forms the anterior part of the roof of the
fourth ventricle. The posterior extremity, the =nodulus=, gives
attachment to the =posterior medullary velum= which covers the posterior
recess of the fourth ventricle. The =hemispheres= (Hemisphæria
cerebelli) are clearly separated from the vermis by two deep paramedian
fissures. They lie in the lateral depressions of the cerebellar
compartment of the cranium.
In tracing the fissures from behind forward it will be noticed that
they are nearly sagittal as far as the anterior surface, where they
diverge widely, so that the vermis forms all of the fore part of the
cerebellum.
The surface of the cerebellum is further cut up into numerous =gyri= or
=folia= by narrow and relatively deep =sulci=, many of which approach a
transverse direction. Certain of the sulci are more pronounced than the
others, and by means of them it is possible to define groups of gyri.
Such groups are termed =lobes=, and have received specific names,
derived chiefly from the systematic descriptions of the human
cerebellum.
The lobes of the vermis are readily distinguished on a median section.
Enumerated from the anterior to the posterior extremity they are: (1)
lingula, (2) lobus centralis, (3) lobus ascendens, (4) lobus culminis,
(5) lobus clivi, (6) tuber vermis, (7) pyramis, (8) uvula, (9)
nodulus. Each hemisphere is cut into laterally by two sulci which mark
off two sagittal discoid masses, termed by Ziehen tabulations. The
external tabulation consists of four or five lobules, the lowest of
which is regarded as the flocculus. The inner part of the hemisphere
is divided into three or four lobes. In the absence of a satisfactory
morphological basis it seems undesirable to deal with the lobation of
the cerebellum in further detail.
The =cerebellar peduncles=, three on each side, join the central white
matter of the cerebellum at the base. The =posterior peduncle= is the
restiform body of the medulla, a large rounded tract derived from the
lateral and ventral columns of the cord. Near the middle of the medulla
it inclines outward, forms the lateral wall of the fourth ventricle, and
ends by entering the central white matter of the cerebellum. The =middle
peduncle= is formed, as previously seen, by the brachium pontis. The
=anterior peduncles= (Brachia conjunctiva) pass forward on either side
on the dorsal surface of the pons, forming the lateral boundary of the
fore part of the fourth ventricle. They disappear under the corpora
quadrigemina into the substance of the mid-brain. At the point of
disappearance the =trochlear= (fourth) =nerve= emerges from the
mid-brain. In some cases two or three bundles of fibers (Fila lateralia
pontis) arise in the angle between the middle and anterior peduncle,
curve obliquely forward and downward over the outer aspect of the
latter, and spread out on the ventral face of the cerebral peduncle just
in front of the pons.
On sagittal section the cerebellum is seen to consist of a layer of
=cortical gray matter= (Substantia corticalis) and the =medullary white
matter=. The white matter consists of a large =basal mass= (Corpus
medullare), which is joined by the peduncles, and gives off primary
laminæ to the lobules; from these secondary and tertiary laminæ arise,
the latter entering the gyri. The arrangement on sagittal section is
tree-like, hence the classical term “arbor vitæ” which is applied to it.
The central gray matter consists of groups of cells which form small
=nuclei= embedded in the central white substance.
As noted above the central gray matter does not form a large nucleus,
the corpus dentatum, which is so conspicuous an object on sagittal
sections of the cerebellar hemisphere in man.
The principal connections established by the peduncular fibers of the
cerebellum are as follows: The posterior peduncle (Corpus restiforme)
is composed of afferent and efferent fibers which connect the
cerebellum with the medulla and spinal cord. The =cerebellospinal
fasciculus= or =direct cerebellar tract=, which arises from the cells
of the nucleus dorsalis (Clarke’s column) of the cord, ends in the
cortex of the vermis; many of its fibers cross to the opposite side.
Numerous =arcuate fibers= from the nucleus gracilis and nucleus
cuneatus of the same and opposite sides establish connections with
=cells= of the cerebellar cortex. =Olivocerebellar= fibers (chiefly
afferent) connect with the olivary nucleus of the same and of the
opposite side of the medulla oblongata. The =nucleo-cerebellar
fasciculus= comprises fibers derived from the nuclei of the fifth,
eighth, and tenth cranial nerves (Edinger). The =descending
cerebellospinal fasciculus= consists of fibers which terminate in
relation with cells of the ventral horns of the spinal cord. The chief
facts concerning the middle peduncle have been mentioned in the
description of the pons. The anterior peduncle is essentially an
efferent tract, the fibers of which pass forward to the tegmentum of
the cerebral peduncle, the subthalamic region, and the thalamus. After
the peduncles disappear under the corpora quadrigemina, they converge
and many of their fibers intercross, forming the =decussation of the
superior peduncle=. A considerable number of fibers end in the nucleus
ruber. Thence impulses are transmitted in two directions: first, by
=thalamo-cortical fibers= to the cerebral cortex; second, by the
=rubrospinal tract= through the brain stem and lateral columns of the
cord to the ventral horn cells. The ventro-lateral cerebellospinal
fasciculus (Gowers’ tract) is an ill-defined tract which connects the
spinal cord with the cerebellum. Its fibers appear to be axones of
cells of the posterior horns of the cord; they pass in the lateral
column of the cord, become scattered in passing through the reticular
formation of the medulla and pons, and enter the cerebellum by way of
the anterior medullary velum.
THE FOURTH VENTRICLE
The =fourth ventricle= (Ventriculus quartus) is the cavity of the
rhombencephalon; it communicates with the central canal of the spinal
cord behind, and through the aqueduct with the third ventricle in front.
It is somewhat rhomboid in outline, elongated from before backward and
narrowest behind. It is lined completely by an epithelium (Ependyma) and
contains a small amount of fluid.
[Illustration:
FIG. 504.—BRAIN STEM AND BASAL GANGLIA OF HORSE, DORSAL VIEW.
The cranial nerve-roots are designated by Roman numerals.
]
Its =floor= (Fossa rhomboidea) is formed by the =medulla= and =pons= and
is marked by three longitudinal furrows which converge behind. It is
widest and deepest a little in front of its middle. The posterior part
narrows to a point at the opening of the central canal, and on account
of its appearance in man it has been termed the calamus scriptorius. The
=median sulcus= (Sulcus medianus) extends the entire length of the floor
and is deepest toward the ends. The =limiting sulci= (Sulci limitantes)
begin on either side of the opening of the central canal and extend
forward as the lateral limits of the rhomboid fossa. Just beyond the
middle of the fossa they expand into a shallow depression, the =anterior
fovea= (Fovea nasalis). On either side of the median sulcus and margined
by the limiting sulcus is a slightly rounded column, the =eminentia
medialis=. Opposite the fovea this presents an elongated prominence, the
=colliculus facialis=, so named because it overlies the bend formed by
the fibers of origin of the facial nerve. External to the limiting
sulcus is a long fusiform elevation, the =area acustica=, from which a
band of fibers (Striæ acusticæ) winds over the anterior end of the
restiform body to the superficial origin of the cochlear nerve.
The =lateral wall= is formed by the restiform body and the anterior
peduncle of the cerebellum.
The =roof= is formed in its middle part by the vermis of the cerebellum,
covered by the epithelium before mentioned. There is commonly a dorsal
recess (Recessus tecti s. fastigium) between the extremities of the
vermis. The anterior part of the roof is formed by a thin lamina of
white substance, the =anterior medullary velum= (or valve of Vieussens),
which extends backward from the corpora quadrigemina, and is attached on
either side to the anterior peduncles of the cerebellum. Its anterior
part is relatively thick and contains the decussation of the fibers of
the trochlear nerves. Posteriorly it blends with the white matter of the
cerebellum. A thin lamina of white matter, the =posterior medullary
velum=, backed by pia mater, completes the roof posteriorly. After
removal of the cerebellum the line of attachment (Tænia ventriculi
quarti) to the medulla is seen; it begins centrally over the opening of
the central canal, runs forward on the inner face of the restiform body,
and turns outward behind the brachium pontis. The thick part which
stretches over the posterior angle of the ventricle is termed the
=obex=. The posterior part of the ventricle forms three recesses, of
which two are lateral and the third median and posterior. The =lateral
recesses= communicate with the subarachnoid space by distinct openings
(Aperturæ laterales). The layer of pia which strengthens the roof here
is named the =tela chorioidea= of the fourth ventricle. It is triangular
in outline and closely adherent to the velum. It forms three fringed
masses which contain vascular convolutions and are designated the
=median= and =lateral chorioid plexuses= of the fourth ventricle. They
appear to lie within the ventricle, but are really excluded from the
cavity by the epithelial lining, which they invaginate.
[Illustration:
FIG. 505.—BRAIN STEM AND BASAL GANGLIA OF HORSE, RIGHT VIEW.
_F.a._, External arcuate fibers; _C.r._, corpus restiforme; _P_,
pyramid; _T_, corpus trapezoideum; _B.p._, middle peduncle of
cerebellum; _P.c._, cerebral peduncle; _S_, sulcus lateralis;
_T.t._, tractus transversus; _L._, trigonum lemnisci; _C.a._, corpus
quad, ant.; _C.p._, corpus quad, post.; _B_, commissure of _C.p._;
_G_, corpus geniculatum internum; _T.o._, olfactory peduncle;
_B.o._, olfactory bulb.
]
THE MESENCEPHALON
The =mesencephalon= or =mid-brain= connects the rhombencephalon with the
fore-brain. In the undissected brain it is covered dorsally by the
cerebral hemispheres. It consists of a dorsal part, the corpora
quadrigemina, and a larger ventral part, the cerebral peduncles, which
are visible on the base of the brain. It is traversed longitudinally by
a narrow canal, the cerebral aqueduct, which connects the fourth
ventricle with the third.
The =corpora quadrigemina=[191] are four rounded eminences which lie
under the posterior part of the cerebral hemispheres. They consist of
two pairs, separated by a transverse groove. The =anterior pair=
(Colliculi nasales) are larger and much higher than the posterior pair.
They are gray in color, almost hemispherical, and are separated by a
narrow furrow which leads forward to the subpineal fovea. A wide groove
intervenes between them and the optic thalami. The =posterior pair=
(Colliculi caudales) are relatively small and are paler than the
anterior pair. They are marked by a wide median depression, and are
limited below by a transverse furrow (Sulcus postquadrigeminus), at
either side of which the =trochlear= (fourth) =nerve= emerges. Laterally
each is prolonged to the inner geniculate body by a band of white matter
termed the inferior brachium.[192]
The =cerebral peduncles= or crura cerebri (Pedunculi cerebri) appear on
the base of the brain as two large rope-like stalks which emerge from
the pons close together and diverge as they extend forward to enter the
cerebrum. At the point of disappearance the =optic tract= winds
obliquely across the peduncle. About half an inch further back a small
tract (Tractus peduncularis transversus) curves across the peduncles,
and behind this near the median line is the superficial origin of the
=oculomotor= (third) =nerve=. The triangular depression between the
diverging peduncles is the =interpeduncular space= (Fossa
interpeduncularis). It is covered to a large extent by the =pituitary
body=, a discoid brown mass which is connected with the base of the
brain by a hollow stalk, the =infundibulum=. The posterior part of the
space is pierced by numerous minute openings which transmit
blood-vessels, and is therefore termed the =locus perforatus posticus=.
The objects in the space belong to the diencephalon, and will be
described later. The lateral aspect of the peduncle is marked by a
groove (Sulcus lateralis mesencephali) which indicates the division into
a dorsal part, the =tegmentum=, and a ventral part the =basis
pedunculi=; these are separated by a layer of dark gray matter, the
=substantia nigra=. The triangular area (Trigonum lemnisci) above the
lateral groove is faintly marked by fibers passing obliquely upward and
backward to the anterior cerebellar peduncle; these belong to the fillet
or lemniscus, an important tract that connects the thalamus and corpora
quadrigemina with the sensory reception nuclei of the opposite side of
the medulla.
The =aqueduct of the cerebrum= or of Sylvius (Aquæductus cerebri) is the
canal which extends through the mid-brain from the fourth to the third
ventricle. It is surrounded by a layer of gray matter (Stratum griseum
centrale), in the ventral part of which are the nuclei of origin of the
oculomotor and trochlear nerves, and laterally nuclei of the
mesencephalic roots of the trigeminal nerves.
THE DIENCEPHALON
The =diencephalon= or =inter-brain= comprises the thalamus and a number
of other structures grouped about the third ventricle, the cavity of
this division of the brain.[193] To expose its dorsal aspect, the
greater part of the cerebral hemispheres, the corpus callosum, the
fornix, the hippocampus, and the tela chorioidea of the third ventricle
must be removed.
The =thalamus= (or optic thalamus) is the principal body in this part of
the brain. It is a large ovoid gray mass placed obliquely across the
dorsal face of each cerebral peduncle, so that the long axes of the two
thalami would meet in front about at a right angle. Medially they are
fused to a large extent, and around the area of adhesion they are
separated by a sagittal circular space, the third ventricle. The dorsal
surface is convex in both directions, and is separated from the
overlying hippocampus by the tela chorioidea (or velum interpositum).
Laterally it is separated from the nucleus caudatus by an oblique groove
in which there is a band of white matter termed the =stria terminalis=
or tænia semicircularis. Internally it is bounded by a narrow band, the
=stria medullaris=, on which is a delicate ridge of ependyma termed the
=tænia thalami=. The striæ unite posteriorly and blend with the stalk of
the pituitary body. Near this point they present a small enlargement
caused by the nucleus habenulæ. Anteriorly there is a small eminence,
the =anterior tubercle=. The posterior part of the thalamus has the form
of a rounded ridge which is continuous laterally with the optic
tract.[194] Behind the point of origin of the tract, in the angle
between the thalamus and the cerebral peduncle, is the =internal
geniculate body= (Corpus geniculatum mediale), a well defined oval
prominence.
The outer surface is separated from the lenticular nucleus by the
=internal capsule=, an important mass of white matter composed of
fibers passing to and from the cerebral cortex. These fibers go to
form a large part of the ventral portion (basis) of the cerebral
peduncle. From the entire external surface of the thalamus fibers pass
into the internal capsule and radiate to reach the cerebral cortex;
similarly fibers coming from the cortex converge in the internal
capsule to enter the thalamus. This arrangement is termed the thalamic
radiation. Ventral to the thalamus proper is the =subthalamic
tegmental region=. This is the continuation of the tegmental part of
the cerebral peduncle into the diencephalon. It contains the =red
nucleus= (Nucleus ruber) an important ganglion on the course of the
motor tracts. It receives numerous fibers from the cerebral cortex and
the corpus striatum. From it fibers proceed to the thalamus and to the
spinal cord; the fibers to the cord (Tractus rubro-spinalis of
Monakow) cross to the opposite side and extend back in the tegmentum
to the lateral columns of the cord. Lateral to the red nucleus a
conspicuous lenticular area of dark gray matter is visible on
cross-sections of the subthalamic region; this is the =subthalamic
nucleus= (Nucleus hypothalamicus s. corpus Luysi), which consists of
pigmented nerve-cells scattered through a dense network of fine
medullated fibers, and is richly supplied with capillary
blood-vessels. The two nuclei are connected by a transverse commissure
(Commissura hypothalamica), which crosses the floor of the third
ventricle above the mammillary body.
The =pineal body= or =epiphysis= is a small ovoid or fusiform red-brown
mass situated in a deep central depression between the thalami and
corpora quadrigemina. It is variable in size, but is commonly about 10
to 12 mm. long and 6 mm. wide. It is attached at the postero-superior
quadrant of the third ventricle by a short stalk, in which is a small
recess of that cavity. Its base blends in front with the junction of the
striæ medullares of the thalamus. Immediately under the posterior part
of the stalk is a short transverse band of white matter, the =posterior
commissure=.
The pineal body is inclosed in a fibrous capsule from which numerous
trabeculæ pass inward, dividing the organ into spaces occupied by
round epithelial cells of the same origin as the ependyma of the
ventricle.
The =mammillary body= (Corpus mammillare) is a white round elevation a
little larger than a pea which projects ventrally at the anterior end of
the median furrow of the interpeduncular space. While it is a single
body in external form in the horse, sections show that it is double in
structure and contains a nucleus of gray matter on either side.
Three sets of fibers are connected with the mammillary body. The
anterior pillar of the fornix curves down in the lateral wall of the
third ventricle to the body and many of the fornix fibers end in it. A
bundle (Fasciculus thalamo-mammillaris) passes upward and backward
from it into the anterior part of the thalamus, and a tract
(Fasciculus pedunculo-mammillaris) extends back in the floor of the
third ventricle to the tegmentum of the mid-brain.
The =pituitary body= or =hypophysis= was mentioned as covering part of
the interpeduncular space. It is oval in outline, flattened
dorso-ventrally, and nearly an inch (ca. 2 cm.) in width. It is attached
by a delicate tubular stalk, the =infundibulum=, to the =tuber
cinereum=, a small gray prominence situated between the optic chiasm in
front and the mammillary body behind.
The pituitary body consists of two parts which can be distinguished
readily on sections by their color. The glandular (or anterior) lobe
is brown in color and is inclosed in a fibrous capsule. It is
glandular in character and there is good ground for the view that it
is an organ of internal secretion. Besides the chief cells which stain
lightly, it contains large deeply staining chromophile cells. It
arises as an outgrowth from the primitive mouth cavity. The cerebral
(or posterior) lobe is pale and is connected with the infundibulum so
as to form a rather flask-shaped arrangement. It is almost entirely
inclosed by the glandular part. It arises as an outgrowth from the
primitive diencephalon, but loses most of its earlier nervous
character.
The optic chiasm and tracts form the anterior boundary of the
interpeduncular space. The =optic chiasm= or =commissure= (Chiasma
opticum) is formed by the convergence of the optic nerves and the
crossing of the major part of the fibers of the nerve of one side to the
tract of the opposite side. From the chiasm each =optic tract= (Tractus
opticus) curves over the cerebral peduncle outward, backward, and upward
to the posterior part of the thalamus and the internal geniculate body;
some fibers reach the anterior quadrigeminal body.
[Illustration:
FIG. 506.—CROSS-SECTION OF BRAIN OF HORSE, NATURAL SIZE.
Section passes through posterior part of third ventricle and is viewed
from behind. _1_, Longitudinal fissure; _2_, hippocampus; _2′_,
fimbria; _3_, septum pellucidum; _4_, lateral ventricle; _5_,
thalamus; _6_, habenula; _7_, third ventricle; _8_, cerebral
peduncle; _8′_, hypothalamus; _9_, mammillary body; _10_, pituitary
body; _11_, pyriform lobe; _12_, ventral end of hippocampus; _13_,
amygdaloid nucleus. Between the upper parts of the tæniæ thalami is
the chorioid plexus of the third ventricle, and above this are the
internal cerebral veins.
]
All the fibers in the chiasm are not derived from the optic nerves.
The posterior part contains fibers which pass from one tract to the
other and are connected with the internal geniculate bodies; this
bundle is called Gudden’s commissure (Commissura inferior). Above it
is Meynert’s commissure (Commissura superior), the fibers of which
enter the subthalamic body.
The =third ventricle= (Ventriculus tertius) is the narrow annular space
between the thalami. It communicates by means of the aqueduct with the
fourth ventricle behind, and in front it is continuous with the lateral
ventricle on each side through the interventricular foramen. Its floor
is formed by the structures of the interpeduncular space and to a small
extent by the tegmentum of the cerebral peduncles. The roof is formed in
the strict sense only by the ependyma, above which is a fold of pia
mater, termed the =tela chorioidea= of the third ventricle or =velum
interpositum=. The roof is invaginated by two delicate =chorioid
plexuses= which appear to lie within the ventricle, although they are
excluded from the cavity by the epithelium. When the tela is removed,
the delicate ependyma of the roof is torn away with it, leaving the line
of attachment to the stria medullaris to constitute the tænia thalami.
The =anterior wall= is formed by the =lamina terminalis= (s. cinerea), a
thin layer of gray matter which extends upward from the optic chiasm to
the corpus callosum. A distinct rounded band of white matter extends
across its posterior face, bulging into the ventricle. This is the
=anterior commissure= (Commissura nasalis) of the cerebrum; its fibers
extend to the olfactory bulb and to the pyriform lobe. A similar but
more slender =posterior commissure= (Commissura caudalis) crosses the
posterior wall above the entrance to the aqueduct; the connections of
its fibers are not yet clearly known. The =interventricular foramen= (of
Monroe) is situated on either side of the anterior part of the ventricle
and leads outward and slightly upward between the anterior pillar of the
fornix and the anterior tubercle of the thalamus. The cavity presents
three =recesses= or diverticula, of which two are ventral and the third
is supero-posterior. The =optic recess= (Recessus opticus) lies above
the optic chiasm. Just behind it is the =infundibular recess= (Recessus
infundibuli) which extends through the infundibulum to the pituitary
body. The =pineal recess= (Recessus pinealis) is in the stalk of the
pineal body.
THE TELENCEPHALON
The =telencephalon= or =end-brain= comprises two principal parts, the
cerebral hemispheres and the optic part of the hypothalamus. The latter
has been considered as a matter of convenience in the description of the
diencephalon.
THE CEREBRAL HEMISPHERES
The =cerebral hemispheres= (Hemisphæria) form the greater part of the
fully developed brain. Viewed from above (Fig. 498) they form an ovoid
mass, of which the broader end is posterior, and the greatest transverse
diameter is a little behind the middle. The two hemispheres are
separated by a deep median cleft, the =longitudinal fissure= of the
cerebrum, which is occupied by a sickle-shaped fold of dura mater, the
falx cerebri. In front the separation is complete, and it appears to be
behind also, but here the two hemispheres are attached to each other
over a small area by the pia mater. When the hemispheres are gently
drawn apart, it is seen that the fissure is interrupted in its middle
part at a depth of a little more than an inch (ca. 3 cm.) by a white
commissural mass, the =corpus callosum=; this connects the hemispheres
for about half of their length. The =transverse fissure= separates the
hemispheres from the cerebellum, and contains the tentorium cerebelli.
The =convex= or =dorso-lateral surface=[195] conforms closely to the
cranial wall. The =medial= or =internal surface= is flat and sagittal
and bounds the longitudinal fissure; to a large extent it is in contact
with the falx cerebri, but behind the great cerebral vein the two
hemispheres are in contact and are attached to each other over a small
area as noted above. In well hardened specimens there is usually an
impression for the vein in front of the area of adhesion. The =base= or
=ventral surface= (Fig. 499) is irregular. Its anterior two-thirds is
adapted to the cerebral fossa of the cranial floor. Crossing this area
in front of the optic tract is a depression, the =transverse fossa=
(vallecula or fossa of Sylvius), which leads outward to the =lateral
fissure= (fissure of Sylvius), and lodges the middle cerebral artery. In
front of the fossa there is a considerable rounded elevation known as
the =trigonum olfactorium=. The trigonum and the inner part of the fossa
are pierced by numerous openings for the passage of small blood-vessels
and are equivalent to the locus perforatus anticus of man. Behind the
outer part of the fossa is the rounded anterior end of the =pyriform
lobe=. Traced backward the lobe curves upward and inward over the optic
tract and the thalamus to the tentorial aspect of the hemisphere; its
continuation, the hippocampus, forms part of the floor of the lateral
ventricle, and will be examined later.
The posterior part or =tentorial area= is flattened, faces inward and
backward as well as downward, and rests largely on the tentorium
cerebelli; on its anterior part there is a shallow depression adapted to
the corpora quadrigemina and the pineal body.
The =frontal pole= or anterior extremity (exclusive of the olfactory
bulb) is compressed laterally, and the =occipital pole= or posterior
extremity forms a blunt point.
[Illustration:
FIG. 507.—LEFT CEREBRAL HEMISPHERE OF HORSE, LATERAL VIEW. THE
OLFACTORY BULB IS CUT OFF.
_1_, Lateral fissure (of Sylvius); _2_, _3_, _4_, middle, posterior,
and anterior branches of _1_; _5_, presylvian fissure; _6_, _6′_,
sulcus rhinalis, anterior et posterior; _7_, suprasylvian fissure;
_8_, ectomarginal fissure; _9_, _9′_, ectosylvian fissure.
]
The hemisphere comprises: (1) the =pallium= or =mantle=, which consists
of an outer layer of gray matter, the =cortex= (Substantia corticalis),
covering a large mass of white matter (Centrum semiovale); (2) the
=rhinencephalon= or olfactory portion of the brain; (3) the =corpus
callosum= and =fornix=, the great commissural white masses; (4) the
=lateral ventricle= and certain important structures associated
therewith.
The =pallium= is thrown into numerous folds, the =gyri cerebri=, which
are separated by =sulci= or =fissures= of varying depth. The general
pattern of the gyri and sulci is similar in normal brains of the same
species, but the details are very variable and are never alike on the
two hemispheres of the same brain. In the horse the arrangement is
complicated by the existence of numerous short accessory fissures which
cut into the gyri at right angles and tend to confuse the observer. The
principal fissures and sulci of the convex surface (Figs. 497, 507) are
as follows:
1. The =lateral fissure= (Fissura lateralis Sylvii) ascends on the
lateral surface of the hemisphere as the continuation of the fossa
transversa in front of the pyriform lobe. After crossing the external
olfactory tract it divides into three branches; of these one passes
upward, one runs obliquely forward and upward, and the third is directed
upward and backward.
2. The =suprasylvian fissure= (F. suprasylvia)[196] is long and divides
a large part of the convex surface of the hemisphere into dorsal and
lateral portions. It begins on the dorso-medial border near its anterior
end and, inclining gradually downward, passes back to end on reaching
the tentorial surface. It is continuous internally with the transverse
fissure usually and in front with the presylvian fissure.
3. The =presylvian fissure= (F. præsylvia) is the continuation forward
of the preceding. It passes forward, outward, and downward almost to the
frontal pole, and then inclines backward to end at the groove which
marks the upper limit of the rhinencephalon (Sulcus rhinalis).
4. The =marginal fissure= (F. marginalis) extends along the dorso-medial
border. It begins a little in front of the middle of the border and
turns around the occipital pole to end on its tentorial aspect.
5. The =entomarginal fissure= (F. entomarginalis) lies internal to the
dorso-medial border. It does not extend quite as far forward as the
marginal fissure, from which it is separated by a narrow gyrus.
6. The =ectomarginal fissure= (F. ectomarginalis) lies about midway
between the marginal fissure and the posterior part of the suprasylvian
fissure.
7. The =sulcus rhinalis= is a very distinct furrow on the lower part of
the lateral surface which marks off the olfactory part of the brain
(rhinencephalon) from the rest of the hemisphere. It is undulating and
is highest where it is crossed by the lateral fissure (of Sylvius).[197]
On the medial surface (Fig. 508) the main fissures and sulci are as
follows:
1. The =calloso-marginal fissure= (F. calloso-marginalis) is extensive
and well defined. It is approximately parallel to the dorso-medial
border of the hemisphere, from which it is about half an inch distant.
It begins in front a short distance below and in front of the anterior
bend (genu) of the corpus callosum and forms a =C=-shaped curve, its
posterior part extending on the tentorial surface to a point behind the
depression for the corpora quadrigemina. It separates the marginal gyri
above from the gyrus fornicatus, which extends down to the corpus
callosum.
2. The =transverse fissure= (F. transversa) begins a little behind the
middle of the calloso-marginal fissure, passes obliquely upward and
forward to the dorso-medial border—into which it cuts deeply—and usually
joins the suprasylvian fissure.[198]
3. The =sublimbic fissure= (F. sublimbica) curves over the gyrus
fornicatus a short distance above the corpus callosum. Its middle part
is commonly indistinct, and it is often divided into anterior and
posterior parts.
4. The =callosal sulcus= (Sulcus corporis callosi) separates the corpus
callosum from the gyrus fornicatus.
The =hippocampus= (or cornu Ammonis) is a gyrus which curves from the
deep face of the pyriform lobe around the thalamus and forms the
posterior part of the floor of the lateral ventricle. It can be
displayed by cutting away the brain stem up to the optic tract and the
interventricular foramen. Viewed from below the hippocampal gyrus is
seen to form a semicircular curve from the apex of the pyriform lobe to
the angle of divergence of the posterior pillars of the fornix, _i. e._,
to a point under the central part of the corpus callosum. It is
separated deeply by the hippocampal fissure from the =gyrus dentatus=.
Along the concave margin of the latter is a band of white matter, termed
the =fimbria=, which is the prolongation of the greater part of the
posterior pillar of the fornix into this region. The ventricular surface
of the hippocampus (Fig. 511) is covered with a thin layer of white
matter, the =alveus=, which is also derived from the posterior pillar of
the fornix, and is therefore continuous with the fimbria. The two
hippocampi are connected at their highest parts by transverse fibers
which constitute the =hippocampal commissure=.
The interval between the hippocampus and fimbria on the one hand and the
brain stem on the other is a lateral continuation of the great
transverse fissure of the brain, and is termed the =chorioid fissure=.
It is occupied by a fold of pia mater, the =tela chorioidea= of the
third ventricle, or =velum interpositum=. This fold is triangular in
outline and its apex reaches to the interventricular foramen. Its base
is continuous at the transverse fissure with the pia which covers the
surface of the brain. Its middle part lies over the epithelial roof of
the third ventricle, as has been seen (Fig. 506). The lateral borders
will be seen on the floor of the lateral ventricles, where they form
thick rounded bands containing convolutions of blood-vessels, known as
the =chorioid plexuses= of the lateral ventricles (Fig. 511).
[Illustration:
FIG. 508.—MEDIAN SECTION OF BRAIN OF HORSE.
The membranes and vessels are removed. _C_, Central white matter
(corpus medullare) of cerebellum; _P.c._, cerebral peduncle; _C.q._,
corpora quadrigemina; _P_, pineal body; _Th._, thalamus; _V.III._,
third ventricle; _r_, optic recess; _r′_, infundibular recess;
_C.m._, mammillary body; _s_, subcallosal gyrus; _A.p._, area
parolfactoria; _G_, genu of corpus callosum; _S_, splenium of same;
_1_, callosal sulcus; _2_, interventricular foramen; _3_, olfactory
bulb. The cerebral lobe of the pituitary body is distinguished by
its lighter color.
]
When the tela is pulled out one may easily get the impression that the
lateral ventricle communicates with the exterior by means of the
chorioid fissure. Such is not the case, since the chorioid plexus is
covered by the epithelial lining of the ventricle, which has been torn
away.
The =rhinencephalon= or olfactory part of the brain comprises the
olfactory bulb, peduncle and tracts or roots, the trigonum olfactorium,
the area parolfactoria, and the pyriform lobe.[199]
The =olfactory bulb= (Bulbus olfactorius) is an oval enlargement which
curves upward in front of the frontal pole of the hemisphere. Its convex
superficial face fits into the ethmoidal fossa and receives numerous
olfactory nerve-fibers through the cribriform plate; hence it is very
difficult to remove the bulb intact. It contains a considerable =cavity=
(Ventriculus bulbi olfactorii) which is connected with the lateral
ventricle by a small canal in the middle olfactory tract. The deep face
is largely in contact with the frontal pole of the hemisphere and is
connected with the olfactory peduncle.
The gray matter of the bulb is external and is thickest on the convex
anterior surface. The posterior surface consists to a large extent of
fibers which are the axones of the mitral cells of the deep layer of
the gray substance and go to form the peduncle and striæ.
The =olfactory peduncle= (Tractus olfactorius) is a very short but wide
band of white substance which arises in the olfactory bulb and extends
back to be continued by the olfactory tracts.
[Illustration:
FIG. 509.—MEDIO-VENTRAL ASPECT OF RIGHT CEREBRAL HEMISPHERE OF HORSE.
The olfactory bulb is cut off. _T.ol._, Olfactory peduncle; _A.p._,
area parolfactoria; _Tr.O._, trigonum olfactorium; _T.op._, optic
tract; _C.o._, chiasma opticum; _G.s._, subcallosal gyrus; _C.c._,
corpus callosum; _S.p._, septum pellucidum; _F_, fornix; _G.c._,
callosal gyrus; _T_, cut surface of thalamus; _F′_, fimbria; _G.d._,
gyrus dentatus; _L.p._, pyriform lobe; _G.h._, hippocampal gyrus.
]
The =olfactory tracts= or =striæ= (Striæ olfactorii) are three in
number. The =external tract= (Stria lateralis) is much the largest and
most distinct. It passes backward, upward, and outward, widens out and
joins the pyriform lobe. It is clearly defined dorsally by the sulcus
rhinalis and is marked off from the trigonum olfactorium by the sulcus
arcuatus. The =intermediate tract= (Stria intermedia) is short, ill
defined, and flat; it contains the canal which opens into the anterior
horn of the lateral ventricle. The =internal tract= (Stria medialis) is
small, short, and not well defined; it bends over to the parolfactory
area (of Broca) on the inner face of the hemisphere below the genu of
the corpus callosum.
The =trigonum olfactorium= is the prominent gray area situated in the
angle of divergence of the internal and external olfactory striæ. It is
bounded externally by the external olfactory stria, from which it is
defined by the arcuate sulcus. It is continuous with the =area
parolfactoria= on the medial surface; behind the latter a band descends
from the rostrum of the corpus callosum and is continuous below with the
anterior perforated space; it is termed the =subcallosal gyrus= or
peduncle of the corpus callosum.
The =pyriform lobe= (Lobus piriformis) is the well-marked prominence on
the base lateral to the optic tract and cerebral peduncle, from which it
is separated by a deep fissure. Its nipple-like apex lies behind the
fossa transversa and covers the optic tract. The external surface is
marked by one or two sulci (lobi piriformis). The lobe contains a
cavity, the ventral horn of the lateral ventricle.
The fibers of the olfactory tracts go to the pyriform lobe and
hippocampus, the trigonum olfactorium, the area parolfactoria, the
subcallosal gyrus, and part of the gyrus fornicatus. The central
connections of the olfactory apparatus are complex and are not yet
fully understood. The anterior cerebral commissure contains fibers
which pass from the olfactory bulb of one side by way of the inner
tracts to the bulb of the opposite side; also fibers which cross in it
from the inner tract of one side to the pyriform lobe of the opposite
side. Many fibers pass by way of the septum pellucidum, fornix, and
fimbria to the hippocampus. Other fibers pass in the anterior pillar
of the fornix to the mammillary body and thence to the thalamus by the
thalamo-mammillary bundle.
[Illustration:
FIG. 510.—LATERAL VIEW OF CAST OF CAVITIES OF BRAIN OF HORSE.
_Bo_, Cavity of olfactory, which communicates through the canal _I_
with a lateral ventricle; _Ca_, anterior horn, _Cm_, body, _Ci_,
ventral horn of lateral ventricle; _M_, isthmus which connects
lateral and third ventricles _Ep_, suprapineal recess, below which
is the small infrapineal recess; _Ro_, optic recess; _Rh_,
infundibular and pituitary recess; _S_, aqueduct; _Fl_, ridge
corresponding to sulcus limitans; _Rl_, lateral recess, _Rm_,
posterior recess, of fourth ventricle; _Cc_, beginning of central
canal of spinal cord. (Dexler.)
]
The =corpus callosum= is the great transverse commissure which connects
the two cerebral hemispheres through about half of their length. On
median section (Fig. 508) it is seen to be arched from before backward,
white in color, and composed substantially of transverse fibers. The
middle part or =truncus= (Truncus corporis callosi) slopes downward and
forward and is thinner than the ends. The anterior thickened end, the
=genu=, bends downward and backward and thins out to form the =rostrum=;
the latter is continuous with the lamina terminalis. The posterior end,
the =splenium=, also thick, lies at a considerably higher level than the
genu. The =upper surface= is convex in its length, concave transversely.
Its central part forms the floor of the longitudinal fissure. It is
covered by a thin layer of gray matter (Induseum griseum), in which are
strands of longitudinal fibers (Striæ longitudinales); the latter are
arranged in median and lateral bundles (Stria medialis, striæ
laterales).[200] The =lower surface= has the reverse configuration, and
forms the roof of the lateral ventricles. Along the median line the
septum pellucidum is attached to it. The fibers of the corpus callosum
(with the exception of the longitudinal striæ) run transversely and
spread out laterally in all directions in the central white matter of
the hemispheres to the cortex, forming the =radiation of the corpus
callosum= (Radiatio corporis callosi).
The =fornix= is a bilateral structure composed of white fibers which
arch chiefly over the thalamus and the third ventricle. It is described
as consisting of a body and two pairs of pillars. The =body= (Corpus
fornicis) is formed by the fusion of the two arches of which the fornix
is composed. It is triangular and overlies the anterior parts of the
thalami and the third ventricle. The upper surface gives attachment to
the septum pellucidum and on either side forms part of the floor of the
lateral ventricle. The lateral border is related to the chorioid plexus
of the lateral ventricle and forms the inner boundary of the
interventricular foramen. The =anterior pillars= or =columns= (Columnæ
fornicis) (Fig. 512) are two slender round bundles which emerge from the
body in front of the interventricular foramen and diverge slightly as
they curve downward and backward to the mammillary body.
[Illustration:
FIG. 511.—BRAIN OF HORSE, WITH LATERAL VENTRICLES OPENED BY REMOVAL OF
UPPER PART OF CEREBRAL HEMISPHERES.
]
From the mammillary body the greater part of these fornix fibers are
continued to the thalamus by the thalamo-mammillary fasciculus (or
bundle of Vicq d’Azyr). Others pass to the cerebral peduncle. A
portion of the fibers cross to the opposite thalamus and cerebral
peduncle.
The =posterior pillars= (Crura fornicis) are much larger bands which
diverge widely from the posterior angles of the body. Each curves
outward and backward over the thalamus (from which it is separated by
the tela chorioidea) and is chiefly continued as the =fimbria= along the
concave border of the hippocampus. The pillars give off fibers to form
the alveus or white matter which covers the ventricular face of the
hippocampi, and between them are transverse fibers which constitute the
hippocampal commissure.
The =septum pellucidum= is the median partition between the two lateral
ventricles. Its convex upper border blends with the corpus callosum and
its concave lower border joins the fornix. Its anterior part is received
into the genu of the corpus callosum. Traced backward it diminishes in
height and the two edges meet at an acute angle at the splenium.
The septum consists of two layers (Laminæ septi pellucidi) which are
in direct contact with each other. They consist of nerve-fibers and
gray matter. The latter exists in considerable amount in the thicker
part of the septum adjacent to the anterior pillars of the fornix.
Many of the fibers of the septum pass up through the corpus callosum
to the gyrus fornicatus. Others are connected with the subcallosal
gyrus and the parolfactory area.
[Illustration:
FIG. 512.—CROSS-SECTION OF BRAIN OF HORSE, ABOUT NATURAL SIZE.
Section passes through chiasma opticum, and is viewed from in front.
_1_, Longitudinal fissure; _2_, septum pellucidum; _3_, columns
(anterior pillars) of fornix; _4_, lateral ventricle; _5_, chorioid
plexus; _6_, corpus medullare (central white matter) of hemisphere;
_7_, caudate nucleus; _8_, lenticular nucleus; _9_, internal
capsule; _10_, external capsule; _11_, insula.
]
The =lateral ventricle= (Ventriculus lateralis) is the irregular cavity
in the interior of each cerebral hemisphere.[201] Each communicates with
the third ventricle through the =interventricular foramen= (of Monro),
and by a small canal with the cavity of the olfactory bulb. It is usual
to describe the ventricle as consisting of three parts, viz., the
central part or body, and anterior and inferior horns. The =anterior
horn= (Cornu nasale) is the part in front of the interventricular
foramen; it communicates ventrally with the olfactory cavity. The
=central part= (Pars centralis) extends back to the splenium of the
corpus callosum. It opens into the third ventricle through the
interventricular foramen, which is situated between the fornix and the
anterior part of the thalamus. The =inferior horn= (Cornu ventrale)
curves downward and forward into the pyriform lobe. The roof of the
ventricle is formed by the corpus callosum and the inner wall is the
septum pellucidum. After removal of the roof the floor is seen to be
formed chiefly by two bodies. The anterior one is the =caudate nucleus=
(Nucleus caudatus), a somewhat pear-shaped gray eminence, the long axis
of which is directed obliquely upward, backward, and outward. Its
anterior large end is termed the head, and the posterior long tapering
end the tail. The posterior body, the =hippocampus=, is white on its
ventricular surface, which is strongly convex. It curves outward and
backward and then turns downward and forward to join the pyriform lobe.
The two bodies are separated by an oblique groove which is occupied by
the =chorioid plexus= of the lateral ventricle. This is the thickened
edge of a fold of pia mater, the tela chorioidea (or velum
interpositum), which lies between the hippocampus and the thalamus. It
contains convolutions of small blood-vessels and in old subjects there
may be calcareous concretions in it. The plexuses of the two sides are
continuous through the interventricular foramen. On drawing the chorioid
plexus backward a narrow white band, the =stria terminalis= (or tænia
semicircularis), is seen along the margin of the caudate nucleus, where
it bounds the intermediate groove. The plexus partially covers a wider
white band which is blended with the white substance of the hippocampus;
this is the =posterior pillar of the fornix= and its continuation, the
=fimbria=.
[Illustration:
FIG. 513.—SAGITTAL SECTION OF BRAIN OF HORSE.
Section is cut about 1.5 cm. to the right of the median plane. _M_,
Medulla oblongata; _P_, pons; _P.c._ (above _M_), chorioid plexus of
fourth ventricle; _C.m._, central white matter (corpus medullare) of
cerebellum and of cerebrum; _P.c._ (in front of _P_), cerebral
peduncle; _H_, hippocampus; _V_, lateral ventricle; _T_, thalamus;
_N.c._, caudate nucleus; _C.i._, internal capsule; _N.l._,
lenticular nucleus; _B.o._, olfactory bulb.
]
The =corpus striatum=[202] is the great basal ganglion of the
hemisphere. It is situated in front of the thalamus and the cerebral
peduncle, and its anterior rounded end appears on the base of the
hemisphere at the trigonum olfactorium. It is composed of two masses of
gray matter, the caudate and lenticular nuclei, separated incompletely
by tracts of white matter which are known collectively as the internal
capsule. The =caudate nucleus= (Nucleus caudatus) is the dorso-medial
and larger of the two gray masses; it has been seen in the examination
of the floor of the lateral ventricle. The =lenticular nucleus= (Nucleus
lentiformis) lies ventro-laterally, over the trigonum olfactorium and
the fossa transversa. It is related externally to a layer of white
matter termed the =external capsule=, which separates it from a stratum
of gray substance known as the =claustrum=. The two nuclei are fused in
front, and further back they are connected by strands of gray matter
which intersect the internal capsule.
The =amygdaloid nucleus= (Nucleus amygdalæ) (Fig. 506) is an ovoid mass
of gray matter situated external to the ventral horn of the lateral
ventricle and below the posterior part of the lenticular nucleus. Some
fibers of the stria terminalis are connected with it.
The =internal capsule= (Capsula interna) is a broad band of white matter
situated between the thalamus and caudate nucleus internally and the
lenticular nucleus externally. A sagittal section through the brain
shows that it is in great part directly continuous with the basis or
ventral part of the cerebral peduncle. It contains most of the so-called
=projection fibers= of the hemisphere, which connect the cerebral cortex
with nuclei of other and more posterior parts of the brain. When the
fibers of the internal capsule are traced forward it is evident that
they spread out in all directions to reach the cerebral cortex. This
arrangement, in which the fibers of the corpus callosum participate, is
termed the =corona radiata=.
The internal capsule also contains fibers which connect the corpus
striatum with the thalamus. These are termed the thalamo-striate and
strio-thalamic fibers respectively, according to the direction in
which they conduct impulses.
The fibers of the stria terminalis connect the amygdaloid nucleus with
the septum pellucidum and trigonum olfactorium. It is therefore
probably part of the complex connections between the primary and
secondary olfactory centers.
THE CRANIAL NERVES
The =cranial= or =cerebral nerves= (Nn. cerebrales) comprise twelve
pairs which are designated from before backward numerically and by name.
Their number, names, and functional characters are given in the
subjoined table:
I. Olfactory Sensory (Small)
II. Optic Sensory (Sight)
III. Oculomotor Motor
IV. Trochlear Motor
V. Trigeminal Mixed
VI. Abducent Motor
VII. Facial Mixed
VIII. Auditory Sensory (Hearing and Equilibration)
IX. Glosso-pharyngeal Mixed
X. Vagus or Pneumogastric Mixed
XI. Spinal accessory Motor
XII. Hypoglossal Motor
THE FIRST OR OLFACTORY NERVE
The =olfactory nerve= (N. olfactorius) is peculiar in that its fibers
are not aggregated to form a trunk, but are connected in small bundles
with the olfactory bulb. They are non-medullated, and are the central
processes of the olfactory cells which are situated in the olfactory
region of the mucous membrane of the nasal cavity. This region is
distinguished by its brown color and comprises most of the lateral mass
of the ethmoid, a small adjacent area of the superior turbinal, and the
corresponding surface of the septum nasi. The nerve-bundles are inclosed
in sheaths derived from the membranes of the brain and pass through the
foramina of the cribriform plate to join the convex surface of the
olfactory bulb. Some fibers come from the vomero-nasal organ of
Jacobson.
THE SECOND OR OPTIC NERVE
The =optic nerve= (N. opticus) is composed of fibers which are the
central processes of the ganglion cells of the retina. The fibers
converge within the eyeball to the optic papilla, where they are
collected into a round trunk, the optic nerve. The nerve thus formed
pierces the chorioid and sclera, emerges from the posterior part of the
eyeball, and passes backward and inward to the optic foramen. After
traversing the latter it decussates with its fellow of the opposite side
to form the optic chiasma or commissure. In the orbit the nerve is
slightly flexuous and is embedded in the fat behind the eyeball and
surrounded by the retractor oculi muscle. Its intraosseous part is an
inch or more (ca. 3 cm.) long. The =sheath= of the nerve is formed by
prolongations of the membranes of the brain, and includes continuations
of the subdural and subarachnoid spaces.
The greater part of the fibers of the optic nerve cross in the chiasma
to the tract of the opposite side. In the tract the fibers proceed to
(1) the internal geniculate body, (2) the posterior part of the
thalamus, and (3) the anterior quadrigeminal body (indirectly). The
fibers which go to the internal geniculate body appear to belong to
Gudden’s commissure and to be nonvisual in function. The visual
fibers, which come from the outer part of the retina of the same side
and the inner part of the retina of the opposite side, terminate about
cells in the anterior quadrigeminal body and the part of the thalamus
which corresponds to the pulvinar and external geniculate body of man.
From the cells of the former fibers pass to the nuclei of the motor
nerves of the eyeball, and complete the reflex arc. Fibers proceed
from the cells of the thalamus to the visual area of the cortex in the
occipital part of the hemisphere.
THE THIRD OR OCULOMOTOR NERVE
The =oculomotor nerve= (N. oculomotorius) arises by several radicles
from the basal surface of the cerebral peduncle, a little lateral to the
interpeduncular furrow. It turns sharply outward and forward, crosses
over the cavernous sinus, and continues above the maxillary nerve and in
company with the ophthalmic nerve to the foramen lacerum orbitale. It
emerges through the foramen with the latter nerve and the abducens and
divides into two branches. The =superior branch= is short and divides
into twigs which supply the rectus superior, retractor, and levator
palpebræ superioris. The =inferior branch= (Figs. 438, 439) is larger
and much longer. It supplies the motor fibers to the ciliary ganglion
(which lies directly on this branch in the horse) and short branches to
the rectus internus and rectus inferior, and continues forward on the
latter to end in the inferior oblique muscle.
The deep origin of the fibers of the oculomotor nerve is in the
oculomotor nucleus situated in the gray matter of the floor of the
cerebral aqueduct in the region of the anterior corpora quadrigemina.
THE FOURTH OR TROCHLEAR NERVE
The =trochlear= or pathetic (N. trochlearis) is the smallest of the
cranial nerves. It arises from the anterior cerebellar peduncle just
behind the corpora quadrigemina, curves outward and forward, pierces the
tentorium cerebelli, and passes forward along the outer border of the
maxillary nerve (Figs. 504, 505). It emerges from the cranium through a
small foramen immediately above the foramen lacerum orbitale or through
the latter and passes forward along the inner wall of the orbit to end
in the posterior part of the superior oblique muscle of the eyeball
(Fig. 439).
The fibers of the fourth nerve spring from a nucleus in the gray
matter of the floor of the cerebral aqueduct behind the oculomotor
nucleus. The fibers run backward in the tegmentum, then turn upward
and inward and undergo total decussation with those of the opposite
nerve in the anterior part of the anterior medullary velum. In
addition to this peculiarity it is the only nerve which is connected
with the dorsal aspect of the brain.
THE FIFTH, TRIGEMINAL, OR TRIFACIAL NERVE
The =trigeminal nerve= (N. trigeminus) is the largest of the cranial
series. It is connected with the lateral part of the pons by a large
=sensory root= and a smaller =motor root= (Fig. 499).
The =sensory root= (Portio major) extends forward through a notch on the
lower part of the petrosal crest and widens out to join the semilunar
ganglion.
The =semilunar= (or Gasserian) =ganglion= (Ganglion semilunare) is a
crescent-shaped mass of nerve-fibers and cells which overlies the
antero-external part of the foramen lacerum basis cranii, and is partly
embedded in the dense fibrous tissue which occupies the foramen except
where vessels and nerves pass through. Its long axis, which is about an
inch (2.5 cm.) in length, is directed forward and inward and its convex
anterior face gives rise to the ophthalmic, the maxillary, and the
sensory part of the mandibular division of the nerve. The surface of the
ganglion is irregularly striated. It is connected by filaments with the
adjacent carotid plexus of the sympathetic, and sends delicate twigs to
the dura mater.
The fibers of the sensory root arise from the ganglion as axones of
the ganglion cells, and the fibers of the nerves which extend
peripherally from the ganglion are dendrites of the cells. The sensory
root-fibers enter the tegmentum of the pons and divide into anterior
and posterior branches, which terminate about the cells of the sensory
nucleus of termination of the trigeminus. This nucleus extends from
the pons to the sixth cervical segment of the spinal cord (Dexler).
The posterior branches of the fibers are collected into a compact
bundle, the spinal tract or root of the trigeminus, which lies lateral
to the substantia gelatinosa in the medulla. The central connections
of the sensory part of the trigeminus are very extensive. The most
important paths are: (1) Axones of cells of the sensory nucleus and
the substantia gelatinosa pass chiefly as arcuate fibers across the
raphé to the thalamus, whence impulses are transmitted by
thalamo-cortical fibers to the cerebral cortex. In ungulates a
distinct tract extends from the anterior part of the sensory nucleus
to the thalamus of the same side (Wallenberg). It is probable that
collaterals of the arcuate fibers go to the motor nuclei of the fifth,
seventh, ninth, and tenth cranial nerves. (2) Axones of cells of the
sensory nucleus enter the posterior cerebellar peduncle of the same
side and reach the cerebellar cortex. (3) Collaterals are distributed
to the nuclei of origin of the hypoglossal and of the motor part of
the trigeminal and facial nerves.
The =motor root= (Portio minor) extends forward beneath the sensory root
and the semilunar ganglion and is incorporated with the mandibular
division of the nerve. Its fibers arise chiefly from the so-called
masticatory nucleus, which is situated in the pons near the inner face
of the sensory nucleus; a few of these fibers come from the nucleus of
the opposite side and cross in the raphé. Other fibers, which constitute
the mesencephalic root, arise from cells in the outer part of the
central gray matter of the mid-brain.
It is evident from the foregoing statements that the trigeminus has
essentially the same arrangement as a typical spinal nerve. It divides
into three branches.
I. The =ophthalmic nerve= (N. ophthalmicus) (Figs. 438, 439, 440) is
purely sensory and is the smallest of the three branches of the
trigeminus. It arises from the inner part of the front of the semilunar
ganglion, passes forward along the outer side of the cavernous sinus,
and is blended with the maxillary nerve for some distance. It enters the
foramen lacerum orbitale with the third and sixth nerves and divides
into three branches.
1. The =lacrimal nerve= (N. lacrimalis) runs forward on the rectus
superior and the levator palpebræ superioris and ramifies chiefly in
the lacrimal gland and the upper eyelid. A branch (Ramus
zygomatico-temporalis) exchanges twigs with the zygomatic branch of
the maxillary nerve, perforates the periorbita, and emerges from the
orbital fossa behind the supraorbital process; it forms a plexus with
branches of the auriculo-palpebral and frontal nerves, and ramifies in
the skin of the temporal region.
2. The =frontal nerve= (N. frontalis), also termed the supraorbital,
runs forward almost parallel with the superior oblique muscle, at first
within, then outside of, the periorbita. It passes through the
supraorbital foramen with the artery of like name and ramifies in the
skin of the forehead and upper eyelid, forming a plexus with the
lacrimal and auriculo-palpebral nerves. It divides into three branches.
3. The =naso-ciliary nerve= (N. naso-ciliaris), also termed the
palpebro-nasal, runs forward along the inner side of the optic nerve
between parts of the retractor muscle and divides into two branches. Of
these the =ethmoidal nerve= (N. ethmoidalis) is the continuation of the
parent trunk. It accompanies the ethmoidal artery through the foramen of
like name into the cranial cavity and crosses the lower part of the
ethmoidal fossa. Leaving the cranium through an opening in the
cribriform plate close to the crista galli, it enters the nasal cavity
and ramifies in the mucous membrane of the septum nasi and the superior
turbinal. The =infratrochlear nerve= (N. infratrochlearis) runs forward
to the inner canthus and ramifies in the skin in this region; it
detaches twigs to the conjunctiva and caruncula lacrimalis, and a long
branch which supplies the third eyelid and the lacrimal ducts and sac.
The naso-ciliary nerve furnishes the =sensory= or =long root= (Radix
longa) of the ciliary ganglion.
The =ciliary ganglion= is placed on the inferior branch of the
oculomotor nerve. It is usually not larger than a millet-seed, and is
best found by following the nerve to the inferior oblique muscle back to
its origin. The ganglion receives (_a_) =sensory fibers= from the
naso-ciliary nerve; (_b_) =motor fibers= from the oculomotor nerve; and
(_c_) =sympathetic fibers= from the sphenopalatine plexus. It detaches
filaments which unite with twigs from the ophthalmic and maxillary
nerves and from the sphenopalatine ganglion to form the ciliary plexus.
From the latter emanate five to eight delicate =short ciliary nerves=
(Nn. ciliares breves), which pursue a somewhat flexuous course along the
optic nerve, pierce the sclera near the entrance of that nerve, and run
forward between the sclera and chorioidea to the circumference of the
iris. Here the branches of adjacent nerves anastomose to form a circular
plexus (Plexus gangliosus ciliaris), from which filaments go to the
ciliary body, iris, and cornea.
The circular fibers of the iris and the ciliary muscle are innervated
by fibers derived from the oculomotor nerve, the radial fibers of the
iris by the sympathetic.
II. The =maxillary nerve= (N. maxillaris), also termed the superior
maxillary, is purely sensory and is much larger than the ophthalmic. It
extends forward from the semilunar ganglion in the middle cranial fossa
in the large groove on the root of the temporal wing of the sphenoid. It
is related internally to the cavernous sinus and superiorly to the
ophthalmic nerve, with which it is blended for some distance. It emerges
through the foramen rotundum, passes forward in the pterygo-palatine
fossa above the internal maxillary artery and embedded in fat, and is
continued in the infraorbital canal as the infraorbital nerve (Fig.
439). Its branches are as follows:
1. The =zygomatic nerve= (N. zygomaticus s. subcutaneus malæ), also
termed the orbital branch, arises before the maxillary nerve reaches the
pterygo-palatine fossa (Figs. 438, 439, 514). It pierces the periorbita
and divides into two or three delicate branches which pass along the
surface of the external straight muscle to the external canthus and
ramify chiefly in the lower lid and the adjacent skin. Anastomoses are
formed with branches of the lacrimal nerve.
2. The =sphenopalatine nerve= (N. sphenopalatinus) is given off in the
pterygo-palatine fossa from the lower border of the maxillary nerve
(Fig. 439). It is broad and flat and forms a plexus in which several
small =sphenopalatine ganglia= are interposed. It divides into posterior
nasal, and greater and lesser palatine nerves. (1) The =posterior nasal
nerve= (N. nasalis aboralis) passes through the sphenopalatine foramen,
in which it bears one or more minute ganglia, enters the nasal cavity,
and divides into internal and external branches (Figs. 440, 464). The
internal branch (N. septi narium) runs forward in the submucous tissue
of the lower part of the septum nasi, gives twigs to the mucous membrane
here and to the vomero-nasal organ (of Jacobson), passes through the
palatine cleft and ramifies in the anterior part of the hard palate. The
external branch (Ramus lateralis) ramifies in the mucous membrane of the
inferior turbinal and the middle and inferior meatus nasi. (2) The
=greater= or =anterior palatine nerve= (N. palatinus major s. anterior)
(Figs. 438, 439) is the largest of the three branches. It runs forward
in the palatine canal and groove and ramifies in the hard palate and
gums. It also supplies twigs to the soft palate, and gives off branches
which pass through the accessory palatine foramina to supply the mucous
membrane of the inferior meatus.
The branches of the two nerves anastomose in the hard palate and form
a plexus about the branches of the palatine arteries.
[Illustration:
FIG. 514.—DISSECTION OF HEAD OF HORSE.
The masseter and superficial muscles and the parotid gland are in
great part removed. _a_, _a_, Levator labii superioris proprius;
_b_, _b_, levator nasolabialis; _c_, dilatator naris inferior; _d_,
buccinator; _e_, common mass of buccinator and depressor labii
inferioris; _f_, depressor labii inferioris; _g_, masseter; _h_,
orbicularis oculi; _i_, temporalis; _k_, occipito-hyoideus; _k′_,
stylo-maxillaris; _l_, sterno-cephalicus; _l′_, tendon of same; _m_,
omo-hyoideus; _n_, crico-pharyngeus; _o_, mastoid tendon of
mastoido-humeralis; _p_, splenius; _q_, inferior buccal and labial
glands; _r_, superior buccal glands; _s_, remnant of parotid gland;
_t_, submaxillary gland; _u_, anterior cervical (subparotid) lymph
glands; _v_, probe passed into diverticulum nasi; _w_, cornu of alar
cartilage; _x_, internal palpebral ligament; _y_, wing of atlas;
_z_, scutiform cartilage of ear; _1_, external nasal nerve; _2_,
anterior nasal nerve; _3_, superior labial nerve; _4_, anterior part
of superior buccal nerve; _5_, buccinator nerve; _6_, _6′_, inferior
alveolar nerve; _6″_, mental nerve-continuation of _6_; _7_,
masseteric nerve; _8_, facial nerve (cut); _9_, superficial temporal
nerve; _10_, anastomosis between _9_ and _8_; _11_, internal
auricular nerve; _12_, posterior auricular nerve; _13_, digastric
nerve; _14_, cervical branch of facial nerve (cut); _15_,
auriculo-palpebral nerve; _16_, lacrimal nerve; _17_, frontal nerve;
_18_, infratrochlear nerve; _19_, n. zygomaticus s. subcutaneus
malæ; _20_, spinal accessory nerve; _21_, ventral branch of spinal
accessory nerve (to sterno-cephalicus); _22_, ventral end branch of
first cervical nerve; _23_, thyro-laryngeal artery; _24_, internal
maxillary artery; _25_, masseteric artery; _26_, great (posterior)
auricular artery; _27_, external branch of _26_; _28_, deep
auricular artery; _29_, superficial temporal artery; _30_,
transverse facial artery; _31_, facial artery; _32_, inferior labial
artery; _33_, superior labial artery; _34_, lateral nasal artery;
_35_, dorsal nasal artery; _36_, angular artery of eye; _37_, labial
twigs of palato-labial artery—left uncolored by oversight; _38_,
branch of buccinator artery; _39_, buccinator vein; _40_, vena
reflexa; _41_, _42_, jugular vein; _43_, external maxillary vein;
_44_, inferior cerebral vein; _45_, stump of great auricular vein;
_46_, ramus of mandible; _47_, facial crest; _48_, zygomatic arch;
_49_, parotid duct. (After Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
(3) The =lesser= or =posterior palatine nerve= (N. palatinus minor s.
posterior), also termed the staphyline, is much the smallest of the
three branches (Figs. 438, 439). It passes downward and forward with the
palatine vein in the groove at the inner side of the tuber maxillare and
ramifies in the soft palate.
The sphenopalatine ganglia and plexus (Fig. 515) lie on the
perpendicular part of the palate bone and the pterygoid process under
cover of the maxillary nerve. The afferent fibers of the plexus and
ganglia come chiefly from the branches of the sphenopalatine nerve and
the nerve of the pterygoid canal. Interspersed in these are several
minute ganglia and one or more larger ones. The =nerve of the
pterygoid canal= or =Vidian nerve= (N. canalis pterygoidei) is formed
by the union of sympathetic fibers with the superficial petrosal
branch of the facial nerve. It passes forward at first between the
Eustachian tube and the sphenoid bone, enters the canal between the
pterygoid bone and process, and joins the posterior part of the
plexus. It is probable that it furnishes the motor fibers to the
levator palati and palatinus muscles. Efferent filaments go to the
periorbita and the ophthalmic vessels, and others accompany the
branches of the maxillary nerve, around which they have a plexiform
arrangement.
3. The =infraorbital nerve= (N. infraorbitalis) is the continuation of
the maxillary trunk. It traverses the infraorbital canal, emerges
through the infraorbital foramen, and divides into nasal and superior
labial branches. Along its course it gives off =superior alveolar= or
=dental branches= (Rami alveolares maxillæ), which supply the teeth,
alveolar periosteum, and gums.
The delicate posterior alveolar branches are given off in the
pterygo-palatine fossa, pass through small foramina in the tuber
maxillare, and supply the posterior molar teeth and the maxillary
sinus. The middle alveolar branches are given off in the infraorbital
canal, and constitute the chief nerve-supply to the cheek teeth and
the maxillary sinus. The anterior or incisor branch runs forward in
the anterior alveolar or incisor canal and supplies branches to the
canine and incisor teeth. The foregoing unite with each other to form
the superior dental plexus, from which the dental and gingival
branches are given off.
The =external nasal branches= (Rami nasales externi), two or three in
number, accompany the levator labii superioris proprius and ramify in
the dorsum nasi and the nasal diverticulum.
The large =anterior nasal branch= (Ramus nasalis anterior) passes over
the nasal process of the premaxilla under cover of the dilatator naris
inferior, gives branches to the nasal mucous membrane, and terminates in
the skin of the upper lip.
The =superior labial branch= (Ramus labialis dorsalis) is the largest of
the terminals of the infraorbital nerve. It passes downward and forward
under the levator nasolabialis and, after supplying the skin of the
anterior part of the cheek, forms a rich terminal ramification in the
skin and mucous membrane of the upper lip. It anastomoses with the
superior buccal branch of the facial nerve.
III. The =mandibular nerve= (N. mandibularis), also termed the inferior
maxillary branch, is formed by the union of two roots; of these the
large sensory root comes from the semilunar ganglion, and the small
motor root is the pars minor of the trigeminus. It emerges from the
cranium through the oval notch of the foramen lacerum, between the
temporal wing of the sphenoid bone and the muscular process of the
petrous temporal, and gives off the following branches:
1. The =masseteric nerve= (N. massetericus) (Figs. 437, 515) passes
outward through the sigmoid notch of the mandible and enters the deep
face of the masseter muscle, in which it ramifies.
2. The =deep temporal nerves= (Nn. temporales profundi) (Fig. 437), two
or three in number, arise by a common trunk with the masseteric. They
supply the temporal muscle.
3. The =buccinator nerve= (N. buccinatorius) passes obliquely forward
through the anterior part of the external pterygoid muscle, then between
the internal pterygoid and the tuber maxillare (Fig. 514). It continues
forward in the submucous tissue of the cheek along the lower border of
the buccinator and divides into branches which ramify in the mucous
membrane and glands of the lips in the vicinity of the commissure. It
supplies small branches to the external pterygoid and temporal muscles
and detaches numerous collateral twigs to the mucous membrane of the
cheek and to the buccal glands. It also communicates with the inferior
buccal branch of the facial nerve.
4. The =pterygoid nerve= (N. pterygoideus) arises in common with the
preceding, passes forward on the guttural pouch, and divides into
branches for the pterygoid muscles (Fig. 515).
The =otic ganglion= (G. oticum) is situated near the origin of the
pterygoid and buccinator nerves, and is related internally to the tensor
palati and the Eustachian tube. It receives motor fibers from the
pterygoid nerve and sensory fibers by the small superficial petrosal
nerve from the tympanic plexus, through which communications are made
with the facial and glosso-pharyngeal nerves. Sympathetic fibers are
derived from the plexus on the internal maxillary artery. Efferent
filaments go to the tensor palati, tensor tympani, and pterygoid
muscles, and to the Eustachian tube.
The ganglion is small and somewhat difficult to demonstrate. In many
cases it is replaced by a number of minute ganglia interspersed in a
fine plexus.
5. The =superficial temporal nerve= (N. temporalis superficialis) (Figs.
437, 514, 515) runs outward across the pterygoideus externus, passes
between the parotid gland and the neck of the ramus of the mandible,
turns around the latter, and divides into two branches. The upper branch
(Ramus transversus faciei) accompanies the transverse facial vessels and
ramifies in the skin of the cheek. The larger inferior branch unites
with the inferior buccal division of the facial nerve.
[Illustration:
FIG. 515.—DEEP DISSECTION OF BASE OF CRANIUM, VIEWED FROM THE RIGHT
AND BELOW.
The tympanic cavity is opened and the paramastoid process is sawn off.
_a_, Occipital condyle; _b_, body of sphenoid; _c_, external
auditory meatus (part removed); _d_, malleus; _e_, incus; _1_, stump
of ophthalmic nerve; _2_, maxillary nerve (cut off); _3_,
sphenopalatine plexus; _4_, Vidian nerve; _4′_, deep petrosal nerve;
_4″_, branch to tympanic plexus; _4‴_, superficial petrosal nerve;
_5_, superficial temporal nerve (cut off); _6_, masseteric nerve
(cut off); _7_, mandibular nerve (raised); _8_, lingual nerve (cut
off); _9_, pterygoid nerve (cut); _10_, nerve to tensor tympani;
_11_, otic ganglion; _12_, facial nerve; _13_, stapedial nerve;
_14_, chorda tympani; _15_, glosso-pharyngeal nerve (cut); _16_,
tympanic nerve; _17_, vagus (cut off); _18_, auricular branch of
vagus; _19_, spinal accessory nerve (cut off); _20_, hypoglossal
nerve (cut off); _21_, sympathetic nerve (cut off); _22_, internal
carotid artery. (After Ellenberger, in Leisering’s Atlas.)
]
Before its division the nerve gives off twigs to the guttural pouch, the
parotid gland, the external ear, and the skin of the external auditory
meatus and the membrana tympani. Branches from it concur with filaments
from the cervical branch of the facial nerve in the formation of the
auricular plexus.
6. The =inferior alveolar= or =dental nerve= (N. alveolaris mandibulæ)
(Figs. 436, 437, 514) arises with the lingual by a common trunk which
passes forward at first on the external pterygoid muscle, then inclines
ventrally between the internal pterygoid and the ramus of the mandible.
The lingual and alveolar separate at an acute angle, and the latter
enters the mandibular foramen and courses in the canal within the ramus
(Fig. 516). Emerging at the mental foramen, it terminates by dividing
into six to eight inferior labial and mental branches, which ramify in
the lower lip and chin. Before entering the bone, the nerve detaches the
=mylo-hyoid nerve= (N. mylo-hyoideus), which runs downward and forward
between the ramus and the mylo-hyoid muscle; it supplies that muscle,
the anterior belly of the digastricus, and the skin of the anterior part
of the submaxillary space. The dental and gingival branches detached
from the nerve within the mandible are arranged like the corresponding
nerves of the upper jaw.
7. The =lingual nerve= (N. lingualis) arises by a common trunk with the
inferior alveolar or dental nerve (Figs. 436, 437). After separating
from the latter it runs downward and forward, lying at first between the
ramus of the mandible and the internal pterygoid muscle, then on the
inner face of the mylo-hyoid. On reaching the root of the tongue it
divides into superficial and deep branches. The =superficial branch=
(Ramus superficialis) runs forward on the stylo-glossus and accompanies
the submaxillary duct on the deep face of the sublingual gland. It
supplies the mucous membrane of the tongue and the floor of the mouth.
At the root of the tongue it gives off a recurrent branch to the isthmus
faucium, which communicates with the lingual branch of the
glosso-pharyngeal nerve. The larger =deep branch= (Ramus profundus)
turns around the lower edge of the hyo-glossus, passes upward and
forward between that muscle and the genio-glossus, and continues forward
on the latter to the tip of the tongue. It gives branches to the mucous
membrane and the fungiform papillæ of the tongue, and anastomoses with
branches of the hypoglossal nerve and with the superficial branch.
Minute ganglia occur on the finer branches of the lingual nerve. The
=chorda tympani= branch of the facial joins the lingual nerve at the
origin of the latter and is incorporated with it in its distribution to
the tongue.
[Illustration:
FIG. 516.—PART OF BRANCH OF LOWER JAW OF HORSE, INTERNAL VIEW.
The bone has been removed to show the vessels and nerves. _1_, _1′_,
Inferior alveolar or dental nerve; _2_, _2_, branches to cheek teeth
and gums; _2′_, branch to canine and incisor teeth; _3_, _3′_,
inferior alveolar or dental artery; _4_, satellite vein. (After
Leisering’s Atlas.)
]
THE SIXTH OR ABDUCENT NERVE
The =abducent nerve= (N. abducens) emerges from the brain behind the
pons and just external to the pyramid (Fig. 499). It passes forward
across the pons, pierces the dura mater, and accompanies the third and
ophthalmic nerves, below which it emerges through the foramen lacerum
orbitale. In the orbit it divides into two branches; the larger of these
enters the external rectus, the smaller supplies the superior and
external parts of the retractor muscle of the eyeball. Within the
cranium it receives filaments from the carotid plexus of the
sympathetic.
The fibers of the abducent nerve are axones of the large multipolar
cells of the abducent nucleus which is situated beneath the eminentia
teres of the floor of the fourth ventricle. The nucleus lies within
the loop formed by the fibers of origin of the facial nerve. It is
connected with (_a_) the anterior olive; (_b_) the oculomotor nucleus
of the opposite side; (_c_) the motor area of the cerebral cortex by
means of the pyramidal tract of the opposite side.
THE SEVENTH OR FACIAL NERVE
The =facial nerve= (N. facialis) has its superficial origin at the
lateral part of the corpus trapezoideum, immediately behind the pons
(Fig. 499). It passes outward in front of the eighth nerve and enters
the internal auditory meatus. At the bottom of the meatus the two nerves
part company, the facial coursing in the facial canal of the petrous
temporal bone. The canal and nerve are at first directed outward between
the vestibule and the cochlea, then curve backward and downward in the
posterior wall of the tympanum to end at the stylo-mastoid foramen. The
bend formed by the nerve is called the =knee= (Geniculum n. facialis)
and bears at its highest point the round =geniculate ganglion= (G.
geniculi).
The nerve consists of two parts, motor and sensory. The =motor part=
constitutes the bulk of the nerve. Its deep origin is from the cells
of the =facial nucleus=, which is situated in the medulla above the
facial tubercle. On leaving the nucleus the root-fibers pass upward
and inward, incline forward close to the median plane, and then bend
sharply downward to the point of emergence. The highest point of the
bend is subjacent to the gray matter of the eminentia teres in the
floor of the fourth ventricle, and the abducent nucleus lies in the
concavity of the curve. The small =sensory part= (N. intermedius)
consists of axones of cells of the geniculate ganglion, which is
interposed on the facial nerve as it bends downward in the facial
canal. The fibers of this part after entering the medulla, pass to the
nucleus of termination which it shares with the ninth and tenth
nerves. The peripheral fibers from the geniculate ganglion constitute
the chorda tympani.
After its emergence through the stylo-mastoid foramen (Fig. 514) the
nerve passes downward, forward, and outward on the guttural pouch under
cover of the parotid gland, and crosses between the origin of the
superficial temporal and internal maxillary arteries internally and the
superficial temporal vein externally. It then crosses the posterior
border of the ramus of the mandible ventral to the transverse facial
artery and about an inch and a half (ca. 3.5 to 4 cm.) below the
articulation of the jaw. Emerging from beneath the parotid gland upon
the masseter muscle, it receives the lower branch of the superficial
temporal nerve, and divides into superior and inferior buccal branches.
The following collateral branches are given off, the first five being
detached within the facial canal, and the others between the
stylo-mastoid foramen and the border of the jaw.
1. The =great superficial petrosal nerve= (N. petrosus superficialis
major) arises from the geniculate ganglion.[203] It passes through the
petrosal canal, contributes a filament to the tympanic plexus, receives
the great deep petrosal nerve from the carotid plexus of the
sympathetic, emerges through the foramen lacerum, and is continued as
the Vidian nerve to the sphenopalatine plexus and ganglia (Fig. 515).
2. A delicate branch (R. anastomoticus cum plexu tympanico) emerges from
the geniculate ganglion and unites with a filament issuing from the
tympanic plexus to form the =small superficial petrosal nerve= (N.
petrosus superficialis minor); this ends in the otic ganglion.
3. The =stapedial nerve= (N. stapedius) (Fig. 515) is a short filament
detached from the facial nerve as it turns down in the facial canal. It
innervates the stapedius muscle.
4. The =chorda tympani= (Fig. 515) is a small nerve which arises a
little below the preceding and pursues a recurrent course in a small
canal in the mastoid part of the temporal bone to reach the tympanic
cavity. It traverses the latter, passing between the handle of the
malleus and the long branch of the incus. Emerging through the
petro-tympanic fissure, the nerve passes downward and forward, crosses
beneath the internal maxillary artery, and joins the lingual nerve. It
sends twigs to the submaxillary and sublingual glands, and through its
incorporation with the lingual nerve furnishes fibers to the mucous
membrane of the anterior two-thirds of the tongue which are believed to
mediate the sense of taste.
5. Anastomotic filaments unite with the auricular branch of the vagus
near the stylo-mastoid foramen.
6. The =posterior auricular nerve= (N. auricularis posterior) arises
from the facial at its emergence from the facial canal (Fig. 514). It
runs upward and backward with the posterior auricular artery under cover
of the parotid gland and supplies the posterior auricular muscles and
the skin of the convex surface of the external ear. It anastomoses with
branches of the first and second cervical nerves.
