^0rtl| Carolina ^tate ^niUersttg ^l{is book itiae preatnteb bg Elizabeth Stone Digitized by tine Internet Archive in 2009 with funding from NCSU Libraries http://www.archive.org/details/textbookofveterOOsiss A TEXT-BOOK of VETERINARY ANATOMY SEPTIMUS SISSON, S.B., V.S. PROFESSOR OF COMPAPATIVK ANATOAW IN OHRi STATE UMVEPSITV. COLUiWBUS. OHIO MEMBEl' OF THE AMERICAN AS5(.)C1AT10N OF ANATOMISTS WITH 588 ILLUSTRATIONS MANY IN COLORS I'HII.ADEIJ'HIA AND. LONDON W. B. SAUNDERS COMPANY 1910 Coi'YRionr, 1910, by W. B. Saunders Co.mpanv KATHERINE OLDHAM SISSON IN GRATEFUL RECOGXITIOX OF COXSFANT INSPIRATION AND ENCOURAGEMENT THIS BOOK IS DEDICATED Bv THE Author PREFACE The lack of a modern and well-illustrated book on the structure of the jjrinci- pal domestic animals has been acutely felt for a long time Ijy teachers, students, and practitioners of veterinary medicine. The work here offered is the expression of a desire to close this gaj) in our literature. The study of frozen sections and of material which has l)een hardened by intra- vascular injection of formalin has profoundly modified our views concerning the natural shajie 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 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, 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 ])ractitioner. It is believed that the use of black tjTie 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 manj^ 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, l)ut considered it desirable to offer a sort of transitional stage at present. The original illustrations are chiefly reprodvictions of photographs, many of wiiich were taken by Air. F. H. Haskett. The preparation of the pictures for reproduction was carried out by Messrs. J. V. Alteneder and W. J. Xorris. 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 Schmultz in Berlin, and to their publishers for permission to use or to copy figures from their most excellent works. Their generositj' in tliis matter has made it possil)le to supply this text with a larger number of high-class illustrations than is to be found in anj' other. A few figures have Ijeen taken from other sources, and proper credit has Ijeen given in each case. For checking over certain data and for assistance in the correction of the ])roofs 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 jjublishers 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 SiSSOX. September, 1910 CONTENTS IXTKODUCTIOX OSTEOLOGY page The Skeleton 19 Structure of Bones 20 Development and Growth of Bone 22 Composition ami Physical Properties of r()n( : 23 Descriptive Terms 23 The Vertebral Column 24 The Rihs and Costal Cartilages 25 Costal Cartilages '21) 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 4.5 Bones of the Skull 47 Cranium 47 Face 57 The Skull as a Whole 65 The Cranial Cavity 69 The Xasal Cavity 71 The Paranasal Sinuses 72 Bones of the Thoracic Limb 74 Bones of the Pelvic Limb "2 Ski:leton 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 1-7 Bones of the Pelvic Limb I'^l Skeleton of the Pig 136 138 139 139 Vertebral Cohmin 1''6 Ribs Sternum Bones of the Skull The Skull as a Whole 1*4 Bones of the Thoracic Limb 146 Bones of the Pelvic Limb 148 Skeleton of the Dou ' _ Vertebral Column ^^^ Rib: 153 12 PAGE Sternum ^^^ Bones of the Skull '-^3 The Skull as a Whole ^^^ Hones of the Thoracic Liml). . '"-' Hones of the Pelvic Liml) "'•'' AKTHROLOCn' SVNARTHIJOSKS. lti'.» DlAHTHKOSES ' ~" AmI'IIIAHTHHOSES ' ' - AuTicri.ATioNs OP tub; House ' '- Joints and Liframents of the Vertebra- ' ''- Atlanto-o(•(•ipital Articulation '''■ Costo-vertebral Articulations I ' ' C'osto-choiKlral Articulations 1 ' ^ f 'hondro-sternal Articulations . ^ '^ Sternal Joints ami Ligament; . ''"^ Articulations of the Skull '"•> Articulations of the Thoracic Limb. . 1^" Articulations of the Pelvic Limb !'•" AiiTiciLATiONs OK TiiK Ox. Pk;. AND Doii -D:! THE MUSCrLAK SYSTEM— MYOLOCY TnK Mfsci.Es AND Accessory Strt'ctires I'll FaSCI.K AND MlSCI.ES OF THE HORSE '-'13 Panniculus carnosus 213 Fascia" and Muscles of the Head -13 Kascia' and Muscles of the Xcck 224 Fascia' and Muscles of the Hack and Loins 23") Fascia' and Muscles of the Tail 23S Muscles of the Thorax 240 Muscles of the Abdomen 24."i Muscles of the Thoracic Limb 2.")() Fascia- and Muscles of the Pelvic Limb 27:i Muscles ok the Ox. 2(t.") Muscles ok the Pig 311 Mi'SCLES OK THE D()(i 31S 1)I( SPLA\(HN()1>()GY- FESTIVE SVSTE.M OF THE IIoRSE The Mouth The Tonjiue The Teeth -TH]'; dk; I'lSTHE SYSTh :m 330 330 335 33S The Salivary Cdands The Pharvnx 34ti 34S The O'".sophaf;us The .\l)doiiiinal Cavity. . The Peritoneum. . . The Pelvic Cavity The Stomach The Snii.ll Intestine The Large hitcsliiK The Pani'ieas The Liver. The Spleen . The Peritoneum 3o0 352 353 354 357 3()0 3()3 371 373 377 379 CONTEXTS 13 Digestive System or the Ox 3,S2 Digestive System of the Sheep 40,-, Digestive System of the Pig 410 Digestive System of the Dog 423 THE RESPIRATOKV SYSTEM Respikatory System of the Horse 436 The Nasal Cavity. 436 Tlio Larynx 44O The Trachea . 448 Tlie Bronchi 4.50 The Thoracic Cavity 4.i0 Tlie Pleura 451 The Lungs 4.'):j The Thyroid Gland of the Horse 457 The Thymts of the Horse 458 Respiratory System of the Ox 458 Respiratory" System of the Pig . . 464 Respiratory- Sy'stem of the Dog 466 THE uri)(;exital system L'rixary Organs of the Horse 469 The Kidneys 469 The Ureters 47") The Urinary Bladch'r 47o The Adrenal Bodies 477 Urinary Organs of the Ox 47s Urinary Organs of the Pic. 4S1 Urinary Organs of the Dog 48o THE MALE GENITAL ORGANS ^L\LE Genital Organs of the Horse.... 48o The Testicles 485 The Scrotum 487 The ^■as Deferens. 488 The Spermatic Conl 489 The Tunica Yaginali.^ 489 Descent of the Testicles. . 490 The YesicuUf Seminales . . 491 The Prostate 493 The Uterds Masculinus 493 The Bulbo-urethral Glands 493 Tlie Penis 494 The Prepuce 496 Male Genital Organs of the Ox -iOO Male Genital Organs of the Pk; ■)04 Male Genital Organs of the Do(; 506 THE FEMALE GENITAL ORGANS Genital Organs of the Mai;e 508 The Ovaries ''08 The Uterine or Fallopian Tubes -'H The Uterus 'H The Vagina -i 1 4 14 CONTENTS PtGE The Vulva 514 Tin- I'lrlhra 515 The Mammary Glaiuls 516 Genital Organs of the Cow 517 Genital Okgans of the Sow 521 Genital Ougans of the Bitch 522 ANGIOLOGY The Organs of CiRriLATioN 524 Ulood-vascvlar System of the Horse 525 The Pericardium 525 The Heart 526 The Pulmonary Artery 535 The Systemic Arteries 535 The Coronary Arteries 537 The BracliiocephaHc 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 Linib 578 The Veins 585 The Pulmonary \'eins 585 The Systemic Veins 585 The Anterior Vena Cava and its Tributaries 586 The Posterior Vena Ca\a and its Tributaries 595 The Lymphatic System 599 Lymphatic System of the Horse tiOO The Lymph (Jlands and Vessels of the Head and Neck 1501 The Lymph Glanils and Vessels of the Thorax 603 The Lymph Glands and Vessels of the Abdomen and Pelvis 604 The Lymph Glands an reference is to be made to histoIoRical works. STRUCTURE OF BONES 21 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 occuiDied 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 laj'er of very dense bone, the tabula vitrea, and between 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 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 l)y 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 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 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 comjjact 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 peri]ihery 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 prolaably are concerned in mediating the muscle sense (Kopsch). 22 OSTEOLOGY DEVELOPMENT AND GROWTH OF BONE ' The priiiiitivp embryonal skeloton consists of cartilaKO and fibrous tissue, in which the l)ones develop. The process is termed ossification or osteogenesis, and is effected essentially by bone-producing cells, calletl osteoblasts. It is customary, therefore, to desijiiiate as membrane bones those which are developed in fibrous tissue, and as cartilage bones those which are preformed in cartilage. The princi- pal membrane bones are those of the roof and sides of the cranium and most of the bones of the face. The cartilage bones comprise, tlierefore, most of the skeleton. Correspondingly we distinguish intramembranous and endochondral ossification. In intramembranous develoiiment the ])ro('ess 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 net- work of bony trabeculae. The trabeculse 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 funda- mentally the same, but not quite so simple. Osteo- blasts emigrate from the deep face of the perichon- drium or primitive periosteum into the cartilage and cau.se 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 b^' pro- cesses of the osteogenic tissue. There is thus formed a sort of scaffolding of calcareous trabeculse on which the bone is constructed l)y the osteoblasts. At the same time perichondral bone is formed by the osteo- blasts of the primitive periosteum. The calcified cartilage is broken do-mi and absorbed through the agency of large cells called osteoclasts, and is re- placed by bone deposited by the osteoblasts. The osteoclasts also cause alisorption 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 epiphyses or extremity. Many bones have secondary centers from which jirocesses 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 con- tinued o.s.sification at either end of the diaphysis is made by a layer of actively growing cartilage— the epiphyseal cartilage— which intervenes between the diaph- 'Only a brief gpneral statement of osteogenesis can be made here; details must be sought in cmbryologiral literature. —Left Femur of Young Pig, ExTKRNAi, View, to .Show Di- vision OF A Long Bonk into Shaft («) and Extremities. Proximal extremity consists of two parts, head (/i) and trochanter major {t. m.), which have separate centers of ossification. Distal extrem- ity consists of trochlea (/) and condyles (c): e.l., epiphyseal cartilages; 8/., supracondyloid fossa. CHEMICAL COMPOSITION OF BONE — DESCRIPTIVE TERMS 23 ysis and the epiphj-sis. 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 ossifica- tion, 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 enlarge- ments. 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 ver.y fragile. Conversely, decalcification, while not affecting the form and size of the bone, renders it soft and pliable. The animal matter when boiled >-ields gelatin. The following table represents the composition in lOU parts of ox bone of average quality : Gelatin 33.30 Phosphate of Ume 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-milIimeter cube of compact bone of the ox will resist pressure up to 852 pounds, if the pressure be applied in the line of the lamellae (Rauber). Its tensile strength is estimated to be nearly twdce 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 appUed 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 i 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 epi- condyle. 24 OSTEOLOOY A trochlea is a puUc^y-likc articular mass. A glenoid cavity (("avitas glenoiilalis) is a shallow articular depression, and a cotyloid cavity or acetabulum is a deeper one. The term facet is eonmionly 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. \ foramen is a perforation for the transmission of vessels, nerves, etc. A sinus nr antrum is an air-cavity. Other terms, such as canal, fissure, notch, etc., require no explanation.' VERTEBRAL COLUMN The vertebral column (Columna vertel)ralis) 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 vertebrae have become fused to form a single bony mass with which the pelvic girdle articulates. Vertebra? so fused are termed fixed or "false" vertebrae (Vertebrae immoliiles), as distinguished from the movable or "true" vertebrae (\'ertebrff mobiles). The column is subdivided for descrip- tion into five regions, which are named ac- cording to the part of the body in which they are placed. Thus the vertebrae are designated as cervical, thoracic (or dorsal), lumbar, sacral, and coccygeal or caudal (Vertebra; cervicales, thoracales, lumbales, sacrales, coccygea?). The number of verte- brae in a given species is fairly constant in each region except the last, so that the ver- tebral formula may be expressed (for the horse, for example) as follows: C,T„L„S,Cy„_,, The vertebrae in a given region have special characters by which they may be distinguished from those of other regions, and individual vertebrae have characters which are more or less clearly recognizable. All typical vertebrae have a common plan of structure, which nnist first be understood. The parts of which a vertebra consists arc the body or centrum, the arch, and the processes. The body (Cor])us vertebra^ is the more or less cylindrical mass on which the other parts are constructed. The anterior and po.sterior extremities of the body are attached to the adjacent vertebra' 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 (Fovete costales) at the extremities for articulation with the heads of two pairs of ribs. The arch (.\rcus vertebra-) 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 ' As mi(ilit 1)0 expected from the history of .iniitoniy, a good many of these terms are more or less interchangeable; furthermore, a given skeletal feature m:iy differgreatly in various species. To illustrate plan of structun Jaeef >F Horse. rtebra;. THE RIBS 25 cut into in front and beliind by tiie vertebral notches (Incisura vortebralis cranialis, caudalis). The notches of two adjacent vertebra? form intervertebral foramina for the passage of the spinal nerves and vessels; in some vertcliru', however, these are complete foramina instead of notches. The laminje are plates which complete the arch dorsallj', 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 con- tains the spinal cord and its coverings and vessels. The articular processes, two anterior and two posterior (Processus articulares craniales. cautlales), project from the borders of the arch on either side. They present joint surfaces adapted to those of adjacent vertebrs, 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 vertebrse. 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 liga- ments. Some vertebrae have also a ventral or haemal spine. Mammillary processes (Processus mammillares) are found in most animals on the last thoracic and anterior lumbar vertebrae 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 vertebrae 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 bodj- 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 epiphj'seal plates at the extremities of the body. Sometimes there are at first two centers for the body which soon fuse. The process of ossifi- cation extends from the lateral centers to form not onlj- 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 (.neuro- central sjTichondrosis), but fuse in the first few months. THE RIBS The ribs (Costae) are elongated curved bones which form the skeleton of the lateral thoracic walls. They are arranged serially in pairs which usually corre- spond in number to the thoracic vertebrae. 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 (Co.stae sternales s. verae); the remainder are asternal or "false" ribs (Costae asternales s. spuriac). Ribs at the end of the series which have their ventral ends free in the abdominal wall are named floating ribs (Costae fluctuantes). The intervals be- tween the ribs are termed intercostal spaces (Spatia intercostalia). A typical rib' consists of a shaft and two extremities. The shaft (Corpus costae) '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. 26 OSTEOLOGY is l)aiul-likc and varies much in l(>ngtli, lircadth, and curvature. In the case of some ribs tlie curvature is not uniform, but is most accentuated at a certain point, termed the angle of the rib (Aiifjulus costa>); this occurs at a variable distance from the vertcl)ral end, and is usually marked by a rough ridge. The direction also varies; the first rib is almost vertical, while the remainder slope liackward in increasing degree. The external surface is convex, and the internal flattened from etige to etlge; on the latter, close to the posterior border, is the costal groove (Sulcus costalis), which fades out vcntrally. It contains the intercostal vein. The anterior and posterior borders ari' thin and sharp on some ribs, rounded on others. The vertebral extremity (Extremitas vertebralis) consists of the head, neck, and tubercle. The head (Capitulum costa;) is the actual end of the rib, and is rounded and .somewhat enlarged. It presents two facets (Fades articularis capituli costa") for articulation with the bodies of two adjacent thoracic vertebrae; these surfaces are separated by a groove in which the conjugal ligament is attached. The neck (CoUum costip) joins the head to the shaft. It varies in length and diameter. Its outer surface is rough, its inner smooth. The tubercle (Tuberculum costa;) projects backward at the junction of the neck and shaft. It has a facet (Facies articularis tuberculi costa?) for articulation with the transverse process of the posterior vertebra of the two with which the head articulates. The tubercle grailually 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 co.stal 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 rilw. 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 tlie thorax ventrally, ami articulates with the cartilages of the sternal ribs laterally. It consists of six to eight bony segments (Sternebne) 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 arc present. Its anterior extremity, the manubrium stemi or presternum, is specially affected by the latter factor, being l)road and strong when the clavicles are well developed and articulate Avith it (as in man), relatively small and laterally com- pre.s.sed 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 mesostemum (Corpus sterni) presents laterally, at the junction of the segments, concave facets (Incisunr costales) for articulation with the cartilages of the .sternal ribs. The posterior extremity or metastemum presents tiie xiphoid (or ensiform) cartilage (Processus xiphoiihnis) ; tliis is thin and plate-like, as in the horse and ox, or narrow and short, as in the jiig 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, anil 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 THE THORAX — THE BOXES OF THE THOKACIC LIMB 27 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 vertebra? dorsally, the ribs and their cartilages laterally, antl 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 riljs 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 cavitie.s) 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 clas.sed 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 immov- able 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 Unes 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 thoracicae), 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 mth 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 develop- ment of the cla\-icle is in conformity with the function of the limb. Thus in typical quadrupeds, 28 OSTEOLOGY such as the horse and ox, in which the forcliniljs arc used only for support and locomotion, the clavicle is absent. Other animals which use these limbs for Rrasprng, burrowinK, climbing, etc. (c.<7.,man, apes, moles), have well-developed clavicle.s which connect the scapula withthesternum. The ann (Brarliiiim) contains a single long bone, the humerus or arm hone. In the forearm (Antihracliiuni) are two long hones, the radius and ulna. These vary in relative size anil mobility. In the horse and ox the two bones are fused, and tiie lower i)art of the limb is fixed in the position of pronation. The radius is plaeed 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 ratlins. In the dog the ulna is also w-cll 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 anti- braciiial, and a tlistal or metacarpal. The bones of the proximal row. named from the radial to the ulnar side (/. e., from within outward), are the radial, intermediate, ulnar, and accessory carpal bones. The bones of the di.^tal 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 anat- omists, 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 ap- pended for comparison. The Latin terms and abbreviated notations are given in parenthesis. Radial (Os carpi radiale, Cr) Scaphoid Internu'iliate (Os carpi intermedium, Ci) Semilunar Ulnar (Os carpi ulnarc, Cu) Cuneiform .Acces.sory (Os carpi accessorium, Ca) Pisiform rir.'^t carpal (Os carpale primum, CI) Trapezium Second carp;d (Os I'arpale secundum, C2) Trapezoid Third carpal (Os carpale tertium, C3) Os magnum P'ourth carpal (Os carpale quartum, C4) Unciform The central carpal bone (Os carpi centrale) is omitted, since it is not a separate clement in the animals under consideration here. The metacarpus contains typically five metacarpal bones (Ossa metacarpalia I-V), one for each digit; the.y arc long bones and are designated numerically from within outward. This arrangement occurs in the dog, although the first meta- carpal 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 artioilactyl forms. In the hor.se the first and fifth metacarpals are absent, the third is the large supporting metacarpal bone and carries the single digit, while the seconil and fourth arc 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 specitil descriptions to follow. The fossil remains of the ancestors of the existing Kquida' illustrate in a most complete man- ner the reduction which has occurred in this respect. The earliest known ancestor of the horse, Eohippus or Ilyracolherium 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 gradu.al evolution of the race from this primitive animal, which was about the size of the domestic cat. There is reason to belie\e that earlier forms had five digits. The digits fDigiti manus) are homologous with the fingers of man, and are typically five in niunber. 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 BONE.S OF THE PELVIC LIMB 29 the weight, while the second and fifth are reduced. The existing horse has a single digit, the third of his polythictyl ancestors. Tlie 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 inclos<>d in the hoof or claw, and is modified to conform to the latter. The sesamoid bones (Ossa sesamoidea) are develo])ed along the course of the flexor tendons or in the joint capsules. Two proximal sesamoids (Ossa sesamoidea phalangis primiB) occur at the flexor side of the meta- carpo-phalangeal joint and form a pulley for the flexor tendon. The distal sesamoids (Ossa sesamoidea phalangis tertiae) 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 meta- carpo-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 pelvinse) consists of the os coxae 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 vertebrae, constitute the bony pelvis. The os coxje 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. The.se 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 30 OSTEOLOGY present, as in the pifj; and dog. They are best designated niiiiu'ticaliy as first tarsal, second tarsal, etc. The central tarsal is interposed between the rows. The prccciiinK terms are anplicizcil abbreviations of those introdueed by Oegenbaur into comparative anatomy. The Latin names and synonyms are given in the following table. Til>ial (Os tarsi tibialc, Tt.) Astragahis or Talus Fibular (Os tarsi filnilare, Tf.) Calcaneus or Os calcis Central (Os tarsi rentrale, Te.) Seaphoid or Navicular First Tarsal (Os tarsale primum, Tl) First or internal cuneiform Second Tarsal (Os tarsale .secundum, T2) Second or middle cuneiform Third Tarsal (<)s tarsale tertium, T3) Third or external cuneiform Fourth Tarsal (Os tarsale (luartuin, 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. Fio. .5.— Skeleton of Hobsk. with Odtline of Tontocr of Tiont. v.,r.,hr».''V/^"^',V"i'""'?u'""";' "'■'"''"'• '"■• '■"•'" """■'"='<' ^""■''™: '■■''■■ ""venteenth thoracic vertebra. /./. first lumbar vertebra; B.L.. s..«h lumbar vertebra; K. .sacrum; /.«.. first corcvgeal vertebra- /«..S..H..xtee„th coccygeal vertebra; ff./e., si.vth rib; e.K.. costal cartilage; /«.«., last rib; 1, scapula; I', cartilage fi 7.Tn', 7 "'""', -T^'- ^ ^'""""'' ••' """■""' •■P'™"''vle of humerus; 5, external tuberosity of humerus; ™ n ZriV; ;i"^ "•^'^"^^ lO.crv..: 11. accessory carpal hone; 12, meta: 7 s^hium- 8 ent rTf,T^ ,„ ; "'^"' '■"""'"''■ "• "'"'"^ '«■ •«'• ^•^•"''•■'' ■'"'' '°"'™"' -"'"-^ of '»"">: ■ ■ bi-Tham "r ■ '»•""■, "".'•" ""'^"' 27, trochanter minor; 28. trochanter tertius; 20. patella UnerElcnblr^ •' »" rr\ ';'''"^ "^^ "'"""■ 22. tarsus: 24. tuber calcis; 25. metatarsus; 26. digit tAiier tllcnbergcr-Baum, Auat. for Kiiuatler.) "■»". THE SKELETON OF THE HORSE 31 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 Pehic limbs 40 205 In this enumeration the average number of coccygeal vertebra- is taken to be IS, the tem- poral and OS coxfe 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^Tj^LgSjCy^^ a>^ "Anterior articu- lar process of axis l" Anterior part of transverse pro- cess Posterior part of transverse pro- cess Dorsal crest ^ Posterior articu- lar process Anterior articu- lar process Fig. 6. — Cervicil Vehtebr.e of Hohse. DoRS.^L View. (After Schmaltz, Atlas d. .\nat. d. Pferdes.) Fossa atlantis Basi-occipital Orri pilal condyle I'(iraiiia.s-loid (sti/l- oid) process :^ERVICAL VeRTEBR.E OF HoRSE, VENTRAL ViEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.) 32 THE SKELETON OF THE HORSE THE CERVICAL VERTEBRA These are quadrangular, massive, and longer than the vertebrae 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 vertebra^. Each presents a median ventral spine or crest, which becomes more prominent as it is traced backward, and is tubercuhite 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 vertebra', and wide at either end; it gives attachment to the superior com- mon 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 Ijy a transverse furrow, in which there are several foramina through which veins emerge from the spongy sub.stance of the body. The anterior extremity presents a head which lias an oval articular surface, strongly convex, and wider above than below. The posterior extremity is larger and has a nearly circular cotyloid cavity. 2. The arches are large and strong. They are perforated on either side by a ArticuUiT processes Anterior arliculnr process^ TninisriTse process Articular cavity Facet for tubercle of first rib Facets for head of first rib Fio. 8.— Last CKRVirAi, an-i. Fms^T TnORAcir Vkhtebr,*: ok Horsk, Lateral View, (.\fter Schmaltz, Atla.« d. Anat. d. Ptcrdes.) foramen which communicates with the foramen transversarium. The vertebral notches are large. 3. The articular processes are large. Their articular surfaces are extensive, oval m outline, and slightly concave; the anterior ones are directed upward and mward, the posterior downward and outward. The remaining surface is mainly roughened for ligamentous and nmscular 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 tli,. arch and one from the body; between these is the foramen transversarium, through which the vertebral artery passes. The process divides externally mto 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 behmd, and is connected by ridges with the posterior articular processes. The sixth cervical vertebra has the following distinctive features: It is shorter and wid.-r than the fifth. The arch is large, especially posteriorly. The posterior THE ATLAS 33 articular processes are shorter, thicker and further apart; they are connected with the anterior ones by a thick ridge. The spinous process is less riuliniontary; it is half an inch or more (ca. 1.5 cm.) in height. The transverse processes iiave three branches; the third part is a thick, ahnost sagittal plate, which form.s 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 vertebnc, but are short and thicker. The foramen transversarium i.s large; below its posterior end is a fossa. The ventral crest is small and is less prominent posteriorly. Tlie third branch of the transverse process and the fossa are sometimes alisent on one side. The seventh cervical vertebra is readily distinguished by the following charac- ters: It is shorter and wider than the others. The body is flattened dor.so-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 jjostcrior pair. The spinous process is an inch or more (ca. 3 cm.) in height. The transverse process is unilivided, 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. Foramen Iransver- sarium Ventral areh atlantis [G. 9. — .\tlas of Horse, .\nterior \\v.\ (.\fter Schmaltz, .\tlas d. .\Dat. d. Pferdes.) Ventral tubercle Fig. 10. — Atlas of Horse. Posterior View Schmaltz, .\tlas d. .\nat. 