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Part 1

A TEXT-BOOK of VETERINARY ANATOMY

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

Reprinted July, 1911

PRINTED IN AMERICA

PRESS OF W. B. SAUNDERS COMPANY PHILADELPHIA

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.