7. The =internal auricular nerve= (N. auricularis internus) springs from
the facial close to or in common with the preceding (Fig. 514). It
ascends in the parotid gland just behind the styloid process of the
conchal cartilage, passes through an opening in the cartilage, and
ramifies in the skin of the concave surface of the ear.
8. The =digastric branch= (R. digastricus) (Fig. 514) arises from the
facial below the auricular nerves. Its branches innervate the posterior
belly of the digastricus, the stylo-hyoideus, and the occipito-hyoideus.
At its origin it gives off a small branch which forms a loop around the
great auricular artery or its posterior branch and rejoins the trunk.
9. The =auriculo-palpebral nerve= (N. auriculo-palpebralis) (Fig. 514)
arises from the upper edge of the facial near the posterior border of
the ramus. It ascends in the parotid gland behind the superficial
temporal artery, and terminates in anterior auricular and temporal
branches. The =anterior auricular branches= form with branches of the
trigeminus the =anterior auricular plexus=. They innervate the anterior
auricular and parotido-auricularis muscles. The =temporal branch= runs
forward and inward over the temporal muscle to the inner canthus of the
eye, forms a plexus with the terminal branches of the ophthalmic nerve,
and is distributed to the orbicularis oculi, corrugator supercilii, and
levator nasolabialis.
10. The =cervical branch= (R. colli) (Fig. 435) arises from the ventral
border of the facial opposite to the preceding nerve. It emerges
obliquely through the parotid gland, passes downward and backward on or
near the jugular vein, and anastomoses with the cutaneous branches of
the cervical nerves. It gives branches to the parotido-auricularis and
the cervical panniculus. In its course along the neck the nerve is
reinforced by twigs from the cutaneous branches of the second to the
sixth cervical nerves.
11. Small branches are detached to the guttural pouch and the parotid
gland. The latter (Rami parotidei) concur with branches of the
superficial temporal nerve in forming the =parotid plexus=.
The facial nerve usually terminates after a short course on the surface
of the masseter by dividing into two buccal branches (Figs. 435, 461).
1. The =superior buccal nerve= (N. buccalis dorsalis) passes forward on
the upper part of the masseter, dips under the zygomaticus, and
continues along the lower border of the dilatator naris lateralis. It
then runs under the last-named muscle and anastomoses with branches of
the infraorbital nerve, and is distributed to the muscles of the cheek,
upper lip, and nostril.
2. The =inferior buccal nerve= (N. buccalis ventralis) crosses the
masseter obliquely and continues forward along the depressor labii
inferioris. It is connected by variable anastomotic branches with the
superior nerve. It gives collateral branches to the panniculus,
buccinator, and depressor labii inferioris, and ramifies with the
terminal branches of the inferior alveolar nerve in the lower lip.
The buccal nerves are subject to much variation in regard to their
course, anastomoses, and relations to the sensory components derived
from the superficial temporal nerve. Their distribution is constant.
The point at which the branch of the superficial temporal nerve joins
the facial is variable.
THE EIGHTH OR AUDITORY NERVE
The =auditory nerve= (N. acusticus) is connected with the lateral aspect
of the medulla just behind and external to the facial (Fig. 499). It has
two roots, vestibular and cochlear (Radix vestibularis et cochlearis).
The auditory nerve consists of two distinct parts which might well be
regarded as separate nerves. The cochlear part mediates the sense of
hearing, while the vestibular part is not auditory in function, but is
concerned in the sense of the position of the body and the mechanism
of equilibration.
The nerve passes outward to the internal auditory meatus, which it
enters behind the facial nerve. In the meatus it divides into two
nerves, of which the upper is the vestibular and the lower is the
cochlear nerve.
1. The =vestibular nerve= (N. vestibuli) is distributed to the
utriculus, the sacculus, and to the ampullæ of the semicircular canals,
of the internal ear. In the internal auditory meatus the nerve is
connected by filaments with the geniculate ganglion of the facial nerve.
At the bottom of the meatus it bears the =vestibular ganglion= (G.
vestibulare), from the cells of which the fibers of the nerve arise.
2. The =cochlear nerve= (N. cochleæ) detaches a filament to the
sacculus, passes through the lamina cribrosa to the labyrinth, and is
distributed to the organ of Corti in the cochlea.
The fibers of the vestibular nerve arise from the vestibular ganglion
as central processes (axones) of the bipolar cells of the ganglion.
The peripheral processes (dendrites) of the cells form arborizations
about the deep ends of the hair cells of the maculæ and cristæ
acusticæ of the utriculus, sacculus, and semicircular canals. The
fibers enter the medulla, pass between the restiform body and the
spinal tract of the trigeminus, and spread out to end in the
vestibular nucleus in the floor of the fourth ventricle. Among the
central connections of the vestibular nerve are: (1) fibers which
connect its nucleus with centers in the cerebellum (chiefly of the
opposite side); (2) the vestibulo-spinal tract, which conveys impulses
to the motor cells of the ventral columns of the spinal cord; (3)
fibers which connect the nucleus with those of the abducent nerve of
the same side, the third and fourth nerves, and the motor part of the
trigeminus of both sides.
The fibers of the cochlear nerve are the central processes of the
bipolar cells of the spiral ganglion of the cochlea. The peripheral
processes of these cells end in relation to the hair cells of the
organ of Corti. Some of the nerve-fibers enter the ventral cochlear
nucleus in the medulla close to the superficial origin of the nerve;
others end in the dorsal nucleus of the tuberculum acusticum at the
lateral angle of the floor of the fourth ventricle. From the ventral
nucleus fibers pass in the corpus trapezoideum to the anterior olivary
nucleus of the same and of the opposite side. Thence tracts pass to
the nuclei of the motor nerves of the eye, and through the lateral
fillet to the posterior quadrigeminal body and the internal geniculate
body. The axones of the cells of the dorsal nucleus pass largely (as
the striæ acusticæ) over the restiform body and across the floor of
the fourth ventricle toward the median plane. They then turn
ventrally, cross to the opposite side, and are continued by the
lateral fillet. From the mid-brain a tract proceeds to the cortex of
the temporal lobe of the hemisphere.
THE NINTH OR GLOSSO-PHARYNGEAL NERVE
The =glosso-pharyngeal nerve= (N. glossopharyngeus) is attached to the
anterior part of the lateral aspect of the medulla by several filaments
(Fig. 499). The root-bundles enter the furrow ventral to the restiform
body; they are separated by a short interval from the origin of the
facial nerve, but are not marked off behind from the roots of the vagus.
The bundles converge laterally to form a nerve which perforates the dura
mater and emerges through the foramen lacerum posterius just in front of
the tenth nerve (Fig. 515). As it issues from the cranium the nerve
bears a considerable ovoid gray enlargement, the =petrous ganglion= (G.
petrosum).[204] It then curves downward and forward over the guttural
pouch and behind the great cornu of the hyoid bone, crosses the deep
face of the external carotid artery, and divides into pharyngeal and
lingual branches (Fig. 437). The collateral branches are as follows:
1. The =tympanic nerve= (N. tympanicus) (Fig. 515) arises from the
petrous ganglion and passes upward between the petrous and tympanic
parts of the temporal bone to reach the cavity of the tympanum. Here it
breaks up into branches to form, along with branches from the carotid
plexus of the sympathetic, the =tympanic plexus=. From the plexus
branches pass to the mucous membrane of the tympanum and the Eustachian
tube. The continuation of the nerve issues from the plexus and unites
with a filament from the geniculate ganglion of the facial to form the
small superficial petrosal nerve; this runs forward and ends in the otic
ganglion.
Filaments also connect the petrous ganglion with the jugular ganglion
of the vagus nerve and with the superior cervical ganglion of the
sympathetic.
2. A considerable branch runs backward on the guttural pouch,
contributes filaments to the pharyngeal plexus, and concurs with twigs
from the vagus and the sympathetic in forming the carotid plexus on the
terminal part of the carotid artery and on its chief branches. In this
plexus is the small ganglion intercaroticum.
The =pharyngeal branch= (R. pharyngeus) (Fig. 437) is the smaller of the
two terminal branches. It runs forward across the deep face of the great
cornu of the hyoid bone and concurs with the pharyngeal branches of the
vagus and with sympathetic filaments in forming the pharyngeal plexus;
from this branches pass to the muscles and mucous membrane of the
pharynx.
The =lingual branch= (R. lingualis) is the continuation of the trunk
(Fig. 437). It runs along the posterior border of the great cornu of the
hyoid bone in front of the external maxillary artery and dips under the
hyo-glossus muscle. It gives collateral branches to the soft palate,
isthmus faucium, and tonsil, and ends in the mucous membrane of the
posterior part of the tongue, where it supplies gustatory fibers to the
vallate papillæ. A considerable branch unites with a twig from the
lingual nerve.
The glosso-pharyngeal is a mixed nerve, containing both motor and
sensory fibers. The latter constitute the bulk of the nerve and
include those which mediate the special sense of taste. They are
processes of the cells of the petrous ganglion. The central processes
of the ganglion cells enter the medulla, pass upward and inward
through the formatio reticularis, and end in the nucleus of
termination in the floor of the fourth ventricle. The motor fibers
arise from dorsal and ventral efferent nuclei in the medulla. The
glosso-pharyngeal shares these nuclei with the vagus and has
practically the same central connections as that nerve (_q. v._).
THE TENTH, VAGUS, OR PNEUMOGASTRIC NERVE
The =vagus= or =pneumogastric= (N. vagus) is the longest and most widely
distributed of the cranial nerves; it is also remarkable for the
connections which it forms with adjacent nerves and with the
sympathetic. It is attached to the lateral aspect of the medulla by
several filaments which are in series with those of the ninth nerve in
front and the eleventh nerve behind (Fig. 499). The bundles converge to
form a trunk which passes outward, pierces the dura mater, and emerges
from the cranium through the foramen lacerum posterius (Fig. 515). In
the foramen the nerve bears on its lateral aspect the elongated
flattened =jugular ganglion= (G. jugulare).
The ganglion communicates with (_a_) the tympanic nerve, (_b_) the
petrous ganglion of the ninth nerve, (_c_) the spinal accessory, and
(_d_) the hypoglossal. It also gives off the =auricular branch= (R.
auricularis), which runs forward below the petrous ganglion and passes
through a small canal in the petrous temporal bone to gain the facial
canal. Here it gives filaments to the facial and emerges with that
nerve through the stylo-mastoid foramen. It ascends behind the
external auditory meatus, dips under the rotator longus muscle, and
passes through a foramen in the conchal cartilage to ramify in the
integument which lines the meatus and the adjacent part of the ear.
Beyond the ganglion the vagus runs backward and downward with the spinal
accessory in a fold of the guttural pouch (Fig. 437). Then the two
nerves separate, allowing the hypoglossal to pass between them, and the
vagus descends with the internal carotid artery and crosses the inner
face of the origin of the occipital artery. Here it is joined by the
cervical trunk of the sympathetic, and the two nerves continue along the
dorsal aspect of the common carotid artery in a common sheath (Fig.
433). At the root of the neck the vagus separates from the sympathetic,
and from this point backward the relations of the right and left vagi
differ somewhat and must be described separately.
[Illustration:
FIG. 517.—CROSS-SECTION OF NECK OF HORSE, PASSING THROUGH POSTERIOR
PART OF ATLAS.
The head and neck were extended. _1_, Dorsal arch of atlas; _2_,
odontoid process; _3_, odontoid ligament; _4_, vertebral sinuses;
_5_, dura mater; _6_, spinal cord; _7_, vertebral artery; _8_, wing
of atlas; _9_, atlanto-axial joint cavity; _10_, œsophagus; _11_,
_11_, recurrent nerves; _12_, _12_, ventral branches of spinal
accessory nerves. By an oversight the obliquus cap. post. (above
wing of atlas) is unmarked.
]
The =right vagus= (Fig. 429) enters the thorax in the angle of
divergence of the right brachial artery and the truncus bicaroticus. It
then passes backward and slightly upward, crossing obliquely the outer
surface of the brachiocephalic artery and the right face of the trachea.
Reaching the dorsal surface of the latter near the bifurcation, it
divides into dorsal and ventral branches.
The =left vagus= (Fig. 428) enters the thorax on the ventral face of the
œsophagus, crosses obliquely under the left brachial artery, and passes
back on the external surface of that vessel in company with a large
cardiac nerve.[205] Separating from the latter, the vagus continues
backward on the left face of the aorta, inclines to the upper surface of
the left bronchus, and divides into dorsal and ventral branches.
The dorsal and ventral branches unite with the corresponding branches of
the opposite nerve, thus forming =dorsal= and =ventral œsophageal
trunks= (Truncus (œsophageus dorsalis, ventralis). These run backward in
the posterior mediastinum, above and below the œsophagus respectively,
and enter the abdominal cavity through the hiatus œsophageus; they
supply branches to the œsophagus and anastomose with each other. The
dorsal trunk receives the major part of its fibers from the right vagus.
After entering the abdomen it passes to the left of the cardia, gives
branches to the visceral surface of the stomach, and ends in the cœliac
and subsidiary plexuses. The ventral trunk passes to the lesser
curvature of the stomach and ramifies on the parietal surface of the
stomach; it forms here the anterior gastric plexus, from which branches
are supplied also to the first part of the duodenum and to the liver.
The collateral branches of the vagus are as follows:
1. The =pharyngeal branch= (R. pharyngeus) is given off in relation to
the superior cervical ganglion, turns around the internal carotid
artery, and runs downward and forward on the guttural pouch to the
dorsal wall of the pharynx (Fig. 437). Here its branches concur with the
pharyngeal branch of the ninth nerve and with filaments from the spinal
accessory and the sympathetic in forming the =pharyngeal plexus=. This
supplies numerous twigs to the pharynx, and a larger branch which passes
along the side of the œsophagus and ramifies in its cervical part.
According to Ellenberger and Baum the pharyngeal plexus receives
filaments also from the digastric, superior laryngeal, hypoglossal,
and first cervical nerves. The branches of the plexus form secondary
intermuscular and submucous plexuses, in which there are numerous
minute ganglia.
2. The =superior= or =anterior laryngeal nerve= (N. laryngeus cranialis)
is larger than the preceding and arises a little behind it (Fig. 437).
It crosses the deep face of the origin of the external carotid artery,
runs downward and forward over the lateral wall of the pharynx behind
the hypoglossal nerve, and passes through the foramen below the anterior
cornu of the thyroid cartilage. Its terminal branches ramify in the
mucous membrane of the larynx, the floor of the pharynx, and the
entrance to the œsophagus; they anastomose with those of the recurrent.
At its origin the nerve gives off its small =external branch= (R.
externus); this descends to the crico-thyroid muscle, which it supplies,
and sends filaments to the crico-pharyngeus also. It may arise from the
trunk of the vagus or from the pharyngeal branch.
At the point of origin of the superior laryngeal nerve there is a
plexiform widening which is regarded by some authors as the homologue
of the ganglion nodosum of man. From it a filament arises which, after
a short course, rejoins the vagus or enters the sympathetic trunk.
Stimulation of its central end causes a reduction of the
blood-pressure, and it is therefore termed the depressor nerve (N.
depressor).
3. The =recurrent nerve= (N. recurrens), also termed the inferior or
posterior laryngeal nerve, differs on the two sides in its point of
origin and in the first part of its course. The =right nerve= (Fig. 429)
is given off opposite the second rib, turns around the dorso-cervical
artery from without inward, runs forward on the lower part of the
lateral surface of the trachea, and ascends in the neck on the ventral
face of the common carotid artery. The =left nerve= (Fig. 428) arises
from the vagus where the latter begins to cross the aortic arch. It
passes back over the ligamentum arteriosum, winds around the concavity
of the aortic arch from without inward, runs forward on the lower part
of the left face of the trachea, and continues in the neck in a similar
position to the right nerve.
It is worthy of note that the left nerve passes beneath the bronchial
lymph glands as it winds around the aorta; also that in the next part
of its course it lies between the left surface of the trachea and the
deep face of the aorta, and is then related to lymph glands which lie
along the ventral aspect of the trachea. The left recurrent is often
incorporated in part of its course in the anterior mediastinum with a
deep cardiac nerve. Further, the left nerve lies at first ventral to,
and then upon, the œsophagus in the neck. The right recurrent is given
off from or in common with a considerable trunk which connects the
vagus with the first thoracic ganglion of the sympathetic. The
arrangement here is commonly more or less plexiform, and from it one
or two cardiac nerves arise.
The terminal part of each nerve (Fig. 517) lies on the dorsal surface of
the trachea, in relation to the œsophagus internally and the carotid
artery above.[206] It passes between the crico-arytenoideus posterior
and the crico-pharyngeus; the =terminal branches= supply all the muscles
of the larynx except the crico-thyroid, and communicate with branches of
the superior laryngeal nerve. =Collateral branches= are given off to the
cardiac plexus (Rr. cardiaci), to the trachea (Rr. tracheales), to the
œsophagus (Rr. œsophagei), and to the inferior cervical ganglion of the
sympathetic.
4. =Cardiac branches= (Rr. cardiaci), usually two or three in number,
are given off from each vagus within the thorax (Figs. 428, 429). These
concur with the cardiac branches of the sympathetic and recurrent nerves
to form the cardiac plexus, which innervates the heart and great
vessels.
5. Small =tracheal= and =œsophageal branches= (Rr. tracheales et
œsophagei) are given off from both vagi in the thorax. These concur with
branches from the recurrent nerves and the inferior cervical and
anterior thoracic ganglia of the sympathetic in forming the =posterior
tracheal= and =œsophageal plexuses=, from which twigs go to the trachea,
œsophagus, heart, and large vessels.
6. =Bronchial branches= (Rr. bronchiales) are detached at the roots of
the lungs and unite with sympathetic filaments in forming the =pulmonary
plexuses=. From the latter numerous branches proceed in a plexiform
manner along the bronchi and vessels into the substance of the lungs.
The vagus and glosso-pharyngeal nerves are so closely associated in
origin and central connections that they may be described together in
this respect.
The =sensory fibers= arise from the petrous and jugular ganglia, and
their central parts enter the lateral aspect of the medulla and divide
into anterior and posterior branches like the fibers of the dorsal
roots of the spinal nerves. Most of the fibers end in arborizations
about the cells of the vago-glosso-pharyngeal nucleus of termination,
which consists of two parts. Of these the =dorsal sensory nucleus=
(Nucleus alæ cinereæ) is situated in the posterior part of the floor
of the fourth ventricle and in the adjacent part of the closed portion
of the medulla near the median plane. The other part is termed the
=nucleus of the solitary tract=, and is so named because its cells are
grouped about the bundle (Tractus solitarius) formed by the posterior
divisions of the afferent nerve-fibers. It ends about the level of the
pyramidal decussation. The secondary central connections are similar
to those of the sensory part of the trigeminus.
The =motor fibers= (and those of the medullary part of the accessory)
arise from the =dorsal motor nucleus= and the =ventral motor nucleus=.
The cells of the former lie in groups along the ventro-medial side of
the dorsal sensory nucleus. The latter, also termed the nucleus
ambiguus, is situated more deeply in the lateral part of the formatio
reticularis.
THE ELEVENTH OR SPINAL ACCESSORY NERVE
The =spinal accessory nerve= (N. accessorius) is purely motor. It
consists of two parts which differ in origin and function.
The =medullary part= arises from the lateral aspect of the medulla by
several rootlets which are behind and in series with those of the vagus
(Fig. 499). The =spinal part= arises from the cervical part of the
spinal cord by a series of fasciculi which emerge between the dorsal and
ventral roots. The bundles unite to form a trunk which is very small at
its origin at the fifth segment of the cord, but increases in size when
traced toward the brain, since it continually receives accessions of
fibers. It passes through the foramen magnum and joins the medullary
part. The trunk thus formed sends its medullary fibers to the tenth and
ninth nerves and emerges through the foramen lacerum posterius. It then
runs backward and downward with the vagus in a fold of the guttural
pouch, separates from that nerve, crosses the deep face of the
submaxillary gland and the occipital artery, and divides in the recessus
atlantis into dorsal and ventral branches.
[Illustration:
FIG. 518.—NECK OF HORSE, AFTER REMOVAL OF PART OF PANNICULUS AND
TRAPEZIUS.
_a_, _a′_, Mastoido-humeralis; _b_, anterior superficial pectoral
muscle; _c_, cervical panniculus; _d_, sterno-cephalicus; _e_,
omo-hyoideus; _f_, sterno-thyro-hyoideus; _g_, trachea; _h_,
_h′_, _h″_, tendons of splenius, mastoido-humeralis, and
trachelo-mastoideus; _i_, trapezius cervicalis; _k_,
supraspinatus; _l_, anterior deep pectoral muscle; _m_,
rhomboideus cervicalis; _n_, serratus cervicis; _o_, splenius,
upper and lower borders of which are indicated by dotted lines;
_p_, parotid gland; _q_, parotido-auricularis muscle; _r_, wing
of atlas; _s_, spine of scapula; _1_, external maxillary vein;
_2_, _3_, jugular vein; _4_, carotid artery; _5_, descending
branch of inferior cervical artery; _6_, cephalic vein; _7–11_,
ventral branches of second to seventh cervical nerves; _12_,
cutaneous branch of second cervical nerve; _13_, cervical branch
of facial nerve; _14_, terminal branches of dorsal divisions of
cervical nerves; _15_, dorsal branch of spinal accessory nerve.
(After Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
It is connected by anastomotic branches with the vagus and hypoglossal
nerves and the superior cervical ganglion of the sympathetic, and
contributes a branch to the pharyngeal plexus.
The =dorsal branch= (R. dorsalis) (Figs. 433, 517, 518) receives a twig
from the second and third cervical nerves and turns around the atlantal
tendon of the splenius under cover of the mastoido-humeralis. It then
passes obliquely through the latter muscle and continues backward on the
splenius and the cervical part of the serratus, inclines upward across
the anterior deep pectoral and the supraspinatus, and enters the deep
face of the trapezius, in which it ramifies.
The =ventral branch= (R. ventralis) (Fig. 436) is smaller. It enters the
sterno-cephalicus muscle behind the cervical angle of the parotid gland.
The fibers of the spinal part of the accessory arise from the
ventro-lateral cells of the ventral gray column of the cord as far
back as the fifth cervical segment. The fibers of the medullary part
come chiefly from the nucleus ambiguus in common with the motor fibers
of the vagus.
THE TWELFTH OR HYPOGLOSSAL NERVE
The =hypoglossal nerve= (N. hypoglossus) is purely motor and innervates
the muscles of the tongue (Fig. 437). Its root-fibers arise from the
ventral face of the medulla in linear series about 3 to 4 mm. lateral to
the posterior half of the pyramid (Fig. 499). The filaments converge to
three or four bundles which perforate the dura mater and unite to form
the trunk. The latter emerges through the hypoglossal foramen (Fig. 515)
and runs downward and backward between the guttural pouch and the
capsule of the atlanto-occipital articulation for a distance of a little
less than an inch (ca. 2 cm.). It then passes between the tenth and
eleventh nerves, turns downward and forward, crosses the external face
of the external carotid artery, and continues over the pharynx parallel
with the great cornu of the hyoid bone and behind the external maxillary
artery. It then crosses beneath the artery, runs forward on the external
face of the hyo-glossus muscle, and divides into its terminal branches
(Rami linguales). The smaller branch supplies the stylo-glossus,
hyo-glossus, and lingualis. The larger branch ramifies on the
genio-glossus and supplies the remaining muscles. Anastomoses occur with
branches of the lingual nerve.
In the first part of its course the nerve communicates with the superior
cervical ganglion and with the ventral branch of the first cervical
nerve, and gives filaments to the pharyngeal branch of the vagus and the
pharyngeal plexus.
The fibers of the nerve arise from the hypoglossal nucleus, an
elongated group of large multipolar cells situated chiefly under the
posterior part of the floor of the fourth ventricle close to the
median plane. The two nuclei are connected by commissural fibers. The
other central connections include: (_a_) communications by the medial
longitudinal fasciculus with the nuclei of termination of other
cranial nerves; (_b_) cortico-nuclear fibers which come from the
cortex by way of the internal capsule and the pyramids and go largely
to the nucleus of the opposite side; (_c_) fibers which join the
dorsal longitudinal bundle of Schütz, a tract which underlies the
floor of the fourth ventricle and is traceable forward below the
cerebral aqueduct.
THE SPINAL NERVES
The =spinal nerves= (Nervi spinales) are arranged in pairs, of which
there are usually forty-two in the horse. They are designated according
to their relations to the vertebral column as =cervical= (8), =thoracic=
(18), =lumbar= (6), =sacral= (5), and =coccygeal= (5). Each nerve is
connected with the spinal cord by two roots, dorsal and ventral (Fig.
497).
The =dorsal= (or superior) =root= (Radix dorsalis) is the larger of the
two. Its fibers (Fila radicularia) spread out in fan shape and join the
cord in a linear series along the dorso-lateral groove. Laterally the
fibers converge to form a compact bundle, on which is a gray nodular
enlargement, the =spinal ganglion= (Ganglion spinale). Beyond the
ganglion the dorsal root joins the ventral root to constitute the nerve.
The ganglia are external to the dura mater, and are situated in the
intervertebral foramina, except in the case of the sacral and coccygeal
nerves, the ganglia of which lie within the vertebral canal. Those of
the coccygeal nerves are intradural.
The ganglia vary greatly in size; that of the first cervical nerve is
scarcely as large as a hemp seed, while that of the eighth cervical is
about 2 cm. long and 1 cm. wide. On the large roots connected with the
cervical and lumbar enlargement of the cord there are multiple ganglia
of varying sizes interposed in the course of the root-bundles. The
fibers of the dorsal roots arise from the cells of the spinal ganglia;
each cell gives off a fiber which enters the spinal cord and another
which passes into the nerve.
The =ventral= (or inferior) =root= (Radix ventralis) contains fewer
fibers than the dorsal root, except in the case of the first cervical
nerve. It arises from the ventral surface of the spinal cord (Fig. 495)
by means of numerous small bundles of fibers which do not form a linear
series but emerge from the cord over an area three to five millimeters
in width (ventral root zone). The fibers are processes of the large
cells of the ventral gray columns of the spinal cord. There is no
ganglion on the ventral root.
In the cervical, thoracic, and anterior lumbar regions the bundles of
both roots pass through separate openings in linear series in the dura
mater before uniting into a root proper. Further back the bundles of
each root unite within the dura. In the anterior part of the cervical
region and in the thoracic part of the cord there are intervals of
varying length between adjacent roots, but in some places the fibers
of adjacent roots overlap and an exchange of fibers may be observed.
Many of the roots are directed almost straight outward or incline
slightly backward, but the posterior lumbar, sacral, and coccygeal
roots and nerves run backward to reach the foramina through which they
emerge. The distance thus to be traversed increases from before
backward, so that these nerves form a tapering sheaf around the conus
medullaris and filum terminale in the last lumbar vertebra and the
sacrum which is known as the cauda equina.
[Illustration:
FIG. 519.—VERTEBRAL CANAL OPENED BY SAWING OFF THE ARCHES. (After
Schmaltz. Atlas d. Anat. a. Pferdes.)
]
The =size= of the spinal nerves varies greatly. The largest are
connected with the cervical and lumbar enlargements.
In or immediately after its emergence from the intervertebral foramen
each spinal nerve gives off a small =meningeal= or =recurrent branch=
(Ramus meningeus). This is joined by a bundle of fibers from the ramus
communicans and enters the vertebral canal, in which it is distributed.
Each nerve then divides into two primary branches, =dorsal= and
=ventral= (Ramus dorsalis, ventralis). The =dorsal branches= are smaller
than the ventral, except in the cervical region. They are distributed
chiefly to the muscles and skin of the dorsal part of the body. The
=ventral branches= supply in general the muscles and skin of the ventral
parts of the body, including the limbs. Each nerve or its ventral branch
is connected with an adjacent ganglion of the sympathetic system by at
least one small short branch known as a =ramus communicans=. Many nerves
have two and some have three such rami. A nerve may be connected with
two ganglia, and a ganglion may be connected with two nerves.
The dorsal root is sensory or afferent, _i. e._, it conveys impulses
to the central system. Its fibers are axones of the cells of the
spinal ganglion. The ventral root is motor or efferent, and conveys
impulses toward the periphery. Its fibers are axones of the large
cells in the ventral gray columns of the spinal cord. The common trunk
or nerve formed by the union of the two roots contains both kinds of
fibers, as do also their primary divisions. In addition to these
fibers, which are distributed to the skeletal muscles and the skin,
the spinal nerves contain fibers derived from the sympathetic system
through the rami communicantes; these go to the glands and unstriped
muscle and are designated secretory and vasomotor fibers.
THE CERVICAL NERVES
The =cervical nerves= (Nervi cervicales) (Figs. 431, 433, 518, 523)
number eight pairs. Of these the first emerges through the
intervertebral foramen of the atlas, the second through that of the
axis, and the eighth between the last cervical and the first thoracic
vertebræ.
The =dorsal branches= are distributed to the dorso-lateral muscles and
skin of the neck. They divide usually into inner and outer branches. The
internal branches (Rami mediales) run in general across the multifidus
and the lamellar part of the ligamentum nuchæ to the skin of the upper
border of the neck; they supply the deep lateral muscles and the skin.
The external branches (Rami laterales) are chiefly muscular in their
distribution. The dorsal branches of the third to the sixth nerves are
connected by anastomotic branches to form the =dorsal cervical plexus=.
The =ventral branches= are smaller than the dorsal ones—an exception to
the general rule. They increase in size from first to last. They supply
in general the muscles and skin over the lateral and ventral aspect of
the vertebræ, but the last three enter into the formation of the
brachial plexus, and the three preceding the last give off the roots of
the phrenic nerve. An irregular =ventral cervical plexus= is formed by
anastomoses established between the ventral branches. The following
special features may be noted:
The =first cervical nerve= emerges through the intervertebral
(antero-internal) foramen of the atlas. Its =dorsal branch= (N.
occipitalis) passes upward and outward between the obliqui capitis and
the recti capitis dorsales and supplies branches to these muscles, the
scutularis and posterior auricular muscles, and the skin of the poll.
The =ventral branch= descends through the alar (antero-external) foramen
of the atlas, crosses over the ventral straight muscles and the carotid
artery under cover of the parotid gland, and divides into two branches.
The anterior branch enters the omo-hyoideus muscle. The posterior branch
passes downward and backward under cover of that muscle, unites with a
branch of the ventral division of the second cervical nerve, and
continues its course on the ventro-lateral surface of the trachea to
enter the sterno-thyro-hyoideus behind the intermediate tendon. In the
recessus atlantis the ventral branch is connected by one or more twigs
with the superior cervical ganglion of the sympathetic, and a little
lower with the hypoglossal nerve. It also sends branches to the ventral
straight muscles of the head and the thyro-hyoideus. Below the atlas the
ventral branch is crossed superficially by the spinal accessory nerve,
the occipital artery, and the inferior cerebral vein.
The =second cervical nerve= is larger than the first. It emerges from
the vertebral canal through the intervertebral foramen of the anterior
part of the arch of the axis. Its =dorsal branch= ascends between the
complexus and the ligamentum nuchæ and ramifies in the skin of the poll.
The =ventral branch= gives off =muscular branches= to the rectus capitis
anterior major, and =anastomotic branches= to the spinal accessory and
the ventral divisions of the first and third cervical nerves; one of
these crosses over the carotid artery and concurs in the formation of
the nerve to the sterno-thyro-hyoideus mentioned above. The ventral
branch then becomes superficial by passing between the two parts of the
mastoido-humeralis, and divides into posterior auricular and cutaneous
branches. The =posterior auricular nerve= passes upward and forward on
the parotid gland parallel with the posterior border of the
parotido-auricularis to ramify on the convex face of the external ear.
The =cutaneous nerve= of the neck (N. cutaneus colli) crosses the
mastoido-humeralis muscle and turns backward along the course of the
jugular vein. On the lower part of the parotid gland it is connected by
a twig with the cervical cutaneous branch of the facial nerve. It gives
off twigs to the subcutaneous muscles and the skin of the parotid and
laryngeal regions and a long branch which passes forward in the
submaxillary space.
The =third cervical nerve= leaves the vertebral canal through the
foramen between the second and third cervical vertebræ. Its =dorsal
branch= emerges between two bundles of the intertransversalis muscle
accompanied by a branch of the vertebral artery, turns upward on the
multifidus, and divides into several branches which radiate on the deep
face of the complexus. It gives branches to these muscles and to the
skin, and a twig which joins the corresponding branch of the fourth
nerve. The =ventral branch= emerges through the intertransversalis below
the bundle above which the dorsal branch appears. It gives branches to
the trachelo-mastoideus, rectus capitis anterior major, longus colli,
splenius, and mastoido-humeralis. It also gives off a large cutaneous
nerve which passes out between the two parts of the mastoido-humeralis
and divides into several divergent branches.
The =fourth= and =fifth cervical nerves= are distributed in general like
the third. Their =dorsal branches= are united by anastomotic twigs with
each other and with those of the third and sixth nerves to form the
dorsal cervical plexus. The =ventral branch= of the fifth nerve often
contributes a small twig to the phrenic nerve.
The =sixth cervical nerve= has a smaller =dorsal branch= than the fifth.
Its =ventral branch= is larger and goes in part to the brachial plexus;
it supplies twigs to the intertransversales, the longus colli, the
mastoido-humeralis, and the cervical parts of the serratus and
rhomboideus, furnishes a root of the phrenic nerve, and gives off
several considerable subcutaneous branches. One of the latter ramifies
on the thick part of the cervical panniculus, to which it gives
branches; another and larger branch (N. supraclavicularis) sends twigs
to the skin over the shoulder joint, and descends to the skin over the
superficial pectoral muscles (Fig. 466).
The =seventh= and =eighth cervical nerves= have small =dorsal branches=,
which ascend between the longissimus and multifidus, giving twigs to
these muscles, the spinalis and semispinalis, the rhomboideus, and the
skin. Their =ventral branches= are very large and concur in the
formation of the brachial plexus; that of the seventh nerve contributes
the posterior root of the phrenic nerve.
PHRENIC NERVE
The =phrenic nerve= (N. phrenicus) (Figs. 428, 429, 433), the motor
nerve to the diaphragm, is formed by the union of two or three roots
which cross the superficial face of the scalenus muscle obliquely
downward and backward. The chief roots come from the ventral branches of
the sixth and seventh cervical nerves. The root derived from the fifth
nerve is small and inconstant. The root from the seventh cervical comes
by way of the brachial plexus. The course of the nerve is not the same
on both sides. On the =right side= the nerve enters the thorax by
passing between the brachial artery and the anterior vena cava. It then
courses backward and somewhat downward over the right face of the
anterior vena cava, crosses the pericardium, and continues along the
posterior vena cava to the diaphragm. In the latter part of its course
it is inclosed in a special fold of the right pleura and inclines
gradually to the ventral face of the vein. On the =left side= the nerve
enters the thorax between the left brachial and inferior cervical
arteries, and then runs its entire course in the mediastinum. In the
anterior mediastinum it lies along the brachiocephalic artery ventral to
the left vagus and cardiac nerves, and crosses over the dorso-cervical
vein. It then passes over the upper part of the pericardium and runs
backward in the posterior mediastinum to reach the tendinous center of
the diaphragm considerably to the left of the median plane. Each nerve
is usually connected near its origin with the first thoracic ganglion of
the sympathetic by a ramus communicans, and each terminates by dividing
into several branches which are distributed to the corresponding part of
the diaphragm.
THE BRACHIAL PLEXUS
The =brachial plexus= (Plexus brachialis) (Fig. 433) results from
anastomoses established between the ventral branches of the last three
cervical and first two thoracic nerves. It appears as a thick, wide band
between the two parts of the scalenus muscle, and is covered by the
anterior deep pectoral and subscapularis muscles. The largest root of
the plexus is derived from the first thoracic nerve, while the root
supplied by the sixth cervical nerve is quite small. Each of the three
chief roots, _i. e._, those from the last two cervical and the first
thoracic nerve, is connected with the sympathetic by a ramus
communicans.
The =branches= emanating from the plexus go for the most part to the
thoracic limb, but some are distributed on the chest-wall. The names of
the branches, and their arrangement so far as they can be conveniently
examined before removal of the fore limb, are as follows:[207]
1. The large =suprascapular nerve= (N. suprascapularis) turns outward
and forward and disappears between the supraspinatus and subscapularis.
2. The much smaller =subscapular nerves= (Nn. subscapulares), usually
two primary trunks, arise close behind the suprascapular, run backward a
short distance, and divide into several branches which enter the lower
third of the subscapularis.
3. The =anterior thoracic= or =pectoral nerves= (N. pectorales
craniales), three or four in number, arise from the anterior part of the
plexus and from the loop formed by the musculo-cutaneous and median
nerves. One enters the anterior deep pectoral muscle. Another passes out
between the divisions of the deep pectoral to supply the superficial
pectoral, giving a twig usually to the posterior deep muscle. The latter
receives one or two other nerves.
4. The =musculo-cutaneous nerve= (N. musculocutaneus) arises from the
anterior part of the plexus and passes over the outer face of the
brachial artery, below which it is connected by a large but short branch
with the median nerve, thus forming a loop in which the artery lies. One
or two branches to the pectoral muscles are given off from the nerve or
the loop.
5. The =median nerve= (N. medianus) is usually the largest branch of the
brachial plexus. It lies at first above the brachial artery, then passes
between the artery and vein to reach the anterior border of the former.
It is easily recognized by its large size and the loop which it forms
with the musculo-cutaneous nerve.
6. The =ulnar nerve= (N. ulnaris) arises with the median by a short
common trunk. It descends behind the brachial artery and is accompanied
a short distance by the radial nerve.
7. The =radial nerve= (N. radialis) arises from the posterior part of
the plexus and is sometimes the largest branch. It descends behind the
ulnar nerve over the origin of the subscapular artery and the lower part
of the teres major, and dips into the interstice between that muscle and
the long and internal heads of the triceps.
8. The =axillary= or =circumflex nerve= (N. axillaris) arises behind the
musculo-cutaneous. It passes downward and backward on the inner face of
the subscapularis and disappears between that muscle and the subscapular
artery.
9. The =long thoracic nerve= (N. thoracalis longus) is wide and thin. It
passes backward across the surface of the serratus magnus, to which it
is distributed. The branches which enter the muscle are given off both
upward and downward in fairly regular fashion.
10. The =thoraco-dorsal nerve= (N. thoracodorsalis) passes upward and
backward across the subscapularis muscle to ramify in the teres major
and the latissimus dorsi.
11. The =external= (or subcutaneous) =thoracic nerve= arises by a common
trunk with the ulnar. It runs backward and downward across the inner
face of the tensor fasciæ antibrachii, communicates with the anterior
pectoral branches, and gives twigs to the deep pectoral muscle. It then
runs backward in company with the external thoracic or “spur” vein,
gives branches to the latissimus dorsi and the deep pectoral, and
ramifies in the panniculus and the skin of the abdominal wall. It
communicates with perforating branches of the intercostal nerves. A
branch from it, accompanied by a large perforating intercostal branch,
winds around the lower border of the latissimus dorsi and ramifies in
the panniculus on the outer surface of the arm.
The term posterior thoracic or pectoral nerves (Nn. pectorales
caudales) may be used to include 8, 9, and 10.
SUPRASCAPULAR NERVE
The =suprascapular= (Fig. 441) is a large nerve derived chiefly, if not
exclusively, from the sixth and seventh cervical components of the
brachial plexus. It passes between the supraspinatus and subscapularis
muscles and turns around the distal fourth of the anterior border of the
scapula to reach the supraspinous fossa. It gives branches to the
supraspinatus and continues backward and upward into the infraspinous
fossa, where it supplies the infraspinatus, deltoid, and teres minor
muscles.
The direct relation of this nerve to the scapula renders it liable to
injury, the result of which may be paralysis and atrophy of the
muscles supplied by it.
MUSCULO-CUTANEOUS NERVE
The =musculo-cutaneous nerve= (Fig. 441) arises close behind the
suprascapular, and is derived chiefly from the part of the brachial
plexus which is supplied by the seventh and eighth cervical nerves. It
descends across the outer surface of the brachial artery, below which a
great part of the nerve unites with the median to form the loop
previously mentioned. It gives off a branch which enters the upper part
of the belly of the coraco-brachialis, passes downward and forward
between the two parts of that muscle or between the muscle and the bone,
and divides into branches which enter the biceps brachii. It contributes
one of the nerves to the pectoral muscles. In some cases this nerve
sends a branch to join the cutaneous branch of the median.
AXILLARY NERVE
The =axillary nerve= (Figs. 441, 520), also termed the circumflex,
derives its fibers from the eighth cervical and first thoracic roots of
the brachial plexus. It runs downward and backward across the lower part
of the subscapularis and dips in between that muscle and the subscapular
artery at the level of the shoulder joint. Continuing outward in the
interval between the teres minor and the long and external heads of the
triceps, it reaches the deep face of the deltoid and divides into
several divergent branches. The =muscular branches= supply the teres
major, capsularis, teres minor, infraspinatus, deltoid, and
mastoido-humeralis. The =cutaneous branch= (N. cutaneus brachii
lateralis) runs downward and a little forward across the external head
of the triceps and ramifies on the fascia on the front of the forearm
and on the superficial pectoral muscle.
RADIAL NERVE
The =radial nerve= (Figs. 441, 443, 520), also called the
musculo-spiral, is sometimes the largest branch of the brachial plexus.
Its fibers are derived from the seventh and eighth cervical and first
thoracic roots of the plexus. It passes downward and backward over the
inner surface of the subscapular artery and the teres major. In this
part of its course it is related in front to the ulnar nerve, which
separates it from the brachial vein. It detaches a branch to the tensor
fasciæ antibrachii, passes outward in the interval between the teres
major and the long and internal heads of the triceps, and gains the
musculo-spiral groove of the humerus. Accompanied by a branch of the
deep brachial artery, it runs obliquely downward and outward in the
groove, covered externally by the external head of the triceps and the
extensor carpi radialis, and reaches the flexion surface of the elbow
joint. In this part of its course it gives off a muscular branch which
ramifies in the long and external heads of the triceps and in the
anconeus, and a =cutaneous nerve= (N. cutaneus antibrachii dorsalis);
branches of the latter emerge below or through the external head of the
triceps and ramify on the dorso-lateral surface of the forearm. At the
elbow the nerve descends with the anterior radial vessels on the joint
capsule between the brachialis and extensor carpi radialis, and supplies
branches to the extensor carpi and the common or anterior extensor of
the digit and (inconstantly) to the brachialis. Below the elbow joint
the nerve detaches a large branch which passes back to the flexor carpi
externus, and terminates by small branches which descend on the radius
to enter the radial and ulnar heads of the common extensor, the lateral
extensor, and the oblique extensor of the carpus. Thus the radial nerve
innervates the extensors of the elbow, carpal and digital joints, and
supplies also the flexor carpi externus.[208]
[Illustration:
FIG. 520.—CUTANEOUS NERVES OF RIGHT FORE LIMB OF HORSE, EXTERNAL FACE.
_a_, Cutaneous branch of axillary nerve; _b_, cutaneous branches of
radial nerve; _c_, posterior cutaneous branch of ulnar nerve; _d_,
cutaneous branch of median nerve; _e_, superficial branch of ulnar
nerve; _f_, external metacarpal nerve; _g_, anastomotic branch
connecting internal and external metacarpal nerves; _1_, external
head of triceps; _2_, extensor carpi radialis; _3_, anterior
extensor; _4_, flexor carpi externus. (After Ellenberger, in
Leisering’s Atlas.)
]
ULNAR NERVE
The =ulnar nerve= (Figs. 441, 442, 443, 520) arises with the median from
the thoracic components of the brachial plexus. It descends between the
brachial artery and vein, accompanied for a short distance by the radial
nerve. It then crosses the vein and continues behind the latter along
the anterior border of the tensor fasciæ antibrachii and dips under that
muscle near the elbow. Here it is joined by the ulnar vessels and passes
downward and backward over the internal epicondyle of the humerus. In
the forearm it crosses obliquely the deep face of the ulnar head of the
flexor carpi medius and descends under the deep fascia with the vessels,
at first on the ulnar head of the perforans, and then between the middle
and external flexors of the carpus. Near the level of the accessory
carpal bone it divides into two terminal branches, superficial and deep.
It gives off two principal collateral branches. The =cutaneous branch=
(Ramus cutaneus palmaris) is detached just before the nerve passes under
the tensor fasciæ antibrachii; it runs downward and backward on that
muscle under cover of the posterior superficial pectoral, becomes
superficial below the elbow and ramifies on the posterior surface and
both sides of the forearm. The =muscular branch= is given off at the
elbow joint and divides to supply the flexors of the digit and the
middle flexor of the carpus. Of the two terminals, the =superficial
branch= (Ramus superficialis) emerges between the tendons of insertion
of the external and middle flexors of the carpus and ramifies on the
dorso-lateral aspect of the carpus and metacarpus. The =deep branch=
(Ramus profundus), after a very short course, unites under cover of the
tendon of the flexor carpi medius with the outer branch of the median
nerve to form the external metacarpal or volar nerve.
[Illustration:
FIG. 521.—CROSS-SECTION OF FOREARM OF HORSE ABOUT THREE INCHES (CA. 8
CM.) BELOW THE ELBOW JOINT.
The deep fascia is designated by red line. _N_, _A_, _V_, Interosseous
vessels and nerve.
]
MEDIAN NERVE
The =median nerve= (Figs. 441, 442, 447, 520, 521) derives its fibers
chiefly from the first thoracic root of the brachial plexus. It is
usually the largest branch and it accompanies the chief arterial trunks
to the distal part of the limb. It descends over the inner face of the
brachial artery, which it crosses obliquely, and continues down the arm
in front of the artery. Near its origin it is joined by a large branch
with the musculo-cutaneous nerve, thus forming a loop in which the
artery appears to be suspended. Near the elbow it crosses obliquely over
the artery (posterior radial) and lies behind it on the internal lateral
ligament. Below the joint it again crosses the artery and lies behind
the radius and the lower part of the long internal lateral ligament.
[Illustration:
FIG. 522.—DISSECTION OF DISTAL PART OF RIGHT FORE LIMB OF HORSE,
VIEWED FROM BEHIND.
_1_, Lateral cartilage; _2_, _3_, _4_, ligaments from first phalanx to
third sesamoid, bulb of heel, and lateral cartilage. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
At the elbow the nerve is covered by the posterior superficial
pectoral muscle and is crossed by the large oblique connection between
the cephalic and brachial veins. The variable and often plexiform
venous arrangement renders approach to the nerve here undesirable. It
can be reached best by an incision just behind the lower part of the
long internal lateral ligament; here the nerve lies under the deep
fascia in the furrow between the radius and the anterior border of the
flexor carpi internus, overlapped by the latter. In some cases the
nerve retains its position in front of the artery at the elbow, and in
others it crosses the deep face of the artery.
Passing beneath the internal flexor of the carpus, the nerve continues
downward in the forearm with the posterior radial vessels, and divides
at a variable distance above the carpus into two branches; these are the
internal volar or metacarpal nerve and the branch which unites with the
ulnar to form the corresponding external nerve.
At the proximal part of the forearm the nerve runs almost straight
downward along the posterior border of the long internal lateral
ligament, while the artery here inclines somewhat backward. Thus the
nerve is superficial to the artery for a short distance, then lies in
front of the latter to about the middle of the region, where it
inclines a little backward and arrives at the interval between the
internal and middle flexors of the carpus. The division may occur
about the middle of the region, but commonly takes place in the distal
third or fourth.
The collateral branches are as follows:
1. The =musculo-cutaneous branch= is in reality the continuation of the
nerve of that name. It is given off about the middle of the arm, passes
beneath the lower part of the biceps, and divides into muscular and
cutaneous branches. The =muscular branch= enters the brachialis. The
=cutaneous branch= emerges between the mastoido-humeralis and the biceps
and divides into two branches; these descend on the fascia of the
forearm with the cephalic vein and its accessory, and ramify on the
front and inner face of the forearm, carpus, and metacarpus.
2. =Muscular branches= to the internal flexor of the carpus and the
flexors of the digit are given off just as the nerve passes under the
first named muscle.
3. The very small =interosseous nerve= passes through the interosseous
space and is distributed chiefly to the periosteum, but in some cases
twigs may go to the extensor muscles.
The =metacarpal= or =volar nerves=,[209] internal and external, are the
continuations of the median and ulnar nerves in the distal part of the
limb.
The =internal metacarpal= or =volar nerve= (N. volaris medialis) arises
as the inner terminal branch of the median nerve at a variable distance
above the carpus (Fig. 442). It descends through the carpal canal along
the inner border of the superficial flexor tendon, and lies at first in
front of the large metacarpal or common digital artery. It then passes
behind the artery to the distal third of the metacarpus, where it lies
behind the vein, the artery here becoming deeper in position. In
addition to cutaneous twigs, the nerve gives off about the middle of the
metacarpus a considerable =anastomotic branch= which winds obliquely
downward and outward over the flexor tendons and joins the external
nerve at the lower third of the metacarpus (Fig. 447). Near the fetlock
the nerve divides into two digital branches.
1. The =dorsal= or =anterior digital branch= (Ramus dorsalis) descends
at first between the digital artery and vein, then crosses over the vein
and ramifies in the skin and the matrix of the hoof on the dorsal
(anterior) face of the digit.
2. The =volar= or =posterior digital branch= (Ramus volaris) is the
direct continuation of the trunk. It descends behind the digital artery,
which it accompanies in its ramification. A =middle digital branch= is
sometimes described as descending behind the vein. In some cases this
branch is distinct, but usually there are instead several small twigs
derived from the posterior branch, which cross very obliquely over the
artery and anastomose in a variable manner with each other and with the
anterior branch.
The =external metacarpal= or =velar nerve= (N. volaris lateralis) is
formed by the union of the external terminal branch of the median with
the deep branch of the ulnar nerve (Fig. 442). It descends with the
internal volar or small metacarpal artery in the texture of the
posterior annular ligament of the carpus. In the metacarpus it descends
along the outer border of the deep flexor tendon behind the external
metacarpal vein, and is accompanied by a small artery from the volar
subcarpal arch. Toward the distal end of the metacarpus it is joined by
the oblique branch from the internal nerve, and beyond this is arranged
like the latter. Below the carpus it detaches a deep branch to the
suspensory ligament and the interossei, and also supplies twigs to the
skin.
Anastomoses are established between the digital branches, and the
areas innervated by them are not well defined, but really overlap each
other. In certain diseased conditions, however, in which the lesions
are confined to the volar structures, relief from pain may be afforded
by section of the volar branches only.
THE THORACIC NERVES
The =thoracic nerves= (Nn. thoracales) number eighteen on either side in
the horse. They are designated numerically according to the vertebræ
behind which they emerge. Most of them are arranged in a very similar
manner and therefore do not require separate description. Each divides
into a dorsal and a ventral branch, the latter being the larger.
The =dorsal branches= (Rami dorsales) emerge behind the levatores
costarum and divide into internal and external branches. The internal
branches ascend on the multifidus and supply the dorsal spinal muscles.
The external branches run outward under the longissimus and emerge
between that muscle and the transversalis costarum; after giving twigs
to these muscles they pass through the latissimus dorsi and the
lumbo-dorsal fascia and ramify as dorsal cutaneous nerves under the skin
of the back (Fig. 523). In the region of the withers they give branches
to the serratus anticus and rhomboideus, and their cutaneous terminals
pass through these muscles and the dorso-scapular ligament to supply the
skin over the ligamentum nuchæ and the scapular cartilage.
The =ventral branches= or =intercostal nerves= (Nn. intercostales) are
much larger than the preceding, and are connected with the sympathetic
by rami communicantes. The first goes almost entirely to the brachial
plexus, but sends a fine branch downward in the first intercostal space
which is expended in the muscle there without reaching the lower end of
the space. The second ventral branch furnishes a considerable root to
the brachial plexus, but its intercostal continuation is typical. The
intercostal nerves (Fig. 184) descend in the intercostal spaces with the
vessels of like name, at first between the intercostal muscles, and
lower down chiefly between the pleura and the internal intercostal
muscle. In the anterior spaces the artery lies along the posterior
border of the rib, with the nerve in front of it; further back the nerve
lies behind the border of the rib, with the artery in front of it. They
supply the intercostal muscles, give off lateral perforating branches,
and terminate in the following manner: The second to the sixth inclusive
emerge through the spaces between the costal cartilages and concur in
supplying the pectoral muscles. The second to the eighth give branches
to the transversus thoracis. The succeeding ones give branches to the
diaphragm, pass between the transverse and internal oblique muscles,
give twigs to these, and end in the rectus abdominis. There are three
series of cutaneous nerves given off by the intercostal nerves. The
upper nerves emerge through the serratus magnus and the external
intercostals about parallel with the digitations of the external
oblique. The middle set perforate the origin of the latter muscle. The
lower ones appear through the abdominal tunic. They supply branches to
the abdominal muscles, the panniculus, and the skin. Some of the
anterior ones anastomose with the posterior thoracic branches of the
brachial plexus. The posterior three supply in part the skin of the
flank. The ventral branch of the last thoracic nerve runs outward behind
the last rib across the dorsal surface of the psoas major and divides
into superficial and deep branches. The superficial branch passes
between the obliquus internus and transversus abdominis, perforates the
obliquus externus, and ramifies under the skin of the flank (Fig. 525).
The deep branch descends on the inner face of the internal oblique to
the rectus abdominis, in which it ends.
THE LUMBAR NERVES
There are six pairs of =lumbar nerves= (Nn. lumbales) in the horse, the
last of which emerge between the last lumbar vertebra and the sacrum.
The anterior two or three are about the same size as the thoracic
nerves, but the others are much larger.
[Illustration:
FIG. 523.—SUPERFICIAL NERVES OF NECK AND TRUNK OF HORSE. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
Their =dorsal branches= are small in comparison with the ventral ones.
They are distributed to the muscles and skin of the loins and croup in a
fashion similar to those of the thoracic nerves.
The =ventral branches= are connected with the sympathetic by small rami
communicantes, and give branches to the sublumbar muscles. Those of the
first two nerves are arranged in a manner analogous to the corresponding
branch of the last thoracic nerve.
The ventral branch of the =first lumbar nerve= is termed the
=ilio-hypogastric nerve= (N. iliohypogastricus). It passes outward
between the quadratus lumborum and the psoas major, and divides at the
outer border of the latter into an anterior or superficial and a
posterior or deep branch. The =anterior= or =superficial branch= passes
over the upper edge of the internal oblique, descends between that
muscle and the external oblique, perforates the latter, and runs
downward and backward and ramifies under the skin of the posterior part
of the flank and the outer surface of the thigh. It gives branches to
the transversus and obliquus externus abdominis. The =posterior= or
=deep branch= is smaller; it runs downward and backward beneath the
peritoneum to the outer border of the rectus abdominis, gives branches
to the internal oblique, and terminates in the rectus abdominis.
[Illustration:
FIG. 524.—LUMBAR NERVES OF HORSE, VENTRAL VIEW. (After Schmaltz, Atlas
d. Anat. d. Pferdes.)
]
The ventral branch of the =second lumbar nerve= is connected by an
anastomotic branch with that of the third nerve. It gives off a large
branch to the psoas muscle and an inguinal branch, and is continued as
the ilio-inguinal nerve. The =inguinal branch= (N. spermaticus externus)
runs backward in the substance of the psoas minor, emerges a short
distance in front of the circumflex iliac vessels, and runs backward and
downward under the peritoneum to the internal inguinal ring. It gives
branches to the internal oblique muscle and descends in the inguinal
canal along the outer border of the cremaster (to which it detaches
filaments) and ends subcutaneously in the scrotum and prepuce in the
male, the mammary gland in the female. The =ilio-inguinal nerve= (N.
ilioinguinalis) may be regarded as the continuation of the ventral
branch. It runs parallel with the ilio-hypogastric nerve and has a
similar arrangement. Its =anterior= or =superficial branch= perforates
the external oblique muscle a little in front of the point of the hip,
runs downward on the front of the thigh and the outer surface of the
stifle, and gives off cutaneous branches. The =posterior= or =deep
branch= runs behind and parallel with that of the iliohypogastricus,
detaches branches to the internal oblique muscle, and descends the
inguinal canal with the inguinal branch, to be distributed to the
external genital organs and the surrounding skin in the inguinal region.
The ventral branch of the =third lumbar nerve= is connected by a small
anastomotic branch with the second nerve and furnishes a root of the
lumbo-sacral plexus. It gives off a branch to the psoas muscles, an
inguinal branch, and is continued as the external cutaneous nerve. The
=inguinal branch= (N. spermaticus externus) passes backward in the
substance of the psoas minor, from which it emerges under cover of or
near the circumflex iliac vessels. It then runs external to and parallel
with the external iliac artery and descends in the inner part of the
inguinal canal. It emerges at the external ring with the external pudic
artery and ramifies in the external genital organs and the skin of the
inguinal region. The =external cutaneous nerve= of the thigh (N.
cutaneus femoris lateralis) runs backward in the substance of the psoas
muscles and emerges at the outer border of the psoas minor. It then
passes outward and backward on the iliac fascia and accompanies the
posterior branch of the circumflex iliac artery. With this vessel it
perforates the abdominal wall by passing between the external oblique
and the iliacus a short distance below the point of the hip, and
descends on the inner face of the tensor fasciæ latæ (near its anterior
border) and ramifies subcutaneously in the region of the stifle.
[Illustration:
FIG. 525.—SUPERFICIAL NERVES OF PELVIC LIMB AND POSTERIOR PART OF
TRUNK OF HORSE.
_a_, Cutaneous branches of sixteenth and seventeenth thoracic nerves;
_b_, cutaneous branches of lumbar nerves; _c_, cutaneous branches of
sacral nerves; _d_, cutaneous branches of coccygeal nerves; _e_,
_f_, _g_, cutaneous branches of last intercostal, ilio-hypogastric,
and ilio-inguinal nerves; _g′_, end of external cutaneous nerve of
thigh; _h_, posterior cutaneous nerve of thigh; _i_, _i_, cutaneous
branches of great sciatic nerve; _k_, posterior cutaneous nerve of
the leg; _l_, superficial peroneal nerve; _m_, terminal part of deep
peroneal nerve; _n_, external plantar nerve; _1_, obliquus abdominis
externus; _2_, tensor fasciæ latæ; _3_, gluteus superficialis; _4_,
biceps femoris; _5_, semitendinosus; _6_, anterior extensor; _7_,
lateral extensor; _8_, flexor tendons; _9_, great metatarsal artery.
(After Ellenberger, in Leisering’s Atlas.)
]
The origin and disposition of some of the foregoing nerves are
variable. In some cases the ilio-inguinal nerve ends in the psoas
major, and appears then to be absent. The mode of formation of the
inguinal nerves is very inconstant. The inner nerve may arise with one
of the outer ones from a common trunk, or they may anastomose. The
inguinal branch of the ilio-inguinal nerve often receives a twig from
the ilio-hypogastric nerve.
The ventral branches of the =fourth=, =fifth=, and =sixth lumbar= nerves
concur in the formation of the lumbo-sacral plexus.
LUMBO-SACRAL PLEXUS
This plexus (Fig. 451) results substantially from the union of the
ventral branches of the last three lumbar and the first two sacral
nerves, but it derives a small root from the third lumbar nerve also.
The anterior part of the plexus lies in front of the internal iliac
artery between the lumbar transverse processes and the psoas minor. The
posterior part lies partly upon and partly in the texture of the
sacro-sciatic ligament. From the plexus are derived the nerves of the
pelvic limb, which are now to be described.
FEMORAL NERVE
The =femoral= (or anterior crural) nerve (N. femoralis) is derived
chiefly from the fourth and fifth lumbar nerves, but commonly receives a
fasciculus from the third nerve also (Fig. 524). It is the larger of the
two nerves which are given off from the anterior part of the
lumbo-sacral plexus. It runs backward at first between the psoas major
and minor, then crosses the deep face of the tendon of insertion of the
latter, and descends under cover of the sartorius in the furrow between
the two heads of the iliacus. It gives off the saphenous nerve, crosses
the lower part of the outer head of the iliacus, and divides into
several branches which dip into the interstice between the rectus
femoris and the vastus internus (Fig. 450). These branches are
accompanied by the anterior femoral vessels and innervate the quadriceps
femoris. Collateral muscular branches are supplied to the ilio-psoas and
sartorius.
The =saphenous nerve= (N. saphenus) (Figs. 450, 451, 457) is given off
as the parent trunk crosses the furrow between the psoas major and the
outer head of the iliacus. It descends with the femoral vessels in the
femoral canal, and gives branches to the sartorius, gracilis, and
pectineus. About the middle of the thigh it divides into several
branches which emerge from between the sartorius and gracilis, perforate
the deep fascia and ramify on the inner surface and the front of the
limb as far downward as the hock. The longer posterior branches
accompany the saphenous vessels, while the anterior branches deviate
forward toward the stifle and the anterior surface of the leg.
OBTURATOR NERVE
This nerve (N. obturatorius) is derived from the ventral branches of the
last three lumbar nerves (Fig. 524). It runs downward and backward, at
first above and then upon the external iliac vein, inclines inward
across the obturator vein, and passes through the anterior part of the
obturator foramen in front of that vessel (Fig. 451). It continues
downward through the obturator externus, and divides into several
branches which innervate the obturator externus, pectineus, adductor,
and gracilis muscles (Fig. 456).
ANTERIOR GLUTEAL NERVE
This nerve (N. glutæus cranialis) is derived chiefly from the last
lumbar and first sacral nerves. It divides into four or five branches
which emerge through the great sacro-sciatic foramen with the divisions
of the anterior gluteal artery and supply the gluteal and tensor fasciæ
latæ muscles. The nerve to the latter and the anterior part of the
superficial gluteus passes between the deep part of the gluteus medius
and the deep gluteal muscle, and is accompanied on the iliacus by
branches of the external circumflex vessels.
POSTERIOR GLUTEAL NERVE
The =posterior gluteal nerve= (N. glutæus caudalis) is derived mainly
from the sacral roots of the lumbo-sacral plexus (Figs. 451, 526). It
divides into two trunks which emerge above the great sciatic nerve. The
upper nerve passes backward on the sacro-sciatic ligament and divides
into branches which enter the two heads of the biceps femoris; it
supplies a branch to the posterior part of the middle gluteus, and a
nerve which turns around the posterior border of the latter and enters
the posterior head of the superficial gluteus. The inferior nerve runs
downward and backward on the sacro-sciatic ligament and divides into the
=posterior cutaneous nerve= and muscular branches which supply the
semitendinosus. The former (N. cutaneus femoris caudalis) passes through
the biceps femoris, emerges between that muscle and the semitendinosus a
little below the level of the tuber ischii, and ramifies subcutaneously
on the outer and posterior surfaces of the hip and thigh (Fig. 525).
[Illustration:
FIG. 526.—VESSELS AND NERVES OF PELVIC WALL OF HORSE.
Nervus ischiadicus = great sciatic nerve; n. glut. inf = anterior
gluteal nerve; n. pudendus = internal pudic nerve. (After Schmaltz,
Atlas d. Anat. D. Pferdes.)
]
GREAT SCIATIC NERVE
The =great sciatic nerve= (N. ischiadicus) (Figs. 451, 455, 526), the
largest in the body, is derived chiefly from the last lumbar and the
sacral roots of the lumbo-sacral plexus, but may receive a fasciculus
from the third sacral nerve also. It emerges through the great
sacro-sciatic foramen as a broad flat band—blended at first with the
posterior gluteal nerve—which passes downward and backward on the lower
part of the sacro-sciatic ligament and on the origin of the deep gluteus
muscle. It turns downward in the hollow between the trochanter major and
the tuber ischii over the gemellus, the tendon of the obturator
internus, and the quadratus femoris. In its descent in the thigh it lies
between the biceps femoris externally and the adductor, semimembranosus,
and semitendinosus internally, and it is continued between the two heads
of the gastrocnemius as the tibial nerve. Its chief branches are as
follows:
1. In the pelvic part of its course the sciatic nerve supplies small
branches to the obturator internus, gemellus, and quadratus femoris; the
branch to the obturator internus reaches the muscle by passing through
the anterior end of the lesser sacro-sciatic foramen.
2. As the sciatic nerve turns down behind the hip joint it gives off a
large branch (Ramus muscularis proximalis) which divides to supply the
semimembranosus and the short heads of the biceps femoris and
semitendinosus.
3. The =posterior cutaneous nerve= of the leg or =external saphenous
nerve= (N. cutaneus suræ posterior) is detached from the sciatic about
the middle of the thigh. It receives a fasciculus from the peroneal
nerve and descends with the recurrent tarsal vein on the outer face of
the gastrocnemius to the distal third of the leg. Here it perforates the
deep fascia and ramifies under the skin on the outer surface of the
tarsus and metatarsus (Fig. 525).
4. The =peroneal= or =external popliteal nerve= (N. peronæus) (Figs.
455, 460, 527) is a large trunk which arises from the great sciatic
nerve very shortly after the latter emerges from the pelvic cavity. It
descends with the parent trunk to the origin of the gastrocnemius; here
the peroneal nerve deviates outward and forward across the external face
of the gastrocnemius under cover of the biceps femoris, and divides at
the origin of the lateral extensor muscle into superficial and deep
branches. The collateral branches include a twig to the biceps femoris,
the reinforcing fasciculus detached about the middle of the thigh to the
posterior cutaneous nerve, and, lower down, the =external cutaneous
nerve= of the leg (Ramus cutaneus suræ lateralis). The latter, also
known as the peroneal cutaneous nerve, emerges between the middle and
posterior divisions of the biceps femoris at the level of the stifle
joint and ramifies under the skin. The =superficial peroneal= or
=musculo-cutaneous nerve= (N. peronæus superficialis) furnishes branches
to the lateral extensor, and descends in the furrow between that muscle
and the anterior extensor, perforates the deep fascia of the leg, and
ramifies under the skin on the front and the outer face of the tarsus
and metatarsus. The =deep peroneal= or =anterior tibial nerve= (N.
peronæus profundus) is the direct continuation in point of size of the
peroneal trunk. It dips in between the lateral and anterior extensors of
the digit, gives branches to these muscles and the tibialis anterior,
and descends in front of the intermuscular septum which separates the
former. It continues downward behind the tendon of the anterior extensor
and divides on the front of the hock into internal and external
branches. The =internal branch= (Ramus medialis) passes down under the
skin on the anterior face of the metatarsus and supplies the cutaneous
fibers of this region. The =external branch= (Ramus lateralis) furnishes
a twig to the extensor brevis muscle and descends with the great
metatarsal artery. It supplies the skin on the outer face of the
metatarsus and the fetlock.
In the greater part of its course in the leg the deep peroneal nerve
is separated from the anterior tibial vessels by the tibialis anterior
(muscular part of the flexor metatarsi). It should be noted that the
outer of the two veins which almost always accompany the artery here
is frequently very large, and the layer of muscle which intervenes
between it and the nerve is often exceedingly thin. In the distal part
of the leg the nerve is in direct contact with the vein, and on the
front of the hock it lies behind the vessels.
TIBIAL NERVE
The =tibial nerve= (N. tibialis), also termed the posterior tibial, is
the direct continuation of the great sciatic nerve (Figs. 451, 455, 458,
459, 527). It passes down between the two heads of the gastrocnemius,
and accompanies the recurrent tibial vessels to the distal third of the
leg, where it divides into internal and external plantar nerves. In the
upper third of the leg it lies along the inner side of the superficial
flexor under cover of the internal head of the gastrocnemius; lower down
it is covered by the common deep fascia and is situated in the space
between the deep flexor and the inner border of the tendo Achillis.
At the usual point of election for tibial neurectomy, _i. e._, about a
handbreadth above the level of the tuber calcis, the nerve lies in
areolar tissue and fat in a fascial compartment formed by the special
fascia of the deep flexor in front and by the common fascia and the
accessory or tarsal tendon of the semitendinosus and biceps femoris
behind and internally.
At its origin the tibial nerve gives off a =muscular branch= (Ramus
muscularis distalis), the divisions of which pass between the two heads
of the gastrocnemius and radiate to supply that muscle, the popliteus,
the soleus, and the flexors of the digit. Small cutaneous twigs are also
detached along the course of the nerve.
[Illustration:
FIG. 527.—CROSS-SECTION OF DISTAL THIRD OF LEFT LEG OF HORSE.
The deep fascia is shown by red line.
]
PLANTAR NERVES
The =plantar nerves=, internal and external (N. plantaris medialis,
lateralis), result from the bifurcation of the tibial nerve in the lower
part of the leg (Figs. 458, 459). They continue at first in the same
direction and relations as the parent trunk, in direct apposition and
inclosed in a common sheath. At the hock they diverge at a very acute
angle and descend in the tarsal canal behind the deep flexor tendon in
company with the plantar arteries. The internal plantar nerve supplies
cutaneous nerves to the inner aspect of the tarsus and metatarsus,
descends along the inner border of the flexor tendons behind the
superficial plantar metatarsal vessels, and is otherwise arranged like
the corresponding volar nerve of the fore limb. The external plantar
nerve deviates outward between the two flexor tendons to reach their
outer border. It supplies a branch to the suspensory ligament, and in
its further course resembles the corresponding nerve of the fore limb.
In so-called “tibial” neurectomy the operator really cuts the two
plantar nerves which have not yet separated. The anastomotic branch
between the two plantar nerves is smaller than that which connects the
corresponding nerves of the fore limb, and is absent in 30 per cent.
of the cases, according to Rudert.
SACRAL NERVES
Five pairs of =sacral nerves= (Nn. sacrales) are present in the horse.
The small =dorsal branches= emerge through the dorsal sacral foramina
and the space between the sacrum and the first coccygeal vertebra, and
ramify in the muscles and skin of the sacral region and the adjacent
part of the tail (Fig. 525). The fifth anastomoses with the dorsal
branch of the first coccygeal nerve.
The =ventral branches= leave the vertebral canal through the ventral
sacral foramina and the interval between the sacrum and first coccygeal
vertebra. They are connected with the sympathetic by rami communicantes,
and contribute branches to the pelvic plexus. The first and second are
the largest, and unite with each other and with those of the last three
lumbar nerves to form the lumbo-sacral plexus. The third and fourth are
connected with each other, and the majority of their fibers go to form
the pudic and posterior hæmorrhoidal nerves.
The =pudic nerve= (N. pudendus) (Figs. 451, 455, 526) accompanies the
internal pudic artery to the ischial arch, turns around the latter,
parting company with the artery, and pursues a flexuous course along the
dorsum penis as the =nervus dorsalis penis= and ramifies in the glans
and the penile layer of the prepuce. Within the pelvis it anastomoses
with the posterior hæmorrhoidal nerve, and gives branches to the bladder
and urethra, the terminal part of the rectum, and the skin and muscles
of the anus (Fig. 452). It also supplies the nerve to the
ischio-cavernosus muscle and numerous branches to the corpus cavernosum
and corpus spongiosum. In the female it terminates in the clitoris and
vulva (Fig. 453).
The =posterior hæmorrhoidal nerve= (N. hæmorrhoidalis caudalis) passes
downward and backward above the pudic nerve, with which it anastomoses.
It gives twigs to the terminal part of the rectum, the sphincter ani
externus, and the surrounding skin (Fig. 452). In the female it supplies
twigs to the vulva also (Fig. 453).
The ventral branch of the fifth nerve is small. It gives twigs to the
sacro-coccygeus ventralis lateralis and the skin of the root of the tail
and joins the first coccygeal nerve.
COCCYGEAL NERVES
The =coccygeal nerves= (Nn. coccygei) commonly number five pairs. Their
dorsal and ventral branches anastomose to form respectively two trunks
on either side, which extend to the tip of the tail and supply its
muscular and cutaneous nerves. The dorsal trunk runs with the
dorso-lateral artery between the sacro-coccygeus dorsalis and
intertransversales muscles (Fig. 454). The ventral trunk accompanies the
ventro-lateral artery below the intertransversales.
THE SYMPATHETIC NERVOUS SYSTEM[210]
The =sympathetic nervous system= (Systema nervorum sympathicum) is that
part of the nervous system which serves (1) to transmit stimuli to the
heart-muscle, unstriped muscle, and glands; (2) to conduct impulses from
the viscera to the cerebrospinal system.
Many of the fibers are derived from the cerebrospinal system and are
rearranged and distributed in the sympathetic system. Numerous
sympathetic fibers are contributed to the cerebrospinal nerves,
through which they are distributed to the unstriped muscular tissue
and glands, as vasomotor, pilomotor, and secretory nerves. The
sympathetic, like the cerebrospinal system, consists of neurones, each
of which comprises the cell-body, an axone, and numerous branched
dendrites. The cell-bodies are aggregated into =ganglia=, some of
which are large and more or less constant in position and form, while
others are microscopic; and are scattered in an irregular manner
through the peripheral part of the system. It is probable that simple
visceral reflexes may be mediated by sympathetic neurones alone.
In descriptive anatomy the sympathetic system is regarded as consisting
of (1) a chain of =ganglia= extending along either side of the vertebral
column and connected by association fibers to form the =sympathetic
trunk=; (2) =central branches= to and from the cerebrospinal nerves; (3)
=peripheral branches=, which form =plexuses= with each other and the
cerebrospinal nerves; (4) the =peripheral ganglia= which are interposed
in the plexuses.
The =sympathetic trunk= (Truncus sympathicus) extends on either side
from the base of the cranium to the tail. In it are interposed, at
intervals of varying regularity, the =ganglia of the sympathetic trunk=
(Ganglia trunci sympathici). These are connected with the cerebrospinal
nerves by central branches, the =rami communicantes=.
Two kinds of rami communicantes occur. Of these, one type consists
largely of medullated fibers derived from the spinal nerves and
ganglia; they have therefore a white appearance, and are termed =white
rami=. They contain both efferent and afferent fibers. The =efferent
splanchnic fibers= are derived from the ventral roots of the spinal
nerves and terminate in great part about the cells of the nearest
sympathetic ganglion; others end in more distant or in peripheral
ganglia. The =afferent splanchnic fibers= are chiefly peripheral
processes of the cells of the spinal ganglia, but some are sympathetic
fibers which enter the spinal nerve-trunk and terminate about cells of
the spinal ganglion. The =gray rami= consist mainly of non-medullated
fibers derived from the sympathetic ganglia directly or through the
trunk, which proceed centrally to the spinal nerves and are
distributed along the somatic divisions of the latter to unstriped
muscle and glands as =vasomotor=, =pilomotor=, and =secretory fibers=.