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 largo vertebral foramen, and consists of two lateral masses connected by dorsal and ventral arches. The lateral masses (Massse laterales) present two deep oval anterior articular cavities (Fovete articulares craniales) which receive the occipital condyles; they are separated by a «ade 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 some- what saddle-shaped; the>- 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 (Tubercu- lum 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 3 34 THK SKELETON OK THE HORSE tlic dorsal. On its lower surface is the ventral tubercle (Tuhorculum ventrale), into which the terminal tendon of the longus colli muscle is inserted. The upper face has po.-iteriorly a transversely concave articular surface (Fovea dentis), on which the dens or odontoid jiroccss of the axis rests. In front of this is a transverse rough excavation for the attachment of the odontoid ligament. The wings ( Ahe) are modified transverse processes. They arc 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 tlie interverte- bral foramen by a short groove. Tiie pc^sterior one is the foramen transversarium. Development. — The atlas o.ssifies 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 Ijirtli the bone consists of three pieces — the ventral arch and two lateral parts, which arc separated by a layer of cartilage in the dorsal median line. These parts are usually fused at about six months. Axis I iilcrverlibrdl for. I l^osl. artic. process j Ant. arlic. process Dorsal crest ^mamen ForaiZt I'll'rrrrlebral trnnsrersarium >"•"""" Foramen IrdHst'ir.sdriiim Veidrid crest Ventral crest Fig. 11.— Fibst Three Cervical Vebtebr.e of IIor.se. Lateral View, (.\fter Schmaltz, .\tlas .1 \nat d Pferdes.) The Axis The axis (Epistropheus) is the longest of the vertebra>, 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 wiiich terminates in a tubercle behind. The anterior extremity presents centrally the odontoid process (Dens); this has a convex articular surface ventrally for articulation witli the ventral arch of the atlas and two rough depressions for the attachment of the odontoid ligament dor^ally' I'lankmg this on either sule are the modified anterior articular processes, which have saddle-shapetl articular surfaces confluent below with that of the dens The posterior extremity has the usual cavity. Th(> arch presents in the young sul)ject a notch on each side of its anterior border; this is converte.l into a foramen by a ligament which usually ossifies later. 1 he posterior border has the usual notches. Tli(> posterior articular processes are typical. The transverse processes are small,^ single, and proi(>ct backward The roramen transversarium is small. Thr spinous process is very large and strong. Its free border is rough, thickens posteriorly, and is continued to the articular processes bv two ridges The lateral surfaces are concave and rough for muscular attachment THE THOHACIC VERTEUR.K 35 Development. — The axis has six or seven centers of ossification. In aiklition to the usual five, one or two appear for the dens, which is regarded as the displaced body of the atlas. A nucleus belli nd the dens, which remains distinct to three or four years of age, is considered by Lesbre to be the head of the axis. Occipital crest Median crest PanimiiMiiiil process^ L Dorsal arch of atlas Anterior articular process nj axis I nterrertebral foramen i^ in i Foramen transversarium Post, articular processes Ant. articular processes Transverse process Dorsal crest — Foramen transversarium Post, articular processes Fig. 12. — Occipital Bo.ve and First Three Ckrvical Vf.htebh.e of Horse, Dorsal View. (After Schmaltz, .Atlas d. .\nat. d. Hfenles.) THE THORAQC VERTEBRA These (Vertebne 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 36 THE SKELETON OF THE HORSE processes. Those in the middle of the series are the most t3'pical 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, cau- dalis), which, with those of adjacent vertebrae, form sockets for the heads of the ribs. 2. The arches are small. Their posterior notches are relatively large and arc often converted into rdrainiiia. 3. The articular processes are small. Tiie anterior jmir are in fact represented Anterior nrliriilar process Facet for head of Posterior artieulnr process Transi'crse processes Faci'ls for tubercles of ribs 'tiects for heads of ribs Intirnrtilirdl foramina Facet fur tubercle of rib .ric Vkrtebr.*: of Ho d. .\nat. d. Pferdes.) (After Schmaltz, Atlas only by two oval facets on the anterior part of the laminae which face almost directly upward. The jiosterior pair spring from the base of the spinous process; their facets face almost directly dowiiward. 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 sK)pes upward and Ijackward. 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 charac- ters: The body is wide and flattened dorso-vcntrally. In front it has a head like THE THORACIC VERTEBRjE 37 the cervical vertebra\ 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 verteljra^ 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 articu- lation 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 transver.se processes. 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 vertebrse at either end of the region. (2) The transverse processes diminish in size and are placed lower down Spine — Facet for head "^"^ Body of rib ^ Fig. 14. — Third Thohacic ^'ERTKBR.K avd I'pi OF Rib of Horse, .\nterior View. Schmaltz. Atlas d. .\nat. d. Pferdes.) Facets , heads of ribs Fig. 15. — Lowe Schmaltz 'ciilnr rarity of body Horse, Posterior View. .\tlas d. .\nat. d. Pferdes.) 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. 38 THE SKELKTON OF THE HORSE THE LUMBAR VERTEBRAE TIk" lumbar vertebrae (N'ertchni' lunil)al('s) are usually six hi number in the horse. They arc cliaractcrized by the size and form of their transverse processes. The bodies of the first three are triangular on cross-section, and present a Spine A nUrior arliciilar processes ■imsrcrse process Transrcrse process Facet far head of lirsl Fio. 16. — First THORAric Vertebra an-d Upper Part of First Rib of Horse, .\n'terior View. (After Schmaltz, .Vtlas d. .\nat. d. Pferdes.) distinct ventral crest. From the fourth backward they i)ecome wider and flatter and the ventral crest fades out. 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. The anterior articular processes are fused with the mammillary processes, and MammiUary processes Facet for head of rib Facet for tubercle of rib liderrerle 'oslcrior iniiciilnr processes Ilciid of rib Fi.;. 17. — Last Two Tii on\ric ANB l-'i .IBAR VeH I d. .\nnt. (.\ftcr Schmaltz present superiorly concave surfaces for articulation with the posterior pair of the precediiiK vertebra. The posterior articular processes project distinctly from the arch at the ba,se of the si)inous i)n)cess, and have vent rally convex articular sur- faces, which fit into the grooved surfaces of the anterior ])air of the next vertebra. The transverse processes are large plates, flattened dorso-ventrallv, which project outward ami usually curve slightly downward; their length increases to THE SACRUM 39 the third and fourth, and then diminishes to the last, which is the shortest. The first one or two usually curve somewhat backwartl, 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 resemlilc those of the last two thoracic vertebra;. 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 vertebra^. The extremi- ties of the transverse processes remain cartilaginous for some time after ossification is otherwise complete. 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 Ma m III illfi rij processes Aiiteriar articular prac Transverse process Ventral spine N^I^LjP^ Body Fig. is. — .Skcoxd Lumbar Vp:rtebra of Horse, Anterior View. (After Schmaltz, .\tla.-5 d. .\nat. d. Pferden.) may or may not be compensated by an aflditional thoracic \-ertebra. This variation is not more common in certain races as Sanson and others have maintained. \ erj' few cases are recorded of seven lumbar vertebra? — 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 vertebrje 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 40 THE SKELETON OF THE HOESE foramina (Foramina sacralia dorsalia); the dorsal branches of the sacral nerves enierKc through tlu'in. 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 (Linea' transversir), which indicate the demarcation of the bodies of the vertebrtr. 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 tlorsal and ventral foramina communicate with the sacral canal and are together eciuivalent to the usual intervertebral foramina. 2 C 2' 1' Fio. 19. — Sacbi-m of Horse, Dobso-latf.hal View. r, Body of first sacral vertebra; .1. arch of first vertebra; Ca. sacral canal; P.s. 1-5 .sacriil .-pines- Pt »in«p. of sacrum; I. 1', surfaces for articulation with transverse processes of last lumbar vertebra- /■' a auricul-i'r rs[!',T -:-''''7'="'»'-»™'=«f»«'- 3-C, dorsal sacral foramina; 7, in.erarcuate space; S, lateral border"; A, apex The lateral borders are rough, thick in front, thin Ijehiiul. The base (Basis (j.ssis .sacri) is directed forward, and is relatively very wide It presents centrally the body of the first sacral segment, which is wide transversely Hattened dor.so-ventrally, and has a rounded .surface which articulates with the last lumbar vertebra through the medium of an intervertebral fibro-cartilage \r ' Ti . '^-'^'■.g'" I'rojects 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 sur a.vs internally for articulation with those of the last lumbar vertebra. On with ,7''',"^/ '''■'^'', '^ ^ «'""°^1' "«t''h which is converted into a foramen bv apposition with the last lumbar. 1 he lateral parts of the base, the wings or al* (Ala- sacrales), THE COCCYGEAL VERTEBRiE 41 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 lum- bar. 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 irregu- lar. The rest of the dorsal surface of the wing is roughened for ligamentous attach- ment, while the ventral surface is smooth. The apex (.\pex ossis sacri) is the posterior aspect of the last sacral vertebra and is ciuite 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 \^-ith the angles rounded off; its width is about twice its height. Traced backward it is seen to diminish in size rapidly, and the po.sterior 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. Spine Vertebral canal Body Posterior end of body Fig. 20. — First Coccvghal Vertebra of Horse, Fig. 21. — First Coccygeal Vertebra of Horse, Left View. (After Schmaltz, Atlas d. Aoat. Dorsal View, (.\fter Schmaltz, Atlas d. .\nat. d. Pferdes.) d. Pferdes.) Development. — The several sacral vertebrte ossify in the t^-pical 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 VERTEBRA These (Vertebrae coccygeal) vary considerably in number, but eighteen maj' 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 bocUes only. The first three have bodies which are somewhat flattened dorso-ventrally, constricted in the middle, and have at the ends slightlj- convex, elliptical, articular surfaces. The ventral surface has a median groove for the coccj'geal arterj-. The arch is small and triangular; it is formed of two fiat 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 42 THE SKELETON OF THE HORSE gradually fade out, and the vertebra? 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 lietween fourteen and twenty- one. In old age the fii-st is often fused with the sacrum, and sometunes with the second. Ihe 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 tlioracic vertebra?, and diminish to the fifteenth or sixteenth thoracic. Behinil this they are about equal in height as far as the last lumbar and first sacral, which arc 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 back- ward is most tlecided 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 tlie sacrum is nachetl; 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 nmscles of the spine. The floor of the groove is formed by the lamina? 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 vertebra? 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 ])rojection or angle. At the second thoracic vertebra a gentle curve, con- cave ventrallj', 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 bj- the bodies. The vertebral canal, of cour.se, corresponds in curvature to the bodies. Its caliber varies greatly at different i)oints. 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 tlie axis (ca. 2..5 cm. wide, 3 cm. high). It widens con.sidcrably 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 consitlerably to contain the lumbar enlargement of the spinal cord. The caliber diminishes very rapidly from the second sacral segment liackward, and the canal cea.ses to l)e 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 lumba- region. The transverse processes arc 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 tlie ribs. On the first thoracic vertebra this facet is large, deeply con- THE RIBS 43 cave, and situated alnio.st directly outward from the cavity for the head of tiie rib; traced backward it becoine.s 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 .seven- teenth thoracic vertebriP. 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 hor.sc 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. 1 60.0 22.7% 37.2% 12.0% 7.6% 20.5% 74.0 100.0 36.5 22.5 58.0 25.4% Thoracic Lumbar Sacral 9S.0 31.5 20.0 .^4 0 34.4% 12.5% 7.7% 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 t3rpical rib has the following characters: The shaft or body (Corpus costae) 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 ])art is, however, grooved longitudin- ally. A distinct angle, ('. 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 costa>) has an articular surface (Fades articularis capituli costa>), 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 vertebrae 44 THE SKELETON OF THE HORSE Tubercle and the intcrvcrtpbral filjro-cartilage. The neck (Collum costse) is roughened above and in front. Tlie tubercle (Tul)ercuhnn cost;e) is placed above and behind the junction of neck and shaft; it has a small surface (Fades articularis tuberculi costa;) for articulation with the transverse process of the corresponding thoracic vertebra. The sternal extremity (Extreniitas 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 jiait 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 flirected 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. 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 six- teenth.) The serial position of the other ribs may l)e determined approximately by the follow- ing considerations: The length increases from the first to the tenth and eleventh and then diminishes. The width increases somewhat to tlie sixth and then diminishes. The anterior border is thin and sharp from tlie 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 de- gree rapidly from the first to the seventh, remains about the same to the sixteenth, and then decreases very noticeably. In regard to florso-ventral direction, the first rib inclines a little forward, the second is about vertical, wliile behind this tliey slope backward in increasing degree, so that a plane tangent to tlie ventral ends of the last pair cuts the tliird lumbar vertebra. The head and tubercle (hminish in size from first to last. Their relative positions change in that tlie tubercle of the first rib lies almost directly outward from the heatl, while further back it gradually comes to lie behind it. The neck is longest on the l()ngest rilis, and is absent on the last two or three. A costo-transverse foramen is foniied 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. Fio. 22. — LkktSkvknth RinoF Horse. Antero- KXTKHNAL ViEW. (After Schmaltz, Atlas <1. Anat. d. Pfenles.) THE COSTAL CARTILA(iES — THE STERNUM 45 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 cartilaKe connrcted by licament with the first lumbar transverse process; in other cases it is (issifie(l by a very thin layer of com- pact substance. The adult sternum thus con- sists to a very considerable extent of persisting cartilage, viz., the interstornobral cartilages, tho ventral keel, and the extremities; in old ago these undergo partial ossification. 'Tlip manubrium .storni of man is cciuivalcnt, slrictlv speaking, to the cariniform faitilage + I lie first osijeous segment of the horse. Fig. 25.— .An WAX O KRIOR APKRTl'RK OF THO HoRKK. (.\fter .Schmaltz .\nat. .1. Pfenles.) THE THORAX — THE OCCIPITAL BONE 47 THE THORAX The bony thorax of tlie horse is reinarkal)ly 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 inclies (10 cm.), and its height 7 to 8 inches (ca. 18 to 20 cm.). The ventral wall or floor is about Hi inches (40 cm.) long, and the dorsal wall or roof aliout 38 to 40 inches (05 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 pos- terior 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 l'^ to 1.^ 2 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. OcciiJttdl rci Occipital ciiiiilyl ^\^Sii priuicci [fital Exliriial auditory iiiealus atinoid cavity of squamous temporal y Parietal Orbital wing of sphenoid ff !)(i ^ Frontal crest Frontal born Vascular iini.ression Fig. 26.— Skull, Atlas, axd .\xis of Horse, Lateral View. 8, Bmlv of mandible; 28', horizontal (molar) part of ramus; 30, vertical part of ramus; 9, zygomatic process of squamous temporal; U. coronoid process of mandible; 12, supraorbital process; 1.3". paramastoid (styloid) process of occipital; 19, orbit; 20, malar bone; 21, lacrimal bone; 22, nasal bone; 2.3, prema.xilla; 23', nasal process of premaxilla; 25, 29, canine teeth; 26, maxilla; 27, facial crest; 31, coiitl.vie of inandible; 32, atlas; 33. axis; x. wing of atlas; e. naso-maxillary (.\fter EUenberger-Baum, .\nal. fiir Kilnstler.) The Occipital Bone The occipital bone (Os occipitale) is situated at the posterior part of the cra- nium, of which it forms the posterior wall and part of the ventral wall or base.' 'The long a.xi.s of the skull is considered to be horizontal in these descriptions. 48 THK SKELETON OF THE JIORSE 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. Aliove the lateral parts- hut not entering into the formation of the foramen magnum— is the squamous part. The lateral parts (Partes laterales) bear the occipital condyles (Condyli occii)itales), whicii 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 Occipilal crest Upper border of Foramen magnum - Hypoglossal foramen "• For. lacerum poslerius Slylo-masloid foramen — Ilyoid process ^ Muscular process .. For. lacerum anterius -"/j Tubercles at spheno- occipital junction Alar foramen -4- Plerygoid process of sphenoid Pterygoid bont Vomer (nice) ._ Pterygoid process of pidate bone Palate bone (perpen- dicular part) Alveolar tuberosity Posterior narcs . Lust molar tooth - ^[edian crest for Ug. nuchce Occipital condyle ParamaMoid process Condyloid fossa Mastoid process Bidhi ossca Postglcnoid /iroccss Glenoid caiity Temporrd condyle Zygomiilir process Ittfratemporal fossa Zygomatic process of malar Pterygo-palatine fossa Maxillary hiatus - MaTillary tuberosity Facial crest Hamulus of pterygoid Vomer Palate lione (horizon- tal part) Ant. palatine foramen Palatine groove Palatine process of maxilla Fir.. 27.— LisK Drawing ov Posterior Half of Base of Skui.i. of Horse, Without Mandiih.e. (Ke.v to Fig. 28.) 1. Inrisiir.i carolica; 2. incisura ovali.s; 3, incisura ^pinosa; 4, external orifice of paricto-tcmporal canal; S. Eustachian canal; fi, iictro-tympanic fiiaure; 7. external auditory canal; 8, hyoiil proces,s; 9, Vidian groove; 10. supraorbital procew; .1. basilar part of occipital; B, body of .sphenoid; C, temporal wing of sphenoid; D, squamous temporal bone; E. petrous temporal bone; /•', orbital part of frontal bone. 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 liackward; its external surface is convex and roughened for muscular attachment. Between the root of this process and the condyle is a smooth deiire.ssion, the condyloid fossa (Fossa condyloidea inferior); in this is the hypoglossal foramen (Foramen hyi)oglossi), 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 THE OCCIPITAL BONE 49 is inuch narrower in front tlian 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 sharji, and form the inner margin of the foramen lacerum (Foramen lacerum et jugulare). The anterior end has, in the young subject, a ' V The skuU is inclined sliglitly. (Notation on liey fig. 27 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. The squamous part (Squama occipitalis) is the somewhat quadrilateral mass 4 50 THE SKELETON OF THE HORSE situated ahovo the lateral portions, from which it remains distinct til! 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.' The crest divides the surface into two verv unequal parts; the small anterior area (Planum parietale) presents a median rid-je which is the posterior part of the external sagittal crest; the lar're area below Ihe crest (Planum nuchale) also has a central eminence, the external occipital protuberance, on the sides of which the funicular part of the ligamentum nucha- 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 articu- late with the atlas. Development.— The occipital ossifies in cartilage from four centers, and con- sists at birth of four pieces as described above.' 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-oecipital suture and the spheno-occipital synchondrosis are ob- literated 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 pari lying in front of the basilar part of the occipital. It consists of a cen- tral part, the l)ody, 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 trans- verse direction: and its anterior part is concealed to a large exient In- the vomer and pterygoid bones. The cerebral surface (Facies cerebralis) presents the fol- lowing features: (1) In front is a raised, flattened part which is subdivided by a median elevation into two slightly concave lateral areas; this part ha.s 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 de- pression, the optic groove (Sulcus chiasiiudis), on which the optic chia.sma rests. (3) From each end of tiiis groove the optic foramen passes forward and outward to terminate in the po.sterior part of the orbital fossa.' (4) Near the posterior end is a central depression, the hypophyseal or pituitary fossa (Fossa hypophysea), which loilges the hypojihysis cerebri or pituitary body. On each side of this is an ill-defined groove for the internal carotid artery and the cavernous sinus. The an- terior end is exi)anded, and is excavated to form the sphenoidal sinuses. These cavities extend back a.s 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.^ The posterior end is flat and is ' The oooipital crest of this description i.s equivalent to the external occipital protuberance and superior nuchal Hne of man. \ curved line a little lower down, which is continued on the paraniiistoid process, represents the inferior nuchal Une of man. 'Other terms for these parts are basioccipital (basilar part), exoccipitals (lateral parts), and supraoccipital (squamous part). It sliould lie noted, however, that the lines between the tuisioccipital and exoccipitals pa,ss through tlie lower part of the condyles. ' This foramen miglit well be called a canal, since it is an inch or more in length. * The cavity so formed may be termed the sphenopalatine sinus. The sphenoidal sinus maj- be a separate cavity which communicates only with the ventral ethmoidal meatuses; this arrange- ment exists in about a lliird of tlic cases, according to PauUi. THE SPHENOID BONE 51 joined to the basilar part of the occipital; at the lino of junction there is dorsally a transverse elevation, the spheno-occipital crest (Crista spheno- occipitalis). The orbital wings (Ake orbitales) curve upward and somewhat outward from the sides of the lioily of the pre-sphenoid. Their inner or cerebral surfaces are concave, and are marked by digital impressions (Impressiones digitat;e) for the gyri of the cerebrum. The external surface is convex and is largely concealed by the overlapping temporal wing and the sciuamous temporal and frontal bones; a narrow part of it (Facies orliitalis) is uncovered on the innei- 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 eth- moid at the spheno-ethmoidal suture; at its lower part it concuis 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. Be- hintl these foramina is the pterygoid crest (Crista pterygoidea), which is continued downward and forward on the iDterygoid process; on its upper part may l)e foimd 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 (Alis temporales) extend outward and somewhat upward from the body of the post-sphenoid; they are irregularly quadrilateral in outline. The external surface (Facies temporalis) enters into the formation of the infra- temporal 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 con- ducts 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),' which transmits the internal maxillary artery. From this canal a liranch 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 con- cealed by the overlapping palate and pterygoid bones, with which it concurs in the formation of the pterygoid or Vidian canal. Development. — Tlie sphenoid is ossified in cartilage, and consists in early life of two distinct parts, the pre-sphenoid and post-sphenoid. 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. ' This is also called the subsphenoidal canal or pterygoid foramen. 52 THE SKELETON OF THE HOHSE Variation — Tlio dorsal bor.icr of the orbital wing may come to the surface through a defect hi the frontal bone at the place whore the horn process is situated in annuals which have frontal horns. The Ethmoid Bone The ethmoid (Os ethinoidalc) is sitiuitod 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.' It consists of four parts— the criliriforin plate, two lateral masses, and the per- pendicular plate. The cribriform plate (Lamina cribrosa) is a sieve-like partition lietween 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 gain, which is the intracranial portion of the perpendicu- lar plate. Each half forms a deep oval cavity, the eth- moidal 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 jwsterior 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 ethmo-turbinals or ethmoidal cells. These are attached to the lamina papyracea, and are separated by narrow intervals termed ethmoidal meatuses, which communicate with the na.sal cavity. In the living aiiinuil the ethuio-turliinals are covered with mucous membrane. The lateral ma-ss is a very complex structure, the arrangement of which may be studied on crass-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 lione, and is hence usually called the n;iso-turbinal or superior turbinal; the second is much .smaller, and is very conuiionly termed the great ethmoid cell, lietween the endoturbinals are twenty-one small ectoturbinals, and all arc beset with secondary and tertiary coiled lamella;. 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 a). Below this junction it curves inward and concurs with the temporal bone in the formation of the parie to-temporal canal (Meatus temporalis). A transverse groove (Sulcus transversus) connects thi.-^ 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 In- th(> internal sagittal crest (Crista sagittalis interna). The external border is beveled and is overla])])e(l by the sciuamous temporal bone, forming the paricto-temporal suture (Sutura jiarieto-sciuamosa). The angle of junction of the external and ])osterior borders articulates wath the posterior angle of the tein|)oral wing of the splienoid. Development. Ivich jiarietal l.one 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 anil forms a iirominence similar to the pronounced tuber parietale of the young child; the external sagittal crest is not present, and the external surface is smooth. The sagitliil suture is usually dosed at four years, the parieto-oceipital at five years, and the paricto-temporal at twelve to fifteen yeans. ' AeeordinR to Martin, tliere are originally four eenters, two anterior and two posterior (smaller) ones, wliieli fuse in a variable manner. THE FRONTAL BONES — THE TEMPORAL BONES 55 The Frontal Bones The frontal bones (Ossa frontalia) are situated on the limits of the cranium and face, lietwccii the parietals behind and the nasal bones in front. Each is irregularly (luadrilaterah 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, anil is smooth and subcutaneous; it is sejiarated 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 z>goiiiatic arch. The process partially separates the orbit from the temporal fos.sa; 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 sliallow fossa for the lacrimal gland (Fossa glandulse lacri- malis). 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 down- ward 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 ]iart l)y 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 orljital mng of the sphenoid in the formation of the ethmoidal or internal oi'bital 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 orliital wing of the sphenoitl. Its external surface forms part of the inner wall of the temporal fossa. The internal surface is largely covered Ijy the orl^ital -ning 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 na.sal 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, (.i) The extremity of the supraorbital process unites with the zygomatic process of the temporal Ijone. 