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A TEXT-BOOK



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VETERINARY ANATOMY



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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

191 1






BIOLOGY
LIBRARY

G



Copyright, 1910, by W. B. Saunders Company



Reprinted July, 1911



PRINTED IN AMERICA

PRESS OF

B. SAUNDERS COMPA^
PHILADELPMIA



TO

KATHERINE OLDHAM SISSON

IN GRATEFUL RECOGNITION OF CONSTANT

INSPIRATION AND ENCOURAGEMENT

THIS BOOK IS DEDICATED

By THE Author



291148



PREFACE

The lack of a modern and well-illustrated book on the structure of the princi-
pal 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 l^y intra-
vascular injection of formalin has profoundly modified our views concerning the
natural shape of many of the viscera and has rendered possible much greater pre-
cision in topographic statements. The experience of the author during the last
ten j^ears, 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, topog-
raphy 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 generosit}'' 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 \'ertebral Column 24

The Rit)s 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

11



4^; •/; '''. ; Z'^. : CONTENTS

PAGE

Sternum 153

Bones of the Skull 153

The Skull as a AMiole 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 Vertebrae 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

Fascle and Muscles of the Horse 213

Panniculus carnosus 213

Fascia? and Muscles of the Head 213

Fasciae and Muscles of the Neck 224

Fascia? and Muscles of the Back and Loins 235

Fasciie and Muscles of the Tail 238

Muscles of the Thorax 240

Muscles of the Abdomen 245

Muscles of the Thoracic Limb 250

Fascia? 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 ( Hands 346

The Pharynx 348

The (Esophagus 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

Tlie Liver 373

The Spleen 377

The Peritoneum 379



CONTENTS 13



PAGE

Digestive System of the Ox



Digestive System of the Sheep.
Digestive System of the Pig . . . ,
Digestive System of the Dog . . .



382
405
410
423



THE RESPIRATORY SYSTEM

Respiratory System of the Horse 43q

The Nasal Cavity 43g

The Larynx 44q

The Trachea 44g



The Bronchi.



450



The Thoracic Cavity 45q

The Pleurae 45j

The Lungs 453

The Thyroid Claxd of the Horse. 457

The Thymus of the Horse 453

Respiratory System of the Ox 458

Respiratory System of the Pig 454

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

L'rinary Or(;ans of the Ox 478

L^rinary Organs of the Pk; 481

L'rinary Organs of the Dog 483



THE MALE GENITAL ORGANS

Male Genital Organs of the Horse 485

Tlie Testicles 485

The Scrotum 487

The \'as Deferens 488

The Spermatic Cord 489

The Tunica Vaginalis 489

Descent of the Testicles 490

The Vesicula* 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 FEi\L\LE GENITAL ORGANS

Genital Organs of the Mare 508

The Ovaries 508

The L^terine or Fallopian Tubes 511

The L'terus 511

The Vagina 514



14 CONTENTS

P4GE

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 Liml) 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 (Hands 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 Foetal Circulation 606

Blood-vascular System of the Ox 608

The Pericardimn and Heart 608

The Arteries 609

The Veins 621

Lymphatic System of the Ox 623

Circulatory System of the Pk; 626

The Pericardium and Heart 626

The Arteries 627

The Veins 630

Lymphatic System of the Pig 630

Circulatory System of the Doc; 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

Nervoi's System of the Horse 648

The Spinal Cord 648

The Brain 652

The Cranial Nerves 676

Tlie Spinal Nerves. 692



CONTENTS 15

PAGE

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



iESTHESIOLOGY

The Sense Organs and Skin of the Horse 734

The Eye 734

The Ear 747

The Skin 761

The Olfactorv 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 disassociat-
ing 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 mi-
croscope 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 im-
portance 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 mth 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 pro-
fessional 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 topo-
graphic. In the former the body is regarded as consisting of systems of organs or
2 17



18 VETERINARY ANATOMY

apparatus which are similar in origin and structure and are associated in the per-
formarice of {.'ertaii>*iunctions. The divisions of systematic anatomy are:

1. Osteo/ogj''' ' *

2. : A:iithrpk'«gy : /.^ ' :

3. -Mybibgr •••■' •'•'

4. Splanchnology

(1) Digestive System

(2) Respiratory System

(3) Urogenital System

(a) Urinary Organs

(b) Genital Organs

5. Angiology

6. Neurology

7. ^sthesiology

(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 presup-
poses 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 under-
stood at the outset. In the explanation of these terms it is assumed here that
thej^ 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 bod}^ 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 corre-
sponding 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 wliich are as far as possible independent of
the position of the body in spaee and eapable of general application, c. 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 sup-
ports 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 zoology 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 cliitinous 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 primi-
tive axial skeleton, which is of entodermal origin.

The skeleton may be divided primarily into three parts: (1) axial; (2) appen-
dicular; (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 foetus
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 vertebrae
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 func-
tion appears to be that of diffusing concussion. Sesamoid bones, which are
developed in the capsules of some joints or in tendons, may be included m 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 vertebra? 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.

19



20



OSTEOLOGY



STRUCTURE OF BONES'

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 arcliitecture 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.





Fu;. 1.-



FiG. 2.



Sa(;ittai. Section of Lar(;k Mktatarsal
Hoxf: OF Horse.



-Frontal Section of Large Metatarsai-
Bo.NE of Morse, Posterior Part.
S.C., Compact substance; S.s., sijongy substance; Cm., medullary cavity; /•'.»., nutrient foramen. Note the
greater thickness of the compact substance of the inner and anterior parts of the shaft.



In typical long bones the shaft is hollowed to form the medullary cavity (Cavum
medullare).

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.



' Only tlio pross stnicturo is discussed here,
be made to histological works.



For the microscopic structure reference is to



STRUCTURE OF BONES 2!

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 pres-
sure 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 sub-
stance 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 1)etween these a variable amount of spongy bone, here termed diploe.

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 filjrous
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 fiava). 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 infiltra-
tion 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



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