Some go to the membranes of the spinal cord, and a few terminate about
cells of the spinal ganglia as sensory sympathetic fibers.
Similar but more complex and irregular communications which exist
between the sympathetic system and the cranial nerves—with the exception
of the first and second—have been referred to in the accounts of the
latter.
It is convenient for descriptive purposes to divide the sympathetic
system into cephalic, cervical, thoracic, abdominal, and pelvic parts.
1. The =cephalic part= (Pars cephalica systematis sympathici) comprises
the =otic=, =sphenopalatine=, and =ciliary ganglia=, which may be
regarded as homologues of the ganglia of the trunk of other regions. It
also includes three plexuses formed by branches derived from the
superior cervical ganglion. The ganglion gives off two or three
filaments which subdivide to form the =internal carotid plexus= around
the artery of like name. The =cavernous plexus= surrounds the artery
within the cavernous sinus and communicates with that of the opposite
side. The =external carotid plexus= is formed around the homonymous
artery, and filaments from it go to the vessel and its branches and to
the salivary glands.
2. The =cervical part= (Pars cervicalis s. sympathici) includes two
ganglia and the trunk which connects them.
The =superior= or =anterior cervical ganglion= (G. cervicale craniale)
lies on the guttural pouch below the occipito-atlantal articulation
(Fig. 437). It is reddish-gray in color, fusiform, and about an inch
(ca. 2 to 3 cm.) in length. It is connected by rami communicantes with
the last four cranial and first cervical nerves, sends branches to form
the plexuses mentioned above, and contributes to the pharyngeal plexus.
The =cervical trunk= of the sympathetic connects the superior and
inferior cervical ganglia. On leaving the former it is associated in a
common sheath with the vagus along the dorsal face of the common carotid
artery. At the root of the neck it separates from the vagus and joins
the inferior ganglion.
The =inferior= or =posterior cervical ganglion= (G. cervicale caudale)
is situated under the first rib and the insertion of the scalenus (Figs.
428, 429). On the right side it lies upon the longus colli and the
trachea, on the left side upon the same muscle and the œsophagus. It is
flattened, very irregular and variable in outline, and is blended more
or less with the first thoracic ganglion. It is connected by large gray
rami with the ventral branches of the last two cervical nerves, and by
small filaments with the recurrent nerve. It receives a nerve—termed by
Schmaltz the nervus transversarius—which accompanies the vertebral
artery; through it rami come from the second to the sixth cervical
nerves inclusive.
A =middle cervical ganglion= may be present, and occurs oftenest on the
right side. It lies on the carotid artery an inch or two in front of the
first rib and is intercalated in the vago-sympathetic trunk.
The =cardiac nerves= (Nn. cardiaci) are formed by branches from the
inferior cervical and first thoracic ganglia, together with twigs from
the sympathetic trunks and the vagi. They form a plexus (P. cardiacus)
on the ventral face of the trachea with each other and with branches of
the vagus and recurrent nerves. They are subject to considerable
variation, but their general arrangement may be stated as follows:
(_a_) On the right side there are usually two cardiac nerves. Of these
one passes back with the vagus in the angle between the right brachial
artery and the common carotid trunk, pierces the pericardium, crosses
the aortic arch, and divides into branches which are mingled with those
of the left nerves. The second crosses obliquely over the right face of
the trachea and joins the vagus, where the latter gives off the right
recurrent nerve; a small plexus is formed here, from which two or three
cardiac branches are detached. These pass back beneath the trachea and
ramify on the atria and ventricles.
(_b_) On the left side there are commonly three cardiac nerves. One of
these is distributed to the great vessels in the anterior mediastinum.
The largest passes back at first with the vagus beneath the arch of the
left brachial artery, inclines downward, perforates the pericardium, and
divides into two branches. One branch passes beneath the bifurcation of
the pulmonary artery and is distributed to the left atrium. The larger
branch dips in between the aorta and the pulmonary artery, gives twigs
to these vessels, and ramifies on the ventricles, especially along the
course of the right coronary artery. The third nerve crosses the deep
face of the left brachial artery, passes back below the trachea, and
unites with filaments of a right cardiac nerve. It passes around the
aorta and ramifies chiefly along the course of the left coronary artery
on the left face of the ventricles.
3. The =thoracic part= (Pars thoracalis systematis sympathici) extends
below the costo-vertebral joints from the inferior cervical ganglion to
the upper border of the diaphragm, and passes between the latter and the
psoas minor to be continued by the abdominal part.
The =trunk= is concealed in the first part of its course by the outer
border of the longus colli, but further back it is visible under the
pleura.
The =ganglia= are arranged segmentally at each intercostal space and
partly on the heads of the ribs. They are flattened and are small and
fusiform, with the exception of the first. This (G. thoracale primum) is
extensive, irregularly quadrilateral in outline, and is united with the
inferior cervical ganglion. The ganglia are connected with the thoracic
nerves by white and gray rami communicantes.
The =visceral branches= comprise aortic, cardiac, pulmonary, and
œsophageal branches, and the splanchnic nerves. The =aortic branches=
ramify on the thoracic artery, forming around that vessel the =thoracic
aortic plexus= (P. aorticus thoracalis). The =cardiac branches= concur
with those of the vagus in forming the =cardiac plexus= (P. cardiacus).
From this branches go to form the =coronary plexuses= (P. coronarii)
along the course of the vessels of like name. The =pulmonary branches=
join with corresponding branches of the vagus and filaments from the
cardiac plexus in forming the =pulmonary plexus= (P. pulmonalis) at the
root of the lung. Branches of the plexus, on which are minute ganglia,
ramify with the bronchi in the substance of the lung.[211] The
=œsophageal branches= join with those of the vagus in the formation of
the =œsophageal plexus= (P. œsophageus).
The =great splanchnic nerve= (N. splanchnicus major) arises by a series
of roots derived from the sixth or seventh to the fifteenth or sixteenth
thoracic ganglia inclusive. It extends at first along the inner side of
the thoracic trunk, then crosses the latter ventrally, passes back
between the crus of the diaphragm and the outer border of the psoas
minor, and joins the cœliac ganglion. It is small at its origin, but
becomes considerably larger than the sympathetic trunk. Near its
termination it bears the small =splanchnic ganglion=, from which and
from the nerve, filaments go to the aorta, the œsophagus, and the
vertebræ.
The =small splanchnic nerve= (N. splanchnicus minor) is formed by roots
derived from the last two or three thoracic ganglia. It runs back with
the great splanchnic nerve, but ends in the cœliac or in the renal and
adrenal plexuses.
This nerve is not always present and is variable in arrangement. The
roots communicate by filaments with the great splanchnic.
4. The =abdominal part= of the sympathetic trunk (Pars abdominalis
systematis sympathici) lies along the inner border of the psoas minor,
above the aorta on the left side and the posterior vena cava on the
right (Fig. 524). The trunk is smaller than the thoracic part, and
presents usually six small fusiform =lumbar ganglia= (G. lumbalia),
which are connected by rami communicantes with the ventral divisions of
the lumbar nerves. Visceral branches go to the aortic and hypogastric
plexuses, and to the cœliac and mesenteric ganglia.
5. The =pelvic part= of the sympathetic trunk (Pars pelvina systematis
sympathici) begins at the last lumbar ganglion and extends along the
pelvic surface of the sacrum internal to the emergence of the ventral
branches of the sacral nerves (Fig. 451). At the third segment of the
sacrum the trunk divides into internal and external branches. The
internal branch inclines to the median plane and unites with the
opposite branch. At the junction there is often found the small
=coccygeal ganglion= (G. impar), which lies on the coccygeal artery at
the joint between the first and second coccygeal vertebræ. A filament
from the ganglion accompanies the artery. The external branch
communicates with the last two sacral nerves and joins the ventral
coccygeal nerves. Ganglia occur near each of the first three sacral
foramina, and are connected by gray rami communicantes with the adjacent
spinal nerves. The visceral branches are distributed through the
hypogastric plexus. They supply motor fibers to the longitudinal and
inhibitory fibers to the circular muscular coat of the rectum, motor
fibers to the bladder and uterus, and the vasodilator fibers (Nn.
erigentes) to the penis.
THE ABDOMINAL AND PELVIC PLEXUSES
The chief plexuses which distribute nerves to the viscera and vessels of
the abdominal and pelvic cavities are two in number, the solar and the
pelvic. From them fibers proceed to form numerous subsidiary plexuses
which are named according to the organs which they supply or the vessels
which they enlace.
THE SOLAR PLEXUS
The =solar plexus= (Fig. 450) is situated on the dorsal wall of the
abdominal cavity in relation to the aorta and the origin of its chief
visceral branches. It comprises the cœliaco-mesenteric ganglia and the
cœliac and anterior mesenteric plexuses.
The =cœliaco-mesenteric ganglia=[212] are two in number, right and left.
They are situated on each side of the aorta, in relation to the origin
of the cœliac and anterior mesenteric arteries. The right ganglion is
concealed by the posterior vena cava; it is irregularly quadrilateral
and is about two inches (4 to 6 cm.) in length. The left ganglion is
largely covered by the left adrenal; it is narrower than the right one
and is three or four inches (ca. 8 to 10 cm.) long. The two ganglia are
united by irregular connecting branches in front of and behind the
anterior mesenteric artery.[213] Each receives the splanchnic nerve of
its own side and branches from the dorsal œsophageal continuation of the
vagus nerves. Branches from the ganglia and the cords which connect them
pass back to the small stellate =posterior mesenteric ganglia=, which
are situated at the origin of the posterior mesenteric artery.
The =cœliac plexus= (P. cœliacus) consists of a feltwork of nerve-fibers
in which are small ganglia. It surrounds the cœliac artery and from it
proceed the following unpaired secondary plexuses which accompany the
arterial branches:
1. The =gastric plexus= (P. gastricus) enlaces the gastric artery and
divides like the artery into two parts, forming the anterior and
posterior gastric plexuses. These receive branches of the vagus nerves.
2. The =hepatic plexus= (P. hepaticus) is formed by several nerves of
considerable size which accompany the hepatic artery and the portal
vein. It receives fibers from the left vagus, ramifies in the liver, and
gives off branches which accompany the collateral branches of the
hepatic artery and supply the areas in which these vessels are
distributed.
3. The =splenic plexus= (P. lienalis) resembles the preceding in its
arrangement. In addition to its terminal branches to the spleen, it
gives collateral twigs to the pancreas and the left part of the greater
curvature of the stomach.
The =anterior mesenteric plexus= (P. mesentericus cranialis) is formed
mainly by branches from the posterior part of the cœliaco-mesenteric
ganglia; it is continuous with the cœliac plexus in front and the
posterior mesenteric behind. It surrounds the anterior mesenteric trunk
and its branches, and supplies the viscera to which these vessels are
distributed.
The =posterior mesenteric plexus= (P. mesentericus caudalis) accompanies
the artery of like name in its distribution.
The secondary plexuses which accompany the branches of the mesenteric
arteries give off branches which form two fine peripheral plexuses in
the wall of the intestine. One of these, the =myenteric plexus= (P.
myentericus) or plexus of Auerbach, lies between the layers of the
muscular coat, and is provided with microscopic ganglia. The other is
in the submucous tissue, and is therefore termed the =submucous
plexus= (P. submucosus) or plexus of Meissner.
The following paired plexuses are derived mainly from branches of the
cœliac and aortic plexuses:
1. The =renal plexuses= (P. renales) proceed largely from the
cœliaco-mesenteric ganglia, but receive fibers also from the small
splanchnic nerves. They enlace the renal arteries and supply the
kidneys. Minute renal ganglia occur on the course of the nerves along
the renal vessels.
2. The =adrenal plexuses= (P. suprarenales) are formed by a relatively
very large number of fine fibers derived in great part directly from the
cœliaco-mesenteric ganglia. Numerous minute ganglia occur in their
meshes.
3 _a_. The =spermatic plexuses= (P. spermatid) proceed largely from the
aortic and renal plexuses. Each accompanies the corresponding (internal)
spermatic artery to the testicle.
3 _b_. The =utero-ovarian plexuses= (P. ovarici) are the homologues in
the female of the preceding. They accompany the utero-ovarian arteries
to the ovary and the cornua of the uterus.
The =hypogastric= or =pelvic plexus= (P. hypogastricus) is the pelvic
continuation of the aortic and posterior mesenteric plexuses. The chief
nerves which form it enter the pelvic cavity ventral to the large
vessels, anastomose with each other and with branches from the third and
fourth sacral nerves, and ramify on the pelvic viscera. The peripheral
plexuses derived therefrom are named according to the organs which they
supply; the chief of these are the =hæmorrhoidal=, =vesical=,
=uterovaginal=, =prostatic=, =cavernous= (of the penis or clitoris).
THE NERVOUS SYSTEM OF THE OX[214]
The =spinal cord= resembles that of the horse in conformation and
structure. In cattle of medium size its length is about 165 to 170 cm.
(ca. 65 to 67 inches) and its weight about 240 to 250 grains (ca. 8
ounces).
In a cow 140 cm. in height Dexler found the weight of the cord
(including the intradural nerve-roots) to be 260 g. and the length 162
cm. The lengths of the regions were: cervical 41 cm., thoracic 72 cm.,
lumbar 32 cm., sacral 7 cm.
The =brain= has an average weight of about 500 grams (ca. 16 to 17
ounces). Its differences in general form are correlated with those noted
in the consideration of the cranial cavity.
The =medulla= is short, wide, and thick. Its ventral face is strongly
convex. The pyramids are narrow, short, and close together in front.
Near the decussation there is a well defined oval prominence on either
side which indicates the position of the posterior olive. The corpus
trapezoideum is large; it has no central part between the pyramids. The
external arcuate fibers are distinct. The restiform bodies are short and
thick and diverge more strongly than in the horse. The floor of the
fourth ventricle is only about two-thirds as long as in the horse. The
area acustica is a well-marked oval prominence lateral to the middle
part of the limiting sulcus. The tuberculum acusticum at the origin of
the auditory nerve is very large. The anterior fovea is distinct. The
posterior recess of the fourth ventricle communicates through the
foramen of Magendie (Apertura mediana) with the subarachnoid space.
[Illustration:
FIG. 528.—BRAIN OF COW, DORSAL VIEW.
_1_, Sulcus transversus; _2_, longitudinal fissure; _3_,
antero-internal frontal gyrus; _4_, olfactory bulb; _5_, marginal or
sagittal pole of hemisphere; _6_, lateral fissure (of Sylvius); _7_,
hemisphere of cerebellum; _8_, vermis of same; _9_, accessory nerve;
_10_, dorsal root of first cervical nerve. (Ellenberger-Baum, Anat.
d. Haustiere.)
]
The =pons= is smaller, both transversely and longitudinally, than that
of the horse. It is strongly convex and has a distinct central
depression.
The =cerebellum= is smaller and more angular in form than in the horse.
The vermis is large and has a distinct depression on its anterior face
for the posterior corpora quadrigemina. The hemispheres are relatively
small and are not clearly divided into tabulations. The anterior
peduncles are very short.
The =cerebral peduncles= are short. A small eminence in the locus
perforatus posticus is caused by the presence of the interpeduncular
ganglion. The =internal geniculate body= is prominent. The =pineal body=
is long and fusiform, and is often pigmented in spots. The third
ventricle forms two considerable recesses in relation to the pineal
body: one (R. pinealis) extends up into the body; the other (R.
suprapinealis) is a long tubular prolongation in front of it.
The =optic tracts= cross the cerebral peduncles almost at a right angle.
The =pituitary body= is situated in a deep fossa and is surrounded by a
plexus of vessels.
The =cerebral hemispheres= are shorter, higher, and relatively wider
than in the horse. The frontal poles are small, the occipital large.
Viewed from the side, the dorsal surface is strongly convex. The highest
point of the dorso-medial border is a little in front of its middle and
forms a marked prominence termed the =sagittal= or =marginal pole=
(Polus sagittalis s. prominentia marginalis dorsalis). Anterior to this
the border drops abruptly, being cut into by the deep transverse
fissure. The arachnoid on the basal and anterior parts of the
hemispheres is usually pigmented. The =corpus callosum= extends through
a little more than a third of the length of the hemisphere. The pattern
of the =fissures= and =gyri= of the pallium is somewhat simpler than in
the horse.
[Illustration:
FIG. 529.—CEREBRAL HEMISPHERES OF OX, DORSAL VIEW.
_a_, Transverse fissure; _b_, lateral fissure (of Sylvius); _c_,
coronal fissure; _d_, diagonal fissure; _e_, entomarginal fissure;
_f_, marginal fissure; _g_, ectomarginal fissure; _h_, suprasylvian
fissure. (After Ellenberger, in Leisering’s Atlas.)
]
1. The =lateral fissure= (of Sylvius) is very deep. Its middle branch
extends almost vertically upward on the middle of the lateral surface
of the hemisphere, and is separated by a gyrus of variable width from
the suprasylvian fissure. The anterior branch runs forward about
parallel with the sulcus rhinalis anterior, from which it is separated
by the short gyri of the insula. The latter are covered to a small
extent only by the overhanging gyri (operculum). The posterior branch
may run back a distance of only about 1.5 cm. and end in T-shaped
manner, or it may join the sulcus rhinalis posterior.
2. The =suprasylvian fissure= is deep and very distinct. It extends in
an undulating manner from the lateral surface of the occipital pole to
the outer side of the sagittal pole. Here it may be interrupted or may
be continued by the =coronal fissure=, which descends to the frontal
pole and divides into two short branches.
3. The =diagonal fissure= (S. diagonalis) begins in front of the stem
of the lateral fissure and runs upward and forward. Its form is very
variable.
4. The =transverse fissure= cuts obliquely into the dorsal border in
front of the sagittal pole. It is short and deep and commonly
communicates with the suprasylvian and coronal fissures.
5. The =marginal fissure= is distinct. It extends from the sagittal
pole to the occipital pole. It is flexuous and deviates outward
somewhat in its posterior two-thirds.
6. The =entomarginal fissure= lies medial and parallel to the
posterior part of the preceding.
7. The =ectomarginal fissure= is lateral and parallel to the marginal
fissure. It does not extend so far in either direction as the latter
and is often more or less broken up by annectent gyri.
8. The =sulcus rhinalis= is more open than in the horse, since it is
not overlapped by the gyri above it.
9. The =calloso-marginal= fissure is flexuous and not so regular as in
the horse. It is often interrupted at or near the level of the genu of
the corpus callosum, in which case the =genual fissure= continues it
downward.
10. The =crucial fissure= is faint and is confined to the medial
surface. It lies about one centimeter in front of the transverse
fissure and commonly joins the calloso-marginal fissure below.
11. Short and variable fissures occur in front of and behind the
middle branch of the lateral fissure (F. ectosylvia anterior,
posterior).
The =olfactory bulb= is much smaller than in the horse. The external
olfactory tract is large, the inner one small and not distinct.
The =cranial nerves= have in general the same superficial origin as in
the horse. The more important differences in other respects are as
follows:
The =oculomotor nerve= is larger than in the horse. It emerges with the
fourth, sixth, ophthalmic, and maxillary nerves through the large
foramen, which is equivalent to the foramen lacerum orbitale and foramen
rotundum of the horse.
The internal branch of the =lacrimal nerve= supplies twigs to the mucous
membrane of the frontal sinus; the large outer branch runs backward and
supplies the matrix of the horn. The =frontal nerve= emerges from the
orbit below the supraorbital process. The =naso-ciliary nerve= is large
and sends filaments to the ocular muscles. The =ciliary ganglion= is
somewhat larger than in the horse and is connected with the lower
division of the oculomotor nerve by several short filaments. In
consequence of the absence of the canine and upper incisor teeth the
corresponding branch of the infraorbital nerve is naturally wanting. The
=mandibular nerve= emerges through the foramen ovale. The =superficial
temporal nerve= gives off a large branch which joins the superior buccal
division of the facial on the masseter, about half-way between the
zygomatic arch and the angle of the jaw. The =otic ganglion= is larger
than in the horse. According to Moussu the buccinator nerve furnishes
excito-secretory twigs to the parotid and inferior buccal glands.
The =facial nerve= divides into its two terminal branches before
reaching the border of the jaw. The =superior buccal nerve= is the
larger of the two; it crosses the masseter much lower than in the horse.
The relatively small =inferior buccal nerve= runs beneath the parotid or
in the gland substance parallel with the border of the lower jaw,
crosses under the insertion of the sterno-cephalicus, and runs forward
along the depressor labii inferioris. At the point where it crosses the
facial vein and parotid duct it gives off an anastomotic branch to the
superior nerve. The =auriculo-palpebral nerve= is large.
The =vagus= bears—in addition to the relatively large =jugular
ganglion=—a =ganglion nodosum= at the point of origin of the superior
laryngeal nerve. The trunk is large. The =pharyngeal branch= is large
and anastomoses with the superior and external laryngeal nerves. The
latter commonly arises directly from the trunk. The =superior œsophageal
trunk= communicates with the splanchnic nerve, contributes twigs to the
hepatic plexus, and ramifies chiefly on the right surface of the rumen
and the adjacent surface of the abomasum. The =inferior œsophageal
trunk= supplies branches to the hepatic plexus and to all the divisions
of the stomach.
The =spinal accessory nerve= presents two special features. The part
which joins the jugular ganglion bears a small ganglion. The ventral
branch supplies both parts of the sterno-cephalicus.
The =hypoglossal nerve= is large. It is connected with the ventral
division of the first cervical nerve by a branch of considerable size,
and detaches a long branch which runs backward along the carotid artery.
The =spinal nerves= resemble those of the horse in origin and general
arrangement. The thoracic nerves number thirteen pairs. The more
important differences in the limb-plexuses and their branches are as
follows:
The =brachial plexus= is formed by the ventral branches of the last
three cervical and first thoracic nerves; the second thoracic nerve
furnishes no root, but the ventral branch of the sixth cervical goes
almost entirely to the plexus after giving off the nerve to the
rhomboideus and the cervical part of the serratus magnus.
The differences in the nerves above the elbow are not of sufficient
moment to receive notice in this brief account, but below this point
there are naturally important special features correlated chiefly with
the arrangement of the digits.
The =radial nerve= is continued below the elbow by a large =cutaneous
branch= (N. cutaneus antibrachii dorsalis) which emerges at the lower
border of the external head of the triceps and descends on the dorsal
aspect of the limb. It communicates above the carpus with the cutaneous
branch of the median nerve and terminates in three =dorsal digital
nerves=; two of these descend along the axial or interdigital side of
the dorsal surface of the chief digits, and the third along the inner
(abaxial) side of the inner chief digit.
[Illustration:
FIG. 530.—NERVES OF DISTAL PART OF RIGHT FORE LIMB OF OX, ANTERIOR
VIEW (SCHEMATIC).
_p_, Dorsal digital nerves.
]
[Illustration:
FIG. 531.—NERVES OF DISTAL PART OF RIGHT FORE LIMB OF OX, POSTERIOR
VIEW (SCHEMATIC).
_p_, Volar digital nerves.
]
The =ulnar nerve= divides at a variable distance down the forearm into
two branches. The =dorsal= or =superficial branch= emerges between the
tendons of the external and middle flexors of the carpus, and is
continued as the =external dorsal digital nerve= on the outer chief
digit. The =volar= or =deep branch= descends along the superficial
digital flexor, gives a branch to the suspensory ligament below the
carpus, and unites with the external branch of the median nerve to form
the =external volar digital nerve=.
The =median nerve= is much larger than the ulnar. It passes beneath the
pronator teres, descends the forearm as in the horse, and divides in the
distal part of the metacarpus into two branches. The =internal branch=
gives twigs to the inner small digit and is continued on the inner side
of the volar surface of the inner chief digit as the =internal volar
digital nerve= (N. digitalis medialis digiti III); it also concurs with
the outer branch in forming the two digital nerves which descend along
the interdigital aspect of the chief digits. The =external branch= is
larger. It bifurcates, and one division unites with the twig from the
internal branch to form a common digital trunk. From the latter two
digital nerves proceed as mentioned above; these are the =external= and
=internal volar digital nerves= of the internal and external chief
digits respectively (N. digitalis volaris lateralis digiti III, medialis
digiti IV). The other division unites with the volar branch of the ulnar
nerve to form the =external volar digital nerve= of the external chief
digit (N. digitalis lateralis digiti IV).
[Illustration:
FIG. 532.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF OX, ANTERIOR
VIEW (SCHEMATIC).
_p_, Dorsal digital nerves.
]
[Illustration:
FIG. 533.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF OX, POSTERIOR
VIEW (SCHEMATIC).
_p_, Plantar digital nerves.
]
The =lumbo-sacral plexus= and its branches to the pelvis and thigh
present no very striking special features.
The =superficial peroneal nerve= is much larger than in the horse. After
crossing beneath the peroneus longus it passes down on the front of the
tarsus and metatarsus and divides into three branches. The internal and
external branches descend as the =internal= and =external dorsal digital
nerves= on the chief digits. The larger middle branch joins a branch of
the deep peroneal nerve in the interdigital space, and from this union
proceed the =dorsal digital nerves= which descend on the opposed
surfaces of the chief digits.
The =deep peroneal nerve= descends in the leg as in the horse and
continues down the anterior groove of the metatarsus with the dorsal
metatarsal artery. Its terminal branches concur with branches from the
superficial peroneal nerve in the formation of the two axial =dorsal
digital nerves= (N. dig. dors. lat. dig. III et dig. dors. med. dig. IV
pedis), and with a branch of the internal plantar nerve in the formation
of corresponding plantar digital nerves.
The =tibial nerve= divides at the back of the hock into internal and
external plantar nerves. The =internal plantar nerve= descends between
the superficial flexor tendon and the suspensory ligament and divides
into two branches; the inner branch descends as the =internal plantar
digital nerve= (N. dig. plant. med. dig. III) along the inner side of
the flexor tendons of the inner chief digit; the outer branch turns
around the flexor tendons to reach the interdigital space, where it
concurs with a branch of the deep peroneal nerve in the formation of two
=axial plantar digital nerves= (N. dig. plant. lat. dig. III et dig.
plant. med. dig. IV) which descend on the opposed surfaces of the chief
digits. The =external plantar nerve= descends along the outer border of
the flexor tendons, gives a branch to the suspensory ligament and to the
external small digit, and continues along the outer face of the external
digit as the =external plantar digital nerve= (N. dig. plant. lat. dig.
IV).
The =sympathetic system= closely resembles that of the horse in its
general arrangement, and only a few differential features will receive
attention. The =superior cervical ganglion= is closer to the cranial
base and is thicker than in the horse; its branches to the carotid and
cavernous plexuses are large, and no connection is formed with the
spinal accessory nerve. The =cervical trunk= is smaller than in the
horse, and arises by two or three bundles from the superior cervical
ganglion behind its middle. The =inferior cervical ganglion= is
distinctly separable from the first thoracic; the latter is large. There
are thirteen pairs of =thoracic ganglia=. The =cœliaco-mesenteric
ganglia= are plexiform, not compact. There are five pairs of =sacral
ganglia=, and the right and left trunks are connected here by transverse
anastomoses.
THE NERVOUS SYSTEM OF THE PIG
The =spinal cord= weighs about 42 grams (Ellenberger-Baum). It is almost
circular in cross-section, except at the enlargements, where it is
somewhat flattened dorso-ventrally. The conus medullaris extends to the
anterior part of the third sacral segment. The epidural space is
occupied by a large quantity of fat.
The =brain= in adults of medium size weighs about 125 grams (ca. 4 to 4½
ounces). When viewed from above, it is seen to have an elongated oval
form. The occipital poles overlie the cerebellum to a small extent only;
the frontal poles are rounded and relatively large, but do not conceal
the ends of the olfactory bulbs. The =medulla= is relatively broad. The
cuneate tubercle is very large and is limited externally by a groove.
The corpus trapezoideum is very wide laterally. The =pons= is less
prominent than in the ox. The =cerebellum= is very wide and short. Its
anterior face is flattened and presents a depression for the corpora
quadrigemina. The vermis is large. The hemispheres consist of an inner
large and an outer small part. The =cerebral peduncles= are very short.
The posterior corpora quadrigemina are wide apart, rounded, and
relatively large. The internal geniculate body is prominent. The
=cerebral hemispheres= are somewhat bean-shaped in lateral profile, the
convex border being dorsal. The arrangement of the gyri and sulci is
simpler than in the horse or ox. The principal fissures are as follows:
1. The =lateral fissure= (of Sylvius) begins at the sulcus rhinalis and
runs upward and somewhat backward on the depressed part of the lateral
surface of the hemisphere; it appears unbranched on superficial
examination, but when the gyrus which almost completely conceals the
insula is raised, an anterior branch is exposed which forms the dorsal
boundary of the insula.
2. The =suprasylvian fissure= pursues a curved course approximately
parallel with the dorso-medial border of the hemisphere. Its posterior
end is separated by a short interval from the sulcus rhinalis posterior.
From its highest point a branch proceeds obliquely upward and forward,
crosses the dorso-medial border, and joins the splenial fissure.
3. The =diagonal fissure= crosses the anterior part of the lateral
surface. It is directed obliquely downward and backward.
4. The =coronal fissure= is constant and deep. It is directed upward and
inward over the frontal pole, continues backward near the dorso-medial
border, and usually ends by passing obliquely over the border to the
inner surface of the hemisphere.
5. The =presylvian fissure= begins—apparently as a branch of the sulcus
rhinalis anterior—about 2 cm. in front of the lateral fissure, and
curves over the lateral aspect of the frontal pole.
[Illustration:
FIG. 534.—CEREBRAL HEMISPHERES OF PIG, DORSAL VIEW.
_a_, Upper part of lateral fissure (of Sylvius); _b_, cruciate
fissure; _c_, suprasylvian fissure, with its anterior branch (_c′_)
and upper branch (_c″_); _d_, diagonal fissure; _e_, coronal
fissure; _f_, presylvian fissure; _g_, marginal fissure; _h_,
ectomarginal fissure; _i_, entomarginal fissure. (After Ellenberger,
in Leisering’s Atlas.)
]
6. The =marginal fissure= begins behind the cruciate fissure close to
the dorso-medial border and extends in a gentle curve backward almost to
the occipital pole.
7. The =ectomarginal fissure= lies above and nearly parallel to the
posterior part of the suprasylvian fissure.
8. The =entomarginal fissure= lies along the posterior part of the
dorso-medial border.
9. The =calloso-marginal fissure= consists of two separate parts. The
more extensive posterior part is termed the =splenial fissure=. It
extends from the tentorial aspect of the hemisphere in a direction
parallel with the corpus callosum nearly to the middle of the medial
surface; it is continued by the cruciate fissure and is also connected
with the suprasylvian and coronal fissures by branches which pass
obliquely upward and forward. The anterior part, the =genual fissure=,
lies about midway between the anterior part of the corpus callosum and
the dorso-medial border.
10. The =cruciate fissure= is short and shallow. It runs obliquely
upward and forward from the anterior end of the splenial fissure on the
inner surface of the hemisphere.
11. The =sulcus rhinalis= extends in an undulating manner along the
entire lower part of the lateral surface of the hemisphere and forms the
upper limit of the rhinencephalon.
The =olfactory bulbs= are very large and the =tracts= extremely broad
and short. The trigonum olfactorium is so prominent as to be termed the
=tuberculum olfactorium=.
The =cranial nerves= present the following special features:
The =third=, =fourth=, =sixth=, and the =ophthalmic= and =maxillary
divisions= of the fifth nerve, emerge together as in the ox.
The =lacrimal nerve= resembles that of the horse, the =frontal= that of
the ox. The =naso-ciliary nerve= is relatively large and sends numerous
filaments to the ocular muscles. The =maxillary nerve= has a very short
course in the pterygo-palatine fossa. The =infraorbital nerve= is large
in correlation with the development of the snout which receives numerous
branches. The =mandibular nerve= emerges through the foramen lacerum
anterius. The =superficial temporal nerve= is small; according to Moussu
it furnishes the excito-secretory fibers to the upper part of the
parotid gland, while those going to the lower part are derived from the
mylo-hyoid nerve.
[Illustration:
FIG. 535.—NERVES OF DISTAL PART OF RIGHT FORE LIMB OF PIG, ANTERIOR
VIEW (SCHEMATIC).
_c_, Dorsal common digital nerves; _p_, dorsal proper digital nerves.
]
[Illustration:
FIG. 536.—NERVES OF DISTAL PART OF RIGHT FORE LIMB OF PIG, POSTERIOR
VIEW (SCHEMATIC).
_p_, Volar proper digital nerves.
]
The =inferior buccal nerve= passes downward and forward under cover of
the parotid gland and accompanies the parotid duct, with which it turns
around the lower border of the jaw in front of the masseter.
The =vagus= bears a =jugular ganglion= and a =ganglion nodosum=; the
latter occurs at the point of origin of the superior laryngeal nerve,
and may be as large as a small pea. Proximal to this the vagus is easily
divided into two strands, one of which is the accessory component. The
œsophageal trunks form a posterior œsophageal plexus, as in man, from
which two nerves issue. The inferior nerve is small and ramifies on the
parietal surface of the stomach. The superior trunk is much larger; it
gives branches to the stomach, crosses the lesser curvature of that
organ, and joins the solar plexus.
The =hypoglossal nerve= may present a small dorsal root, on which there
is a minute hypoglossal ganglion (of Froriep).
The =spinal nerves= number on each side eight in the cervical region,
fourteen (commonly) in the thoracic, seven in the lumbar, and four in
the sacral. Some of the special features of the nerves of the limbs are
as follows:
The =brachial plexus= is derived from the same nerves as in the ox, but
the root furnished by the sixth cervical is relatively smaller. The
plexus consists of two parts, the upper of which emerges above the
scalenus, the lower between the two parts of that muscle. The more
important differences in the nerves emanating from the plexus from the
arrangement in the ox occur in the lower part of the limb. The cutaneous
branch of the =radial nerve= divides at the carpus into branches which
concur with the dorsal branch of the ulnar nerve in supplying the
=dorsal digital nerves=, two for each digit. The =volar digital nerves=,
also two for each digit, are formed by the terminal branches of the
=median nerve= and the volar or deep branch of the =ulnar nerve=. The
formation and arrangement of the digital nerves are indicated in the
annexed schematic figures.
[Illustration:
FIG. 537.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF PIG, ANTERIOR
VIEW (SCHEMATIC).
_p_, Dorsal proper digital nerves.
]
[Illustration:
FIG. 538.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF PIG, POSTERIOR
VIEW (SCHEMATIC).
_p_, Plantar proper digital nerves.
]
The =lumbo-sacral plexus= is derived from the ventral branches of the
last three lumbar and first sacral nerves. The distribution of the
branches of the plexus differs chiefly in the distal part of the limb.
The =superficial peroneal nerve= is large and terminates by forming the
greater part of the =dorsal digital nerves=. The latter, two for each
digit, are also in part formed by the terminal branches of the =deep
peroneal nerve=.
The =tibial nerve= divides at the tarsus into =internal= and =external
plantar nerves=. The latter divide to form the =plantar digital nerves=,
two for each digit. In addition, the external plantar nerve supplies a
branch to the dorsal aspect of the outer (fifth) digit. The arrangement
of the digital nerves is indicated by the annexed schematic figures.
The =sympathetic system= of the pig has received very little attention
from anatomists. The =superior cervical ganglion= is long and fusiform.
It gives off filaments which join the vagus near the ganglion nodosum.
The =cervical trunk= is short and relatively larger than in the ox; it
is inclosed in a common sheath with the vagus in the neck and separates
from that nerve to join the =middle cervical ganglion= at the thoracic
inlet.
THE NERVOUS SYSTEM OF THE DOG
The =spinal cord= is almost circular in cross-section except at the
well-marked cervical and lumbar enlargements, where it is compressed
dorso-ventrally. The conus medullaris lies over the junction of the
sixth and seventh lumbar vertebræ. The length of the cord of a rather
large dog was found to be about 38 cm.; of this, the cervical part was
11 cm., the thoracic 17.4 cm., the lumbar about 7 cm., and the
sacro-coccygeal about 2.6 cm. (Flatau-Jacobson).
[Illustration:
FIG. 539.—BASE OF BRAIN OF DOG.
_a_, Olfactory bulb; _a′_, _a″_, external and internal olfactory
tracts; _b_, optic nerve; _c_, oculomotor nerve; _d_, trochlear
nerve; _e_, trigeminus; _f_, abducens; _g_, facial; _h_, auditory;
_i_, glosso-pharyngeal; _k_, vagus; _l_, spinal accessory; _m_,
hypoglossal; _2_, trigonum olfactorium; _3_, anterior perforated
substance; _4_, tuber cinereum and infundibulum; _4′_, mammillary
body; _5_, pyriform lobe; _6_, temporal lobe; _7_, parietal lobe;
_8_, frontal lobe; _9_, pons; _10_, medulla oblongata; _11_,
cerebellum; _12_, cerebral peduncle; _13_, occipital lobe.
(Ellenberger-Baum, Anat. d. Hundes.)
]
[Illustration:
FIG. 540.—BRAIN STEM OF DOG, DORSAL VIEW.
_a_, Spinal cord; _b_, dorsal median groove; _c_, _c′_, funiculus
gracilis; _c″_, clava; _d_, _d′_, funiculus cuneatus; _d″_,
tuberculum cuneatum; _e_, funiculus lateralis; _e′_, tuberculum
Rolandi; _f_, medulla oblongata; _I_, _II_, _III_, floor of fourth
ventricle (fossa rhomboidea); _g_, limiting groove; _h_, median
fissure; _i_, eminentia medialis; _k_, ala cinerea; _l_, _l′_, pons;
_m_, posterior peduncle, and _n_, middle peduncle of cerebellum
(cut); _o_, anterior peduncle of cerebellum; _p_, _p′_, corpora
quadrigemina, anterior and posterior; _q_, _q′_, peduncles (brachia)
of corpora quadrigemina; _r_, thalamus; _s_, massa intermedia; _t_,
stria medullaris; _u_, anterior tubercle of thalamus; _v_, pulvinar;
_w_, corpus geniculatum laterale; _x_, corpus geniculatum mediale.
(After Ellenberger, in Leisering’s Atlas.)
]
The =brain= weighs about 60 to 70 g. in dogs of medium size, but there
is, of course, a wide range of weight in the different breeds. Thus in
small terriers the weight is 30 g. or even less, while in very large
dogs it may exceed 150 g. It corresponds much more closely with the
cranium in size and general form than in the animals previously
described; this is specially true of the small breeds, in which the bony
crests and frontal sinuses are little developed.
The =medulla= is broad and thick. Its ventral surface is strongly convex
from side to side. The pyramids are large and prominent and are limited
by distinct median and lateral grooves. The olivary eminence is a well
defined oval elevation situated between the pyramid and the superficial
origin of the hypoglossal nerve. The external arcuate fibers form a wide
band which crosses the lateral surface obliquely upward and forward, and
obscures the groove which limits the restiform body externally. The
cuneate tubercle is distinct. The rhomboid fossa is deep and narrow.
[Illustration:
FIG. 541.—PART OF CROSS-SECTION OF BRAIN OF DOG, PASSING THROUGH
GANGLION HABENULÆ.
_Al_, Ansa lenticularis of thalamic radiation; _C a d_, dorsal end of
hippocampus; _C a v_, ventral end of same; _C c_, corpus callosum;
_C g m_, corpus geniculatum mediale; _C m_, corpus mammillare; _F i
d_, fimbria; _F i v_, ventral part of fimbria; _G h_, ganglion
habenulæ; _M B_, fasciculus retroflexus; _P p_, pes pedunculi; _T
h_, thalamus; _T o_, tractus opticus; _T t_, habenula; _V A_,
fasciculus thalamo-mammillaris; _V F_, fornix ventralis; _II_,
lateral ventricle; _III_, third ventricle. (After Probst.)
]
The =pons= is relatively small. The =corpus trapezoideum= is very wide
and is divided by the pyramids into two lateral parts. The =cerebellum=
is very broad, but is low and also compressed from before backward.
Rather more than half of it is overlapped by the cerebral hemispheres.
The anterior surface is accurately adapted to the concave tentorial
surfaces of the hemispheres and to the posterior corpora quadrigemina
and their commissure. The posterior surface is almost vertical and is
convex centrally and flattened laterally. The vermis is prominent and in
general well defined, although it is connected in its middle part with
the hemispheres. The latter are three-sided and consist of four lobules.
The anterior peduncles are very short.
The =posterior corpora quadrigemina= are large, very wide apart, and
prominent, and are connected by a curved commissure. The =internal
geniculate body= is large. In the deep interpeduncular fossa are two
small bands which indicate the course of the fasciculi retroflexi,
tracts which connect the habenular and interpeduncular ganglia. The
=mammillary body= is double. The =tuber cinereum= is relatively large.
The =pituitary body= is circular and rather small.
The =cerebral hemispheres= are very broad behind and diminish in width
anteriorly; there is a sudden narrowing at the frontal poles, which are
flattened laterally. The tentorial surfaces are concave and form a deep
cavity which receives the anterior part of the cerebellum. The
arrangement of the fissures and gyri is simpler than in the animals
previously examined. The chief fissures are as follows:
1. The =lateral fissure= (of Sylvius) extends upward and backward from
the sulcus rhinalis a little behind the middle of the lateral surface of
the hemisphere.
2. The =ectosylvian fissure= has approximately the shape of an inverted
u, and curves over the lateral fissure. It is regarded as consisting of
three parts—anterior, middle, and posterior (F. ectosylvia anterior,
media, posterior).
3. The =suprasylvian fissure= lies above and approximately concentric
with the preceding. It also consists of three parts—anterior, middle,
and posterior.
4. The =ectomarginal= or =collateral fissure= runs forward on the dorsal
aspect of the hemisphere almost parallel with the dorso-medial border. A
little in front of the middle of the surface it gives off a short
=ansate fissure= (F. ansata) which runs obliquely inward and forward,
and is continued by the coronal fissure.
[Illustration:
FIG. 542.—CEREBRUM OF DOG, DORSAL VIEW.
_a_, End of lateral fissure (of Sylvius); _b_, ectosylvian fissure;
_c_, _c′_, _c″_, suprasylvian fissure; _d_, fissura ansata minor;
_e_, ectolateral fissure; _f_, ectomarginal or collateral fissure;
_g_, fissura ansata; _h_, coronal fissure; _i_, medilateral fissure;
_k_, entomarginal fissure; _l_, postcruciate fissure; _m_, cruciate
fissure; _o_, presylvian fissure; _p_, fissura prorea. (After
Ellenberger, in Leisering’s Atlas.)
]
[Illustration:
FIG. 543.—FISSURES OF LATERAL SURFACE OF CEREBRUM OF DOG, RIGHT SIDE.
_a_, Fissura prorea; _b_, frontal fissure; _c_, olfactory fissure;
_d_, _d′_, sulcus rhinalis; _e_, presylvian fissure; _f_,
precruciate fissure; _g_, postcruciate fissure; _h_, cruciate
fissure; _i_, lateral fissure (of Sylvius); _k_, _k′_, _k″_,
suprasylvian fissure; _l_, _l′_, _l″_, ectosylvian fissure; _m_,
fissura ansata minor; _n_, ectomarginal or collateral fissure; _o_,
fissura ansata; _p_, coronal fissure; _q_, ectolateral fissure; _r_,
medilateral fissure; _s_, entomarginal fissure. (After Ellenberger,
in Leisering’s Atlas.)
]
[Illustration:
FIG. 544.—RIGHT CEREBRAL HEMISPHERE OF DOG, INNER SIDE.
_1_, Corpus callosum; _1′_, genu, _1″_, splenium of corpus callosum;
_a_, genual fissure; _b_, splenial fissure; _c_, suprasplenial
fissure; _d_, hippocampal fissure; _e_, sulcus corporis callosi;
_f_, postsplenial fissure; _g_, lesser cruciate fissure; _h_,
cruciate fissure. (After Ellenberger, in Leisering’s Atlas.)
]
5. The =coronal fissure= is the continuation of the ectomarginal. It
runs forward and downward, curving around the cruciate fissure, and ends
behind the middle of the presylvian fissure.
6. The =ectolateral fissure= lies between the posterior part of the
ectomarginal fissure and the suprasylvian fissure.
7. The =entomarginal fissure= lies between the anterior part of the
ectomarginal fissure and the dorso-medial border. It is often indistinct
and not rarely absent.
8. The =presylvian fissure= begins at the sulcus rhinalis, a little in
front of its middle, and curves over the anterior third of the lateral
surface of the hemisphere in front of the coronal fissure.
9. The =cruciate fissure= is the deepest and most characteristic. It
cuts deeply into the anterior third of the dorso-medial border and runs
almost straight outward. It is continuous on the inner surface of the
hemisphere with the calloso-marginal or splenial fissure.
10. The =sulcus rhinalis= is continued on the tentorial surface of the
hemisphere by the occipito-temporal fissure. Anteriorly it is prolonged
as the olfactory fissure, which is concealed by the olfactory bulb and
tract.
[Illustration:
FIG. 545.—DEEP DISSECTION OF HEAD OF DOG, SHOWING ESPECIALLY
TRIGEMINAL AND HYPOGLOSSAL NERVES.
_a_, Hypoglossal nerve; _b_, cervical branch of _a_; _c_, mandibular
division of trigeminus; _d_, lingual nerve; _e_, nerve to
submaxillary gland; _f_, deep temporal nerve; _g_, pterygoid nerve;
_h_, buccinator nerve (cut); _i_, inferior alveolar or dental nerve;
_k_, staphyline branch of lingual nerve; _l_, chorda tympani; _m_,
mylo-hyoid nerve; _n_, sphenopalatine nerve; _o_, lesser palatine
nerve; _p_, great palatine nerve; _q_, infraorbital nerves; _r_,
subcutaneus malæ; _s_, branch of oculomotor nerve to inferior
oblique muscle; _t_, lacrimal nerve; _u_, frontal nerve; _v_,
trochlear nerve; _w_, abducens; _1_, carotid artery; _2_, lingual
artery; _3_, internal maxillary artery; _4_, thyro-pharyngeus
muscle; _5_, hyo-pharyngeus muscle; _6_, thyro-hyoideus; _7_,
sterno-hyoideus; _8_, baseo-glossus. _9_, genio-hyoideus; _10_,
genio-glossus; _11_, stylo-glossus; _12_, pterygoideus internus;
_13_, outline of submaxillary gland (dotted); _14_, atlas; _15_,
bulba ossea; _16_, zygomatic arch (dotted); _17_, rectus oculi
inferior; _18_, obliquus oculi inferior. (Ellenberger-Baum, Anat. d.
Hundes.)
]
11. The =calloso-marginal= or =splenial fissure= is parallel with the
splenium and middle part of the corpus callosum on the inner surface of
the hemisphere. It is continuous in front with the cruciate fissure and
runs downward and outward across the tentorial surface to join the
occipito-temporal fissure and sulcus rhinalis. It gives off from its
highest part the short lesser or accessory cruciate fissure.
12. The =suprasplenial fissure= runs almost parallel with the posterior
part of the calloso-marginal fissure on the inner and tentorial surfaces
of the hemisphere.
The =olfactory bulb= is large and is strongly compressed laterally; its
anterior end projects beyond the frontal pole of the hemisphere. The
tract is short and is also flattened laterally. Both contain a narrow
cavity which communicates with the lateral ventricle. The =pyriform
lobe= is large and rounded.
The =cranial nerves= present the following special features which are
worthy of notice:
The =ophthalmic nerve= gives off lacrimal, frontal, long ciliary,
ethmoidal, and infratrochlear branches. The =lacrimal nerve= arises from
the ophthalmic at its origin;[215] its recurrent branch emerges at the
orbital ligament and concurs with the zygomatic and frontal nerves in
the formation of the anterior auricular plexus. The =frontal nerve=
emerges from the orbit in front of the upper end of the orbital
ligament, ramifies in the upper lid and the adjacent skin of the
forehead, and sends branches backward to the anterior auricular plexus.
The =long ciliary nerve= accompanies the optic nerve and divides into
several branches which pierce the posterior part of the sclera. The
=ethmoidal nerve= gives off internal nasal branches and ends in the
muzzle. The =infratrochlear nerve= runs forward between the internal
straight and the superior oblique muscles of the eye and ramifies on the
face in the vicinity of the inner canthus.
[Illustration:
FIG. 546.—NERVES OF FACE OF DOG. PAROTID GLAND IS REMOVED.
_a_, Facial nerve; _b_, posterior auricular nerve; _c_, internal
auricular nerve; _d_, digastric nerve; _e_, inferior buccal nerve;
_f_, cervical branch of facial; _g_, auriculo-palpebral; _h_,
superior buccal nerve; _i_, temporal branch; _k_, _k′_, _k″_,
zygomatic branch; _l_, auriculo-temporal; _m_, malar branch of _l_;
_n_, buccinator nerve; _o_, mylo-hyoid branch; _p_, subcutaneus
malæ; _q_, lacrimal nerve; _r_, frontal nerve; _s_, infratrochlear
nerve; _t_, infraorbital nerve; _1_, paramastoid process; _2_,
digastricus muscle; _3_, base of concha; _4_, masseter; _5_,
zygomaticus; _6_, scutularis; _7_, zygomatic arch; _8_, maxilla.
(Ellenberger-Baum, Anat. d. Hundes.)
]
The =maxillary nerve=, after giving off the zygomatic, divides into
infraorbital and sphenopalatine branches. The =zygomatic nerve= emerges
through an opening in the upper part of the orbital ligament and
ramifies in the lower lid and on the adjacent surface of the face. The
=infraorbital nerves=, two in number, divide within the infraorbital
canal and after their emergence upon the face, thus forming seven or
eight =external nasal= and =superior labial branches=. The
=sphenopalatine nerve= gives off =lesser= and =greater palatine= and
=posterior nasal nerves=.
The =mandibular nerve= passes out through the foramen ovale. The
=superficial temporal nerve= divides into auricular, temporal, and malar
branches; the last-named crosses the masseter and ramifies with the
buccal nerves. The =mylo-hyoid nerve= is given off from the mandibular
nerve almost immediately after the latter emerges from the cranium; it
innervates the mylo-hyoideus and digastricus and gives off a branch
which turns around the lower jaw, joins the inferior buccal nerve, and
ramifies on the lateral surface of the face. The =inferior alveolar
nerve= arises by a common trunk with the mylo-hyoid; it gives off dental
branches and terminates in mental and inferior labial branches. The
=lingual nerve= supplies vasodilator and excito-secretory filaments to
the submaxillary and sublingual salivary glands; these fibers are
derived from the chorda tympani.
The =facial nerve= divides near the posterior border of the jaw into
four branches. The upper branch is the =auriculo-palpebral nerve=, which
divides after a very short course into anterior auricular and zygomatic
branches. The latter curves upward and forward across the zygomatic arch
toward the eye, and divides into branches which supply the eyelids and
nasal region and concur with the frontal and lacrimal nerves in forming
the anterior auricular plexus. The =superior buccal nerve= accompanies
the parotid duct across the masseter. The =inferior buccal nerve= runs
forward along the lower border of the masseter and the mandible. The two
nerves ramify on the cheek and anastomose with each other and the
infraorbital nerves to form a plexus from which branches go to the
muscles of the lips and nostrils. The =cervical branch= runs downward
and backward over the submaxillary gland and ramifies in the cervical
panniculus; it communicates with the inferior buccal nerve and sends
twigs to the parotido-auricularis muscle and the submaxillary space.
The =vagus= bears a =jugular ganglion= and a =ganglion nodosum=. The
latter is situated near the superior cervical ganglion on the rectus
capitis anterior major and dorsal to the carotid artery; it is
fusiform and may be about half an inch (ca. 1 to 1.5 cm.) long in a
large dog. In its course in the neck the nerve is inclosed with the
sympathetic trunk in a common sheath and is related ventrally to the
common carotid artery. The formation of dorsal and ventral =œsophageal
trunks= by the union of the dorsal and ventral divisions of the two
nerves takes place at the hiatus œsophageus. The =dorsal trunk=
concurs with branches of the solar plexus in forming the =posterior
gastric plexus= on the visceral surface of the stomach. The =ventral
trunk= ramifies on the parietal surface of the stomach, forming the
=anterior gastric plexus=, from which a considerable branch passes
along the lesser curvature to the pylorus. Some special features of
the collateral branches are: Two pharyngeal branches are present. The
=superior pharyngeal branch= arises from the vagus above the ganglion
nodosum. It passes under the deep face of the carotid artery and
descends on the lateral surface of the pharynx to end in the
crico-thyroid muscle. It furnishes a root of the inferior pharyngeal
branch, and communicates with the pharyngeal branch of the ninth and
with the superior laryngeal and hypoglossal nerves. The =inferior
pharyngeal branch= is formed by the union of roots derived from the
superior pharyngeal nerve and the ganglion nodosum, together with
filaments from the superior cervical ganglion. It crosses the side of
the pharynx behind the superior pharyngeal and ramifies on the
posterior constrictor of the pharynx and the origin of the œsophagus.
It contributes filaments to the pharyngeal plexus, communicates with
the recurrent nerve, and supplies twigs to the thyroid gland. The
=pharyngeal plexus= is formed on the lateral surface of the pharynx by
branches of the pharyngeal nerves and the communications above
described; branches from it innervate the muscles and mucous membrane
of the pharynx. The =superior laryngeal nerve= arises from the
ganglion nodosum and descends over the side of the pharynx, crossing
beneath the carotid artery and the superior laryngeal nerve. It passes
through the thyroid notch and ramifies in the mucous membrane of the
larynx. It communicates with the superior cervical ganglion and the
superior pharyngeal branch of the vagus, and gives twigs to the
hyo-pharyngeus muscle. Immediately after its entrance into the larynx
it gives off a large branch which, instead of uniting with the
recurrent as in the other animals, has a peculiar arrangement. It runs
back near the dorsal border of the thyroid cartilage, gives a branch
to the crico-arytenoideus posterior as it passes over that muscle, and
continues along the trachea internal to the recurrent nerve. At the
thoracic inlet it communicates with the inferior cervical ganglion and
continues backward to unite with the vagus at or near the point of
origin of the recurrent nerve. Its collateral filaments supply the
trachea and concur with the inferior pharyngeal branch in forming a
plexus on the cervical part of the œsophagus which innervates that
tube.[216] The =depressor nerve= is a very delicate filament which
arises usually from the superior laryngeal nerve and accompanies the
vago-sympathetic trunk to the thorax; its fibers reach the heart
through the cardiac nerves. The =pulmonary= and =posterior œsophageal
plexuses= are highly developed.
The =hypoglossal nerve= gives off a long branch (R. descendens) which
runs downward and backward across the pharynx and larynx, communicates
with the ventral branch of the first cervical nerve, and supplies the
thyro-hyoid, sterno-hyoid, and sterno-thyroid muscles.
The =spinal nerves= number thirty-six or thirty-seven on either side,
and comprise eight cervical, thirteen thoracic, seven lumbar, and five
or six coccygeal.
The =brachial plexus= (Fig. 487) is derived from the ventral branches of
the last four cervical and first thoracic nerves; the root supplied by
the fifth cervical nerve is very small. The roots unite at the lower
border of the scalenus. The more important special features in the
arrangement of the nerves which emanate from the plexus are as follows:
The =musculo-cutaneous nerve= passes between the coraco-brachialis and
the brachial artery and descends in the arm in front of the artery. At
the shoulder joint it gives off branches to the biceps and
coraco-brachialis, and in the lower third of the arm is connected with
the median nerve by an oblique branch. It terminates near the elbow by
dividing into a branch for the brachialis and a small cutaneous nerve
which passes down over the inner face of the elbow and, inclining a
little forward, descends over the deep fascia of the forearm to the
carpus.
The =radial nerve= descends behind the ulnar nerve, gives branches to
the extensors of the elbow, dips in between the internal head of the
triceps and the accessory head of the anconeus, winds around the arm,
and divides between the brachialis and the external head of the triceps
into two branches. The =deep branch= (R. profundus) supplies the
extensor and supinator muscles on the forearm. The =superficial branch=
(R. superficialis) emerges upon the flexor surface of the elbow and
divides into two branches which terminate by supplying two =dorsal
digital nerves= to each digit, except the fifth, which receives its
outer dorsal nerve from the ulnar. The inner branch descends along the
inner side of the cephalic vein to the carpus, where it divides into
dorsal digital nerves for the first digit and the inner side of the
second. The outer branch is much larger. It runs downward on the middle
of the front of the forearm and supplies the remaining dorsal digital
nerves except that to the outer side of the fifth digit.
The =ulnar nerve= is as large as or larger than the median, with which
it is united for some distance. At the distal third of the arm it
separates from the median and passes over the internal epicondyle of the
humerus. At the proximal part of the forearm it gives off the =dorsal
branch= (R. dorsalis), which supplies cutaneous twigs to the
dorso-lateral surface of the lower part of the forearm and carpus and
terminates as the =external dorsal digital nerve= of the fifth digit.
Descending under cover of the flexor carpi ulnaris, the ulnar nerve
inclines inward under the tendon of insertion of that muscle and divides
into superficial and deep branches. The =superficial branch= (R.
superficialis) runs downward along the outer border of the flexor
tendons, gives off the =external volar digital nerve of the fifth digit=
(N. dig. vol. lat. dig. V), and a branch (N. met. vol. IV) which
descends in the space between the fourth and fifth metacarpal bones and
unites with the deep branch. The =deep branch= (R. profundus) descends
in the carpal canal and divides under the deep flexor tendon into its
terminal branches. The smaller of these supply the volar metacarpal
muscles. The larger terminals are the three =volar common digital
nerves= (Nn. dig. vol. comm. II, III, IV), which descend along the
second, third, and fourth intermetacarpal spaces, subdivide, and concur
with the volar metacarpal branches of the median nerve in forming the
=volar proper digital nerves= (Nn. dig. vol. proprii).
The =median nerve= descends behind the brachial artery, passes over the
internal epicondyle of the humerus, then under the pronator teres, and
continues in the forearm under cover of the flexor carpi radialis. It
gives branches below the elbow to the flexor and pronator muscles, and
lower down a palmar branch to the skin on the inner and posterior aspect
of the carpus, and terminates between the superficial and deep flexor
tendons by dividing into three =volar metacarpal nerves= (N. met. vol.
I, II, III). These descend in the first, second, and third
intermetacarpal spaces and unite with the volar common digital nerves in
forming volar proper digital nerves. The arrangement of the digital
nerves is indicated in the annexed schematic figures.
[Illustration:
FIG. 547.—NERVES OF DISTAL PART OF RIGHT FORE LIMB OF DOG, ANTERIOR
VIEW (SCHEMATIC).
_p_, Dorsal proper digital nerves.
]
[Illustration:
FIG. 548.—NERVES OF DISTAL PART OF RIGHT FORE LIMB OF DOG, POSTERIOR
VIEW (SCHEMATIC).
_p_, Volar proper digital nerves.
]
The =lumbo-sacral plexus= is formed from the ventral branches of the
last five lumbar and first sacral nerves. The more important special
facts in regard to the nerves of the pelvic limb are as follows:
The =saphenous nerve= (Fig. 492) is relatively large, and, in fact,
might be considered as the continuation of the femoral nerve. It
descends at first in front of the femoral artery, then passes over the
lower part of the inner surface of the thigh with the saphenous artery,
continues down the leg with the dorsal branch of that vessel, and
anastomoses with branches of the superficial peroneal nerve. It supplies
cutaneous twigs from the stifle to the metatarsus.
The =peroneal nerve= separates from the tibial above the origin of the
gastrocnemius, runs downward and forward across the outer head of that
muscle, passes between the deep flexor of the digit and the peroneus
longus, and divides into superficial and deep branches. The =superficial
peroneal nerve= descends the leg along the peroneus tertius and longus,
gives off a =dorsal branch= to the first digit (N. cutaneus dorsalis
medialis), and divides at the proximal part of the metatarsus into three
=dorsal common digital nerves= (Nn. dig. pedis dors. comm. II, III, IV).
These descend with the superficial dorsal metatarsal arteries and concur
with branches of the deep peroneal nerve in forming =dorsal proper
digital nerves= (Nn. dig. ped. prop. dorsales). The =deep peroneal
nerve= passes down the leg with the anterior tibial vessels. It gives
twigs to the hock joint and the extensor brevis muscle, and divides into
three =dorsal metatarsal nerves= (Nn. met. dors. II, III, IV); these
descend with the corresponding arteries along the intermetatarsal spaces
and unite with the dorsal common digital nerves in supplying the dorsal
proper digital nerves.
[Illustration:
FIG. 549.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF DOG, ANTERIOR
VIEW (SCHEMATIC).
_p_, Dorsal proper digital nerves.
]
[Illustration:
FIG. 550.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF DOG, POSTERIOR
VIEW (SCHEMATIC).
_p_, Plantar proper digital nerves.
]
The =tibial nerve= divides at the tarsus into two plantar branches. The
=internal plantar nerve= descends along the inner border of the
superficial flexor tendon and divides near the middle of the metatarsus
into two branches. Of these, the internal branch constitutes the =first
plantar common digital nerve= (N. dig. comm. plant. I). The outer branch
descends on the superficial flexor tendon and divides into three
=plantar metatarsal nerves= (Nn. met. plant. II, III, IV), which unite
with the plantar common digital nerves. The =external plantar nerve=
passes down between the flexor tendons, sends twigs to the muscles on
the plantar surface of the metatarsus, and divides into three =plantar
common digital nerves= (Nn. dig. comm, plant. II, III, IV). These
descend with the deep plantar metatarsal arteries in the second, third,
and fourth intermetatarsal spaces, receive the plantar metatarsal
nerves, and divide into =plantar proper digital nerves=, which pass down
the opposed surfaces of the second to the fifth digits.
The =sympathetic system= presents few special features worthy of
mention. The =superior cervical ganglion= lies above the ganglion
nodosum close to the cranial base and internal to the origin of the
internal carotid and occipital arteries. It forms connections directly
or through the carotid plexus with the last seven cranial and first
cervical nerves. The =cervical trunk= unites with the vagus so
intimately as to form a vago-sympathetic trunk. There may be a small
=middle cervical ganglion= in front of the inferior cervical ganglion.
The latter is usually distinct from the first thoracic ganglion, which
is stellate and lies on the longus colli opposite the second rib and
intercostal space.
ÆSTHESIOLOGY
THE SENSE ORGANS AND COMMON INTEGUMENT
The =organs of the senses= (Organa sensuum) receive external stimuli and
conduct impulses to the brain which result in sensations of sight,
hearing, taste, smell, and touch. They consist essentially of specially
differentiated cells, the neuro-epithelium, and a conduction path which
is simple in the more generalized sense organs, elaborate in those which
are highly specialized—the eye and the ear.
THE SENSE ORGANS AND SKIN OF THE HORSE
THE EYE
The =eye= or =organ of vision= (Organon visus) in the broader sense of
the term comprises the eyeball or globe of the eye, the optic nerve, and
certain accessory organs associated therewith. The accessory organs
(Organa oculi accessoria) are the orbital fasciæ and muscles, the
eyelids and conjunctiva, and the lacrimal apparatus. These structures
will be considered in the order in which they may be most conveniently
examined, taking the horse as a type. The bony walls of the orbit have
been described in connection with the skull; the periorbita, a fibrous
membrane which incloses the eyeball together with its muscles, vessels,
and nerves, may be appropriately included in the account of the fasciæ.
[Illustration:
FIG. 551.—LEFT EYE OF HORSE.
_9_, Zygomatic arch; _10_, supraorbital depression; _12_, supraorbital
process; _27_, facial crest. (After Ellenberger-Baum, Anat. für
Künstler.)
]
THE EYELIDS AND CONJUNCTIVA
The =eyelids=, upper and lower (Palpebra superior et inferior), are
movable folds of integument situated in front of the eyeball. When
closed, they cover the entrance to the orbit and the anterior surface of
the eyeball. The upper lid is much more extensive and more movable than
the lower one, and its free edge is more concave. The interval between
the lids is termed the =palpebral fissure= (Rima palpebrarum). When the
eye is closed, it is an oblique slit about two inches (ca. 5 cm.) in
length; when open, it is biconvex in outline. The ends of the fissure
are the =angles= or =canthi=, and are distinguished as =internal= or
=nasal=, and =external= or =temporal= (Angulus oculi medialis,
lateralis). The external angle is rounded when the eye is open, but the
internal angle is narrowed to form a ᑐ-shaped bay or recess, termed the
=lacrimal lake= (Lacus lacrimalis). In this there is a rounded,
pigmented prominence known as the =lacrimal caruncle= (Caruncula
lacrimalis); it is about the size of a small pea and is covered with
modified skin, connected with that of the inner commissure, from which
project a number of hairs provided with sebaceous glands. The lids unite
on either side and form the =commissures=, internal and external
(Commissura palpebrarum medialis, lateralis). The =anterior surface= of
the lids (Facies anterior palpebrarum) is convex and presents a variable
number of long tactile hairs in addition to the ordinary but very short
hairs. A considerable number of tactile hairs are scattered over the
lower part of the lower lid, but on the upper lid they are very scanty.
The infrapalpebral depression (Sulcus infrapalpebralis) indicates
somewhat indistinctly the limit of the lower lid. The upper lid is
marked by two furrows when raised. The =posterior surface= (Facies
posterior palpebrarum) is adapted to the free surface of the eyeball and
is covered by the palpebral conjunctiva. The free border of the lid is
smooth and usually black. It has a well defined posterior margin (Limbus
palpebralis posterior), along which the ducts of the tarsal glands open.
The anterior margin (Limbus palpebralis anterior) bears stiff hairs
termed the cilia or eyelashes. On the upper lid the cilia are long and
numerous except at its inner third, where they are very small or absent.
On the lower lid the cilia are often scarcely distinguishable from the
ordinary hairs; in other cases they may be clearly seen except near the
external canthus, and are much finer and shorter than those of the upper
lid. The edge of each lid is pierced near the internal angle by a
minute, slit-like opening, the =punctum lacrimalis=, which is the
entrance to the lacrimal duct or canaliculus.
[Illustration:
FIG. 552.—VERTICAL, SECTION OF ANTERIOR PART OF EYE OF HORSE, WITH
LIDS HALF CLOSED.
_1_, Tarsal gland of upper lid; _2_, palpebral conjunctiva; _3_,
fornix conjunctivæ; _4_, levator palpebræ superioris; _5_,
orbicularis oculi; _6_, cornea; _7_, anterior chamber; _8_, iris;
_9_, _9′_, granula iridis; _10_, posterior chamber; _11_, ciliary
process; _12_, ciliary muscle; _13_, ciliary zone or suspensory lig.
of lens; _14_, chorioid; _15_, sclera; _16_, lens; _17_, root of
tactile hair. (After Bayer, Augenheilkunde.)
]
=Structure of the Eyelids.=—The skin of the eyelids is thin and freely
movable, except near the free edge, where it is more firmly attached.
The underlying subcutaneous tissue is destitute of fat. The =muscular
layer= consists chiefly of the elliptical bundles of the orbicularis
oculi, with which are associated fibers of the corrugator supercilii in
the upper lid and the malaris in the lower lid. At the inner side there
is a fibrous band, the =palpebral ligament=, which is attached to the
lacrimal tubercle and furnishes origin to some fibers of the
orbicularis. At the inner commissure a bundle detached from the
orbicularis passes inward behind the lacrimal sac, and is known as the
pars lacrimalis or Horner’s muscle. At the outer side an indistinct
palpebral raphé occurs where fibers of the orbicularis decussate. The
=fibrous layer= is thicker and denser along the free edge of the lid,
forming here the =tarsus=. The tarsus furnishes insertion to a layer of
unstriped muscle known as the tarsal muscle (of Müller). The =tarsal
glands= (Glandulæ tarsales) are partly embedded in the deep face of the
tarsus, and are visible when the lid is everted if the conjunctiva is
not too strongly pigmented. They are arranged in a linear series, close
together, and with their long axes perpendicular to the free edge of
each lid. In the upper lid they number forty-five to fifty; in the
lower, thirty to thirty-five. Each consists of a tubular duct beset with
numerous alveoli, in which a fatty substance, the =palpebral sebum=, is
secreted. The =palpebral conjunctiva= lines the posterior surface of the
eyelids.
[Illustration:
FIG. 553.—PIECE OF UPPER EYELID, INNER SURFACE.
_1_, Cilia; _2_, limbus palp. posterior; _3_, tarsal glands. (After
Ellenberger, in Leisering’s Atlas.)
]
[Illustration:
FIG. 554.—CARTILAGE OF THIRD EYELID OF HORSE, CONVEX SURFACE.
_1_, Gland; _2_, fat surrounding deep part of cartilage. (After
Ellenberger, in Leisering’s Atlas.)
]
The =conjunctiva= is the mucous membrane which lines the lids as
=palpebral conjunctiva= (C. palpebrarum) and is reflected upon the
anterior part of the eyeball as =bulbar conjunctiva= (C. bulbi); the
line of reflection is termed the =fornix conjunctivæ=. The palpebral
part is closely adherent to the tarsus, but is loosely attached further
back. It is papillated and is covered with stratified cylindrical
epithelium in which many goblet cells are present. In the fornix and its
vicinity there are tubular glands (of Henle). Near the inner angle there
are numerous lymph nodules. The conjunctiva of the outer part of the
upper lid is pierced near the fornix by the orifices of the excretory
ducts of the lacrimal gland. The bulbar conjunctiva is loosely attached
to the anterior part of the sclera and is pigmented in the vicinity of
the corneo-scleral junction. On the cornea it is represented by a
stratified epithelium.
When the lids are in apposition, the conjunctiva (including the
epithelium of the cornea) forms a complete =conjunctival sac=, as the
capillary space between the lids and the eyeball is termed.
The =third eyelid= (Palpebra tertia) is situated at the inner angle of
the eye (Figs. 551, 556). It consists of a semilunar fold of the
conjunctiva, known as the =membrana nictitans=, which covers and partly
incloses a curved plate of hyaline cartilage. Its marginal part is thin
and usually more or less pigmented. The cartilage has an elongated
quadrilateral outline. The part of it which lies in the membrana is wide
and thin. The deep part is narrower and thicker and is embedded in fat
at the inner side of the eyeball. Numerous minute lymph nodules occur in
the membrana nictitans, and the deep part of the cartilage is surrounded
by a gland which resembles the lacrimal gland in structure (Glandula
superficialis palpebæ tertiæ).
Ordinarily the third eyelid extends very little over the inner end of
the cornea, but when the eyeball is strongly retracted (as in tetanus)
the membrana is protruded over it so as to measure about an inch (ca.
2 to 3 cm.) in its middle. This effect results from the pressure of
the eyeball and its muscles on the fat which surrounds the deep part
of the cartilage.
=Vessels and Nerves.=—The =arteries= which chiefly supply the eyelids
and conjunctiva are branches of the ophthalmic and facial arteries, and
the blood is drained away by corresponding veins. The =sensory nerves=
are branches of the ophthalmic and maxillary divisions of the
trigeminus. The =motor nerves= to the orbicularis oculi, corrugator
supercilii, and malaris come from the facial nerve, the levator palpebræ
superioris is innervated by the oculomotor, and the unstriped muscle of
the lids by the sympathetic.
THE LACRIMAL APPARATUS
The =lacrimal apparatus= (Apparatus lacrimalis) comprises: (1) the
lacrimal gland, which secretes the clear lacrimal fluid; (2) the
excretory ducts of the gland; (3) the two lacrimal ducts or canaliculi,
lacrimal sac, and naso-lacrimal duct, which receive the fluid and convey
it to the nostril.
The =lacrimal gland= (Glandula lacrimalis) is situated between the
supraorbital process and the dorso-lateral surface of the eyeball (Fig.
438). It is flattened, oval in outline, and measures about two inches
(ca. 5 cm.) transversely and an inch or more (2.5 to 3 cm.) in the
sagittal direction. Its upper face is convex and is related to the
concave lower surface of the supraorbital process. The lower face is
concave in adaptation to the eyeball, from which it is separated by the
periorbita. The =excretory ducts= (Ductuli excretorii) are very small
and are twelve to sixteen in number; they open into the outer part of
the conjunctival sac along a line a little in front of the fornix
conjunctivæ superior. In appearance and structure the gland resembles
the parotid. It receives its blood-supply chiefly from the lacrimal
artery. The sensory nerve is the lacrimal, and the secretory fibers are
derived from the sympathetic.
The =puncta lacrimalia= are the entrances to the two lacrimal ducts.
Each is a fine slit-like opening (about 2 mm. long), situated close
behind the free edge of the lid and about a third of an inch (ca. 8 mm.)
from the internal canthus. The =lacrimal ducts= (Ductus lacrimales),
upper and lower, begin at the puncta and converge at the inner
commissure to open into the =lacrimal sac=. The latter (Saccus
lacrimalis) may be regarded as the dilated origin of the naso-lacrimal
duct. It occupies the funnel-like origin of the bony lacrimal canal, and
leads to the =naso-lacrimal duct= (Ductus naso-lacrimalis), which passes
forward and a little downward along the outer wall of the frontal sinus
and the nasal cavity and opens near the lower commissure of the nostril.
Its length is about ten to twelve inches (ca. 25 to 30 cm.). In the
first part of its course it is inclosed in the osseous lacrimal canal;
further forward it lies in the lacrimal groove of the maxilla, covered
at first by a plate of cartilage and then by the mucous membrane of the
middle meatus. The terminal part lies in the inferior turbinal fold and
opens on the skin of the floor of the nostril near the transition to
mucous membrane. Accessory openings may occur a little further back.
The first part of the duct, about 6 to 7 mm. in diameter, extends in a
gentle curve, convex dorsally, from the internal commissure toward a
point just above the level of the infraorbital foramen. The second
part (isthmus) is narrower (ca. 3 to 4 mm.); it extends forward and a
little ventrally about to a transverse plane through the first cheek
tooth and lies in the groove above the inferior turbinal crest. Beyond
this the duct inclines upward and widens very considerably, crosses
the nasal process of the premaxilla obliquely, and contracts at its
termination. The mucous membrane may present valvular folds, the most
distinct of which is situated at the origin.
THE PERIORBITA
The =periorbita= or ocular sheath is a conical fibrous membrane which
incloses the eyeball with its muscles, vessels, nerves, etc. Its apex is
attached around the optic and lacerated foramina, and its base is in
part attached to the bony rim of the orbit, in part continuous with the
fibrous layer of the lids. Its inner part, which is in contact with the
orbital wall, is thin; incorporated with it beneath the root of the
supraorbital process is the bar of cartilage around which the superior
oblique muscle is reflected. The outer part is thicker, and is
strengthened by an elastic band which is attached to the pterygoid crest
and furnishes origin to the thin unstriped orbital muscle. A quantity of
fat (Corpus adiposum extraorbitale) lies about the periorbita, and
within it is the intraorbital adipose tissue (Corpus adiposum
intraorbitale) which fills the interstices between the eyeball, muscles,
etc.