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 cartilagin- ous 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 surround- ing bones, but its central part is free and presents digital impressions and vascular grooves. 56 THE SKELETON OF THE HORSE The external surface (Facies temporalis) is convex, and enters into the forma- tion of the temporal fossa. From its lower part there springs the zygomatic process (Processus zygomatieus), which forms the external boundary of the tem- poral fossa. It is at first directed outward, and is wide and flattened dorso-ven- trally. It then turns forward, becomes narrower, and is twisted so that its surfaces are internal anil external. Its anterior end is pointed and joins the zygomatic process of the malar bone, with which it forms the zygomatic arch (Arcus zygo- matieus). The narrow anterior ])art has a convex outer surface and a concave inner one. Its ui)per bonier 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 limiteil behind by the post-glenoid process, the anterior surface of which is articu- lar. 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 fo.ssa. The superior border is sinuous and is continuous behind with the temporal crest. The posterior process (Processus posterior) s])rings 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 diviiles into two branches, upper and lower; the upper branch unites with the occipital bone, while the lower one curves downward l)ehind the external autlitory 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 tiie posterior with the parietal. 2. The petrous temporal (Os ix'trosum) 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 seiuanunis temporal, Init 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 outwartl, upward, and a little forward. It gives attachment to the annular cartilage of the ear. Its lumen, the external auditory meatus (Meatus acusticus extcrnus), 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 |)rojects ventrally in the interval lietween the posterior process of the siiuamous temi)oral and the root of the paramastoid (or styloid) process of the occijiital 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 con- cave and sii til l)iit irregular. In its lower part is the entrance to a short canal, the internal auditory meatus, which transmits the seventh and eighth cranial nerves. Tlic fun. Ins .)f till, meatus is divided liy a orost into a superior and an inferior fossa. In the superior one is the oriKin of the facial canal, wliicli eurves through the bone and opens exter- nally at the stylo-ni;usloid foramen; it transmits the faeial (seventh cranial) nerve. The in- ferior fossa presents small foramina for (he passage of filjers of the auditory (eiehth cranial) nerve. . v a / Behind the meatus and near the posterior margin of the surface is the slit-like opening of the aquicductus vestibuli, covered by a scale of bone. Below this is a narrow fissure, the orifice of the aquaeductus cochleae. BONES OF THK FACE 57 Tlif anterior surface looks upward and forwartl. The outer part articulates with the jjarietal bone ami the inner part faces into the cerebral fossa of the cranium. A sharp bortler, 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 l^oundary of the foramen lacerum basis cranii. It is very irreoular 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 tul>e: it is connected by a bar of cartilage with the hyoiil bone. The stylo-mastoid foramen is situated lietween 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 emi- nence situated centrally: it is thin-walled and incloses a cavity which is part of the tympanum. The muscular process' is a sharp spine which projects downward and forwanl 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 lietween the squamous temporal and the occipital Ijone. 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 trans- verse groove which extends outward from the base of the tentorium Oisseum. 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 (A'ena 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 ba.se, 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 an- terius), and a narrow posterior part (Foramen lacerum posterius s. jugulare). It transmits the internal carotid artery, the middle meningeal artery, the mandi- bular, 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 opemngs m front for the internal carotid artery, the mandibular nen'e, and the middle memngeal artery; thp.-^c arc (from within outward) the foramen caroticum, ovale, spinosum. (Bi BONES OF THE FACE The bones of the face (Ossa faciei) are the Maxilla, Premaxilla, Palatine, Pterygoid, Nasal, Lacrimal, Malar, Superior Turbinal, Inferior Turbinal, ^ omer, Mandible, and Hyoid. The last three are single, the others paired. > This is commonly termed the styloid process. It is not the homologue of the styloid process of man. 58 THE SKELETON OF THE HORSE The Maxillae Tlio maxillae arc the principal bones of the upper jaw and carry the upper cheek teetli. They arc situated on the lateral aspect of the face, and articulate with almost all of the facial bones and the frontal and temporal also. For descrip- tion each may be dividcti into a body and two processes. The body (Corpus iiiaxilhcl i)ri'scnts two surfaces, two borders, and two ex- tremities. Tlic external or facial surface (Facies lateralis) is somewhat concave in front and convex behind. On its i)osterior part is a horizontal ridge, the facial or zygomatic crest (Crista facialis); in a skull of medium size its anterior end is about an incii and a half (3 to 4 cm.) above the third or fourth cheek tooth, and it is continued behind liy a corresponding ridge on the malar bone. About two inches (5 cm.) above; an llic anterior part of tlic surface is convex over the enibetUletl parts of the teeth. AJi 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 i)art of the lateral wall of the nasal cavity. Its upper part is crossetl obli(iuel\- forward and downwarti 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 wdth 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 liy a gr()()\-e 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 antl scaly. Its anterior part is grooved and its posterior part beveled for articulation witli the nasal process of the premaxilla anil the nasal and lacrimal Imnes. The inferior or alveolar border (Processus alveolaris) is thick, and presents six large cavities, tlu^ alveoli, for the cheek teeth. I'he alveoli are separated by tran.s- verse interalveolar septa. There is often a small alveolus for the first premolar ("wolf tooth") close to the first large one. iMirther forward the border is narrow and forms part of the interdental or interalveolar space (Margo interalvcolaris). Behind the last alveolus is a rough area, the alveolar tuberosity. The anterior extremity is pointed. It joins the iiremaxilla, and forms with it the alveolus for the canine tooth. The posterior extremity forms a rounded prominence, the maxillary tuberosity (Tuber ntaxillarc). Internal to the tuberosity is a deep cavity, the maxillary hiatus, in which are three foramina. The upper one, tlie maxillary foramen, leads into the infraorbital canal. The lower one, the posterior palatine foramen, is the entrance to the palatine canal. Tlie spheno-palatine 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 tlw floor of the oH)it. The palatine process (Processus palatinus) is a plate which projects horizon- tally inward from the lower part of the inner surface of the body. It forms the THE 1>REMAX1LL^ 59 greater part of the basis of the hard palate. Its superior (jr 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 liart 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. The infraorbital or superior dental canal extends almost hori- zontally from the maxillary fora- men 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 pre- maxilla, carrying vessels and nerves to the teeth there. Development. — The maxilla ossifies in memljrane 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 premaxillae (Ossa incis- iva) form the anterior part of the upper jaw and carry the incisor teeth. Each consists of a body and two processes, nasal and pala- tine. The body is the thick an- terior part which carries the in- cisor 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.' Tlie internal surface is rough, and joins the opposite hone; it is marked by a curved groove, which forms with that on the opposed surface, the incisive ' This foramen is somewhat variable in position, but is commonly opposite the comer in- cisor. Smaller inconstant foramina are often present. -Upper Ja Half OF Horse About Four Years Old, Ventral View. 1. 1. Po.sterior nares; 2. vomer; 3, horizontal p.irt 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; 1.3. anterior end of facial crest; 14. interalveolar space; 1. 1-3. incLsor teeth; C. canine tooth; PI. first premolar or "wolf" tooth. 60 THE SKELETON- OF THE HORSE foramen { Foramen iiK-i.sivuiii). The alveolar border (Limbus alveolaris) separates the ijahitiiio aiul lal)ial surfaces; it is curved and thick, and presents three alveoH for the incisor teeth; behind the third alveolus it is rounded and free, forming part of the interalveolar space. Tlie nasal process (Processus nasalis) projects baclvward and uinvard from the bodv, forming Iicre 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 witii the latter the alveolus for the permanent canine tooth.' 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 an- terior i)art 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. Tiie palatine or inferior surface is flat. The internal border is serrated and meets its fellow at the median palatine suture. The external border is seji- arated from the maxilla and the nasal process by the palatine cleft (Fissura pala- tina). The posterior extremity fits into the interval between the vomer and the palatine process of tiie maxilla. Development. — The i)remaxilla ossifies from a single center. Fusion of the two Ijones is complete at the end of the third or the beginning of the fourth year. The Palatine Bones The palatine bones (O.ssa 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 ])late which forms the ]ios- terior part of tlie iianl palate. It presents smooth nasal antl palatine surfaces. The internal border meets its fellow at the median jialatinc suture, on the nasal aspect (if which is tiie nasal crest. The anterior border joins the palate process of the maxilla at tiie transverse palatine suture, and forms with it the anterior pala- tine 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 tlie 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 max- illaris) presents three areas for consideration. The largest articulates with the maxilla; it is rough ami is crossed by a groove which enters into the formation of tiic iiahitine canal. Behind this is a smooth part which assists in forming the pterygo-palatine fossa. The rough area below this is overlap])ed by the jiterygoid ])r(i((ss of the spiieiioid bone. The superior border is jierforated by the spheno- palatine foramen. Behind the foramen tlie two i)lates of the bone separate to inclose part of the spheno-palatine sinus. The inner plate curves inward to articu- late with the vomer. Tiie outer i)late joins the maxilla anil frontal anil the orbital wing of the spiienoid. Development. — The palatine bone ossifies in membrane from a single center. The Pterygoid Bones The pterygoid bones (Ossa ptcrygoidea) are narrow, thin, bent plates, situated on either side of tjic |)osterior 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 smface articulates with the palatine, vomer, and sphenoid, ' The alveolus for the temporary canine is commonly formed in the maxilla alone. THE NASAL BONES — THE LACRIMAL BOXES 61 concurrinp; with the hist in the formatiiMi 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 (0,ssa 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 jiresents 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 tlie end of the nasal process, the maxilla, and the lacrimal, forming the naso-maxillary and naso-lacrimal sutures. The base or posterior end is lieveled 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 (Fades 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 slightl}' 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 ma.x- illary sinuses. It is concave antl very irregular, and is crossed almo.st 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. 62 the skeleton of the horse The Malar Bones The malar or zygomatic bones (Ossa zygomatica) arc placed between the lac- rimal above and tlic maxilla Itelow and in front. Each is irregularly triangular in ouUine and jin-sents 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 ])resents 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. Tlie orbital surface is separated from the facial surface by the concave orbital margin. It is concave ami smootli, 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 considcraiilc part of it articulates with the maxilla. The superior border articvilates 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 bj- the zygomatic process of the temporal bone. Development. — Each ossifies in niemlirane from one or two centers. The Turbinal Bones The.se (Ossa turbinata) are delicate, scroll-like bones, four in nund)er, which are attached to the lateral walls of the nasal cavity. They project into the cavity and greatly tliniinish 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 jiairs, superior and inferior. The superior or naso-turbinal (Concha tlorsalis)' is somewhat cylindrical in form, small at its anterior ]iart, ami flattened transversely. It is attached to the tur- binal crest of the nasal tjonc 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 com- municates 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 fron- tal 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 ca\ity. 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. Tlie inferior or maxillo-turbinal bone (Concha ventralis) is shorter and smaller posteriorly than the upptT 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 expros.s l)rieflv the mode of coiling of tho two bone.s of tho samp side wo may sav 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 maxillarv sinus. The lower .-surface is separated from the floor of the nasal cavitv 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. ' This bone is really a greatly developed first ethmo-turbiiial. the vomer — the mandible 63 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 hent (except in its posterior part) so as to form a narrow groove (Sulcus sei)ti narium),in wliich the lower part of the perpendicular ])late 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- \'entrall\-, and are covered by the nasal mucous membrane during life. The in- ferior 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 jiro- cesses of the prcmaxillse. The posterior extremity consists of two wings (Ahe vomeris) which extend outward below tlie body of the pre-sphenoid; 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 laminaj 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.' The body (Corpus mandibulse) 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; dm'ing 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 metlian furrow which indicates the position of the primitive symphysis maiidibula\ The curved alveolar border (Limbus alveolaris) jiresents six alveoli for the incisor teeth, and a little further liack two alveoli for the canine teeth in the male; in the mare the latter are usually absent or small. The rami (Rami mandibulse) extenil 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 mandibulse) 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 tle- pression in its middle; above this there is often a faint mylo-hyoid line for the at- tachment 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 ' In the Stuttgart Xomenclator 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. 64 THE SKELETON OF THE HORSE posterior part Ijy 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 mandibulae). 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 alvcolaris incisivus), which carries the vessels and nerves to the incisor teeth. Tlie superior or alveolar border forms anteriorly part of the interalveolar space; here it is thin, liehind this it is thick and is excavated by six alveoli for the lower cheek teeth. Beliind 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 lioriler curves sharply upward, forming the angle (Angulus mandi- buhe); this part is thick and has two roughened lii)s, internal and external, sep- arated by a considerable intermediate space; near tlie condyle it becomes narrower. The anterior extremity joins the l)ody. The superior extremity comprises the coronoid process in front and the condyle l)eliin(i, tlie two being s(>]iarated by the sigmoid notch (Incisura niandibuhe), 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 fo.ssa, and furnishes insertion to the temporal muscle. The condyle (Capitulum mandiljulaj) 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 (Colluin mandibuhc); 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 consi.sts 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 connec- tive ti.ssue which overlies the paired Meckel's cartilages. At birth it consists of two symmetrical halves which meet at a median symphy.sis. Fusion usually occurs in the second or third month. Age changes.— Thcsp are associatpil largely i\-ith the prowth and later with the reduction of the teetli. In the yoiinf; horse, m 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 lanuis is also 11 T^''^''' "■'^ ''^'^*'' '"''' '"^""U''"'' 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 arc more pronounced. The Hyoid Bone The hyoid bone (Os hyoideum) is situated chiefly between the vertical parts of the rami of the mandilile, 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 bodv, a lingual process, and three pairs of cornua. The body or basihyoid (Basis ossishyoidei) is a short transverse bar, compressed dorso- vent rally. The ui)per surface is concave and smooth in its middle, and pre- sent.s 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 THE SKULL AS A WHOLE G5 lingual process, anil 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 embeilded in the root of the tongue during life. It is compre.s.sed laterally and has a blunt-pointed free end. The lateral surfaces are slightly con- cave. The upper border is narrow, the lower thick and irregular. The thyroid comua or thyrohyoids (t'ornua laryngea)' extend backward and upwaril 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 comua of the th>Toid cartilage of the larynx. The small comua or keratohyoids (C'ornua 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 cornvi when present. The great comua 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. Tlie middle comua 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 ailult. 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 bv extension from the body. The latter has primarily two centers (:Martin). Fig. 32. — Hvoid Boxe of Horse, Viewed from the Side AND Somewhat from i.v Front. a. Body; b, lingual process; c, thyroid cornu; c', car- tilage of c; d. small cornu; e, middle cornu; /, great cornu; /'. muscular angle of great cornu; f/. cartilage of great cornu. (EUenberger-Baum, .\nat. d. Haustiere.) THE SKULL AS A WHOLE The skull of the hor.se 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 1 These correspond to the great comua of man. 5 66 THE SKELETON OF THE HORSE divided into parietal, frontal, nasal, and premaxiUary regions. The panetal region extends from the occipital crest t.) the parieto-frontal or coronal suture. It is marked mediallv l.v the external sagittal crest, which bifurcates ui front, the branches becomin}-; continuous with the frontal crests. The latter curve outward to'the root of the supraorl)ital 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 Fiii 33. — Cranial and Obbitai. Regions of Skull of Horse, Lateral View. The Zvcomatic .\rch Sfl'RAORBlTAL PROCESSES Have Been S.awn Off. 1, Occipital condyle; 2, condyloid fossa; 3. paramasloid or styloid process; .J, occipital crest; 5, external ocri|iilal protuberance; 6, external auditory meatus; 7. mastoid process; 8, hyoid process; 9. stylomastoid fora- men; 10, muscular process; 11, foramen lacerum anterius; 12, postglenoid process; 13, glenoid cavit.\-; 14, tem- poral condyle; 15, Vidian groove; 16, alar canal of pterygoid i)rocess indicated by arrow; 17, temporal foramen; IS, ethmoidal foramen; 19, optic foramen; 20, foramen lacerum orbitale; 21, maxillary foramen; 22, spheno- palatine foramen; 2,'J. posterior palatine foramen; 24, supraorbital foramen (o])ened): 25, lacrimal fossa; 26, ilepression for origin of obliquus oculi inferior; 27. facial crest; 28, maxinar.v tuberosit.v; 29, alveolar tuberosity; oO, hamulus of pterygoid bone; S.o., supraoccipital; P, parietal; .S, scitiamoiis temporal; B.o., basioccipital; B.f.. basisphenoid; .1.?.. temi>oral wing of sphenoid; .4. o., orbital wing of sphenoid: /*/. p. . pterj-goid process of -phenoid; P.p., perpendicular part of palate bone; F.F'. facial and orbital i>arts of frontal bone; L.L', orbital and facial parts of lacrimal bone; .U, facial jiart of malar bone; ^t.r.. maxilla; a. parieto-occipital suture; b, parielo-temporal or squamous suture; c.d, spheno-squamous suture; c, palato-frontal suture; /, fronto-lacrimal suture. by the supraorbital foramen. The nasal region is convex from side to side, wide behind, narrow in front. Its ])rofile is in some cases nearly straight; in others it is undulating, with a variably marked depression about its middle and at the an- terior end. The premaxiUary region presents the osseous nasal aperture ( Apcrtura nasalis ossea) and the foramen incisivum. The lateral surface ( Norma lateralis) may l)e diviiled into cranial, ortiital, and maxillary or preorbital regions. THE SKULL AS A WHOLE 67 The cranial region jiresonts the temporal fossa, the zygomatic arch, and the outer part of the petrous temporal hone. The temporal fossa is l)oumled 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 attachmtuit 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 tlisc. Behind the glenoid cavity is the post-glenoid process. The external auditory process projects outward through a deep notch in the lower margin of the s(iuamous 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 fo.ssa for the lacrimal sac. Behind this is a small de- pression in which the inferior oblique muscle of the eye arises; here the i)late 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 ex- treme posterior part is the orbital group of foramina. Four are situated in front of the pterygoid crest. Of these, the uppermo.st 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 \vith 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 orbitiB) is circumscribed by a complete bony ring, which is nearly circidar. Its antero-inferior part (Margo infraorbitalis) is smooth and rounded; the remainder (Margo supraorbitalis) is rough and irregularly notchctl. 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 infraorliital canal, which transmits the infraorl)ital nerve and ves.sels. The spheno-palatine foramen trans- (J8 THK SKELETON OF THE HORSE mits vosscls ami 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 attach- ment of the internal pterysroid muscle, but is crossed in front by a smooth groove in which the jialatinc 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 abruptl>- at a i)()int about an inch and a half (3 to 4 cm.) above the third or fourth cheek tooth;' its inferior aspect is rough for the attachment of the masse- ter muscle. The infraorbital foramen is situated in a transverse plane about an inch (ca. 2 to 3 cm.) in front of lli(> 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 l)one. 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, consi-sts of cranial, guttural, and palatine regions. The cranial region (Basis cranii externa) extends forward to the vomer and pterygoid iiroccsscs (Fig. 2S). At its posterior end is the foramen magnum, flanked i)y the occipital condyles. External to the latter is the condyloid fossa, in which is tlu" hypoglossal foramen, which transmits the hypoglossal nerve and the con- dyloid artery and vein. Further outward are the paramastoid or styloid proc- esses (Processus jugulares) of the occipital bone. Extending forward centrally is a i)rismatic bar, formed l)y the basilar part of the occipital and the body of the sphenoid bone; at the junction of these parts are tubercles for the attach- ment 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 ba.se of the petrous tein])oral 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. Beyonil 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 cither side of the body of the sphenoid is the infratemporal fossa, formed by the temjiora! wing ;uid 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 ])terygo-palatine fossa. In it is the pterygoid or alar foramen, which transmits the internal maxillary artery. A little lo^^er is the entrance to the ptery- goid (\'idian) canal. The guttural region presents the pharyngeal orifice of the nasal cavity. This is ellii)tical and is ilivided in its depth medially by the vomer into two posterior nares or choanae. It is bounded in front and laterally l)y the palate and pterygoid ijones. Ix'hind by the vomer. It is flanked by tiie hamular jn-ocess of the i)terygoid 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 ' This relation vario,'; with aRc; in the young hor.se the third tooth, in the old subject the fourth, lies below the end of the cre.st. THE CRANIAL CAVITY 69 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 preinaxilhe and maxilhn, 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 im- planted. The interalveolar space (Margo intcralveolaris) 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 ])alatine vessels and nerve. It is con- tinuous at the anterior pala- ^2' tine foramen with the palatine canal, which is situated be- tween the maxilla and the pal- ate bone. The palatine cleft (Fissura palatina) is the nar- row 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 pala- tina transversa) is about half an inch from the posterior bor- der. The latter is in a plane through the last molar teeth, and is concave antt free. The posterior or nuchal surface (\orma occipitalis) is formed by the occipital bone. It is trapezoidal in outline, wider below than above, con- cave 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 (Linea? nucha> 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 nucluc 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 premaxilla- and mandible, carrying the incisor teeth. Fio. 34. — Craniai. Cavity of Horse as Seen on Sagittal Sec- tion' OF Skull. O. Frontal sinus; r, sphenoidal sinus; (, cerebral compartment of cranium; 1-3, ridges (juga) corresponding to fissures of lateral surface of cerebrum: 4, groove for middle cerebral artery; 5, en- trance to for. lacerum orbitale; 6, entrance to optic foramen; 7, S, 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 aqua^ductus vestibuli; 18, orifice of aquEeductus cochleie; 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 CRANIAL CAVITY This cavity incloses the brain, with its membranes and vessels, small, and is ovoiil in shape. It is relatively 70 THE SKF.LETON OF THE HORSE The superior wall or roof (Calvaria) is formed by the supraoccipital, inter- parietal, parietal, and frontal hones. In the middle line is the internal sagittal crest, wiiich joins the crista galli in front, and furnishes attachment to the falx cerel)ri. Posteriorly the crest is continued liy the sharj) anterior margin of the tentorium osseum, which projects downward and forward into the cavity, and gives attachment to the tentorivnn ccrehclh by its sharp lateral edges. Behind this the roof is groovetl centrally for the mitldle lobe or vermis of the cerebellum. Trans- verse grooves pass from the base of the tentorium osseum to the parieto-temporal canals. The anterior part of the roof is hol- lowed by the frontal sinus. The occipital part is verj- thick and strong. The lateral walls are formed by the occipital, parietal, tem- poral, and frontal bones, and in part by the orbital wings of the sphenoid. Each is crossed ob- liquely by the petrosal crest, which concurs with the project- ing 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 aquae- ductus vestibuli and aquaeductus cochlea^ The roof and lateral walls are marked by digital impres- sions and vascular grooves. The inferior wall or floor (Basis cranii interna) may l)e regarded as forming three fossa>. The anterior fossa (Fossa cranii anterior) supports the frontal and olfactory parts of the cerebrum. It is formed chiefly by the pre- sphenoid, and lies at a higher level than the middle fossa. In front the fossa i.s divided medi- ally by the crista galli, lateral to •which are the deeji ethmoidal or olfactory fossae for tlie olfactorv lobes. Ihe ethmoidal or internal orbital foramen perforates the cranial wall at the outer side of these fossa. Further back the central part of the surface IS slightly elevated, and is flanked by shallow depressions which support the ol- factoo- peduncles. Po.steriorly is a bony shelf which covers the entrance to the optic foranuna ; the edge of this shelf and the posterior borders of the orbital wings of the si)henoid may be taken as the line of demarcation between the anterior and Fig. 3.'). — Fi.oon of Cramai. Tavitv or Hobsf. The roots of the cranial nerves are shown on the left side and are (lej^ijcnated by number. /. .