THE ORBITAL FASCIÆ AND OCULAR MUSCLES (Figs. 438, 439, 555)
The straight muscles of the eyeball and the oblique muscles in part are
inclosed in fibrous sheaths (Fasciæ musculares), formed by superficial
and deep layers of fascia, which are united by intermuscular septa in
the interstices between the muscles. The =superficial fascia= is thin;
it blends in front with the fibrous layer of the eyelids and is attached
behind around the optic foramen. The =deep fascia= consists anteriorly
of two layers, one of which is continuous with the fibrous tissue of the
lids, while the other is attached at the corneo-scleral junction.
The posterior part of the eyeball is covered by the =bulbar fascia= or
capsule of Tenon (Fascia bulbi), so that between them a lymph space
(Spatium interfasciale) is inclosed which communicates with the subdural
space along the course of the optic nerve.
The =levator palpebræ superioris= muscle[217] is a thin band about half
an inch in width which lies above the rectus superior. It is narrow at
its origin above and behind the ethmoidal foramen and ends by an
expanded tendon in the upper lid. Its action is to raise the upper lid.
The =recti oculi= (Mm. recti bulbi) are four in number and are
designated according to their positions as =superior=, =inferior=,
=internal=, and =external=. They are all band-like, arise close together
around the optic foramen, and diverge as they pass forward to the
eyeball. On reaching the latter they end in thin tendons which are
inserted into the sclera in front of the equator of the eyeball.
The =retractor oculi= (M. retractor bulbi) surrounds the optic nerve,
and is incompletely divided into four parts which alternate with the
recti. They arise around the optic nerve and are inserted into the
sclera behind the recti.
The =obliquus oculi superior= (M. obliquus bulbi dorsalis s. superior)
is the longest and narrowest of the ocular muscles. It arises near the
ethmoidal foramen and passes forward internal to the rectus internus.
Under the root of the supraorbital process it is reflected almost at a
right angle around a cartilaginous pulley (trochlea), which is attached
to the anterior part of the inner wall of the orbit, a bursa being
interposed here. The muscle is then directed outward and somewhat
forward, and ends in a thin tendon which passes between the rectus
superior and the eyeball, and is inserted into the sclera between the
superior and external recti, about half an inch behind the margin of the
cornea.
The =obliquus oculi inferior= (M. obliquus bulbi ventralis s. inferior)
is wide and much shorter than the recti. It arises from the inner wall
of the orbit in the small depression (Fossa muscularis) behind the
lacrimal fossa. It curves around the rectus inferior and is inserted
into the sclera near and partly beneath the rectus externus.
=Actions.=—The superior and inferior recti rotate the eyeball about a
transverse axis, moving the vertex of the cornea upward and downward
respectively. Similarly the internal and external recti rotate the
eyeball about a vertical axis, turning the vertex of the cornea inward
and outward respectively. The oblique muscles rotate the eyeball about a
longitudinal axis; the superior oblique raises the outer end of the
pupil, while the inferior oblique lowers it. The retractor as a whole
draws the eyeball backward, and its parts may separately reinforce the
corresponding recti. Also the four recti acting together will retract
the eyeball.
[Illustration:
FIG. 555.—VERTICAL, AXIAL SECTION OF ORBIT OF HORSE.
_a_, Eyelids; _b_, bulbar fascia (Tenon’s capsule); _c_, _c′_,
retractor bulbi; _d_, rectus oculi inferior; _e_, obliquus oculi
inferior (in cross-section); _f_, rectus oculi superior; _g_,
levator palpebræ superioris; _h_, obliquus oculi superior (in
cross-section); _i_, lacrimal gland; _k_, _k′_, periorbita; _l_,
superficial fascia; _m_, deep fascia; _n_, skin; _o_, retrobulbar
fat; _p_, extraorbital fat; _q_, temporalis muscle; _r_,
supraorbital process; _s_, cranial wall; _1_, cornea; _2_, sclera;
_3_, chorioidea; _4_, ciliary muscle; _5_, iris; _6_, granula
iridis; _7_, retina; _7′_, optic papilla; _8_, optic nerve; _9_,
crystalline lens; _10_, capsule of lens; _11_, ciliary zone; _12_,
posterior chamber; _13_, anterior chamber; _14_, conjunctiva bulbi;
_15_, vitreous body. (After Ellenberger, in Leisering’s Atlas.)
]
The actual movements of the eyeball are by no means so simple as might
be inferred from the foregoing general statements. Practically all
movements are produced by the coördinated actions of several muscles,
involving combinations which are quite complex and difficult to
analyze accurately. Further complication is caused by the fact that
the recti are not inserted at equal distances from the equator and the
axes of rotation of the oblique muscles do not correspond to the
longitudinal axis of the eyeball.
=Nerve-supply.=—The oculomotor nerve supplies the foregoing muscles,
with the exception of the rectus externus and obliquus superior, which
are innervated by the abducens and trochlearis respectively.
THE EYEBALL
The =eyeball= (Bulbus oculi) is situated in the anterior part of the
orbital cavity, protected in front by the eyelids and conjunctiva, in
its middle by the complete orbital ring, and related behind to the
bulbar fascia, fat, and ocular muscles.
It has the form approximately of an oblate spheroid, but is composed of
the segments of two spheres of different sizes. The anterior,
transparent, corneal segment has a radius of curvature of about 17 mm.,
and the posterior, opaque, scleral segment a radius of about 25 mm. The
anterior segment therefore projects more strongly, and the junction of
the two segments is marked externally by a broad, shallow groove, the
sulcus scleræ. The central points of the anterior and posterior
curvatures of the eyeball are termed respectively the =anterior= and
=posterior poles= (Polus anterior, posterior), and the line connecting
the poles is the =optic axis= (Axis oculi externa). The angle of
divergence of the optic axes is about 137 degrees. The =equator=
(Æquator) is an imaginary line drawn around the eyeball midway between
its poles, and =meridians= (Meridiani) are lines drawn around it through
the poles.
The average transverse diameter of the eyeball is about 5 cm., the
vertical about 4.5 cm., and the axial about 4.25 cm. The distance from
the anterior pole to the point of entrance of the optic nerve is about
3 cm.
[Illustration:
FIG. 556.—LEFT EYEBALL OF HORSE, _in situ_, AFTER REMOVAL OF UPPER AND
LOWER LIDS.
_9_, Zygomatic arch; _12_, supraorbital process; _19_, orbital fat;
_27_, facial crest. (After Ellenberger-Baum, Anat. für Künstler.)
]
The eyeball consists of three concentric tunics or coats, within which
three refractive media are inclosed.
THE FIBROUS TUNIC
The =fibrous tunic= (Tunica fibrosa oculi) is the external coat and is
composed of a posterior opaque part, the sclera, and a transparent
anterior part, the cornea.
The =sclera=, popularly termed the “white of the eye,” is a dense
fibrous membrane which forms about four-fifths of the fibrous tunic.
Thickest in the vicinity of the posterior pole (ca. 2 mm.), it thins at
the equator (ca. 0.4 mm.), and increases in thickness toward the
junction with the cornea (ca. 1.3 mm.). It is in general white, but may
have a bluish tinge in its thinnest parts. Its external surface
furnishes insertion to the ocular muscles and is covered by the
conjunctiva scleræ in its anterior part. The episcleral tissue, which is
richly supplied with vessels and nerves, attaches the conjunctiva to the
sclera; it is abundant and loosely meshed except at the junction with
the cornea. The inner surface is attached to the chorioid coat by a
layer of delicate, pigmented, connective tissue, the =lamina fusca=. The
anterior border is oval, the long axis being transverse, and is
continuous with the cornea. The transition from the opaque scleral
tissue to the transparent corneal substance occurs in such manner that
the sclera appears to form a groove (Rima cornealis), into which the
cornea fits somewhat as a watch-glass in the case. Near the
corneo-scleral junction there is a circular venous plexus, the =plexus=
s. =sinus venosus scleræ=, formerly called the canal of Schlemm. The
optic nerve passes through the posterior part of the sclera a little
below and external to the posterior pole. The opening for the nerve is
crossed by interlacing fibrous strands, forming the =lamina cribrosa
scleræ=.
The sclera consists of interlacing bundles of white fibrous tissue,
associated with which there are a few elastic fibers. The bundles are
arranged chiefly in meridional and equatorial layers. The very limited
blood-supply is derived from the ciliary arteries, and the veins open
into the venæ vorticosæ and ciliary veins. The lymphatics are
represented by intercommunicating cell spaces. The nerves are derived
from the ciliary nerves.
[Illustration:
FIG. 557.—VERTICAL SECTION OF EYEBALL OF HORSE, ABOUT ³⁄₂.
The contour of the crystalline lens is dotted.
]
The =cornea= forms the anterior fifth of the fibrous tunic. It is
transparent, colorless, and non-vascular. Viewed from in front it is
oval in outline, the long axis being transverse and the broad end
internal; it appears more nearly circular when viewed from behind. Its
=anterior surface= (Facies anterior) is convex and is more strongly
curved than the sclera; its central part is termed the =vertex corneæ=.
The =posterior surface= (Facies posterior) is concave; it forms the
anterior boundary of the anterior chamber, and is in contact with the
aqueous humor. The margin (limbus corneæ) joins the sclera; the latter
overlaps the cornea more in front than behind, and more above and below
than at the sides, thus explaining the difference in outline of the two
surfaces. The cornea is thinnest at the vertex.
The cornea consists, from before backward, of the following layers: (1)
The =epithelium corneæ= is continuous with that of the conjunctiva
scleræ, and is of the stratified squamous type. (2) The =lamina limitans
anterior= is merely a condensation of the next layer. (3) The
=substantia propria= forms the bulk of the cornea and is composed of
interlacing bundles of connective tissue, arranged in part in lamellæ
disposed parallel with the surface. In the amorphous cement substance
between the lamellæ are flattened connective-tissue cells, the corneal
corpuscles. These have branching processes which unite with those of
other cells, thus forming a protoplasmic network.[218] (4) The =lamina
elastica posterior=, also termed the membrane of Descemet or Demours, is
a thin and practically homogeneous membrane which is less intimately
attached to the substantia propria than the anterior lamina. It is
clear, glistening, and elastic. At the periphery the lamina divides into
three sets of fibers. The anterior fibers join the sclera, the middle
give attachment to the ciliary muscle, while the posterior pass into the
iris and form the =ligamentum pectinatum iridis=. (5) The =endothelium=
(cameræ anterioris) consists of a layer of flattened polygonal cells,
and is reflected on to the anterior surface of the iris.
The cornea is without =blood-vessels= except at its periphery, where the
terminal twigs of the vessels of the sclera and conjunctiva terminate in
loops. The =nerves= are derived from the ciliary nerves. They form a
plexus around the periphery (Plexus annularis), from which fibers pass
into the substantia propria, become non-medullated, and form the
fundamental or stroma plexus. From this perforating branches pass
through the anterior limiting layer and form a subepithelial plexus,
from which filaments ascend between the epithelial cells. Other branches
from the plexuses in the substantia propria end as fibrils which are in
close relation with the corneal corpuscles.
[Illustration:
FIG. 558.—TAPETUM OF HORSE.
_a_, Optic papilla; _b_, lower border of tapetum. (After Ellenberger,
in Leisering’s Atlas.)
]
THE VASCULAR TUNIC
The =vascular tunic= (Tunica vasculosa oculi) lies internal to the
fibrous coat; it comprises three parts—the chorioid, the ciliary body,
and the iris.
1. The =chorioid= (Chorioidea) is a thin membrane which lies between the
sclera and retina. It is in general rather loosely attached to the
sclera by the lamina fusca, but is intimately adherent at the point of
entrance of the optic nerve and less closely in places where the ciliary
vessels and nerves pass through. The inner surface is in contact with
the layer of pigmented cells of the retina, which adhere so closely to
the chorioid that they were formerly regarded as a part of the latter.
The general color of the chorioid is dark brown, but an extensive
semilunar area a little above the level of the optic papilla has a
remarkable metallic luster, and is termed the =tapetum= of the chorioid
(Tapetum chorioideæ). The appearance here varies in different
individuals, but the prevailing colors in most cases are iridescent blue
and green in various nuances shading into yellow. Posteriorly the
chorioid is perforated by the optic nerve, and anteriorly it is
continuous with the ciliary body.
The chorioid consists of four layers, which from without inward are as
follows: (1) The =lamina suprachorioidea= consists of interlacing fine
lamellæ of fibrous tissue, each containing a network of elastic tissue.
Among these are large-branched, pigmented, connective-tissue cells. The
spaces between the lamellæ are lined with endothelium, and form a system
of lymph-clefts which together form the perichorioid space (Spatium
perichorioideale). (2) The =lamina vasculosa= is the outer part of the
proper tissue of the chorioid. It contains the larger blood-vessels,
which are supported by connective-tissue and elastic fibers. (3) The
=lamina choriocapillaris= consists of an extremely rich network of
capillaries embedded in an almost homogeneous matrix. Between it and the
lamina vasculosa is a layer of fibro-elastic tissue, the =tapetum
fibrosum=, which causes the metallic luster mentioned above. (4) The
=lamina basalis= is very thin and transparent. It is composed of an
inner homogeneous part and an outer elastic part.
2. The =ciliary body= (Corpus ciliare), the middle part of the vascular
coat, connects the chorioid with the periphery of the iris. In
meridional section it has the form of a narrow triangle, the base of
which is next to the iris. On its inner side are the ciliary processes
and on its outer side the ciliary muscle. It consists of three parts—the
ciliary ring, ciliary processes, and ciliary muscle. The =ciliary ring=
(Orbicularis ciliaris) is the posterior zone, which is distinguished
from the chorioid mainly by its greater thickness and the absence of the
choriocapillaris. Its inner face presents numerous fine meridional
ridges, by the union of which the ciliary processes are formed. The
=ciliary processes= (Processus ciliares), more than a hundred in number,
form a circle of radial folds which surround the lens and furnish
attachment to the zonula ciliaris or suspensory ligament of the latter.
They are small at their origin on the ciliary ring and become much
thicker and higher toward their inner ends. The width of the circle
formed by them is narrower at the inner side than elsewhere. Their bases
extend forward to the periphery of the iris, and their inner ends are
close to the margin of the lens. They bear numerous secondary folds.
Their inner surface is covered by a continuation of the lamina basalis
of the chorioid, on which there are two layers of epithelial cells which
constitute the pars ciliaris retinæ. They consist of a rich network of
tortuous vessels supported in pigmented connective tissue. The =ciliary
muscle= (M. ciliaris) (Figs. 552, 555, 559) constitutes the outer part
of the ciliary body, and lies between the sclera and the ciliary
processes. It forms a circular band of unstriped muscle, the fibers of
which are for the most part directed meridionally. They arise from the
inner surface of the sclera and from the ligamentum pectinatum iridis
close to the corneo-scleral junction, and run backward along the sclera
to be inserted into the ciliary processes and ring. When the muscle
contracts, it pulls the processes and ring forward, thus slackening the
ciliary zone or suspensory ligament of the lens, and allowing the latter
to become more convex. This is the mechanism of accommodation for near
objects.
[Illustration:
FIG. 559.—VASCULAR TUNIC OF EYEBALL OF HORSE, FRONT VIEW.
The cornea is removed and the sclera is reflected in flaps. _1_,
Sclera; _1′_, lamina fusca; _2_, chorioidea; _2′_, ciliary veins;
_3_, ciliary muscle; _4_, iris; _5_, _5′_, granula iridis; _6_,
pupil, through which the lens is visible. (After Ellenberger, in
Leisering’s Atlas.)
]
In man the muscle has the form of a prismatic ring which is triangular
in meridional section, the base being directed toward the periphery of
the iris. It consists chiefly of meridional fibers, but a ring of
circular fibers forms the inner angle of its base. In the horse the
muscle is much less developed, and has the form of a flat band; it
does not contain circular fibers, but the arrangement is rendered more
or less plexiform by the existence of oblique and equatorial fibers.
3. The =iris= (Figs. 552, 557, 559) is a muscular diaphragm placed in
front of the lens, and is visible through the cornea. It is pierced
centrally by an elliptical opening, the =pupil= (Pupilla), which varies
in size during life and determines the amount of light admitted to act
on the retina. In strong light the vertical diameter of the pupil is
very short, but the opening is almost circular when the pupil is fully
dilated. The =ciliary border= (Margo ciliaris) or periphery of the iris
is continuous with the ciliary body and is connected with the
corneo-scleral junction by the ligamentum pectinatum iridis. The
ligament consists of strands of connective tissue which are attached
externally to the corneo-scleral junction. Its bundles interlace and
inclose spaces (Spatia anguli iridis) which are lined with endothelium
and communicate with the anterior chamber. The =pupillary border= (Margo
pupillaris) surrounds the pupil. Its upper part bears in its middle
several black masses of variable size, termed the =granula iridis= or
corpora nigra; similar, but much smaller, projections may be seen on the
lower margin of the pupil. The =anterior surface= (Facies anterior)
determines the color of the eye, which is dark brown usually. It is
marked by delicate concentric lines (Plicæ iridis), which fade out near
the pupil. The smooth, narrow, central part is termed the pupillary zone
or annulus iridis minor, while the much broader plicated part is the
ciliary zone or annulus iridis major. The =posterior surface= (Facies
posterior) is usually black. It bears numerous fine radial lines except
at the pupillary margin. Its central part is in contact with the
anterior surface of the lens, but peripherally the two are separated by
a narrow space termed the posterior chamber. The iris consists chiefly
of the =stroma iridis=, a delicate framework of connective tissue, which
supports numerous blood-vessels, and contains branched pigmented cells.
The muscular tissue (unstriped) consists of a sphincter and a dilator of
the pupil. The =sphincter pupillæ= lies in the posterior part around the
pupil, with which the fibers are largely concentric. The =dilatator
pupillæ= consists of fibers which radiate outward from the sphincter to
the ciliary border. The anterior surface of the iris is covered by a
continuation of the endothelium of the cornea. Beneath this is a
condensation of the stroma, in which the cells are close together and
are full of pigmented granules.[219] There appear to be minute clefts
here by which the lymph-spaces of the stroma communicate with the
anterior chamber. The posterior surface is covered by a pigmented
epithelium, the stratum pigmenti iridis, which is a continuation of that
of the ciliary body.
The =arteries= of the vascular tunic come from the ciliary branches of
the ophthalmic artery. The arteries of the chorioidea are derived
chiefly from the short posterior ciliary arteries. These perforate the
sclera around the posterior pole, run forward in the lamina vasculosa,
and form the rich capillary network of the choriocapillaris. The two
long ciliary arteries perforate the sclera obliquely near the optic
nerve; they run forward in the lamina suprachorioidea in the horizontal
meridian, one on the inner, the other on the outer, side of the eyeball.
On reaching the ciliary body each divides into diverging branches; the
subdivisions of these unite with each other and with twigs of the
anterior ciliary arteries to form a circular anastomosis, the =circulus
arteriosus major=. From this branches go to the ciliary muscle and
processes and to the iris. The two anterior ciliary arteries, dorsal and
ventral, form an episcleral plexus around the corneo-scleral junction,
and give off branches which perforate the sclera. These supply twigs to
the ciliary muscle and recurrent branches to the chorioid, and assist in
forming the circulus arteriosus major.
The blood is carried away from the vascular tunic chiefly by four or
five venous trunks, the =venæ vorticosæ=, which are formed by the
convergence in whorls of numerous veins, coming not only from the
chorioid, but also from the ciliary body and iris. The venæ vorticosæ
perforate the sclera about at the equator and join the veins of the
ocular muscles.
The =nerves= come from the long and short ciliary nerves. They form a
plexus in the lamina suprachorioidea, which contains ganglion cells, and
sends numerous non-medullated fibers chiefly to the blood-vessels of the
chorioid. At the ciliary muscle a second plexus (P. gangliosus ciliaris)
is formed, which supplies the muscle and sends fibers to the iris. The
sphincter pupillæ is supplied by fibers derived from the oculomotor
nerve, while the dilatator pupillæ is innervated by the sympathetic.
THE RETINA
[Illustration:
FIG. 560.—INNER SURFACE OF ANTERIOR PART OF EYEBALL OF HORSE
(EQUATORIAL SECTION).
_1_, Sclera; _2_, chorioidea; _3_, retina (drawn away from
chorioidea); _4_, ciliary processes; _5_, crystalline lens, through
which the pupil (_6_) is seen. (After Ellenberger, in Leisering’s
Atlas.)
]
[Illustration:
FIG. 561.—FUNDUS OCULI, SEEN ON EQUATORIAL SECTION OF EYEBALL OF
HORSE.
_1_, Sclera; _2_, chorioidea; _3_, retina (loosened); _4_, tapetum;
_5_, optic papilla; _6_, optic nerve. (After Ellenberger, in
Leisering’s Atlas.)
]
The =retina= or nervous tunic of the eyeball is a delicate membrane
which extends from the entrance of the optic nerve to the margin of the
pupil. It consists of three parts. The large posterior part, which alone
contains the nervous elements, including the special neuro-epithelium
and the optic nerve-fibers, is termed the =pars optica retinæ=. It
extends forward to the ciliary body, where it terminates at an irregular
line called the =ora serrata=. Here the retina rapidly loses its nervous
elements, becomes much thinner, and is continued over the ciliary body
and the posterior surface of the iris by two layers of epithelial cells.
In the =pars ciliaris retinæ= the inner stratum is non-pigmented, while
the outer layer is a direct continuation of the stratum pigmenti of the
pars optica. In the =pars iridica retinæ= both are pigmented. In the
dead subject the pars optica is an opaque, gray, soft membrane which can
be stripped of the chorioid, leaving most of its outer pigmented layer
on the latter. During life it is transparent, except as to its pigmented
epithelium, and the reddish appearance of the fundus as viewed by the
ophthalmoscope is caused by the blood in the network of the
choriocapillaris. The entrance of the optic nerve forms a sharply
defined, oval, light area, the =optic papilla= (Papilla nervi optici),
situated about 15 mm. below the horizontal meridian and 3 to 4 mm.
external to the vertical meridian. The central part of the papilla is
slightly depressed (Excavatio papillæ n. optici).
The transverse diameter of the papilla is about 6 to 7 mm., and the
vertical about 4 to 5 mm. It is commonly situated a little below the
margin of the tapetum, but the latter may extend down somewhat on
either side of the papilla. The lower margin is often indented a
little. In inspection of the fundus with the ophthalmoscope numerous
fine branches of the arteria centralis retinæ are seen radiating from
the periphery of the papilla.
The optic nerve-fibers converge from all parts of the pars optica to the
papilla, where they collect into bundles which traverse the lamina
cribrosa of the chorioidea and sclera, and constitute the optic nerve.
The =area centralis retinæ= is a round spot, 2 to 3 mm. in diameter,
situated above and external to the optic papilla; it corresponds to the
macula lutea of man, which is histologically more highly differentiated
than the rest of the retina and is the area of most acute vision.
The =structure= of the retina is very complex. It consists of nervous
elements which are supported in a peculiar sustentacular tissue, and are
covered externally by a layer of pigmented epithelium (Stratum pigmenti
retinæ). The nervous elements comprise a highly specialized
neuro-epithelium, the rods and cones; ganglion cells, the axones of
which form the optic nerve; and intermediate neurones. Ten layers may be
recognized in sections microscopically.[220]
The =arteries= of the retina are derived from the arteria centralis
retinæ and anastomotic branches from the short ciliary arteries. The
arteria centralis enters the optic nerve a short distance behind the
eyeball and runs in the axis of the nerve. The artery divides 2 to 3 mm.
before reaching the papilla, and gives off thirty to forty branches
which radiate in the posterior part of the retina and divide
dichotomously into end-arteries. The anterior part of the retina is
non-vascular. The veins accompany the arteries except in the capillary
plexuses; their walls consist merely of a layer of endothelial cells,
around which are a lymph-channel and sheath.
CHAMBERS OF THE EYE AND AQUEOUS HUMOR
The =anterior chamber= of the eye (Camera oculi anterior) is inclosed in
front by the cornea and behind by the iris and lens (Figs. 552, 555,
557). It communicates through the pupil with the =posterior chamber=
(Camera oculi posterior); this is a small annular space, triangular in
cross-section, which is bounded in front by the iris, behind by the
peripheral part of the lens and its ligament, and externally by the
ciliary processes. The chambers are filled by the =aqueous humor= (Humor
aqueus), a clear fluid which consists of about 98 per cent. of water,
with a little sodium chlorid and traces of albumin and extractives. It
is carried off chiefly through the spaces (of Fontana) in the zonula
ciliaris or suspensory ligament of the lens into the plexus venosus
scleræ.
REFRACTIVE MEDIA OF THE EYEBALL
The =vitreous body= (Corpus vitreum) is a semifluid transparent
substance situated between the crystalline lens and the retina. In front
it presents a deep cavity, the =fossa hyaloidea=, which receives the
posterior surface of the lens. It consists of a framework of delicate
fibrils, the =stroma vitreum=, the meshes of which are filled by the
fluid =humor vitreus=. The surface is covered by a condensation of the
stroma known as the membrana hyaloidea.
The =crystalline lens= (Lens crystallina) is a biconvex, transparent
body, situated in front of the vitreous body and in partial contact with
the posterior surface of the iris. Its periphery, the =æquator lentis=,
is almost circular and is closely surrounded by the ciliary processes.
The =anterior surface= (Facies anterior) is convex; it is bathed by the
aqueous humor and is in contact with the iris to an extent which varies
with the state of the pupil. The =posterior surface= (Facies posterior)
is much more strongly curved than the anterior. It rests in the fossa of
the vitreous body. The central points of the surfaces are the =anterior=
and =posterior poles= (Polus anterior et posterior lentis), and the line
which connects them is the axis of the lens (Axis lentis).
The transverse diameter of the lens is about 2 cm., the vertical
diameter is slightly smaller, and the axis measures about 13 mm. The
radius of curvature of the anterior surface is 13.5 mm., and of the
posterior surface 9.5 to 10 mm. But the curvatures of its
surfaces—especially that of the anterior—vary during life according as
the eye is accommodated for near or far vision.
The =zonula ciliaris= (of Zinn) or suspensory ligament of the lens (Fig.
552) consists of delicate fibers (Fibræ zonulares) which pass in a
meridional direction from the ciliary processes to the capsule of the
equator of the lens. Many fibers cross each other, and the spaces
between the fibers (Spatia zonularia) are filled with aqueous humor;
they communicate with each other and with the posterior chamber.
The =substance= of the lens (Substantia lentis) is inclosed by a
structureless, highly elastic membrane, the =capsule= of the lens
(Capsula lentis), and consists of a softer =substantia corticalis=, and
a dense central part, the =nucleus lentis=. The capsule is thickest on
the anterior surface, and here it is lined by a layer of flat polygonal
cells, the epithelium of the lens capsule. The lens substance, when
hardened, is seen to consist of concentric laminæ arranged somewhat like
the layers of an onion, and united by an amorphous cement substance. The
laminæ consist of lens fibers, hexagonal in section, and of very
different lengths. Faint lines radiate from the poles and indicate the
edges of layers of cement substance which unite the groups of lens
fibers. These lines, the =radii lentis=, are three in number in the
fœtus and new-born, and form with each other angles of 120 degrees. On
the anterior surface one is directed upward from the pole and the other
two diverge downward; on the posterior surface one is directed downward
and the others diverge upward. The developed lens has neither vessels
nor nerves.
In the fœtus the lens is nearly globular, and is soft and pinkish in
color. During part of fœtal life it is surrounded by a vascular
network, the tunica vasculosa lentis. This is derived chiefly from a
temporary vessel, the hyaloid artery, which is a continuation forward
of the arteria centralis retinæ through the hyaloid canal that
traverses the vitreous body. In old age the lens tends to lose its
elasticity and transparency; it also becomes flatter and the nucleus
especially grows denser.
THE EAR
The ear or organ of hearing (Organon auditus) consists of three natural
divisions—external, middle, and internal.
THE EXTERNAL EAR
The =external ear= (Auris externa) comprises (1) the =auricula=, a
funnel-like organ which collects the sound waves, together with its
muscles, and (2) the =external auditory canal=, which conveys these
waves to the tympanic membrane, the partition which separates the canal
from the cavity of the middle ear.
The =auricula= or pinna is attached by its base around the external
auditory canal in such a manner as to be freely movable. In the
following description it will be assumed that the opening is directed
outward and that the long axis is practically vertical. It has two
surfaces, two borders, a base, and an apex. The convex surface or dorsum
(Dorsum auriculæ) faces inward and is widest in its middle part; its
lower part is almost circular in curvature, while above it narrows and
flattens. The concave surface (Scapha) is the reverse of the dorsum; it
presents several ridges which subside toward the apex. The anterior
border is sinuous; it is largely convex, but becomes concave near the
apex. It divides below into two diverging parts (crura helicis). The
posterior border is convex. The apex is flattened, pointed, and curved a
little forward. The base is strongly convex. It is attached to the
external auditory process of the petrous temporal bone, and around this
there is a quantity of fat. The parotid gland overlaps it below and
externally. The structure of the external ear comprises a framework of
cartilages (which are chiefly elastic), the integument, and a
complicated arrangement of muscles.
The =conchal= or =auricular cartilage= (Cartilago auriculæ) determines
the shape of the ear; its form can be made out without dissection,
except below, where it is concealed by the muscles and the parotid
gland. The basal part is coiled to form a tube, which incloses the
cavity of the concha (Cavum conchæ). This part is funnel-shaped and
curves outward and a little backward. Its internal (medial) surface is
strongly convex, forming a prominence termed the =eminentia conchæ=. The
lowest part of the internal margin bears a narrow, pointed prolongation,
the =styloid process=. This process is about an inch long and projects
downward externally over the annular cartilage; the guttural pouch is
attached to its free end. Behind its base there is a foramen through
which the auricular branch of the vagus passes.
The basal part of the posterior border is cut into by a notch, which
separates two irregular quadrilateral plates. The upper plate (Tragus)
is overlapped by the anterior border, and is separated from the
adjacent part of the posterior border (Antitragus) by a notch
(Incisura intertragica). The lower plate is curved to form a half ring
and partly overlaps the anterior border and the annular cartilage.
Behind the notch there is a foramen, which transmits the internal
auricular artery and internal auricular branch of the facial nerve.
[Illustration:
FIG. 562.—CONCHAL AND ANNULAR CARTILAGES OF EAR OF HORSE, EXTERNAL
VIEW.
_1_, Base of concha; _2_, posterior border, _3_, anterior border of
concha; _4_, intertragic notch; _5_, eminentia conchæ; _6_, styloid
process; _7_, annular cartilage; _9_, zygomatic arch. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =annular cartilage= (Cartilago annularis) is a quadrilateral plate,
curved to form about three-fourths of a ring; its ends are a little less
than half an inch (ca. 1 cm.) apart internally and are united by elastic
tissue. It embraces the external auditory process and forms with the
lower part of the conchal cartilage the cartilaginous part of the
external auditory canal.
The =scutiform cartilage= (Cartilago scutiformis s. scutulum) is an
irregular quadrilateral plate which lies on the temporal muscle in front
of the base of the conchal cartilage. Its superficial face is slightly
convex from side to side and its deep face is correspondingly concave.
The anterior end is thin and rounded; the posterior part or base is
wider and thicker, and its inner angle is prolonged by a pointed process
half an inch or more in length. The cartilage moves very freely over the
underlying parts.
The =external auditory canal= or =meatus= leads from the cavum conchæ to
the tympanic membrane. It does not continue the general direction of the
cavity of the concha, but extends inward, downward, and slightly
forward. It consists of a cartilaginous part formed by the lower part of
the conchal cartilage and the annular cartilage, and an osseous part
formed by the external auditory process of the temporal bone. These are
united by elastic membranes to form a complete tube. Its caliber
diminishes from without inward, so that the lumen of the inner end is
about half of that of the outer end.
The =skin= on the convex surface of the concha presents no special
features; it is attached to the cartilage by a considerable amount of
subcutaneous tissue except at the apex. The integument which lines the
concave surface is intimately adherent to the cartilage and is
relatively dark in color. There are three or four cutaneous ridges which
run about parallel with the borders of the conchal cartilage, but do not
extend to the apex or the cavum conchæ. The upper and marginal parts and
the ridges are covered with long hairs, but between the ridges and below
it is thin, covered sparsely with very fine hairs, and supplied with
numerous sebaceous glands. In the external auditory canal the skin
becomes thinner; in the cartilaginous part it is supplied with numerous
large, coiled, =ceruminous glands= (Glandulæ ceruminosæ) and is sparsely
covered with very fine hairs; in the osseous part the glands are small
and few or absent and there are no hairs.
THE AURICULAR MUSCLES
The =auricular muscles= may be subdivided into two sets, viz., (_a_)
extrinsic muscles, which arise on the head and adjacent part of the
neck, and move the external ear as a whole, and (_b_) intrinsic muscles,
which are confined to the auricula. In this connection the scutiform
cartilage may be regarded as a sesamoid cartilage intercalated in the
course of some of the muscles.
The =extrinsic muscles= are as follows:
1. The =scutularis= is a thin muscular sheet situated subcutaneously
over the temporalis muscle. Its fibers arise from the zygomatic arch and
the frontal and sagittal crests, and converge to the scutiform
cartilage. It consists of three parts.
(_a_) The =fronto-scutularis= comprises temporal and frontal parts,
which arise from the zygomatic arch and the frontal crest, and are
inserted into the outer and anterior borders of the scutiform cartilage
respectively.
(_b_) The =interscutularis= arises from the sagittal crest, over which
it is in part continuous with the muscle of the opposite side. Its
fibers converge to the inner border of the scutiform cartilage.
(_c_) The =cervico-scutularis= is not well defined from the preceding
muscle. It arises from the occipital crest and is inserted into the
inner border of the scutiform cartilage.
2. The =anterior auricular muscles= (Mm. auriculares nasales) are four
in number.
(_a_) The =zygomatico-auricularis= arises from the zygomatic arch and
the parotid fascia, and is inserted into the outer face of the base of
the conchal cartilage under cover of the parotido-auricularis.
(_b_) The =scutulo-auricularis superficialis inferior= arises on the
outer part of the superficial face of the scutiform cartilage and ends
on the base of the conchal cartilage with the preceding muscle.
(_c_) The =scutulo-auricularis superficialis medius= arises from the
posterior part of the deep surface of the scutiform cartilage and is
inserted into the dorsum of the conchal cartilage, close to the lower
part of its anterior border and above and behind the preceding muscle.
It receives a slip from the cervico-scutularis.
(_d_) The =scutulo-auricularis superficialis superior= is a thin slip
which is detached from the interscutularis over the inner border of the
scutiform cartilage. It ends on the anterior aspect of the lower part of
the dorsum of the conchal cartilage.
3. The =superior auricular muscles= (Mm. auriculares dorsales) are two
in number.
(_a_) The =scutulo-auricularis superficialis accessorius= is a narrow
band which is largely covered by the preceding muscle. It arises from
the posterior prolongation and the adjacent part of the superficial face
of the scutiform cartilage, and is inserted into the convex surface of
the conchal cartilage internal to the preceding muscle, the two crossing
each other at an acute angle.
(_b_) The =parieto-auricularis= is flat and triangular; it arises from
the sagittal crest under cover of the cervico-scutularis, runs outward
and a little backward, and is inserted by a flat tendon into the lower
part of the convex surface of the concha under cover of the
cervico-auricularis superficialis.
4. The =posterior auricular muscles= (Mm. auriculares caudales) are
three in number.
[Illustration:
FIG. 563.—EXTERNAL EAR OF HORSE AND ITS MUSCLES, LATERAL VIEW.
_2_, Posterior border; _3_, anterior border of auricula; _8_,
scutiform cartilage; _9_, zygomatic arch; _n_, parotido-auricularis;
_o_, zygomatico-auricularis; _o′_, scutulo-auricularis superficialis
inferior; _o″_, scutulo-auricularis superficialis medius et
superior; _p_, interscutularis; _p′_, fronto-scutularis (pars
temporalis); _q_, cervico-auricularis profundus major; _s_, small
(or anterior) oblique muscle of head; _t_, splenius; _y_, tendon of
mastoido-humeralis; _c_, mastoido-humeralis; _x_, wing of atlas.
(After Ellenberger-Baum, Anat. für Künstler.)
]
(_a_) The =cervico-auricularis superficialis= is a thin triangular
sheet. It is wide at its origin from the occipital crest and the
adjacent part of the ligamentum nuchæ, and becomes narrower as it passes
outward to be inserted into the inner side of the convex surface of the
concha.
(_b_) The =cervico-auricularis profundus major= arises from the
ligamentum nuchæ, partly beneath and partly behind the preceding muscle.
It is directed outward and is inserted into the postero-external aspect
of the base of the ear, partly under cover of the parotido-auricularis.
(_c_) The =cervico-auricularis profundus minor= arises under the
preceding muscle and passes downward and outward to be inserted into the
lowest part of the convex surface of the concha, partly under cover of
the parotid gland.
5. The =parotido-auricularis= (s. M. auricularis inferior) is a
ribbon-like muscle which lies on the parotid gland. It is thin and wide
at its origin from the fascia on the lower part of the parotid gland and
becomes somewhat narrower and thicker as it passes upward. It is
inserted into the conchal cartilage just below the angle of junction of
its borders.
6. The =deep auricular= or =rotator muscles= (M. auriculares profundis,
rotatores auriculæ), two in number, are situated under the scutiform
cartilage and the base of the concha and cross each other.
(_a_) The =scutulo-auricularis profundus major= is the strongest of the
auricular muscles. It is flat and is about an inch wide. It arises from
the deep face of the scutiform cartilage and passes backward to end on
and below the most prominent part of the base of the concha (eminentia
conchæ).
(_b_) The =scutulo-auricularis profundus minor= lies between the base of
the concha and the preceding muscle, and is best seen when the latter is
cut and reflected. It is flat and about an inch in length. It arises
from the posterior part of the deep face of the scutiform cartilage and
from the cervico-scutularis, and passes downward, backward, and outward
to be inserted into the base of the concha under cover of the preceding
muscle.
[Illustration:
FIG. 564.—MUSCLES OF EXTERNAL EAR OF HORSE, VIEWED FROM ABOVE.
On the right side parts of the superficial muscles have been removed
and the scutiform cartilage turned back to display the
deeper muscles. _a_, Frontal part, _a′_, temporal part of
fronto-scutularis; _b_, interscutularis; _c_, cervico-scutularis;
_d_, _e_, scutulo-auricularis superficialis superior and medius;
_f_, zygomatico-auricularis; _g_, scutulo-auricularis superficialis
accessorius; _o_, cervico-auricularis superficialis; _q_,
scutulo-auricularis superficialis inferior; _t_, scutiform
cartilage; _u_, parieto-auricularis; _v_, cervico-auricularis
profundus major; _w_, cervico-auricularis prof. minor; _x_, _x′_,
scutulo-auricularis prof. major et minor; _y_, temporalis.
(Ellenberger-Baum, Anat. d. Haustiere.)
]
7. The =tragicus= or mastoido-auricularis is a small muscle which arises
from the temporal bone just behind the external auditory process and
from the annular cartilage; it passes upward to be inserted into the
lower part of the anterior border of the conchal cartilage.
The =intrinsic muscles= are very small and of little importance. They
are as follows:
1. The =antitragicus= consists of a few bundles which are attached to
the conchal cartilage behind the junction of its two borders, and are
partially blended with the insertion of the parotido-auricularis.
2. The =helicis= is a small muscle attached in a position opposite to
the preceding on the anterior border of the conchal cartilage; it
extends also into the depression between the two divisions of the
border. It is in part continuous with the insertion of the
parotido-auricularis.
3. The =verticalis auriculæ=[221] is a thin stratum of muscular and
tendinous fibers which extends upward on the posterior surface of the
concha from the eminentia conchæ.
=Actions.=—The base of the concha is rounded and rests in a pad of fat
(Corpus adiposum auriculæ), so that the movements of the external ear
resemble those of a ball-and-socket joint. It is noticeable that
movements about the longitudinal and transverse axes are accompanied by
rotation. When the ear is vertical or drawn forward (“pricked up”), the
opening is usually directed forward; conversely, when the ears are “laid
back,” the opening faces backward. These movements evidently result from
the coördinated actions of several muscles which are very complex and
cannot be discussed in detail here. The scutularis acting as a whole
fixes the scutiform cartilage, so that the muscles which arise on the
latter act efficiently on the concha. The anterior auricular muscles in
general erect the ear and turn the opening forward. The interscutularis
concurs in this action, causing adduction and a symmetrical position of
the ears; it also acts directly on the conchal cartilage, since the
scutulo-auricularis superficialis superior is in reality a conchal
insertion of the interscutularis. The scutulo-auricularis superficialis
accessorius draws the concha forward and turns the opening outward. The
parieto-auricularis adducts the concha and inclines it forward. The
cervico-auricularis superficialis is chiefly an adductor of the conchal
cartilage, and directs the opening outward. The cervico-auricularis
profundus major turns the opening outward and, acting with the
parotido-auricularis, inclines the ear toward the poll. The
cervico-auricularis profundus minor tends to direct the opening downward
and outward. The parotido-auricularis draws the ear downward and
backward, and acts with the cervico-auricularis profundus major in
“laying back the ears”; the deep auricular muscles concur in these
actions. The tragicus shortens the external auditory canal. The actions
of the intrinsic muscles are inappreciable.
The =arteries= of the external ear are derived from the anterior
auricular branch of the superficial temporal, the posterior or great
auricular branch of the internal maxillary, and the anterior branch of
the occipital artery.
The =motor nerves= to the muscles come from the auricular and
auriculo-palpebral branches of the facial nerve and from the first and
second cervical nerves. The sensory nerves are supplied by the
superficial temporal branch of the mandibular nerve and the auricular
branch of the vagus.
THE MIDDLE EAR
The =middle ear= (Auris media) or =tympanic cavity= (Cavum tympani) is a
space in the tympanic and petrous parts of the temporal bone situated
between the membrana tympani and the internal ear. It is a pneumatic
cavity, which is lined by mucous membrane, and communicates with the
pharynx and the guttural pouch by the Eustachian tube. It contains a
chain of auditory ossicles by which the vibrations of the membrana
tympani are transmitted to the internal ear.
The cavity consists of: (1) A main part or atrium, which lies
immediately to the inner side of the membrana tympani; (2) the recessus
epitympanicus, situated above the level of the membrane and containing
the upper part of the malleus and the greater part of the incus; (3) a
relatively large ventral recess in the bulla ossea.
The =external wall= (Paries membranacea) is formed largely by the thin
=membrana tympani=, which closes the inner end of the external auditory
canal, and thus forms the septum between the external and middle parts
of the ear. The membrane is an oval disc, which slopes obliquely
downward and inward at an angle of about 30 degrees with the lower wall
of the external auditory canal. The circumference is attached in a
groove (Sulcus tympanicus) in the thin ring of bone (Annulus tympanicus)
which almost completely surrounds it. The handle of the malleus (the
outermost of the auditory ossicles) is attached to the inner surface of
the membrane and draws the central part inward, producing a slight
concavity of the outer surface. The periphery is thickened, forming the
annulus fibrosus. The membrana tympani consists of three layers. The
external =cutaneous layer= (Stratum cutaneum) is a prolongation of the
lining of the external auditory meatus. The middle =fibrous layer= or
=membrana propria= includes two chief sets of fibers; the outer stratum
(Stratum radiatum) consists of fibers which radiate from the handle of
the malleus, while the inner stratum (Stratum circulare) is composed of
circular fibers which are best developed peripherally. There are also
branched or dendritic fibers in part of the membrane. The internal
=mucous layer= (Stratum mucosum) is a part of the general mucous
membrane which lines the tympanic cavity.
[Illustration:
FIG. 565.—RIGHT PETROUS TEMPORAL BONE OF HORSE, ANTERO-INTERNAL VIEW.
_1_, External auditory meatus; _2_, annulus tympanicus; _3_, laminæ;
radiating from _2_; _4_, membrana tympani; _5_, malleus; _6_, incus;
_7_, stapes; _8_, fenestra cochleæ (s. rotundum); _9_, facial canal;
_11_, _11″_, semicircular canals; _11′_, vestibule; _12_, cochlea.
(After Ellenberger, in Leisering’s Atlas)
]
[Illustration:
FIG. 566.—RIGHT AUDITORY OSSICLES AND MEMBRANA TYMPANI, ENLARGED AND
VIEWED FROM INNER SIDE AND BELOW.
_1_, Malleus; _2_, incus; _2′_, _2″_, short and long processes of _2_;
_3_, stapes; _4_, tensor tympani; _5_, ligament attaching long
process of malleus; _6_, stapedius muscle; _7_, fenestra cochleæ (s.
rotundum). (After Ellenberger, in Leisering’s Atlas.)
]
The =internal wall= of the tympanic cavity (Paries labyrinthica)
separates it from the internal ear; it presents a number of special
features. The =promontory= (Promontorium) is a distinct eminence near
the center which corresponds to the first coil of the cochlea, and is
marked by a faint groove for the superficial petrosal nerve. Above this
is the =fenestra vestibuli= (s. ovalis), a reniform opening which is
closed by the foot-plate of the stapes and its annular ligament. The
=fenestra cochleæ= (s. rotundum) is situated below and behind the
preceding; it is an irregularly oval opening and is closed by a thin
membrane (Membrana tympani secundaria), which separates the tympanic
cavity from the scala tympani of the cochlea.
The =anterior wall= (Paries tubaria) is narrow, and is pierced by the
slit-like tympanic opening of the Eustachian tube. Above this and
incompletely separated from it by a thin plate of bone is the semicanal
for the tensor tympani muscle.
The =superior wall= or =roof= (Paries tegmentalis) is crossed in its
inner part by the facial nerve; here the facial canal is more or less
deficient ventrally, and the nerve is covered by the mucous membrane of
the tympanum.
The =posterior wall= (Paries mastoidea) presents nothing of importance;
a tympanic antrum and mastoid cells, such as are found behind the
tympanic cavity proper in man and many animals, are not present in the
horse.
The =inferior wall= or =floor= (Paries tympanica) is concave and thin.
It is crossed by delicate curved ridges, which radiate from the greater
part of the annulus tympanicus.
The =auditory ossicles= (Ossicula auditus) form a chain which extends
from the outer to the inner wall of the cavity. They are named, from
without inward, the =malleus=, the =incus=, the =os lenticulare=, and
the =stapes=. The first is attached to the inner surface of the tympanic
membrane and the last is fixed in the fenestra vestibuli.
[Illustration:
FIG. 567.—AUDITORY OSSICLES AND MEMBRANI TYMPANI, INNER VIEW,
ENLARGED.
_1_, Annulus tympanicus; _2_, membrana tympani; _3_, malleus; _4_,
incus; _5_, stapes. (After Ellenberger, in Leisering’s Atlas.)
]
[Illustration:
FIG. 568.—RIGHT AUDITORY OSSICLES, ENLARGED AS INDICATED BY LINES
GIVING THEIR ACTUAL LENGTH.
_a_, Malleus; _1_, head; _2_, neck; _3_, handle; _4_, long process;
_5_, muscular process. b, Incus; _1_, body; _2_, short branch; _3_,
long branch; _c_, os lenticulare. c, Stapes; _1_, head; _2_, crus;
_3_, base; _4_, attachment of stapedius. (After Ellenberger, in
Leisering’s Atlas.)
]
The =malleus= or hammer, the largest of the ossicles, consists of a
head, neck, handle, and two processes. The =head= (Capitulum mallei) is
situated in the epitympanic recess. It is smooth and convex above and in
front, and presents on its postero-internal aspect a concave facet for
articulation with the body of the incus. The =neck= (Collum mallei) is
the constricted part below the head; its inner surface is crossed by the
chorda tympani. The =handle= (Manubrium mallei) is directed downward,
inward, and a little forward from the neck, and is attached along its
entire length to the membrana tympani. On its inner surface, near the
upper end, there is a slight projection to which the tendon of the
tensor tympani muscle is attached. The =long process= (Processus longus)
is a pointed spicule which projects forward from the neck toward the
petro-tympanic fissure. The =short process= (Processus brevis) is a
slight projection of the outer side of the neck, and is attached to the
upper part of the membrana tympani.
The =incus= or anvil is situated chiefly in the epitympanic recess. It
may be said to resemble a bicuspid tooth with two divergent roots, and
consists of a body and two processes. The =body= (Corpus incudis)
articulates with the head of the hammer. The =long process= (Crus
longum) projects downward from the body and then curves inward; its
extremity has attached to it a small nodule of bone, the os
=lenticulare=, which articulates with the head of the stapes. The =short
process= (Crus breve) projects chiefly backward, and is attached to the
wall of the recess by a small ligament.
The =stapes= or stirrup consists of a head, two crura, and a base. The
=head= (Capitulum stapedis) is directed outward and articulates with the
os lenticulare. The =crura=, anterior and posterior (Crus anterius,
posterius), are directed inward from the head, and join the ends of the
base. The =base= or foot-plate (Basis stapedis) occupies the fenestra
vestibuli, to which it is attached. The space between the crura and the
base is closed by a membrane.
The =articulations= and =ligaments= of the auditory ossicles comprise:
(1) A diarthrodial joint between the head of the malleus and the body of
the incus (Articulatio incudomalleolaris), inclosed by a capsule. (2) An
enarthrosis between the os lenticulare and the head of the stapes
(Articulatio incudostapedia), also surrounded by a capsule. (3) The base
of the stapes is attached to the margin of the fenestra vestibuli by a
ring of elastic fibers (Lig. annulare baseos stapedis). (4) Small
ligaments attach the head of the malleus and the short crus of the incus
to the roof of the epitympanic recess. (5) The axial ligament (of
Helmholtz) attaches the neck of the malleus to a small projection (Spina
tympanica anterior) above and in front of the annulus tympanicus.
The =muscles= of the auditory ossicles are two in number, viz., the
tensor tympani and the stapedius. The =tensor tympani= arises from the
upper wall of the osseous Eustachian tube, and ends in a delicate tendon
which bends outward and is inserted into the handle of the malleus near
its upper end. When it contracts, it draws the handle of the malleus
inward and tenses the membrana tympani; it probably also rotates the
malleus around its long axis. It is innervated by the motor part of the
trigeminus through the otic ganglion. The =stapedius= arises from a
small prominence (Eminentia pyramidalis) of the posterior wall of the
tympanum, runs forward on the facial nerve, and is inserted into the
neck of the stapes. Its action is to draw the head of the stapes
backward and rotate the anterior end of the base outward, thus tensing
the annular ligament. It is innervated by the facial nerve.
The =tympanic mucous membrane= (Tunica mucosa tympanica) is continuous
with that of the pharynx and the guttural pouch through the Eustachian
tube. It is thin, closely united with the underlying periosteum, and is
reflected over the ossicles, ligaments, and muscles, the chorda tympani,
and the facial nerve in the open part of the facial canal. It contains
minute lymph nodules and small mucous glands (Glandulæ tympanicæ). The
epithelium is in general columnar ciliated, but over the membrana
tympani, ossicles, and promontory it is flattened.
The =artery= of the tympanum is the stylo-mastoid, a small vessel which
arises from the posterior auricular branch of the internal maxillary
artery. It enters the tympanum through the stylo-mastoid foramen, and
forms a circle around the tympanic membrane. The =nerves= of the mucous
membrane come from the tympanic plexus.
THE EUSTACHIAN TUBE
The =Eustachian= or =auditory tube= (Tuba auditiva [Eustachii]) extends
from the tympanic cavity to the pharynx; it transmits air to the former
and equalizes the pressure on the two surfaces of the membrana tympani.
It is directed forward, downward, and slightly inward, and is four to
five inches (ca. 10 to 12 cm.) in length. Its posterior extremity lies
at the inner side of the root of the muscular process of the petrous
temporal, and communicates with the anterior part of the tympanic cavity
by the small slit-like =tympanic opening= (Ostium tympanicum tubæ
auditivæ). For a distance of about a quarter of an inch (ca. 6 to 7 mm.)
in front of this opening it is a complete tube, with a curved lumen
which is little more than a capillary space. Further forward it has the
form of a plate which widens anteriorly and is curved to inclose a
narrow groove, that opens ventrally into an extensive diverticulum
termed the guttural pouch. The =pharyngeal opening= (Ostium pharyngeum
tubæ auditivæ) is situated on the postero-superior part of the lateral
wall of the pharynx just below the level of the posterior nares. It is a
slit, an inch or more (ca. 3 cm.) in length, which slopes downward and
backward. It is bounded internally by the thin free edge of the tube,
from the lower part of which a fold of mucous membrane (Plica
salpingo-pharyngea) extends in the same direction on the lateral wall of
the pharynx for a distance of a little more than an inch usually. The
outer boundary of the opening is the lateral wall of the pharynx. The
basis of the tube is a plate of fibro-cartilage (Cartilago tubæ
auditivæ) which is firmly attached dorsally to the fibrous tissue which
closes the foramen lacerum basis cranii, the temporal wing of the
sphenoid, and the pterygoid bone.[222] On cross-section the cartilage
(except at its tympanic end) is seen to consist of two laminæ which are
continuous with each other above. The internal lamina (Lamina medialis)
gradually widens toward the pharyngeal end, where it forms a broad
valvular flap. This is convex internally, and its thin anterior edge
forms the inner margin of the pharyngeal opening. Behind this the lamina
has a thick free edge which projects ventrally from the roof of the
guttural pouch. The external lamina (Lamina lateralis) is narrow and
thin, and is related externally to the levator and tensor palati
muscles, which are in part attached to it; it does not exist at the
pharyngeal end of the tube. The mucous membrane of the tube is
continuous behind with that of the tympanum and in front with that of
the pharynx. On either side it is reflected to form a large
diverticulum, the guttural pouch. It is covered with ciliated
epithelium, and contains mucous glands and lymph nodules.
The pharyngeal opening appears to be closed ordinarily, but the tube
opens during deglutition. This action is apparently produced by the
part of the palato-pharyngeus muscle which is attached to the tube.
THE GUTTURAL POUCHES
The =guttural pouches=, right and left (Figs. 255, 256, 569), are large
mucous sacs, each of which is a ventral diverticulum of the Eustachian
tube (Diverticulum tubæ auditivæ); they are not present in the
domesticated animals other than the equidæ. They are situated between
the base of the cranium and the atlas above and the pharynx below.
Medially they are in apposition in great part, but are to some extent
separated by the intervening ventral straight muscles of the head. The
anterior end is a small cul-de-sac which lies below the body of the
presphenoid between the Eustachian tube and the median recess of the
pharynx. The posterior extremity lies near or below the atlantal
attachment of the longus colli. The pouch is related dorsally to the
base of the cranium, the atlanto-occipital joint capsule, and the
ventral straight muscles. Ventrally it lies on the pharynx and the
origin of the œsophagus. Laterally the relations are numerous and
complex. They comprise the pterygoid, levator palati, tensor palati,
stylo-hyoideus, and digastricus muscles; the parotid and submaxillary
glands; the external carotid, internal maxillary, and external maxillary
arteries; the internal maxillary and jugular veins; the pharyngeal or
guttural lymph glands; the glosso-pharyngeal, hypoglossal, and superior
laryngeal nerves. The vagus, accessory, and sympathetic nerves, the
superior cervical ganglion, the internal carotid artery, and the
inferior cerebral vein are situated in a fold of the upper wall of the
pouch. The pouch is reflected around the anterior border of the great
cornu of the hyoid bone so as to clothe both surfaces of the upper part
of the latter. It thus forms an outer compartment, which extends
backward external to the great cornu and the occipito-hyoideus muscle;
it is related externally to the parotid gland, the articulation of the
jaw, the ascending part of the internal maxillary artery, the
superficial temporal artery, and the facial nerve; dorsally it covers
the mandibular nerve and its chief branches, and is attached to the
styloid process of the conchal cartilage.
Each pouch communicates with the pharynx through the pharyngeal orifice
of the Eustachian tube, and is in direct continuity with the mucous
membrane of the latter.
The wall of the pouch is a delicate mucous membrane which is in general
rather loosely attached to the surrounding structures. It is covered
with ciliated epithelium and is supplied with mucous glands.
[Illustration:
FIG. 569.—CROSS-SECTION OF HEAD OF HORSE.
The section passes through the base of the external ear and just
behind the posterior border of the lower jaw. _1_, Rectus capitis
anterior minor; _2_, rectus capitis anterior major; _3_, inner walls
of guttural pouches in apposition; _4_, _4_, arytenoid cartilage,
upper piece apex; _5_, posterior pillar of soft palate; _6_, false
vocal cord; _7_, lateral ventricle of larynx; _8_, true vocal cord;
_9_, vocal muscle; _10_, thyro-hyoideus muscle.
]
It is worthy of note that the pharyngeal orifice of the Eustachian
tube is at such a level as to provide (in the ordinary position of the
head) only an overflow outlet for the escape of fluid which may
accumulate in the pouch. The two pouches are often unequal in size,
and variations in regard to the distance which they extend backward
are not uncommon. In one case, a small aged horse, the right pouch
extended along the œsophagus about five inches (ca. 12 cm.) behind the
ventral tubercle of the atlas, and the left one a little more than two
inches (ca. 6 cm.). No pathological changes were apparent, and the
condition was not recognizable externally. Cases of extreme
size—so-called tympanites—of the pouches occur, and are apparently
congenital defects. In a case in a yearling colt, the head of which
was 24 inches long, the left pouch extended about 12 inches (ca. 30
cm.) behind the tubercle of the atlas, and had a capacity of six
quarts. The anterior end formed a cul-de-sac about two inches (ca. 5
cm.) long between the Eustachian tube and levator palati internally
and the internal pterygoid muscle externally.
THE INTERNAL EAR
The =internal ear= or =labyrinth= (Auris interna s. Labyrinthus)
consists of two parts, viz.: (1) a complex membranous sac, which
supports the auditory cells and the peripheral ramifications of the
auditory nerve; (2) a series of cavities in the petrous temporal bone,
which inclose the membranous part. The first is called the =membranous
labyrinth=, and contains a fluid, the =endolymph=. The second is the
=osseous labyrinth=. The two are separated by the =perilymphatic space=,
which is occupied by a fluid termed the =perilymph=.
THE OSSEOUS LABYRINTH
The =osseous labyrinth= (Labyrinthus osseus) (Fig. 565) is excavated in
the petrous temporal bone to the inner side of the tympanic cavity. It
consists of three divisions: (1) a middle part, the =vestibule=; (2) an
anterior one, the =cochlea=; and (3) a posterior one, the =semicircular
canals=.
1. The =vestibule= (Vestibulum) is the central part of the osseous
labyrinth, and communicates in front with the cochlea, behind with the
semicircular canals. It is a small, irregularly ovoid cavity, which is
about 5 to 6 mm. in length. Its outer wall separates it from the
tympanic cavity, and in it is the =fenestra vestibuli=, which is
occupied by the base of the stapes. The inner wall corresponds to the
fundus of the internal auditory meatus. It is crossed by an oblique
ridge, the =crista vestibuli=, which separates two recesses. The
anterior and smaller of these is the =recessus sphæricus=, which lodges
the saccule of the membranous labyrinth. In its lower part there are
about a dozen minute foramina which transmit filaments of the vestibular
nerve to the saccule. The posterior and larger depression is the
=recessus ellipticus=, which lodges the utricle of the membranous
labyrinth. The crista vestibuli divides below into two divergent
branches, which include between them the small =recessus cochlearis=;
this is perforated by small foramina, through which nerve-bundles reach
the ductus cochlearis. Similar foramina in the recessus ellipticus and
the crista vestibuli transmit nerve filaments to the utricle and the
ampullæ of the superior and external semicircular ducts. The anterior
wall is pierced by an opening which leads into the scala vestibuli of
the cochlea. The posterior part of the vestibule presents the four
openings of the semicircular canals. The inner opening of the
=aquæductus vestibuli= is a small slit behind the lower part of the
crista vestibuli. The aquæductus passes backward in the petrous temporal
bone, and opens on the inner surface of the latter near the middle of
its posterior border; it contains the ductus endolymphaticus.
2. The =osseous semicircular canals= (Canales semicirculares ossei),
three in number, are situated behind and above the vestibule. They are
at right angles to each other, and are designated according to their
positions as superior, posterior, and external. They communicate with
the vestibule by four openings only, since the inner end of the superior
and the upper end of the posterior canal unite to form a common canal
(Crus commune), and the ampullate ends of the superior and external
canals have a common orifice. Each canal forms about two-thirds of a
circle, one end of which is enlarged and termed the =ampulla=. The
=superior canal= (Canalis semicircularis superior) is nearly vertical
and is placed obliquely with regard to a sagittal plane, so that its
outer limb is further forward than the inner one. The antero-external
end is the ampulla and opens into the vestibule with that of the
external canal. The opposite non-dilated end joins the adjacent end of
the posterior canal to form the crus commune, which opens into the
supero-internal part of the vestibule. The =posterior canal= (Canalis
semicircularis posterior) is also nearly vertical. Its ampulla is below,
and opens into the vestibule directly, while the non-dilated end joins
that of the superior canal. The =external canal= (Canalis semicircularis
lateralis) is nearly horizontal. Its ampulla is external and opens into
the vestibule with that of the superior canal.
3. The =cochlea= is the anterior part of the bony labyrinth. It has the
form of a short blunt cone, the =base= of which (Basis cochleæ)
corresponds to the anterior part of the fundus of the internal auditory
meatus, while the =apex= or =cupola= (Cupula) is directed outward,
forward, and downward. It measures about 7 mm. across the base and about
4 mm. from base to apex. It consists of a =spiral canal= (Canalis
spiralis cochleæ), which forms two and a half turns around a central
column termed the =modiolus=. The modiolus diminishes rapidly in
diameter from base to apex. Its base (Basis modioli) corresponds to the
area cochleæ of the fundus of the internal auditory meatus, and its apex
extends nearly to the cupola. Projecting from the modiolus like the
thread of a screw is a thin plate of bone, the =lamina spiralis ossea=.
This begins between the two fenestræ and ends near the cupola as a
hook-like process (Hamulus laminæ spiralis). The lamina extends about
half-way to the periphery of the cochlea and partially divides the
cavity into two passages; of these, the upper one is termed the =scala
vestibuli=, and the lower the =scala tympani=. The membrana basilaris
extends from the free margin of the lamina to the outer wall of the
cochlea and completes the septum between the two scalæ, but they
communicate through the opening (Helicotrema) at the cupola. The
modiolus is traversed by an axial canal which transmits the nerves to
the apical coil, and by a spiral canal (canalis spiralis modioli), which
follows the attached border of the lamina spiralis, and contains the
spiral ganglion and vein. Close to the beginning of the scala tympani is
the inner orifice of the =aquæductus cochleæ=, a small canal which opens
behind the internal auditory meatus, and establishes a communication
between the scala tympani and the subarachnoid space.
The =internal auditory meatus= has been described in part (_vide_
Osteology). The fundus of the meatus is divided by a ridge (Crista
transversa) into upper and lower parts. The anterior part of the upper
depression (Area n. facialis) presents the cranial opening of the facial
canal; and the posterior part (Area vestibularis superior) is perforated
by foramina for the passage of nerves to the utricle and the ampullæ of
the superior and external membranous semicircular canals. The anterior
part of the inferior depression (Area cochleæ) presents a central
foramen and a spiral tract of minute foramina (Tractus spiralis
foraminosus) for the passage of nerves to the cochlea. Behind these is
an area of small openings which transmit nerves to the saccule (Area
vestibularis inferior), and a single foramen (F. singulare) for the
passage of a nerve to the ampulla of the posterior semicircular canal.
THE MEMBRANOUS LABYRINTH
The =membranous labyrinth= (Labyrinthus membranaceus) lies within, but
does not fill, the osseous labyrinth. It is attached to the latter by
delicate trabeculæ which traverse the perilymphatic space. It conforms
more or less closely to the bony labyrinth, but consists of four
divisions, since the vestibule contains two membranous sacs—the utricle
and saccule.
1. The =utricle= (Utriculus), the larger of the two sacs, lies in the
postero-superior part of the vestibule, largely in the recessus
ellipticus. It receives the openings of the membranous semicircular
canals, and the small =ductus utriculo-saccularis= leads from its lower
part to the ductus endolymphaticus.
2. The =saccule= (Sacculus) is situated in the recessus sphæricus of the
vestibule. From its lower part the =ductus reuniens= proceeds to open
into the ductus cochlearis, a little in front of the blind end of the
latter. A second narrow tube, the =ductus endolymphaticus=, passes from
the posterior part of the saccule, and is joined by the ductus
utriculo-saccularis; it then traverses the aquæductus vestibuli, and
terminates under the dura mater on the posterior part of the internal
surface of the petrous temporal bone in a dilated blind end, the saccus
endolymphaticus.
3. The =membranous semicircular canals= (Ductus semicirculares)
correspond in general to the osseous canals already described, but it
may be noted that while the ampullæ of the membranous canals nearly fill
those of the osseous canals, the other parts of the membranous canals
only occupy about one-fourth of the bony cavities.
4. The =cochlear duct= (Ductus cochlearis) is a spiral tube situated
within the cochlea. It begins by a blind end (Cæcum vestibulare) in the
cochlear recess of the vestibule, and ends by a second blind end (Cæcum
cupulare), which is attached to the cupola of the cochlea. The
vestibular part is connected with the saccule by the ductus reuniens.
The duct is triangular in cross-section, and it is usual to regard it as
having three walls. The vestibular wall or roof, which separates the
cochlear duct from the scala vestibuli, is formed by the very delicate
=membrana vestibularis= (of Reissner), which extends obliquely from the
lamina spiralis ossea to the outer wall of the cochlea. The tympanic
wall or floor intervenes between the cochlear duct and the scala
tympani; it is formed by the periosteum of the marginal part of the
lamina spiralis and the =membrana basilaris=, which stretches between
the free edge of the lamina and the outer wall of the cochlea. The outer
wall consists of the fibrous lining of the cochlea, which is greatly
thickened to form the =ligamentum spirale cochleæ=.
[Illustration:
FIG. 570.—LEFT MEMBRANOUS LABYRINTH (ENLARGED).
_1_, Cochlea; _2_, fenestra vestibuli; _3_, fenestra cochleæ; _4_,
ductus endolymphaticus; _5_, superior, _6_, external, _7_, inferior
semicircular canal. (After Ellenberger, in Leisering’s Atlas.)
]
[Illustration:
FIG. 571.—SCHEMATIC SECTIONAL VIEW OF LABYRINTH (ENLARGED).
_1_, _2_, _3_, Superior, external, and inferior semicircular canals;
_4_, utricle; _5_, saccule; _6_, cochlea; _7_, auditory nerve.
(After Ellenberger, in Leisering’s Atlas.)
]
=Structure.=[223]—The membranous labyrinth consists in general of an
outer thin fibrous layer, a middle transparent tunic, and an internal
epithelium, composed of flattened cells. But in certain situations
special and remarkable structures occur, among which are the following:
(1) The =maculæ acusticæ= appear as small whitish thickenings of the
inner walls of the saccule and utricle. The epithelium here consists of
two kinds of cells, viz., supporting cells and hair cells. The latter
are flask-shaped and are surrounded by the fusiform supporting cells.
The free end of each hair cell bears a stiff, hair-like process composed
of a bundle of cilia. Fibers of the saccular and utricular branches of
the vestibular nerve form arborizations about the basal parts of the
hair cells. Adherent to the surface of the maculæ are fine crystals of
lime salts, embedded in a mucoid substance, and termed otoconia. (2) The
=cristæ acusticæ= are linear thickenings of the wall of each ampulla of
the membranous semicircular canals. Their structure is similar to that
of the maculæ. (3) The =spiral organ of Corti= (Organon spirale) is an
epithelial elevation which is situated upon the inner part of the
membrana basilaris, and extends the entire length of the ductus
cochlearis. It is very complicated in structure, but consists
essentially of remarkable supporting cells and hair cells. Fibers of the
cochlear nerve ramify about the basal parts of the hair cells.
=Vessels and Nerves.=—The =artery= of the internal ear is the internal
auditory artery, a very small vessel which usually arises from the
posterior cerebellar artery, and enters the internal auditory meatus.
The =veins= go to the inferior petrosal sinus. The =vestibular nerve= is
distributed to the utricle, saccule, and membranous semicircular canals,
and mediates equilibration. The =cochlear nerve= gives a branch to the
saccule and enters the central canal of the modiolus. Along its course
it gives off fibers which radiate outward between the two plates of the
lamina spiralis ossea, and ramify about the hair cells of the organ of
Corti. The =ganglion spirale= or ganglion of Corti is situated in the
spiral canal of the modiolus near the fixed border of the lamina
spiralis. The cochlear nerve mediates the sense of hearing.
THE SKIN
The =skin= or =common integument= (Integumentum commune) is the
protective covering of the body, and is continuous at the natural
openings with the mucous membranes of the digestive, respiratory, and
urogenital tracts. It contains peripheral ramifications of the sensory
nerves, and is thus an important sense organ. It is the principal factor
in the regulation of the temperature of the body, and by means of its
glands it plays an important part in secretion and excretion. Some of
its special horny modifications or appendages are used as organs of
prehension or as weapons.
The =thickness= of the skin varies in the different species, on
different parts of the body of the same animal, and also with the breed,
sex, and age. The color also varies greatly, but this is masked in most
places by the covering of hair or wool. The skin is in general highly
elastic and resistant.
Permanent =folds= of the skin (Plicæ cutis) occur in certain situations,
and in some places there are cutaneous =pouches= or =diverticula= (Sinus
cutis).
The skin is attached to the underlying parts by the =subcutis= or
=superficial fascia= (Tela subcutanea). This consists of connective
tissue containing elastic fibers and fat. When the fat forms a layer of
considerable thickness, it is termed the =panniculus adiposus=. Over a
considerable part of the body the subcutis contains striped muscle, the
=panniculus carnosus= (M. cutaneus); in some regions the fibers of the
muscle are inserted into the skin, and their contraction twitches the
skin or produces temporary folds.[224] The amount of subcutaneous tissue
varies widely; in some places it is abundant, so that the skin can be
raised considerably; in other situations it is practically absent and
the skin is closely adherent to the subjacent structures. =Subcutaneous
bursæ= often develop over prominent parts of the skeleton where there is
much pressure or friction.
=Structure.=—The integument consists of the cutis or skin proper and its
epidermal appendages, _e. g._, hairs, hoofs, claws, horns, etc. The
cutis consists of two distinct strata, viz., a superficial epithelial
layer, the =epidermis=, and a deep connective-tissue layer, the
=corium=.
The =epidermis= is a non-vascular, stratified epithelium of varying
thickness. It presents the openings of the cutaneous glands and the
hair-follicles, and its deep surface is adapted to the corium.[225] It
is divisible into a superficial, harder, drier part, the =stratum
corneum=, and a deeper, softer, moister part, the =stratum
germinativum=. The cells of the latter contain pigment, and by their
proliferation compensate the loss by desquamation of the superficial
part of the stratum corneum. In many places further subdivision into
strata is evident on properly prepared cross-sections.
The =corium= consists essentially of a feltwork of connective-tissue and
elastic fibers. It is well supplied with vessels and nerves, and
contains the cutaneous glands, the hair-follicles, and unstriped muscle.
The deeper part of the corium, the =tunica propria=, consists of a
relatively loose network of coarse bundles of fibers, and in most places
there is no clear line of demarcation between it and the subcutis. The
superficial part, the =corpus papillare=, is of finer texture and is
free from fat. Its superficial face is thickly beset with blunt conical
prominences, the =papillæ=, which are received into corresponding
depressions of the epidermis. They contain vascular loops and nerves,
or, in certain situations, special nerve-endings.
The papillæ are best developed where the epidermis is thick and hairs
are small or absent. On thickly-haired regions they are small or even
absent. On certain parts of the body (anus, vulva, prepuce, scrotum,
eyelids, etc.) the corium contains pigment in its connective-tissue
cells.
The =glands= of the skin (Glandulæ cutis) are chiefly of two kinds,
sudoriferous and sebaceous.
The =sudoriferous= or =sweat glands= (Glandulæ sudoriferæ) consist of a
tube, the lower, secretory part of which is coiled in the deep part of
the corium or in the subcutis to form a round or oval ball (Corpus
glandulæ sudoriferæ). The excretory duct (Ductus sudoriferus) passes
almost straight up through the corium, but pursues a more or less
flexuous course through the epidermis, and opens into a hair-follicle or
by a funnel-shaped pore (Porus sudoriferus) on the surface of the skin.
The =sebaceous glands= (Glandulæ sebaceæ) are in great part associated
with the hairs, into the follicles of which they open. Their size varies
widely, and is in general in inverse ratio to that of the hair. The
larger ones are easily seen with the naked eye, and appear as small,
pale yellow or brownish bodies. In certain situations (_e. g._, the
labia vulvæ, anus, prepuce) they are independent of the hairs and are
well developed. In form they may be branched alveolar, simple alveolar,
or even tubular in type. They secrete a fatty substance, the =sebum
cutaneum=, which serves as a protective against moisture, and may also
(by its aromatic constituents) play an important part in the sexual life
of animals.
The two kinds of glands described above are those which are most
widely distributed, but many special types occur. Some of these are to
be regarded as modified sweat glands, _e. g._, the naso-labial glands
of the ox, the glands of the snout of the pig, and the glands of the
plantar cushion of the horse. Others, _e. g_., the tarsal (or
Meibomian) glands of the eyelids, are modified sebaceous. Still others
are not yet classified satisfactorily. Some of these special types
have been referred to in previous chapters, and others will receive
attention in the special descriptions which follow. The mammary glands
are highly modified cutaneous glands, which are intimately associated
in function with the genital organs, and have been described with the
latter.
=Vessels and Nerves.=—The =arteries= of the skin enter from the
subcutis, where they communicate freely. In the deeper part of the
corium they form a plexus, and another network is formed under the
papillæ. Small vessels from the deep plexus go to the fat and sweat
glands, and the subpapillary plexus sends fine branches to the papillæ,
hair-follicles, and sebaceous glands. The =veins= form two plexuses, one
beneath the papillæ, and another at the junction of the corium and
subcutis. The =lymph vessels= form subpapillary and subcutaneous
plexuses.
The =nerves= vary widely in number in different parts of the skin. The
terminal fibers either end free in the epidermis and in certain parts of
the corium, or form special microscopic corpuscles of several kinds.
THE APPENDAGES OF THE SKIN
The appendages of the skin are modifications of the epidermis, and
comprise the hairs, hoofs, claws, horns, etc.
The =hairs= (Pili) cover almost the entire surface of the body in the
domesticated mammals, and some parts which appear at first sight to be
bare are found on close inspection to be provided with sparse and very
fine hair. The hairs are constantly being shed and replaced, but at
certain periods in the horse, for example, they fall out in great
numbers, constituting the shedding of the coat. It is customary to
distinguish the ordinary hairs (the coat), which determine the color of
the animal, from the special varieties found in certain places. Among
the latter are the long =tactile hairs= about the lips, nostrils, and
eyes; the =eyelashes= or =cilia=; the =tragi= of the external ear; and
the =vibrissæ= of the nostrils. Other special features will be noted in
the discussion of the skin of the various species. The hairs are
directed in such a way as to form more or less definite =hair-streams=
(Flumina pilorum), and at certain points these converge to form
=vortices= (Vortices pilorum).
[Illustration:
FIG. 572.—LATERAL VIEW OF HORSE TO SHOW HAIR-STREAMS AND VORTICES.
(After Ellenberger-Baum, Anat. für Künstler.)
]
The part of the hair above the surface of the skin is the =shaft=
(Scapus pili), while the =root= (Radix pili) is embedded in a depression
termed the =hair-follicle= (Folliculus pili). A vascular =papilla=
(Papilla pili) projects up in the fundus of the follicle and is capped
by the expanded end of the root, the =bulb= of the hair (Bulbus pili).
The hair-follicles extend obliquely into the corium to a varying depth;
in the case of the long tactile hairs they reach to the underlying
muscle. Most of the follicles have attached to them small unstriped
muscles known as the =arrectores pilorum=; these are attached at an
acute angle to the under side of the deep part of the follicle, and
their contraction causes erection of the hair and compression of the
sebaceous glands, one or more of which open into the follicle.
The hairs are composed of epidermal cells, and consist from without
inward of three parts. The =cuticle= is composed of horny, scale-like
cells which overlap like slates on a roof. The =cortex= consists of
horny fusiform cells which are packed close together and contain
pigment. The =medulla= is the central core of softer, cubical or
polyhedral cells; it contains some pigment and air-spaces.
The hair-follicles, being invaginations of the skin, are composed of a
central epidermal part, and a peripheral layer which corresponds in
structure to the corium. The follicles of the tactile hairs have
remarkably thick walls which contain blood-sinuses between their outer
and inner layers; in ungulates the sinuses are crossed by trabeculæ and
assume the character of cavernous or erectile tissue.
The =hoofs=, =claws=, =horns=, and other horny structures consist of
closely packed epidermal cells which have undergone cornification. In
structure they might be compared to hairs matted together by intervening
epidermal cells. They cover a specialized corium known as their
=matrix=, from which the stratum germinativum derives its nutrition.
THE SKIN OF THE HORSE
The =thickness= of the skin of the horse varies from 1 to 5 mm. in
different regions, and is greatest at the attachment of the mane and the
ventral surface of the tail.
The =glands= are numerous and are larger than those of the other
domesticated animals. The sebaceous glands are specially developed on
the lips, the prepuce, mammary glands, perineum, and labia of the vulva.
The sweat glands are yellow or brown in color. They occur in almost all
parts of the skin, but are largest and most numerous on the outer wing
of the nostril, the flank, mammary glands, and free part of the penis.
In addition to the ordinary and tactile =hairs= certain regions present
coarse hairs of great length. The mane (Juba) springs from the dorsal
border of the neck and the adjacent part of the withers; its anterior
part, which covers the forehead to a variable extent, is termed the
foretop (Cirrus capitis). The tail, with the exception of its ventral
surface, bears very large and long hairs (Cirrus caudæ). The tuft of
long hairs on the flexion surface of the fetlock (Cirrus pedis) gave
rise to the popular name of this region.
The development of these special hairs varies widely, and is in
general much greater in the draft breeds than in others. In Shire and
Clydesdale horses, for instance, the hair on the volar aspect of the
metacarpus and metatarsus and fetlock is often so long and abundant as
to account for the term “feather,” which is commonly applied to it by
horsemen.
THE HOOF
The =hoof=[226] (Unguis) is the horny covering of the distal end of the
digit. It is convenient to divide it for description into three parts,
termed the wall, sole, and frog.
1. The =wall= is defined as the part of the hoof which is visible when
the foot is placed on the ground.[227] It covers the front and sides of
the foot, and is reflected posteriorly at an acute angle to form the
=bars=. The latter (Pars inflexa medialis, lateralis) appear on the
ground surface of the hoof as convergent ridges, which subside in front
and are fused with the sole; they are united with each other by the
frog. For topographic purposes the wall may be divided into an anterior
part or “toe” (Pars ungulæ dorsalis), lateral parts or “quarters” (Pars
ungulæ medialis, lateralis), and the angles or “heels” (Pars ungularis
medialis, laterales). It presents two surfaces and two borders.
The outer surface is convex from side to side and slopes obliquely from
edge to edge. In front the angle of inclination on the ground plane is
about 50° for the fore limb, 55° for the hind limb; on the sides the
angle gradually increases and is 100° at the angles. The curve of the
wall is wider on the external than on the internal side, and the
external quarter is more oblique than the internal one. The surface is
smooth and is crossed by more or less distinct ridges, which are
parallel with the coronary border and indicate variations in the
activity of the growth of the hoof. It is also marked by fine parallel
striæ, which extend from border to border in an almost rectilinear
manner.
The =slope= of the wall varies considerably in apparently normal
hoofs. Lungwitz found by careful measurements of 56 fore and 36 hind
feet the following average angles:
FORE FOOT HIND FOOT
Toe 47.26° 54.1°
Inner angle 101.57° 96.50°
Outer angle 101.37° 96.1°
The wall of the fore foot may even be more upright than that of the
hind, and may have an angle of 60°. The =length= of the wall at the
toe, quarters, and heels is in the ratio of about 3 ∶ 2 ∶ 1 in the
fore foot and about 2 ∶ 1½ ∶ 1 in the hind hoof.
The inner surface is concave from side to side, and bears about six
hundred thin =primary laminæ= (Cristæ ungulæ), which extend from the
coronary groove to the junction of wall and sole. Each bears a hundred
or more =secondary laminæ= on its surfaces, so that the arrangement is
pennate on cross-section. These horny laminæ are continued on the inner
surface of the bars, and alternate with corresponding laminæ of the
matrix.
The =proximal= or =coronary border= (Margo occultus) is thin. Its outer
aspect is covered by a layer of soft horn known as the =periople=; this
appears as a ring-like prominence above and gradually fades out below;
at the angle it forms a wide cap or bulb and blends centrally with the
frog. The inner aspect of the border is excavated to form the =coronary
groove= (Sulcus coronalis ungulæ), which contains the thick coronary
matrix. The groove is deepest in front, narrows on the sides, and is
wide and shallow at the heels.[228] It is perforated by innumerable
small, funnel-like openings which are occupied by the papillæ of the
coronary matrix in the natural state.
[Illustration:
FIG. 573.—DIGIT OF HORSE, SHOWING SURFACE RELATIONS OF BONES AND
JOINTS. THE LATERAL CARTILAGE IS EXPOSED.
_a_, First phalanx; _b_, second phalanx; _c_, third phalanx; _d_,
lateral cartilage; _e_, third sesamoid or navicular bone; _f_,
pastern joint; _g_, coffin joint; _h′_, cut edge of wall of hoof
(_h_); _i_, laminar matrix. (After Ellenberger, in Leisering’s
Atlas.)
]
The =distal= or =ground border= (Margo liber) of the unshod hoof comes
in contact with the ground. Its thickness is greatest in front and
decreases considerably from before backward on the sides, but there is a
slight increase at the angles. Its inner face is united with the
periphery of the sole by horn of lighter color and softer texture, which
appears on the ground surface of the hoof as the =white line=.
In the case of horses at liberty the wall is usually worn off to the
level of the adjacent sole, but if the ground is too soft the wall is
likely to become unduly long and split or break or undergo
deformation. On very hard or rough ground, on the other hand, the wear
may be in excess of the growth. In the case of shod horses it is
necessary to remove the excess of growth of the wall at each shoeing.
The =thickness= of the wall at the toe, quarters, and heels is about
in the ratio of 4 ∶ 3 ∶ 2 for the fore foot and about 3 ∶ 2½ ∶ 2 for
the hind foot.
2. The =sole= (Solea ungulæ) forms the greater part of the ground
surface of the hoof. It is somewhat crescentic in outline, and presents
two surfaces and two borders.
The =superior= or =inner surface= is convex, and slopes with a varying
degree of obliquity downward to the convex border. It presents numerous
small funnel-like openings which contain the papillæ of the sole matrix
in the natural state.
[Illustration:
FIG. 574.—CROSS-SECTION OF FOOT OF HORSE, CUT PARALLEL WITH THE
CORONARY BORDER.
]
The =inferior= or =ground surface= is the converse of the preceding. It
is normally arched—and more strongly in the hind than in the fore
foot—but the curvature is subject to wide variation; in heavy draft
horses the sole is commonly less curved than in the lighter breeds and
may even be flat. The surface is usually rough, since the horn
exfoliates here in irregular flakes.
[Illustration:
FIG. 575.—HALF OF HOOF OF HORSE, INTERNAL SURFACE
]
The =convex border= is joined to the wall by relatively soft horn,
previously referred to as forming the white line on the ground surface
of the hoof. The angle of junction is rounded internally and presents a
number of low ridges and specially large openings for the papillæ of the
matrix. There is frequently a ridge of larger size at the toe.
The =concave border= has the form of a deep angle which is occupied by
the bars and frog. By its junction with these it forms two pronounced
ridges in the interior of the foot. The parts of the sole between the
wall and bars may be termed its angles.
3. The =frog= (Furca ungulæ) is a wedge-shaped mass which occupies the
angle between the bars and sole, and extends considerably below these on
the ground surface of the foot. It may be described as having four
surfaces, a base, and an apex.
[Illustration:
FIG. 576.—INTERNAL SURFACE OF PART OF HOOF OF HORSE. (After Schmaltz,
Atlas d. Anat. d. Pferdes.)
]
The =superior= or =internal surface= is deeply concave from side to
side. It bears a central ridge, the =spine= or “=frog-stay=” (Spina
furcæ ungulæ), which is high posteriorly and subsides abruptly in front.
On either side of this is a deep depression, bounded outwardly by the
rounded ridge formed by the junction of the frog with the bar and sole.
This surface presents fine striæ and openings for the papillæ of the
frog matrix.
The =inferior= or =ground surface= presents a =central furrow= (Sulcus
intercruralis), which is bounded by two ridges or crura (Crura furcæ
ungulæ); these converge and form the apex.
The =sides= (Facies medialis et lateralis) are united at the upper part
with the bars and sole, but are free below and form the central wall of
the deep =lateral furrows= (Sulci cruroparietales), which are bounded
outwardly by the bars.
The =base= is wide and high. It is depressed centrally and prominent at
the sides, where it unites with the angles of the walls; the junction
here is covered by the expanded periople and constitutes the bulb of the
hoof.
[Illustration:
FIG. 577.—HOOF OF HORSE, RIGHT FORE FOOT, GROUND SURFACE.
_37_, Inner quarter; _38_, outer quarter; _39_, ground border of wall
(toe); _40_, white line; _41_, sole; _42_, apex of frog; _43_,
lateral ridge of frog; _44_, central furrow of frog; _45_, lateral
furrow between frog and bar; _46_, bar. (After Ellenberger-Baum,
Anat. für Künstler.)
]
[Illustration:
FIG. 578.—HORIZONTAL SECTION OF HOOF OF HORSE.
The section is cut just above the ridges of the frog and bars and
parallel with the ground surface. _1_, Wall; _2_, sole; _3_, median
ridge of frog; _4_, lateral ridge formed by junction of frog and
bar; _5_, median furrow over apex of frog; _6_, laminæ of wall; _7_,
laminæ of bar.
]
The =apex= occupies the central angle of the concave border of the sole,
and forms a blunt, round prominence a little in front of the middle of
the ground surface of the hoof.
=Structure of the Hoof.=—The hoof is composed of epithelial cells which
are more or less completely keratinized except in its deepest part, the
=stratum germinativum=; here the cells have not undergone cornification,
and by their proliferation maintain the growth of the hoof. The cells
are in part arranged to form tubes which are united by intertubular
epithelium, and inclose medullary cells and air-spaces.
[Illustration:
FIG. 579.—FRONTAL SECTION OF HOOF OF HORSE, POSTERIOR PART VIEWED FROM
IN FRONT.
_1_, Wall; _2_, sole; _3_, bar; _4_, frog; _5_, median ridge of frog;
_6_, lateral ridge formed by junction of frog and bar; _7_, laminæ
of bar; _8_, laminæ of wall; _9_, coronary groove; _10_, periople of
heel.
]
The =wall= may be regarded as consisting of three layers. The external
layer consists of the periople and the stratum vitreum. The =periople=
is composed of soft, non-pigmented tubular horn. It is continuous with
the epidermis above, and extends downward a variable distance. Usually
it forms a distinct band somewhat less than an inch wide, except at the
heels, where it is much wider, and caps the angle of inflection of the
wall proper. The =stratum vitreum= is a thin layer of horny scales which
gives the wall below the periople its smooth, glossy appearance. The
=middle= or =tubular layer= forms the bulk of the wall, and is the
densest part of the hoof. Its horn tubes run in a straight direction
from the coronary to the ground border. In dark hoofs it is pigmented
except in its deep part. The internal or laminar layer consists of the
=primary= and =secondary laminæ= and is non-pigmented. The laminæ are
narrow and thin at their origin at the lower margin of the coronary
groove, but become wider and thicker below. At the junction of the wall
and sole they are united by interlaminar horn to form the white line.
Only the central part of the laminæ becomes fully keratinized. They are
composed of non-tubular horn in the normal state.
The =sole= consists of tubular and intertubular horn. The tubes run
parallel with those of the wall and vary much in size.
The =frog= is composed of relatively soft horn, which is much more
elastic than that of the wall or sole, and is not fully keratinized. The
horn tubes in it are slightly flexuous.
The hoof is non-vascular and receives its nutrition from the matrix. It
is also destitute of nerves.
THE MATRIX OF THE HOOF
The =matrix= of the hoof (Matrix ungulæ) is the specially modified and
highly vascular part of the corium of the common integument which
furnishes nutrition to the hoof. It is convenient to divide it into five
parts which nourish corresponding parts of the hoof.
1. The =perioplic matrix= or =ring= (Margo matricis ungulæ) is a band 5
to 6 mm. in width which lies in a groove between the periople and the
coronary border of the wall. It is continuous above with the corium of
the skin, and is marked off by a groove from the coronary matrix. At the
heels it widens and blends with the matrix of the frog. It bears very
fine, short papillæ which curve downward and are received in depressions
of the periople, to which it supplies nutrition.
2. The =coronary matrix= or =cushion= (Corona matricis ungulæ) is the
thick part of the corium which occupies the coronary groove, and
furnishes nutrition to the bulk of the wall. It diminishes in width and
thickness posteriorly, and along the upper border of the bar it is not
very clearly defined from the matrix of the frog. The convex superficial
surface is thickly covered with papillæ 4 to 6 mm. in length, which are
received into the funnel-like openings of the coronary groove. At the
heels and along the bars the papillæ are arranged in rows, separated by
fine furrows. The deep surface is attached to the extensor tendon and
the lateral cartilages by an abundant subcutis which contains many
elastic fibers and a rich venous plexus.
3. The =laminar matrix= (Latus matricis ungulæ)—also termed the
sensitive laminæ—bears primary and secondary laminæ which are
interleaved with the horny laminæ of the wall and bars in the natural
state. It is attached to the wall surface of the third phalanx by a
modified periosteum (Stratum periosteale) which contains a close-meshed
network of vessels, and to the lower part of the lateral cartilages by a
subcutis which contains a rich venous plexus. The laminæ are small at
their origin above, become wider below, and end in several papillæ 4 to
5 mm. in length. The sensitive laminæ supply nutrition to the horny
laminæ and to the interlaminar horn of the white line.
4. The =sole matrix= (Latus volare matricis ungulæ)—also termed the
sensitive sole—corresponds to the horny sole, to which it supplies
nutrition. It is often more or less pigmented and bears long papillæ,
which are specially large along the convex border and at the angles.
Centrally it is continuous with the matrix of the frog and bars. The
deep surface is attached to the sole surface of the third phalanx by a
modified and highly vascular periosteum.
[Illustration:
FIG. 580.—LATERAL VIEW OF FOOT OF HORSE AFTER REMOVAL OF HOOF AND PART
OF SKIN. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
[Illustration:
FIG. 581.—GROUND SURFACE OF FOOT OF HORSE AFTER REMOVAL OF HALF OF
HOOF. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]
5. The =frog matrix= (Furca matricis ungulæ)—also called the sensitive
frog—is moulded on the deep surface of the frog and bears small papillæ.
Its deep face is blended with the plantar cushion. The germinal cells of
the frog derive their nutrition from this part of the matrix.
The =digital= or =plantar cushion= (Torus digitalis) is an important
part of the elastic apparatus of the foot. It is a wedge-shaped mass
which overlies the frog. It presents for description four surfaces, a
base, and an apex. The =superior surface= faces upward and forward and
is connected with the distal fibrous sheath of the deep flexor tendon.
The =inferior surface=, covered by the matrix of the frog, is moulded on
the upper face of the frog. The =lateral surfaces= are related chiefly
to the lateral cartilages; inferiorly the cushion is closely attached to
the cartilages, but higher up a rich venous plexus intervenes. The
=base=, situated posteriorly, is partly subcutaneous, and is divided by
a central depression into two rounded prominences termed the bulbs of
the plantar cushion. The =apex= lies under the terminal part of the deep
flexor tendon. The cushion is poorly supplied with vessels. It consists
of a feltwork of fibrous trabeculæ and elastic fibers, in the meshes of
which are masses of fat. The bulbs are soft and loose in texture and
contain a relatively large amount of fat, but toward the apex the
cushion becomes denser and more purely white fibrous in structure.
Branched =coil glands= occur chiefly in the part of the cushion which
overlies the central ridge of the frog. Their ducts pursue a slightly
flexuous course through the matrix and pass in a spiral manner through
the frog. Their secretion contains fat.
[Illustration:
FIG. 582.—CROSS-SECTION OF DIGIT OF HORSE, THROUGH DISTAL END OF
SECOND PHALANX.
_a_, Second phalanx; _b_, deep flexor tendon; _b′_, digital synovial
sheath; _c_, plantar cushion; _d_, lateral cartilage; _e_, skin;
_f_, hoof; _g_, anterior extensor tendon; _h_, cavity of coffin
joint; _i_, suspensory ligament of navicular bone; _k_, lateral
ligament of coffin joint; _l_, digital artery; _m_, digital nerve.
(After Ellenberger, in Leisering’s Atlas.)
]
=Vessels and Nerves.=—The matrix is richly supplied with blood by the
=digital arteries=. The =veins= are valveless, and form remarkable
plexuses which communicate freely with each other and are drained by the
digital veins. The =lymph vessels= form subpapillary plexuses in the
matrix of the sole and frog, and a wider-meshed plexus at the base of
the plantar cushion. A considerable lymph vessel lies in the attached
edge of each of the laminæ. The =nerves= are branches of the digital
nerves; some fibers end in lamellar corpuscles and end-bulbs.
The =ergot= is a small mass of horn which is situated in the tuft of
hair at the flexion surface of the fetlock. It is the vestige of the
second and fourth digits of extinct equidæ and hence is absent in cases
in which these digits are developed. A small tendinous band, 3 to 5 mm.
in width, extends downward and slightly forward from the fibrous basis
of the ergot on each side, crosses over the digital vessels and nerves
very obliquely, and blends below with the digital fascia and the plantar
cushion. It is known as the ligament or tendon of the ergot.
The term =chestnut= is applied to the masses of horn which occur on the
inner surface of the forearm about a handbreadth above the carpus, and
on the lower part of the inner face of the tarsus. They have an
elongated oval form and are flattened. They are regarded usually as
vestiges of the first digit. That of the hind limb is absent in the
donkey and very small in the mule.
These horny vestiges are quite variable in form and size and are
correlated with the fineness or coarseness of the integument in
general. The supracarpal chestnut is about 1½ to 2½ inches long, oval
in outline, the proximal end being pointed; it overlies the flexor
carpi internus at a quite variable distance above the carpus, and
hence should not be used as a surgical landmark. The tarsal chestnut
lies at a point behind the lower part of the internal lateral ligament
of the hock. When well developed it is about 2 to 2½ inches long,
broad below and produced above to form a long pointed end, with a
short blunt anterior process. They are composed of horn somewhat like
that of the frog.
ORGAN OF SMELL
The peripheral part of the olfactory apparatus or organ of smell
(Organon olfactus) is that part of the nasal mucous membrane which was
referred to in the description of the nasal cavity as the olfactory
region; this (Regio olfactoria) is limited to the ethmoturbinals and the
adjacent part of the superior turbinal and the septum nasi, in which the
fibers of the olfactory nerve ramify. It is distinguished by its
yellow-brown color, thickness, and softness. It contains characteristic
tubular =olfactory glands= (of Bowman), which are lined by a single
layer of pigmented cells, and a neuro-epithelium, the =olfactory cells=,
the central processes of which extend as non-medullated fibers to the
olfactory bulb.
The epithelium is non-ciliated and is covered by a structureless
limiting layer. It consists essentially of three kinds of cells,
supporting, basal, and olfactory. The supporting cells are of long
columnar form above and contain pigment granules; below they taper and
often branch, and their central processes unite with those of adjacent
cells to form a protoplasmic network. The basal cells are branched and
lie on a basement membrane. The olfactory cells are situated between
the supporting cells; they have the form of long narrow rods, with an
enlarged lower part which is occupied by the nucleus. The peripheral
end pierces the limiting membrane and bears a tuft of fine hair-like
cilia (olfactory hairs). A central process extends from the nucleated
pole of the cell to the olfactory bulb as a non-medullated olfactory
nerve-fiber.
The =vomero-nasal organ= (of Jacobson) lies along each side of the
anterior part of the lower border of the septum nasi. It communicates
with the nasal cavity through the naso-palatine canal. It consists of a
tube of hyaline cartilage lined with mucous membrane; a small part of
the latter along the inner side is olfactory in character.
THE ORGAN OF TASTE
The peripheral part of the gustatory apparatus (Organon gustus) is
formed by the microscopic =taste buds= (Calyculi gustatorii), which
occur especially in the foliate, fungiform, and vallate papillæ, in the
free edge and anterior pillars of the soft palate, and the oral surface
of the epiglottis. The taste buds are ovoid masses, which occupy
corresponding recesses in the ordinary epithelium; each presents a
minute opening, the gustatory pore. The buds consist of fusiform
supporting cells grouped around central =gustatory cells=. The latter
are long and narrow; the peripheral end of each bears a small filament,
the gustatory hair, which projects at the gustatory pore; the central
end is produced to form a fine process which is often branched. The
taste buds are innervated by fibers of the glosso-pharyngeal nerve and
the lingual branch of the trigeminus.
SENSE ORGANS AND SKIN OF THE OX
THE EYE
The =eyelids= are thick, prominent, and less pliable than those of the
horse. The lower lid bears a considerable number of cilia, which are,
however, finer than those of the upper lid. The tarsal glands are more
deeply embedded and therefore not so evident. The =conjunctiva= of the
lower lid presents folds or ridges, and one or two prominences which
contain numerous leukocytes; the conjunctival epithelium is transitional
in type. The superficial part of the cartilage of the =third eyelid= is
leaf or shovel-shaped and thicker than in the horse; the edge bears a
narrower process, on which there is a transverse bar, giving the
arrangement some resemblance to an anchor. The =gland= of the third
eyelid is very large—an inch or more in length—and may be divided into
two parts. The deep part is pink and consists of loose lobules, but the
much larger superficial part is more compact. There are two large and
several smaller excretory ducts. The subconjunctival tissue of the third
eyelid contains lymph nodules, which are specially numerous on the
bulbar side.
[Illustration:
FIG. 583.—EYE OF OX. (After Ellenberger-Baum, Anat. für Künstler.)
]
The =lacrimal gland= is thick and distinctly lobulated. It is more or
less clearly divided into a thick upper and a thinner lower part
(Glandula lacrimalis superior, inferior). There are six to eight larger
excretory ducts and several smaller ones. The =naso-lacrimal duct= is
shorter than in the horse, and is almost straight. Its terminal part is
inclosed between two plates of cartilage, and it opens near the nostril
on the outer wall; the orifice is placed on the inner side of the alar
fold of the inferior turbinal, and is therefore not easily found.
[Illustration:
FIG. 584.—LEFT EYEBALL OF OX _in situ_, EXTERNAL VIEW.
_19_, Orbital fat. (After Ellenberger-Baum, Anat. für Künstler.)
]
The =eyeball= resembles that of the horse in shape, but is considerably
smaller.
The average transverse diameter is about 42 mm., the vertical diameter
41 mm., and the axis 36 mm. The angle between the axes is about 119°.
The =sclera= is often more or less pigmented; where non-pigmented it may
have a bluish tinge. The point of entrance of the optic nerve is about 2
mm. external to the vertical meridian, and about 7 mm. below the
horizontal meridian.
The thickness of the sclera is about 2 mm. at the posterior pole, 1
mm. at the equator, and 1.2 to 1.5 mm. near the cornea.
The =cornea= is thicker than that of the horse.
The =tapetum= of the chorioidea is extensive at the outer side, but is a
narrow strip internally. It has a metallic luster, shading from a
brilliant green to a deep blue; centrally it has a reddish sheen.
The =iris= is usually very dark colored. The granula form a continuous
series of small nodules along the upper margin of the pupil and are most
prominent centrally; they are very small on the lower margin.
The =optic papilla= is much smaller and is not so sharply defined on
ophthalmoscopic examination as that of the horse. Several relatively
large retinal arteries radiate from the center of the papilla to the
periphery of the retina. They may be seen to wind spirally around the
veins, which are very large.
The arteria centralis retinæ arises from a posterior ciliary artery
and divides close to the optic papilla into three branches usually; of
these the upper is larger than the two lateral branches. The retina is
more vascular than that of the horse; it has a round area centralis at
the inner side, which is continued outward by a narrow strip of a
similar histological structure.
The =vitreous body= is less fluid than that of the horse.
THE EAR
The =external ear= is inclined outward. The middle part is much wider
and less curved than in the horse. The apex is also wide and does not
curve forward. The lower part of the anterior border is bent backward
and bears long hairs. The posterior border is thin and is regularly
convex, except below, where it is indented. The opening is wide and the
concave surface presents four ridges; the convex surface presents
corresponding depressions. The styloid process of the conchal cartilage
is short and blunt. The edges of the annular cartilage are in contact at
the inner side and the upper border is notched externally. The scutiform
cartilage is a very irregular quadrilateral plate; it is situated on the
lateral aspect of the cranium with its concave surface in contact with
the fat and temporalis muscle. The osseous external auditory meatus is
directed practically straight inward; it is about twice as long as that
of the horse, and tapers very gradually from without inward. The chief
special characters of the =auricular muscles= are as follows: (1) The
scutularis blends with the frontalis muscle. The interscutularis arises
from the base of the processus cornu (or the corresponding area in
polled cattle) and from the frontal crest. (2) The cervico-scutularis
arises from the posterior surface of the cranium below the frontal
eminence, and receives slips from the parieto-auricularis and
cervico-auricularis superficialis. (3) The zygomatico-auricularis and
scutulo-auricularis superficialis inferior are fused. (4) The
scutulo-auricularis superficialis superior is distinct from the
interscutularis; it arises from the superficial face of the scutiform
cartilage. (5) The cervico-auricularis superficialis arises from the
ligamentum nuchæ and ends on the convex surface of the conchal
cartilage. (6) The parieto-auricularis arises from the nuchal surface of
the frontal bone, the adjacent part of the parietal bone, and the
ligamentum nuchæ; it is inserted below the preceding muscle. (7) The
scutulo-auricularis superficialis accessorius arises from the
superficial face of the scutiform cartilage and is inserted by a round
tendon into the anterior part of the convex surface of the conchal
cartilage. (8) The cervico-auricularis profundus minor consists of two
fasciculi; the inner, narrow part is deep red in color, and arises from
the fascia of the cervical muscles external to the occipital attachment
of the ligamentum nuchæ; the outer, wider part is pale, and arises
beneath the cervico-auricularis superficialis, indirectly from the
scutiform cartilage. The two unite and are inserted into the lower
aspect of the base of the conchal cartilage. (9) The scutulo-auricularis
profundus minor arises from the temporal crest above the external
auditory meatus and is inserted into the anterior part of the deep face
of the scutiform cartilage.
The =cavum tympani= is small; it communicates ventrally with the
air-cells of the bulla ossea. The tympanic membrane is nearly circular
and is not so oblique as in the horse. The auditory ossicles are smaller
than those of the horse; the malleus is more curved, the body of the
incus is longer, and there is a small prominence on the front of the
head of the stapes for the attachment of the stapedius muscle.
The =Eustachian tube= is small and is only about two inches long. The
pharyngeal opening is small and is situated on the side of the fornix of
the pharynx close to the base of the cranium. There is no flap-like
expansion of the cartilage, but the inner border of the orifice is
formed by a fold of mucous membrane.
The =internal ear= has essentially the same arrangement as in the horse.
COMMON INTEGUMENT
The thickness of the =skin= of the ox is greater than that of any of the
other domesticated animals; in general it is about 3 to 4 mm., but at
the root of the tail and the point of the hock it is about 5 mm. and on
the brisket 6 to 7 mm. The variably developed prominence at the anterior
part of the pectoral region known as the brisket consists of a fold of
skin (Plica colli ventralis longitudinalis), which contains posteriorly
a mass composed of coarse fibrous trabeculæ and fat.
The =cutaneous glands= are fewer and less developed than in the horse.
Except about the natural openings, at the point of the hock, and the
flexion surface of the fetlock, the =sweat glands= do not form a coil,
but are enlarged at the deep end and are variably flexuous. The
=sebaceous glands= are best developed about the natural openings and on
the udder, but there are none on the teats. The =naso-labial glands=
form a thick layer under the bare skin of the muzzle. They are compound
tubular glands and are lined with cubical epithelium. The openings of
their excretory ducts are easily seen.
The =hairs= are extremely variable in color and size in the different
breeds and in different individuals. The hair of the frontal region is
often curly, especially in the bull. There is no mane, and the long
hairs of the tail occur only at the end, where they form the “brush”
(Cirrus caudæ).
[Illustration:
FIG. 585.—CLAWS OF OX, VOLAR ASPECT. (After Ellenberger-Baum. Anat.
für Künstler.)
]
The =claws=, four in number on each limb, cover the ends of the digits.
Those of the chief digits conform in a general way to the shape of the
third phalanges, and each may be regarded as having three surfaces. The
abaxial or outer surface is convex from side to side, and is marked by
ridges parallel with the coronary border. Its anterior part is concave
from edge to edge, and the angle which it forms with the ground is about
30°. The interdigital or inner surface is concave and grooved; it
touches the opposite claw only at its ends. The inferior or ground
surface consists of two parts, viz., a slightly concave sole, which is
pointed in front and widens behind, and a prominent bulb of soft thin
horn, which is continuous above with the skin. The claw may be regarded
as consisting of three parts—periople, wall, and sole. The periople
surrounds the coronary border in the form of a flat band, which is about
half an inch wide, except at the heels, where it widens to cover the
entire surface. The wall forms most of the abaxial or outer part of the
claw and is reflected in front upon the interdigital surface. It thins
out toward the bulb or heel, which appears, as stated above, to consist
of the thin expansion of the periople. The sole occupies the angle of
inflection of the wall; it is continuous without demarcation with the
periople of the bulb. The perioplic matrix bears relatively long
papillæ. The coronary matrix is much less developed than in the horse
and its papillæ are short. The sensitive laminæ are much narrower and
are more numerous than in the horse; secondary laminæ are not present.
The matrix of the sole is not marked off behind from that of the
periople; its papillæ are very small and close together. The matrix of
the bulbs is separated from the flexor tendon by a mass of elastic,
fatty tissue, which is analogous with the plantar cushion of the horse.
The papillæ here are long and often compound.
[Illustration:
FIG. 586.—SAGITTAL SECTION OF DISTAL PART OF FORE LIMB OF OX.
]
The accessory digits bear short conical horn capsules which resemble in
a general way those of the chief digits, and have a similar matrix,
which covers one or two nodular vestigial phalanges. From these a
fibrous band descends obliquely on the volar aspect of each chief digit
and is attached below to the distal phalanx and sesamoid bones, sending
fibers also to the elastic pad of the heel.
The =horns= (Cornua) inclose the horn processes of the frontal bones
(except in the polled breeds). They vary very greatly in size, form, and
curvature. The root or base of the horn (Radix cornus) has a thin edge
which is continuous with the epidermis. It is covered by a thin layer of
soft horn similar to the periople of the hoof of the horse. Near the
root the horn is encircled by variable rings. Toward the apex (Apex
cornus) the thickness of the horn increases till it becomes practically
a solid mass. The horn consists mainly of tubes which are very close
together, except at the rings, where there is more intertubular horn.
The =matrix= of the horn (Matrix cornus) is united to the horn process
by periosteum which is traversed by numerous blood-vessels. The matrix
at the root of the horn is thick and bears long, slender papillæ; in the
body of the horn it becomes thin and the papillæ are smaller, but
increase in size apically. Rudimentary papillated laminæ also occur.
The =skin= of the =sheep= varies in thickness from 0.5 to 3 mm., but
differs greatly in fineness and in other respects in various breeds. In
Merinos considerable folds occur on the neck. Cutaneous pouches (Sinus
cutis) are constantly present in certain situations. The =infraorbital=
or =lacrimal pouch= (Sinus cutaneus infraorbitalis) is an invagination
about half an inch in depth, which is situated in front of the inner
angle of the eye. It bears scattered fine hairs, into the follicles of
which large compound sebaceous glands open; coil glands are also
present. The secretion of the glands is fatty and forms a yellow sticky
covering on the skin when dry. The =inguinal= (or mammary) =pouch=
(Sinus cutaneus inguinalis) is much more extensive, and is situated in
the inguinal region in both sexes. The skin of the pouch bears scattered
fine hairs and contains well-developed sebaceous glands and exceedingly
large coil glands. The =interdigital pouch= (Sinus cutaneus
interdigitalis) is a peculiar tubular invagination of the integument
which opens at the anterior part of the interdigital cleft. On sagittal
section it appears as a bent tube, an inch or more (ca. 2.5 to 3 cm.) in
length, and about a fourth of an inch (ca. 6 to 7 mm.) in diameter. The
pouch extends downward and backward, and then curves sharply upward
between the distal ends of the proximal phalanges. Its deep blind end is
somewhat ampullate. The subcutis forms a capsule around it. The skin of
the pouch is thin and pale; it bears fine colorless hairs, the follicles
of which receive the secretion of several sebaceous glands. The coil
glands here are compound and very large; they open into the
hair-follicles or directly into the pouch. The secretion of the glands
is a colorless fatty substance. The skin is covered in great part by
wool, which is similar in structure to hair, but is finer, curly, and
usually contains no medullary cells. The follicles of the wool are
curved, and are arranged more or less distinctly in groups of ten or a
dozen, several of which open in common on the surface. A considerable
part of the face and the limbs is covered with short, stiff hair, and
long hairs occur more or less interspersed among the wool. The claws
resemble those of the ox. The horns, when present, are more or less
prismatic, distinctly ringed, and vary in length and curvature in
different breeds. Their structure is similar to those of the ox.
The olfactory and gustatory organs resemble in general those of the
horse.
SENSE ORGANS AND INTEGUMENT OF THE PIG
THE EYE
The posterior part of the orbital margin is formed chiefly by the
orbital ligament, which extends from the extremely short supraorbital
process to the small eminence at the junction of the malar and the
zygomatic process of the temporal.
Cilia occur only on the upper eyelid. The inner canthus is prolonged by
a groove on the infraorbital region. The tarsal glands are very short
and curved. The conjunctival epithelium is of the transitional type with
many goblet cells.
The deep part of the cartilage of the third eyelid is broad and
spoon-like, the superficial part somewhat anchor-shaped. In addition to
the gland which surrounds the deep part of the cartilage, there is a
deeper gland of Harder (Glandula palpebræ tertiæ profunda), which is
surrounded by a distinct capsule and a blood-sinus. This gland is
brownish or yellowish-gray in color, elliptical in outline, and about an
inch (2 to 3 cm.) in length. It is situated deeply below the attachment
of the inferior oblique muscle.
The caruncula lacrimalis has the form of a ridge; it divides into two
branches which join the skin at the inner commissure. It is red in color
and contains numerous large coil glands.
The lacrimal gland is mucous in type. There is no lacrimal sac, and the
two lacrimal ducts pass through separate openings at the infraorbital
margin. The naso-lacrimal duct is usually short and opens into the
inferior meatus at the posterior end of the inferior turbinal.[229]
The eyeball appears small, partly on account of the narrowness of the
palpebral opening; it closely approaches the spherical form. The cornea,
although in reality almost circular, appears oval when viewed from the
front, the inner end being much the broader. The chorioid has no
tapetum. The iris is usually dark grayish-brown or yellowish-brown, but
sometimes has a blue tinge. The pupil is a transverse oval in ordinary
light, but almost circular when dilated; granula are not present. The
optic papilla is nearer the posterior pole than in the horse and ox, and
has a distinct central artery and vein.
THE EAR
The external ear differs considerably in size, thickness, and position.
It may be carried vertically, inclined inward, or hang downward. It is
relatively wide and is little curved except at the base. The concave
surface presents several cutaneous ridges which correspond approximately
with the long axis of the ear. The anterior border of the concha is
strongly recurved in its lower part, and divides into two branches, one
of which passes almost horizontally backward in the cavum conchæ, while
the other continues the general direction of the border. The posterior
border is slightly concave above, strongly convex below, forming a
prominence somewhat analogous to the lobule of the human ear. The
osseous external auditory meatus is very long and is directed downward
and inward. The tympanic membrane is almost circular.
The tympanic cavity proper is small, but it is continuous with the
numerous cells of the large bulla ossea. The Eustachian tube is short;
its pharyngeal opening is situated in the upper part of the wall of the
pharynx immediately behind the posterior nares. It is somewhat
infundibular, and is bounded internally by a thick fold of mucous
membrane (Torus tubarius).
THE SKIN AND APPENDAGES
The thickness of the skin in improved breeds is 1 to 2 mm. Fat usually
accumulates in the subcutis and forms a distinct and often extremely
thick panniculus adiposus over the greater part of the body.
The sebaceous glands are in general small and much fewer than in the
other animals. The sweat glands, on the other hand, are large, yellow or
brownish in color, and are in many places visible to the naked eye. At
the inner side of the carpus there are small cutaneous diverticula, the
so-called carpal glands, into which numerous compound coil glands open.
Large glands also occur in the skin of the digits and interdigital
space. Compound tubular glands are present in the skin of the snout.
Large sebaceous and sweat glands are found at the entrance to the
preputial diverticulum.
The hairs are sparsely scattered in improved breeds—indeed, in some
cases the skin is almost bare. The long hairs or bristles are arranged
usually in groups of three. They are most developed on the neck and
back. The bristles about the snout and the chin are sinus hairs.
The =claws= and their matrix resemble those of the ox, but the bulbs are
more prominent and form a greater part of the ground surface; they are
also better defined from the sole, which is small. The claws of the
accessory digits are more developed and their parts better
differentiated than those of the ox.
The olfactory region is extensive in correlation with the large size of
the olfactory bulbs; the mucous membrane here is brown in color.
SENSE ORGANS AND INTEGUMENT OF THE DOG
THE EYE
The posterior margin of the orbit is formed by the orbital ligament, as
in the pig. The orbital axes if produced backward would include an angle
of about 79°, the optic axes an angle of about 92.5° (Koschel).
The lower eyelid has no distinct cilia. The inner angle is wide, the
lacus lacrimalis shallow, and the caruncula lacrimalis small and
yellowish-brown. The conjunctival epithelium is cylindrical, with many
goblet cells. The gland which surrounds the deep end of the cartilage of
the third eyelid is large and pink; it is a mixed gland.
The lacrimal gland is flat and lies chiefly under the orbital ligament.
It is pink in color and mixed in structure. The naso-lacrimal duct is
variable in arrangement and may differ on the two sides. It may open
into the inferior meatus immediately after its emergence from the
osseous lacrimal canal; thence it continues forward and opens on the
lateral wall of the nostril below the inferior turbinal fold.
The eyeball is almost spherical and is relatively large, especially in
the small breeds. The sclera is thick in the ciliary region, where it
contains a well-developed venous plexus; in the vicinity of the equator
it is thin, and the chorioid shows through it. The cornea is almost
circular. The chorioid is richly pigmented, and presents a well defined
=tapetum cellulosum=; this is somewhat triangular in outline and has a
metallic luster. Its color is often golden green, shading to blue
peripherally, but the blue tone may predominate, and in other cases it
is mainly golden yellow or reddish-yellow. The appearance is due to
several layers of peculiar flattened polygonal cells. The ciliary muscle
is more developed than in the other species. The iris is commonly light
or yellow brown, but not rarely has a blue tinge; the color often
differs in the two eyes. The pupil is round; its edge is either smooth
or bears minute round prominences. The retina presents a round area
centralis external to the optic papilla. The latter is variable in
outline; commonly it has the form of a triangle with the angles rounded
off, but is often round or oval. Branches of the central vessels of the
retina radiate from the middle of the papilla. The surfaces of the lens
are not so strongly curved as in the other domestic animals, and there
is little difference in the radius of curvature of the two surfaces.
THE EAR
The external ear differs greatly in size and form in the various breeds;
in most it is relatively wide and thin and the greater part of it hangs
down over the opening. The anterior border has a prominence (Spina
helicis) at its lower part, and below this it divides into two branches
(Crura helicis). One of these continues down to a blunt point, while the
other turns in to the cavity of the concha. The posterior border forms a
pouch below its middle, and is thick and rounded in its basal part. Here
the conchal cartilage bears a pointed process (Processus uncinatus),
which projects upward and backward. The outer wall of the cavum conchæ
is supported by a quadrilateral plate (Tragus) above and a semiannular
cartilage below. The concave surface presents several cutaneous folds,
and in the cavum conchæ there are ridges and irregular prominences.
There are long hairs on the borders, apex, and the folds of the concave
surface, but the skin of the cavum conchæ is bare. The annular cartilage
is a complete ring. The osseous external auditory meatus is wide and
extremely short.
The auricular muscles are thin. The scutularis is extensive and is
divisible into interscutularis and fronto-scutularis. It partly covers
the occipitalis muscle, which is oval and unpaired and ends in the
fascia of the frontal region. The scutulo-auriculares superficiales,
inferior et accessorius, and the cervico-scutularis are not
differentiated as separate muscles. The cervico-auricularis
superficialis and the parieto-auricularis both bifurcate and are
inserted into the base of the concha and the scutiform cartilage. The
parotido-auricularis is narrow and almost long enough to meet the
opposite muscle. The tragicus consists of two parts; of these the
lateral one is long and arises from the border of the mandible above the
angular process. The helicis and the verticalis auriculæ are well
developed.
The tympanic cavity is very roomy, extending ventrally into the large
but simple cavity of the bulla ossea. The tympanic membrane is extensive
and oval. The promontory is very pronounced. The auditory ossicles are
large. The Eustachian tube is short, and has a fibrous outer wall. Its
pharyngeal opening is an oblique slit situated on the lateral wall of
the naso-pharyngeal meatus, and is margined internally by a thick mucous
fold.
The cochlea has three and a half turns and is more sharply pointed than
in the ungulates.
THE SKIN AND APPENDAGES
The skin varies greatly in thickness in different breeds. It is
remarkably loose on the dorsal aspect of the neck and trunk, where it
can be raised in extensive folds. The coat is also subject to extreme
variation in length, thickness, color, etc. The hairs are arranged in
groups of three to a large extent. The sebaceous glands are best
developed in the short and rough haired breeds. They are largest and
most numerous at the lips, anus, dorsal surface of the trunk, and
sternal region. The sweat glands are relatively better developed in the
long and fine haired breeds. The largest are found in the digital pads.
Coil glands occur in the skin of the muzzle, the perineum, and the
paranal pouches.
On the flexion surface of the carpus and digit there are hairless,
cushion-like pads. The carpal pad (Torus carpalis) is situated medial
and distal to the accessory carpal bone. The metacarpal and metatarsal
pads (Torus metacarpalis, metatarsalis) are the largest and are situated
behind the distal ends of the metacarpal or metatarsal bones and the
greater part of the first phalanges. They are somewhat heart-shaped,
with two unequal lateral lobes, and the apex distal. The
metapodiophalangeal joints rest on them when the paw supports the
weight. The digital pads (Tori digitales) are oval and are much smaller;
they similarly support the second digital joints. That of the first
digit is small on the fore limb, and usually absent from the hind limb.
Each receives two suspensory bands from the tubercles at the distal end
of the corresponding second phalanx. The pads have a basis of
fibro-elastic tissue and fat, which is intimately adherent to the skin
and is connected by trabeculæ with the bones and tendons. The epidermis
is thick and largely keratinized, and is studded with numerous rounded
papillæ which are readily seen with the naked eye. The corium has large
papillæ, and contains sweat glands and lamellar corpuscles.
The =claws= (Ungues) correspond in form to the ungual part of the distal
phalanges which they inclose. The horn of the claw consists of a body or
wall and a sole. The former is strongly curved in both directions, and
is compressed laterally. Its root or coronary border fits into the
depression under the bony collar or ungual crest of the third phalanx
and is covered by skin. The lateral borders converge and inclose the
sole anteriorly. The matrix presents a coronary part which bears papillæ
only near the coronary border. On the dorsal surface it is thickened to
form a ridge, and the corresponding part of the horny covering is thick
and maintains the pointed character of the claw. The matrix of the sides
of the wall bears small laminæ which converge to the matrix of the sole.
The latter is papillated. When the flexor muscles are inactive, the
distal phalanges and the claws are maintained in dorsal flexion by two
elastic ligaments. These arise from the tubercles at the proximal end of
the second phalanx and converge to the dorsal aspect of the ungual crest
of the third phalanx.
[Illustration:
FIG. 587.—PADS OF PAW OF DOG.
_a_, Carpal pad; _b_, metacarpal pad; _c^1-c^5_, digital pads. (From
Leisering’s Atlas.)
]
[Illustration:
FIG. 588.—HALF OF CLAW OF DOG, INNER SURFACE.
_a_, _a′_, Coronary part, _b_, volar part of wall; _c_, sole; _d_,
section of _c_; _e_, section of wall; _1_, coronary border; _2_,
apex; _3_, dorsal surface. (From Leisering’s Atlas.)
]
OLFACTORY AND GUSTATORY ORGANS
The =olfactory region= lies above the lamina transversa, which separates
it from the naso-pharyngeal meatus. The mucous membrane is distinguished
by its thickness and yellow color, and is very extensive. It covers
about half of the large ethmoturbinals, and one-third to one-half of the
septum nasi. The ethmoturbinal which projects into the frontal sinus and
the adjacent inner wall of the sinus is olfactory in character.
Olfactory nerve-fibers ramify in the vomero-nasal organ (of Jacobson).
The gustatory apparatus presents no special features of importance.
INDEX
Abdomen, muscles of, 245
of dog, 326
of pig, 313
muscles of, 301, 313
Abdominal aorta, 536
branches of, 566
of dog, 638
artery, anterior, 541
posterior, 579
subcutaneous, 580
cavity of horse, 352
of ox, 390
fascia of horse, 245
muscles of dog, 326
of horse, 245
of pig, 301, 313
panniculus, 245
plexuses, 713
tunic of horse, 245
of pig, 313
veins, 598
Abducent nerve, 683
Abduction of joints, 172
Abductor cruris posterior muscle, 327
digiti quinti muscle, 324, 329
hallucis muscle, 329
pollicis brevis et opponens pollicis muscle, 324
Abomasum of ox, 390, 392 cavity of, 396
of sheep, 409
Accelerator urinæ, 499
Accessory carpal bone, 84
fibro-cartilage of patella, 105
organs, 330
pancreatic duct of dog, 431
of horse, 373
pillars of rumen, 393
spleens of horse, 379
thyroids of dog, 468
of horse, 458
of ox, 464
Acetabular angle, 94, 96
fossa, 96
notch, 96
Acetabulum of dog, 167
of horse, 96
of ox, 131
of pig, 148
Acromion of dog, 162
of ox, 127
Adduction of joints, 172
Adductor brevis muscle of horse, 282
digiti quinti muscle of dog, 324
secunda muscle of dog, 324
hallucis muscle of dog, 329
longus muscle of horse, 282
magnus muscle of horse, 282
Adductor muscle of dog, 328
of horse, 282
of ox, 308
of pig, 316
parvus muscle of horse, 282
pollicis muscle of dog, 324
Aditus laryngis of horse, 447
Adrenal bodies of dog, 484
of horse, 477
structure of, 478
of ox, 481
of sheep, 481
plexus, 714
Adventitia of seminal vesicles, 492
of vas deferens, 489
Æquator lentis, 746
Æsthesiology, 734
Air-cells of lungs, 457
Alæ nasi, 436
Alar canal, 51
cartilage, 437
of ox, 459
fold, 437
foramen, 68
Alimentary canal, 330
Alveolar arch, superior, 69
artery, inferior, 552
of dog, 635
of pig, 627
border of mandible, 64
ducts of lungs, 457
nerve of dog, 729
of horse, 681, 682
periosteum of teeth, 339
tuberosity of horse, 69
vein, 589
inferior, 587
Alveoli of horse, 58
of lungs of horse, 457
of thyroid gland of horse, 458
Alveus, 669
Amphiarthroses, 172
Ampulla ductus deferentis, 489
of semicircular canals, 758
of uterus of bitch, 523
recti of horse, 370
Amygdaloid nucleus, 676
Anal glands of dog, 432
lymph glands, 605
of ox, 626
of pig, 632
sacs of dog, 432
Anastomosis of arteries, 524
Anatomy, 17
gross, 17
macroscopic, 17
microscopic, 17
philosophical, 17
special, 17
Anatomy, systematic, 17, 18
topographic, 17, 18
veterinary, 17
Anconeus muscle, 262
of pig, 315
Angiology, 524
Angle, duodenal, of horse, 372
of mandible, 64
splenic, 372
Angular artery of eye, 550
of ox, 611
movements of joints, 171
process of mandible of dog, 159
Annular cartilage of ear, 748
ligament, 212
anterior, of horse, 263
of manus of horse, 263
of pelvic limb of horse, 274
posterior, of carpus of horse, 263
Annulus tympanicus, 753
Ansate fissure of dog, 726
Anterior angle of pancreas, 372
of scapula, 76
annular ligament of horse, 263
aorta, 537
aperture of thoracic cavity, 450
fossa of skull, 70
nares, 436
Antero-external angle of ischium, 95
Antero-internal angle of ischium, 95
Antibrachial artery of dog, 635
Anticlinal vertebræ of horse, 42
Antitragicus muscle, 751
Antitragus, 748
Antrum pylori, 358
Anus of horse, 371
of ox, 400
Aorta, 535
abdominal, 536
branches of, 566
of dog, 638
anterior, 537
arch of, 535
of ox, 609
of pig, 627
thoracic, 536
branches of, 565
Aortic orifice of heart of horse, 533
plexus, 712
Aperture, anterior, of thoracic cavity, 450
of abdominal cavity, 353
pharyngeal, of horse, 447
Apex cæci, 364
Apical lobe of lungs of ox, 462, 463
Aponeuroses, 211
Aponeurosis of external oblique muscle, 246
of internal oblique muscle, 248
of transversus abdominis muscle, 249
pharyngeal, 350
Appendages of skin, 762
Appendix testis, 485
ventriculi laryngis, 447
Aquæductus cochleæ, 759
vestibuli, 758
Aqueduct of cerebrum, 664
of Sylvius, 664
Aqueous humor, 746
Arachnoid granulations, 647
Arachnoidea, 646
spinal, 647
Arch, alveolar, superior, of horse, 69
of aorta, 535
of cricoid cartilage, 441
plantar, 581
venous, 595
zygomatic, 56, 67
Arciform ligaments, 182
Arcuate fibers, external, 657, 658
internal, 658
of cerebellum, 661
Arcus terminalis, 564
venosus plantaris, 599
volaris, 595
Area acustica, 662
of ox, 715
centralis retinæ, 746
cochlæ, 759
parolfactoria, 671
radicularis ventralis, 649
tentorial, 668
vestibularis superior, 759
Arm, bones of, 28
muscles of, 259
of ox, muscles of, 302
of pig, muscles of, 314
Arrectores pilorum, 763
Arterial circle of Willis, 546
plantaris lateralis of ox, 620
reticularis of ox, 615
Arteries or artery, 534, 535
abdominal, anterior, 541
posterior, 579
alveolar, 552
of dog, 635
of pig, 627
anastomosis of, 524
angular, of eye, 550
of ox, 611
antibrachial, of dog, 635
asternal, 541
auricular, 550
of dog, 635
of ox, 611
of pig, 627
posterior, 550
axillary, 556
basilar, 546
bicipital, of dog, 635
brachial, 538, 556
deep, 559
of dog, 633, 635
of ox, 609, 612
of pig, 627
brachiocephalic, 538
of dog, 633
of pig, 627
bronchial, 457, 565
of ox, 614
of pig, 627
broncho-œsophageal, 565
buccinator, 555
of pig, 627
cæcal, 570
carotid, common, 541
of dog, 634
right, 542
external, 547
of ox, 611
internal, 546
of dog, 633, 634
of ox, 610
of pig, 627
central, of retina, 554
cephalic, 541
cerebral, 546
posterior, 546
cerebrospinal, 545
of dog, 634
cervical, deep, 540
inferior, 541
of dog, 633
of ox, 609
of pig, 627
superior, 540
ciliary, 554
circumflex, anterior, 558
external, 577
of ox, 619
of dog, 635
of ox, 612
of scapula, 556
posterior, 556
coccygeal, lateral, 577
middle, 575
of dog, 641
of ox, 618
cœliac, 566
of dog, 638
of ox, 614
of pig, 627
colic, 570
communicating posterior, 546
condyloid, 545
of dog, 634
of ox, 611
coronary, 535, 537
of dog, 632
of ox, 609
cremasteric, 578
dental, 552
inferior, 555
digital, 564
common, 563
of ox, 621
external, of ox, 614, 620
of dog, 637, 641
of pig, 629, 630
dorsal, 538
of dog, 633
of ox, 609
dorso-intercostal, 538
end, 524
ethmoid, 554
external coat, 525
facial, 547
of dog, 635
transverse, 550
femoral, 579
anterior, 580
deep, 580
of dog, 639
of ox, 619
of pig, 630
posterior, 580
femoro-popliteal, 580
frontal, 553
gastric, 506
of dog, 638
gastro-duodenal, 569
gastro-epiploic, 569, 570
gastro-hepatic, of pig, 627
gastro-splenic, of dog, 638
gluteal, anterior, 577
of dog, 641
of ox, 619
posterior, 575
hæmorrhoidal, 594
of dog, 641
hepatic, 377, 567
of dog, 638
of ox, 614
hypogastric, 573
ideal, 570
ileo-cæcal, 570
ileo-cæco-colic, of ox, 617
iliac, circumflex, 578
of dog, 639
external, 578
of ox, 619
internal, 573
of ox, 618
iliaco-femoral, 577
of ox, 619
ilio-lumbar, 577
of dog, 641
of ox, 619
of pig, 630
incisor, 552
infraorbital, 555
of dog, 635
of pig, 627
intercostal, 565
of ox, 614
of pig, 627
internal coat of, 525
interosseous, common, 561
dorsal, 562
of dog, 635
of ox, 612
recurrent, 561
intestinal, 570
intima of, 525
ischiatic, 575
of ox, 619
labial, 549
of ox, 611
superior, 550
lacrimal, 553
laryngeal, of ox, 610
lingual, 548
of dog, 634
of ox, 611
lumbar, 571, 573
of ox, 618
of pig, 629
malar, 555
mammary, 580
of ox, 619
masseteric, inferior, 547
of ox, 612
mastoid, 545
maxillary, external, 547
internal, 551
of ox, 612
of dog, 635
of ox, 611
of pig, 627
maxillo-muscular, 547
median, 559
of ox, 612
meningeal, anterior, 546
middle, 552
of dog, 634
posterior, 545
mental, 552
mesenteric, great, 570
of dog, 638
of ox, 615
of pig, 628, 629
posterior, of ox, 618
small, 571
metacarpal, dorsal, 562
external volar, 562
internal volar, 562
large, 563
of dog, 635, 636, 637
of ox, 614
of pig, 629
palmar, 563
metatarsal, 581
dorsal, 585
of ox, 620
great, 585
internal superficial plantar, 619
of dog, 640, 641
of pig, 630
middle coat of, 525
nasal, 550
of ox, 611
nutrient, of femur, 580
of humerus, 559
of tibia, 581
obturator, 577
of ox, 619
occipital, 544
of dog, 634
of ox, 611
of pig, 627
œsophageal, 565, 567
of ox, 614
of pig, 627
of adrenal bodies of horse, 478
of articulations, 171
of bladder of horse, 477
of bulb, 575
of clitoris, 575
of conjunctiva, 737
of corpus callosum, 546
of dog, 633
of external ear, 752
of eyelids, 737
of Fallopian tubes of mare, 511
of first phalanx, 564
of hoof, 771
of internal ear, 761
of ox, 609
of pelvic limb of ox, 619
of penis, 496
dorsal, 580
of pig, 627
of plantar cushion, 564
of rete carpi volare, 562
of retina, 746
of second phalanx, 564
of skin, 762
of small intestine, 570
of third phalanx, 564
of tympanum, 755
of uterus, 513
of vagina, 514
of vascular tunic of eye, 744
omaso-abomasal, of ox, 615
ophthalmic, 553
of dog, 635
of ox, 612
orbital, 555
ovarian, 571
of mare, 510
palatine, 555
of pig, 627
palato-labial, 555
pancreatic, 569
pancreatico-duodenal, 569
parotid, 543
of pig, 627
perineal, 574
of dog, 641
peroneal, 585
perpendicular, 564
pharyngeal, 548
of ox, 611
phrenic, 565
of ox, 614
phrenico-abdominal, of dog, 639
of pig, 628
plantar, 581
of dog, 640
of ox, 619
popliteal, 581
of ox, 619
of pig, 630
preplantar, 564
prepubic, 579
prevertebral, 545
pterygoid, 552
pudic, external, 580
internal, 573
of pig, 630
pulmonary, 457, 524, 535
pyloric, 569
radial, anterior, 559
of dog, 635
of ox, 613
posterior, 559
of ox, 612
renal, 475, 571
of dog, 639
of ox, 618
of pig, 628
reticular, of ox, 615
ruminal, of ox, 615
sacral, lateral, 575
middle, of ox, 618
of ox, 619
saphenous, 580
of dog, 640
of ox, 619
of pig, 630
sheath of, 525
spermatic, 487, 489, 571
of dog, 639
of ox, 618
of pig, 627
sphenopalatine, 555
splenic, 569
of dog, 658
of ox, 615
of pig, 628
staphyline, 555
structure of, 525
stylo-mastoid, 550
subcostal, 539
of dog, 633
of ox, 609
sublingual, 548
of dog, 635
submaxillary, 547
submental, 549
subscapular, 556
of dog, 635
of ox, 612
supraorbital, 553
suprascapular, 556
systemic, 524
tarsal, external, 581
of pig, 630
perforating, 585
temporal, anterior deep, 553
of dog, 635
of ox, 612
posterior, deep, 552
superficial, 550
terminal, 524
thoracic, external, 541
internal, 540
of dog, 633
of ox, 609
of pig, 627
thoracico-dorsal, 556
thyroid, accessory, 543
of ox, 610
of pig, 627
thyro-laryngeal, 543
tibial, anterior, 583
of dog, 641
of ox, 620
of pig, 630
posterior, 581
recurrent, 581
tympanic, 552
ulnar, 559
of dog, 637
of ox, 613
superior collateral, of ox, 612
umbilical, 574, 606
of ox, 619
uterine, 571
middle, 578
of dog, 641
of ox, 619
posterior, 574
utero-ovarian, 571
of dog, 639
of ox, 618
vertebral, 540
of dog, 633
of ox, 609
vesical, 574
vesico-prostatic, 574
volar, deep, 562
of second phalanx, 564
Arthrodia, 172
Arthrology, 169
comparative, 203
Articular cartilage, 170
discs, 171
Articularis genu muscle of ox, 307
Articulatio carpi of horse, 183
Articulations, 169, 172
abduction of, 172
adduction of, 172
angular movements, 171
arteries of, 171
atlanto-axial, 176
atlanto-occipital, 176
basi-cornual, 180
capsule, 170
carpal, 183
of dog, 205
of ox, 205
of pig, 205
carpo-metacarpal, 183
cavity of, 170
chondro-sternal, 178
circumduction of, 171
classification of, 169
coccygeal, 175
coffin, 189
costo-central, 177
costo-chondral, 178
costo-transverse, 177
costo-vertebral, 177
crico-arytenoid, 444
crico-thyroid, 444
dorsal flexion of, 171
elbow, 181
of dog, 205
of ox, 205
of pig, 205
extension of, 171
femoro-patellar, 194
femoro-tibial, 196
fetlock, 185
flexion of, 171
folds of, 170
gliding movements of, 171
hip, 192
of dog, 209
of ox, 209
of pig, 209
hock, 199
of dog, 210
of ox, 210
of pig, 210
hyoidean, 180
intercarpal, 183
intercentral, 173
intercornual, 180
intermetacarpal, of dog, 206
of ox, 206
of pig, 206
interneural, 173
interphalangeal, distal, 189
of dog, 209
of ox, 208
of pig, 208
proximal, 188
intertransverse, 175
knee, 183
metacarpo-phalangeal, 185
of dog, 208
of ox, 206
of pig, 208
movable, 170
movements of, 171
Articulations, nerves of, 171
of larynx, 444
of pelvic limb, 190
of dog, 209
of ox, 209
of pig, 209
of ribs, 177
of skull, 179
of thoracic limb, 180
of dog, 205
of ox, 205
of pig, 205
of thorax, 177
of dog, 204
of ox, 204
of pig, 204
overextended, 171
pastern, 188
plantar flexion of, 171
radio-carpal, 183
radio-ulnar, 182
rotation of, 172
sacral, 175
sacro-iliac, 190
of dog, 209
of ox, 209
of pig, 209
shoulder, 180
of dog, 205
of ox, 205
of pig, 205
sternal, 178
stifle, 194
of dog, 209
of ox, 209
of pig, 209
surfaces of, 170
synovial layer of, 170
temporo-hyoid, 180
temporo-mandibular, 179
of dog, 204
of ox, 204
of pig, 204
thyro-hyoid, 444
tibio-fibular, 199
of dog, 210
of ox, 209
of pig, 210
tibio-tarsal, 199
true, 170
veins of, 171
vertebral column, 172
of dog, 204
of ox, 203
of pig, 204
villi of, 170
volar flexion of, 171
Arytenoid cartilages of larynx, 443
of dog, 467
of ox, 459
of pig, 465
ligament, transverse, of larynx, 444
Arytenoideus transversus muscle of larynx of horse, 446
Asternal artery, 541
ribs, 25
of horse, 43
Astragalo-calcaneal ligaments, 202
Astragalo-scaphoid ligaments, 202
Atlantal gland of ox, 623
Atlanto-axial articulation of horse, 176
ligament, inferior, 176
superior, 176
Atlanto-occipital articulation, 176
membrane, inferior, 176
superior, 176
Atlas, 33, 34
of dog, 150
of ox, 112
of pig, 147
Atrio-ventricular groove of heart, 527
opening in left atrium, 530
in right atrium, 530
left, of ventricle, 533
right, of ventricle, 531
Atrium of heart, 529
left, 530
right, 529
openings in, 529
sinus of, 529
ventriculi of ox, 393
Auditory canal, external, 747, 748
meatus, external, 56, 748
internal, 56, 759
nerve, 686
ossicles, 754
process, external, 56, 67