\nterior cranial fossa; //. middle cranial fossa; ///, po,sterior cranial fossa; a, ethmoitlai fossa: b, ethmoidal foramen: c, foramen for nasal branch of ophthalmic artery: d, orbital wing of sphenoid bone; e. optic fo.Hsa; /. sella turcica: g, spheno-occipital crest; li, h' , dotted line indicatinK contour of pituitary body; h", slight elevation repre- senting dorsum selisc: i, k, grooves for nerves and cavernous sinus; /, ilepression for pyriform lobe of cerebrum; m, groove for middle meningeal artery; n, depression for pons; o. foramen iaccrum anterius; p, foramen lacerum posterius; q, incisura carotica; <;', incisura ovalis; (i", incisura spinosa; r, depression for medulla oblongata: ». hypoglossal foramen: (, internal audi- tory meatus; u, foramen magnum; r. frontal sinus; w, zygomatic process of tetnporal bone; x, .section of |)etrous temporal: y, section of occipital bone: j, crista galli; 1, 1', 1", dotted lines indicating position of olfactory tracts and peduncle, (.\fter Ellenberger-Haum, Top. .Vnat. il, I'fcrdes.) THE NASAL CAVITY 71 middle fossse. The middle fossa (Fossa craiiii media) is the widest part of the cavity. It extends l)ackward to the internal spheno-occipital and petrosal crests, thus corresponding to the post -sphenoid. 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 rotuntlum, 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 transverseh' and slopes gently dowmwartl 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 l)y the cribriform plate of the ethmoid, which separates the cranium from the nasal cavnt}-. It is perforated by numerous foramina for the passage of the olfactorj- nerve-bundles. Fig. .36. — Median- Sncnox of Skull of Horse Without the M.\.vdiblc. The septum nasi is removed, but the mucous membrane on the turbinal bones is retained. a, a', Superior turbinal bone, dotted line indicating Umit between anterior coiled part and posterior uncoiled part; 6, 6', 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, /. inferior turbinal folds, former (alar fold) inclosing bar of cartilage; ff, h, t, superior, middle, inferior meatus; o, o', frontal sinus; partial septum between o and o'; y. 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, (.\fter Eilenberger, in Leisering's .\tlaa.) THE NASAL CAVITY The nasal cavity (Cavum nasi) is a longitudinal passage which exiends through the upper part of the face. It is divided into right and left halves by a median septimi nasi. The lateral walls are formed by the maxilla, premaxilla, and the perpendicular part of the palate liones. 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 spheno-palatine foramen. The superior wall or roof is formed by the frontal and nasal bones. It is concave from side to sitle, and nearly straight longitudinally, except in the posterior part, where it curves dowmward. It presents a median elevation, the nasal crest. The inferior wall or floor is formed by the palatine processes of the premaxillae and maxilhe, and the horizontal parts of the palate bones. It is ^^^der 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 premax- illae is the palatine cleft. 72 THE SKELETON OF THE HORSE Tlio 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 completeil bv 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 turbmal bones. In its posterior part is the very narrow opening into the maxillary smus. 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 i)etween the anterior and posterior nares. The external aperture is bounded by the nasal bones and the premaxilla;. Fid. 37. — Crosr-skction of Nasal Rkcion of Skull OF Horsk; thk Skction Passks Through THK .\ntkrior End of thk Facial Crest, A.ND BkTWKKN THE ThIRO AND FoURTH ChEEK Teeth. a, Superior, h, inferior tiirhitiul bone; c, d, cavi- ties of a ami b; e, common meatus; /. i;, h, s\iperior, middle, inferior meatus; i', k, passages to cavities of turbinal boiie-s; /, naso-lacrimal duct; m, infraorbital canal; n, anterior end of maxillary sinus; o, septal cartilage. (After Kllenberger, in Lcisering's .\tla.'i.) Flo. .SR. — Cross-section of Nasal Region of .Skull OF Horse; the Section is Cct About Half- way between the Orbit and the Anterior End of the Facial Crest, and P.\sses be- tween the Fifth and Sixth Cheek Teeth. a, Superior, b, inferior turbinal bone; c, d, cavi- ties of a and b\ e, common meatus; /, superior, (?, middle, h, inferior meatus; (', placed over ridge in maxillary sinus; k, communication between outer and inner (turbinal) part of maxillary sinus; /, naso- maxillary opening; m, naso-lacrimal canal; n, infra- orbital canal, (.\fter EUenberger, in Leisering's Atlas.) The posterior extremity or fundus is sejiarated from the cranial cavity by the cribriform i)late of the ethiiioid, 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 diver- ticula, are four pairs of air-sinuses (Sinus paranasales), viz., maxillary, frontal, spheno-palatine, and ethmoidal. The maxillary sinus (Sinus maxillaris) is the largest. Its external wall is formed by tlie 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 a])proximately by a line dra\vn from the anterior end of the facial crest to the infraorbital foramcm. Its upper boundary corresponds to a line drawn backward from the .supraorbital foramen parallel to the facial crest. The floor is forineil by the alveolar i)art of the maxilla; it is very irregular and is crossed by bony plates running in various directions. The last THE PARANASAL SINUSES 73 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 obHque 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 verj' delicate and usually cribriform. The position of the septum is quite variable. It is not rare to find it further forward, and in some eases it is further back than is stated above. In the recent state, j. c, 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 l)y 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 spheno-palatinc sinus. It comnumicates dorsally Fig. 39. — .Skcll of Horpf:. Lateral View without Mandibi.k. Thf. SixrPFP are Opened rp. a. Posterior part, b and c. anterior part of frontal sinus; d, roof of superior meatus: c. lateral ma-ss of eth- moid bone: /, /'. naso-Iacrimal duct, exposed in its posterior part: ». h, posterior and anterior compartments of maxiUarj- sinus (also designated as superior and inferior maxillary sinuses); i'. septum between » and h; k. lower limit of upper thin and partly membranous portion of septum; h 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, (.\fter EUenberger, in Leiseriug's Atlas.) with the frontal sinus through the large oval fronto-maxiUary 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 aljout 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 ca^^ty (with the exception of its turbinal part) is largely occupied by the developing teeth. In horses five to six vears 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 cavitv becomes free, until in old age only the short roots project up in the floor, covered by a layer of" bone. Other facts in thi.s connection will be given in the description of the teeth. In exceptional ca-ses the posterior part of the inferior turbinal is sniallcr than usual and leaves a considerable intenal, through which the maxillary sinus communicates with the nasal cavity. The frontal sinus fSinus concho-frontalis) consists of frontal and turbinal parts. The frontal part is l)ounded 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 fon^-ard to a 74 THE SKELETON OF THE HORSE plane tlirough the anterior margins of the orbits, backward to one through the tem- poral condyles, and outward into the root of the supraorbital process. It is separ- ated from the sinus of the opposite side by a complete septum. It is partially subdivided by a number of bony jilates. The turbinal ]3art is situated in the posterior part of the superior tur- binal 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. Be- hind it is in free communication with the frontal part over the lateral mass of the eth- moid. It is separated from the nasal cavity by the thin turbinal plate. The frontal and maxillary sinuses communicate through the large opening describeil above. The spheno-palatine sinus (Sinus sjiheno- palatinus) consists of two parts which communi- cate under the lateral mass of the ethmoid. The sphenoidal (posterior) part is excavated in the bod}^ of the pre-sphenoid. The palatine (an- terior) part is between the two plates of the per- pendicular 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 onp-third of the cases (according to Paulli) the splicnoidal and palatine parts are separated by a trans- verse septum, and the sphenoidal part then communicates only with the lower ethmoidal meatuses. The term ethmoidal sinus is often ajiplied to the cavity of the largest ethmo-turbinal. It communicates with the maxillarv sinus. Fio. 40.— RKti.i. OK HonsR, D0R.1A1. View, wiTit S1NU8KA Exi'OSKD By Re- moval OK THE Outer Plate ok Bone. J, Frontal bone: 3. nasal bone; 3, lacrimal bone; 4, maxilla; a, po.stenor part of frontal sinus; a', middle part of frontal sinus; 6, anterior (turoinal) part of frontal sinus; r. lateral mu»n of ethmoid bone; d, roof of superior meatus; e, fronto- maxillar)' openinK; /. naso-inuxillury open- ing below plate which forms the anterior margin of c; ff. h, posterior unje(ts is thin, irregular, and jiorous. The anterior or cervical angle (Angulus cranialis) is at the junction of the DuTsat Vascular ijrooK Tuhcrosilij Glenoid cavity Corncoid process Fio. 42— Left Scapula or HoRsi:. Costal SuRFArF..— (.\fter Schmaltz. Atlas d. .Vnat. d. Pferdes.) anterior and vertebral borders and lies opposite to the second thoracic spine. It is relatively thin and is al)out a right angle. The posterior or dorsal angle (Angulus caudalis) is thick and rough: its position can be dctcrtnincd readily in the living animal. The inferior or articular angle (Angulus glenoidalis) is joined to the bodv of the bone by the neck of the scajnila (Colluin scapuhe). It is enlarged, especially in the sagittal direction. It iiears the glenoid cavity (Cavitas glenoidalis) for articu- lation wth 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 THE HUMERUS 77 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 scapulae is the large rough prominence in front, to which ttie tentlon 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 o.ssification, for the liody of the bone, the liicipital and cora- coid processes, the anterior part of the glenoid cavity, and the tuber spinse. The last ossifies after birth and fuses \^-ith the spine about the third year. The bicipital tuberosity and coracoid fuse with the body of the bone about the end of the first vear. viz., one each Tuberosity In old subjects the spongj' substance disappears at the middle part of the fossae, so that the bone consists here of a thin layer of compact substance. Considerable ossifica- tion of the cartilage is usual, tlie bordei's become much rougher, the muscular lines are more pronounced, and a medullary ca\dty may appear in the neck. Much varia- tion 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 (2^^ to 3 cm.), and the chief nutrient foramen may be on the f)os- terior border or in the subscapular fossa. Fig. 43.— Distal Exi OF Horse, End ' Schmaltz, Atlas 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 obliquelj' downward and backward, form- Internal tuberosity f Posterior pa \ ( Anterior par Posterior part Anterior port J J. External tuberosity Fin. 44. — Proximal End of Lf.ft Hr: Bicipital groove ■ OF Horse, Exd \'ie\v. (.\fter Schn .\tla5 d. .\nat. d. Pferdes.) ing an angle of about 55 degrees with a horizontal plane. It may be divided into a shaft and two extremities. 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 78 THE SKELETON OF THE HORSE tubercle (Tuberositas tores), to which the tendon of the latissinuis dorsi and teres major nuiscles is attaclied. The nutrient foramen is in the lower third of this sur- face. The anterior surface is triangular, wide and smooth above, narrow and roughened below. It is separated from the external surface by a distinct border, wiiicii ijears on its uijper 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 Cut red line Deltoid tuberosity Miisculo-sinrdl (jrooi'c Olecranon fossa Fill, 45.— LKtT lU.MKRua OF Hon.sK, Is TERNAL SuRKACK. (.\fter Schmallz -Atlas d. Anat. d, Pferdes.) Exicrmil condyle ExUrnnl epicondylc Fio. 46.— Lki-t HrniF.nus or Hor.sk. Extkrv.u. {.\fler Schmaltz, .\tla.s il. .\nat. .1. I'fenles.) tuberosity the border inclines forward, becomes less salient, and ends at the coronoid fossa, Tiie posterior surface is rounded from side to side and smooth. Tile proximal extremity consists of the h(>a(l, neck, two tuberosities, and the l)icipital groove. The head (Caput humeri) presents an almost circular convex articular surface, which is about twice as extensive as the glenoid cavitv of the scapula, with which it articulates. In front of the head is a fossa, in which are several foramina. The neck (("olluni humeri) is well defined behind, but is prac- tically aiwent elsewhere. The external tuberosity (Tuberculum majus) is placed THE HUMERUS 79 antero-externally, and consists of two parts; the anterior part forms the outer houndary of tlie bicipital groove antl gives attachment to the external branch of the supraspinal us muscle; the posterior part gives attachment to the short inser- tion 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 lioundary of the bicipital groove, and furnishes insertion to the inner branch of the supraspinatus above, and the posterior deep pectoral muscle below; Inhriud tuberosity Intcrniil tubercle Coronoid fossa Internal epicondyle Internal condyle Fig. 47. — Left Himehus of Horse, .\nterior V: Exlcnial I uberos ity Dilloid tiiUrusity Muscido-spiral groove External condyloid crest Externid condyle (.\fter Schmaltz .Vtliw d, .\nat. d. Pferdes.) the posterior part gives attachment to the subscapularis muscle. The bicipital or intertubercular groove (Sulcus intertubercularis) is situated in front; it is boundetl l)y the anterior parts of the tuberosities, and is subdivided by an inter- mediate 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. 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. Pos- gQ THE SKELETON OF THE HOKSE tcriorlv tho groove oxteiuls upward considerably above the rest of the articular surfa.'e 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 ami further back, giving the extremity an oblique ap- pearance ■ it is marked by a wide shallow groove. The coronoid fossa ( Fossa coro- noidea) 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 irom which the anterior or common extensor of the digit arises. Behind and above the coiKlyles are two thick ridges, the ei)ic()ndyles. The internal or flexor epicondyle (Epicondylus medialis s. flexorius) is the more salient; it furnislies origin to licxor muscles (if the carpus and digit, and presents internally a tubercle for the attach- ment of the internal lateral ligament of the elbow joint. The external or extensor epicondyle (i^picondylus lateralis s. extensorius) bears externally the external supracondyloid crest (Cri.sta condyloidea lateralis), which forms here the outer ]K)undary of the musculo-spiral groove, and gives origin to the extensor carpi. Below tliis is a rough excavation in which the external lateral ligament is attached. The lower border of the epicondyle gives attachment to the flexor carpi cxternus. 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 epiphy.ses, ami three secondary centers for the external tuberosity, the ileltoid tuberosity, and the internal condyle. The proximal end fuses witii 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 hum- erus, 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 exijanded 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 tlie ulna is attached by an interosseous ligament; in the adult the two bones are fused here. A variable rough elevation below the middle of tiie surface and cIo.se to tlie internal border gives attachment to the superior check ligament. The internal border (Margo medialis) is slightly eon- cave in its length and is larg(>ly subcutaneous; at its proximal end there is a smooth area on which tiie tendon of insertion of tlie brachialis muscle lies, and a small rough area just below gives attachment to that muscle and the long internal lateral ligament of ttie elbow-joint. Th(> external border (JNIargo lateralis) is more strongly curved, but presents no special features. The proximal extremity or head (("aiiituluni radii) is flattened from before backward and wide transversely. It presents an articular surface (Fovea capituli) wliirh corresponds to that on the distal end of the humerus; it is crossed by a central sagittal ridge, wiiich has a synovial fossa on its posterior part, and ends in front at a prominent lip, the coronoid process (Processus coronoideus). Just i)elow the i>osterior border there are two concave facets for articulation with the ulna, and between these and the interosseous sjiace is a quadrilateral rough area at which the two bones are united by an interosseous ligament. At the inner side THE RADIUS g] of the anterior surface is the bicipital tuberosity (Tulierositas radii), into whieh the Ijiceps tendon is inserted. Tiie internal tuberosity is continuous with the pre- ceding eminence, and furnishes attachment to tiie sliort part of the internal lateral DIT'S AND UlXA OF HoRSE, EXTER' NAL View, (.\fter Schmaltz, Atlas d. Anat. d. Pferdes.) Distal external tuberosity of radius Facet for radial carpal Fio. 40. — Left Radius and Ulna of Horse. Pos- terior View, (.\fter Schmaltz. Atlas d. .Anat. d. Pferdes.) 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. The distal extremity is also compressed from before backward. It presents S2 THE SKELETON OK THE HORSE tho carpal articular surface (Facics articularis carpca) which consists of three parts. The inner facet is the largest, is quadrihiteral, concavo-convex from before back- ward 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 witii tiie ulnar carpal (or cuneiform) and behind with the accessory carpal (or pisi- form) The anterior surface presents three grooves, separated by ridges. The middle one is vertical and gives passage to tiie tendon of the extensor carpi radiahs; tlie outer one is similar and contains the tendon of the anterior extensor oi the digit; the inner one is small and oblique and lodges the tendon of the extensor carpi ()l4i(iuus. The posterior aspect is crossed by a rough ridge, below which are three depressions. On either side is a tuberosity (Tul)erculum ligamenti) to which the lateral ligament is attached. The outer one is marked l)y a small vertical groove for the passage of tlie 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. Priircssiix iiiicottaiis nutch HoilHI Atlna ■KR Half OK RAnirs an , Intkrnal ViKW. (.\fte 1. .\nat. d. Pferdes.) THE ULNA The ulna of the horse is a reduced long bone situated behind the radius, with which it is ]iartially fused in the adult. The shaft (Corpus ulnse) is three-sided and tapers to a point below. The anterior surface (Fades dorsalis) is applied to the pos- terior 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, excej)! at the interosseous s])ace. Tlie posterior border is slightly concave in its length and is rounded. The lower end is pointed and is usually a little lielow 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 Ijone. 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 inuscl(>s of the ell)ow. The internal surface is concave and smooth. Tiie external surface is convex and is rougheiu'd above. The anterior border bears on its middle a pointed projection, the processus anconaeus or "l)eak," which overhangs the semilunar notch or sigmoid cavity (Incisura semihi- naris). The latter is triangular in outline, concave from above downward, and y":!!^-!^' THE CARriS — THE INTERMEDIATE CARPAL BONE So 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 witii those on the posterior aspect of the proximal end of the radius. The posterior border is nearlj- 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 f(jr tiie main part of the bone, one for the olecranon, and one for the tlistal end. The cartilaginous embryonic ulna extends the entire length of the forearm. The lower part of the .'lij.'., shaft is usually reduced to a small fibrous band .v;;/;'V*!?'^'"'- or may disappear entirely' ; in some cases a vari- able remnant of it ossifies. The distal extremity fuses early with the radius. The olecranon miites 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 state- ments 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 metacar- pal. The (abbreviated) names and relative posi- tions of the bones of the left carpus as seen from in front are indicated below. Proximal Roic: 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 ]i 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 tuherculate. 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 sxirface is saddle-shaped, and articulates with the middle facet on the distal ciul of 51 . — Sagittal Section- i OF I-PPER IT 1 DF Radius and Ul.va o F Horse. c- n, Mwlullary cavity of i ulna. 84 THE SKELETON OF THE HORSE the radius. The inferior or distal surface is smaller, convex in front, concave be- hind, and articulates with the third and fourth carpal bones. The internal surface has ui)pcr 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 slightlj- convex. The posterior or volar surface bears a tuberosity on its lower part. The Ulnar Carpal Bone Tlic ulnar carpal bone (Os carpi ulnare, cuneiform) is the smallest and most irregular bone of the ujiiier ro\v. The superior or proximal surface is concave, and fits the lower jiart of the outer facet on the distal end of the radius. The inferior or distal surface is obliciue anfl undulating for articulation with the fourth carpal lione. 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. 'I'he posterior or volar surface is oblitiue, and bears a concave facet for articidation with the accessoiy carpal Ijone; below this is a tubercle. Fig. S2.— Lkft Cari-ai. Bonis dk IIobsk, with Dis- Fig. S3.— Left Carpal Bonfs of Hor.sf., with TAI, End of Radius and Proximai, Knd of Adjacent Ends of Radius and Metacarpus; MKTArAiiprs; Internal View. External View. C'a, Accessiory carpal bone; Cr, radial carpal; Ci, intermediate carpal; Cii, ulnar cari)al; Cl-4, first to fourth carpals; Mc. II, III, IV, metacarpal bonef^; I, 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, .\tlus d. .\nat. 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 descrii)tion two surfaces and a circumference. The internal surface is concave and forms the outer wall of the cari^al 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. Tlie accessory docs not directly boar weight, and may bo regarded as a sesamoid hone interposed m 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 tran.sversc carpal hganienl, which completes the carpal canal for the flexors of the digit. THE FIRST CARPAL BONE — THE SECOND CARPAL BONE 85 The First Carpal Bone The first carpal bone (Os carpale primuni, 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 tlio eases; 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 eases 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 con- stant bone of the lower row, and is irregularly hemispherical in shape. The su- perior or proximal surface is a convex facet which is continued tipon the pos- 2 I tenor or volar surface and articulates ■RTth the posterior jxirt uf the radial carpal. The external surface faces ob- liquely outward and forward, and bears three facets for articulation ■n-ith 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 Mc. IV Mczzr Fig. 54.— Carpal Boxes of Hohsk, with Adjacent Fig. 55.— Carpal Articular Surface of Radius Ends of Radius axd Metacarpus; Anterior and Proxi-mal Articular Surfaces of Car- View. The Accessort and First Carpal pal and Metacarpal Bones, Left Side. Bones are Not Shown. The Accessory and First Carpal Bones are not Shown. Cr. Radial carpal; CI. interme.liate carpal; Cu. ulnar carpal; C3, CS. C4. second, third, and fourth car- pals; Mc.Il. 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 radiahs; 3, meta- carpal tuberosity. Arrows indicate relations of facets. Short arrow points to facet on ulnar carpal for articu- lation with accessory carpal. (After Schmaltz, Atlas, d. Anat. d. Pferdes.) 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 mth the first carpal bone. g6 THE SKELETON- OF THE HORSE The Thii?d Carpal Bone Tlic third carpal liono (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 intermediat(> carpal— is concave in front and convex behind, where it encroaches on tlie posterior surface. The inferior or distal surface is slightly un- dulating, and articulates almost entirely with the large (third) metacarpal bone, but it usually i)ears a .small oiilique facet at its inner side for the inner (second) meta- carpal, and there is connnonly a non-articular depression externally. The internal surface faces liackward 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 witli 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 upi)er jiart is encroaclied upon by the superior articular surface, below which it is rough. The Fourth Carpal Bone The fourth carpal bone (Os carpale ciuartum, unciform) is somewhat wedge- shaped, and is readily ilistinguished from the second by its greater size and its posterior tui)ercle. The superior or proximal surface articulates with the inter- mediate and ulnar; it is convex and curves outward, backward, and downward, encroaching on the external and jiosterior surfaces. The inferior or distal surface JK-ars two inner facets for the large (third) metacarpal antl an outer one for the ex- ternal (fourth) metacarpal bone. The internal surface has two or three facets for articulation witli the tliird carpal, between which it is excavated and rough. The anterior or dorsal surface is convex and rough. The external surface is small, ix'iiig encroached upon by the superior articular surface. Tlie posterior or volar surface bears a tubercle on its lower part.' The Carpus as a Whole The bones of the carpus, exclusive of the accessory, form an irregular quadran- gular mass, the width of which is about twice the height or the antero-posterior diameter. Tlie anterior or dorsal surface is convex from side to side, depressed along the line of junction of the two rows, and i^rominent 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 l)y the posterior ligament; it is converted into the carpal canal (Canalis carpi) for the flexor tendons by the transverse carpal ligament, which stretches a(Toss from the acces.sory bone to the inner side. The proximal surface is widest in- tiTnally and is elevated in front, concave behind; it is entirely- articular and adaj^ted 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 Ixjnes usually articulates with two metacari)al 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 excei)tion of the acces.sory, ulnar, and .second, each bone articulates with two bcmes of the other row. Development. — Each ossifies from a single center. ' 'l")ii.s lione is probably equivalent to the fourth and fifth carpals of forms in which five carpal elements are present in the lower row. THE METACARPUS — THE LARGE METACARPAL BONE 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 secontl and fourth, are much reduced, and are commonly called the internal anil external small metacarpal or "splint" hones. Tabirosity Fin B0NK.-i o Schmailz The Large Metacarpal Bo^fE This (Os metacarpale tertium) is a very strong long bone, placed between the carpus above and the first phalanx below two extremities. vertically It consists of a shaft and 88 THE SKELETON OF THE HORSE The shaft (('(npus) is scmicylindrical, and presents two surfaces and two Ijorders. The anterior or dorsal surface is smooth, convex from side to side, and nearly straight in its length. Tlie posterior or volar surface is somewhat convex from side to side and, with the small l)ones, 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 roundetl. The proximal extremity (Basis) bears an undulating articular surface adapted to the lower row of carpal bones. The greater jnu-t supports the third carpal bone; the oblique outer ])art, separated from the precechng Ijy a ridge, articulates with the fourth, and a small facet for the second is usually found at the postero-internal angle. On either sitle is a notch separating two small facets which articulate with the proximal ends of the small metacarpal l)ones. 