tube, 755
Auricle of horse, 747
Auricular artery, anterior, 550
of dog, 635
of pig, 627
posterior, 550
of ox, 611
branch of vagus, 687
cartilage, 748
lymph gland of dog, 643
muscles, 749
of dog, 780
of ox, 774
nerve, 685
posterior, 695
vein, 588
Auriculopalpebral nerve, 685
of dog, 729
of ox, 717
Axillary artery, 556
ligament of Helmholtz, 755
lymph glands, 605
of dog, 643
of ox, 625
of pig, 631
nerve of horse, 697
Axis, 34
development of, 35
lentis, 747
of dog, 150
of ox, 112
of pelvis, 97
of ox, 133
of pig, 137
optic, 740
Azygos uvulæ, muscle of, 333
Back, fasciæ of, 235
superficial, 235
muscles of, 235
of dog, muscles of, 325
of ox, muscles of, 300
Back of pig, muscles of, 313
Ball-and-socket joint, 172
Bands, longitudinal, of cæcum, 364
muscular, of great colon, 368
Bars of hoof, 764
Bartholin’s ducts of mare, 515
glands of cow, 519
Basi-cornual articulation, 180
Basihyoid bone, 64
Basilar artery, 546
plexus, 592
venous, 592
process, 48
of third phalanx, 91
Basis pedunculi, 664
Belly of muscle, 212
Biceps brachii, 259
of dog, 322
of pig, 314
femoris muscle, 278
of dog, 326
of ox, 306
of pig, 316
rotator tibialis, 280
of ox, 302
Bicipital artery of dog, 635
bursa of horse, 259
groove of humerus, 79
tuberosity of radius, 81
of scapula, 77
Bicuspid valve, 533
Bifurcation of trachea, 449
Bile-duct, common, of sheep, 410
of dog, 431
of ox, 398
of pig, 419, 422
Bipennate muscle, 212
Biventer cervicis muscle of dog, 325
Bladder, 469, 475
arteries of, 477
blood-supply of, 477
fixation of, 476
lateral ligaments of, 476
lymph vessels of, 477
middle ligament of, 476
mucous coat of, 476
muscular coat of, 476
neck of, 416
nerves of, 477
of dog, 484
of ox, 480
of pig, 483
relations of, 476
round ligament of, 476
serous coat of, 476
sphincter of, 476
structure of, 476
trigonum of, 476
veins of, 477
vertex of, 476
Blind sacs of rumen of ox, 392
Blood-vascular system, 524, 525
of dog, 632
of ox, 608
Blood-vessels, 524
of cornea, 742
Body, ciliary, 743
geniculate, 665
of dog, 725
of ox, 716
Body, mammillary, 665
of dog, 726
pineal, 665
of ox, 716
pituitary, 664, 665
of dog, 726
of ox, 716
restiform, 656
vitreous, 746
of ox, 774
Bone or bones, acetabulum, of pig, 148
acromion, of dog, 162
air-spaces, 21
arteries, 21
atlas, 33
of dog, 150
of ox, 112
of pig, 137
axis, 34
of dog, 150
of ox, 112
of pig, 137
basihyoid, 64
carpal, 28, 83
of dog, 164
of ox, 129
of pig, 147
cartilage, 22
cavities, 23
chemical composition, 23
chevron, of dog, 152
clavicle, 27
of dog, 162
compact substance, 20
coracoid, 27
cranial, 27, 47
of dog, 154
of ox, 115
of pig, 139
depressions, 23
descriptive terms, 23
development and growth, 22
digital, 28, 30
diploë, 21
eminences, 23
ethmoid, 52
of dog, 157
of ox, 116
of pig, 142
facial, 27, 57
of dog, 157
of ox, 120
of pig, 142
femur, 29, 97
of dog, 167
of ox, 133
of pig, 148
fibula, 29, 104
of dog, 168
of ox, 134
of pig, 149
flat, 19
frontal, 55
of dog, 155
of ox, 118
of pig, 141
hock, 105
of ox, 134
of pig, 149
humerus, 28, 77
of dog, 162
of ox, 127
of pig, 146
Bone, hyoid, 64
of dog, 159
of ox, 122
of pig, 144
ilium, 29, 93
of dog, 165
of ox, 131
of pig, 148
interparietal, 53
of dog, 155
of ox, 116
of pig, 140
irregular, 19
ischium, 29, 95
of dog, 165
of ox, 131
of pig, 148
lacrimal, 61
of dog, 158
of ox, 121
of pig, 143
long, 19
lymph vessels, 21
malar, 62
of dog, 158
of ox, 121
of pig, 143
mandible, 63
of dog, 158
of ox, 122
of pig, 143
marrow, 21
maxilla, 58
of dog, 157
of ox, 120
of pig, 142
medullary arteries, 21
cavity, 20
membrane, 22
metacarpal, 28, 87
of dog, 164
of ox, 130
of pig, 147
metatarsal, 30, 110
of dog, 168
of ox, 135
of pig, 149
nasal, 61
of dog, 158
of ox, 121
of pig, 143
navicular, 92, 111
nerves, 21
number, 19
occipital, 47
of dog, 154
of ox, 115
of pig, 139
of arm, 28
of face, 27
of forearm, 28
of forefoot, 28
of hand, 28
of leg, 29
of pelvic limb, 29, 92
of dog, 165
of ox, 131
of pig, 148
of skull, 27, 47
of dog, 153
of ox, 115
of pig, 139
of thoracic limb, 27, 74
of dog, 162
Bones, of thoracic limb of ox, 127
of pig, 146
of thorax, 27, 47
of dog, 153
of ox, 115
of pig, 139
os coxæ, 29, 92
of pig, 14
palatine, 60
of ox, 120
of pig, 142
parietal, 54
of dog, 155
of ox, 117
of pig, 140
patella, 29, 104
of dog, 168
of ox, 134
of pig, 149
pelvic, 96
of dog, 167
of ox, 132
of pig, 148
perforations, 23
periosteal arteries, 21
periosteum, 21
phacoid, of cat, 164
phalanges, 29, 89, 111
of dog, 165
of ox, 130, 136
of pig, 148, 150
physical properties, 23
premaxilla, 59
of dog, 157
of ox, 120
of pig, 142
prenasal, of pig, 143
prominences, 23
pterygoid, 60
of dog, 158
of ox, 121
of pig, 143
pubic, 29, 95
of dog, 167
of ox, 131
of pig, 148
radius, 28, 80
of dog, 163
of ox, 127
of pig, 147
red marrow, 21
ribs, 25, 43
of dog, 153
of ox, 114
of pig, 138
rostri, of pig, 143
sacrum, 39
of dog, 151
of ox, 114
of pig, 138
scapula, 27, 74
of dog, 162
of ox, 127
of pig, 14
sesamoid, 29, 92, 111
developing in tendon tissue, 211
distal, 29
of dog, 165
of ox, 131, 136
of pig, 148
proximal, 29
short, 19
Bone, sinuses, 21
sphenoid, 50
of dog, 156
of ox, 115
of pig, 141
spongy substance, 20, 21
sternum, 26, 45
of dog, 153
of ox, 115
of pig, 139
structure of, 20
tarsal, 29, 105
of dog, 168
of ox, 134
of pig, 149
temporal, 55
of dog, 156
of ox, 120
of pig, 141
thigh, 29
thorax, 47
of dog, 153
of ox, 115
of pig, 139
tibia, 29, 100
of dog, 167
of ox, 134
of pig, 149
tibial, 29
tissue, 20
tubula vitrea, 21
turbinal, 62, 438
of dog, 158
of ox, 122
of pig, 143, 465
ulna, 28, 82
of dog, 163
of ox, 128
of pig, 147
veins, 21
vertebræ, 24, 31
anticlinal, 42
caudal, 24
cervical, 24
coccygeal, 24, 41
diaphragmatic, 42
lumbar, 24, 38
of dog, 150
of ox, 112
of pig, 136
sacral, 24
thoracic, 24, 35
vessels, 21
vomer, 63
of dog, 158
of ox, 122
of pig, 143
yellow marrow, 21
zygomatic, of horse, 62
Brachia conjunctiva, 661
Brachial artery, 538, 556
deep, 559
of dog, 633, 635
of ox, 609, 612
of pig, 627
plexus, 696
of dog, 730
of ox, 717
of pig, 723
triceps, 260
vein, 593
of dog, 642
Brachialis anticus, 260
muscle, 260
Brachialis muscle of dog, 322
of pig, 315
Brachiocephalic artery, 538
of dog, 633
of pig, 627
trunk of aorta, 537
veins of dog, 641
Brachio-radialis muscle of dog, 322
Brachium pontis, 659
Brachycephalic breed of dogs, 159
Brain, development of, 655
of dog, 724
of horse, 652
of ox, 715
of pig, 720
veins of, 592
Bristles of pig, 778
Broad ligaments of uterus, 356
of bitch, 523
of cow, 518
of mare, 513
Broca’s parolfactory area, 671
Bronchi, interlobular, 457
of dog, 468
of horse, 450, 456
structure of, 456
of ox, 460
of pig, 466
Bronchial artery, 457, 565
of ox, 614
of pig, 627
branches of lungs, 456
of vagus, 690
lymph glands, 457, 603
of dog, 643
of pig, 631
vein, 587
Bronchioles, lobular, 457
respiratory, 457
Broncho-œsophageal artery, 565
Brush of ox, 775
Buccal fascia, 213
glands, 332
of ox, 383
of pig, 410
nerve, 685
of dog, 729
of ox, 717
of pig, 722
Buccinator artery, 555
of pig, 627
muscle, 216
of dog, 318
of ox, 295
nerve of horse, 681
vein, 590
of pig, 630
Bulb of hair, 763
olfactory, 671
of dog, 727
of ox, 717
of pig, 721
Bulbar conjunctiva, 736
fascia of horse, 738
Bulbi vestibuli of mare, 515
olfactorius, 671
Bulbo-cavernosus muscle of penis of ox, 503
of urethra of horse, 499
Bulbo-urethral glands of dog, 506
Bulbo-urethral glands of horse, 493
structure of, 494
of ox, 503
of pig, 505
Bulbus aortæ, 536
oculi, 739
Bulla, lacrimal, of ox, 121
ossea, 57
Burdach’s column, 652
Bursa, bicipital, 259
navicular, of deep digital flexor muscle, 272
of biceps femoris muscle, 279, 280
of flexor pedis perforatus muscle, 293
of gastrocnemius muscle, 290
of rectus femoris muscle, 284
of semitendinosus muscle, 280
ovarica of mare, 511
ovarii of bitch, 522
podotrochlearis, 272
supra-atloid, 174
supraspinous, of horse, 175
of anterior digital extensor muscle, 265
synovial, of infraspinatus muscle, 256
of lateral digital extensor muscle, 266
of teres minor muscle, 257
Bursal synovial membrane, 211
Cæcal artery, 570
lymph glands of pig, 632
Cæco-colic fold, 367
orifice, 364
Cæcum, 363
of dog, 431
of ox, 398
of pig, 420
of sheep, 409
cupulare, 760
vestibulare, 760
Calcaneo-cuboid ligaments, 202
Calcaneo-cunean ligaments, 202
Calcaneo-metatarsal ligament, 201
Calcaneo-scaphoid ligament, 202
Caliber of great colon of horse, 367
Callosal sulcus, 669
Callosomarginal fissure, 669
of dog, 727
of ox, 716
of pig, 721
Calyces majores, 480
minores, 480
Camera oculi, 746
Canal, alar, 51
auditory, external, 748
carotid, 156
carpal, 86
cervical, of cow, 518
of mare, 512
condyloid, of ox, 115
dental, inferior, of horse, 64
Canal, dental, superior, of horse, 59
facial, of horse, 56
femoral, of horse, 282
for naso-lacrimal duct of horse, 71
infraorbital, of horse, 59
inguinal, of horse, 249
lacrimal, osseous, of horse, 61
mandibular, of horse, 64
medullary, of metacarpus of ox, 130
naso-palatine, of ox, 384
of Gartner, 519
of tarsus of horse, 109
of temporal bone of dog, 156
palatine, of horse, 58
parieto-temporal, of horse, 54, 57
petro-basilar, of dog, 156
pterygoid, of horse, 51, 61
sacral, of horse, 41
semicircular, membranous, 760
osseous, 758
semilunar, 91
spiral, of cochlea, 759
subsphenoidal, of horse, 51
supraorbital, of ox, 119
vertebral, of horse, 42
Vidian, of horse, 51, 61
Canalis centralis, 650
Canine teeth, 338, 341, 346
of dog, 425
of ox, 386
of pig, 412
Canthi of eye, 735
Capillaries, 524
Capped hock, 293
Capsular ligament, 170
Capsularis muscle of dog, 328
of horse, 258, 286
of ox, 307
of pig, 314, 317
Capsule, external, 675
fibrous, of liver, 376
internal, 676
joint, 170
of horse, 174
of articulation, 176
of carpal joints, 183
of coffin joint, 189
of elbow joint, 181
of femoro-patellar articulation, 194
of femoro-tibial articulation, 197
of fetlock joint, 185
of hip joint, 192
of hock joint, 200
of lens, 747
of pastern joint, 188
of sacro-iliac articulation, 190
of shoulder joint, 180
of temporo-mandibular articulation, 179
of tenon, 738
of tibio-fibular articulation, 199
splenic, 379
Caput laterale tricipitis, 261
Caput longum tricipitis, 261
mediale tricipitis, 261
Cardiac bronchus of vagus, 690
glands of stomach of horse, 360
impression of lungs of horse, 454
lobe of lungs of ox, 463
muscle, 211
nerves, 712
notch of lungs of horse, 456
plexus, 712
sphincter of horse, 359
veins, 586
Cariniform cartilage, 46
Carnassial teeth of dog, 426
Carotid artery, common, 541
left, 543
of dog, 634
of ox, 610
right, 542
external, 547
internal, 546
of dog, 633, 634
of ox, 611
of pig, 627
canal of dog, 156
foramen of dog, 156
notch of horse, 51
plexus, 711
Carpal articular surface of radius of horse, 82
bones, 28
accessory, 84
canal of horse, 86
fascia of horse, 263
glands, 778
groove of horse, 86
joints of dog, 205
of horse, 183
of ox, 205
of pig, 205
pads of dog, 780
sheath of deep digital flexor muscle, 272
of superficial digital flexor muscle, 271
Carpo-metacarpal joint of horse, 183
sac of horse, 183
Carpus, 28
of dog, 164
of horse, 83
development of, 86
of ox, 129
of pig, 147
Cartilage, or cartilages, alar, of horse, 437
of ox, 459
annular, of cow, 748
articular, 170
arytenoid, of larynx, 443
of dog, 467
of ox, 459
of pig, 465
auricular, 748
bones, 22
cariniform, 46
conchal, 748
costal, 25, 26
of horse, 45
cricoid, of dog, 467
of horse, 441
Cartilage, cricoid, of ox, 459
of pig, 465
ensiform, of horse, 46
epiglottic, of dog, 467
of horse, 442
of ox, 459
of pig, 465
epiphyseal, 22
interarytenoid, of dog, 467
of pig, 465
lateral, of third phalanx of horse, 91
marginal, 171
of larynx of horse, 441
of nasal septum of horse, 437
of nostrils of ox, 459
parietal, of nasal cavity of horse, 437
scapular, of horse, 75
scutiform, 748
semilunar, of horse, 196
thyroid, of dog, 467
of horse, 442
of ox, 459
of pig, 465
xiphoid, 26
of horse, 46
Cartilagines tracheales of horse, 450
Caruncle, lacrimal, 735
Caruncula lacrimalis, 735
of dog, 779
of pig, 778
sublingualis of horse, 334
Cauda equina of horse, 648
Caudate ligament of horse, 375
lobe of liver, 433
of ox, 402
of pig, 421
nucleus, 675
Cavernous plexus, 711
sinus, 542
Cavity, abdominal, of ox, 390
cranial, of dog, 161
of horse, 69
of ox, 124
of pig, 145
glenoid, of horse, 67, 68, 76
joint, 170
nasal, of dog, 161, 466, 467
of horse, 71, 436
of ox, 125, 458
of pig, 145, 464
of abomasum of ox, 396
of larynx of horse, 447
of mouth of horse, 330
of omasum of ox, 395
of rumen of ox, 393
of tunica vaginalis of horse, 490
of uterus of mare, 513
pelvic, of horse, 97
of ox, 133, 390
sigmoid, of ulna of horse, 82
thoracic, of horse, 450
of ox, 461
Cavum conchæ of dog, 780
epidurale, 646
subdurale, 646
tympani, 752
of dog, 780
of ox, 775
Cavum tympani of pig, 778
Cells, air, of lungs of horse, 457
ethmoidal, of horse, 52
gustatory, 772
Cement of teeth, 339
Center, tendinous, of diaphragm of horse, 243
Central artery of retina, 554
canal of cord, 650
tarsal bone of horse, 107
of ox, 134
Cephalic artery, 541
index of dog, 159
part of sympathetic system, 711
vein, 591, 593
of dog, 642
of ox, 622
Cerebellar peduncles, 661
middle, 659
tract, direct, 661
veins, 592
Cerebello-olivary fasciculus, 658
Cerebellospinal fasciculus, 661
Cerebellum of dog, 725
of horse, 660
of ox, 716
of pig, 720
Cerebral arteries, 546
posterior, 546
fissures of horse, 668
of ox, 716
gyri of horse, 668
hemispheres, 667
of dog, 726
of ox, 716
of pig, 721
nerves of horse, 676
peduncles, 664
of ox, 716
of pig, 720
vein, 588, 592
of ox, 621
Cerebro-spinal artery, 545
of dog, 634
fasciculi, 660
Ceruminous glands, 749
Cervical artery, deep, 540
inferior, 541
of dog, 633
of ox, 609
of pig, 627
superior, 540
branch of facial nerve, 685
canal of cow, 518
of mare, 513
enlargement of horse, 648
ganglia, 711
of dog, 733
of ox, 720
of pig, 724
lymph glands, 601
of dog, 643
of pig, 631
nerves of horse, 694
part of sympathetic nervous system, 711
plexus, 694
vein, deep, 586
inferior, 591
vertebræ, 24
of dog, 150
of horse, 32
Cervical vertebræ of ox, 112
of pig, 136
Cervicalis ascendens muscle, 225
Cervico-auricularis, 750
of dog, 780
of ox, 784
Cervico-scutularis, 749
of dog, 780
of ox, 774
Cervix uteri of cow, 517
of mare, 513
of sow, 522
Chambers of eye, 746
Check ligament, inferior, of carpal joints, 183
of deep digital flexor muscle, 272
of hock joint, 200
superior, of superficial digital flexor muscle, 270
Cheek teeth, 338, 342
deciduous, of horse, 346
of dog, 425
of ox, 386
of pig, 412
of sheep, 405
Cheeks of dog, 423
of horse, 332
muscles of, 213
of ox, 382
of pig, 410
of sheep, 405
Chestnut, 771
Chevron bones of dog, 152
Chiasma opticum, 666
Choanæ, posterior, of horse, 68
Chondro-pharyngeus muscle of horse, 350
Chondro-sternal articulations of horse, 178
Chorda tympani, 683, 684
Chordæ tendineæ, 531, 533
Chorioid, 742
fissure, 670
of dog, 779
of pig, 778
plexus of fourth ventricle, 657, 663
of lateral ventricle, 670, 675
of third ventricle, 666
Cilia, 735
Ciliary arteries, 554
body, 743
border of iris, 744
ganglion, 679, 711
of ox, 717
muscle, 743
nerve of dog, 728
of horse, 679
processes, 743
ring, 743
Circle, coronary, 564
of Willis, 546
Circulation, fœtal, 606
pulmonary, 607
Circulatory system of dog, 632
of ox, 608
of pig, 626
Circulus arteriosus major, 744
Circumanal glands of dog, 432
Circumduction of joints, 171
Circumflex artery, anterior, 558
external, 577
of ox, 619
of coronary cushion, 564
of dog, 635
of ox, 612
of scapula, 556
posterior, 556
iliac artery, 578
nerve of horse, 697
vein, external, 598
Cistern, milk, of cow, 521
Cisterna chyli, 600
of dog, 643
Cisternæ subarachnoidales, 646
Clarke’s column, 651
Claustrum, 675
Clavicle, 27
of dog, 162
Claws of dog, 781
of ox, 775
of pig, 779
Cleft, palatine, of horse, 60, 69, 71
vulvar, of mare, 514
Cleido-cervicalis muscle of dog, 320
Cleido-mastoideus muscle of dog, 320
of horse, 252
of pig, 314
Cleido-occipitalis muscle of pig, 314
Cleido-transversarius muscle of horse, 252
Clinoid process of sphenoid bone of dog, 156
of pig, 142
Clitoris, artery of, 575
of bitch, 523
of cow, glans of, 519
of mare, 515
prepuce of, 515
of sow, 522
Coccygeal artery, lateral, 577
middle, 575
of dog, 641
of ox, 618
fascia of horse, 238
ganglion, 713
nerves of horse, 710
vertebræ, 24
of dog, 152
of horse, 41
of ox, 114
of pig, 138
Coccygeus muscle of dog, 325
of horse, 238
ventralis lateralis muscle of horse, 240
Cochlea, 759
of dog, 780
Cochlear nerve, 686, 761
Cœliac artery, 566
of dog, 638
of ox, 614
of pig, 627
lymph gland of ox, 626
plexus, 714
Cœliaco-mesenteric ganglia, 714
Coffin bone of horse, 90
joint, 189
Coffin joint, capsule of, 189
lateral ligaments of, 189
movements of, 190
Colic arteries, 570
lymph glands of pig, 632
mesentery of horse, 354, 369
Collateral fissure of dog, 726
vessel, 524
Colliculus facialis, 662
seminalis of horse, 499
of ox, 504
Colon, great, of horse, 365
of dog, 432
of ox, 398
of pig, 420
of sheep, 409
small, of horse, 369
tæniæ of, 370
Column of Burdach, 652
of Goll, 652
of spinal cord, 651
renal, of horse, 473
Columna grisea of cord, 650
Columnæ fornicis, 673
Comma-shaped tract, 652
Commissura grisea, 650
hypothalamica, 665
Commissure, hippocampal, 670
of nostrils of horse, 436
of spinal cord, 650
of vulva of mare, 515
optic, 666
Common bile-duct of sheep, 410
Communicating artery, posterior, 546
Compact substance of bone, 20
Complexus muscle of dog, 325
of horse, 231
of pig, 312
Compressor coccygis muscle of horse, 238
Concha of pig, 778
Conchal cartilage, 748
Condyle, external, of humerus of horse, 80
internal, of humerus of horse, 79
occipital, of horse, 48, 68, 69
of femur of horse, 99
of mandible of horse, 64
of temporal bone of horse, 55
of tibia of horse, 101
Condyloid artery, 545
of dog, 634
of ox, 611
canal of ox, 115
fossa of horse, 48, 68
vein, 588
Conjugal ligament of horse, 177
Conjugate diameter of pelvis of horse, 97
of ox, 132
Conjunctiva, 736
of ox, 772
Conjunctival sac, 736
Constrictor vestibuli muscle of mare, 515
vulvæ of mare, 515
Conus arteriosus of horse, 530
Conus medullaris of horse, 648, 649
vasculosus of epididymis of horse, 487
Coraco-brachialis muscle of dog, 322
of horse, 258
of ox, 302
of pig, 314
Coracoid, 27
process of horse, 77
Coraco-radialis muscle of horse, 259
Cord, spinal, of dog, 724
of horse, 648
of ox, 715
of pig, 720
Cores, horn-, of ox, 118
Corium, 762
of dog, 780
Cornea of dog, 779
of horse, 741
of ox, 774
of pig, 778
Cornu ammonis, 669
anterior, of thyroid cartilage of horse, 442
of nostrils of horse, 437
posterior, of thyroid cartilage of horse, 442
Cornua, great, of horse, 65
middle, of horse, 65
small, of horse, 65
thyroid, of horse, 65
uteri of cow, 517
of mare, 511
Corona glandis of penis of horse, 495
radiata, 676
Coronal border of hoof, 765
fissure of dog, 726
of ox, 716
of pig, 721
Coronary arteries, 535, 537
of dog, 632
of ox, 609
circle, 564
groove of heart, 527
of hoof, 765
of rumen of ox, 392
ligament of horse, 374
matrix, 769
pillars of rumen of ox, 393
plexus, 595
sinus, 585
of horse, opening of, 529
veins, 535, 586
Coronoid fossa of humerus of horse, 80
process of mandible of horse, 64
of radius of horse, 80
Corpora quadrigemina, 663
of dog, 725
Corpus adiposum of eye, 738
albicans of mare, 510
callosum, 672
of ox, 716
cavernosum penis of horse, 495
fornicis, 673
geniculatum mediale, 665
luteum of mare, 510
Luysi, 665
Corpus medullare of cerebellum, 661
papillare, 762
rubrum of mare, 510
spongiosum of horse, 495
striatum, 675
trapezoideum, 655
of dog, 725
of ox, 715
of pig, 720
vitreum, 746
Corpuscles, Malpighian, of horse, 379, 473
renal, of horse, 473, 474
Corrugator supercilii muscle of horse, 218
Cortex of thymus gland of horse, 458
Corticopontile fibers, 660
Costal arch, 26
cartilages, 25, 26
of horse, 45
facets of thoracic vertebræ, 36, 37
groove, 26
pleura of horse, 451
Costo-central articulations of horse, 177
Costo-chondral articulations of horse, 178
Costo-sternal ligament, superior, of horse, 178
Costo-transverse articulations of horse, 177
Costo-vertebral articulations of horse, 177
Cotyledons, uterine, of cow, 518
Cotyloid ligament of horse, 192
Cowper’s glands of horse, 493, 506
of ox, 503
of pig, 505
Coxal angle of ilium of horse, 94
Cranial bones, 27
of dog, 154
of horse, 47
of ox, 115
of pig, 139
cavity of dog, 161
of horse, 69
of ox, 124
of pig, 145
nerves of dog, 728
of horse, 676
of ox, 717
of pig, 722
roots of, 656
superficial origins of, 653
region of horse, 67, 68
sutures of horse, 179
Cranio-facial index of dog, 159
Cremaster, external, of horse, 249, 490
of ox, 500
of pig, 313
of testicle of pig, 504
Cremasteric artery, 578
Crest, facial, of horse, 58, 62, 68
frontal, of horse, 55, 66
nasal, of horse, 71
Crest, occipital, of horse, 50, 69
of femur of horse, 99
of ilium of horse, 94
of sacrum of ox, 114
parietal, of ox, 117
petrosal of horse, 57, 70
pterygoid, of horse, 51
renal, of horse, 473
sagittal, of horse, 54, 66
semilunar, of third phalanx of horse, 91
spheno-occipital, of horse, 51
sublingual, of horse, 348
supracondyloid, of femur of horse, 97
tibial, of horse, 100
turbinal, inferior, of horse, 58
superior, of nasal bones of horse, 61
urethral, of male horse, 499
zygomatic, of horse, 58, 62
Cribriform plate of ethmoidf horse, 52
Crico-arytenoid joints of horse, 444
Crico-arytenoideus lateralis muscle of horse, 445, 446
Cricoid cartilage of dog, 467
of horse, 441
of ox, 459
of pig, 465
Crico-pharyngeus muscle of horse, 350
Crico-thyroid joints of horse, 444
membrane of horse, 444
Crico-thyroideus muscle of horse, 445
Crico-tracheal membrane of horse, 445
Crista galli of horse, 52, 70
terminales of horse, 530
vestibuli, 758
Cristæ acusticæ, 760
ungulæ, 765
Crown of tooth, 339
Crucial fissure of ox, 717
ligaments of femoro-tibial articulation of horse, 198
Cruciate fissure of dog, 727
of pig, 721
Crura cerebri, 664
fornicis, 673
helicis, 748
of dog, 779
of diaphragm of horse, 243
Crural fascia of horse, 274
nerve, anterior, of horse, 706
triceps muscle of horse, 284
Crureus muscle of horse, 286
Crystalline lens, 746
Cubital lymph glands, 606
of dog, 643
Cuboido-cunean ligaments of horse, 202
Cuboido-scaphoid ligament of horse, 202
Cuneate tubercle of pig, 720
Cuneiform cartilage of larynx of dog, 467
Cupola, 759
Curvator coccygis muscle of horse, 239
Cushion of hoof, 769
plantar, 771
Cutaneous glands of ox, 775
nerve of leg of horse, 708
of neck, 695
Cutaneus maximus muscle of abdomen, 245
scapulæ et humeri muscle, 255
Cuticular ridge of stomach, 360
Cystic duct of ox, 403
Dartos of scrotum of horse, 488
Deciduous canine teeth, 346
cheek teeth, 346
incisor teeth, 346
of ox, 386
teeth, 346
Decussatio lemniscorum, 658
Decussation of fillet, 658
of pyramids, 655
of superior peduncle of cerebellum, 661
pyramidal, 658
Deep abdominal fascia, 245
digital flexor muscle, 271
of dog, 323, 329
of leg, 293
of ox, 305
of pig, 316, 317
fascia, 212
of forearm, 262
of head of horse, 213
of neck of horse, 224
of shoulder of horse, 255
flexor muscle of ox, 311
gluteus muscle, 278
pectoral muscle, 253, 254
of dog, 320
of ox, 302
of pig, 314
sesamoidean ligament, 188
Deferential fold of testicles, 491
Deltoid muscle, 255
of dog, 320
of ox, 302
of pig, 314
tuberosity of horse, 78
Dental artery, 552
superior, 555
canal, inferior, 64
superior, 59
nerve, 681, 682
plate of ox, 384
vein, 587
Dentine, 339
Depressor coccygis muscle, 240
labii inferioris muscle, 216
of dog, 318
of ox, 295
of pig, 311
superioris muscle of ox, 295
nerve of dog, 730
rostri muscle of pig, 311
Descemet, membrane of, 742
Descent of testicles, 490
Descriptive terms, 18
Diagonal fissure of ox, 716
of pig, 721
Diameter, conjugate, of pelvis, 97
of ox, 132
sacro-pubic, of pelvis, 97
transverse, of pelvis, 97
Diaphragm of dog, 325
of horse, 243
of ox, 300
of pig, 313
Diaphragma sellæ, 646
Diaphragmatic flexure, 366
lobe of lung of ox, 463
pleura, 451
vertebra, 42
Diarthroses, 170
Diencephalon, 664
Digastric muscles, 213
nerve, 685
Digastricus muscle, 222
of dog, 319
of ox, 297
of pig, 311
Digestive system, 330
of dog, 423
of ox, 382
of pig, 410
of sheep, 405
Digit or digits, 28
of dog, 165, 780
extensor muscles of, 322, 328
of horse, fascia of, 263
muscles of, 295
of ox, 130, 775
of pig, muscles of, 315
Digital artery, 564
common, 563
of ox, 620
external, of ox, 614, 620
of dog, 641, 637
of pig, 629, 630
volar, of ox, 614
bones, 28, 30
cushion, 771
extensor muscle, anterior, of dog, 328
of ox, 304, 309
of pig, 317
common, of dog, 322
of ox, 304
of pig, 315
internal, of ox, 304, 309
lateral, of dog, 322, 328
of ox, 304, 309
of pig, 315, 317
of ox, 304, 309
of pig, 315
fascia, 274
flexor muscle, deep, of dog, 323, 329
of ox, 305
of pig, 316
superficial, of dog, 323, 329
of ox, 305
of pig, 316
fossa of epididymis, 485
nerves of dog, 730, 732
of horse, 701
of ox, 718, 719
of pig, 723
pads, 780
Digital veins, 595
of dog, 642, 643
of ox, 621, 623
Dilatator naris apicalis muscle
of ox, 296
inferior muscle of horse, 218
of ox, 296
lateralis muscle of horse, 217
of ox, 295
of pig, 311
superior muscle of horse, 218
of ox, 296
transversus muscle of horse, 217
of pig, 311
pupillæ, 744
Diploë, 21
Diploic veins, 593
Discs, articular, 171
of temporo-mandibular articulation, 179
Distal interphalangeal joint of horse, 189
sesamoid bones of ox, 131
Diverticulum duodeni of horse, 362
nasi of horse, 436
preputial, of pig, 506
suburethral, of cow, 519
of sow, 522
tubæ auditivæ, 756
ventriculi of stomach of pig, 418
Dolichocephalic breed of dogs, 159
Dorsal artery, 538
of dog, 633
of ox, 609
of penis, 580
of pig, 627
columns of spinal cord, 651
common ligament of carpal joints, 183
flexion of joints, 171
groove of third phalanx, 91
ligaments of hock joint, 201
of interphalangeal joints of dog, 209
plexus, 595
sacro-iliac ligament, 190
sesamoids of dog, 165
vein, 586
Dorso-intercostal artery, 538
Dorso-scapular ligament of horse, 235
Dorsum of tongue of horse, 335
Duct or ducts, alveolar, of lungs, 457
Bartholin’s, of mare, 515
bile, common, of sheep, 410
of ox, 398
of pig, 419, 422
cystic, of ox, 403
ejaculatory, 488, 492, 499
hepatic, 376
lacrimal, 737
lactiferous, of cow, 521
of mare, 516
lymphatic, right, 601
naso-lacrimal, 436, 737
of ox, 773
Ducts of bulbo-urethral glands, 494, 499
of epididymis, 487
of mammary glands of mare, 516
of pancreas, 372
of prostate, 493
orbital, of dog, 427
pancreatic, accessory, of dog, 431
of horse, 373
of dog, 431, 434
of horse, 372
of ox, 398
of pig, 419, 423
parotid, of dog, 423, 427
of horse, 347
of pig, 411, 414
prostatic, of horse, 499
of ox, 502
Santorini’s, of horse, 373
sublingual, of dog, 427
of horse, 348
submaxillary, of dog, 427
of horse, 348
thoracic, of dog, 643
of horse, 600
of pig, 630
tracheal, 603
Wirsung’s, of horse, 372
Ductus arteriosus, 535, 607
endolymphaticus, 759
reuniens, 759
sublingualis major, of pig, 416
minores, of pig, 416
utriculo-saccularis, 759
venosus, 607
of ox, 403
Duodenal angle of horse, 372
glands of horse, 363
Duodenum of horse, 360
of ox, 398
Dura mater, 645
spinal, 646
Ear, external, of horse, 747
internal, of horse, 758
middle, of horse, 752
of dog, 779
of horse, 747
of ox, 774
of pig, 778
Ectolateral fissure of dog, 727
Ectomarginal fissure, 669
of dog, 726
of ox, 716
of pig, 721
Ectosylvian fissure of dog, 726
Ectoturbinals of ethmoid of horse, 52
Eighth nerve, 686
Ejaculatory ducts, 488, 492, 499
Elastic membrane of trachea, 449
Elbow joint of dog, 205
of horse, 181
of ox, 205
of pig, 205
Eleventh nerve, 690
Embryology, 17
Eminence, frontal, of ox, 118
Eminence, ilio-pectineal, of pubis, 95
intercondyloid, of tibia, 101
olivary, of dog, 725
Eminentia conchæ, 748
medialis, 662
pyramidalis, 755
Emissary veins, 591
Enamel of teeth, 339
Enarthrosis, 172
Encephalon of horse, 652
End-arteries, 524
End-brain, 667
Endocardium, 530, 534
Endothoracic fascia, 450
Endoturbinals of ethmoid, 52
Ensiform cartilage, 46
Entomarginal fissure of dog, 727
of horse, 669
of ox, 716
of pig, 721
Epicardium, 525, 534
Epicondyle, external, of femur, 100
of humerus, 80
internal, of femur, 100
of humerus, 80
Epidermis, 761
of dog, 780
Epididymis of dog, 506
of horse, 485
structure of, 485
of ox, 500
of pig, 504
Epidural space, 646
Epigastric zone of horse, 353
Epiglottis of dog, 467
of horse, 442
of ox, 459
of pig, 411, 465
Epihyoids of horse, 65
Epiphyseal cartilage, 22
Epiphysis, 665
Epiploic foramen, 379
of ox, 396
Epithelium, corneæ, 741
germinal, of ovary, 510
of Fallopian tubes, 511
Equator of eye, 740
Erectile tissue of urethra, 499
Erector clitoridis muscle, 515
penis muscle, 496
Ergot, 771
Esophageal membrane, 360
Esophagus. See _Œsophagus_.
Ethmoid artery, 554
bone of dog, 157
of horse, 52
development of, 52
of ox, 116
of pig, 142
sinus, 74
Ethmoidal cells, 52
foramen, 51, 52, 67, 70
fossa, 52, 70
meatuses, 52
of nasal cavity, 440
nerve, 678
of dog, 728
Ethmo-turbinals, 52
Eustachian tube, 348, 755
of dog, 780
of ox, 775
Eustachian tube of pig, 778
osseous, 57
Excavatio pupillæ nervi optici, 745
Excretory ducts, 737
Exoskeleton, 19
Extension of joints, 171
Extensor brevis muscle of ox, 310
carpi muscle of dog, 322
obliquus muscle, of dog, 322
of horse, 267
of ox, 304
of pig, 315
radialis brevis muscle of dog, 322
longus muscle of dog, 322
muscle of horse, 263
of ox, 304
of pig, 315
ulnaris muscle of dog, 323
of horse, 268
digitalis brevis muscle of dog, 328
of pig, 317
communis muscle of dog, 322
of horse, 263
lateralis muscle of dog, 322
of horse, 265
of leg of horse, 288
longus muscle of leg of horse, 288
digiti quinti muscle of dog, 323
tertii et quarti muscle of dog, 323
fossa of femur of horse, 100
hallucis longus muscle of dog, 328
of pig, 317
indicis proprius muscle of pig, 315
metacarpi obliquus muscle of horse, 267
muscle of digits of dog, 322, 328
pedis brevis muscle of horse, 295
muscle of horse, 264, 288
External angle of ilium, 94
of pubis, 96
auditory meatus, 56
process, 56, 67
condyle of humerus, 80
cremaster muscle, 249, 490
epicondyle of femur, 100
of humerus, 80
frontal crest, 55
inguinal ring, 246, 250
intercostal muscles of dog, 325
of horse, 240
of pig, 313
interosseous muscle of horse, 273
lateral ligament of carpal joints, 183
of coffin joint, 189
of elbow joint, 182
External lateral ligament offemoro-tibial articulation, 197
of fetlock joint, 185
of hock joint, 200
of pastern joint, 188
ligament of temporo-mandibular articulation, 179
malleolus of tibia, 101
metatarsal bone, 111
oblique muscle of abdomen, 246
occipital protuberance, 50
patellar ligament, 195
pterygoideus muscle, 220
sagittal crest, 54, 66
supracondyloid crest of humerus, 80
trochanter of femur, 99
tuberosity of humerus, 78
of radius, 81
urethral orifice of cow, 519
of horse, 499
of mare, 515
of ox, 503
Eye of dog, 779
of horse, 734
of ox, 772
of pig, 777
Eyeball of dog, 779
of horse, 739
of ox, 773
of pig, 778
Eyelashes, 735
of pig, 777
Eyelid of dog, 779
of horse, 735
muscles of, 218
of ox, 772
of pig, 777
structure of, 736
third, 736
of ox, 772
of pig, 777
Face, bones of, of dog, 157
of horse, 57
of ox, 120
of pig, 142
of dog, muscles of, 318
of ox, muscles of, 295
Facets, anterior, of larynx, 441
costal, of thoracic vertebræ, 36, 37
of tibia, 102
of ulna, 83
posterior, of larynx, 441
Facial artery, 547
of dog, 635
transverse, 550
bones, 27
canal, 56
crest, 58, 62, 68
nerve, 684
of dog, 729
of ox, 717
nucleus, 684
panniculus of pig, 311
tuberosity of ox, 120
veins, 588
of pig, 630
Facies articulares arytænoideæ, 441
Facies articulares thyreoideæ, 441
costalis, 454
diaphragmatica, 456
mediastinalis, 454
Falciform ligament, 374
Fallopian tubes of bitch, 522
of cow, 517
of mare, 511
structure of, 511
of sow, 522
False nostril of horse, 436
ribs, 25, 43
vertebræ, 24
vocal cords of dog, 467
of horse, 447
Falx cerebri, 645
Fascia, 211, 212
abdominal, deep, 245
superficial, 245
buccal, 213
carpal, 263
coccygeal, 238
common, of leg, 274
crural, 274
deep, 212
of head, 213
digital, 274
endothoracic, of horse, 450
femoral, internal, 274
gluteal, 273
iliac, 273
lata of gluteal region, 273
lumbo-dorsal, 235
metatarsal, 274
of back, 235
of forearm, 262
of head, 213
of horse, 213
of loins, 235
of mammary glands, 516
of manus, 262
of metacarpus, 263
of neck, 224
of pelvic limb, 273
of shoulder of horse, 255
of tail, 238
orbital, 738
pectoral, 252
pelvic, 273
pharyngeal, 213
propria of neck, 224
scrotal, 488
superficial, 212
of gluteal region, 273
of head, 213
tarsal, 274
temporal, 213
transversalis, 249
Fasciculus, cerebello-olivary, 658
cerebellospinal, 661
cerebrospinal, 660
cuneatus, 652
dorsal longitudinal, 658, 660
gracilis, 652
intracommissuralis ventralis, 652
nucleo-cerebellar, 661
pedunculo-mammillaris, 665
pyramidal, 660
thalamo-mammillaris, 665
Faucial tonsil, 333
Femoral artery, 579
anterior, 580
deep, 580
of dog, 639
of ox, 619
of pig, 630
posterior, 580
canal, 282
fascia, internal, 274
layer of external oblique muscle, 246
nerve of horse, 706
vein, 598
of dog, 642
Femoro-patellar articulation, 194
ligaments, lateral, 195
Femoro-popliteal artery, 580
vein, 598
Femoro-tibial articulation, 196
Femur, 29, 97
development of, 100
of dog, 167
of ox, 133
of pig, 148
Fenestra cochleæ, 753
ovalis, 753
rotundum, 753
vestibuli, 753, 758
Ferrein’s pyramid, 473
Fetlock joint, 185, 764
Fibers of heart, 534
of stomach, 359
Fibræ arcuatæ externæ, 657
zonulares, 747
Fibro-cartilage, accessory, of patella, 105
intervertebral, 173
Fibrous capsule of liver, 376
layer of articulations, 170
of pericardium, 525
ring of heart, 534
of intervertebral fibro-cartilages, 173
tunic of eye, 740
Fibula, 29
of dog, 168
of horse, 104
development of, 104
of ox, 134
of pig, 149
Fibular tarsal bone, 106
ligaments of, 202
of ox, 134
sustentaculum tali of, 106
tuber calcis of, 106
Fifth nerve of horse, 677
spinal root of, 658
Fila lateralis pontis, 661
radicularia, 651
Filiform papillæ of tongue of horse, 336
Fillet, 658
lateral, 660
medial, 660
terminale of horse, 648, 649
Fimbria of brain, 669
of Fallopian tubes, 511
ovaricæ of mare, 511
First carpal bone, 85
intertarsal sac, 200
nerve of horse, 676
phalanges of dog, 165
First phalanges of horse, 89, 111
development of, 89
of ox, 130
tarsal bone, 109
of ox, 135
Fissura calloso-marginalis, 669
ectomarginalis, 669
entomarginalis, 669
lateralis Sylvii, 668
marginalis, 669
mediana ventralis, 649
sublimbica, 669
thyreoidea of dog, 467
transversa, 669
Fissure, ansate, of dog, 726
calloso-marginal, 669
of dog, 727
of ox, 716
of pig, 721
central, of dog, 726
of horse, 668
of ox, 716
chorioid, 670
collateral, of dog, 726
coronal, of dog, 726
of ox, 716
of pig, 721
crucial, of ox, 717
cruciate, of dog, 727
of pig, 721
diagonal, of ox, 716
of pig, 721
ectolateral, of dog, 727
ectomarginal, 669, 721
of dog, 726
of ox, 716
ectosylvian, of dog, 726
entomarginal, of dog, 727
of horse, 669
of ox, 716
of pig, 721
genual, of ox, 717
of pig, 721
Glaserian, of horse, 57
lateral, of cerebrum, 667
of dog, 726
of horse, 668
of ox, 716
of pig, 721
longitudinal, of brain, 667
marginal, of horse, 669
of ox, 716
of pig, 721
naso-maxillary, of horse, 73, 439
of lungs of ox, 462
of Sylvius, 667, 668
of dog, 726
of ox, 716
of pig, 721
orbital, 51
petro-tympanic, 57
portal, of dog, 433
of horse, 373
of ox, 402
præsylvian, 669
of dog, 727
of horse, 669
of pig, 721
splenial, of pig, 721
sublimbic, 669
suprasplenial, of dog, 727
suprasylvian, of dog, 726
of horse, 668
Fissure, suprasylvian, of ox, 716
of pig, 721
transverse, 669
of ox, 716
umbilical, 374
ventral median, 249
Fixed vertebræ, 24
Flat muscles, 211
Flexion of joints, 171
Flexor brachii muscle of horse, 259
carpi externus muscle of horse, 268
of pig, 316
internus muscle of dog, 323
of horse, 267
of pig, 315
medius muscle of dog, 323
of horse, 268
of pig, 315
digitalis pedis muscle of dog, 329
digiti quinti muscle of dog, 324
hallucis brevis muscle, 329
longus muscle, 329
muscle, deep, of ox, 311
superficial, of ox, 311
of carpus of ox, 305
pedis perforatus muscle of horse, 271, 292, 293
perforans muscle, 271
perforatus muscle, 269
pollicis brevis muscle, 324
Flexure, diaphragmatic, 366
gastro-hepatic, 366
pelvic, 366
sigmoid, 503
sternal, 366
Floating ribs, 25
Floccular fossa of temporal bone of dog, 156
Floor of mouth of horse, 334
Fœtal circulation, 606
lung of horse, 454
Fold, alar, 437
cæco-colic, 367
deferential, of testicles, 491
gastro-pancreatic, 358
of articulations, 170
rumino-reticular, 393
sagittal, of pleura, 452
turbinal, inferior, 440
superior, 440
urogenital, 355
valvular, of cæcum, 365
Folia cerebelli, 661
Foliate papillæ of tongue, 336
Follicle, Graafian, of mare, 510
hair, 763
lymph, 600
of small intestine of horse, 363
of thyroid gland of horse, 458
Foot of horse, muscles of, 287
of ox, muscles of, 309
of pig, muscles of, 317
Foramen, alar, 68
alare, 34
cæcum of medulla, 655
carotid, of dog, 156
ethmoidal, 51, 52, 67, 70
Foramen, hypoglossal, 48, 68, 71
incisive, 59, 69
infraorbital, 58, 68
interventricular, 667, 674
intervertebral, of horse, 33
of ox, 112
lacerum basis cranii, 57, 68, 71
of horse, 49
orbitale of horse, 51, 67
magnum of horse, 48, 68
mandibular, 64
maxillary, 58, 67
mental, 63
nutrient, of femur, 97
of humerus, 78
of ilium, 94
of metacarpus, 88
of tibia, 100
obturator, of dog, 167
of horse, 96
of ox, 132
of Monro, 667, 674
optic, of horse, 50, 51, 67, 70
orbital, internal, 67, 70
ovale, 607
of horse, 530
of ox, 115
palatine, posterior, 58, 68
pathetic, 67
pterygoid, 51, 68
rotundum, 51, 67
sacral, 40
inferior, of ox, 114
sciatic, great, of horse, 94
singulare, 759
sinistrum, 244
sphenopalatine, 58, 60, 67, 71
stylo-mastoid, 57
supraorbital, of horse, 55, 66
of ox, 119
supratrochlear, of humerus
of dog, 163
temporal, of horse, 51, 67
thyreoideum, 442
transversarium of axis of ox, 112
venæ cavæ, of horse, 245
volar, of third phalanx, 91
Winslow’s, of horse, 379
of ox, 396
Foramina papilloma of kidney of ox, 480
Forearm, bones of, 28
of horse, fasciæ of, 262
deep, 262
superficial, 262
muscles of, 262
of ox, muscles of, 304
of pig, muscles of, 315
Forefoot, bones of, 28
Foretop, 764
Formatio reticularis, 651, 660
Fornix, 673
conjunctivæ, 736
vaginæ of mare, 514
Fossa, acetabular, 96
anterior, of skull, 70
atlantis of, 34
condyloid, of horse, 48, 68
coronoid, of horse, 80
digital, of epididymis, 485
ethmoidal, 52, 70
Fossa, extensor, of femur, 100
floccular, of temporal bone of dog, 156
glandis of penis, 495
glenoid, 56
hyaloidea, 746
hypophyseal, 50
infraspinous, 75
infratemporal, 68
intercondyloid, anterior, of tibia, 102
of femur, 99
posterior, of tibia, 102
interpeduncularis, 664
masseteric, of mandible of dog, 159
middle, of skull, 71
ovulation, of mare, 509
ovalis, 607
of horse, 530
of Sylvius, 667
olecranon, 80
olfactory, 52, 70
pituitary, 50
posterior, of skull, 71
postglenoid, 56
pterygo-palatine, 60, 67
subscapular, 75
supracondyloid, of femur of horse, 99
supraspinous, 75
synovial, of tibial tarsal bone, 105
temporal, 67
transverse, 658
trochanteric, of femur, 99
synovial, 170
vaginæ of mare, 514
Fourth carpal bone of horse, 86
metatarsal bone of horse, 111
nerve of horse, 677
tarsal bone of horse, 109
of ox, 134
ventricle of horse, 662
Fovea capitis of femur of horse, 99
nasalis, 662
trochlearis of horse, 55
Frænula labii of horse, 331
Frenum linguæ of horse, 334, 335
of pig, 411
preputial, of horse, 497
Frog matrix, 770
of hoof, 767
sensitive, 770
structure of, 769
Frog-stay, 767
Frontal artery, 553
bone of dog, 155
of horse, 55
of ox, 118
of pig, 141
crest of horse, 55, 66
eminence of ox, 118
nerve of dog, 728
of horse, 678
of ox, 717
process of dog, 157
region of skull of horse, 66
sinus of dog, 161
of horse, 55, 73
Frontal sinus of ox, 125
of pig, 145
surface of skull of horse, 65
of ox, 123
suture of horse, 55
vein of ox, 621
Frontalis muscle of ox, 295
Fronto-lacrimal sutures of horse, 55
Fronto-maxillary opening of horse, 73
Fronto-scutularis, 749
Fundus glands of stomach of horse, 360
Fungiform papillæ of tongue of horse, 336
Funiculi dorsales, 651
ventrales, 651
Furca ungulæ, 767
Gall-bladder of dog, 434
of ox, 403
of pig, 422
Ganglia, cervical, of ox, 720
cœliaco-mesenteric, 714
definition of, 644
sacral, of ox, 720
thoracic, of ox, 720
Ganglion, cervical, 711
of dog, 733
of pig, 724
ciliary, 679, 711
of ox, 717
coccygeal, 713
Gasserian, 678
impar, 713
jugular, 687
of dog, 729
of ox, 717
of pig, 722
lumbar, 713
mesenteric, 714
nodosum of dog, 729
of ox, 717
of pig, 722
otic, 681, 711
of ox, 717
petrous, 686
semilunar, 678
sphenopalatine, 711
spinal, 692
spirale, 761
thoracic, 712
vestibular, 686
Gartner, canals of, of vagina of cow, 519
Gasserian ganglion, 678
Gastric artery, 506
of dog, 638
lymph glands, 604
of ox, 626
of pig, 632
plexus, 714
of dog, 729
vein, 597
Gastrocnemius muscle of dog, 329
of horse, 290
of ox, 311
of pig, 317
Gastro-colic omentum of horse, 358
Gastro-duodenal artery, 569
Gastro-duodenal vein, 597
Gastro-epiploic artery, 569, 570
Gastro-hepatic artery of pig, 627
flexure of horse, 366
omentum of horse, 354, 358
Gastro-pancreatic fold of horse, 358
Gastro-phrenic ligament of horse, 358
Gastro-splenic artery of dog, 638
omentum of horse, 354, 358, 379
Gemellus muscle of horse, 284
of ox, 308
of pig, 317
Geniculate body, internal, 665
of dog, 725
of ox, 716
Genio-glossus muscle of horse, 338
Genio-hyoideus muscle of ox, 298
Genital organs, 469
female, 508
male, 485
of dog, 506
of horse, 485
of ox, 500
of pig, 504
of bitch, 522
of cow, 517
of mare, 508
of sow, 521
Genito-hyoideus muscle of horse, 223
Genu of corpus callosum, 672
Genual fissure of ox, 717
of pig, 721
Germinal epithelium of ovary of mare, 510
Ginglymus, 172
Girdle, pelvic, 29
of horse, 92
shoulder, 27
of horse, muscles of, 250
of ox, muscles of, 302
of pig, muscles of, 314
Glands or gland, anal, of dog, 432
buccal, of horse, 332
of ox, 383
of pig, 410
bulbo-urethral, of dog, 506
of horse, 493
of ox, 503
of pig, 505
cardiac, of stomach of horse, 360
carpal, 778
ceruminous, 749
circumanal, of dog, 432
Cowper’s, of dog, 506
of horse, 493
of ox, 503
of pig, 505
duodenal, of horse, 363
fundus, of stomach of horse, 360
hæmolymph, 600
labial, of horse, 332
lacrimal, of dog, 779
of horse, 737
Glands, lacrimal, of ox, 773
lingual, of horse, 336
lymph, 599
bronchial, of horse, 457
of ox, 623
of pig, 630
mammary, of bitch, 523
of cow, 519
of mare, 516
of sow, 522
molar, of ox, 383
mucous, of larynx of horse, 448
of trachea of horse, 450
nasal, of horse, 440
of Bartholin of cow, 519
of Bowman, 772
of Henle, 736
of rectum of horse, 370
of skin, 762
of small intestine of horse, 362
of uterus of cow, 518
olfactory, of horse, 440
orbital, of dog, 427
palatine, of horse, 333
parathyroid, of dog, 468
of horse, 458
of ox, 464
parotid, of dog, 427
of horse, 346
of ox, 388
of pig, 414
preputial, of horse, 497
prostate, of dog, 506
of horse, 493
of ox, 502
of pig, 505
pyloric, of stomach of horse, 360
salivary, of dog, 427
of horse, 346
of ox, 388
of sheep, 407
sebaceous, 762
of dog, 780
of ox, 775
of pig, 778
solitary, of rectum of horse, 370
of small intestine of horse, 363
of pig, 420
sublingual, of dog, 427
of horse, 348
of ox, 388
of pig, 415
submaxillary, of dog, 427
of horse, 347
of ox, 388
of pig, 415
sudoriferous, 762
suprarenal, of horse, 477
sweat, 762
of dog, 780
of ox, 775
of pig, 778
tarsal, 735
thymus, of dog, 468
of horse, 458
of ox, 464
of pig, 466
thyroid, of dog, 468
of horse, 457
Glands, thyroid, of ox, 464
of pig, 466
urethral, of horse, 499
uterine, of cow, 518
of mare, 513
zygomatic, of dog, 427
Glandula laryngeæ of horse, 448
palpebræ tertiæ profunda, 779
tympanicæ, 755
vestibulares majores of cow, 519
of mare, 515
minores of mare, 515
Glans clitoridis of dog, 519
of mare, 515
penis of dog, 506
of horse, 495
of ox, 503
Glasserian fissure of horse, 57
Glenoid cavity of horse, 67, 68, 76
fossa of horse, 56
notch of horse, 76
Gliding joint, 172
movement of joints, 171
Glomerulus of kidney of horse, 474
Glosso-pharyngeal nerve, 686
Glottis of horse, 447
vocalis of horse, 448
Gluteal artery, anterior, 577
of dog, 641
of ox, 619
posterior, 575
fascia of horse, 273
line of horse, 93
nerve of horse, 706
Gluteo-biceps muscle of horse, 278
Gluteus accessorius muscle of horse, 278
medius muscle of dog, 326
of horse, 277
of ox, 306
of pig, 316
profundus muscle of dog, 326
of horse, 278
of ox, 306
of pig, 316
superficialis muscle of dog, 326
of horse, 277
of ox, 306
of pig, 316
Goll’s column, 652
Gomphosis, 169
Graafian follicles of mare, 510
Gracilis muscle of dog, 328
of horse, 281
of ox, 308
of pig, 316
Granula iridis, 744
Gray commissure of cord of horse, 650
matter of nervous system, 644
Great colon of horse, 365.
See also _Colon, great_.
cornua of horse, 65
mesentery of horse, 354, 362
Great oblique muscle of abdomen of horse, 246
omentum of horse, 354, 358
of ox, 396
sciatic foramen of horse, 94
trochanter of femur of horse, 99
Groove, bicipital, of humerus of horse, 79
carpal, of horse, 86
coronary, of heart of horse, 527
of rumen of ox, 392
dorsal median, in horse, 649
of third phalanx of horse, 91
dorso-lateral, in horse, 649
lacrimal, of horse, 58
longitudinal, of heart of horse, 528
musculo-spiral, of horse, 77
œsophageal, of ox, 394
of sheep, 408
of heart of horse, 527
of radius of horse, 82
of sacrum of ox, 114
of tibia of horse, 102
optic, of horse, 50
palatine, of horse, 59, 69
sagittal, of horse, 54
subpubic, of horse, 95
supraorbital, of ox, 119
urethral, of horse, 495
vertebral, of horse, 42
Gross anatomy, 17
Gubernaculum testis of horse, 491
Gudden’s commissure, 666
Gums of horse, 332
Gustatory cells, 772
hair, 772
organs of dog, 781
pore, 772
Guttural pouches, 756
region of horse, 68
Gyri, cerebellar, 661
cerebral, 668
of ox, 716
of pig, 721
Gyrus dentatus, 669
subcallosal, 671
Hæmal arches of coccygeal vertebræ of dog, 152
spine, 25
Hæmolymph glands, 600
Hæmorrhoidal artery, 574
of dog, 641
nerve of horse, 710
Hair, gustatory, 772
Hair-follicle, 762
Hairs, 762
of horse, 764
of ox, 775
of pig, 778
tactile, 763
Hamulus of horse, 61
Hand. See _Manus_.
Hard palate of dog, 423
of horse, 69, 332
of ox, 383
of pig, 411
Hard palate of sheep, 405
Harder’s gland, 777
Head of horse, fasciæ of, 213
muscles of, 213
of pig, muscles of, 311
Heart, 524
of dog, 632
of horse, 526
structure of, 534
of ox, 608
of pig, 626
veins of, 585
Heels, 764
Helicis muscle, 752
Helicotrema, 759
Hemispheres, cerebellar, 660
cerebral, 667
of dog, 726
of ox, 716
of pig, 721
Henle, glands of, 736
Hepatic artery, 567
of dog, 638
of horse, 377
of ox, 614
duct of horse, 376
lymph glands, 605
of ox, 626
of pig, 632
plexus, 714
of horse, 377
veins, 596
of horse, 377
Hepato-renal ligament of horse, 375
Hiatus aorticus of horse, 244
œsophageus of horse, 244
Hilus of lungs of horse, 454
of ovary of mare, 510
of spleen of horse, 378
renalis, of horse, 470
Hinge-joint, 172
Hip joint of horse, 192
of ox, 209
of pig, 209
Hippocampal commissure, 670
Hippocampus, 669
Histology, 17
Hock, 29
capped, 293
joint of dog, 210
of horse, 199
of ox, 210
of pig, 210
of horse, 105
of ox, 134
of pig, 149
Hoof of horse, 764
matrix of, 769
structure of, 768
Horn-cores of ox, 118
Horner’s muscle, 736
Horns of lateral ventricle, 674
of ox, 776
Humeralis obliquus muscle of horse, 260
Humerus, 28
of dog, 162
of horse, 77
development of, 80
of ox, 127
of pig, 146
Humor, aqueous, 746
Humor, vitreous, 746
Hydatid of Morgagni of Fallopian tubes of mare, 511
of testicles of horse, 485
Hymen of mare, 514
Hyo-epiglottic ligament, 444
Hyo-epiglotticus muscle, 445
Hyo-glossus muscle, 338
Hyoid bone of dog, 159
of horse, 64
of ox, 122
of pig, 144
muscle of dog, 319
of horse, 222
of ox, 297
process of horse, 57
Hyoidean articulations, 180
Hyoideus transversus muscle, 224
of ox, 298
Hyo-pharyngeus muscle, 350
Hyo-thyreoideus muscle, 445
Hyperdactylism, 29
Hypogastric arteries, 573
plexus, 715
vein, 597
zone, 353
Hypoglossal foramen, 48, 68, 71
nerve, 692
of dog, 730
of ox, 717
of pig, 722
nucleus, 692
Hypophyseal fossa of horse, 50
Hypophysis, 653, 665
Ileal artery, 570
Ileo-cæcal artery, 570
orifice, 364
value of dog, 431
of horse, 362, 364
Ileo-cæco-colic artery of ox, 617
Ileum, 361
Iliac artery, circumflex, 578
of dog, 639
external, 578
of ox, 619
internal, 573
of ox, 618
fascia, 273
layer of oblique muscle of abdomen, 246
lymph glands, 604
of dog, 643
of ox, 625
of pig, 631
vein, common, 597
external, 597
internal, 597
of dog, 642
Iliaco-femoral artery, 577
of ox, 619
vein, 598
Iliacus muscle of dog, 326
of horse, 275
of ox, 306
Iliocostalis cervicis muscle of horse, 227
muscle of horse, 236
of ox, 300
Iliohypogastric nerve of horse, 704
Ilio-inguinal nerve of horse, 704
Ilio-lumbar artery, 577
of dog, 641
of ox, 619
of pig, 630
ligament of horse, 191
vein, 597
Ilio-pectineal line of horse, 93
Ilio-psoas muscle of horse, 275
Ilio-pectineal eminence of pubis, 95
Ilium, 29
of dog, 165
of horse, 93
of ox, 131
of pig, 148
Impression, cardiac, of lungs, 454
Incisive foramen, 59
Incisivus inferior muscle of horse, 216
of ox, 295
superior muscle, 216
Incisor artery, 552
teeth, 338, 341
deciduous, of ox, 386
of dog, 425
of ox, 386
of pig, 412
of sheep, 405
Incisura intertragica, 748
thyreoidea caudalis, 442
Incus, 754
Index, cephalic, of dog, 159
cranio-facial, of dog, 159
Inferior angle of scapula, 76
atlanto-axial ligament, 176
atlanto-occipital membrane, 176
border of mandible, 64
check ligament of carpal joints, 183
of deep digital flexor muscle, 272
commissure of vulva, 515
common vertebral ligament, 173
dental canal, 64
dilatator naris muscle, 218
incisivus muscle, 216
interdigital ligaments of ox, 208
ischiatic spine, 95
maxillary foramen, 64
sinus, 73
meatus of nasal cavity of dog, 467
of horse, 439
of pig, 465
of nose, 62, 72
navicular ligament, 190
sacral foramen of ox, 114
sacro-coccygeus muscle, 240
sesamoidean ligaments, 188
thyro-arytenoid ligament, 444
turbinal bone of dog, 158
of horse, 62
of ox, 122
crest, 58
fold of horse, 440
Infraorbital artery, 555
of dog, 635
of pig, 627
canal, 59
foramen, 58, 68
nerve of dog, 728
of horse, 681
of pig, 722
pouch, 777
vein, 589
Infraspinatus muscle of dog, 321
of horse, 256
of ox, 302
of pig, 314
Infraspinous fossa, 75
Infratemporal fossa, 68
Infratrochlear nerve of dog, 728
of horse, 679
Infundibular recess, 667
Infundibulum, 653
of Fallopian tubes, 511
of incisor teeth, 341
Inguinal canal, 249
ligament, 246
lymph glands, 604
of dog, 643
of ox, 625
of pig, 632
pouch of sheep, 777
ring, external, 246, 250
internal, 248, 249
Inlet of pelvis of dog, 167
of horse, 96
of ox, 132
of pig, 148
of thoracic cavity, 450
Inscriptiones tendineæ of rectus abdominis of horse, 248
Insertion of muscles, 212
Interalveolar septa, 58
space, 58, 69
Interarytenoid cartilage of larynx of dog, 467
of pig, 465
Interbrain, 664
Intercarpal joint, 183
sac, 183
Intercentral articulations of vertebræ, 173
Interchondral ligaments, 178
Intercondyloid fossa, anterior, of tibia, 102
eminence of tibia, 101
fossa of femur, 99
posterior, of tibia, 102
Intercornual articulation of horse, 180
Intercostal arteries, 565
of ox, 614
of pig, 627
lymph glands, 603
muscles, external, of dog, 325
of horse, 240
of pig, 313
internal, of horse, 242
of pig, 313
nerves of horse, 702
spaces, 25
veins, 587
Interdental space of horse, 58
Interdigital ligaments, inferiorm of ox, 208
Interdigital ligaments, superior, of ox, 206
pouch, 777
Interlobular bronchi of horse, 457
tissue of lungs, 457
Intermediate carpal bone of horse, 83
zone of kidney, 473
Intermetacarpal joints of dog, 206
of ox, 206
of pig, 206
Intermuscular septa, 212
of forearm, 262
of gluteal region, 273, 274
of leg, 274
of shoulder, 255
Internal angle of ilium, 94
of pubis, 95
auditory meatus, 56
capsule, 665, 676
ondyle of humerus of horse, 79
digital extensor muscle of ox, 304, 309
ear of horse, 758
epicondyle of femur, 100
of humerus, 80
femoral fascia, 274
flexor muscle, 267
inguinal ring, 248, 249
intercostal muscles, 242
of pig, 313
interosseous muscle, 273
lateral ligament of carpal joints, 184
of coffin joint, 189
of elbow joint, 181
of femoro-tibial articulation, 197
of fetlock joint, 185
of hock joint, 201
of pastern joint, 188
malleolus of tibia, 103
metatarsal bone, 111
muscles of thigh of ox, 308
oblique muscle of abdomen, 247
occipital protuberance, 54
orbital foramen, 67, 70
patellar ligament, 196
pterygoideus muscle, 219
sagittal crest, 54
trochanter of femur, 97
tubercle of humerus, 78
tuberosity of humerus, 79
of radius, 81
urethral orifice of horse, 477
of mare, 499
Interneural articulations of vertebræ, 173
Interosseous artery, common, 561
dorsal, 562
of dog, 635
of ox, 612
recurrent, 561
ligament of radio-ulnar articulation, 182
medius muscle of ox, 305
membrane of tibio-fibular articulation, 199
muscles of dog, 324, 329
Interosseous muscles of horse, 273, 295
plexus, 595
space of forearm, 80
of leg, 29
vein, 595
Interparietal bone of dog, 155
of horse, 53
of ox, 116
of pig, 140
suture of horse, 54
Interpeduncular space, 664
Interphalangeal articulation, distal, 189
proximal, 188
joints of dog, 209
of ox, 208
of pig, 208
Interscutularis, 749
of dog, 780
of ox, 774
Intersesamoidean ligament, 187
Interspinales muscles of dog, 325
of ox, 300
of pig, 313
Interspinous ligaments of horse, 175, 176
Interstitial tissue of mammaryglands, 516
Intertarsal sac, first, 200
second, 200
Intertransversales caudæ, 239
colli muscle, 228
lumborum muscle, 238, 276
muscle of dog, 324, 325
of ox, 300
of pig, 312, 313
Intertransverse articulations, 175
ligaments, 175
Intertubercular groove of humerus, 79
Interventricular foramen, 667, 674
grooves of heart, 528
septum of left ventricle, 534
Inervertebral fibro-cartilages, 173
foramen, 33
of ox, 112
foramina, 25
Intestinal arteries, 570
Intestine, large, of dog, 433
of horse, 363
of ox, 398
of pig, 420
of dog, 430
of ox, 397
of pig, 419
of sheep, 409
small, of dog, 430
of horse, 360
of ox, 398
of pig, 419
of sheep, 409
Intima of arteries, 525
of veins, 525
Intraarticular ligaments, 171
Intumescentia cervicalis of horse, 648
lumbalis, 648
Iris of dog, 779
Iris of horse, 744
of ox, 774
of pig, 778
Ischiatic artery, 575
of ox, 619
lymph glands, 604
of ox, 626
of pig, 632
spine, inferior, of horse, 95
superior, of horse, 94, 95
Ischio-cavernosus muscle of clitoris, 515
of penis, 496
of ox, 503
Ischio-coccygeus muscle, 238
Ischio-femoralis muscle, 283
Ischio-urethral muscles of horse, 499
Ischium, 29
of dog, 165
of horse, 95
of ox, 131
of pig, 148
Isthmus faucium of horse, 335, 348
of ox, 385
œsophagi of dog, 428
of prostate, 493
of thyroid gland, 457
of dog, 468
of urethra masculina, 498
pharyngeal, 350
Jacobson’s organ of horse, 440
Jejuno-ileum, 361
Jejunum, 361
Joint, 169. See also _Articulations_.
Jugular ganglion, 687
of dog, 729
of ox, 717
of pig, 722
veins, 587
of dog, 642
of ox, 621
of pig, 630
Jugulomandibularis muscle, 222
Kerato-hyoideus muscle, 223
of ox, 298
Kerato-hyoids of horse, 65
Kerato-pharyngeus muscle of horse, 350
Kidneys, 469
of dog, 483
of horse, 469
arteries of, 475
blood-supply of, 475
cortical substance of, 473
fibrous capsule of, 473
coat of, 474
fixation of, 472
glomerulus of, 474
intermediate zone of, 473
left, 470
lobules of, 473
lymph vessels of, 475
Malpighian corpuscles, 473
pyramid of, 473
medullary substance, 473
Kidneys of horse, mucous coat of, 474
muscular coat of, 474
papilla of, 474
pelvis of, 473
right, 469
stroma of, 475
structure of, 473
tubules of, 474
veins of, 475
vessels and nerves of, 754
weight and size of, 472
of ox, 478
of pig, 481
of sheep, 480
Labia of vulva, 515
vocalis of horse, 448
Labial artery, 549
of ox, 611
superior, 550
glands of horse, 332
nerve of horse, 681
veins, 589
of ox, 621
Labyrinth, membranous, 759
of ethmoid bone, 52
osseous, 758
Lacrimal apparatus, 737
artery, 553
bone of dog, 158
of horse, 61
of ox, 121
of pig, 143
bulla of ox, 121
canal, osseous, 61
caruncle, 735
duct of horse, 737
gland of dog, 779
of horse, 737
of ox, 773
groove, 58
lake, 735
nerve of dog, 728
of horse, 678
of ox, 717
of pig, 722
pouch, 777
process of dog, 158
sac of horse, 737
sinus of ox, 126
tubercle of horse, 61
Lactiferous ducts of cow, 521
of mare, 516
sinus of cow, 521
Lacus lacrimalis, 735
Lamina basalis, 743
choriocapillaris, 743
cribrosa scleræ, 741
elastica posterior, 742
fusca, 740
limitans anterior, 741
of hoof, 765
of nostrils, 437
of omasum of ox, 395
of thyroid cartilage, 442
papyracea, 52
spiralis ossea, 759
suprachorioidea, 742
terminalis of third ventricle, 667
Lamina, transverse, of ethmoid bone of dog, 157
vasculosa, 742
Laminar matrix, 769
Laryngeal artery of ox, 610
nerve of dog, 729
recurrent, 689
superior, 689
orifice, 348
saccule, 447
Larynx of dog, arytenoid cartilage of, 467
cricoid cartilage of, 467
cuneiform cartilage, 467
interarytenoid cartilage of, 467
of horse, 440
arytenoid cartilages, 443
arytenoideus transversus muscle of, 446
cartilages of, 441
cavity of, 447
crico-arytenoideus dorsalis muscle of, 445
lateralis muscle of, 446
cricoid cartilage of, 441
facets, 441
joints of, 444
lateral ventricle of, 447
ligaments of, 444
membranes of, 444
middle ventricle of, 447
mucous glands of, 448
membrane of, 448
muscles of, 445
transverse arytenoid ligament of, 444
ventricular ligament, 444
vessels and nerves of, 448
vestibule of, 447
walls of, 441
of ox, 459
of pig, 465
Lateral cartilages of phalanges, ligaments of, 190
of third phalanx, 91
column of spinal cord, 651
digital extensor muscle of dog, 322, 328
of horse, 265
of leg of horse, 288
of ox, 304, 309
of pig, 315, 317
femoro-patellar ligaments of horse, 194
fissure of cerebrum, 667
of dog, 726
of horse, 668
of ox, 716
of pig, 721
ligament, external, of carpal joints, 183
of coffin joint, 189
of elbow joint, 182
of femoro-tibial articulation, 197
of fetlock joint, 185
of hock joint, 200
of pastern joint, 188
internal, of carpal joint, 184
of coffin joint, 189
of elbow joint, 181
Lateral ligament, internal, of femoro-tibial articulation, 197
of fetlock joint, 185
of hock joint, 201
of pastern joint, 188
left, of liver, 375
of atlanto-occipital articulation, 177
of bladder, 476
of horse, 356
right, of liver, 375
masses of ethmoid, 52
muscles of neck, 229
pterygoideus muscle, 220
rectus capitis, 228
sacro-coccygeus muscle, 239
sacro-iliac ligament, 190
sesamoidean ligaments, 187
surface of skull of dog, 160
of horse, 66
of ox, 123
of pig, 144
ventricle, 674
of larynx of horse, 447
of ox, 459
Lateralis sterni muscle of horse, 242
Latissimus dorsi muscle of dog, 320
of horse, 251
of ox, 302
of pig, 314
Layer, femoral, of external oblique muscle, 246
fibrous, of articulations, 170
of pericardium, 525
iliac, of external oblique muscle, 246
muscular, of trachea, 450
serous, of pericardium, 525
synovial, of articulations, 170
visceral, of pericardium, 525
Leg, bones of, 29
of horse, muscles of, 287
anterior, 288
posterior, 290
of ox, muscles of, 309
of pig, muscles of, 317
Lemniscus, 658
lateralis, 660
medialis, 660
Lens, crystalline, 746
Lenticular nucleus, 675
Levatores costarum muscle of dog, 325
of horse, 240
of ox, 300
of pig, 313
labii superioris proprius of dog, 318
of horse, 215
of ox, 295
of pig, 311
nasolabialis muscle of dog, 318
of horse, 214
of ox, 295
of pig, 311
palati muscle of horse, 333
palpebræ superioris, 219, 738
rostri muscle of pig, 311
scapulæ hominis, 254
Ligament or ligaments, annular, 212
anterior, of horse, 263
of manus of horse, 263
of pelvic limb of horse, 274
posterior, of carpus of horse, 263
arciform, of radio-ulnar articulation of horse, 182
arytenoid, transverse, of larynx of horse, 444
astragalo-calcaneal, 202
astragalo-scaphoid, 202
atlanto-axial, inferior, 176
superior, 176
axillary, of Helmholtz, 755
broad, of uterus of bitch, 523
of cow, 518
of horse, 356
of mare, 513
calcaneo-cuboid, 202
calcaneo-cunean, 202
calcaneo-metatarsal, 201
calcaneo-scaphoid, 202
capsular, 170
caudate, of liver, 375
check, inferior, of carpal joints of horse, 183
of deep digital flexor muscle of horse, 272
of hock joint of horse, 200
superior, of superficial digital flexor muscle of horse, 270
common vertebral, inferior, of horse, 173
superior, of horse, 173
conjugal, of horse, 177
coronary, of horse, 374
costo-sternal, superior, 178
costo-transverse, superior, 177
cotyloid, of horse, 192
crucial, of femoro-tibial articulation of horse, 198
cuboido-cunean, 202
cuboido-scaphoid, 202
dorsal common, of carpal joints of horse, 183
of hock joint of horse, 201
of interphalangeal joints of dog, 209
dorso-scapular, of horse, 235
external lateral, of carpal joints of horse, 183
of coffin joint, 189
of elbow joint, 182
of femoro-tibial articulation of horse, 197
of fetlock joint, 185
of hock joint, 200
of pastern joint, 188
of temporo-mandibular articulation, 179
falciform, of horse, 374
femoro-patellar, lateral, 195
gastro-phrenic, of horse, 358
hepato-renal, of horse, 375
hyo-epiglottic, of horse, 444
ilio-lumbar, of horse, 191
inguinal, of horse, 246
interchondral, of horse, 178
Ligament, interdigital, inferior, of ox, 208
superior, of ox, 206
internal lateral, of carpal joints of horse, 184
of coffin joint, 189
of elbow joint, 181
of femoro-tibial articulation of horse, 197
of fetlock joint, 185
of hock joint, 201
of pastern joint, 188
interosseous, of radio-ulnar articulation of horse, 182
intersesamoidean, 187
interspinous, of horse, 175, 176
intertransverse, 175
intraarticular, 171
lateral, left, of liver of horse, 375
of atlanto-occipital articulation, 177
of bladder of horse, 476
of horse, 356
right, of liver of horse, 375
long, of hock joint, 201
middle of bladder, 476
of horse, 356
navicular, inferior, 190
suspensory, of horse, 189
odontoid, of horse, 176
of auditory ossicles, 755
of fibular tarsal bone, 202
of larynx of horse, 444
of lateral cartilages of phalanges of horse, 190
of liver of horse, 374
of lung of horse, 452
of neck of rib, of horse, 177
of peritoneum of horse, 354
of scrotum of horse, 488
of tibial tarsal bone, 202
of vertebræ of dog, 204
of horse, 172
of ox, 203
of pig, 204
ovarian, of bitch, 522
of mare, 509
palpebral, 736
patellar, of horse, 195
periarticular, 171
plantar, of hock joint, 201
posterior, of pastern joint, 188
of temporo-mandibular articulation, 179
Poupart’s, of horse, 246
pubo-femoral, 193, 250
radiate, of horse, 177
round, of bladder, 476
of hip joint of horse, 193
of horse, 356
of liver of horse, 375
of uterus of bitch, 523
of cow, 518
of mare, 513
sacro-iliac, dorsal, 190
sacro-iliac, lateral, 190
ventral, 190
sacro-sciatic, of horse, 190
scaphoido-cunean, 202
scrotal, of horse, 488
sesamoidean, of horse, 186, 187, 188
of ox, 207
short, of hock joint, 201
sternal, of horse, 178
structure of, 171
subcarpal, of horse, 183
subtarsal, of horse, 200
supraspinous, of horse, 174
suspensory, of penis, 494
of spleen of horse, 379
tarso-metatarsal, 202
thyro-arytenoid, inferior, 444
superior, 444
thyro-epiglottic, 444
transverse, of carpus, 263
of hip joint of horse, 192
of radio-ulnar articulation of horse, 182
umbilical, of bladder, 476
vaginal, 212
ventricular, of larynx, 444
vocal, of horse, 444
volar, of carpal joints, 183
of pastern joint, 188
V-shaped, of horse, 188
Y-shaped, of horse, 188
Ligamenta annularia of trachea, 450
flava, 174
sternopericardiaca of ox, 608
Ligamentum arteriosum, 535, 607
crico-thyreoideum, 444
denticulatum, 647
nuchæ, 174
pectinatum iridis, 742
spirale cochleæ, 760
Limbus palpebralis, 735
Line, curved, superior, of skull, 69
gluteal, 93
ilio-pectineal, 93
popliteal, of tibia, 100
terminal, 353
Linea alba, 246
Lingual artery, 548
of dog, 634
of ox, 611
branch of ninth nerve, 687
glands, 336
nerve, 683
of dog, 729
process of horse, 65
vein, 590
dorsal, 587
Lingula, 660
Lips of dog, 423
of horse, 330
muscles of, 213
of ox, 382
of pig, 410
of sheep, 405
Liquor folliculi of mare, 510
pericardii of horse, 525
pleuræ of horse, 453
Liver of dog, 432
of horse, 373
structure of, 376
of ox, 400
of pig, 421
Liver of sheep, 409
Lobe, apical, of lungs of ox, 462, 463
cardiac, of lungs of ox, 463
caudate, of liver, 433
of ox, 402
of pig, 421
cerebellar, 661
diaphragmatic, of lung of ox, 463
mediastinal, of lung of horse, 456
of ox, 463
of liver of dog, 432
of horse, 374
of pig, 421
of lungs of dog, 468
of horse, 456
of ox, 462, 463
of pig, 466
of mammary glands, 516
of prostate of horse, 493
of thymus gland of horse, 458
of thyroid gland of dog, 468
of horse, 457
precardiac, of lung of horse, 463
pyriform, 668
of dog, 728
Lobular bronchioles, 457
Lobulation of lungs, 456
of ox, 463
of sheep, 464
Lobules of epididymis, 487
of kidney of horse, 473
of liver of pig, 422
of lung of horse, 457
of mammary glands, 516
of prostate of horse, 493
of testicles of horse, 486
of thymus gland, 458
of thyroid gland, 458
Lobus piriformis, 672
Locus perforatus posticus, 664
Loins of dog, muscles of, 325
of horse, fasciæ of, 235
muscles of, 235
of ox, muscles of, 300
of pig, muscles of, 313
Long ligament of hock joint, 201
muscles, 211
Longissimus capitis et atlantis muscle of horse, 229
muscle of dog, 325
of horse, 237
of ox, 300
Longitudinal bands of cæcum of horse, 364
fissure of cerebrum, 667
of brain, 654
grooves of heart, 528
sinus, superior, 591
Longus capitis muscle, 227
colli muscle of dog, 324
of horse, 228
of pig, 312
Lower, tubercle of, 530
Lumbar arteries, 571, 573
of ox, 618
of pig, 629
enlargement of horse, 648
ganglia, 713
Lumbar lymph glands, 604
of dog, 643
of ox, 625
of pig, 631
nerves of horse, 702
veins, 596, 597
vertebræ, 24
of dog, 151
of horse, 38
of ox, 112
of pig, 138
Lumbo-dorsal fascia, 235
Lumbo-sacral plexus of dog, 731
of horse, 705
of ox, 719
of pig, 723
Lumbricales muscles of dog, 324, 329
of horse, 273, 295
of ox, 305
of pig, 316
Lung, fœtal, of horse, 454
of dog, 468
lobes of, 468
of horse, 453
air-cells of, 457
alveolar ducts of, 457
alveoli of, 457
apex of, 456
basal border of, 456
base of, 456
bronchial branches of, 456
cardiac impression of, 454
notch of, 456
color of, 454
costal surface of, 454
dorsal border of, 455
form of, 454
hilus of, 454
interlobular tissue of, 457
ligament of, 451
lobes of, 456
lobulation of, 456
lobule of, 457
lymph vessels of, 456, 457
mediastinal lobe of, 456
surface of, 454
precardiac lobe of, 463
root of, 456
ventral border of, 454
vessels and nerves of, 457
of ox, 462
apical lobe of, 462, 463
cardiac lobe of, 463
diaphragmatic lobe, 463
fissures of, 462
lobes of, 462, 463
lobulation of, 463
mediastinal lobe of, 463
of pig, 466
lobes of, 466
of sheep, lobulation of, 464
Luys’s body, 665
Lymph, 599, 600
follicles, 600
of small intestine, 363
glands, 599
anal, 605
of pig, 632
atlantal of ox, 623
auricular, of dog, 643
axillary, 605
of dog, 643
Lymph glands, axillary, of ox, 625
of pig, 631
bronchial, 603
of horse, 457
of ox, 624
of pig, 631
cæcal, of pig, 632
cervical, 601
of dog, 643
of ox, 624
of pig, 631
colic, of pig, 632
cubital, of dog, 643
gastric, 604
of pig, 632
hepatic, 605
of pig, 632
iliac, 604
of dog, 643
of ox, 625
of pig, 631
inguinal, 604
of pig, 632
intercostal, 603
ischiatic, 604
of pig, 632
lumbar, 604
of dog, 643
of ox, 625
of pig, 631
mediastinal, 603
of dog, 643
mesenteric, 605
of dog, 643
of pig, 632
of cæcum, 605
of colon, 605
of dog, 643
of Fallopian tubes, 511
of mammary glands of cow, 521
of mare, 517
of ovaries of mare, 510
of ox, 623
of penis, 496
of pig, 630
of prepuce, 497
of spermatic cord, 489
of uterus, 513
of vagina, 514
orbital, 606
pancreatic, 605
parotid, of dog, 643
of pig, 630
pectoral, 601
pharyngeal, 602
of dog, 643
of ox, 623
of pig, 630
popliteal, 606
of dog, 643
of pig, 632
precrural, 606
of pig, 632
prepectoral, of pig, 631
prescapular, 602
of dog, 643
of ox, 624
of pig, 631
renal, of ox, 625
sacral, 604
splenic, 605
of pig, 632
Lymph glands, sternal, of ox, 624
subiliac, 606
submaxillary, 601
of dog, 643
of ox, 623
of pig, 630
subparotid, of ox, 623
thoracic, of pig, 631
nodes, 599. See _Lymph glands_.