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 sus- pensory 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 ligami-nt, 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 iioiie it usually bears two facets above which support the second and third carpal bones, while the outer l)one has here a single facet for articulation with the fourth carpal bone. Each has also two facets for articulation with the large meta- carpal, 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 ma- jority of ca-scs 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 ye^ir. The small metacarpal bones ossify from two cen- ters, one of which is for the proximal extremity. Their distal ends are cartilaginous THE PHALANGES — THE FIRST PHALANX — THE SEfOND PHALANX 89 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)' is a long bone, situated between the large metacarpal bone above and the second phalanx below. It is directed obliquely downwarrl 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 w-ider 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 triangu- lar 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 sur- face adapted to the distal end of the large metacarpal bone, consisting of two glen- oid cavities separated by a sagittal groove; the inner ca'sitj' 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 at- tachment 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 phalan.x, consisting of a shallow central groove and two lateral convex areas or condyles; the iimer 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 at- tached. Behind the tubercle is a distinct facet to which the superficial flexor ten- don 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 tn-isted 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)- is situated between the first and third phalanges, its direction corresponding to that of the first phalaiLx. 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 j^resents 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 phal- anx 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 1 It is also called the large pastern bone or os suffraginis. ^ This bone is also called the small pastern bone or os coronae. 90 THE SKELETON OF THE HORSE middle; on its U»\ver part are lateral rough depressions, surmounted Ijy tuljerosities, to both of whicii ligaments are attached. The posterior or volar surface is smooth, flattened, and slopes obliquely down- ward and forward. The borders which separate the anterior and posterior surfaces are concave from above downward, rounded from before backwartl. Development. — The second phalanx ossifies like the first, but the proximal end unites with the shaft two or three months earlier. Distnl border Dorsal or wall surface ^. Extensor process - - Articular surface Coronary border '-T, ' Dorsal groove Depression for Intmil liyament Third I'lmlnn Third Scs-imM Second I'halam- First Phalanx Fig. .t8.— Pn Angle or iring Articular surface of third sesatnoiil or nancular bone Distal articxdar surface Eminence for lateral ligament Dorsal surface Proximal articular surface Distal articular surface Eminence for latind liyiimetU Dorsal surface " Eminence for extensor tendons — Tuberosity — Proximal articular surface — Intermediate groove MOID OF IioR8E, DoRSAL .ASPECT. The Third Phalanx The third or ungual phalanx (Phalanx tertia)' 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 (Fades articularis) faces upward and backward, and is chiefly adai)1ed to the distal surface of the second phalanx, but a narrow flattened area along the posterior liorder articulates with the third sesamoid. The an- ' This bone is also called the os pedis or coffin bone. THE THIRD I'HALANX 91 terior or coronary border forms a central ciiiinencc, the extensor (or pyramidal) process (Procei^sus extensorius), to the front of which the anterior extensor tendon is attacheil. On either side is a depression for the attachment of the lateral liga- m(>nt. 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 liy nu- merous 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 semihmar canal, where they meet and form a terminal arch, from wliich branches pass through canals in tlie 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.' The upper border carries the lateral carti- lage. The lateral cartilages (C'artilagines ungulse) are rhomboid curved plates, which surmount the wings on either side. They arc 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 no*ed that the size and form of the wings vary mucli in different specimens. In the new-born foal the wing is a small, pointed projection. Later the process of o.ssification invades the lower part of the cartilage to a var>'ing 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. Whih> 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 ' The upper and lower divisions of the wing are sometimes termed the basilar and retrossal processes respectively. 92 THE SKELETON OK THE HORSE vessels, most of which nuUatc fruiu the st'inihuiar 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 ami flexor surfaces and the extensor process, ('. c, at the points of greatest pressure and traction. THE SESAMOID BONES The two proximal or great sesamoids (Ossa sesamoidea phalangis primse) are situated behind the distal end of tlic large metacarpal bone, and are closely at- tached to the first i)halanx \>y 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 mcta(ari)al bone. The posterior or flexor surface is flattened and obliciue; in the fresh state it is covered by a layer of carti- lage which also fills the interval between the opposed borders of the two bones, and forms a smooth groove for the deej) 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 u|)ward and is rountled. The third sesamoid or navicular lione (Os sesamoideum phalangis tertia^) is shuttle-shai)ed, and is situated behind the junction of the second and third phal- anges. Its long axis is transverse, and it possesses two surfaces, two Ijorders, and two extremities. The articular surface (Facies articularis) faces upward and forward; it consists of a central emi- . ,. , ,,,,., - nence, flanked by concave areas, and phalanx articulates with the distal end of the /'// bonier Second phalanx. The flexor or tendon surface (Facies flexoria) is directed "M,„?!v~Vw',"r«T"'l!"'i,i' i\" VV'iJ'"r\"'' downward and backward. It resem- HoKSK. (.After Schmait z, .\tla3 (1. .-\uat. d. Pfenles.) i 1 1 • , bles the articular surface in form, but is more extensive and not so smooth. In the fresh state it is coated with cartilage and the dee]) flexor tendon plays over it. The proximal border (Margo liber) is wid(> 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 promi- nent edge. The extremities are blunt-pointed. Development. — It ossifies from a single center. The Bones of the Pelvic Limb The pelvic girdle consists of the ossa coxse, which unite ventrally at the .sym- physis pelvis, and articulate with the .sacrum dorsally. OS COXiE The OS coxae (or o.s innoininatum) forms the skeleton of the hip or haunch, and is the largest of the flat liones. 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. The.se parts are fused at about one year of age, but it is convenient to describe them separately. THE ILIUM 93 THE ILIUM The ilium (Os ilium) is the largest of the three parts. It is irregularly triangu- lar anil presents twu surfaces, three borders, and three angles. Tlie gluteal surface (Facies glutica) 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 glutsea), which extends from the middle of the inner border toward the external angle. This surface gives attachment to the middle and dee]i gkitcal muscles. The pelvic surface (Facies pelvina) faces in the opposite direction; it is convex, Fig. tiO. — OssA CoxARUM of Mare, Dorsal View. Oil Ilium: O.p., pubis; O./s.. ischium; .4 .o.>., wing of ilium; Co.!., shaft of ilium; Cr.o.i anterior border (crest) of iUum; /, obturator foramen; 2, acetabulum; S. internal angle of ilium; 4, external angle of ilium- a gluteal line; S. psoas tubercle; 7, S, acetabular and symphyseal branches of pubis; S, /O acetabular and .,'vmphvseal branches of ischium; 13. lesser sciatic notch; IS. ischial arch; U. great sciatic notch; ia. sym- physis pelvis; /r,ilio-pectineal eminence; /5. anterior borders of pubic bones; ;9, posterior gluteal hne. (btruska, Anat. d. Haustiere.) and consists of two distinct parts. The inner triangular part (Pars articularis) is roughened for ligamentous attachment, and liears an irregular facet, the auncu- lar surface (Facies auricularis), for articulation wdth the sacrum. The outer quad- rilateral part (Pars iliaca) is in general smooth. It is crossed by the ibo-pectmeal line (Crista iliopectinea), which begins below the auricular surface and is contmued on the shaft of the bone to join the anterior border of the pubis. The Ime is inter- rupted bv furrows for the iliaco-femoral vessels, and below these it bears the psoas tubercle (Tuberculum psoadicum), which gives attachment to the psoas minor mus- cle. The iliacus muscle is attached to the surface external to the ilio-pectineal line. 94 THK ski;letox of thk horse The anterior border or crest (Crista iliaca) is concave, thick, and rough. The internal border is deeply concave; its middle part forms the lower bouiid- ary 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 i>y fjruoves for the ilio-lumbar vessels, which are continued on the pelvic surface. The nutrient foramen is usually situated on or near the posterior part ef this border. The internal or sacral angle i Tuber sacrale) curves upwaril and a little back- VU:. til. OSSA C'OXARVM OK Muii:. \ i:\TBM. VllW. n. Ilium; >•.;,.. pubis; .S, ischium; a. anterior border (crest) of ilium; l>. iTiternal angle of ilium; <■'. external anRlc of ilium; ft. great sciatic notch; e. external border of ilium; /, iliac surface; a, linea arcuata: li, rouKh ligamentous area; /. auricular surface; b, ilio-pectineal line; /, psoas tubercle; m, transverse branch, and n. symphyseal branch of pubis; o. o', symphysis pelvis; p, anterior border of pubis (peclen); ./. tuberculum pubi- cum: r. ilio-pectineal eminence; «, tuber ischii; (. ischial arch; w, lesser sciatic notch; r, acetabular branch, and w. symphyseal branch of ischium; x, obturator foramen; i/, articular surface of acetabulum; r fossa acetabuli; 1, groove for ilio-lumbar artery. 3, groove for iliaco-femoral artery; ,•?, subpubic groove; 4. depression for inner tendon of origin of rectus femnris; .1, rough area for attachment of adductor muscles. (Ellenberger-Baum. Anat. d. Ilauslierc.J ward close to tlie first sacral spine, and forms here the highest point of the skeleton. It is somewhat thickened and rough. The external or coxal angle (Tulier coxa») forms the basis of the point of tlie hip. It is a large quadrangular mass, narrow in its middle, and enlarged at either end, where it i)ears a pair of tuberosities. It is roughened for muscular attachment. The posterior or acetabular angle meets the other two bones at the acetabu- lum, of which it forms about two-fiftlis. Its prominent upper border forms part of the superior ischiatic spine, which is roughened externally, smooth internally. Two depressions al-ove and in front of the acetabulum give attachment to the THE I8CHUXI — THE PVBIS 95 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 hori- zontal 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 (Fades pelvina) is smooth and slightly concave from side to side. The inferior surface (Facies externa) is nearly flat, and is in great part rough- ened 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 for- ward to meet the border of the other side, forming with it the ischial arch ( Arcus ischiaclicus) . 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-intemal angle or symphyseal branch (Ramus symphyseos) meets the pubis, with which it forms the iiuKT boundary of the obturator foramen. The antero-extemal 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 ob- turator vessels. The postero-extemal angle is a thick three-sided mass, the tuber ischii (Tuber ischiadicum) ; its lower border is the inferior ischiatic spine, to whicli the biceps femoris and semitendinosus muscles are attached. THE PUBIS The pubis (Os pubis) is the smallest of the three parts of the os coxje. 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 l)ladder 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 I)one 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 96 THE SKF.LETOX OK THE HORSE part is very thick in the young subject and the stalHon, 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 acetabu- lum. 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 (Ranms sym- physeos). 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 acetalnili). 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- cxternally for the obturator nerve and vessels. Development. — Each division of the os coxffi o.ssifies from one chief center. The center for the ilium appears first near the acetabulum, followed quickly by one for the ischium, and a httle 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 Fio. 62. — OssA CoxARCM OF Stallion, Dorsal , , . _,, , . , . .'^ ViKw. (After Eiienberger-Baum, Anat. the puljis. 1 he pubis and ischmui are fvir Kiinsticr.) unltctl at birth or soon after, but are not fusetl with the ihum until the second year. The epiphyseal parts fuse with the main mass at four and a half to five years of age. The acr(iiliul:ir p:irt of the pubis ossifies from a separate eenter. It is most distinrt in the embryo at three iikhiiIis, and is often ealled the os aeetaljuh. JMartin savs that the ilium has a center for the ai-edibular part, one for tlie shaft and wing, and a tUrd for the crest. He also states that tln-rc is a special center for the acetabular part of the ischium, and a transitory nucleus iu the symphyseal part of the pubis. THE PELVIS The bony pelvis is composed of the ossa coxarum, the sacrum, and the first three coccygeal vertebra;. Th(> dorsal wall or roof is formed by the sacrum and first three coccygeal vertebra', and tlie ventral wall or floor by the puliic and ischial bones. The lateral walls are formeil 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 (Aj^ertura pelvis cranialis) is bounded by the terminal line (Linea terminalis) or brim, composed of the base of the sacrum dor- sally, the ilio-pectineal lines laterally, and the anterior border of the pubis ventrally. THE FEMUR f)7 It is almost circular in the marc, semi-elliptical in the stallion, and faces ob- liquely downward and forward. It has two principal diameters. Of these, tiie conjugate or sacro-pubic diameter (C'onjugata) is measured from the sacral prom- ontory to the anterior end of the symphysis. The transverse diameter (Diameter transversa) is measured at the greatest width, /. c, just ahox-e the ])s()as tubercle. The posterior aperture or outlet (Apcrtura pelvis caudalis) is nnich smaller and is very incomplete in the skeleton. It is bounded above by the third coccygeal vertebra anil below by the ischial arch; in the fresh state it is comj)leted laterallv 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. — ]\Iarked differences exist in the size and form of the pel- vis in the two sexes. The average conjugate diameter is about 9} 2 inches (ca. 23 to 24 cm.) in the mare, 7J-2 inches (ca. IS to 20 cm.) in the stallion. The transverse diameter of the inlet averages about 9 inches (ca. 22 to 23 cm.) in the mare, antl 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 th(> 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 relativelj- narrow, and is concave from side to side. The obturator foramina are corresponilingly 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 al)ove than below. The anterior and lateral surfaces are con- tinuous and .strongly convex from side to side; there is often a central vertical rough line on the proximal part, l)ut 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 7 98 THE bKELETOX OF THE HORSE -Rit;nT Femur of IIorsk EXTKRNAL ViKW. UilT FKMt'R OF HOHS TERioR View. Fi<;. 65. — Right Femur of Horse, In- TERXAE View. /, Anterior part, 1\ posterior part of trochanter major; 2, neck; S, fovea capitis; 4, crest; />, trochanteric fossa; 6, ex- ternal or third trochanter; 7, trochanter minor; 8, eminence for attachment of biceps femoris; 9. internal border; 10, nutrient foramen; //, groo/e for femoral vessels; /3, supracondyloid crest; IS. supracondyloid fossa; i.^, trochlea; /.t, external epicon- dyle; 16, external condyle; 17, extensor fo-t-in: /-V. internal condyle; 19, internal epicondyle; SO, intercondyloid fossa. (After Schmaltz Atlas d. Anat. d. Pferdes.) THE FEMl-R 99 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 tro- chanter (Trochanter tertius); this process is curved forward, anil furnishes in- sertion to the tendon of tlie superficial gluteus muscle. At the lower part is found the supracondyloid or plantar fossa (Fossa plantaris), in which the superficial fle.xor arises; it is bounded externally by a thick rough margin, to which the outer head of the gastroc- nemius muscle is attached. The proximal extremity (Extremitas proximalis) is large and consists of the head, neck, and great tro- chanter. The head (Caput femoris) is placed at the inner side and is directed inward, upward, and some- what 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 mar- gin. The neck (CoUum femoris) is most distinct in front and internally. The great trochanter (Tro- chanter 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 "svith cartilage, over which a tendon of the middle gluteus passes, to be inserted into the crest, which is placed below and behind the convex- ity. 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 con- vexity. 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, ami forms an extensive surface (Facies patellaris) for articulation with the patella. It is very unsym- metrical; the inner ridge or lip is much wider, more prominent, and extends up higher than the ex- ternal one, and the two converge below. The con- dyles, internal and external (Condylus medialis. lateralis), are separated Viy 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 ligamentsof 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. Fig. 66. — Front Femur o . Section of Left Horse, .\ntebior The figure dullar>' cavity is tr part by fi :hows that the me- y is traversetl for the most bony trabecuI.T. 100 THE SKELETON OF THE HORSE Tlu' internal epicondyle (Epicondylus medialis) is a roundetl prominence on the internal surface of the internal condyle, to which the internal lat(>ral ligament and the adductor muscle are attached. The corresponding external epicondyle (Epicondylus lateralis) is less distinct; it presents a mark where the lateral liga- ment 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 anteii(M- extensor and peroneus tertius is attached. Development. — The shaft and the distal end each ossify from one center, Init the ]iroxiinal end has two centers, one of which is for the great trochanter. The edge of the external trochanter al.so 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. Trochlea Kxlciisiir fonsa ^^^^^^ _^^^^ Inlrriinl cpiciiiiihjle External cpii-oiuli/le — | Dcjirissioii for oriiji)) of poplitcwi Exlcrnal condyle -^^^^^^^ \ L^^g^ -Internal condyle Intercondyloid fossa 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 tibiie), 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 sub- cutaneous. The external surface (Facies lateralis) is smooth and somewhat spiral. It is wide and concave in its upper i^art, below which it becomes narrower and slightly convex, and winds gradually to the front of the l)one; 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 upjier 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 (Lineae 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 ijrominent in its uiii)er third, forming the tibial crest (Crista tibise) ; below it is reduced to a rough line, which ends at a THE TIBIA 101 small elevation near the distal end of the hone. The internal border (Margo niedi- alis) is rountled 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 hones. The external border (Crista interossea) is concave in its upper part and concurs with the fihula in the formation of the interosseous space of the leg; a smooth im- pression indicates the course of the anterior tibial vessels through the space to the a pine External condyh Head of fibula Vascular impressi Shaft of Jihula External border of tibia — ,^Tuberosity ' Groove far tendon of anterior extensor and peroneus lertius -1 — Cruovefor lateral extensor tendon External malleolus Fio. 68. — Right Tibia and Fibula of Horse, Exter.val View. front of the leg. Lower clown the border divides and incloses a narrow triangular surface. The proximal extremity (Extreniitas jiroximalis) 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 intercondy- loid eminence (Eminentia intercondyloidea) is the central prominence. ui)on which the articular surfaces are continued; it consists of a high inner jiart and a lower 102 THE SKELETON OF THE HORSE outer part (Tuherculum intercoinlyloidcum mediale, laterale). On, before, and behind the spine are the anterior and posterior intercondyloid fossae, in which the anterior crucial Hgament and the seniihniar 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 Spine Intcniiit condyle Tubercle for posterior crucial ligament Tubercle Nutrivnl foramen — Groom for tendon of inner head _ of flexor perforans Internal malleolus Fig. r,!).— Ku-.ht T ,- Fossa for anterior crucial liyament Popliteal notch " External condyle Head of fibula -' Impression of anterior tibial vessels - Interosseous space Shaft of fibula Muscular lines - External malleolus Horse. Postkrior Vie a facet for articulation with the fibula. The large anterior eminence is the tu- berosity of the tibia (Tuberositas tibiff). 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. .\ 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. THE TIBIA 1U3 The distal extremity (Extrmuitas distalis) is much smaller than the pruxinial; it is quaihansular in form and larger internally than externally. It presents an articular surface (Cochlea tibiae), which is adapted to the trochlea of the til)ial tarsal bone (astragalus), and consists of two grooves separated by a ridge. The ridge and grooves are directefl obliquely forward and outward, and are bounded laterally by the malleoli, to which the lateral ligaments of the hock joint are at- Spiiie Tubcr troclilea of the fennir. It presents for tlescrijjtion two surfaces, two iHirders, a base, and an apex. The anterior or free surface (Facies libera) is irregularly quatlrilateral, convex, and rough for musnilar 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 THE TARSUS 105 the ^■^ much the hirger, and is not verj- well adapted to the inner lip of the trochlea the fresh state, however, it is coinpletetl and rendered more congruent by curved accessory fibro-cartilage. The lateral borders converge to the apex below, and each forms a jironiinence or angle at the base. The inner angle and the adjacent part of the border give attach- ment 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 patelUv) faces upward anil back- ward, and is convex transversely, concave from before backward. The apex forms a Ijlunt point directed downward. Development. — The patella develops as a .sesamoid bone from a single center in a cartilaginous deposit in the tendon of the ciuadriceps 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 extremelj' irregular in form, but may be considered as offering six surfaces for description. The superior and the anterior or dorsal surface are continuous, and form a trochlea for articulation «ith 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 fo.ssa (Sulcus tali) forms with a corresponding one on the fibular [JHT Tibia TEBIOR Vi Accexsory cartilage Fig. 73.— Right Patella of Horse, Antehior View. Fig. 74.— Right Patella or Horse. Posterior View 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 106 THE SKELETON OF THE HORSE internal lateral ligament. The external surface is smaller than the internal, and is marked by a wide rough fussa in which the external ligament is attached. The Fibular Tarsal Bone Tlie fibular tarsal lione (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 Tuber calcis Melatars,!! luherosihi Third mcln- tarsal FlQ. 73.— RicHT TAnsr.s and Ui-i-kr Part of Mkta- TAnaus or House, Intkrnai. Vif:w. (After SfhmMltz, Atla,s d. Atiat. <1. Pfenlea.) Part of Mi:ta- PosTERioR (Plantar) (After Schmaltz, Atla.s d. Anat. d. for the muscles which extend the hock joint. It consists of a liody and an inner process, the sustentaculum tali. The body (Corptis calcanei) is enlarged at its proximal end to form the tuber Groove of trochlea r Tibial Tarsal Bonk of Horse. Anterior View. (After Schmaltz, Atlas d. .\nat. d. Pferdes.) 78. — Right Tibial Tarsal Bone of Horse, External View. (After Schmaltz, Atlas d. Anat. d. Pferdes.) calcis or "i)oint of the hock." The posterior part of this eminence gives attach- ment to the tendon of the gastrocnemius, while in front and laterally it furnishes uisertion to tendons of the flexor perforatus, biceps, and semitendinosus nuiscles. 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 sustentacu- lum tali, which projects inward. The process has a large, oval, slightly concave THE TARSUS 107 facet in front fur articulation with the til)ial tarsal, and sonictimcs a small articular surface below for the central tarsal bone. Its plantar surface forms with the smoot h inner surface of the body a groove for the deep flexor tendon (Sulcus musculi flexoris hallueis longi). Its inner surface has a prominence on the lower part for the at- tachment 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 Facets fur tibial tarsal bone Fig 79.— Right Fibular Taf Bone of Horse, .\ntkf View. (After Schm:i Atlas (l.Anat.d. Pferde 80. — Right Fourth Tar- sal Bone of Horse, Upper Surface. (After Schmaltz, Atlas d. Anat. d. I'ferdes.) FtiGHT Central Tar- sal Bone of Horse, Upper Surface. (After Schmaltz, Atlas d. Anat. d. I'ferdes.) ligament. The anterior or dorsal border is concave in its length, smooth and rounded in its upper ]3art. About its middle is a l)lunt-pointed pro,iection (Pro- cessus 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 Fused first awl second tarsals Facets for cen- tral tarsal Facets for central larsfd Third tarsal Fig. 82.— Right First, Second, and Third Tarsa Bones of Horse, Uppep Surface. (.\fte Schmaltz, .\tlas d. .\nat. d. Pferdes.) Fourth (external) metatarsal Facets for sec- "* Facets far ond and third Facet far third fourtli tar- tarsals tarsal sid I'll.. .S.!. — Proximal .Articular .Surfai Metat.irsal Bonks of Hoh: Schmaltz, Atla,- d. Anat. d. Pferde ' I.F.I-T (After straight and thick, and widens a little at either end: it ment to the long plantar ligament. rough, and gives attach- The Central Tarsal Bone The central tarsal bone (( )s tarsi centralc, scaphoid, or navicular) is irregularly quadrilateral, and is situated between the tibial tarsal above and the third tarsal below. It is flattened from above do\TOward, and may be described as luiviim two 108 THE SKELETON OF THE II0RSE surfaces and four liorders. 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 bj' a non-articu- lar groove, which separates facets for articulation with the third and the first and Tuhtr calcis Fihuliir liimal Fourlh taiviil \' ■ Trochlea of tibial tarsal ' Di]>ression for external lateral ligament .Central tarsal Third tarsal \ J- droovc. for great meta- ,J^-"; tarsal artery i. Fourth (e.rlernal) meta- _^ tarsal \iiscular canal Third (large) metatarsal Fig. 84.— Right T.vrsai, .\m) Mi Eminence for lateral ligament . Bonks ok IIonsK, Extkrnai. \'i .\n:it. .1. I'fenles.) ;.\ffcr Schmaltz, Atlas d. second (fused) tarsals. The anterior or dorsal border and the internal border are continuous, convex, and rough . Tiic posterior or plantar border 1 lear.s two prom- inences, separated bj- a notch. The external border is oblique, and bears anterior and po.stcrior facets for articulation with the fourth tarsal, between which it is ex- cavated and rough. THE TARSUS 109 First and SEco^fD 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, situ- ated 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 back- ward and inward, and is convex. Its anterior part is ridged, and gives attach- ment to the internal lateral ligament, and its posterior part bears an imjjriiit where the inner tendon of the tibiahs 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 articuhitidu 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 earl_y 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 o\-erlapped 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 aird 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. 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 chiefl\- 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 ])assage 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. 85.— CROSS-6ECTION-S llETA CARP.VL AND MkI TARS.I iL Bones of Hors C.\fte: r Schmaltz, Atlas Anat. d. Pferile^.) 110 THE SKELETON OF THE HORSE 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 cen- ters, but fusion usually occurs liefore birth. Each of the other bones ossifies from a single center. Tuberosilij Flexor surface Via. SG. — Digital Bones o Volar As THE METATARSUS The metatarsal bones (Ossa metatarsalia), three in number, have the same general arrangement as the metacarpal bones, but present some important differ- ences. Their direction is slightly ol)lique, downward and a little forward The large or third metatarsal bone is about one-sixth longer than the corre- sponding metacarpal ; ill 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 ui)i)er piirt of its external surface there is a groove, which is directed ol)li(iuely downward and backward, and is continued by the furrow formed by the appt)sition 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 THE PHALANGES AND SESAMOIDS 111 marks the position of the corresponding vein. The nutrient foramen is rehitively higher than on the metacarpal bone. The proximal extremity is much wider from before Imckward than that of the metacarpal bone. Its articular surface is slightly concave, and is marked by a large central non-articular depression, continued out- ward 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 postero- internally for the second tarsal bone. Posteriorly there are two pairs of facets for articulation uath the small metatarsal bones. The front is crossed by a rough ridge for insertion, which liecomes larger and turns downward on the outer side beliind the vascular groove. The distal extremitj' closely resembles that of the corresponding metacarpal bone. In some ca-ses the lower part of the shaft is bent backward somewliat. Tlio artieiihir sur- face extends a little liigher behind than in the ca.se of the metacarpal bone. The large metatarsal bone is even more strongly constructed tlian tlie 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 meta- carpals. The external (fourth) metatarsal is relatively massive, especiallj' 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 meta- tarsal; elsewhere it is roughened for attachment. The internal (second) meta- tarsal 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 arc as follows: The first phalanx is a little shorter, wader 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. 112 SKELETON OF THE OX SKELETON OF THE OX VERTEBRAL COLUMN The vertebral formula is C'jT|.,lv,,S5C"y,„_,„. The cervical vertebrae are nuich 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 jorocess is single, short, and thick, and presents no foramen transvcrsa- rium; 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 i.s usually bifid. The ventral spines are ])rominent 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 trans- versarium (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, funning an extensive area for the odon- toid 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 vertebrae, 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 aildition 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 pDSterior end of the series) ; the last two, although prominent, do not always articulate with the ribs. The spinous processes are long. The first is nuich 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 tlie 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 some- times have thick {wsterior margins. The lumbar vertebrae, six in number, are much longer than in the horse. The bodies are nuich constricted in the middle, expanded at either end, and bear rudi- mentary 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 VERTEBRAL COLUMN 113 114 SKELETON OF THE OX very large further hack. The articular processes are large, and tiieir facets are more .strongly curved than in the horse. The transverse processes all curve forwartl. Tliey are separated by consideral>le intervals, and form no articulations wdth 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 ^\-ide, the last being the smallest: their summits are moder- ately thickened. The sacrum is longer than tliat of the horse. It consists originally of five segments, but fusion is more eomjilete anil 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 \>y 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 ihum. The body of the first segment is very wide, and the entraiut' to the sacral canal correspondingly wide and low. The anterior articular processes are large, and are concave and semi-cylindrical in curvature internally. The lateral borders are thin, sharp, and irregular. The apex is wider than in the horse, antl tlie po.sterior end of the crest forms a j'Xjinted projection over the opening of the sacral canal. The coccygeal vertebras 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 haemal groove for the middle coccygeal artery. Vertebral curves: The cervical curve is very slight and is concave dorsally. The thoracic and lumliar regions form a gentle curve, concave ventrally. Tlic promontory is more pronounced than in tlie horse, especially in subjects in which the sacrum is inclined upward behind. Another promontory occurs at the junction of the sacnun and first coccygeal vertebra^. 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 7.5 cm. 261 cm. Variations: Sometimes fourteen thoracic vertebra; and fourteen pairs of ribs arc present; reduction to twelve with the normal number of lumbar vertebrje is very rare. According to Franck, there are sometimes seven lumbar vertebra; with the normal number in the thoracic region. The number of coccygeal vertebrae may vary from sixteen to twenty-one. THE RIBS Thirteen pairs of ribs arc 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 vridth 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 THE THOR.\X BONES OF THE SKULL BONES OF THE CRANIUM 115 cartilages. The first costal cartilages are very short; they articulate by tlieir internal surfaces wnth the sternum, but not with each other. Tlic pre:seiice of a fourteenth rib is not very rare. It is usually float ing ami may correspond to an ail- 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 ef|ui\-alent to the foramen rotundum, lacerum orbitale, and patheticum of the horse. The posterior one is the foramen ovale, which transmits the inferior maxillary nerve. 116 SKELETON OF THE OX 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 dose to the sphenopalatine foramen, and contains a small sinus which communi- cates with an ethmoidal meatus. The temporal wing is small, but forms a promi- nent thick pterygoid crest. The pterygoiil process is wide, and the pterygoid or alar foramen is absent. The sphenoidal sinus is absent in the calf and small in SO' Fig. sn. — Skdll and .\tlas of 0,x. Lateral View. .9. Zygomatic arch: 11, coronoid process; IS, supraorbital process; 13", paramastoid or styloid process: IS", occipital comlyle; 14, parietal bone; IS, frontal bone; 16, squamous temporal bone; 17, external audi- tory meatus; IS, temporal condyle; 19, orbital s\irface of lacrimal bone; £0, malar bone; SI, facial surface of lacrimal bone; 25, nasal bone; 5.j, nasal process of prema.villa; 24', incisor teeth; 26, maxilla; ^7, facial tuber- osity; infraorbital foramen in front of gT; I SS' . molar part of ramus of mandible; 30, broad vertical part of ramus; SO", angle of jaw; SI, condyle of mandible; .ie, atlas; j. wing of atlas, (.\fter EUenberger-Baum, .\nat. fiir Kiinstler.) the adult; it communicates by one or two small openings with an ethmoidal meatus, and so with the nasal cavity. 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 proj(>cts forward between the upper and lower turbinals. The lamina papyracea appears to a small extent externally in the pterygo-palatine fossa, forming jiart of the upper margin of the sphenopalatine foramen. The interparietals are primitively jiaired, but unite before birth. As already BONES OF THE CRANIUM 117 mentioned, fusion occurs before or shortly after birth mth the parietais and supra- occipital. Xo tlistinct tentorium osseum is present. 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 Fig. 90. — Skcli. of Ox, Bas.^l View, Without M.^ndible. F, Pterjgoid bone; G. horizontal and C, perpendicular part of palate bone; H, occipital bone; J . malar bone; A', sphenoid bone; O. ma.xilla; P, vomer; Sch., squamous temporal; S(., frontal bone; Z, preiua.xiUa; 1, for. magnum; 2, occipital condyle; S, paramastoid (styloid) process of occipital; i, hypoglossal and condy- loid foramina; 5, for. lacerum; 6, pharyngeal tubercles; 7, bulla ossea; S, muscular process (left one is removed to expose for. ovale); 9, hyoid process; /O, ext. auditon,' meatus; J ;, zygomatic process; /«. external opening of parieto-temporal canal; IS, postglenoid process; H, temporal condyle; IB, for. ovale; 16. for. lac. orbitale + for. rotundum; /T, optic foramen; W, ethmoidal foramen; /9. orbital opening of supraorbital canal; £0, ptery- goid crest; 31, hamulus of pterygoid bone; 22, lacrimal bulla; 2i, temporal process of malar; 2i. pterjgoid process of maxilla; 23, sphenopalatine foramen; 26, maxillary foramen; 27, posterior palatine foramen; 2S, anterior palatine foramen; 29, acces.sory palatine foramina; SO, palate process of maxilla; SI, interalveolar border; 32, palatine cleft; 33, palate process of premaxilla; Si, fissura incisiva; So, facial tuberosity; S6, pos- terior nares. (EUenberger-Baum, Anat. d. Haustiere.) 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 parietais are excavated to form part of the frontal sinuses in the adult animal. 118 SKELETON OF THE OX Tlie conilition in the youiiK 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 lor the attachment of the Ugamentum nucha". From either side of this a line (■ur\-es outward, and divides the stn-face 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. Fig. 91. — Skull of Ox, Dorb.^l Vikw (with Mandible). 12, Supraorbital process; 14, parietal bone; 16, frontal bone; 16, squamous temporal bone; 19, orbit; SOt malar bone; St, lacrimal bone; 22, nasal bone; 2J, prema.xilla; 26, maxilla; 27, facial tiibcrusily; 24, incisor teeiii. U-Vfter EUenberger-Baum, Anat. f. Kiinstler.) 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 witii the i)arietals a large central frontal eminence (Torus frontalis), the highest point of the skull. At the junction of tht^ posterior and the lateral borders are the processus comu or "horn-cores," for the support of the horns. These processes arc 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 matri.x of the horns. The base has a constriction, the neck. The interior is excavated to form a number BONES OF THE CRANIUM 119 of irregular intercommunicatiiif!; spaces, divided hy hony septa, and communicat- ing with tiie 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 anil posterior margins; it is short and joins the frontal process of the malar bone. The supra- orbital foramen (often double) is situated about an inch inward from the root of the process; it is the external orifice of the supraorbital canal (C'analis supraorbi- Winy of alia Squamous temporal Imne Zygomatic arcti Angle of jaw Malar bone Facial tuberosity- Ramus of mandible Premaiilla Exttriial auditory meatus Fic. 92.— .Skv: IS. Basi-occipital; IS". p.iramastoi.l or styloid process; l.i". occipital comlyb body of mandible; .i/. condyle of mandible; ,J J, ventral tubercle of all: Kunstler.) (.\fter Ellcnl.erger-Bau teeth; 28, .. Anat. fiir talis), which passes dowTiward 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 Iwnes, and sutural or Wormian bones are often found at this junction (naso-frontal suture). The orbital part is extensive; it is perforated behind bv 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 bv the orbital wing of the sphenoid. The temporal part is also more 120 SKELETON OF THE OX extensive tlum in the horse. The frontal sinus is very extensive, being continued into the parietals and oceipital, and the horn professes 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 tlie 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 articu- lates with the malar only. The condyle is convex in both directions. The post- glenoid 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 dowTiward 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 occipi- tal 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 bj* the occi- pital bone. Bones of the Face The maziUa 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, form- ing 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 closetl 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 liefore 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 liones. The body of the premaxilla is thin antl 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 sur- face 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 iiard palate. The anterior palatine foranicii (i|iens near the junction with the maxilla, about half an inch from the meilian jjalatine suture and crest. BONES OF THE FACE 121 Accessory palatine foramina are also prosent. The ])alatiiie groove is usually not very distinrt. 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 pos- terior part of the lateral wall of the nasal cavity and in part hounils the narrow pos- terior nares. Its internal surface is nearly flat, and is smooth and free, except behind, where it is overlapped liy the pterygoid bone. The external surface is attached to a small extent to the pterygoid process behind, and is free elsewhere. The spheno-palatine foramen is a long elliptical opening, formed l)y 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. 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 Fig. 93. — Median Sectiox of Skull of Ox, Without the M.\ndible. The mucoiLs 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: /, inferior turbinal; g, alar fold: h, inferior turbinal fold: i, lateral mass of ethmoid (ethmoturbinals): i', large ethmoturbinal or middle turbinal: k. frontal sinus; /, 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: 3, 3, inner and outer plates of frontal bone; 4, 4', outer and inner plates of parietal bone; 6, o* , 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), (.\fter EUenberger, in Leisering's .\tlas.) to the palate bone and the pterygoid process, but a small part is free in the jiterjgo- 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 stronglj' curved from side to side. It does not fuse later- ally 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 tlie 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; 122 SKELETON OF THE OX 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 over- lapped by the zygomatic process of the temporal bone, completing the zygomatic arch. The superior turbinal bone is less cril)riform 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 ilownward, outward, and upward to be applied out- wardly to th(> frontal and lacrimal bones. It thus incloses a cavity which communi- cates with the mitldle meatus nasi. (In the macerated skull it opens into the frontal sinus, l)ut this communication is closed by mucous membrane in the fresh state.) The inferior turbinal bone is shorter liut much broader than in the horse. It is attacihed to the ma.xilla by a basal lamella about an inch (ca. 2 to 3 em.) 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 premaxillte. The anterior third of its thin lower edge fits into the nasal crest of the maxilla; behind this it is free and separated bj' a considera!)le interval from the nasal floor. The two halves of the mandible do not fuse completely even in ad- vanced age. The symphyseal sur- faces 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 sharj). 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 (luite 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 fora- men 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 jirocess is extensive and curves backwartl. The hyoid bone has a short tuberous lingual process. The middle cornua are almost as larfj;e as the small cornua. The great cornua are narrow, except at the ends. The ujiper end divides into two branches, which correspond a. Boil cartilage, c'; d, sin j7. muscular aiigli Haustiere.) . 94.— Htoid Bone of Ox. '', lingual process: c, tli,\Toid cornu and nail cornu; e, middle cornu; /, great cornu; /. (Ellenberger-Baum, Anat. d SKULL OF THE OX AS A WHOLK 123 to the two angles of that of the liorse. The thyroid cornua do not fuse with the l)odv. SKULL OF THE OX AS A WHOLE The skull of the ox is more clearly ])yraniidal than that of the horse, and is shorter antl 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 ca^'it^•, which is smaller than in the horse. The superior or frontal surface is formed by the frontals, nasals, and pre- maxillae. The frontal part is quadrilateral and very ex-tensive, 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 premaxillaj do not bend downward as in the horse; they are relatively thin and weak, and are separated by an interval which has a mde anterior part in place of the foramen incisivum. The lateral surface is more triangular than in tb.e horse. Tiie 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-extemal 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 ^\•ide from before backward. The glenoid ca\'ity 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 siuface is short and wide, especially in its cranial part. The occipi- tal condyles are limited in front by transverse ridges. The tubercles at the junc- tion of the occipital and sphenoid are large. The condyloid fossa; 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 compres.sed prominence. The muscular processes are usually long and narrow triangular plates, with one or two sharp points. The ex-ternal auditory process is directed almost straight outward. A curved plate extends do^\•nward 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 f(,r.nniiia. 124 SKELETON' OF THE OX Tlie anterior i)alatine I'uruiniiui arc an incli or moro from tho posterior margin, and about the same distance apart. The palatine grooves are tlistinct for a short distance only. Just beyond the cheek teeth the palate narrows and becomes con- cave; 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 nucha^. P>om this a median crest extends toward the foramen mag- num, and laterally two lines (Linete nucha; 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 extremi- Fio. 93. — Cnoss-SKCTiON of Skoll of Ox. Sfption Fin. 96. — Cross-section of Skull of Ox. Section Passes Through Fifth Cheek Tooth. Passes through Second Cheek Tooth. a, b, c, Superior, middle, inferior meatus: h' , 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; c, /, outer and inner walls of d: «, 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 cav- il, maxillary sinus; p, palatine sinus; q, septum between ma.xillary anil palatine sinuses; , septum between palatine sinuses; (, common meatus; «, na.so-lacrimal canal; v, floor of of palatine sinus; /, septum na.si; 2, posterior part of second cheek tooth; S, posterior i; .;, Iiard palate, (.\fter Ellenberger, in Leisering's .A.tlas.) ity; m, lacrimal sin r, infraorbital canal nasal cavity and ro part of fifth cheek to ties the processus cornu — except in the polled breeds. The condyles ar(< further apart, and the articular surfaces are more clearly dividetl into upper aiul U)wer parts than in the horse. 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 fossce are smaller, and the sella turcica is nmch 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 sellse). The internal sagittal crest is promi- nent 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 inijiressions are very pronounced. The parieto-temjK)ral canal is formed entirely in tlie temjioral bone, and opens at SKULL OF THE OX AS A WHOLE 125 the apex of the petrous, where it is joined hy the condyloid canah The foramen lacerum is (Hvided into two parts (For. lacerum anterius et posterius). Tiie nasal cavity is inconii)Ietely divided by the septum, which does not reacli the floor posteriorly. The floor is relatively long, and is more concave from side to side than in the horse. In the ilry skull it has a large oval opening into the palatine sinus, which is closed during life hy mucous membrane. The middle meatus is divided behind into u]iper and lower branches by the great ethmoturbinal. The posterior nares are narrow and oblique. Fig. 97.— Skii , .r. ~ ' i ■ ,, ,i Vn.w. The outer plate of bone has been removed to show the sinu.ses. a. Frontal sinus; a', cranial plate of frontal bone ; o", anterior part of frontal sinus, which is separated from remainder by a septum (W; c, e', communications between frontal sinus and nasal cavity; d, supraorbital foramen; e, supraorbital canal; /, 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: /, orbit; /, frontal bone; 1' , processus cornu; ^. nasal bone; S, premaxilla (nasal process); .i, maxiila: .5. lacrimal bone: ff, malar bone; 7, dotted line indicating course of naso- lacrimal duct. (After EUenberger, in Leisering's .\tlas.) 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 dis- tance 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 hmits the temporal fossa aliove, and into the root of the supraorbital process. At the highest part of the cranial cavity and at the tuberosity on the posterior surface 126 SKELETON OF THE OX the two plates of the bone come together. The cavity is very irregular and is sub- divided 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 communi- cations 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 nuicous memlirane. The maxillary sinus is excavated chiefly in the maxilla, lacrimal, and malar, and is not divitled 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 u])per 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 Fig. 9S. — Skull of Ox, Lateral View withott ^lANniBLE. The maxillary, lacrimal, and turbiual sinuses have been opened, and a ijortion of the orbit removed, a. Cavity of superior turbinal bone; 6, lacrimal sinus; c, maxillary sinus; d, communication between ma,\illary and palatine sinuses; e, opening between maxillary and lacrimal sinuses; /, thin osseous bulla; f/, lacrimal bulla; It, orbit; 1-6, cheek teeth; 7, nasal bone; S, premaxilla (nasal process): 9, maxilla; 9', infraorbital foramen; 10, frontal bone; 11, lacrimal bone; IS, 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 (perjjendicular i)art); 19, pterygoid bone (hamulus); BO, tympanic part of temporal; £0' , mus- cular i)roce99 of i>etri>us teinjioral. (After EUenberger, in Leisering's Atlas.) lacrimal, frontal, ethmoid, and turbinal bones, at the inner side of the orbit.' The floor of the cavity is irregular and the roots of the last three or four cheek teeth pro,ject up into it, covered by a plate of bone. The sinus communicates with the jialatine sinus freely over the infraorbital canal through an oval oj^ening 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 opjiosite 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 thecavity is sometimes regarded as a partof that sinus. The large defect in the bony roof of the sinus is closed by two layers of nmcous membrane in the fresh state. The palatine canal passes oblicnidy through the posterior part of the sinus. ' This is termed the lacrimal sinus by some authors. It is similar in location and in the posi- tion of i(s orifice to the turliinal part of the frontal sinus of the horse, with the important difference that it iloos not cominimicate with the frontal shui.ses in the o.\. BONES OF THE THORACIC LIMB 127 The sphenoidal sinus is almost entirely in the sjjhenuid 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 verteliral 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 Ijelow. Its free border is somewhat tliickened 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 promi- nent 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 fossae are deep and wnde. The external condyloid crest is represented b_y 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 pro- nounced 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 128 SKELETON OF THE OX part of the limb in flexion. The facets for the radial and intermediate carpals are narrower than in tlie 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. The ulna is more fully developed than in the horse. The shaft is complete, Bicipilal groove External tnberosily of humerus Deltoid tuberosity Musculo-si)iral groove ExteriKit eoiidijloiil crest _ •_ y- HxleriKU eoiu Exlcnial tuberosity of radius Shaft of radium Radial carpal bone . Fused second and third carpal bones . Ulnar carpal bone . Intermediate carpal bone Fourth carpal bone Metacarixd tuberosity Anterior groove of large metacarpal bone First phalanx - Second phalanx ■ Third pludjinx Fig. 99. — Skelkton of Lkft Fore Limb of Ox, from SnorLDKn Downward, Anterior \'iew. (After Ellen- herger-Baum, .\nat. fiir Kvinstler.) throe-sided, and strongly curved. It is fused with the radius in the adult, excejit at the two interosseous spaces mentioned above. Its upper part contains a medul- lary canal which extends somewhat into the proximal end. The olecranon is large and bears a rounded tuberositv above. The distal end is fused with the BONES OF THE THORACIC LIMB 129 radius; it projects belowthe level of the latter, formingthe styloid process (Processus styloideus ulnse), which furnishes part of the facet for the ulnar carpal. The proxi- mal and distal ends unite with the shaft at three and one-half to four years. 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 ratlial and intermediate resemble in general those of the horse, but External condyle of humerus External tuberosity of radius Proximal interosseous space Shaft of ulna Distal end of radius - Intermediate carpal bone Radial carpal bone Fused second and third carpal bones Metacarpal tuberosity > - Distal interrosseous space Sliihiid jtrocess of ulna Accessory carpal bans . Ulnar carpal hone . Fourth carp(d bone . Small metacarpal bone Large metacarpal bone Proximal sesamoid ■ First phalanx Pig. 100.— Skel - Second phalanx ■ Distal scsa7nmd Third phalanx Fore Limb of Ox. from Elbow Downward, External Vi lierger-Baum, .\nat. fur Kunstler.) are less regular in shape, and their long axes are directed obliquely backward and inward. The radial is narrower tlian in the horse and curves upward hehinrt. i no intermediate is constricted in its middle, and wider behind than in front, ine ulnar is large and verv irregular. Its proximal surface is extensive and sinuous ana articulates with both radius and ulna. Behind is a large oval facet for ;"-t>;"la 'OT with the accessory carpal. The accessory is short, thick, and rounded; it articu- 9 130 SKELETON OF THE OX latos with the uhiar carpal only. The first carpal is absent. The second and third carpals arc 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 meta- carpal bone. The large metacarpal bone (JNIc. 3 + 4) results from the fusion of the third and fourth bones of the foetus, 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 iwsterior surface is flat and presents a similar but much fainter groove. The borders are rough in the ujiper third. The proximal end bears two slightly concave facets for articulation with the bones of the lower row of the car- pus; the inner area is the Lirger, 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 ]iart 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 hors(>, but nuich smaller. The medullary canal is divided into two parts by a vertical septum which is usually incomplete in the adult. The small metacarpal bone (^Ic. 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 foetal state, viz., the second, third, fourth, and tiftli. 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 develojied and liave 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 intcrdigital surface is flattened and its posterior part bears a promi- nence for the attachment of the intcrdigital 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 s. 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 tlircr-sidcd. 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 tuliercles behind. The distal ex- tremity is smaller than the proximal. Its articular surface encroaches consider- ably 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 inter- digital 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. BONES OF THE PELVIC LIMB 131 Each has four surfaces. The dorsal or wall surface is marked in its lower part V)y a shallow groove, along which there are several foramina of considerable size; tlie 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 oblicjue 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 l)lunt, 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 correspond- ing part of the distal end of the large metacarpal bone by their anterior surfaces, Vvith 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 olslique 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 back- ward, 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. Tlie 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 nm is rounded and !s usually marked bv 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 132 SKELETON' OF THE OX into a foramen by a bar of bone. The other notch is antoro-internal, small, and sometimes replaced by a foramen or absent. The obturator foramen is large and elliptical. Its inner border is thin and sharp. External condyle of femur ■ External tuberosity of tibia ■ Exlcrnnl iiiiilUohis Filiiilftr larsiil bune Inieriitil ninllrohis Tibial tarsal bone ■ Central + fourth lorsnl bone ' Scconil Inrsal hone Fir^l l,ii:<„l hnnr Si/iiill iiiitiiUirsal bone Proximal sisinnnid ' First jihtilaiix Second phiilinii- Distal .