nodules, 600
of spleen of horse, 379
spaces, 600
Lymphatic duct, right, 601
system, 599
Lymphocytes, 599, 600
Lymph vessels, 524, 599
of adrenal bodies, 478
of dog, 643
of heart, 535
of kidneys of horse, 475
of lungs of horse, 456, 457
of ox, 623
of pig, 630
Lyssa of dog, 424
Macroscopic anatomy, 17
Maculæ acusticæ, 760
Malar artery, 555
bone of dog, 158
of horse, 67
of ox, 121
of pig, 143
Malaris muscle of horse, 218
of ox, 296
Malleolus, external, of tibia, 103
internal, of tibia, 103
Malleus, 754
Malpighian corpuscles, 379
of kidney, 473, 474
pyramids of kidney, 473
Mammary artery, 580
of ox, 619
glands of bitch, 523
teats of, 523
of cow, 519
of mare, 516
of sow, 522
lymph glands, 604
vein of ox, 622
Mammillary body, 653, 665
of dog, 726
processes, 25, 43
Mandible of dog, 158
of horse, 63
of ox, 122
of pig, 143
Mandibular canal, 64
foramen, 64
nerve of dog, 728
of horse, 681
of ox, 717
of pig, 722
teeth of horse, 344
Mane, 764
Mantle, brain, 668
Manubrium mallei, 754
sterni, 26
of horse, 46
Manus, bones of, 28
of horse, fasciæ of, 262
Manus of horse, muscles of, 262
Marginal cartilage, 171
fissure of horse, 669
of ox, 716
of pig, 721
pole, 716
Margo ciliaris, 744
pupillaris, 744
Marrow of bone, 21
Masseter muscle of dog, 318
of horse, 219
of ox, 297
Masseteric artery, inferior, 547
of ox, 612
fossa of mandible of dog, 159
nerve of horse, 681
vein, 588
Mastication, muscles of, of dog, 318
of horse, 219
of ox, 297
of pig, 311
Mastoid artery, 545
process of horse, 67
Mastoido-humeralis muscle of dog, 320
of horse, 225, 252
of ox, 302
of pig, 314
Matrix of horn, 776
of hoof, 769
Maxilla of dog, 157
of horse, 58
inferior, 63
of ox, 120
of pig, 142
Maxillary artery, external, 547
internal, 551, 612
of dog, 635
of ox, 611
of pig, 627
foramen of horse, 58, 64, 67
nerve of dog, 728
of horse, 679
of pig, 722
process of dog, 158
region of horse, 68
sinus, inferior, of horse, 73
of dog, 161
of horse, 72
of ox, 126
of pig, 146
superior, of horse, 73
teeth of horse, 343
tuberosity of horse, 58
vein, 588
internal, 587
of dog, 642
Maxillo-muscular artery, 547
vein, 588
Maxillo-turbinal bone, 62
Meatus, auditory, external, 56, 748, 759
internal, of horse, 56
common, of nasal cavity, 440
ethmoidal, of nasal cavity, 440
inferior, of nasal cavity of dog, 467
of horse, 439
of pig, 465
of nose of horse, 72
Meatus, middle, of nasal cavity of dog, 467
of horse, 438
of pig, 465
of nose of horse, 72, 71
common, 62
inferior, 62
middle, 62
superior, 62
superior, of nasal cavity of horse, 438
of pig, 465
of nose of horse, 72
Median artery, 559
of ox, 612
nerve, 696
of dog, 731
of horse, 699
of ox, 719
of pig, 723
palatine suture, 69
Mediastinal lobe of lung of horse, 456
of ox, 463
lymph glands, 603
of dog, 643
of ox, 624
pleura of horse, 451
Mediastinum of horse, 450
testis of horse, 486
Medulla oblongata of dog, 735
of horse, 655
of ox, 715
of pig, 720
of thymus gland, 458
Medullary artery, 21
canal of metacarpus of ox, 130
cavity, 19, 20
substance of adrenal bodies, 478
of kidney, 473
velum, 660, 663
Meissner, plexus of, 714
Membrane, atlanto-occipital, inferior, of horse, 176
superior, of horse, 176
basilaris, 760
bones, 22
crico-thyroid, of horse, 444
crico-tracheal, of horse, 445
elastic, of trachea, 449
interosseous, of tibio-fibular articulation, 199
obturator, of horse, 191
œsophageal, of horse, 360
of Descemet, 742
of larynx of horse, 444
of Reissner, 760
synovial, 211
bursal, 211
of anterior digital extensor muscle, 265
of carpal joints, 183
of elbow joint, 181
of hip joint, 193
of lateral digital extensor muscle, 265
vaginal, 211
Membrani nictitans, 736
tympani, 753
secundaria, 753
vestibularis, 760
Membranous labyrinth, 759
Meningeal artery, anterior, 546
middle, 552
of dog, 634
posterior, 545
veins, 592
Meninges, 645
Meniscus, 171
Mental artery, 552
foramen, 63
Mentalis muscle, 216
Mentum of horse, 331
Meridians of eye, 740
Mesaticephalic breed of dogs, 159
Mesencephalon, 663
Mesenteric artery, great, 570
of dog, 638
of ox, 615
of pig, 628, 629
posterior, of ox, 618
small, 571
ganglia, 714
lymph glands, 605
of dog, 643
of ox, 626
of pig, 632
plexus, 714
vein, 597
Mesentery, colic, 354, 369
great, 354, 362
Mesethmoid of ethmoid of horse, 52
Mesocolon of dog, 432
Mesoduodenum, 361
Mesogastric zone of horse, 353
Mesorchium, 489, 490
Mesorectum, 355, 370
Mesosalpinx of bitch, 522
of mare, 511
Mesosternum, 26
Mesotendon, 212
Mesovarium of mare, 509
Metacarpal artery, dorsal, 562
external volar, 562
internal volar, 562
large, 563
of dog, 635, 636, 637
of ox, 614
of pig, 629
palmar, 563
bones, 28
large, 87
of ox, 130
small, of horse, 88
of ox, 130
muscles of horse, 273
of ox, 305
nerves of dog, 731
of horse, 701
tuberosity of horse, 88
vein, 595
of dog, 642
of ox, 621
Metacarpo-phalangeal joints of dog, 208
of horse, 185
of ox, 206
of pig, 208
Metacarpus, 28
of dog, 164
of horse, 87
development of, 88
fascia of, 263
Metacarpus of ox, 128
of pig, 147
Metasternum, 26
Metatarsal arteries, 581
dorsal, 585
of ox, 620
internal superficial plantar, of ox, 619
great, 585
of dog, 640, 641
of pig, 630
bones, 30
of horse, 110, 111
of ox, 135
fascia of horse, 274
nerves of dog, 732
veins, 599
of dog, 643
of ox, 622
Metatarsus of dog, 168
of horse, 110
muscles of, 295
of ox, 135
of pig, 149
Meynert’s commissure, 666
Microscopic anatomy, 17
Mid-brain, 663
Middle cornua of horse, 65
ear of horse, 752
fossa of skull of horse, 71
gluteus muscle of horse, 277
ligament of bladder, 476
of horse, 356
meatus of nasal cavity of dog, 467
of horse, 438
of pig, 465
of nose of horse, 62, 72
patellar ligament, 195
sesamoidean ligament of horse, 188
ventricle of larynx of horse, 447
Milk cistern of cow, 521
teeth of horse, 346
of cow, 521
vein, 301
Mitral valve of horse, 533
Modiolus, 759
Molar glands of ox, 383
Molars, 338, 342
Monakow’s rubrospinal tract, 652
Morgagni, hydatid of, of Fallopian tubes, 511
of testicles, 485
Morphology, 17
Mouth of dog, 423
of horse, 330
cavity of, 330
floor of, 334
mucous membrane of, 330
of ox, 382
of pig, 410
Movable joints, 170
vertebræ, 24
Movements of joint, 171
Mucous glands of larynx, 448
of trachea of horse, 450
membrane, nasal, of horse, 440
of abomasum of ox, 397
of cæcum of dog, 432
of larynx of horse, 448
Mucous membrane of mammary gland of cow, 521
of mouth of horse, 330
of œsophagus of horse, 352
of omasum of ox, 397
of pharynx of horse, 350
of rectum of horse, 370
of reticulum of ox, 395
of stomach of ox, 397
of rumen of ox, 394, 397
of seminal vesicles, 492
of small intestine, 362
of stomach of dog, 430
of tongue of horse, 335
of trachea of horse, 450
of ureters of horse, 475
of urethra of mare, 516
masculina of horse, 499
of uterus of cow, 518
of mare, 513
of vas deferens, 489
of vulva of mare, 515
Müller, muscle of, 736
Multifidus cervicis muscle, 231
dorsi muscle of horse, 238
muscle of pig, 313
Muscles or muscle, 211
abdominal, of horse, 245
of pig, 313
abductor cruris posterior, of dog, 327
digiti quinti, of dog, 324, 329
hallucis, of dog, 329
pollicis brevis et opponens pollicis, of dog, 324
accelerator urinæ, 499
action of, 212
adductor brevis, 282
digiti quinti, of dog, 324
secundi, of dog, 324
hallucis, of dog, 329
longus, of horse, 282
magnus, of horse, 282
of dog, 328, 329
of horse, 282
of ox, 308
of pig, 316
parvus, of horse, 282
pollicis, of dog, 324
anconeus, of horse, 262
of pig, 315
anterior digital extensor, 263
of leg of horse, 288
of ox, 304, 309
extensor, of phalanges, 264
of thigh of ox, 307
antitragicus, 751
arrectores pilorum, 763
articularis genu, of ox, 307
arytenoideus transversus, of larynx of horse, 446
attachments of, 211, 212
auricular, 749
of ox, 774
azygos uvulæ, of horse, 333
belly of, 212
biceps brachii, of dog, 322
of horse, 259
of pig, 314
femoris, of dog, 326
of horse, 278
of ox, 306
Muscle, biceps femoris, of pig, 316
of ox, 302
bipennate, 212
biventer cervicis, of dog, 325
brachial triceps, of horse, 260
brachialis, of dog, 322
of horse, 260
of pig, 315
brachio-radialis, of dog, 322
buccinator, of dog, 318
of horse, 216
of ox, 295
bulbo-cavernosus, of penis of ox, 503
of urethra of horse, 499
capsularis, of dog, 328
of horse, 258, 286
of ox, 307
of pig, 314, 317
cardiac, 211
cervicalis ascendens, of horse, 227
cervico-auricularis, 750
cervico-scutularis, 749
of dog, 780
of ox, 774
chondro-pharyngeus, 350
ciliary, 743
cleido-cervicalis, of dog, 320
cleido-mastoideus, of dog, 320
of horse, 252
of pig, 314
cleido-occipitalis, of pig, 314
cleido-transversarius, 252
coccygeus, of dog, 325
of horse, 230
ventralis lateralis, 240
common digital extensor, 263
of ox, 304
complexus major, of dog, 325
of dog, 325
of horse, 231
of pig, 312
compressor coccygis, of horse, 238
constrictor vestibuli, of mare, 515
vulvæ, of mare, 515
coraco-brachialis, of dog, 322
of horse, 258
of ox, 302
of pig, 314
coraco-radialis, of horse, 259
corrugator supercilii, 218
cremaster, external, 249, 490
of pig, 313
of testicles of ox, 500
of pig, 504
crico-arytenoideus dorsalis, of larynx of horse, 445
lateralis, of horse, 446
crico-pharyngeus, 350
crico-thyroideus, 445
crural triceps, of horse, 284
crureus, of horse, 286
curvator coccygis, 239
cutaneus maximus, of abdomen of horse, 245
scapulæ et humeri, 255
Muscle, deep digital flexor, 271
of leg of horse, 293
of ox, 305
flexor, of ox, 311
gluteus, of horse, 278
pectoral, of ox, 302
deltoid, of dog, 320
of horse, 255
of ox, 302
of pig, 314
depressor coccygis, 240
labii inferioris, of dog, 318
of horse, 216
of ox, 295
of pig, 311
superioris, of ox, 295
rostri, of pig, 311
diaphragm, of dog, 325
of horse, 243
of ox, 300
of pig, 313
digastric, 213
digastricus, of dog, 319
of horse, 222
of ox, 297
of pig, 311
digital extensor, anterior, of dog, 328
of pig, 317
common, of dog, 322
of pig, 315
lateral, of dog, 322, 328
of pig, 315, 317
of ox, 304, 309
of pig, 315
flexor, deep, of dog, 323, 329
of pig, 316, 317
superficial, of dog, 323, 329
of pig, 316, 317
dilatator naris apicalis, of ox, 296
inferior, of horse, 218
of ox, 296
lateralis, of horse, 217
of ox, 295
of pig, 311
superior, of horse, 218
of ox, 296
transversus, of horse, 217
of pig, 311
pupillæ, 744
erector clitoridis, of mare, 515
penis, of horse, 496
extensor brevis, of ox, 310
carpi obliquus, of dog, 322
of horse, 267
of ox, 304
of pig, 315
of dog, 322
radialis brevis, of dog, 322
longus, of dog, 322
of horse, 263
of ox, 304
of pig, 315
ulnaris, of dog, 323
of horse, 268
digitalis brevis, of dog, 328
Muscle, extensor digitalis brevis, of pig, 317
communis, of horse, 263
lateralis, of horse, 265
of leg of horse, 288
longus, of leg of horse, 288
digiti quinti, of dog, 323
tertii et quarti, of dog, 323
hallucis longus, of dog, 328
of pig, 317
indicis proprius, of pig, 315
metacarpi obliquus, of horse, 267
of digits of dog, 322, 329
of second digit of pig, 315
pedis brevis, of horse, 295
of horse, 264, 288
flat, 211
flexor brachii, of horse, 259
carpi externus, of horse, 268
of pig, 316
internus, of dog, 323
of horse, 267
of pig, 315
medius, of dog, 323
of horse, 268
of pig, 315
digitalis pedis, of dog, 329
digiti quinti, of dog, 324
hallucis brevis, of dog, 329
longus, of dog, 329
pedis perforans, of horse, 292, 293
perforans, of horse, 271
perforatus, of horse, 269
pollicis brevis, of dog, 324
form of, 211
frontalis, of ox, 295
fronto-scutularis, 749
gastrocnemius, of dog, 329
of horse, 290
of ox, 311
of pig, 317
gemellus, of horse, 284
of ox, 308
of pig, 317
genio-glossus, of horse, 338
genio-hyoideus, of ox, 298
genito-hyoideus, 223
guteo-biceps, of horse, 278
gluteus accessorius, 278
medius, of dog, 326
of horse, 277
of ox, 306
of pig, 316
profundus, of dog, 326
of horse, 278
of ox, 306
of pig, 316
superficialis, of dog, 326
of horse, 277
of ox, 306
of pig, 316
gracilis, of dog, 328
of horse, 281
of ox, 308
of pig, 316
head of, 213
Muscle, helicis, 752
Homer’s, 736
humeralis obliquus, 260
hyo-epiglotticus, 445
hyo-glossus, of horse, 338
hyoid, of dog, 319
of horse, 222
of ox, 297
hyoideus transversus, 224
of ox, 298
hyo-pharyngeus, 350
hyo-thyreoideus, 445
iliacus, of dog, 326
of horse, 275
of ox, 306
ilio-costalis cervicis, 227
of horse, 236
of ox, 300
ilio-psoas, of horse, 275
incisivus inferior, 216
of ox, 295
superior, of horse, 216
infraspinatus, of dog, 321
of horse, 256
of ox, 302
of pig, 314
insertion of, 212
intercostal, external, of dog, 325
of horse, 240
of pig, 313
internal, of horse, 242
of pig, 313
internal digital extensor, of ox, 304, 309
flexor, of metacarpus, 267
of thigh of ox, 308
interossei, of dog, 324, 329
of horse, 273, 295
of ox, 305
interscutularis, 749
of dog, 780
of ox, 774
interspinales, of dog, 325
of ox, 300
of pig, 313
intertransversales caudæ, 239
colli, of horse, 328
lumborum, 238, 276
of dog, 324, 325
of ox, 300
of pig, 312, 313
ischio-cavernosus, of clitoris of mare, 515
of penis of horse, 496
of ox, 503
ischio-coccygeus, 238
ischio-femoralis, 283
ischio-urethral, 499
jugulomandibularis, 222
kerato-hyoideus, 223
of ox, 298
kerato-pharyngeus, 350
lateral digital extensor, 265
of leg of horse, 288
of ox, 304, 309
lateralis sterni, of horse, 242
latissimus dorsi, of dog, 320
of horse, 251
of ox, 302
of pig, 314
levator labii superioris proprius, of dog, 318
Muscle, levator labii superioris proprius, of horse, 215
of ox, 295
of pig, 311
nasolabialis, of dog, 318
of horse, 214
of ox, 295
of pig, 311
palati, of horse, 333
palpebræ superioris, 219, 738
rostri, of pig, 311
scapulæ hominis, 254
levatores costarum, of dog, 325
of horse, 240
of ox, 300
of pig, 313
long, 211
longissimus capitis et atlantis, of horse, 229
of dog, 325
of horse, 237
of ox, 300
longus capitis, of horse, 227
colli, of dog, 324
of horse, 228
of pig, 312
lumbricales, of dog, 324, 329
of horse, 273, 295
of ox, 305
of pig, 316
malaris, of horse, 218
of ox, 296
masseter, of dog, 318
of horse, 219
of ox, 297
mastoido-humeralis, of dog, 320
of horse, 225, 252
of ox, 302
of pig, 314
mentalis, of horse, 216
metacarpal, of horse, 273
of ox, 305
middle gluteus, of horse, 277
multifidus cervicis, 231
dorsi, of horse, 238
of pig, 313
mylo-hyoideus, of dog, 319
of horse, 222
of ox, 297
names of, 212
nasal, of dog, 318
nerve-supply of, 213
non-striated, 211
oblique extensor, of metacarpus of horse, 267
great, of abdomen, 246
small, of abdomen, 247
of head of horse, 233
obliquus abdominis externus, of dog, 326
of horse, 246
of ox, 301
of pig, 313
internus, of dog, 326
of horse, 247
of ox, 301
of pig, 313
capitis anterior, 233
posterior, of horse, 233
of pig, 313
Muscle, obliquus oculi inferior, 738
superior, 738
obturator externus, 283
of ox, 308
of pig, 317
internus, of horse, 283
of ox, 308
of pig, 317
occipito-hyoideus, 223
of ox, 298
ocular, of horse, 738
of abdomen of dog, 326
of ox, 301
of anus of horse, 371
of arm of horse, 259
of ox, 302
of pig, 314
of auditory ossicles, 755
of back of dog, 325
of horse, 235
of ox, 300
of pig, 313
of cheeks of horse, 213
of digit of horse, 295
of pig, 315
of dog, 318
of eyelids of horse, 218
of face of dog, 318
of ox, 295
of foot of horse, 287
of ox, 309
of pig, 317
of forearm of horse, 262
extensor division, 263
flexor division, 267
of ox, 304
of pig, 315
of head of horse, 213
of pig, 311
of hip, external, of horse, 276
of ox, 306
of pig, 316
of horse, 213
of larynx of horse, 445
of leg of horse, 287, 288, 290
of ox, 309
of pig, 317
of lips of horse, 213
of loins of dog, 325
of horse, 235
of ox, 300
of pig, 313
of manus of horse, 262
of mastication of dog, 318
of horse, 219
of ox, 297
of pig, 311
of metatarsus of horse, 295
of Müller, 736
of neck of dog, 324
of horse, 224, 229
of ox, 298
of pig, 311
of nostrils of horse, 217
of ox, 295
of pelvic limb of dog, 326
of horse, 274
of ox, 306
of pig, 316
of penis of horse, 496
of pharynx of horse, 348
of pig, 311
Muscle of shoulder girdle of horse, 250
of ox, 302
of pig, 314
joint of horse, 181
of horse, 255
of ox, 302
of pig, 314
of tail of dog, 325
of horse, 238
of ox, 300
of pig, 314
of thigh, anterior, 284
external, of horse, 276
of ox, 306
internal, of horse, 281
of pig, 316
of thoracic limb of dog, 319
of horse, 250
of ox, 302
of pig, 314
of thorax of dog, 325
of horse, 240
of ox, 300
of pig, 313
of tongue of horse, 337
omo-hyoideus, 224, 226
of ox, 298
of pig, 312
omo-transversarius of dog, 319
of ox, 302
of pig, 312, 314
orbicular, 211
orbicularis oculi, 218
of ox, 296
oris of dog, 318
of horse, 213
of ox, 295
of pig, 311
origin of, 212
palato-pharyngeus, 349
palmaris brevis, of dog, 324
longus accessorius, of dog, 323
palpebral, of dog, 318
panniculus carnosus, of dog, 318
of pig, 311
of ox, 295
of pig, 311
paramero-biceps, 278
parieto-auricularis, 750
of dog, 780
of ox, 774
parotido-auricularis, 750
pectineus, of dog, 328
of horse, 282
of ox, 308
of pig, 316
pectoral, anterior superficial, of pig, 314
deep, of dog, 320
of horse, 253
of pig, 314
of horse, 252
posterior deep, of pig, 314
superficial, of dog, 320
of horse, 253
of pig, 314
peroneus brevis, of dog, 328
longus of dog, 328
of pig, 317
of horse, 288
Muscle, peroneus tertius, of dog, 328
of horse, 289
of ox, 310
of pig, 317
plantar, of pig, 317
popliteus, of dog, 329
of horse, 294
of pig, 317
preputial, of ox, 503
pronator quadratus, of dog, 324
teres, of dog, 323
of horse, 268
of pig, 315
protractor, of prepuce of ox, 503
psoas major, of dog, 326
of horse, 275
of ox, 306
of pig, 316
minor, of dog, 326
of horse, 275
of ox, 306
of pig, 316
pterygoideus externus, 220
internus, of horse, 219
lateralis, of horse, 220
of ox, 297
pterygo-pharyngeus, of horse, 349
pyriformis, of dog, 326
of horse, 284
quadratus femoris, of dog, 328
of horse, 283
of ox, 308
of pig, 317
lumborum, of dog, 326
of horse, 276
of ox, 306
of pig, 316
plantæ, of dog, 329
quadriceps femoris, 284
of ox, 307
of pig, 317
radialis volaris, of dog, 323
rectus abdominis internus, of pig, 313
of dog, 326
of horse, 248
of ox, 301
of pig, 313
capitis anterior major, of dog, 324
of horse, 227
of ox, 300
minor, of horse, 227
of ox, 300
dorsalis major, of horse, 234
minor, of horse, 234
lateralis, of horse, 228
of ox, 300
of pig, 313
posterior major, of horse, 234
minor, of horse, 234
femoris, of dog, 327
of horse, 284
lateralis, of dog, 324
minor, of dog, 324
oculi, 738
parvus, of horse, 286
Muscle, rectus thoracis, of horse, 242
of pig, 313
relations of, 213
retractor ani, of dog, 432
of horse, 371
costæ, of horse, 242
of pig, 313
oculi, 738
of prepuce of ox, 503
penis, of horse, 496
of ox, 503
rhomboideus capitis, of dog, 320
cervicalis, of dog, 320
of horse, 251
of dog, 320
of horse, 251
of ox, 302
of pig, 314
thoracalis, of dog, 320
of horse, 251
ring-like, 211
rotator, 757
sacro-coccygei, of pig, 314
sacro-coccygeus accessorius, of dog, 325
inferior, of horse, 240
lateralis, of horse, 239
of dog, 325
superior, of horse, 238
ventralis lateralis, of horse, 240
sartorius, of dog, 328
of horse, 281
of ox, 308
of pig, 316
scalenus dorsalis, of dog, 324
of ox, 300
of horse, 227
of pig, 312
ventralis, of dog, 324
of ox, 298
of pig, 312
scansorius, of horse, 278
scapulo-humeralis posticus, of horse, 258
scapulo-ulnaris, of horse, 260
scutularis, 749
semimembranosus, of dog, 327
of horse, 280
of ox, 306
of pig, 316
semispinalis capitis, of horse, 231
colli, of horse, 231
semitendinosus, of dog, 327
of horse, 280
of ox, 306
of pig, 316
serratus anterior hominis, of horse, 254
anticus, of dog, 325
of horse, 235
of ox, 300
of pig, 313
cervicis, of horse, 254
magnus, of dog, 320
of horse, 254
of ox, 302
of pig, 314
posticus, of dog, 325
of horse, 236
Muscle, serratus posticus, of ox, 300
thoracis, of horse, 254
ventralis, of horse, 254
shape of, 212
short, 211
skeletal, 211
small posterior straight, of head of horse, 234
soleus, of horse, 292
of ox, 311
of pig, 317
sphincter, 211, 213
ani externus, of horse, 371
internus, of horse, 371
pupillæ, 744
spinalis et semispinalis, of pig, 313
of horse, 233
spinous, transverse, of neck of horse, 231
splenius, of dog, 324
of horse, 229
of ox, 300
of pig, 312
stapedius, 755
sterno-cephalicus, of dog, 324
of neck of horse, 225
of ox, 298
of pig, 312
sterno-mandibularis, 225
sterno-maxillaris, 225
sterno-thyro-hyoideus, of dog, 319
of horse, 224, 226
of ox, 298
of pig, 312
sterno-thyroideus et sterno-hyoideus, of horse, 226
straight, of head of pig, 312
striated, 211
structure of, 212
stylo-glossus, of horse, 337
stylo-hyoideus, of dog, 319
of horse, 223
of ox, 297
stylo-mandibularis, 222
of ox, 297
stylo-maxillaris, 222
stylo-pharyngeus, 349
sublumbar, of horse, 274
of ox, 306
of pig, 316
subscapularis, of dog, 321
of horse, 257
of ox, 302
of pig, 314
subscapulo-hyoideus, 226
superficial digital flexor, 269
of leg of horse, 292
of ox, 305
flexor, of ox, 311
gluteus, of horse, 277
pectoral, of ox, 302
supinator, of dog, 323
of pig, 315
supraspinatus, of dog, 321
of horse, 256
of ox, 302
of pig, 314
tarsal, 736
temporalis, of dog, 318
Muscle, temporalis, of horse, 219
of ox, 297
tendo femorotarseus, 289
tensor fasciæ antibrachii, of dog, 322
of horse, 260
of ox, 303
of pig, 315
latæ, of dog, 326
of horse, 276
of ox, 306
of pig, 316
palati, of horse, 333
tympani, 755
teres major, of dog, 322
of horse, 258
of ox, 302
of pig, 314
minor, of dog, 321
of horse, 256
of ox, 302
of pig, 314
thyro-arytenoideus, 446
thyro-hyoideus, 445
thyro-pharyngeus, 350
tibialis anterior, of dog, 328
of horse, 290
of ox, 310
of pig, 317
posterior, of dog, 329
trachelo-mastoideus, of dog, 325
of horse, 229
of pig, 312
tragicus, 751
transversalis costarum, of dog, 325
of horse, 236
of ox, 300
of pig, 313
transversus abdominis, of dog, 326
of horse, 248
of ox, 302
of pig, 313
costarum, of horse, 242
thoracis, of horse, 242
of pig, 313
trapezius cervicalis, of horse, 250
of dog, 319
of horse, 250
of ox, 302
of pig, 314
thoracalis of horse, 251
triangularis sterni, 242
triceps brachii, of horse, 260
of dog, 322
of ox, 303
of pig, 315
suræ, of horse, 292
ulnaris lateralis, of dog, 323
medialis, of dog, 323
unipennate, 212
unstriped, 211
urethral, of dog, 507
of horse, 499
of mare, 516
of ox, 504
of pig, 506
vastus externus, of horse, 285
intermedius, of horse, 286
of ox, 307
Muscle, vastus internus, of horse, 286
ventricularis et vocalis, 446
vocalis, of horse, 446
volar, of pig, 315
Wilson’s, of dog, 509
of ox, 504
zygomatico-auricularis, 749
of ox, 774
zygomaticus, of dog, 318
of horse, 215
of ox, 295
of pig, 311
Muscular bands of great colon
of horse, 368
coat of œsophagus, 352
layer of trachea of horse, 450
process of arytenoid cartilages of larynx, 443
of temporal bone, 57
ring of cæcum of horse, 365
system, 211
Muscularis mucosæ of small intestine, 362
Musculi papillares of left ventricle, 533
of right ventricle, 531
pectinati, in right atrium, 530
Musculo-cutaneous nerves, 696
of dog, 730
of horse, 697
of leg of horse, 708
Musculo-spiral groove, 77
nerve of horse, 698
Myenteric plexus, 714
Mylo-hyoid nerve, 682
of dog, 728
Mylo-hyoideus muscle of dog, 319
of horse, 222
of ox, 297
Myocardium, 534
Myology, 211
Nares, anterior, of horse, 436
posterior, of horse, 68, 348, 440
Nasal artery, 550
of ox, 611
bones of dog, 158
of horse, 61
of ox, 121
of pig, 143
cavity of dog, 161, 466, 467
of horse, 71, 436
common meatus of, 440
ethmoidal meatuses, 440
inferior meatus of, 439
middle meatus of, 438
parietal cartilage, 437
superior meatus of, 438
vessels and nerves, 437
of ox, 125, 458
of pig, 145, 464
structure of, 436
crest of horse, 71
glands of horse, 440
mucous membrane, 440
muscles of dog, 318
nerve of dog, 728
of horse, 679
Nasal process of horse, 60
region of horse, 66
septum, 71, 72, 73, 437
vein of ox, 621
of pig, 630
Naso-ciliary nerve, 678
of ox, 717
of pig, 722
Nasofrontal suture, 55, 61
of ox, 119
Naso-labial glands of ox, 775
Naso-lacrimal duct of horse, 436, 737
canal for, 71
groove for, 71
of dog, 779
of ox, 773
suture of horse, 61
Naso-maxillary fissure, 73, 439
notch of horse, 61
suture of horse, 61
Naso-palatine canal of ox, 384
Naso-turbinal bones, 62
Navicular bone, 92, 111
bursa of deep digital flexor muscle, 272
ligaments, inferior, 190
suspensory, of horse, 189
Neck of dog, muscles of, 324
of horse, fascia of, 224
fascia propria of, 224
muscles of, 224, 229
panniculus carnosus, 224
transverse spinous muscle of, 231
of ox, muscles of, 298
of pig, muscles of, 311
of tooth, 339
Nerve or nerves, abducent, 683
alveolar, 681, 682
of dog, 729
auditory, 686
auricular, 685
posterior, 695
auriculo-palpebral, 685
of dog, 729
of ox, 717
axillary, 697
of horse, 697
buccal, 685
of dog, 729
of ox, 717
of pig, 722
buccinator, of horse, 681
cardiac, 712
cervical, of horse, 694
chorda tympani, 683, 684
ciliary, of dog, 728
of horse, 679
circumflex, of horse, 697
classification of, 644
coccygeal, of horse, 710
cochlea, 686
cranial, of dog, 728
of horse, 676
of ox, 717
of pig, 722
crural, anterior, 706
cutaneous, of leg, 708
of neck, 695
dental, 681, 682
depressor, of dog, 730
digastric, 685
digital, of dog, 730, 732
Nerve, digital, of horse, 701
of ox, 718
of pig, 723
eighth, 686
eleventh, 690
ethmoidal, 678
of dog, 728
facial, 684
of dog, 729
of ox, 717
femoral, of horse, 706
fifth, of horse, 677
first, of horse, 676
fourth, of horse, 677
frontal, of dog, 728
of horse, 678
of ox, 717
glosso-pharyngeal, 686
gluteal, of horse, 706
hemorrhoidal, of horse, 710
hypoglossal, 692
of dog, 730
of ox, 717
of pig, 722
ilio-hypogastric, 704
ilio-inguinal, of horse, 704
infraorbital, of dog, 728
of horse, 681
of pig, 722
infratrochlear, 679
of dog, 728
intercostal, of horse, 702
labial, of horse, 681
lacrimal, of dog, 728
of horse, 678
of ox, 717
of pig, 722
laryngeal, of dog, 729
recurrent, 689
superior, 689
lingual, 683
of dog, 729
lumbar, of horse, 702
mandibular, of dog, 728
of horse, 681
of ox, 717
of pig, 722
masseteric, of horse, 681
maxillary, of dog, 728
of horse, 679
of pig, 722
median, 696
of dog, 731
of horse, 699
of ox, 719
of pig, 723
metacarpal, of dog, 731
of horse, 701
metatarsal, of dog, 732
musculo-cutaneous, 696
of dog, 730
of horse, 697, 698
of leg of horse, 708
musculo-spiral, of horse, 698
mylo-hyoid, 682
of dog, 728
nasal, of dog, 728
of horse, 697, 681
naso-ciliary, 678
of ox, 717
of pig, 722
ninth, 686
oculomotor, of horse, 677
of ox, 717
Nerve, obturator, of horse, 706
œsophageal, of dog, 729
of adrenal bodies, 478
of articulations, 171
of bladder of horse, 477
of cornea, 742
of external ear, 752
of eye, 737
of Fallopian tubes, 511
of hoof, 771
of mammary glands of cow, 521
of mare, 517
of ovaries of mare, 510
of penis of horse, 496
of prepuce of horse, 497
of pterygoid canal, 681
of skin, 762
of spermatic cord, 489
of tympanum, 755
of uterus of mare, 513
of vagina of mare, 514
of vascular tunic of eye, 745
of veins, 525
olfactory, of horse, 676
ophthalmic, 678
of dog, 728
optic, of horse, 676
palatine, of dog, 728
of horse, 679, 680
pectoral, 696
peroneal, deep, of ox, 720
of dog, 732
of horse, 708
of pig, 723
petrosal, 684
pharyngeal, of dog, 729
phrenic, 695
plantar, of dog, 732
of horse, 709
of ox, 720
of pig, 723
pneumogastric, 687
pterygoid, of horse, 681
pudic, of horse, 710
pulmonary, of horse, 457
radial, of dog, 730
of horse, 696, 698
of ox, 718
sacral, of horse, 710
saphenous, external, of horse, 708
of dog, 731
of horse, 706
sciatic, of horse, 707
second, of horse, 676
seventh, 684
sixth, 683
spermatic, external, 704
sphenopalatine, of dog, 728
of horse, 679
spinal accessory, 690
of ox, 717
of dog, 730
of horse, 692
of ox, 717
of pig, 723
splanchnic, 713
stapedial, 684
subscapular, 696
supply of eye muscles, 739
suprascapular, 696
of horse, 697
temporal, 682
Nerve, temporal, of dog, 728
of horse, 681
of ox, 717
of pig, 722
tenth, 687
third, of horse, 677
thoracic, anterior, 696
of horse, 697, 702
thoraco-dorsal, 697
tibial, anterior, 708
of dog, 732
of horse, 708
of ox, 720
trifacial, of horse, 677
trigeminal, of horse, 677
trochlear, of horse, 677
twelfth, 692
tympanic, 686
ulnar, of dog, 730
of horse, 696, 698
of ox, 718
of pig, 723
vagus, 687
of dog, 729
of ox, 717
of pig, 722
ventral, of dog, 729
vestibular, 686, 761
Vidian, 681
volar, of horse, 701
of ox, 718, 719
zygomatic, of dog, 728
of horse, 679
Nerve-cells, 644
Nerve-plexus, 645
Nervous system, 644
of dog, 724
of horse, 724
of ox, 715
of pig, 720
symphathetic, 710
Nervus accessorius, 690
lacrimalis, 678
oculomotorius, of horse, 677
olfactorius of horse, 676
ophthalmicus, 678
opticus of horse, 676
trigeminus, 677
trochlearis, 677
Neuroglia, 644
Neurology, 644
Neurone, 644
Ninth nerve, 686
Nippers, 339
Nipple of mammary gland of mare, 516
Nodules, lymph, 600
of spleen of horse, 379
Nodulus, 660
Nose of horse, common meatus of, 62
inferior meatus of, 62, 72
meatuses of, 71
middle meatus of, 62, 72
superior meatus of, 62, 72
Nostrils of dog, 466
of horse, 436
of ox, 458
of pig, 464
Notch, acetabular, of horse, 96
cardiac, of lungs, 456
carotid, of horse, 51
glenoid, of horse, 76
naso-maxillary, of horse, 61
Notch, œsophageal, of dog, 434
of tibia of horse, 102
oval, of horse, 51
popliteal, of tibia, 102
sciatic, lesser, of horse, 95
semilunar, of ulna, 82
sigmoid, of horse, 64
sphenoidal, of horse, 55
spinous, of horse, 51
Nuchal surface of skull of dog, 160
of horse, 69
of ox, 124
of pig, 145
Nuclei of origin of nerves, 644
Nucleocerebellar fasciculus, 661
Nucleus alæ cinereæ, 690
amygdalæ, 676
caudatus, 675
cuneatus, 658
dorsal sensory, 690
dorsalis, 651
facial, 684
gracilis, 658
hypoglossal, 692
hypothalamicus, 665
lenticular, 675
lentiformis, 675
lentis, 747
of solitary tract, 690
olivaris caudatis, 658
nasalis, 660
ruber, 665
subthalamic, 665
Nutrient artery, 21
of femur, 580
of humerus, 559
of tibia, 581
foramen of femur, 97
of humerus, 78
of ilium, 94
of metacarpus, 88
of tibia, 100
Obex, 663
Oblique extensor muscle of metacarpus of horse, 267
muscle, small, of head of horse, 233
Obliquus abdominis externus muscle of dog, 326
of horse, 246
of ox, 301
of pig, 313
internus muscle of dog, 326
of horse, 247
of ox, 301
of pig, 313
capitis anterior muscle of horse, 233
posterior muscle of horse, 233
of pig, 313
oculi inferior, 738
superior, 738
Obturator artery, 577
of ox, 619
externus muscle of horse, 283
of ox, 308
Obturator externus muscle of pig, 317
foramen of dog, 167
of horse, 96, 97
of ox, 132
internus muscle of horse, 283
of ox, 308
of pig, 317
membrane of horse, 191
nerves of horse, 706
vein, 598
Occipital artery, 544
of dog, 633
of ox, 611
of pig, 627
bone of dog, 154
of horse, 47
development, 50
of ox, 115
of pig, 139
condyles of horse, 48, 68, 69
crest of horse, 50, 69
protuberance, external, 50
internal, 54
sinus, 591
vein, 588
Occipito-hyoideus muscle, 223
of ox, 298
Ocular muscles of horse, 738
sheath of horse, 738
Oculomotor nerve of horse, 677
of ox, 717
Odontoid ligament, 176
process of axis of horse, 34
of ox, 112
Œdema glottidis of horse, 448
Œsophageal artery, 565, 567
of ox, 614
of pig, 627
groove of ox, 394
of sheep, 408
nerve of dog, 729
notch of dog, 434
opening of horse, 348
plexus, 713
of dog, 730
vein, 587
Œsophagus of dog, 428
of horse, 350
of ox, 389
of pig, 417
of sheep, 407
Olecranon fossa, 80
of horse, 83
Olfactory bulb, 653, 671
of dog, 727
of ox, 717
of pig, 721
cells, 772
fossa of horse, 52, 70
glands of horse, 440, 772
nerve of horse, 676
organs of dog, 781
of pig, 779
peduncle, 671
striæ, 671
tracts, 671
of pig, 721
Olivary eminence of dog, 725
nucleus, anterior, 660
posterior, 658
Olivocerebellar fibers, 661
Omaso-abomasal artery of ox, 615
Omaso-abomasal orifice of ox, 396
Omasum of ox, 390, 392
of sheep, 408
Omental cavity of horse, 380
Omentum, gastro-colic, 358
gastro-hepatic, 354, 358
gastro-splenic, 354, 358, 379
great, of horse, 354, 358
of ox, 396
lesser, of ox, 396
Omo-hyoideus muscle, 224, 226
of ox, 298
of pig, 312
Omo-transversarius muscle of dog, 319
of ox, 302
of pig, 312, 314
Ophthalmic artery, 553
of dog, 635
of ox, 612
nerve, 678
of dog, 728
vein, 590
Optic axis, 740
chiasm, 666
commissure, 666
foramen, 50, 51, 67, 70
groove of horse, 50
nerve of horse, 676
papilla, 745
of ox, 774
of pig, 778
recess, 667
thalamus, 664
tract, 664, 666
of ox, 716
Ora serrata, 745
Orbicular muscles, 211
Orbicularis oculi muscle, 218
of ox, 296
oris muscle of dog, 318
of horse, 213
of ox, 295
of pig, 311
Orbit of horse, 67
Orbital artery, 555
ducts of dog, 427
fascia of horse, 738
fissure of horse, 51
foramen, internal, 67, 70
gland of dog, 427
region of horse, 67
veins of ox, 621
wings of horse, 51
Organ of Corti, 760
of Jacobson, 772
of sense, 734
vomero-nasal, of horse, 440
Orifice, aortic, of heart, 533
atrio-ventricular, left, of ventricle, 530, 533
right, of ventricle, 530, 531
cæco-colic, of horse, 364
fronto-maxillary, 73
ileo-cæcal, of horse, 364
laryngeal, of horse, 348
of anterior vena cava of horse, 529
of coronary sinus, 529
of posterior vena cava, 529
omaso-abomasal, of ox, 396
preputial, of horse, 496
Orifice, pulmonary, of right ventricle, 531
reticulo-omasal, of ox, 394
rumino-reticular, of ox, 393
ureteral, of horse, 477
urethral, external, of cow, 519
of horse, 499
of mare, 515
of ox, 503
internal, of horse, 477
of male horse, 499
of pig, 505
Os coronæ of horse, 89
coxæ, 29
of horse, 92
of pig, 148
pedis of dog, 506
of horse, 90
rostri of pig, 143, 464
suffraginis of horse, 89
uteri externum of mare, 513
internum of mare, 513
Ossa cordis of ox, 609
Osseous labyrinth, 758
Ossicles, auditory, 754
Ossification, 22
endochondral, 22
intramembranous, 22
of vertebræ, 25
Osteoblasts, 22
Osteoclasts, 22
Osteogenesis, 22
Osteology, 19
Ostium abdominale of mare, 511
uterinum of mare, 511
Otic ganglion, 681, 711
of ox, 717
Outlet of pelvis, 97, 354
Ova of mare, 510
Oval notch of horse, 51
Ovarian artery, 571
of mare, 510
ligament of bitch, 522
of mare, 509
Ovaries of bitch, 522
of cow, 517
of mare, 508
of sow, 521
Overextended joints, 171
Overshot dog, 425
Ovulation fossa of mare, 509
in mare, 510
Pacchionian bodies, 647
Pad, dental, of ox, 384
Pads of dog, 780
Palate, hard, of dog, 423
of horse, 69, 332
of ox, 383
of pig, 411
of sheep, 405
soft, of dog, 424
of horse, 332
of ox, 384
of pig, 411
Palatine artery, 555
of pig, 627
bones of horse, 60
of ox, 120
of pig, 142
canal of horse, 58
Palatine cleft of horse, 60, 69, 71
foramen, posterior, 58, 68
glands of horse, 333
groove of horse, 59, 69
nerve of dog, 728
of horse, 679, 680
process of dog, 157
of maxillæ of horse, 58
of premaxillæ of horse, 60
region of horse, 68
sinus of ox, 120, 126
suture, median, 69
transverse, of horse, 69
vein, 589
Palato-labial artery, 555
Palato-pharyngeus muscle, 349
Pallium, 668
Palmar metacarpal artery, 563
Palmaris brevis muscle of dog, 324
longus accessorius muscle of dog, 323
Palpebral fissure of horse, 735
ligament, 736
muscle of dog, 318
sebum, 736
Pampiniform plexus of testicles of horse, 487
Pancreas aselli of dog, 643
of dog, 434
of horse, 371
of ox, 404
of pig, 423
of sheep, 410
Pancreatic arteries, 569
duct, accessory, of dog, 431
of horse, 373
of dog, 431, 434
of horse, 372
of ox, 398
of pig, 419, 423
lymph glands, 605
vein, 597
Pancreatico-duodenal artery, 569
Panniculus, abdominal, 245
adiposus of horse, 761
carnosus of dog, 318
of head of horse, 213
of horse, 213, 761
of neck of horse, 224
of pig, 311
facial, of pig, 311
muscle of ox, 295
scapulo-humeral portion, 255
thoracic portion, 255
Papilla communis of kidney, 474
filiform, of tongue, 336
foliate, of tongue, 336
fungiform, of tongue, 336
hair, 763
of cheeks of ox, 382
of skin, 762
of tongue, 336
optic, 745
of ox, 774
renalis of ox, 480
vallate, of tongue, 336
Paramastoid process, 48, 68, 69
Paramero-biceps muscle, 278
Paranasal sinuses of horse, 72
Parapharyngeal lymph gland of ox, 623
Parathyroid gland of dog, 468
of horse, 458
of ox, 464
Parenchyma of adrenal bodies, 478
of liver, 377
of mammary glands, 516
testis, 486
Parietal bones of dog, 155
of horse, 54
of ox, 117
of pig, 140
cartilage of nasal cavity, 437
crest of ox, 117
pleura of horse, 451
region of skull of horse, 66
Parieto-auricularis, 750
of dog, 780
of ox, 774
Parieto-frontal suture, 54, 55
Parieto-occipital suture, 54
Parieto-temporal canal, 54, 57
suture, 56
Parolfactory area, 671
Parotid artery, 543
of pig, 627
duct of dog, 423, 427
of horse, 347
of pig, 411, 414
gland of dog, 427
of horse, 346
of ox, 388
of pig, 414
lymph gland of dog, 643
of pig, 630
Parotido-auricularis, 750
of dog, 780
of ox, 774
Pars basilaris pontis, 660
ciliaris retinæ, 745
dorsalis pontis, 660
intercartilaginea of larynx, 448
intermembranacea of larynx, 448
iridica retinæ, 745
optica retinæ, 745
Pastern bone, 89
joint, 188
movements of, 189
Patches, Peyer’s, of horse, 363
of ox, 398
of pig, 419
Patella, 29
of dog, 168
of horse, 104
of ox, 134
of pig, 149
Patellar ligaments, 195, 196
Pathetic foramen, 67
Pectineus muscle of dog, 328
of horse, 282
of ox, 307
of pig, 316
Pectoral fascia of horse, 252
lymph glands, 602
muscle, anterior superficial, of pig, 314
deep, of dog, 320
of horse, 253, 254
of ox, 302
of pig, 314
Pectoral muscle, deep, posterior, of pig, 314
of horse, 252
posterior superficial, of pig, 314
superficial, of dog, 320
of horse, 253
of ox, 302
nerve, 696
Peduncles, cerebellar, 661
cerebral, 664
of ox, 716
of pig, 720
middle cerebellar, 659
olfactory, 671
Pelvic artery of horse, 97, 354
of ox, 133, 390
fascia of horse, 273
flexure of horse, 366
girdle, 29
of horse, 92
limb, bones of, 29
of dog, articulations of, 209
bones of, 165
muscles of, 326
of horse, articulations of, 190
bones of, 92
fasciæ of, 273
muscles of, 274
of ox, articulations of, 209
bones of, 131
muscles of, 306
of pig, articulations of, 209
bones of, 148
muscles of, 316
peritoneum of horse, 355
plexus, 713, 715
Pelvis of dog, 167
inlet of, 167
of horse, 96
axis of, 97
conjugate diameter, 97
inlet of, 96
outlet of, 97
sacro-pubic diameter, 97
sexual differences of, 97
transverse diameter, 97
of kidney of horse, 473
of ox, 132
axis of, 133
conjugate diameter, 132
inlet of, 132
of pig, 148
inlet of, 148
Penis, glans, of dog, 506
of horse, 495
of ox, 503
of dog, 506
glans, 506
os of, 506
prepuce of, 507
of horse, 494
arteries of, 496
body of, 494
corona glandis of, 495
corpus cavernosum, 495
spongiosum, 495
fossa glandis of, 495
glans, 495
Penis of horse, ischio-cavernosus muscle of, 496
lymphatics of, 496
muscles of, 496
nerves of, 496
root of, 494
sheath of, 496
structure of, 495
suspensory ligaments, 494
veins of, 496
vessels and nerves, 496
of ox, 503
bulbo-cavernosus muscle of, 503
glans, 503
ischio-cavernosus muscle of, 503
prepuce of, 503
retractor muscle of, 503
septum of, 503
of pig, 505
prepuce of, 506
Periarticular ligaments, 171
Pericardiac pleura, 452
Pericardium of dog, 632
of horse, 525
of ox, 608
of pig, 626
Perichorioid space, 742
Perineal artery, 574
of dog, 641
vein of ox, 622
Periople, 765
of ox, 775
structure of, 768
Perioplic matrix, 769
Periorbita of horse, 738
Periosteal artery, 21
Periosteum, 21
alveolar, of teeth, 339
Peritoneal ring of horse, 490
Peritoneum of horse, 353, 379
pelvic, 355
Permanent teeth of horse, 340
Peroneal artery, 585
nerve, deep, of ox, 720
of dog, 732
of horse, 708
of pig, 723
superficial, of ox, 719
Peroneus brevis muscle of dog, 328
longus muscle of dog, 328
of pig, 317
muscle of horse, 288
tertius muscle of dog, 328
of horse, 289
of ox, 310
of pig, 317
Perpendicular artery, 564
plate of ethmoid, 52
Petro-basilar canal of temporal bone of dog, 156
Petrosal crest of horse, 57, 70
nerve, 684
sinus, inferior, 592
superior, 591
Petro-tympanic fissure, 57
Petrous ganglion, 686
temporal bone, 56
of ox, 120
Peyer’s patches of horse, 363
of ox, 398
Peyer’s patches of pig, 419
Phacoid bone of cat, 164
Phalanges, 29
distal, 29
first, 29
of dog, 165
of horse, 89, 111
of ox, 130
middle, 29
of dog, 165
of horse, 89, 111
ligaments of lateral cartilages of, 190
of ox, 130, 136
of pig, 148, 150
proximal, 29
second, 29
of dog, 165
of horse, 89, 111
of ox, 130
third, 29
of dog, 165
of horse, 90, 111
of ox, 130
Pharyngeal aperture, 447
aponeurosis, 350
artery, 548
of ox, 611
fascia of horse, 213
isthmus of horse, 350
lymph glands, 602
of dog, 643
of pig, 630
nerve of dog, 729
opening of Eustachian tube, 755
plexus of dog, 729
recess, 350
Pharynx of dog, 427
of horse, 348
of ox, 389
of pig, 416
of sheep, 407
Philosophical anatomy, 17
Philtrum of horse, 331
Phrenic artery, 565
of ox, 614
nerve, 695
vein, 596
Phrenico-abdominal artery of dog, 639
of pig, 628
Pia mater, 647
Pillar, anterior, of soft palate of horse, 333
of fornix, 173
of rumen of ox, 393
posterior, of soft palate, 333, 350
Pilomotor fibers, 711
Pinchers, 339
Pineal body, 665
of ox, 716
recess, 667
Pinna of horse, 747
Pituitary body, 653, 664, 665
of dog, 726
of ox, 716
fossa of horse, 50
Pivot joint, 172
Plantar arch, 581
arteries, 581
of dog, 640
of ox, 619
Plantar cushion, 771
artery of, 564
flexion of joints, 171
fossa of femur, 99
ligament of hock joint, 201
muscles of pig, 317
nerves of dog, 732
of horse, 709
of ox, 720
of pig, 723
venous arch, 599
Planum nuchale of horse, 50
parietale of horse, 50
Plate, dental, of ox, 384
Pleura of horse, 451
costal, 451
diaphragmatic, 451
mediastinal, 451
parietal part, 451
pericardiac, 452
pulmonary, 452
sagittal fold of, 452
visceral, 452
of ox, 461
of thoracic cavity, 450
pericardica of horse, 525
Plexus, abdominal, 713
adrenal, 714
annularis, 742
aortic, 712
basilar, 592
brachial, of dog, 730
of horse, 696
of ox, 717
of pig, 723
cardiac, 712
carotid, 711
cavernous, 711
cervical, 694
chorioid, 666
cœliac, 714
coronary, 595
dorsal, 595
gangliosus ciliaris, 745
gastric, 714
of dog, 729
hepatic, 714
of horse, 377
hypogastric, 715
interosseous, 595
lumbo-sacral, of dog, 731
of horse, 705
of ox, 719
of pig, 723
mesenteric, 714
myenteric, 714
œsophageal, 713
of dog, 730
of Meissner, 714
pampiniform, of testicle, 487
pelvic, 715
pharyngeal, of dog, 729
pulmonary, 690, 712
of dog, 730
renal, 714
solar, 713
spermatic, 487, 714
splenic, 714
submucous, 714
tympanic, 687
utero-ovarian, 714
venosi, 524
venosus scleræ, 741
venous, of urethra, 516
Plexus, volar, 595
Plica iridis, 744
salpingo-pharyngea, 756
venæ cavæ of horse, 452
ventriculares of horse, 447
vocalis of horse, 448
Pneumogastric nerve, 687
Point of hock, 106
Polus lentis, 747
Polymastia of cow, 520
Polythelia of cow, 520
Pons of dog, 725
of horse, 659
of ox, 716
of pig, 720
Popliteal artery, 581
of ox, 619
of pig, 630
line of tibia, 100
lymph glands, 606
of dog, 643
of ox, 626
of pig, 632
nerves, external, 708
notch of tibia, 102
vein, 599
of dog, 642
Popliteus muscle of dog, 329
of horse, 294
of pig, 317
Portal fissure of liver of dog, 434
of horse, 373
of ox, 402
ring of horse, 372
system, 524
vein, 596
of horse, 377
of ox, 623
Portio clavicularis, 253
prescapularis, 253
sternocostalis, 253
Posterior angle of ilium, 94
of pubis, 96
of scapula, 76
annular ligament, 263
clinoid process of dog, 156
of pig, 142
cornu of thyroid cartilage, 442
crucial ligament of horse, 198
deep pectoral muscle of horse, 254
of pig, 314
facets of horse, 441
ligament of pastern joint, 188
of temporo-mandibular articulation, 179
nares of horse, 68, 348, 440
obliquus capitis muscle, 233
palatine foramen, 58, 68
pillar of soft palate, 333, 350
straight muscle, small, of head, 234
superficial pectoral muscle of horse, 253
of pig, 314
tibialis muscle of dog, 329
Postero-external angle of ischium of horse, 95
Post-glenoid fossa, 56
process, 67
Pouch, cutaneous, of sheep, 111
recto-genital, of horse, 356
recto-vesical, of horse, 356
vesico-genital, of horse, 356
Poupart’s ligament, 246
Precrural lymph glands, 606
of ox, 626
of pig, 632
Premaxilla of dog, 157
of horse, 59
of ox, 120
of pig, 142
Premaxillary region, 66
Premolars, 338, 342
Prenasal bone of pig, 143
Preorbital region of horse, 68
Prepectoral lymph glands of ox, 624
of pig, 631
Preplantar artery, 564
Prepubic artery, 579
tendon of horse, 250
Prepuce of clitoris of mare, 515
of dog, 507
of horse, 496
raphé of, 496
structure of, 497
of ox, 503
of pig, 506
Preputial diverticulum of pig, 506
frenum of horse, 497
glands of horse, 497
muscles of ox, 503
orifice of horse, 496
ring of horse, 497
Prescapular lymph glands, 602
of dog, 643
of ox, 624
of pig, 631
Presternum, 26
Presylvian fissure of dog, 727
of horse, 669
of pig, 721
Prevertebral artery, 545
Process, angular, of mandible of dog, 159
auditory, external, of horse, 56, 67
basilar, of horse, 48
of third phalanx, 91
ciliary, 743
clinoid, anterior, of sphenoid bone of dog, 156
posterior, of sphenoid bone of dog, 156
of pig, 142
coracoid, of horse, 77
coronoid of mandible of horse, 64
of radius of horse, 80
frontal, of dog, 157
hyoid, of horse, 57
lacrimal, of dog, 158
lingual, of horse, 65
mammillary, 25
of horse, 43
mastoid, of horse, 67
maxillary, of dog, 158
muscular, of arytenoid cartilages of horse, 443
of temporal bone, 57
nasal, of horse, 60
Process, odontoid, of axis of horse, 34
of ox, 112
of urethra masculina, 498
palatine, of dog, 157
of maxillæ of horse, 58
of premaxillæ, 60
paramastoid, 48, 68, 69
postglenoid, of horse, 67
pterygoid, of horse, 51
retrossal, of horse, 91
spinous, of axis of horse, 34
of ox, 112
of cervical vertebræ of ox, 112
of lumbar vertebræ of horse, 39
of ox, 114
of thoracic vertebræ of horse, 36
of ox, 112
of vertebræ of horse, 42
styloid, of horse, 48, 68, 69
of radius of dog, 161
of temporal bone, 57
of ulna of horse, 82
of ox, 129
supraorbital, of horse, 55, 56
of ox, 119
temporal, of maxillary bone of horse, 58
urethral, of horse, 495
vocal, of horse, 443
zygomatic, of frontal bone, 55
of maxillary bone, 58
of temporal bone, 56
Processus anconæus of horse, 82
cornu of ox, 118
uncinatus of dog, 780
vaginalis of horse, 491
Projection fibers, 676
Prominentia laryngea, 442
Promontory, 753
Pronator quadratus muscle of dog, 324
teres muscle of dog, 323
of horse, 268
of pig, 315
Prostate of dog, 506
of horse, 493
of ox, 502
of pig, 505
Prostatic ducts of horse, 499
of ox, 502
utricle of horse, 493
Protractor muscles of prepuce of ox, 503
Protuberance, occipital, external, 50
internal, 54
Proximal border of hoof, 765
interphalangeal joint, 188
sesamoid bones of horse, 92
of ox, 131
Psoas major muscle of dog, 326
of horse, 275
of ox, 306
of pig, 316
minor muscle of dog, 326
of horse, 275
of ox, 306
of pig, 316
Psoas tubercle of horse, 93
Pterygoid artery, 552
bones of dog, 158
of horse, 60
of ox, 121
of pig, 143
canal of horse, 51, 61
crest of horse, 51
foramen of horse, 51, 68
nerve of horse, 681
processes of horse, 51
veins, 587
Pterygoideus externus muscle of horse, 220
internus muscle of horse, 219
lateralis muscle of horse, 220
muscle of ox, 297
Pterygo-palatine fossa, 60
of horse, 67
Pterygo-pharyngeus muscle of horse, 349
Pubis, 29
of dog, 167
of horse, 95
of ox, 131
of pig, 148
Pubo-femoral ligament of horse, 193, 250
Pudic artery, external, 580
internal, 573
of ox, 619
of pig, 630
nerve of horse, 710
vein, external, 598
of ox, 622
Pulmonary artery, 524, 535
of horse, 457
circulation, 607
nerves of horse, 457
orifice of right ventricle, 531
pleura of horse, 452
plexus, 690, 712
of dog, 730
valve of horse, 532
veins, 524, 585
of horse, 457
openings of, left atrium, 530
Pulp cavity of teeth, 339
of teeth, 339
spleen, of horse, 379
Puncta lacrimalia of horse, 737
Punctum lacrimale in pig, 778
lacrimalis, 736
Pupil, 744
of dog, 779
of pig, 778
Pupillary border of iris, 744
Pyloric artery, 569
glands of stomach, 360
sphincter of horse, 359
Pyramid or pyramids, of Ferrein, 473
of oblongata, 655
renal, of horse, 473
of ox, 480
Pyramidal decussation, 655, 658
fasciculi, 660
tracts, 658
of oblongata, 658
Pyriform lobe, 653, 668, 672
of dog, 728
Pyriformis muscle of dog, 326
of horse, 284
sinus of horse, 350
Quadratus femoris muscle of dog, 328
of horse, 283
of ox, 308
of pig, 317
lumborum muscle of dog, 326
of horse, 276
of ox, 306
of pig, 316
plantæ muscle of dog, 329
Quadriceps femoris muscle of horse, 284
of ox, 307
of pig, 317
Quarters, 764
Radial artery, anterior, 559
of dog, 635
of ox, 613
posterior, 559
of ox, 612
carpal bone, 83
nerve of dog, 730
of horse, 696, 698
of ox, 718
veins, 595
of dog, 642
Radialis volaris muscle of dog, 323
Radiate ligament of horse, 177
Radiatio corporis callosi, 672
Radii lentis, 747
Radio-carpal joint, 183
sac of horse, 183
Radio-ulnar articulation, 182
Radius, 28
of dog, 163
of horse, 80
development of, 82
of ox, 127
of pig, 147
Radix pulmonalis of horse, 456
Rami communicantes, 711
of lower jaw of horse, 63
Ramus communicans, 693
Raphé palati of horse, 233
præputii of horse, 496
scroti of horse, 488
Receptaculum chyli, 600
Recess, pharyngeal, 350
Recessus cochlearis, 758
ellipticus, 758
infundibuli, 667
lienalis of horse, 380
opticus, 667
pinealis, 667
sphæricus, 758
tecti s. fastigium, 663
Recto-genital pouch, 356
Recto-vesical pouch, 356
Rectum of dog, 432
of horse, 370
of ox, 400
of pig, 420
Rectus abdominis internus muscle of pig, 313
Rectus abdominis muscle of dog, 326
of horse, 248
of ox, 301
of pig, 313
capitis anterior major muscle of dog, 324
of horse, 227
of ox, 300
minor muscle of horse, 227
of ox, 300
dorsalis major muscle of horse, 234
minor muscle of horse, 234
lateralis of horse, 228
of ox, 300
muscle of pig, 313
posterior major muscle of horse, 234
minor muscle of horse, 234
femoris muscle of dog, 327
of horse, 284
lateralis muscle of dog, 324
minor muscle of dog, 324
oculi, 738
parvus muscle of horse, 286
thoracis muscle of horse, 242
of pig, 313
Recurrent laryngeal nerve, 689
Red nucleus, 665
Regio olfactoria of horse, 440
Region, cranial, 67, 68
frontal, of skull of horse, 66
guttural, of horse, 68
maxillary, of horse, 68
nasal, of horse, 66
orbital, of horse, 67
palatine, of horse, 68
parietal, of skull of horse, 66
premaxillary, of horse, 66
preorbital, of horse, 68
Renal arteries, 571
of dog, 639
of horse, 475
of ox, 618
of pig, 628
columns of horse, 473
corpuscles of horse, 473, 474
crest of horse, 474
lymph glands of ox, 625
papilla of ox, 480
plexus, 714
pyramids of horse, 473
of ox, 480
sinus of horse, 470
tubules of horse, 474
veins, 596
of ox, 621
Respiratory bronchioles, 457
system, 436
of dog, 466
of horse, 436
of ox, 458
of pig, 464
Restiform bodies, 656
of ox, 715
Rete carpi dorsale, 562
mirabile, 524
of ox, 609
testis of horse, 486
Retia vasculosa, 524
Reticular artery of ox, 615
Reticulo-omasal orifice of ox, 394
Reticulum of ox, mucous membrane of, 395
of stomach of ox, 390, 392
of sheep, 408
splenic, of horse, 379
Retina of dog, 779
of horse, 745
Retractor ani muscle of dog, 432
of horse, 371
costæ muscle of horse, 242
of pig, 313
muscles of prepuce of ox, 503
oculi, 738
penis muscle of horse, 496
of ox, 503
Retrossal process of third phalanx, 91
Rhinencephalon, 670
Rhombencephalon, 655
Rhomboideus capitis muscle of dog, 320
cervicalis muscle of dog, 320
of horse, 251
muscle of dog, 320
of horse, 251
of ox, 302
of pig, 314
thoracalis muscle of dog, 320
of horse, 251
Ribs, 25
angle, 26
anterior borders, 26
articulations of, of horse, 177
asternal, 25
of horse, 43
costal cartilage, 25
groove, 26
development, 26
extremities, 25
external surface, 26
false, 25
of horse, 43
floating, 25
head, 26
intercostal spaces, 25
internal surface, 26
neck, 26
of dog, 153
of horse, 43
articulations of, 177
development, 44
of ox, 114
of pig, 138
posterior borders, 26
shaft, 25
sternal, 25
extremity, 26
of horse, 43
true, 25
of horse, 43
tubercle, 26
vertebral extremity, 26
Ridge, cuticular, of stomach, 360
trochanterie, of femur, 99
Rima glottidis of horse, 447
of pig, 465
oris of dog, 423
of pig, 410
Ring or rings, fibrous, of heart of horse, 534
Rings or ring, fibrous, of intervertebral fibro-cartilages, 173
inguinal, external, 246, 250
internal, 248, 249
muscular, of cæcum, 365
of trachea, 450
peritoneal, 490
portal, 372
preputial, 497
subperitoneal, 490
vaginal, 248, 290
of ox, 500
Ring-like muscles, 211
Root of hair, 763
of teeth, 339
of tongue of horse, 335
Rostri of pig, 143
Rostrum suis, 464
Rotation of joints, 172
Rotator muscle, 751
Round ligament of bladder of horse, 476
of hip joint of horse, 193
of horse, 356
of liver of horse, 375
of uterus of bitch, 523
of cow, 518
of mare, 513
Rubrospinal tract, 661
of Monakow, 652
Rugæ palatini of horse, 332
Rumen of ox, 390, 391
blind sacs of, 392
cardiac orifice of, 394
cavity of, 393
coronary grooves, 392
dorsal curvature of, 391
longitudinal furrows, 391
mucous membrane of, 394, 397
muscular coat of, 396
pillars of, 393
ventral curvature of, 391
of sheep, 408
of stomach, serous coat, 396
Ruminal artery of ox, 615
Rumino-reticular fold of ox, 393
orifice of ox, 393
Sac, anal, of dog, 432
blind, of rumen of ox, 392
carpo-metacarpal, 183
conjunctival, 736
intercarpal, of horse, 183
intertarsal, first, 200
second, 200
radio-carpal, of horse, 183
synovial, of hock joint, 200
tarso-metatarsal, 200
tibio-tarsal, of horse, 200
Sacculations of cæcum, 364
Saccule, 759
laryngeal, of horse, 447
Saccus cæcus of horse, 357
Sacral angle of ilium, 94
artery, lateral, 575
middle, of ox, 618
of ox, 619
canal of horse, 41
foramen, inferior, of ox, 114
of horse, 40
ganglia of ox, 720
Sacral lymph glands, 604
nerves of horse, 710
vertebræ, 24
of dog, 151
of horse, 39
articulations of, 175
development, 41
of ox, 114
of pig, 138
Sacro-coccygeus accessorius muscle of dog, 325
inferior muscle of horse, 240
lateralis muscle of horse, 239
muscle of dog, 325
of pig, 314
superior muscle of horse, 238
ventralis mediales muscle of horse, 240
Sacro-iliac joint of dog, 209
of horse, 190
of ox, 209
of pig, 209
ligament of horse, 190
Sacro-pubic diameter of pelvis of horse, 97
Sacro-sciatic ligament, 190
Sacrum of dog, 151
of horse, 39
development, 41
of ox, 114
of pig, 138
Sagittal crest, external, of horse, 54, 66
internal, of horse, 54
fold of pleura of horse, 452
groove of horse, 54
pole, 716
sinus, 591
suture of horse, 54
Salivary glands of dog, 427
of horse, 346
of ox, 388
of sheep, 407
Santorini’s duct, 373
Saphenous artery, 580
of dog, 640
of ox, 619
of pig, 630
nerve of dog, 731
external, of horse, 708
of horse, 706
vein, 598
of dog, 642
of ox, 622
Sartorius muscle of dog, 328
of horse, 281
of ox, 308
of pig, 316
Satellite vein, 524
Scala tympani, 759
vestibuli, 759
Scalenus dorsalis muscle of dog, 324
of ox, 300
of pig, 312
muscle of horse, 227
of pig, 312
ventralis muscle of dog, 324
of ox, 298
of pig, 312
Scansorius muscle of horse, 278
Scapha of auricle, 747
Scaphoido-cunean ligaments of horse, 202
Scapula, 27
of dog, 162
of horse, 74
of ox, 127
of pig, 146
Scapular cartilage of horse, 75
Scapulo-humeral portion of panniculus, 255
Scapulo-humeralis posticus muscle, 258
Scapulo-ulnaris muscle, 260
Schütz, longitudinal bundle of, 692
Sciatic foramen, great, 94
nerve of horse, 707
notch, lesser, of horse, 95
Sclera of dog, 779
of horse, 740
of ox, 773
Scrotum of dog, 506
of horse, 487
of ox, 500
of pig, 504
Scutiform cartilage, 748
Scutularis, 749
of dog, 780
of ox, 774
Scutulo-auricularis, 749, 751
of dog, 780
of ox, 774
Sebaceous glands, 762
of dog, 780
of ox, 775
of pig, 778
Sebum cutaneum, 762
Second carpal bone, 85
intertarsal sac, 200
metatarsal bone, 111
nerve of horse, 676
phalanges of dog, 165
of horse, 89, 111
of ox, 130
tarsal bone of horse, 109
of ox, 135
Sectorial teeth of dog, 426
Segments of spinal cord, 648
Sella turcica of horse, 71
Semicircular canals, membranous, 760
osseous, 758
Semilunar canal of third phalanx, 91
cartilages of femoro-tibial articulation, 196
crest of third phalanx, 91
ganglion, 678
notch of ulna, 82
Semimembranosus muscle of dog, 280
of horse, 280
of ox, 306
of pig, 316
Seminal vesicles of dog, 506
of horse, 491
of ox, 502
of pig, 505
Seminiferous tubules of testicles of horse, 486
Semispinalis capitis muscle, 231
colli muscle, 231
Semitendinosus muscle of dog, 327
of horse, 280
Semitendinosus muscle of ox, 306
of pig, 316
Sense organs of dog, 779
of horse, 734
of ox, 772
of pig, 777
Sensitive, frog, 770
sole, 769
Septum, interalveolar, 58
intermuscular, 212
of forearm, 262
of gluteal region, 273, 274
of leg, 274
of shoulder, 255
interventricular, of left ventricle, 534
medianum dorsale, 650
mediastinum, 450
nasi, 71, 72, 73, 437
of testicles of horse, 486
of thoracic cavity, 450
pellucidum, 674
penis of ox, 503
scroti of horse, 488
vertical, of metacarpus of ox, 130
Serous layer of pericardium, 525
Serratus anterior hominis of horse, 254
anticus muscle of dog, 325
of horse, 235
of ox, 300
of pig, 313
cervicis of horse, 254
magnus muscle of dog, 320
of horse, 254
of ox, 302
of pig, 314
posticus muscle of dog, 325
of horse, 236
of ox, 300
thoracis muscle of horse, 254
ventralis muscle of horse, 254
Sesamoid bones, 29
developing in tendon tissue, 211
distal, 29
of dog, 165
of horse, 92, 111
of ox, 131, 136
of pig, 148
proximal, 29
Sesamoidean ligaments, 186, 273
of ox, 207
Seventh nerve, 684
Sexual differences of pelvis of horse, 97
Shaft of hair, 763
Sheath, carpal, of deep digital flexor muscle, 272
of superficial digital flexor muscle, 271
ocular, of horse, 738
of arteries, 525
synovial. See _Synovial sheath_.
tarsal, of flexor pedis perforans muscle, 294
tendon, 211
Short ligament of hock joint of horse, 201
muscles, 211
sesamoidean ligament, 188
Shoulder girdle, 27
of horse, muscles of, 250
of ox, muscles of, 302
of pig, muscles of, 314
joint of dog, 205
of horse, 180
of ox, 205
of pig, 205
of horse, fascia of, 255
muscles of, 255, 257
of ox, muscles of, 302
of pig, muscles of, 314
Sidebone of horse, 91
Sigmoid cavity of ulna of horse, 82
flexure of ox, 503
notch of horse, 64
Sinus or sinuses, cavernous, 592
coronary, 585
opening of, 529
cutis, 761
ethmoid, of horse, 74
frontal, of dog, 161
of horse, 55, 73
of ox, 125
of pig, 145
lacrimal, of ox, 126
lactiferous, of cow, 521
longitudinal, superior, 591
maxillary, inferior, 73
of dog, 161
of horse, 72
of ox, 126
of pig, 146
superior, of horse, 73
occipital, 591
of aorta, 536
of dura mater, 541
of right atrium of heart, 529
of Valsalva, 536
palatine, of maxilla of ox, 120
of ox, 126
paranales of dog, 432
paranasal, of horse, 72
petrosal, inferior, 592
superior, 591
phrenico-costalis, 456
pyriform, of horse, 350
rectus, 581
renal, of horse, 470
sagittal, 591
sphenoidal, of horse, 50
of ox, 127
of pig, 146
sphenopalatine, 60
of horse, 50, 74
straight, 591
tarsi of horse, 105
tonsillaris of ox, 385
transverse, 591
urogenital, of mare, 514
venosus scleræ, 741
Sixth nerve, 683
Skeletal muscle, 211
Skeleton, 19
appendicular, 19
axial, 19
flat bones, 19
irregular, bones, 19
Skeleton, long bones, 19
medullary cavity, 19
number of bones, 19
of dog, 150
of horse, 31
of ox, 112
of pig, 136
short bones, 19
splanchnic, 19
Skin, appendages of, 762
of dog, 780
of horse, 761, 764
of mammary glands of mare, 516
of nostrils of horse, 436
of ox, 775
of pig, 778
of prepuce of horse, 497
of sheep, 777
Skull, bones of, 27
of dog, 153
of horse, 47
of ox, 115
of pig, 139
of dog, 159, 160
of horse, 47, 65
apex of, 69
articulations of, 179
cranial region, 68
frontal region of, 66
guttural region, 68
middle fossa of, 71
palatine region, 68
parietal region of, 66
posterior fossa of, 71
superior curved lines, 69
sutures of, 179
synarthroses of, 179
synchondroses of, 180
of ox, 115, 123
of pig, 144
Smegma præputii of horse, 497
Smell, organ of, of horse, 772
Snout of pig, 464
Soft palate of dog, 424
of horse, 332
of ox, 384
of pig, 411
Solar plexus, 713
Sole matrix, 769
of horse, 765
sensitive, 769
Soleus muscle of horse, 292
of ox, 311
of pig, 317
Solitary glands of rectum, 370
of small intestine, 363
of pig, 420
Space, interalveolar, 58, 69
interdental, of horse, 58
interosseous, of forearm, 80
submaxillary, of horse, 62
Spatia anguli iridis, 744
zonularia, 747
Spatium perichorioideale, 742
Special anatomy, 17
Spermatic artery, 571
of dog, 639
of horse, 487, 489
of ox, 618
of pig, 628
cord, lymphatics of, 489
of dog, 506
of horse, 489
Spermatic cord of ox, 500
of pig, 504
nerve, external, of horse, 704
plexus, 714
of horse, 487
veins, 596
of horse, 487, 489
Spheno-frontal suture, 55
Sphenoid bone of dog, 156
of horse, 50
of ox, 115
of pig, 141
Sphenoidal notch of horse, 55
sinus of horse, 50
of ox, 127
of pig, 146
Spheno-occipital crest, 51
Sphenopalatine artery, 555
foramen, 58, 60, 67, 71
ganglion, 711
nerve of dog, 728
of horse, 679
sinus, 60
of horse, 50, 74
vein, 589
Spheno-squamous suture, 56
Sphincter, 211, 213
ani externus of horse, 371
internus of horse, 371
cardiac, of horse, 359
of bladder of horse, 476
of mammary gland of cow, 521
of mare, 516
of uterus of mare, 513
pupillæ, 744
pylori of horse, 358, 359
Spina furcæ ungulæ, 767
helicis of dog, 779
Spinal accessory nerve, 690
of ox, 717
arachnoidea, 647
cord of dog, 724
of horse, 648
of ox, 715
of pig, 720
tracts of, 652
ganglion, 692
nerves of dog, 730
of horse, 692
of ox, 717
of pig, 723
root of fifth nerve, 658
veins, 543
Spinalis et semispinalis muscle of pig, 313
muscle of horse, 233
Spine, hæmal, 25
ischiatic, of horse, 94, 95
of hoof, 767
of scapula of horse, 74
of tibia of horse, 101
ventral, 25
of cervical vertebræ of ox, 112
Spinous muscle, transverse, of neck of horse, 231
notch of horse, 51
process of axis of horse, 34
of ox, 112
of cervical vertebræ of ox, 112
of lumbar vertebræ of horse, 39
Spinous process of lumbar vertebræ of ox, 114
of thoracic vertebræ of horse, 36
of ox, 112
of vertebræ of horse, 42
Spiral canal of cochlea, 759
organ of corti, 760
Splanchnic nerve, 713
Spleen, accessory, of horse, 379
of dog, 435
of horse, 377
of ox, 404
of pig, 423
of sheep, 410
pulp of horse, 379
Splenial fissure of dog, 727
of pig, 721
Splenic angle of horse, 372
artery, 569
of dog, 638
of ox, 615
of pig, 628
lymph glands, 605
of pig, 632
plexus, 714
vein, 596
Splenium, 672
Splenius muscle of dog, 324
of horse, 229
of ox, 300
of pig, 312
Spongy substance of bone, 21
Spur vein, 593
Squamous part of occipital bone of horse, 49
temporal bone of horse, 55
of ox, 120
Stapedial nerve, 684
Stapedius, 755
Stapes, 754
Staphyline artery, 555
Sternal articulations of horse, 178
flexure of horse, 366
ligament of horse, 178
lymph glands of ox, 624
ribs, 25
of horse, 43
Sterno-cephalicus muscle of dog, 324
of horse, 225
of ox, 298
of pig, 312
Sterno-mandibularis muscle, 225
Sterno-maxillaris muscle, 225
Sterno-thyro-hyoideus muscle of dog, 319
of horse, 224, 226
of ox, 298
of pig, 312
Sterno-thyroideus et sterno-hyoideus muscle, 226
Sternum, 26
of dog, 153
of horse, 45
of ox, 115
of pig, 139
Stifle joint, 194
movements of, 198
of dog, 209
of ox, 209
of pig, 209
Stomach of dog, 428
of horse, 357
cardia of, 358
coats of, 359
fibers of, 359
greater curvature of, 357
lesser curvature of, 357
mucous coat of, 360
muscular coat of, 359
œsophageal orifice of, 358
pyloric extremity, 358
orifice of, 358
serous coat of, 359
structure of, 359
submucous coat of, 359
vessels and nerves of, 360
of ox, 390
of pig, 417
of sheep, 408
Stop of face of dog, 160
Straight muscles of head of pig, 312
sinus, 591
Stratum corneum, 761
germinativum, 761
of hoof, 768
periosteale of hoof, 769
vitreum of body, 769
Stria lateralis, 671
medullaris, 665
terminalis, 665
Striæ acusticæ, 662
olfactorii, 671
Striated muscle, 211
Stroma iridis, 744
of kidney of horse, 475
of ovary of mare, 510
vitreum, 746
Stylo-glossus muscle, 337
Stylo-hyoideus muscle, 223
of ox, 297
Stylohyoids of horse, 65
Styloid process, 748
of horse, 68, 69
of radius of dog, 161
of temporal bone, 57
of ulna of horse, 82
of ox, 129
Stylo-mandibularis muscle, 222
of ox, 297
Stylo-mastoid artery, 550
foramen of horse, 57
Stylo-maxillaris muscle, 222
Stylo-pharyngeus muscle, 349
Subarachnoid cisterns, 646
space, 646
Subcallosal gyrus, 671
Subcarpal arch, 562
check ligament of horse, 272
ligament of horse, 183
Subcostal artery, 539
of dog, 633
of ox, 609
Subcutaneous bursæ, 761
Subcutis, 761
Subdural space, 646
Subiliac lymph glands, 606
Sublimbic fissure, 669
Sublingual artery, 548
of dog, 635
crest of horse, 348
ducts of dog, 427
Sublingual ducts of horse, 348
gland of dog, 427
of horse, 347
of ox, 388
of pig, 415
vein, 590
of ox, 621
Sublumbar muscles, 274
of ox, 306
of pig, 316
Submaxillary artery, 547
duct of dog, 427
of horse, 348
gland of dog, 427
of horse, 347
of ox, 388
of pig, 415
lymph glands, 601
of dog, 643
of pig, 630
space of horse, 63
Submental artery, 549
Submucous plexus, 714
Subperitoneal ring, 490
Subpubic groove of horse, 95
Subscapular artery, 556
of dog, 635
of ox, 612
fossa of horse, 75
nerve, 696
Subscapularis muscle of dog, 321
of horse, 257
of ox, 302
of pig, 314
Subscapulo-hyoideus muscle of horse, 226
Subsphenoidal canal, 51
confluents, 592
Substantia alba, 644
corticalis of lens, 747
gelatinosa, 644
of cord, 651
grisea, 644
of cord, 650
Subtarsal ligament, 200
Subthalamic nucleus, 665
tegmental region, 665
Suburethral diverticulum of cow, 519
of sow, 522
Sudoriferous glands, 762
Sulcus aortæ of horse, 454
basilaris of pons, 659
callosal, 669
coronalis ungulæ, 765
corporis callosi, 669
cruroparietalis, 767
dorsalis lateralis, 649
intercruralis, 767
intermedius dorsalis, 649
of ox, 608
ventralis of oblongata, 655
limitantes, 662
medianus dorsalis, 649
œsophagus of horse, 454
of brain, 654
rhinalis, 669
of dog, 727
of ox, 716
of pig, 721
tympanicus, 753
Superficial digital flexor muscle of dog, 323, 329
of horse, 269, 270
of leg of horse, 292
of ox, 305
of pig, 316, 317
fascia, 212
of back and loins, 235
of forearm of horse, 262
of gluteal region, 273
of head of horse, 213
of neck of horse, 224
of shoulder of horse, 255
flexor muscle of ox, 311
gluteus muscle of horse, 277
muscles of head of horse, 213
pectoral muscle of dog, 320
of horse, 253
of ox, 302
sesamoidean ligament, 188
Superior alveolar arch, 69
atlanto-axial ligament, 176
atlanto-occipital membrane of horse, 176
border of mandible, 64
check ligament of superficial digital flexor muscle, 270
commissure of vulva, 515
common vertebral ligament of horse, 173
costo-sternal ligament, 178
costo-transverse ligament of horse, 177
curved lines of skull, 69
dental canal of horse, 59
dilatator naris muscle, 218
incisivus muscle, 216
interdigital ligament of ox, 206
ischiatic spine, 94, 95
levator palpebræ muscle, 219
maxillary sinus of horse, 73
meatus of nasal cavity, 438
of pig, 465
of nose of horse, 62, 72
sacro-coccygeus muscle, 238
sesamoidean ligament of horse, 187, 273
thyro-arytenoid ligament of horse, 444
turbinal bone of dog, 158
of horse, 62
of ox, 122
crest of nasal bones, 61
fold of horse, 440
Supinator muscle of dog, 323
of pig, 315
Supra-atloid bursa, 174
Supracondyloid crest, external, of humerus, 80
of femur, 97
fossa of femur of horse, 99
Supraorbital artery, 553
canal of ox, 119
foramen of horse, 55, 66
of ox, 119
groove of ox, 119
process of horse, 55, 66
of ox, 119
Suprarenal glands, 477
Suprascapular artery, 556
nerve, 696, 697
Supraspinatus muscle of dog, 321
Supraspinatus muscle of horse, 256
of ox, 302
of pig, 314
Supraspinous bursa, 175
fossa of horse, 75
ligament of horse, 174
Suprasplenial fissure of dog, 727
Suprasylvian fissure of dog, 726
of horse, 668
of ox, 716
of pig, 721
Supratrochlear foramen of humerus of dog, 163
Suspensory ligament of penis of horse, 494
of spleen of horse, 379
navicular ligaments, 189
sesamoidean ligament of horse, 187, 273
Sustentaculum tali of fibular tarsal bone, 106
Sutura, 169
harmonia, 169
serrata, 169
squamosa, 169
Suture, 169
cranial, of horse, 179
frontal, of horse, 55
fronto-lacrimal, of horse, 55
interparietal, of horse, 54
naso-frontal, of horse, 55, 61
of ox, 119
naso-lacrimal, of horse, 61
naso-maxillary, of horse, 61
palatine, median, 69
transverse, of horse, 69
parieto-frontal, 54, 55
parieto-occipital, 54
parieto-temporal, 56
sagittal, of horse, 54
spheno-frontal, of horse, 55
spheno-squamous, 56
Sweat glands, 762
of dog, 780
of ox, 775
of pig, 778
Sympathetic system, 710
of dog, 733
of ox, 720
of pig, 724
trunk, 711
Symphysis, 169
of lower jaw of horse, 180
pelvis of horse, 191
Synarthroses, 169
of skull of horse, 179
Synchondroses of skull, 180
Synchondrosis, 169
Synovia, 170
Synovial bursa of anterior digital extensor muscle of horse, 265
of infraspinatus muscle of horse, 256
of lateral digital extensor muscle of horse, 266
of teres minor muscle of horse, 257
fossa, 170
of tibial tarsal bone, 105
layer of articulations, 170
Synovial membrane, 211
bursal, 211
of anterior digital extensor muscle, 265
of carpal joints, 183
of elbow joint, 181
of hip joint of horse, 193
of lateral digital extensor muscle of horse, 265
vaginal, 211
sacs of hock joint, 200
sheath at carpus of ox, 305
of anterior digital extensor muscle, 265
of coraco-brachialis muscle of horse, 258
of deep digital flexor muscle of horse, 272
of extensor carpi radialis of horse, 263
pedis muscle, 288
of flexor carpi externus muscle of horse, 269
pedis perforans muscle of horse, 294
of lateral digital extensor muscle of horse, 266
of peroneus muscle, 288
of superficial digital flexor muscle of horse, 271
Systematic anatomy, 17, 18
Systemic arteries, 524
Tactile hairs, 763
Tænia of small colon, 370
semicircularis, 665
thalami, 665
Tail of dog, muscles of, 325
of horse, 764
fasciæ of, 238
muscles of, 238
of ox, muscles of, 300
of pig, muscles of, 314
Tapetum cellulosum, 779
fibrosum, 743
of chorioid, 742
of ox, 774
Tarsal artery, external, 581
of pig, 630
perforating, 585
bones, 29
central, of horse, 107
of ox, 134
fibular, of horse, 106
ligaments of, 202
of ox, 134
first, of horse, 109
of ox, 135
fourth, of horse, 109
of ox, 134
second, of horse, 109
of ox, 135
third, of horse, 109
of ox, 135
tibial, of horse, 105
ligaments of, 202
of ox, 134
fascia of horse, 274
glands, 736
muscle, 736
sheath of flexor pedis perforans muscle, 294
sinus of horse, 105
Tarsal vein of ox, 622
recurrent, 598
Tarso-metatarsal ligaments, 202
sac of horse, 200
Tarsus, 29
of dog, 168
of eye, 736
of horse, 105
canal of, 109
development of, 110
of ox, 134
of pig, 149
Taste buds, 772
organs of horse, 772
Teats of mammary glands of bitch, 523
of cow, 520
of mare, 516
Teeth, 338
alveolar periosteum of, 339
canine, 338
deciduous, of horse, 346
of dog, 425
of horse, 341
of ox, 386
of pig, 412
carnassial, of dog, 426
cement of, 339
cheek, 338
deciduous, of horse, 346
of dog, 425
of horse, 342, 343, 344
of ox, 386
of pig, 412
of sheep, 405
crown of, 339
deciduous, of horse, 346
enamel of, 339
incisor, 338
deciduous, of horse, 346
of ox, 386
of dog, 425
of horse, 341
of ox, 386
of pig, 412
of sheep, 405
lower, of horse, 344
mandibular, of horse, 344
maxillary, of horse, 343
milk, of horse, 346
molar, 338
of horse, 342
neck of, 339
nippers, 339
of dog, 424
of horse, 340
of ox, 386
of pig, 411, 412
of sheep, 405
permanent, of horse, 340
pinchers, 339
premolar, 338
of horse, 342
pulp cavity of, 339
pulp of, 339
root of, 339
sectorial, of dog, 426
structure of, 339
temporary, of horse, 346
upper, of horse, 343
vessels and nerves of, 339
wolf, 339
of horse, 58, 64
Tegmentum, 664
Tela choroidea, 647, 657, 663
of third ventricle, 666, 670
Telencephalon, 667
Temporal artery, anterior deep, 553
of dog, 635
of ox, 612
posterior deep, 552
superficial, 550
bone of dog, 156
of horse, 55
of ox, 120
of pig, 141
fascia of horse, 213
foramen of horse, 51, 67
fossa of horse, 67
nerve, 682
of dog, 728
of horse, 681
of ox, 717
of pig, 722
process of maxillary bone of horse, 58
vein, 587, 588
wings of horse, 51
Temporalis muscle of dog, 318
of horse, 219
of ox, 297
Temporary teeth of horse, 346
Temporo-hyoid articulation, 180
Temporo-mandibular articulation of dog, 204
of horse, 179
of ox, 204
of pig, 204
Tendinous center of diaphragm of horse, 243
Tendo femorotarseus muscle of horse, 289
Tendon, prepubic, 250
sheath, 211
Tendons, 211
Tenon, capsule of, 738
Tensor fasciæ antibrachii muscle of dog, 322
of horse, 260
of ox, 303
of pig, 315
latæ muscle of dog, 326
of horse, 276
of ox, 306
of pig, 316
palati muscle of horse, 333
tympani, 755
Tenth nerve, 687
Tentorial area, 668
Tentorium cerebelli, 646
osseum of horse, 70
Teres major muscle of dog, 322
of horse, 258
of ox, 302
of pig, 314
minor muscle of dog, 321
of horse, 256
of ox, 302
of pig, 314
tubercle of humerus, 77
Terminal arch of digital arteries, 564
arteries, 524
line of horse, 353
nuclei, 658
Testicles of dog, 506
epididymis of, 506
tunica vaginalis of, 506
of horse, 485
appendix of, 485
deferential fold of, 491
descent of, 490
gubernaculum testis, 491
hydatid of Morgagni, 458
lobules of, 486
mediastinum testis, 486
pampiniform plexus, 489
parenchyma of, 486
rete testis, 486
seminiferous tubules, 486
septa of, 486
structure of, 485
tubules of, 486
tunica albuginea of, 486
vaginalis propria of, 485
vasculosa of, 486
vas deferens of, 488
vessels and nerves of, 487
of ox, 500
cremaster externus muscle of, 500
epididymis of, 500
tunica vaginalis of, 500
vas deferens of, 501
of pig, 504
cremaster externus muscle of, 504
epididymis of, 504
vas deferens of, 504
Thalamocortical fibers, 661
Thalamus, optic, 664
Theca folliculi of mare, 510
Thigh, 29
of horse, muscles of, 276, 281, 284
of ox, muscles of, 306, 307, 308
of pig, muscles of, 316
Third carpal bone of horse, 86
eyelid, 736
of ox, 772
of pig, 777
metatarsal bone of horse, 110
nerve of horse, 677
phalanges of dog, 165
of horse, 90, 111
of ox, 130
sesamoid bone, 92, 111
tarsal bone of horse, 109
of ox, 135
trochanter of femur, 99
ventricle, 666
Thoracic aorta, 536
branches of, 565
artery external, 541
internal, 540
of dog, 633
of ox, 609
of pig, 627
cavity, 27
of horse, 450
of ox, 461
duct of dog, 643
of horse, 600
of ox, 623
of pig, 630
ganglia, 712
of ox, 720
limb, bones of, 27
Thoracic limb of dog, articulations of, 205
bones of, 162
muscles of, 319
of horse, articulations of, 180
bones of, 74
muscles of, 250
of ox, articulations of, 205
bones of, 127
muscles of, 302
of pig, articulations of, 205
bones of, 146
muscles of, 314
lymph glands of pig, 631
nerves, anterior, 696
of horse, 697, 702
portion of panniculus, 255
of sympathetic system, 712
vein, 586, 593
vertebræ, 24
of dog, 150
of horse, 35, 36, 37
of ox, 112
of pig, 137
Thoracico-dorsal artery, 556
Thoraco-dorsal nerve, 697
vein, 593
Thorax, articulations of, of dog, 204
of horse, 177
of ox, 204
of pig, 204
bones of, 27
of dog, 153
of horse, 47
of ox, 115
of pig, 139
muscles of, of dog, 325
of horse, 240
of ox, 300
of pig, 313
Thymus gland of dog, 468
of horse, 458
of ox, 464
of pig, 466
Thyro-arytenoid ligament, 444
Thyro-arytenoideus muscle of horse, 446
Thyro-epiglottic ligament, 444
Thyro-hyoid joints, 444
Thyro-hyoideus muscle, 445
Thyrohyoids of horse, 65
Thyroid artery, accessory, 543
of ox, 610
of pig, 627
cartilage of dog, 467
of horse, 442
of ox, 459
of pig, 465
cornua of horse, 65
gland of dog, 468
accessory, 468
of horse, 457
accessory, 458
of ox, 464
accessory, 464
of pig, 466
vein, 590
Thyro-laryngeal artery, 543
Thyro-pharyngeus muscle, 350
Tibia, 29
Tibia of dog, 167
of horse, 100, 102, 103
of ox, 134
of pig, 149
Tibial artery, anterior, 583
of dog, 641
of ox, 620
of pig, 630
posterior, 581
recurrent, 581
bones, 29
crest of horse, 100
nerve, anterior, of horse, 708
of dog, 732
of horse, 708
of ox, 720
tarsal bone of horse, 105
ligaments of, 202
synovial fossa of, 105
trochlea of, 105
of ox, 134
vein, anterior, 599
of dog, 642
posterior, 599
recurrent, 598
Tibialis anterior muscle of dog, 328
of horse, 290
of ox, 310
of pig, 317
posterior muscle of dog, 329
Tibio-fibular articulation, 199
joints of dog, 210
of ox, 209
of pig, 210
Tibio-tarsal articulation, 199
sac of horse, 200
Toe of horse, 764
Tongue of dog, 424
of horse, 335
of ox, 385
of pig, 411
of sheep, 405
Tonsil, faucial, of horse, 333
of pig, 411
of sheep, 407
Topographic anatomy, 17, 18
Torus carpalis, 780
metacarpalis, 780
tubarius, 778
Trabeculæ carneæ of right ventricle, 532
of corpus cavernosum penis, 495
of prostate, 493
of thyroid gland, 458
splenic, of horse, 379
Trachea of dog, 468
of horse, 448
of ox, 460
of pig, 466
Tracheal ducts, 603
of dog, 643
Trachelo-mastoideus muscle of dog, 325
of horse, 229
of pig, 312
Tract of spinal cord, 652
olfactory, 671
optic, 666
of ox, 716
pyramidal, 658
Tractus centralis of thymus gland, 458
Tractus olfactorius, 671
opticus, 666
Tragicus muscle, 751
Tragus, 748
of dog, 780
Transversalis costarum muscle of dog, 325
of horse, 236
of ox, 300
of pig, 313
fascia of horse, 249
Transverse arytenoid ligament of larynx, 444
diameter of pelvis, 97
fissure, 669
of ox, 716
fossa of brain, 667
hyoideus muscle, 224
lamina, ethmoid bone of dog, 157
ligament of carpus, 263
of hip joint of horse, 192
of radio-ulnar articulation of horse, 182
palatine suture of horse, 69
sinuses, 591
spinous muscle of neck, 231
Transversus abdominis muscle of dog, 326
of horse, 248
of ox, 302
of pig, 313
costarum muscle, 242
thoracis muscle of horse, 242
of pig, 313
Trapezius cervicalis muscle, 250
muscle of dog, 319
of horse, 250
of ox, 302
of pig, 314
thoracalis muscle, 251
Triangularis sterni muscle, 242
Triceps brachii, 260, 261
extensor cubiti of horse, 260
muscle of dog, 322
of ox, 303
of pig, 315
suræ muscle of horse, 292
Trifacial nerve of horse, 677
Trigeminal nerve of horse, 677
Trigonum lemnisci, 664
olfactorium, 653, 667, 671
vesicæ of horse, 476
Trochanter, external, of femur of horse, 99
great, of femur of horse, 99
internal, of femur, 97
Trochanteric fossa of femur of horse, 99
ridge of femur of horse, 99
Trochlea of femur of horse, 99
of tibial tarsal bone of horse, 105
Trochlear foramen of horse, 51, 67
nerve of horse, 677
origin of, 664
Trochoid, 172
True joints, 170
ribs, 25
of horse, 43
vertebræ, 24
vocal cords of dog, 468
of horse, 448
Truncus bicaroticus, 541
Tuber calcis of fibular tarsal bone of horse, 106
cinereum, 653, 665
of dog, 726
ischii of horse, 95
scapulæ of horse, 77
Tubercle, cuneate, of pig, 720
internal, of humerus, 78
lacrimal, of horse, 61
of Lower, 530
of scapula of horse, 75
psoas, of horse, 93
teres, of humerus, 77
Tuberculum cinereum, 656
faciale, 655
intervenosum of horse, 530
olfactorium of pig, 721
Tuberosity, alveolar, 69
bicipital, of radius, 81
of scapula, 77
deltoid, of horse, 78
external, of humerus, 78
of radius of horse, 81
facial, of ox, 120
internal, of humerus, 79
of radius of horse, 81
maxillary, of horse, 58
metacarpal, of horse, 88
of atlas of ox, 112
of tibia of horse, 102
Tubules of testicles, 486
renal, of horse, 474
seminiferous, of testicles, 486
uriniferous, of horse, 474
Tunic, abdominal, 245
of pig, 313
fibrous, of ape, 740
Tunica albuginea, 486, 495
fibrosa of kidney, 473
mucosa laryngis, 448
propria of skin, 762
vaginalis communis, 490
of dog, 506
of horse, 489
of ox, 500
propria of horse, 485, 490
vasculosa of testicles, 486
Turbinal bones of dog, 158
of horse, 62, 438
of ox, 122
of pig, 143, 465
crest, inferior, of horse, 58
superior, of nasal bones of horse, 61
fold, inferior, of horse, 440
superior, of horse, 440
Twelfth nerve, 692
Tympanic artery, 552
cavity of dog, 780
of horse, 752
of ox, 775
of pig, 778
membrane, 753
nerve, 686
opening of Eustachian tube, 755
plexus, 687
Udder of cow, 519
Ulna, 28
of dog, 163
of horse, 82
Ulna of ox, 128
of pig, 147
Ulnar artery, 559
of dog, 637
of ox, 613
superior collateral, of ox, 612
carpal bone of horse, 84
nerve of dog, 730
of horse, 696, 698
of ox, 718
of pig, 723
vein, 595
of dog, 642
Ulnaris lateralis muscle of dog, 323
medialis muscle of dog, 323
Umbilical artery, 574, 606
of dog, 641
of ox, 619
fissure of horse, 374
ligament of bladder, 476
vein, 607
Undershot dog, 425
Ungual phalanx of horse, 90
Unipennate muscle, 212
Unstriped muscle, 211
Ureters, 469
of bladder, fundus of, 476
of dog, 484
of heart, pelvic part, 475
of horse, 475
abdominal part, 475
of ox, 480
of pig, 483
Urethra, 469
masculina of dog, 507
of horse, 497, 498, 499
of ox, 504
of pig, 506
of cow, 519
of mare, 515
of sow, 522
Urethral crest of horse, 499
glands of horse, 499
groove of horse, 495
muscle of dog, 507
of horse, 499
of mare, 516
of ox, 504
of pig, 506
orifice, external, of cow, 519
of male horse, 499
of mare, 515
of ox, 503
internal, of horse, 477, 499
of horse, 477
of pig, 505
process of horse, 495
sinus of horse, 495
Urinary bladder. See _Bladder_.
organs, 469
of dog, 483
of horse, 469
of ox, 478
of pig, 481
Uriniferous tubules, 474
Urogenital fold of horse, 355
sinus of mare, 514
system, 469
Uterine artery, 571
middle, 578
of dog, 641
Uterine artery of ox, 619
posterior, 574
cotyledons of cow, 518
glands of cow, 518
of mare, 513
tubes of bitch, 522
of cow, 517
of mare, 511
of sow, 522
Utero-ovarian artery, 571
of dog, 639
of ox, 618
plexus, 714
veins, 596
Uterus masculinus of dog, 506
of horse, 493
of ox, 503
of pig, 505
of bitch, 522
of cow, 517, 518
of horse, broad ligaments, 356
of mare, 511, 512, 513
of sow, 522
Utricle, 759
prostatic, of horse, 493
Uvula of pig, 411
Vagina of bitch, 523
of cow, 518
of mare, 514
of sow, 522
tendinis, 211
Vaginal ligaments, 212
ring of horse, 248, 490
of ox, 500
synovial membrane, 211
Vagus, 687
of dog, 729
of ox, 717
of pig, 722
Vallate papillæ of tongue, 336
Vallecula of Sylvius, 667
Valve, bicuspid, of horse, 533
ileo-cæcal, of dog, 431
of horse, 362, 364
mitral, of horse, 533
of vein, 525
of Vieussens, 663
pulmonary, of horse, 532
Valvula foraminis ovalis, 607
Valvular fold of cæcum, 365
Vas deferens of horse, 488
of ox, 501
of pig, 504
of spermatic cord, 489
vasorum of veins, 525
Vascular system, 524
blood-, 524
of horse, 525
tunic, 742
Vastus externus muscle, 285
intermedius muscle, 286
of ox, 307
internus muscle of horse, 286
Veins or vein, 524, 585
abdominal, 598
alveolar, 589
inferior, 587
auricular, 588
azygos, 586
brachial, 593
of dog, 642
brachiocephalic, of dog, 641
Veins, bronchial, 587
buccinator, 590
of pig, 630
cardiac, 586
cephalic, 591, 593
of dog, 642
of ox, 622
cerebellar, 592
cerebral, 588, 592
of ox, 621
cervical, deep, 586
inferior, 591
circumflex, external, 598
condyloid, 588
coronary, 535, 586
dental, 587
digital, 595
of dog, 642, 643
of ox, 621, 623
diploic, 593
dorsal, 586
emissary, 591
esophageal, 587
facial, 588
of pig, 630
femoral, 598
of dog, 642
femoro-popliteal, 598
frontal, of ox, 621
gastric, 597
gastro-duodenal, 597
hepatic, 596
of horse, 377
hypogastric, 597
iliac, common, 597
of dog, 642
ilio-femoral, 598
ilio-lumbar, 597
infraorbital, 589
intercostal, 587
interosseous, 595
intima of, 525
jugular, 587
of dog, 642
of ox, 621
of pig, 630
labial, 589
of ox, 621
lingual, 590
dorsal, 587
lumbar, 596, 597
mammary, of ox, 622
maxillary, 588
internal, 587
of dog, 642
maxillo-muscular, 588
meningeal, 592
mesenteric, 597
metacarpal, 595
of dog, 642
of ox, 621
metatarsal, 599
of dog, 643
of ox, 622
middle coat of, 525
milk, 301
of cow, 521
nasal, of ox, 621
of pig, 630
nerves of, 525
obturator, 598
occipital, 588
of adrenal bodies, 478
of articulations, 171
Veins of bladder of horse, 477
of brain, 592
of dog, 641
of Fallopian tubes, 511
of Galen, 592
of heart, 585
of horse, 585
of internal ear, 761
of kidney of horse, 475
of mammary glands of cow, 521
of mare, 516
of ovaries of mare, 510
of ox, 621
of penis of horse, 496
of pig, 630
of prepuce of horse, 497
of uterus of mare, 513
of vagina of mare, 514
ophthalmic, 590
orbital, of ox, 621
palatine, 589
pancreatic, 597
perineal, of ox, 622
phrenic, 596
popliteal, 599
of dog, 642
portal, 596
of horse, 377
of ox, 623
pterygoid, 587
pudic, external, 598
of ox, 622
pulmonary, 524, 585
of horse, 457
openings of, left atrium, 530
radial, 595
of dog, 642
renal, 596
of ox, 622
saphenous, 598
of dog, 642
of ox, 622
satellite, 524
spermatic, 596
of horse, 487, 489
sphenopalatine, 589
spinal, 593
splenic, 596
spur, 593
structure of, 525
sublingual, 590
of ox, 621
tarsal, of ox, 622
recurrent, 598
temporal, 587
superficial, 588
thoracic, 593, 586
thyroid, 590
tibial, anterior, 599
of dog, 642
posterior, 599
recurrent, 598
ulnar, 595
of dog, 642
umbilical, 607
utero-ovarian, 596
valves of, 525
vas vasorum of, 525
vertebral, 586
Velum interpositum of third ventricle, 666
medullary, 660, 663
Vena azygos, 586
of dog, 642
of horse, opening of, 529
cava, 524
anterior, 586
opening of, 529
of dog, 641, 642
of ox, 622
posterior, 595
opening of, 529
comitans, 524
hemiazygos, 587
of dog, 642
of ox, 621
jugularis of ox, 621
reflexa, 589
of ox, 621
Venæ vorticosæ, 745
Venous arch, 595
plexus of urethra of mare, 516
Venter of scapula of horse, 75
Ventral columns of spinal cord, 651
muscles of neck of horse, 224
nerve of dog, 729
sacral foramina of horse, 40
sacro-iliac ligament, 190
spine, 25
of cervical vertebræ of ox, 112
Ventricle, fourth, of horse, 662
lateral, 674
of larynx of horse, 447
of ox, 459
middle, of larynx, 447
of heart of horse, left, 533
right, 530
third, 666
Ventricular ligament of larynx of horse, 444
Ventricularis et vocalis muscle of horse, 446
Ventriculus bulbi olfactorii, 671
laryngis medianus of horse, 447
lateralis, 674
laryngis of horse, 447
quartus, 662
tertius, 666
Vermis, 660
of dog, 725
Vertebræ, 24
accessory processes, 25
anticlinal, of horse, 42
arch, 24
articular processes, 25
body, 24
caudal, 24, 25
centrum, 24
cervical, 24
of dog, 150
of horse, 32
of ox, 112
of pig, 136
coccygeal, 24
of dog, 152
of horse, 41
of ox, 114
of pig, 138
development, 25
diaphragmatic, of horse, 42
Vertebræ, false, 24
fixed, 24
foramen, 25
hæmal spine, 25
ligaments of, of dog, 204
of horse, 172
of ox, 203
of pig, 204
lumbar, 24
of dog, 151
of horse, 38
of ox, 112
of pig, 138
mammillary processes, 25
movable, 24
notches, 25
of horse, intercentral articulations of, 173
interneural articulations of, 173
ossification of, 25
primary centers of ossification, 25
sacral, 24
of dog, 151
of horse, 39
articulations of, 175
development, 41
of ox, 114
of pig, 138
secondary centers of ossification, 25
spinous process, 25
thoracic, 24
of dog, 150
of horse, 35, 36, 37
of ox, 112
of pig, 137
transverse processes, 25
true, 24
ventral spine, 25
Vertebral artery, 540
of dog, 633
of ox, 609
of pig, 627
canal, 25
of horse, 42
column, 24
of dog, 150
of horse, 31
of ox, 112
of pig, 136
foramen, 25
formula, 24
groove of horse, 42
ligaments of dog, 204
of horse, 172
of ox, 203
of pig, 204
notches, 25
vein, 586
Vertex corneæ, 741
Vertical septum of metacarpus of ox, 130
Vesical artery, 574
Vesicles, seminal, of dog, 506
of horse, 491
of ox, 502
of pig, 505
Vesico-genital pouch, 356
Vesico-prostatic artery, 574
Vestibular ganglion, 686
nerve, 686, 761
Vestibule of ear, 758
Vestibule of larynx of horse, 447
of omental cavity, 380
Veterinary anatomy, 17
Vibrissæ, 763
Vidian canal of horse, 51, 61
nerve, 681
Villi of articulations, 170
Visceral layer of pericardium, 525
pleura of horse, 452
Vitreous body, 746
of ox, 774
Vocal cords, false, of dog, 467
of horse, 447
of ox, 459
of pig, 465
true, of dog, 468
of horse, 448
ligament of horse, 444
process of horse, 443
Vocalis muscle of horse, 446
Volar arch, 562
artery, deep, 562
of second phalanx, 564
common digital artery of ox, 614
digital nerves of dog, 731
flexion of joints, 171
foramen of third phalanx, 91
ligament of carpal joints, 183
of pastern joint, 188
muscle of pig, 315
nerve of horse, 701
of ox, 718, 719
plexus, 595
sesamoids of dog, 165
Vomer of dog, 158
of horse, 63, 431
of ox, 122
of pig, 143
Vomero-nasal organ, 772
of horse, 440
Vortex cordis of horse, 534
V-shaped ligament, 188
Vulva of bitch, 523
of cow, 519
of mare, 514
of sow, 522
Vulvar cleft of mare, 514
Wall of horse’s hoof, 764
White commissure of cord, 650
line of hoof, 765
matter of nervous system, 644
Wilson’s muscle of dog, 507
of ox, 504
Winslow’s foramen, 379
of ox, 396
Wirsung’s duct of horse, 372
Wolf tooth, 339
of horse, 58, 64
Wool, 777
Xiphoid cartilage, 26
of horse, 46
Y-shaped ligament, 188
Zone, epigastric, of horse, 353
hypogastric, of horse, 353
intermediate, of kidney, 473
mesogastric, of horse, 353
Zonula ciliaris, 743, 747
of Zinn, 747
Zygomatic arch of horse, 56, 67
bones of horse, 62
crest of horse, 58, 62
gland of dog, 427
nerve of dog, 728
of horse, 679
process of frontal bone, 55
of maxillary bone, 58
Zygomatic process of temporal bone, 56
Zygomatico-auricularis, 749
of ox, 747
Zygomaticus muscle of dog, 318
of horse, 215
of ox, 295
of pig, 311
-----
Footnote 1:
Only the gross structure is discussed here. For the microscopic
structure reference is to be made to histological works.
Footnote 2:
Only a brief general statement of osteogenesis can be made here;
details must be sought in embryological literature.
Footnote 3:
As might be expected from the history of anatomy, a good many of these
terms are more or less interchangeable; furthermore, a given skeletal
feature may differ greatly in various species.
Footnote 4:
The term is employed here, as is usual in descriptive anatomy, to
designate only the bony part of the rib (Os costale); morphologically
it includes the cartilaginous part also.
Footnote 5:
The manubrium sterni of man is equivalent, strictly speaking, to the
cariniform cartilage + the first osseous segment of the horse.
Footnote 6:
The long axis of the skull is considered to be horizontal in these
descriptions.
Footnote 7:
The occipital crest of this description is equivalent to the external
occipital protuberance and superior nuchal line of man. A curved line
a little lower down, which is continued on the paramastoid process,
represents the inferior nuchal line of man.
Footnote 8:
Other terms for these parts are basioccipital (basilar part),
exoccipitals (lateral parts), and supraoccipital (squamous part). It
should be noted, however, that the lines between the basioccipital and
exoccipitals pass through the lower part of the condyles.
Footnote 9:
This foramen might well be called a canal, since it is an inch or more
in length.
Footnote 10:
The cavity so formed may be termed the sphenopalatine sinus. The
sphenoidal sinus may be a separate cavity which communicates only with
the ventral ethmoidal meatuses; this arrangement exists in about a
third of the cases, according to Paulli.
Footnote 11:
This is also called the subsphenoidal canal or pterygoid foramen.
Footnote 12:
On account of its deep situation, and the fact that it cannot be
separated from its surroundings, the ethmoid must be studied by means
of appropriate sagittal and transverse sections of the skull.
Footnote 13:
According to Martin, there are originally four centers, two anterior
and two posterior (smaller) ones, which fuse in a variable manner.
Footnote 14:
This is commonly termed the styloid process. It is not the homologue
of the styloid process of man.
Footnote 15:
This foramen is somewhat variable in position, but is commonly
opposite the corner incisor. Smaller inconstant foramina are often
present.
Footnote 16:
The alveolus for the temporary canine is commonly formed in the
maxilla alone.
Footnote 17:
This bone is really a greatly developed first ethmoturbinal.
Footnote 18:
In the Stuttgart Nomenclator Anatomicus (S. N. A.) the body (Corpus)
is the part which bears the teeth, and is divided into a pars incisiva
and a pars molaris. The ramus is the rest of the bone.
Footnote 19:
These correspond to the great cornua of man.
Footnote 20:
This relation varies with age; in the young horse the third tooth, in
the old subject the fourth, lies below the end of the crest.
Footnote 21:
This bone is probably equivalent to the fourth and fifth carpals of
forms in which five carpal elements are present in the lower row.
Footnote 22:
It is also called the large pastern bone or os suffraginis.
Footnote 23:
This bone is also called the small pastern bone or os coronæ.
Footnote 24:
This bone is also called the os pedis or coffin bone.
Footnote 25:
The upper and lower divisions of the wing are sometimes termed the
basilar and retrossal processes respectively.
Footnote 26:
This is termed the lacrimal sinus by some authors. It is similar in
location and in the position of its orifice to the turbinal part of
the frontal sinus of the horse, with the important difference that it
does not communicate with the frontal sinuses in the ox.
Footnote 27:
This third bone was termed the phacoid in the cat by Strauss-Durckeim,
and is regarded by some authors as the vestige of an additional digit,
the prepollex.
Footnote 28:
It is doubtful whether the synovia is a true secretion or a transudate
containing products of friction. The view given above is that which is
more commonly accepted.
Footnote 29:
This classification makes no claims to scientific accuracy, but is
simply a statement of the terms in general use. A grouping based on
mechanical principles seems desirable, but appears to be almost
impossible on account of the great variety and irregularity of form of
the articular surfaces.
Footnote 30:
The movements in some of these joints are more extensive and varied
than in some diarthroses. To illustrate this we may compare the
movements of the cervical or coccygeal vertebræ with those possible in
the carpo-metacarpal or the sacro-iliac joints.
Footnote 31:
In dissecting-room subjects these bursæ and the adjacent structures
are commonly the seat of pathological changes. They appear to be the
starting-point of “poll evil” and “fistulous withers.”
Footnote 32:
No natural line of demarcation exists between the ligamentum nuchæ and
the lumbo-dorsal continuation of the supraspinous ligament, since the
change from the purely elastic to the white fibrous structure is
gradual.
Footnote 33:
The term is a very unfortunate one, since it is a distinct
misapplication of the name as it is used in regard to man. It is,
however, very firmly established, and appears likely to persist
indefinitely in the absence of a convenient popular equivalent.
Footnote 34:
This is often called the Y-shaped ligament—a rather
undesirable name, since it is not bifurcate.
Footnote 35:
It is also called the V-shaped ligament.
Footnote 36:
This should be noted in regard to resection of the lateral cartilage
or other operations in this vicinity.
Footnote 37:
These are termed the postero-lateral ligaments by M’Fadyean. They may
well be called, as by German authors, the suspensory ligaments of the
navicular bone.
Footnote 38:
In this figure the patella is pushed up above the trochlea—a position
which it does not occupy normally.
Footnote 39:
This section consists necessarily only of a brief statement of the
most important differences in the joints of the other animals.
Footnote 40:
These movements are best seen in man, in whom the back of the hand may
be turned forward (pronation) or backward (supination).
Footnote 41:
The student will note in dissection that transition forms occur; also
that the same sheath may belong to two or more tendons in common, _e.
g._, the sheath of the two flexors on the back of the carpus. In such
cases the synovial membrane is reflected from one tendon to the other,
and may form a secondary mesotendon.
Footnote 42:
This muscle is probably the homologue of the sternal portion of the
sterno-cleido-mastoid of man. On account of the differences in its
insertion in the various animals, it seems desirable to adopt the name
sterno-cephalicus.
Footnote 43:
The upper part of this maybe separated from the scalenus proper, and
is then termed the cervicalis ascendens or ilio-costalis cervicis—a
continuation in the neck of the transversalis costarum.
Footnote 44:
This seems due to pressure produced by pathological changes in the
supra-atloid bursa, which are frequently extensive in dissecting-room
subjects.
Footnote 45:
The lumbar part of this muscle is subject to variation. It may, in
quite exceptional cases, extend as far as the ilium.
Footnote 46:
The muscle as here described includes the spinalis and semispinalis
components, as the separation of these is largely artificial in the
horse.
Footnote 47:
The function of the intercostal muscles is still a subject of much
discussion. The statements made above seem to represent the view most
commonly held in regard to their action.
Footnote 48:
It should be noted, however, that in the embryo the diaphragm appears
as a paired structure, extending from the lateral walls of the cœlom
to fuse with the septum transversum.
Footnote 49:
In order to get a clear idea of the relative positions of these
foramina and of the form of the diaphragm, the thoracic surface of the
latter should be examined while the abdominal viscera remain _in
situ_.
Footnote 50:
It is narrow and slit-like in the natural condition, but may appear
oval in the dissecting-room, especially if the hind limb is drawn back
and abducted.
Footnote 51:
It must be admitted that the term “ring” is rather misleading as
applied to the abdominal opening of the canal, since normally it is a
mere dilatable slit. The ring-like constriction which exists here in
the male is constituted by the peritoneum, which descends into the
canal to form the tunica vaginalis. This peritoneal ring is termed the
=vaginal ring= (Annulus vaginalis), and must not be confused with the
subperitoneal ring, _i. e._, the internal inguinal ring.
Footnote 52:
As might be expected, the cremaster usually undergoes more or less
atrophy, and is paler in the castrated subject. In the mare the muscle
is small, and ends in the connective tissue in the lower part of the
inguinal canal.
Footnote 53:
The term canal is somewhat misleading; it is rather a slit-like
passage or space between the two oblique muscles, since the inguinal
ligament is that part of the aponeurosis of the external oblique
muscle which stretches between the external angle of the ilium and the
prepubic tendon.
Footnote 54:
The obliquity of the tendon and the angle which it forms with the
pelvic floor are of clinical importance in regard to manipulation of
the fœtus in obstetrical cases. The slope varies in different
subjects. In some cases the tendon forms about a right angle with the
pubic bones.
Footnote 55:
The terms dorsal and ventral are here used in the topographic and not
in the morphological sense. All the muscles of the group are ventral
in the latter sense.
Footnote 56:
This is regarded as a vestige of the clavicle. On this basis the
portion of the muscle from the vestige to the arm represents the
clavicular part of the deltoid of man.
Footnote 57:
Günther states that this muscle assists in extension or flexion
according to the position of the head of the humerus relative to the
glenoid cavity.
Footnote 58:
M’Fadyean and Vaughan term this muscle the scapulo-ulnaris, while
Arloing and Lesbre term it “Ancone accessoire du grand dorsal.” The
above name seems to agree best with the chief insertion and action,
although it certainly arises largely from the tendon of insertion of
the latissimus dorsi.
Footnote 59:
This is considered to represent the part of the common extensor for
the fourth and fifth digits.
Footnote 60:
Martin considers that this muscle represents the extensor indicis
proprius and the part of the common extensor for the second digit.
Footnote 61:
In man the muscle is an extensor of the hand.
Footnote 62:
On account of the intimate union between the psoas major and iliacus
they are frequently considered a single muscle, to which the name
ilio-psoas is applied; some anatomists include the psoas minor also
under this term.
Footnote 63:
By some anatomists the portion inserted into the crest is termed the
gluteus accessorius, but Lesbre considers this the deep gluteus,
homologous with the gluteus minimus of man. The portion inserted into
the trochanteric ridge apparently represents the piriformis of man.
Footnote 64:
Apparently the muscle represents the biceps, together with part of the
gluteus superficialis of man. Hence the names gluteo-biceps and
paramero-biceps have been suggested.
Footnote 65:
This muscle was incorrectly designated the adductor magnus by
Percivall and Strangeways. Its name, however, is not at all
descriptive of its structure in the domesticated animals.
Footnote 66:
It has been customary to describe two adductors—a parvus or brevis,
and a longus or magnus. This division is largely artificial, and has
been abandoned in the new nomenclature—a return to the views of
Bourgelat and Girard.
Footnote 67:
This has been termed by various authors the adductor parvus or brevis.
Footnote 68:
Termed by various authors the adductor magnus or longus.
Footnote 69:
The iliac head is described by some authors as a separate muscle, and
termed the pyriformis. This does not seem desirable, especially since
it is at least probable that the homologue of the pyriformis of man is
that portion of the middle gluteus which is inserted into the back of
the trochanteric ridge.
Footnote 70:
The name is based on the arrangement in man, in whom the muscle
consists of two fasciculi forming a groove between them for the tendon
of the obturator internus. In the horse it is undivided, and is
grooved for the obturator tendon, so that at first sight it appears to
be double. The gemellus may be regarded as the extrapelvic head of the
obturator internus (Gegenbaur).
Footnote 71:
While it is true that the separation of the intermedius is probably
never entirely a natural one in the horse, it varies in individual
cases, and is usually clear on cross-sections. In some subjects it is
possible to separate another slip which may represent the articularis
genu of man.
Footnote 72:
It seems inadvisable to retain the old nomenclature, since it is
inapplicable to other domesticated animals in which the muscle is well
developed (_e. g._, ox, pig).
Footnote 73:
The soleus may, therefore, be included with the two heads of the
gastrocnemius under the name triceps suræ.
Footnote 74:
The origins of these heads are given in the order in which they may be
most conveniently dissected, not in order of size and importance.
Footnote 75:
This is probably the homologue of the subclavius of man.
Footnote 76:
Movements of individual digits are specified with regard to the axis
of the manus (hand, paw), and not to the median plane of the body.
Footnote 77:
The term “mouth” is commonly used to signify either the oral cavity
(Cavum oris) or the entrance to it (Rima oris).
Footnote 78:
The epiglottis may be either in front of or behind the soft palate;
most often it is prevelar.
Footnote 79:
In the undisturbed state of the parts there is no space between the
tongue and the rami of the lower jaw; consequently the tongue must be
drawn aside to see the sublingual crest.
Footnote 80:
It will be noted that this definition of crown and root does not agree
exactly with the popular view that the crown is the free portion and
the root the embedded portion. The objection to the latter statement
lies in the fact that it is not capable of general application. Thus
the morphological crown of the permanent molars in the horse is
extremely long, and is, for the most part, embedded in the bone in the
young animal. The root proper begins to form at four or five years of
age, and continues its growth for about eight years. As the exposed
part of the crown wears down, the embedded part pushes out of the
alveolus, thus preventing deficiency of length. On the old basis we
should have to say that successive portions of the root become crown,
while in point of fact it is only in very extreme age that the true
root comes into wear.
Footnote 81:
Ellenberger found, as the result of extensive observations (8000
subjects), that about 2 to 3 per cent. of mares have erupted canines
in both jaws; that 6 to 7 per cent. have them in the upper jaw; while
20 to 30 per cent. have them in the lower jaw.
Footnote 82:
It is interesting to notice that vestigial canines are not at all
uncommon in mares, especially in the lower jaw. They are very small,
and do not usually erupt; their presence is indicated in the latter
case by a prominence of the gum. This is in conformity with the fact
that they were present in both sexes in Eocene and Miocene ancestors
of existing equidæ.
Footnote 83:
It is common in veterinary works to call all the cheek teeth molars,
since, in the horse particularly, the premolars are molariform, _i.
e._, do not differ materially from the true molars in size or form.
The term cheek teeth conveniently includes the premolars and molars.
Footnote 84:
The student is advised to amplify these very general statements by the
examination of heads of subjects of varying ages. It may also be noted
that the position of the septum between the two divisions of the sinus
varies much.
Footnote 85:
Careful observations (especially on frozen subjects and those in which
the organs have been hardened _in situ_) show that there is no
abdominal part of the œsophagus in the strict sense of the term. The
stomach here lies directly on the diaphragm, so that the last inch or
so of the œsophagus is placed obliquely in the hiatus œsophageus, and
is partly covered by the pleura, but not by peritoneum. In soft
subjects the weight of the stomach, or traction on it, draws part of
the œsophagus into the abdomen, inclosed in a collar of peritoneum.
Footnote 86:
The potential lumen is difficult to determine at all accurately. When
distended, its diameter (according to Rubeli) varies from 5.7 cm. at
its origin to 4 cm. at its cardiac end. The thickness of the wall
varies (inversely as the lumen) from 4 mm. to 1.2 cm. or more.
Footnote 87:
At the origin of the tube muscular bundles arise on the raphé
pharyngis and blend with the crico-pharyngeus. Ventrally fibers come
from the depression between the cricoid and arytenoid cartilages.
Bundles of striped fibers may be continued in the superficial part of
the muscular coat as far as the cardia.
Footnote 88:
This method of division, although long in use, is of very little value
for accurate description. It is mentioned here chiefly because
agreement on a more useful topographic method has not been arrived at.
Footnote 89:
Only a general account of the arrangement of the peritoneum is given
in this section, since a detailed description cannot be understood
without a knowledge of the viscera concerned.
Footnote 90:
This is the position in the expiratory phase as usually seen in the
dead subject. In inspiration the saccus cæcus lies under the upper
parts of the sixteenth and seventeenth ribs.
Footnote 91:
This occlusion is usually so complete that distention of the stomach
by air or fluid forced in through the pylorus may be carried far
enough to rupture the stomach without ligating the œsophagus.
Footnote 92:
No natural line of demarcation exists, but there is a marked increase
of the thickness of the wall toward the terminal part. Other
differences will be noted in the further description.
Footnote 93:
It will be noticed that the mesoduodenum is not continuous with the
great mesentery, but ends by a free edge. The mesentery begins on the
opposite surface of the end of the duodenum, so that the bowel is
attached by two peritoneal folds at this point.
Footnote 94:
Abnormal displacement, _e. g._, torsion of the left parts, is not
rare, and is liable to produce death if not promptly reduced.
Footnote 95:
There is no natural line of demarcation between the small colon and
rectum: the plane of the pelvic inlet is selected for convenience of
description.
Footnote 96:
The anterior part of the rectum is very variable in position and
relations. It is not often median, but may be deflected either to
right or left. Most often it is pushed to the left by the pelvic
flexure of the colon. In other cases—especially when empty—it may lie
against the right wall, and the space to the left is occupied by the
small colon. The amount covered by peritoneum dorsally and laterally
is very variable, and appears to be in inverse proportion to the
fullness of the bowel.
Footnote 97:
A descriptive method based on that in use in human anatomy cannot be
applied with clearness to the organ in the horse.
Footnote 98:
These impressions are not evident on the soft organ. In hardened
material they are clearly mapped out, although of course variable in
size, in conformity with the degree of fullness of the various hollow
viscera. The cæcal impression may not be evident if, as often happens
in old horses, the right lobe of the liver is much atrophied.
Footnote 99:
Flower and Ruge describe the mammalian liver as being primarily
divided by the umbilical fissure into two parts, the right and left
lobes. Secondary fissures on either side may subdivide each of these
primary lobes. On this basis we may recognize in the liver of the
horse right lateral, right central, left central, and left lateral
lobes. In the young foal these four lobes are distinctly recognizable.
The two central lobes would correspond to the middle lobe of the
foregoing description, and the right central lobe would be the
equivalent of the quadrate lobe of man.
Footnote 100:
In the young foal the interlobular tissue is more abundant and the
lobulation correspondingly distinct.
Footnote 101:
The hepatic veins may be recognized on section from the fact that they
remain open, being connected closely with the parenchyma.
Footnote 102:
The ductless glands are organs which elaborate substances which pass
directly into the veins or lymphatics, instead of being conveyed away
by ducts. This process is termed internal secretion. The ductless
glands include the lymph glands, which are described with the organs
of circulation; the thyroid and thymus bodies, described usually with
the respiratory organs; the adrenal or suprarenal bodies, described
with the urinary organs; the pineal and pituitary bodies, described
with the brain; and the spleen, described with the digestive system as
a matter of convenience. The spleen is not, strictly speaking, a gland
at all: it is not epithelial in origin or structure, but is
mesenchymatous.
Footnote 103:
The student is strongly recommended to study the peritoneum of a foal
or other small subject when the opportunity occurs, as in these the
viscera are easily handled, and the course of the peritoneum can be
followed without difficulty.
Footnote 104:
The passage is subject to a good deal of variation in caliber and is
sometimes completely occluded.
Footnote 105:
In dissecting-room subjects (which are usually aged) the omentum often
exhibits pathological changes, such as adhesions, rents, tumors,
formation of twisted strands, etc.
Footnote 106:
The student will note here the difference between the structure and
behavior of the brachydont (short-crowned) incisors of the ox and the
hypsodont (long-crowned) type of the horse.
Footnote 107:
In popular language these are conveniently regarded as so many
stomachs, and termed accordingly “first,” “second,” etc. Other names
are in common use, _e. g._, paunch, honeycomb, manifold or manyplies,
and rennet or true stomach.
Footnote 108:
It has been customary to term the sacs left and right respectively,
but these do not represent the relations as they exist _in situ_ and
as they are presented on frozen sections.
Footnote 109:
It is important to notice that the reticulum is separated from the
pericardium by an interval of about 1 to 1½ inches (ca. 2 to 4 cm.)
only, since foreign bodies which are often swallowed by cattle lodge
in the reticulum, and not rarely (if sharp) perforate the reticulum
and diaphragm.
Footnote 110:
The epiglottis in the pig seems to be constantly retrovelar. The pig
frequently breathes through the mouth, and this is no doubt possible
only when the soft palate is raised; it seems probable that it is also
shortened.
Footnote 111:
The canines of the pig are “permanent pulp” teeth and therefore
capable of continued growth, and are without roots in the strict
sense.
Footnote 112:
It is usually stated that the cardiac end is funnel-shaped, but it is
not so in formalin-hardened cadavers nor in frozen sections. The
hiatus œsophagus is a long slit in the right crus of the diaphragm,
and the terminal part of the œsophagus, which lies in it, is flattened
transversely.
Footnote 113:
It will be noted that the fundus gland region does not extend up to
the lesser curvature; here the cardiac mucosa joins the pyloric.
Footnote 114:
The description here given is based mainly on the appearance of the
organ as hardened _in situ_, which differs radically from that of the
soft organ, as is seen on comparison of the annexed figure (Fig. 321).
Footnote 115:
In the bulldog, which is very prognathic (“undershot”), the lower
canines are opposite to or slightly in front of the plane of the upper
incisors, and the upper canines are about opposite to the first lower
cheek teeth. In the epignathic (“overshot”) dachshund the lower
canines are under or slightly behind the upper ones.
Footnote 116:
Increase in number also occurs, the supernumerary teeth being at
either end of the series.
Footnote 117:
The valve does not seem to be efficient, since experience shows that
rectal injections can be made to pass beyond it. This may be partly
due also to the fact that the terminal part of the ileum runs
horizontally forward, and the ileo-cæcal orifice faces into the
beginning of the colon.
Footnote 118:
Ellenberger and Baum state that the cæcum may reach a length of 20 cm.
in very large dogs.
Footnote 119:
When the stomach is very full, it pushes the left portion of the colon
over to the right, producing an acute angle in place of a transverse
branch. The terminal part of the colon is thus oblique in direction.
Footnote 120:
An external nose (Nasus externus), such as exists in man, forming a
projection distinctly marked off from the rest of the face, does not
exist in the domesticated animals.
Footnote 121:
The septal cartilage is to be regarded as an unossified part of the
mesethmoid. It will be noted that the line of demarcation between the
bone and the cartilage is irregular and varies with age; extensive
ossification for calcification) of the cartilage is commonly found in
old animals. The process often results in the formation of calcareous
islands in the cartilage.
Footnote 122:
In the ordinary position of the head and neck, and while the parts are
at rest, about half of the larynx lies between the branches of the
mandible; when the head and neck are extended, proportionately more of
the larynx lies behind a plane through the posterior borders of the
rami. It is here described in the position it occupies when the head
and neck are extended.
Footnote 123:
The term glottis is commonly used to designate the interval between
the vocal bands and arytenoid cartilages or the structures that
inclose that space.
Footnote 124:
In so-called œdema glottidis this loose submucous tissue becomes
infiltrated with fluid, in some cases causing occlusion of the
vestibule.
Footnote 125:
The arrangement of the muscles should be noted, since the space
inclosed by the divergence of the sterno-cephalici and the convergence
of the omo-hyoidei is the area of election for the operation of
tracheotomy.
Footnote 126:
The student should bear in mind that these terms are employed simply
as a matter of convenience in description; all the parts, though
differently named, form a continuous whole.
Footnote 127:
The apertures do not exist in the fœtus, and are sometimes absent in
the adult subject. Some of them may be produced in dissection by the
necessary disturbance of the parts. Clinicians state that a serous
exudate formed in one pleural sac usually passes through to the other
side in the horse.
Footnote 128:
A correct idea of the natural form and size of the lung cannot be
obtained from a specimen in this state. The lungs should be hardened
_in situ_ for this purpose.
Footnote 129:
Some authors consider each lung to be divided into anterior and
posterior lobes by the cardiac notch, so that the right lung would
have three lobes and the left lung two lobes.
Footnote 130:
In fœtal lung the lobulation is much more distinct. Pigmentation of
the lung is sometimes seen in horses, and in such cases the pigment is
deposited mainly in the interlobular tissue, thus mapping out the
lobules.
Footnote 131:
It must not be inferred from the necessarily brief account here given
that the two sets of vessels are quite distinct. On the contrary,
competent observers state that numerous small branches of the
bronchial arteries anastomose with pulmonary vessels. Part of the
blood conveyed to the lungs by the bronchial arteries is returned by
the pulmonary veins. In the horse bronchial veins are absent or
inconstant.
Footnote 132:
The cervical part of the gland is very variable. The thoracic lobe of
one side may have no cervical continuation; the other lobe may then
give off a single prolongation which bifurcates. The thoracic part in
the new-born foal occupies most of the space which is later taken up
by the apices of the lungs. Its two lobes are in contact, and its deep
surface is molded on the anterior part of the pericardium and the
large vessels.
Footnote 133:
It is therefore often termed the precardiac lobe.
Footnote 134:
The arrangement here is one of the most striking features of the pig’s
larynx. The short, thick middle hyo-epiglottic ligament and the
anterior part of the thyro-hyoid membrane are inelastic, while the
posterior part of the membrane is thin and elastic and allows the
epiglottis to be separated by a considerable interval from the thyroid
cartilage. Moreover, the borders of the epiglottis are connected with
the thyroid cornua of the hyoid bone by lateral hyo-epiglottic
ligaments.
Footnote 135:
The kidneys are soft, plastic organs, and hence an accurate knowledge
of their form can be gained only from a study of specimens which have
been hardened _in situ_. The description here given is based on this
method. For this purpose subjects should be hardened in the standing
position to avoid artefacts.
Footnote 136:
The most instructive sections are those made in the horizontal and
transverse planes, through the pelvis in each case.
Footnote 137:
The fœtal kidney is divided by furrows into a number of polygonal
areas, each of which is the base of a pyramidal lobe or renculus.
These furrows usually disappear before or soon after birth in the
foal, although traces of them are sometimes seen in the adult.
Footnote 138:
In the kidney of the horse the renal columns dip in between the
pyramids very superficially as compared with the arrangement in the
human kidney. Breuer states that the pyramids are 40 to 64 in number,
and are arranged in four rows. Only the middle ones are distinct.
Footnote 139:
The crest is the result of fusion of the papillæ or apices of the
pyramids in the embryo.
Footnote 140:
This is commonly termed the fundus by veterinarians, but is not the
homologue of the fundus of the human bladder.
Footnote 141:
This would correspond to the fundus vesicæ of man.
Footnote 142:
From the standpoint of comparative anatomy the term “adrenal” seems
decidedly preferable to “suprarenal.”
Footnote 143:
This is a remnant of the gubernaculum testis of the fœtus.
Footnote 144:
The tunica vaginalis is not a part of the scrotum in the strict or
narrow sense of that term, but is included here on practical grounds.
Footnote 145:
Sometimes one vesicula or both are very large in the gelding. The
writer has seen four cases in the dissecting room, three of which were
bilateral, the other unilateral. The vesicula resembled the urinary
bladder in appearance and contained about a quart of thick,
amber-colored secretion.
Footnote 146:
It has been customary to divide the pelvic part of the urethra into
prostatic and membranous parts. These terms apply well in human
anatomy, but have no special value in comparative anatomy. In the
horse a prostatic part hardly exists, unless we assume that it and the
neck of the bladder together are only about an inch in length. There
is no membranous part in the sense in which that term is used in
regard to man.
Footnote 147:
The statement often made that it acts as a sphincter of the bladder is
a hypothesis of doubtful plausibility. In material hardened _in situ_,
in which the internal urethral orifice is tightly closed, the urethral
muscle apparently takes no part in the closure.
Footnote 148:
This is clinically important, since enlargement of the prostate may
interfere with micturition.
Footnote 149:
These terms apply properly only when the adjacent viscera are removed
and the ovaries are actually “suspended” by the broad ligaments. When
the ovary is in its natural position, the surfaces are dorsal and
ventral, the former corresponding to the “external” surface if the
free border is directed outward, to the “internal” if the free edge is
medial.
Footnote 150:
The Fallopian tubes may be regarded, both in structure and morphology,
as prolongations of the uterus (McMurrich).
Footnote 151:
The arrangement is the only exception to the general rule that the
serous cavities are closed. In this case the mucous membrane of the
fimbriated extremity is continuous with the adjacent peritoneum, a
persistence of the embryonic relations of the Müllerian duct.
Footnote 152:
In formalin-hardened subjects there is frequently a pronounced
ring-like constriction at the beginning of the vulva.
Footnote 153:
The term vulva is used here in the sense in which it is understood
generally by English and French veterinarians. In the German works it
is applied only to the labia and other structures around the external
orifice of the urogenital sinus, while the sinus itself is termed the
vestibule of the vagina (Vestibulum vaginæ).
Footnote 154:
Lesbre states that the cornua may attain a length of 45 to 50 cm.
Footnote 155:
The pericardium is described before the heart since it must be
examined first in the laboratory.
Footnote 156:
This is termed the tubercle of Lower in human anatomy and the
tuberculum intervenosum by German veterinary anatomists.
Footnote 157:
These vessels will be described later in their systematic order.
Footnote 158:
The relation to the guttural pouch is not constant. In some
cases—especially when the head and neck are extended—the artery lies
behind the pouch. The backward extension of the latter is variable.
Footnote 159:
By some authors the term facial is applied to the artery only after it
turns around the lower border of the jaw.
Footnote 160:
The artery is conveniently placed at its inflection for taking the
pulse, since it is superficial and lies directly on the bone.
Footnote 161:
This vessel appears to represent both the supraorbital and frontal of
man.
Footnote 162:
The term axillary is often applied to the artery from the first rib to
the point of origin of the subscapular branch.
Footnote 163:
The pulse can be taken where the artery lies on the lateral ligament,
since the pectoral muscle is thin here.
Footnote 164:
This vessel is also termed the A. metacarpea volaris superficialis or
the palmar metacarpal artery.
Footnote 165:
In the great majority of subjects this vessel and some of its branches
are the seat of more or less extensive verminous aneurysm, produced by
the Sclerostomum armatum. In the author’s experience an entirely
normal specimen is quite exceptional in adult horses.
Footnote 166:
The left branch is a descriptive convention rather than a reality,
since the arteries of the small intestines spring from the mesenteric
trunk either directly or by short common stems with an adjacent
vessel.
Footnote 167:
The obliteration in the adult extends a variable distance from the
vesical end toward the origin, but usually involves only a small part.
Footnote 168:
Most of the veins are depicted in the illustrations of the section on
the arteries, to which reference is to be made.
Footnote 169:
Chauveau says “the bronchial veins, which ramify on the bronchi like
the arteries of which they are satellites, open into the great
coronary vein very near its mouth, after having united to form a
single vessel, which sometimes opens directly into the atrium.”
Ellenberger and Baum state that the bronchial and œsophageal veins
open into the vena azygos separately or by a common trunk. Martin
describes a short broncho-œsophageal trunk, but the vein which he
figures as the bronchial does not come from the lungs, but is a small
mediastinal vessel. The author finds such a vessel entering the
terminal part of the œsophageal vein, but no distinct bronchial vein
in the horse.
Footnote 170:
M’Fadyean records a case in which the vein lay on the deep face of the
omo-hyoideus with the carotid artery.
Footnote 171:
The venous angle formed by this junction indicates the position of the
thyroid gland.
Footnote 172:
These are termed by Chauveau and M’Fadyean the subsphenoidal
confluents.
Footnote 173:
The place and mode of termination is quite variable. It may disappear
from the surface of the thigh at any point above the distal third. In
some cases it passes through the anterior part of the gracilis instead
of dipping in between that muscle and the sartorius.
Footnote 174:
This often joins the posterior femoral or the popliteal vein.
Footnote 175:
The term chyle is often applied to the lymph carried by the efferent
vessels of the intestine when it contains products of digestion, and
these vessels may be designated as lacteals or chyle vessels.
Footnote 176:
The lymph vessels of these organs appear to vary considerably in their
mode of termination, and the arrangement needs further study. Some
ducts from the stomach, liver, and spleen open directly into the
cistern.
Footnote 177:
Abscess here can be reached readily by an incision between the vein
and the omo-hyoideus.
Footnote 178:
It is, of course, only the pericardium which comes in contact with the
wall, but it is customary as a matter of convenience to speak of the
relation of the heart as though it were direct.
Footnote 179:
Only the most important differential features of the arrangement of
the vessels as compared with those of the horse will be considered.
Footnote 180:
The homologies of the vessels of the lower parts of the limbs are
still uncertain. The account given here is mainly based on the views
of Sussdorf and Baum.
Footnote 181:
It is difficult to make the arrangement of these vessels clear in a
brief textual description, but a reference to the schematic figure
will explain the main facts.
Footnote 182:
Most of the differences in the veins of the ox are correlated with
those of the arteries of which they are satellites and will not be
described. The account here given consists chiefly of those
differential features which could not be deduced from a knowledge of
the arteries.
Footnote 183:
The upper series is continuous with the posterior mediastinal
(œsophageal) glands and the lower or tracheal glands with the
bronchial. Hence we might well designate the mediastinal glands as
œsophageal (anterior and posterior) and tracheo-bronchial.
Footnote 184:
When enlarged, as is often the case in tuberculosis, this gland
frequently causes difficulty in swallowing and in rumination and
produces chronic or recurrent bloating.
Footnote 185:
The relative weight is subject to wide variation. It is large in
hunting dogs and such as are trained for speed or worked.
Footnote 186:
Limitations of space and the purpose of this work preclude
consideration of the finer structure of the nervous system, for which
ample literature is available.
Footnote 187:
The description given here is intended to present the chief facts in
regard to the brain as they may be studied in the dissecting room. The
vessels and membranes which must be examined first have been
described.
Footnote 188:
Unless care is used in removing the brain the infundibulum is likely
to be torn and the pituitary body left in the cranium. In this case
there is a small opening which communicates with the third ventricle.
Footnote 189:
The fossa corresponds in position to the locus perforatus anticus of
the human brain, but is not pierced by numerous openings for vessels
in the horse.
Footnote 190:
The decussation varies superficially in different specimens. In some
there is a distinct superficial crossing of fibers so that the median
fissure is practically effaced at this point.
Footnote 191:
In the new nomenclature the term lamina quadrigemina is applied to the
dorsal mass of the mid-brain, and the four eminences which it bears
are the corpora quadrigemina.
Footnote 192:
In man a distinct superior brachium connects the superior pair with
the lateral geniculate body, but in the domesticated animals the union
with the optic thalamus is too direct to allow of any definite arm
being recognized.
Footnote 193:
On a strictly embryological basis the optic part of the hypothalamus,
comprising the anterior part of the third ventricle and the structures
associated with it, belong to the telencephalon, but will be
considered here as a matter of convenience.
Footnote 194:
This backward projection of the thalamus is equivalent to the pulvinar
and lateral geniculate body of man, which are not superficially
divided in the domestic animals.
Footnote 195:
In order to study the configuration of the hemisphere it should be
separated from its fellow by median section and from the brain stem by
cutting across the mid-brain. Material for this purpose should be
hardened _in situ_.
Footnote 196:
Termed by Lesbre the parietal fissure and by M’Fadyean the great
oblique fissure.
Footnote 197:
Just above this point is a lobe which is homologous with the insula of
man. When the overhanging gyri which partly conceal it—forming the
operculum—are removed, there are disclosed several short, deeply
placed gyri (Gyri breves).
Footnote 198:
By some authors this is regarded as the homologue of the cruciate
fissure of the dog, but it seems likely that the latter is represented
by a short and inconstant sulcus situated further forward.
Footnote 199:
From the morphological point of view other structures should be
included, but in descriptive anatomy it is usual to limit the
application of the term to the parts enumerated above.
Footnote 200:
It is generally believed that these constitute an olfactory path.
Footnote 201:
It is hardly possible to get an accurate idea of the shape of the
ventricle except by studying a cast of it. The size of the ventricles
varies in different subjects, and it is not rare to find more or less
disparity between the two ventricles of the same brain.
Footnote 202:
The term arose from the striated appearance of the mass in sections
cut in certain planes, the gray matter being cut up into strands by
tracts of white fibers.
Footnote 203:
Although this nerve springs directly from the ganglion, it contains
motor as well as sensory fibers.
Footnote 204:
This ganglion appears to be equivalent to the jugular or superior and
petrous ganglia of man.
Footnote 205:
In some cases the left vagus passes back below the junction of the
jugular veins and the termination of the left brachial vein. It then
runs backward and somewhat dorsally across the left face of the
anterior vena cava to reach its usual position.
Footnote 206:
The nerve lies here about a finger’s breadth above the thyroid gland.
If, however, the gland is enlarged it may come in contact with the
nerve. The same is true in regard to the relation to the anterior
cervical lymph glands.
Footnote 207:
In order to examine the plexus and the origins of its chief branches
conveniently and with as little disturbance of relation as possible,
the subject should be suspended in imitation of the natural position
and the fore limb abducted as much as is necessary.
Footnote 208:
Morphologically the last-named muscle belongs to the extensor group.
In man and in the dog and many other animals it is an extensor in
function.
Footnote 209:
In veterinary works these are frequently termed plantar nerves, which
is an unfortunate misnomer. The writer inclines to the use of the old
term metacarpal or common digital to designate the nerves as far as
their divisions, and the term digital beyond this.
Footnote 210:
The special statements of this description refer to the system of the
horse. A few important differential features will be mentioned in the
account of the nervous system of the other animals.
Footnote 211:
The right and left plexuses communicate with each other, so that both
lungs receive fibers from both vagi.
Footnote 212:
It has been customary to designate these in veterinary works as the
semilunar or cœliac ganglia, but in the horse they evidently include
the anterior mesenteric ganglia as well.
Footnote 213:
A good preparation of the ganglia in the horse is often difficult to
obtain on account of aneurysm of the artery and the formation of a
quantity of connective tissue about it.
Footnote 214:
Only the most salient differences as compared with the horse will be
mentioned.
Footnote 215:
The origin of the lacrimal nerve is such that Ellenberger-Baum and
Martin describe it as a branch of the maxillary nerve.
Footnote 216:
Lesbre terms this the tracheo-œsophageal branch, and considers that it
must be regarded as an accessory or internal recurrent nerve.
Footnote 217:
This belongs to the upper eyelid, but is described here on account of
its position.
Footnote 218:
According to Piersol the system of spaces and canaliculi in the
substantia propria is completely filled by the cells and their
processes, upon which the nutrition of the cornea largely depends. The
lamina elastica anterior, formerly described as a distinct layer
between the corneal epithelium and the substantia propria, does not
exist as such, but there is a condensation of the superficial part, of
the latter, which Rollett termed the anterior limiting layer; it is
not elastic.
Footnote 219:
In albinos the pigment is absent here, as elsewhere, and the iris is
pinkish in color.
Footnote 220:
For the minute structure of the retina reference must be made to
histological works.
Footnote 221:
Ellenberger and Baum regard this as the homologue of the transversus
and obliquus auriculæ of man.
Footnote 222:
There is, strictly speaking, no osseous part of the tube such as
occurs in man. In the horse the cartilage extends to the tympanic
orifice.
Footnote 223:
For the finer structure reference is to be made to the histological
literature.
Footnote 224:
This muscle has been described in the Myology.
Footnote 225:
To prevent a possible misapprehension, it may be stated that the
epidermis primarily molds the corium, and that the glands and
hair-follicles are invaginations of the epidermis.
Footnote 226:
The hoof may be loosened and removed intact by allowing the foot to
macerate or by boiling it.
Footnote 227:
The term foot is used here in the popular sense, _i. e._, to designate
the hoof and the structures inclosed within it.
Footnote 228:
The wide groove at the heels, however, contains chiefly the matrix of
the periople.
Footnote 229:
The lower punctum lacrimale is frequently absent and the corresponding
duct therefore blind. There is often a duct or its remnant which opens
below the inferior turbinal fold, but is not connected behind with the
functional duct.
------------------------------------------------------------------------
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