■^csiniiunl Third jihatanx Fig. 101. — Skeleton of Left Hind Limb of Ox, from Middle of Thigh Dow.nward. Posterior View. SI, Tibia; S4, tiihcr oalcis; ^5, large metatarsal bone, (.\fter Ellcnbergcr-Baiim, .Viial. fiir KOnstler.) The pelvic inlet is elliptical and is more oblique than in the honse. In a cow of medium size the conjugate diameter is about nine and a half inches (ca. 23 to 24 cm.), and the transverse al)0ut seven inches (ca. 18 cm.). The anterior end of the symphysis lies in a transverse plane throush the junction of the third and fourth BONES OF THE PELVIC LIMB 133 sacral segments. The roof is concave in l)otli directions. The floor is deeply con- cave, particularly in the transverse direction. The cavity is narrower and its axis is indineil strongly upward in the posterior part. The distance between theacetah- ulum 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. The femur has a relatively small shaft, which is cylindrical in its middle, pris- matic 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 intcrtrochanterica posterior) connects it with the tro- Front.ii- Slctio-v of Left Tibia or Ox, Anterior View. Fig. 102.— Froktal Section of LEt-r FEiwrR of Ox, Fio. 103.- Fron't View. These figures show the internal architecture of these bones, and e,si,eeiaU.v the great extent of the me 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 articula- tion with the distal end of the fibular tarsal bone. The posterior surface bears two BOXES OF THE PELVIC LIMB 135 tuberosities, of which the outer one is rounded, the inner more prominent and nar- rower. The first tarsal bone is quadrihiteral anil 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 proxi- mal 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 tar-sal component, and the posterior sur- face 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 distinctlj' Central + fourth tarsal bone First tarsal bone Proximal sesamoid Distal sesamoid Tibial tarsal bone Second + third tarsal bone Fig. 104. — ^Skeleton" of Distal Part of Left Hind Limb of Ox. Internal View. S4, Tuber ealcis; i?-5. large metatarsal bone; 30, first phalanx; 3/, second phalanx; 35, third phalan.x. (.\fter EUenberger-Baum, Anat. fur Kunstler.) 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 obhquely through the extremity, opening on the posterior part of its proximal surface. The postero-internal angle of the pro.ximal end bears a facet for articulation with the small metatarsal bone. 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 ca\'ity is subdi\-ided 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. 136 SKELETON OF THE PIG The phalanges and sesamoids resemble those of the thoracic hmb so closely as to render separate description unnecessary. SKELETON OF THE PIG VERTEBRAL COLUMN The vertebral formula is CjT,,_,5L„-7^4*^"y2o-23- The cervical vertebrae 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 laminae 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 Fig. 105. — Skeleton of Pig, L.\terai. View. a, Cranium; h, upper jaw; c, lower jaw; III. -711 ., cervical vertebra-; IR.w., first thoracic vertebra; IS R.W., thirteenth thoracic vertebra (ne.xt to last); IL.. first lumbar vertebra; 61.., sixth lumbar vertebra (next to last usually); A'., sacrum; .S., coccygeal vertebra; IR., first rib; HR., last rib; R.kn., costal cartilages; St., sternum; d, supraspinous fossa of scapula; d\ infraspinous fossa; /, spine of scapula; 2, neck of scapula; c, humerus; S, head of humenis; 4, tuberosities of humerus; S, deltoid tuberosity; 6, external epicondyle of humerus; /, radius; o, ulna; 7, olecranon; /j, carpus; 1S~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 coxae); 9. internal angle of ilium (tuber sacrale); /O, superior ischiatic spine; ((.ischium; //.tuber ischii; r, pubis; 12, acetabulum; s. femur; 13, trochanter major; /4, trochanter minor; 15, external epicondyle; (, patella; w. tibia; W, crest of tibia; 17, external condyle of tibia; r, fibula; w, tarsus; 26-31, tarsal bones; SB', tuber calcis. (.\fter Ellcnberger, in Leisering's Atlas.) 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 i.^ 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 in- clined backward, the posterior ones forward. The last cervical is recognized by the groat 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 liody, which liears a pair of VERTEBRAL COLUMN 137 small facets on its posterior margin for the heads of the first ribs. It has foramina transversaria, and usually two foramina in cither side of the arch. The dorsal arch of the atlas hears 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 jias.ses through tiie po.sterior 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 ])art, 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. The thoracic vertebrse are often fifteen in number. Their bodies are relatively long, constricted in the middle, and without ventral crests. Their extremities are Fig. 106. — Atlas of Pig, Dorsal View. Fig. 107. — Axis of Pig. Lkft Lateral View. a, Wing; b, ventral tubercle; c, foramen transver- a, Odontoitl process (dens); b, spinous process; ; d, alar foramen; e, intervertebral foramen; /, ilor- c. anterior articular process; d, posterior articular pro- sal tuberosity; ff, articular surface corresponding to that of cesses; e, transverse process; /.foramen transversar- posterior articular process of typical vertebra; h. facet on ium; n, bar of bone which bounds h. intervertebral ventral arch for odontoid process. (Ellenberger-Baum, foramen; i, vertebral foramen. (Ellenberger-Baum, Anat, d. Haustiere.) Anat. d. Haustiere.) 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 communi- cates with the former or with the posterior intervertebral foramen. Sometimes there is a foramen in the anterior part of the process also. There are manmiillary processes except on the first two; in the posterior five or six vertebra? 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 al)out 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, lieyond which there is a gradual increase. The summits are slightly enlarged and lie almost in a straight line. 138 SKELETON OF THE PIG The occurrence of fifteen tlioracic vertebrae 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 vertebrae 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 i)()storior part of the series. The arches are deeply notched, and are separated l)y an increasing sjiace dorsally. The mammillary processes project outward and jjackward. The transverse processes are bent downward and incline a little for- ward. 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 ])osterior edge of the root of the process is marked by a notch in the anterior part of the series, a fora- men 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 vertebrae occur with ahiiost equal frequency. The number may be reduced to five, and the number of presacral vertebra; varies from twenty-six to twenty-nine. The sacrum consists usually of four vertebrae, which fuse later and less com- pletely 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 seg- ments. 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 fora- mina, and tubercles which indicate the fused articular processes. The wings re- semble 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. The coccygeal vertebrae are specially characterized by the presence of func- tional 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 ]ilate-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 %vhich is at the jtmction of the two regions. The sacral promontory is not so pronounced as in the ox, and the sacral curve is flatter. Fiti. lOS. — Sacrum of Pig, Dorsal \'i a. Wing; b, dorsal sacral foramina; c, :i process; I-4, segments or sacral vertebrse. berger-Baum. Anat. (1. Haustiere.) 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 THE STERNUM — BOXES OF THE SKULL — CRANIUM 139 breeds, so tliat there is a fairly distinct angle, except toward the end of the series. The liackward 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 com- pletely fused in the adult. The last segment has a long narrow part which liears the xi])hoid 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. Parietal bone Fronlal bone Supraorbital I'remaxilla ■^ 12 // Fig. 109. — Skull of Pig, Lateral View without Mandible. 1, Occipital condyle; 2, paramastoid or styloid process; 3, bulla ossea; i, e.TiternaI auditory meatus, 5, zygomatic process of temporal bone; 6, sphenoid bone; 7, orbital opening of supraorbital canal; ^, malar bone: B, pterygoid bone; 10, pterygoid process of sphenoid; 11, pterygoid process of palate bone; 11-S, teeth; C, canine tooth; Pl-A, premolars; Ml-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 diver- gent 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 140 SKELETON OK THE PIG into the cranial cavity. The foramen magnum is ahnost 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 hypo- glossal 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. Parietal bone Temporal fo! Squamous leiiiijora bone External auiL meatus Zygomatic process of temporal bone Supraorbital tyro- cess Frontal hone Supraorbital fora- men Zygomatic process of malar bone Lacrimal bone I nfraorbilal foramen Nasal process of premaxilla Nasal bone Canine tootli Palatine cleft Body of premaxilla Occipital crest Temporal crest Parietal crest Lacrimal foramen Preorbital fossa Fin. 110.— Skfi.i. of Pin. Oorsai. V The interparietal fuses bcfon; l)irth with the occipital. The tentorium osseum is absent. The parietal is o^'crlappod by the occipital bone behind and concurs in the formation of the occipital crest. Its external surface is divided liy the parietal crest into two parts. The inner part (Planum parictale) 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 conca^•e, 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 141 forward and outward to the supraorbital process. The internal surface is concave and is niarketl 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 paricto-tcm]ioral 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 sujDraorbital 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 w-all 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 per- forated 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 wnng of the sphenoid. The temporal part is very narrow antl is separ- ated 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 resem- blance to that of the ox. The zygomatic pro- cess 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 direc- tion. The postglenoid process is absent, but the articular surface is bounded behind and in- ternally by a crest. There is no parieto-tem- poral canal. The external auditorj' 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 zyg;omatic process) contains an air-cavity, which is continuous with the sphenoidal sinus. The sphenoid bone is short and resembles that of the ox in general. The- body Fig. 111. — Basal Scrface of .Skull of Young Pig, without the Mandible. Sq.o., Supraoccipitai; £".0., exoccipital; B.O., basioccipital; B.s.. body of sphenoid; Sfj., squamous temporal bone; V, vomer; J/x., maxilla; Pa., horizontal part of palate bone; P.p., palate process of maxilla; Z .. malar bone; J. premaxilla; D.c, canine tooth; Jl-S, in- cisor teeth; O, temporal fossa; /.occipital crest; 2. for. magnum; J, occipital condyle; 4. para- mastoid (styloid) process; o, bulla ossea; fi, for. lacerum basis cranii; 7, pterjgoid process of sphenoid; S, posterior nares; 9, anterior palatine foramen; /(?, palatine cleft. (Struska, .\nat. d. Haustiere.) 142 SKELETON OF THE PIG is narrow. The pituitary fossa is very deej), and is limited behind hy a prominent dorsum sellae; the dorsum bears lateral projections, the posterior clinoid processes. The foramen ovale is absent, being included in the foramen laccrum 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 \v\th the pterygoid and palate bones in the formation of the pterygoid fossa, which opens Inickward 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 ptery- goid 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 corresj^onding to the ethmoidal meatuses. The cribriform plate is ex- tensive 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 endoturljinals 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 maxil- lary 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 trans- verse 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 Ijody of the premaxilla is narrow and prismatic. It presents three alveoli for the incisor teeth, which are separated b^' 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 rhomljoid 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 i^alatine 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 externallj^ by the maxilla and concurs in forming part of the palatine canal. Superiorly the two plates separate and inclose FACE 143 an air-cavity which opens into an etlinioidal meatus. The inner jilatc curves inward and unites with the vomer and ethmoid to form a horizontal plate (Lamina transversalis), which ilivides 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 pterj'goitl 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 l)y 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 oljlique muscle of the eyel)all 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 upjier 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 regardefl as dividing into frontal and temporal branches.) The lower border is convex and becomes thinner behind. Theturbinal bones resemble those of the ox. Thesuperiorturbinalis, 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 pre- maxilla or very close to it. The lower border is received into a groove formed by the nasal crest of the maxillse and palate bones and in front by the palatine processes of the premaxillte. 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 liy 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 promi- nence is a pair of foramina. The alveolar border presents six alveoli for thi^ in- cisor 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 numlier 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 144 SKELETON OF THE PIG 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, l)ut 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 rela- tively 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 transverselj-, 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 cartila- ginous in the young subject and does not ossify at either end. The great cornu is a very slender rod, slightly en- larged at either end ; the upper extremity is attached to the hyoid process of the temporal by a rather long and wide bar of cartilage. t'TXl^'^^ ,/ Fig. lis -Mandible of Pig. a, Body of mandible; b, horizontal part of ramus; /, vertical part of ramus; c, interalveolar border; c', interval between canine and corner incisor; c" , interval between first and second premolars; d, mental foramina; c, vascular impression; g, coronoid proces.s; h. condyle; i, sigmoid notch; k\ mandibular foramen; I~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 dif- ferent subjects. Primitively the skull is long — especially in its facial ]5art — and the frontal profile is almost st raight . The condition is very ])ronounced in wild or semi-feral pigs, and exists also in the improved breeds during extreme youth. Most of the latter are decidedly brachyccphalic when full.y tlcveloped; the face is "dished" in a pro- nounced fashion. The frontal region slopes sharply upward, and the nasal region is shortened, and in some specimens even distinctly concave in profile. The supra- orbital 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 seijanito the nasal and lateral regions. The lateral surface is triangular when the mandilile is included. The tem- poral 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 cavitj' 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 antl forms a pointed recurved projection al)Ove and in front of the external auditory meatus. THE SKULL AS A WHOLE 145 The orbit is small. Its margin is deficient behind in the dry skull, thick and rounded in front and Ijclow. The ca'V'ity 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 ptery go-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 pre- orbital region is deeply grooved in its length and is clearlj' 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 check 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 paramas- toid 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 hypoglo-ssal foramen, and in front of it are the stjdo-mastoid foramen and a deep cavity in which the hyoid process is concealed. The bulla ossea is long, compressed lateralh', 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 sur- face is separated from the temporal fosste 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 fossae are extensive and very oblique. The floor resembles that of the ox, but the foramen ovale is absent, the dorsum sellae 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 10 146 SKELETON OF THE PIG 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 com- municates 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 mafinum 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 fioor, 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 bod.y, 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 jDalate bone which com- municates with an ethmoidal meatus. BONES OF THE THORACIC LIMB The scapula is very wide, the index being about 1 : 0.7. The spine is tri- angular and is very wide in its middle, which curves backward over the infra- spinous 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 / minus the cross-bar; this is due to the marked backward and forward inclination of the prox- imal 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 roundetl 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 tuber- osity 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 phite of bone which separates it from the coronoid fossa is thin and some- BONES OF THE THORACIC LIMB 147 times perforated. The proximal end unites with the shaft at three and years, the distal at one year. The radius is short antl narrow, hut 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 con- siderably 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 liga- ment. 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 exten- sive, 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 ex- tremity 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 articu- lates 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. Four metacarpal bones are present. The first is absent, the third and fourth arc 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, solidated at about two years of age. half Fig. Ma Forearm OF Pig, Axtero-ex- TKRNAL View. a, Radius; b, ulna; c, radial carpal; d, intermediate carpal; c, ulnar carpal; /, ac- cessory carpal; g, first carpal; /(, second carpal; /, third car- pal; k, fourth carpal; l-o, second to fifth metacarpal bones; ;>-«, second to fifth dig- its; /, olecranon; 2. beak of ulna (proc. anconeus); S. semi- lunar notch; 4, styloid process of ulna; 6, styloid process of radius; 6. distal epii>hyseal lines; 7, first phalanx; S. second phalanx; 9, third phalanx. (Ellenberger-Baum, Anat. d. Haustiere.) The bones are con- 148 SKELETON OF THE PIG The third aiui fourth metacarpals are flattened from l)efore backward, three-sided, and phiced 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 laehind. 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 coxae is long and narrow. The ilium and ischium are almost in line with each other and sagittal in direction. The wing of the iliiun bends outward much less than in the horse or ox. The gluteal surface is divided into two fossae 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 prom- inent 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-pectincal 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 coxoe 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 anchjdosis. 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 su])erior ischiatic spines are more incurved, and the ischial arch is nmch narrower and tlceper. 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 supra- condyloid crest. There is no supracondyloid (plantar) fossa. The head is strongly curved, and is marked toward the iimer side by a rather large depression for the BONES OF THE PELVIC LIMB 149 attachment of the round Hgament. The neck is distinct. The trochanter major, ahhough massive, does not extend up as high as the head. The trochanteric ridge and fossa resemble those of the o.\. 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 rela- tively narrower transversely and thicker from before liackward. 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 di.stal end forms the external malleolus. It is grooved externally, and articulates wnth the tibia and tibial tarsal internally, with the fibular tarsal bone dis- tally. The patella is very much compressed lateralh' and presents three sur- faces. The tarsus comprises seven bones. The tibial and the fibular tarsal re- semble in general those of the ox. The axis of the tibial is, however, slightly oblique downward and in- ward, and its distal end bears a double trochlea for articulation with the cen- tral 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 lielow. 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 l)y 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 Fig. 114. — Cox.\l Boxes of Pig, Left Po-sterior View. a. Wing, b. shaft, c, external angle, d. anterior border, <■, internal angle, /, gluteal line of ilium; g, great sciatic notch; h, smooth, i, rough part of ventral surface of ilium; k, psoas tubercle; (, ilio-pectineal emi- nence; m, acetabular branch, n. symphyseal branch of pubis; o, obtur- ator foramen; p, p', ischium; q, 9', tuber ischii; r, symphysis; s, ischial arch; t. (', superior ischiatic spine; n, acetabulum; r, epiphyseal line. (EUenberger-Baum, Anat. d. Haustiere.) 150 SKELETON OF THE DOG with a discoid sesamoid bone. The second and fifth are placed more on the pos- terior aspect of the large Ijones tlian is the case in the fore limb. The first and second phalanges are a little longer and narrower than those of the fore linil). SKELETON OF THE DOG VERTEBRAL COLUMN The vertebral formula is CjT^Ljfj^SjCyjj.^s- The cervical vertebrae are relatively longer than in the ox and the pig. The bodies of the typical vertebrae diminish in length from first to last and are com- pressed 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 forwaril. The transverse processes of the thirtl, 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 down- ward 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 ujipcr svu'face 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 fossae. 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 ter- minated 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 vertebrae are wide and com]3ressed 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 manmiillary 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 acces- sory 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. VERTEBRAL COLUMN 151 The bodies of the lumbar vertebrae are decidedly flattened dorso-ventrallj', 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 Ijackward over the posterior notches of the first five. The anterior articular processes are large, compressed laterally, and bear Fig. lis. — Skeleton of Dog, Lateral View. a, Cranium; b, face; c, mandible; 1H-7H, cervical vertebrae; ISB, last thoracic vertebra; 1L~7L. lumbar vertebra"; iv, sacrum; 6', coccygeal vertebrae; lR-lSl{,T\hs\ iif.A-M., costal cartilages; ^7., sternum; c^, scapula; Fig. 117. — Axis of Dog, Left Lateral View. a. Odontoid process; b, articular surface for atlas; c, transverse process; d; foramen transversarium; d', pos- terior opening of d; e, spine; /, posterior articular pro- cess. (EUenberger-Baum, Anat. d. Hundes.) 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. The coccygeal vertebrae 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 an- ,,,,1 terior ones become non-articular and flj gradually reduced in size. The trans- verse processes of the first five or six Fig. lis. — Sixth Cervical Vertki View. a, Ventral plate, 6, lateral part of transverse process; c, foramen transversarium; rf, anterior artic- ular process; /, accessory process; ff, spinous process: h, articular head of body. (EIlenberger-Baum, Anat. d. Hundes.) Dog, Left Fig. 119. — Fourth Thoracic Vertebra of Dog, Left- View. n. Head; b, glenoid cavity; c, facet for head of rib; d, transverse process; e, facet for tubercle of rib; /, mammillary process; f?, posterior articular process; h, spinous process. (EUenberger-Baum, .\nat. d. Hundes.) are relatively large; behind this they (luickly disappear. Haemal 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 pas.ses between pairs of ventral tubercles further back. THE RIBS — THE STERNUM — BONES OF THE SKULL 153 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 vertebrae 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 \'entrally. In long-tailed dogs the sacro-coccygoal region is somewhat S-shaped. Variations. — Numerical variations are not common except in the coccygeal region. The number of thoracic vertebra; 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 vertebrae. Six lumbar with fourteen thoracic vertebric 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 a.sternal. 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. Fig. 120. — Fourth Lumbar Vertebra of Dog. Left View. a, b. Articular surfaces of body; c, transverse process; d, accessory process; e, anterior articular pro- cess; e', mammillarj' process; /, jjosterior articular pro- cess: g, spinous process. (Ellenberger-Baum, Anat. d. Hundes.) Fir,. 121. — Sacrum or Dog, Dorsal View. a. Dorsal sacral foramina; b, articular surface of body of first segment; c, d, anterior articular pro- cesses; f, wing; /, rudiments of articular processes; g, lateral part; h, spinous processes. (Ellenberger- Baum, .\nat. d. Hundes.) The costal cartilages are long and curve forward; the length and curvature of the first pair is a striking special feature. THE STERNUM This is long, laterally compressed, and consists of eight sternebrae, 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 follo\\-ing descriptions of the separate bones an intermediate type — e. g., a fox terrier- is selected, and the most striking differences in the brachycephalic and dohchocephahc breeds will be considered in the section on the skull as a whole. 154 SKELETON OF THE DOG Cranium The occipital bone is similar in position to that of the horse. The crest is prominent, angular, and directed Ijackward. Just below the crest are two rough Fig. 122. — Base of Skull of Dog. without Mandible. /, Occipital; //, tympanic part of temporal; lla, squamous part of temporal: lib, mastoid part of tem- poral; ///, sphenoid; 'IV , pterygoid: V, palate bone; 1'/, vomer; VII, malar; VIII , zygomatic arch; IX, inner wall of orbit; A', palatine process of maxilla; .X/, premaxilla; A'//, orbital cavity; /, i, tubercles above foramen magnum; S, foramen magnum; S, occipital condyle; i, notch between occipital condyles; B, condyloid fossa; 6, hypoglossal foramen; 7, paramastoid (styloid, jugular) process; S, for. lacerum and posterior opening of carotid canal; 9, pctro-occipital synchondrosis; 10, petro-tympanic fissure; 11, tubercle; 12, bulla ossea; IS, muscular process of petrous; H, carotid foramen; lo, osseous Eustachian tube; 16, postglenoid process; /~, glenoid cavity; IS, for. ovale; 19, posterior opening of alar canal; SO, external opening of parieto-temporal canal; 21, stylomastoid foramen: 23, e.xternal auditory meatus; 2S, temporal crest; 24, zygomatic process of temporal bone; 25, body of postsphenoid; 26, body of presphenoid; 27, anterior opening of alar canal; 2S, for. lacerum orbitalc; 29, optic foramen; 30, hamulus of pterygoid; SI, horizontal part of palate bone; 32, perpendicular part of palate bone; S3, median palatine suture; Si, palato-maxillary suture: SB, jjosterior nasal spine; Se, anterior palatine foramen: S7, palatine groove; 3.9, 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; 4.4, alveolar border of premaxilla; .{fl. supraorbital process of frontal bone. (Ellenherger-Baum, Anat. d. llundes.) imprints or tubercles for muscular attachment. The surface below these is convex from side to side and concave from above downwaril. On either side, at the junction CRANIUM 155 with the squamous, there is a foramen wliich coiumunicates with the parieto- temporal canal. The condyles an; somewhat Hattened 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 liulla ossea on either side; its lower surface is flattened and the tubercles are at the junction with the bulla. The hj-poglossal foramen is small and is close to the foramen lacerum posterius; the latter is bounded in front by the l^ulla 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 parie- tal bones in the formation of a trans- verse canal which is continuous with the parieto-temporal canals. 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 mth the squamous temporal in the remainder of its extent. The external surface enters into the for- mation 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 m^^rgm is incomplete as in the pig. The supraorbital foramen is absent. mala Fig. 123. — Skull of Dog, Dorsal View. /. Occipital; //, parietal; ///, frontal; IV, lacrimal; VI, squamous temporal; VII, nasal; VIII, max- illa; IX, premaxilla; i, supraoccipital; S, interparietal; 3, parieto-occipital suture; 4, occipital crest; 6, sagittal crest; 6, parieto-frontal suture; 7, squamous suture; S, parietal emi- nence: 9, antero-external angle of parietal bone; 10, frontal crest; 11, 14, orbital margin; 1£, supraorbital process; IS, frontal fossa; 13, temporal part of frontal bone; 16, nasal process of frontal bone; IT, frontal suture; IS, lacrimal fora- men; 19, maxillary process of frontal bone; 20, lacrimo-ma.xil- lary suture; 31, frontal process of malar bone; 23, lacrimal process of malar; 23, zygomatic process of malar; 24, zygo- matic process of squamous temporal; 24', posterior end of nasal bone; Bo, nasal suture; 2e, anterior end of nasal bone; 27, infraorbital foramen; 2S, canine tooth; 29, cheek tooth; 30. frontal process of maxilla; 31, body, 32, nasal process, 33. palatine process of premaxilla; 34. palalii incisor teeth. (Ellenberger-Ba , Anat. i.les.) In front there 15G SKELETON OF THE DOG is a narrow pointed nasal part which fits in between the nasal bone and the maxilla. Theorliital and temporal parts are reiativelj' 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 forwanl. 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 bulla 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 basi- / occipital 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 de- pression and is situated behind the bulla ossea. In its pos- _ ^ terior part is a foramen which I / {J^ILII '**' ^-»' ^nr^^^^a-^tj^ transmits the ninth, tenth, and ^'^— !_ ^ - ^ ^^^Haai^B^^i^HaM^^M^:. eleventii cranial nerves. The carotid canal branches off from the i^etrobasilar, passes forward external to it through the inner part of the bulla ossea, and opens in front at the carotid foramen; it transmits the in- ternal carotid artery. The Eu- stachian opening is immedi- ately 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 sur- face presents a deep floccular fossa above the internal auditory meatus. The anterior surface is also fre(>. The anterior angle is perforated by a canal for the fifth ci'anial nerve (Canalis nervi trig(>mini). The body of the sphenoid bone is flattened dorso-ventrally. The sella turcica is shallow, but the dorsum sellic is well developed and bears posterior clinoid processes. A jxiir 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 Fig. 124. — Cranial Cavity of Dog, as Seen on Sagittal Sec- tion OF Skull. /, Roof of cranium; //, base of cranium; ///, posterior wall of cranium: IV, anterior wall of cranium; .1, anterior cranial fossa; B, middle cranial fossa; C, posterior cranial fossa; a, body of pre- sphenoid; a', body of postsphenoid; c, palate bone; rf, vomer; e, occipital; /, occipital condyle; g, sagittal crest; h, frontal sinus; h', cranial plate of frontal bone; i, cribriform plate of ethmoid bone; i', ethmoidal foramen; A-, ethmoturbinals; I, parietal bone; V , I", SQuamotis temporal hone; /'", temporal wing of .sphenoid bone; m, sella turcica; ?«'. dorsum selljc; w, optic foramen: o, foramen lacerum orbitale: p, foramen rotundum: g, foramen ovale: >', r', carotid foramina: s, tentorium osseum; /, foramen lacerum; v, u' , orifices of parieto-temporal canal; r, condyloid canal; w, canal for trigeminal nerve; x, internal auditory meatus; ?/, )/. orifices of canal for inferior occipital sinu.s; 2, floccular fossa, (.\fter Ellenberger, in Leisering's Atlas.) FACE 157 foramen ovale is near the posterior border of the temporal wing. There is no sphenoidal sinus. The ethmoid bone i.s highly developed. The cribriform plate is extensive, and the olfactory fossae 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 endo- turbinals 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 ])art of the palate hone in forming the transverse lamina (Lamina transversalis), which divides the olfactory fundus of the nasal cavity from the naso-pharyngcal meatus. Face The maxilla is short, but very high posteriorly. The facial crest is absent. The infraorliital 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 com- pletes the inner wall of the large alveolus for the canine tooth. The foramen incisivum is verj- 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 back- ward a long distance between the nasal lione 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 maxillae, 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 commonlv another foramen which opens into the nasal 158 SKELETON OF THE DOG cavity. The ])osterior palatine and si)lieno-palatine foramina are situated furtiier back and a little lower; the former is immediately below the latter. A horizontal plate extends from tlie inner surface, meets that of the opposite bone and com- pletes 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 borders 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 leng-th and is inclined toward the median suture so as to fonn a central groove. The inner liorders turn do\raward and form an internal nasal crest which becomes very prominent behind. The pos- terior 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 lacri- mal canal. The large zygomatic process con- stitutes 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 jiart of the orliital margin, lieveled behind for articulation with the similar process of the temporal bone. Between these it bears an emi- nence, 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 lacri- mal and maxilla, and a maxillary pro- cess directed downward. The facial surface is convex. The superior turbinalbone 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 witler and resembles the ethmo- turbinals, with wliich it is connected. The inferior turbinal bone is short and very complex. It is attacheil to th(> nasal surface of the maxilla by a basal lamina, which divides into two secondary lamellse. The latter detach numerous tertiary lamella, which are coiled and have thick free edges (Fig. 373). The vomer is not in contact with the posterior jiart of the floor of the nasal cavity, and does not divide the posterior nares. The posterior end is narrow and deeply notdied. Near the posterior nares the two plates curve outwartl 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 down- ward 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 hori- zontal part is convex in its length and is thick and rounded. The alveolar border is slightly concave in its length and is a little everted, esjiecially in its middle; Fig. 125. — Mandible of Dog, Right Anterior View. a, Right ramus; b, left ramus; c, body: rf, alveolar border; e, processus angularis; /, condyle: ff, coronoid process; A, masseteric fo.ssa; i, k, crests which form the upper and lower boundaries of fossa; /, mandibular fora- men; m, mental foramina; «, masseteric line; o, sigmoid notch. (Ellenberger-Baum, .\nat. d. Hundes.) THE SKULL AS A WHOLE 159 it presents seven alveoli for the lower cheek teeth, which resemble those of the upper jaw except that the fourth and sixth arc 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 eciuivalent 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 trans- versely 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 do\^^lward and forward. The coronoid process is very exten- sive 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 liave a long narrow skull (e. - chanter minor; e, rudimentary trochanter tertius; /, rough line; (;, trochlea; h, i, condyles; k, supra- patellar fossa. (EUenberger-Baum, Anat. d. Hundes.) Fig. 136, — Left Tibia and Fibula of Dog, Antero- EXTKRNAL ViEW. A, Tibia; B, fibula; a, external condyle of tibia; b. spine; c, crest of tibia; d, muscular notch; e, internal malleolus; /. head of fibula; fjt intero.sseoua space: h, external malleolus (distal end of fibula); i, groove for tendon. (Ellenberger-Baura, Anat. d. Hundes.) and has a prominent outer lip. There is no lesser sciatic notch. is relatively small and is semi-elliptical. The ischial arch BOXES OF THE PELVIC LIMB 167 It is almost circular in the female, 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 tul>er isrhii. The fossa acetabuli is deep, and is bounded internally by a fiat 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 eciuilatcral triangle with the angles rounded off. The inlet of the pelvis is very obliciue. but in the male it is elliptical and the con jugate diameter is the longer. The cavity is narrowest between the acetabula, and very wide behind. The floor is concave antl rela- tively 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 back- ward. 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 (supracondy- loid) fossa are absent. There are two supra- condyloid 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 in- ternal trochanter has the form of a blunt tuber- osity. The trochanteric fossa is round and deep. The ridges of the trochlea are practi- cally 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 \'esal), 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 Ijefore 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, Init bears a distinct mark where the ligamentum patella; 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. Fig. 137.— Skeleton of Disx.ti. P.vrt of Pelvic Limb of Dog, External View. 6, Tibial tarsal bone: 7, fibular tarsal; S, central tarsal; 9, second tarsal; 10, third tarsal; 11, fourth tarsal; 13, metatarsal bone-s; 13. first phalanx. The first tarsal bone is not vLsible in the figure, (.\fter Leisering's .\tlas,) 168 SKELETON OF THE DOG Tlic fibula extends the entire length of the region. It is slender, somewhat twisted, and enhirged 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 direc- tions. 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 articula- tion 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 ir- regularly quadrangular; it articulates above with the central and below with the first metatarsal. The second tarsal is the smallest and is wedge-shaped; it articu- lates 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 pero- neus longus crosses its outer and posterior surface, and above it are one or two tubercles. Five metatarsal bones are present. The first is conuiionly 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 carti- lages bj' 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 b^' 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 develop- ment, the nature of the uniting media, and the form of the joint surfaces; (6) 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 Hep- burn are: (1) Tliose 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 im- portance clinically. Three chief subdivisions of joints are usually recognized — viz., synarthroses, diarthroses, ami amphiarthroses. SYNARTHROSES In this group the segments are united by fibrous tissue or cartilage, or a mix- ture 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 lieveled and overlap, forming the sutura squamosa, e. g., the parieto-temporal sutia-e. If the edges are plane or slightly roughened, the term sutura harmonia is ap])lied 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 mandibulte. 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. 169 170 THE ARTICULATIONS OK JOINTS DIARTHROSES These joints are characterized by the i)resence 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 ex- panded. 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 (ridr Osteology) the surface is interrupted by non- articular cavities known as synovial fossae. 2. The articular cartilages (C'artilagines articulares), usually hyaline in type, form a covering over the articular surfaces of the })ones. 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. 3. The joint capsule (Capsula articularis) is, in its simplest form, a sac, the margins of which are attached around the articulating surfaces. It con- sists of two layers — an external one, composed of fibrous tissue (Stratum fibrosum), and an internal one, the synovial layer or membrane (Stratum syno- viale). Th(> 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 cap- sule 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 syno- vial 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 (Plicae 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.' In many places the membrane forms extra- articular ]i()uches, which facilitate the play of nmsdes and tendons. The joint cavity (C'avum 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 rnu.st 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 ' 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. Fig 13b — Di\gr\m of Section of DiARTHROSIS. /./., Fibrous layer, s.l., synovial layer of joint capsule. Tiie articular cartilages are white, bones dotted, ami the joint cavity black in the figure. DIAKTHROSE3 171 one might suppose, and that the capsule is often very irreguhir 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 tliscs or menisci, and marginal cartilages. 4. Ligaments. — These are strong bands or membranes, usually composed of white, hbrous tissue, which bind the bones together. They are pliable, l)ut practically inelastic. In a few cases, however, e. g., ligamenta flava, ligamentum nuchae, they are composed of elastic tissue. They may be subdivided, according to position, into periarticular anil intraarticular. Periarticular ligaments are fre- quently blended with or form part of the hbrous 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. Liga- ments which coimect directh' opposed surfaces of bones are termed interosseous. The special names are ba.sed 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 fasciae 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. 0. Articular discs or menisci are plates of fibro-cartilage or dense fibrous ti.ssue 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 variet}' of movement, and diminish concussion. 6. A marginal cartilage (Labruni glenoidale) is a ring of fibro-cartilage which encircles the rim of an articular cavity. It enlarges the cavity and tends to pre- vent fracture of the margin. Vessels and Nerves. — The arteries form anastomoses around the larger joints, ami give off l:)ranehes to the extremities of the bones and to the joint capsule. The synovial memljrane 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 lymph- atics. 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 vertebrae. 2. Angular Movements. — In these cases there is movement around one or more axes. Motion which diminishes the angle included liy 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 172 THE ARTICULATIONS OR JOINTS performed, but in quadrupeds it is possi])le 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 to- ward 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 move- ments which occur. The following chief classes may be recognized: 1. Arthrodia, or gliding joint. In these the surfaces are practically flat, ad- mitting of gliding movement. Examples: carpo-metacarpal joints; joints be- tween the articular processes of the cervical and thoracic vertebrae. 2. Gingl}rmus, 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 cor- responding 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, ex- tension, rotation, abduction, adduction, circumduction. Examples: hip and shoulder joints.' 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.- These joints are all medial in position, and are best illustrated by the joints between the bodies of the vertebrae. There is usually no joint cavity, but in certain situations a rudimentary one exists. THE ARTICULATIONS OF THE HORSE Joints and Ligaments of the Vertebrae The m()vai)le vertebra' form two sets of articulati(ins, viz., those formed by the bodies, and those formed by the articular processes of adjacent vertebra'; the fot-mer are termed intercentral, and the latter, intemeural. 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 'This classification makes no claims to scientific acruraey, but is simply a statement of tlie 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. '^The movements in .some of these joints are more extensive anil varied tlian in some diar- throses. To illustrate this we may compare the movements of the cer\-ical or coccygeal vertebra; with those possible in the carpo-metacarpal or the sacro-iliac joints. IN'TERCENTRAL ARTICULATIONS — INTERNEURAL ARTICULATIONS 173 vertebral column or a consitlerable 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 l)y the junction of the extremities of the bodies of adjacent vcrtclirie. The articular surfaces in the cervical region consist of a cavity on the posterior end of the body of the anterior vertebra, and a cor- responding convexity or head of the succeeding vertebra. In the other regions the surfaces are much fiattencil. The uniting media are: 1. The intervertebral fibro-cartilages (Fibrocartilagines intervertebrales). Each of these is a disc which fits into the space between the bodies of two adjacent vertebrae, to which it is intimatelj' 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 pul- Supraspi- posus). nousliga- '^ merit The fibrous ring consists of lamina? of fibrous tissue and fibro-cartilage, whieli pass ob- liquely between the two verte- bra^ and alternate in direction, forming an X-shaped arrange- ment. 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 pecuUar clear, transparent Fm. 139. — g, cells of various sizes. It is a Lvmba remnant of the notochord. (Mkdui There are joint cavities in the cervical intercentral joints, and in those between the last cer\-ical 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 vertebrae 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 inter- vertebral fibro-cartilages, to which it is very firmly attached. This ligament is in relation \%nth the spinal veins on either .side, and in the middle of each vertebra a transverse anastomotic branch passes under the ligament. GITTAL Sf.OTIOX OF LaST TwO ThORACIC AND FiRET ; VeRTEBR.E. SHOWIXG L1GAMENT.S AND SPINAL CORD la). (After Schmaltz, Atlas d. Anat. d. Pferdes.) INTERNEURAL ARTICULATIONS Each tvpical vertebra presents two pairs of articular processes, which form diarthroses with the two adjacent vertebra;. The articular surfaces are extensive, 174 THE ARTICULATIONS OF THE HORSE 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 tliese 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 vcrtebrte. They arc membranous and consist largely of elastic tissue. 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 Expansion at ivilhcrs Last cervical ivrlcbra First thoracic vertebra ^^*% 1, .Scajjula; /', cartilage of srapviia; . 140. — Li{;.\MKXTrM Nuch. , lamellar part of Hgamentur Baum, Anat. fiir Kiinsi ng of atla.>i. (After Ellenberger- remarkably modified to form the ligamentum nucha', which requires more extended notice. The ligamentum nuchae is a powerful elastic apjiaratus, the princiixil 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 supra- si)in(>us ligament. It consists of two parts— funicular and lamellar. The funic- ular part (Pars occipitalis) arises from the external occipital protul)erance and the fossa below it, and is in.serted into the summits of the vertel)ral sjiines at the withers. Two bursse are usually found under it in the adult. The supra-atloid bursa lies between th(> ligament and the dorsal arch of tlie atlas. The supra- MOVEMENTS OF THE VEKTEBRAL COLUMN 175 spinous bursa oicurs usually over the fourth thoracic spine, but may be over the third and may extend to the fifth.' In the neck the funicular part consists for the greater i)art 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 antl rhomboideus muscles. Behind the higher spines it becomes narrower and thinner, and is continued by the white fibrous lumbo-dorsal ligament.^ 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 lamiuie separated medially by a layer of loose connective tissue. Each lamina is formed of digitations which arise from the second and third thoracic spines antl from the funicular portion, are directed downward and forward, and end on the spines of the cervical vertebra^, except the first and last. The digita- tion 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 ciuite thin and feeble, or may be absent. The interspinous ligaments (Ligamenta interspinalia)extend between the spines of contiguous vertebrae. In the cervical region they are narrow elastic bands, and in the thoracic and lumbar regions the.y consist of white fibers directed obliquely ilownward and forward. The intertransverse ligaments (Ligamenta intertransversaria) are membranes which connect adjacent transverse processes in the lumbar region. INTERTRANSVERSE ARTICULATIONS These joints (peculiar to eriuicke) are diarthroses formed l\v the transverse processes of the last two lumbar vertebrae and the alae 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 vertebrae form joints which resemble somewhat those in the posterior part of the lumbar region. These joints are in- vaded l)y the process of ossification early, so that the consolidation of the sacrum is usually complete, or nearly so, at three years. The coccygeal vertebrae 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 verj' small, but the sum of the movements is considerable. The ' In (li.ssecting-room subjects these bursae and the adjacent structures are commonly the seat of pathological changes. They appear to be the starting-point of "poll evil" and "fistulous withers." - Xo natural line of demarcation exists between the ligamentum nucha and the lumbo-dorsal continuation of the supraspinous ligament, since the change from the purely elastic to the white fibrous structure is gradual. 176 THE ARTICULATIONS OF THE HORSE movements are freest in the cervical and coccygeal regions, limited in the thoracic and lumbar regions. Rotation is extremely 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 pro- cess and are confluent on its ventral aspect. It will be observed that the joint surfaces are not at all accur- ately 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 (Ligament uin interarcuale) is memljranous 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 in- ternum) 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. Fig. 141. — Atlanto -OCCIPITAL AND Ati.anto-axial Joints OP Horse, Dorsal View after Removal of Dor- sal Arch of Atlas. a, Joint capsule of left part of atlanto-occipital joint; 6, lat- eral ligament of same; c, c', odon- toid ligament; d, atlanto-occipital joint capsule; e, joint capsule of articulation between axis anti third cer\'ical vertebra: /, inter- spinous ligament; /, occipital bone; «, atlas; .*. axis; 4, third cervical vetrebra. (Ellenberger- Baum, Anat. d. Haustiere.) THE ATLANTO-OCCIPITAL ARTICULATION Tliis joint maybe 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 tlio 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 ca])sules and contains many elastic fibers. The inferior atlanto-occipital membrane extends from the ventral arch of the ARTICULATIONS OF THE THOUAX — COSTO-VERTEBRAL ARTICULATIONS 177 atlas to the lower margin of the foramen magnum. It is narrower and thinner than the superior memlirane, and also fuses with the joint capsules. The lateral ligaments are two short hands which are partiall.y 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. Articular processes // r^- Transverse process 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. I. The costo-central articulations (Articulationes capitulorum) are trochoid or rotatory joints, formed b.y the junction of the head of the rib with the bodies of two adjacent vertebra and the intervertebral fibro-cartilage. The two facets on the head of the rib are separ- ated by a non-articular groove, and correspond to the tv/o con- cave facets (Fovese costales) on the vertebral bodies. The cap- sules are rather tight, and are covered by the accessory liga- ments, which are as follows: 1. The radiate ligament (Ligamen- tum capituli costs radiatum) ex- tends ventrally from the neck of the rib to spread out on the vertebral bodies and the inter- vertebral fibro-cartilage. 2. The conjugal ligament (Ligamentum conjugale) — absent from the first joint — is attached to the groove on the head of the rib, j^asses 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 costs) is a strong band which crosses the joint dorsally. It is attached on the vertebra above the costal facet and on tlie 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 vertebra-. They are gliding joints. The capsule is reinforced by the superior costo-trans- verse 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 costse muscle, and begins to be quite distinct at the fifth joint. 12 erse ligament lament of neck Capsule Radiate ligament Conjugal ligament Fig. 142. — CosTo- (After Schmalt 178 THE ARTICULATIONS OF THE HORSE The cavity for thp head of the first rilj is formed by concave facets on the bodies of the last cervical and first thoracic vertebra?. 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 arc conflueiit, and the various structures are correspondingly modified. Movements. — The chief movement is rotation around an axis which connects till' 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 deeplj' 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 cfTcct nf which is to enlarge (chiefly) the transverse diameter of tlic 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 tlic sternal ligament. Each of the other capsules is reinforced dorsally by the superior costo-sternal ligament (Ligamentum sterno- costale radiatum), composed of radiating fibers whicli blend with the sternal liga- ment. 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 xijihoid carti- lage. 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 (Sternebrse) , 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 pos- teriorly. The sternal ligament (Ligamentum .sterni iiroprium internum) lies on the thoracic surface of the sternum. It arises on the first segment, and divides oppo- site 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 THE SYNARTHROSES OF THE SKULL 179 lateral liranrhes — thicker and wider — lie along the lateral borders above the chon- dro-sternal joints, and end at the cartilage of the eighth rib;, they are covered by the trans versus thoracis muscle. The Articulations of the Skull temporo-mandibular articulation This joint (Articulatio niantlibularis) is the only diarthrosis formed lictween 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 some- what forward; it consists of a glenoid cavit^y, which is continued upon the post- glenoid process behind, and a condj'le in front. The mandible presents a trans- versely elongated condyle. The articular disc is placed between the joint surfaces, which it renders con- gruent. 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 ]}ostglenoid 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 pass- ing 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 pre- formed in cartilage. Most of these joints are temporary, and are obliterated at various periods during development and gro^\'th. 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. q., spheno- squamous, naso-frontal, internasal, etc. Special names (borrowed froni human anatomy) are sometimes used; thus the interparietal, the parieto-occipital, and the parieto-frontal sutures are often called the sagittal, lambdoid, and coronal re- spectively. Detailed description of the sutures has not sufficient chnical value to justif.v much addition to the statementsTmade in the osteology in this connection. The obliteration or closure of the sutures is, however, worthy of brief mention. The cranial sutures are usuall.v all closed at se\-en 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 180 THE ARTICULATIONS OF THE HORSE 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 sphcnt)i(l (Synchonch-osis sphenooccipitaUs) ; (2) that between the presphenoid and postsphenoid (Synchondrosis intersphenoidalis) ; (3) those Ijetween 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 mandibulae) 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 liar of cartilage to the hyoid process of the petrous temporal bone. The cartilage (Arthro- hyal) 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 intercomual articulation is an amphiarthrosis formed by the junction of the distal extremity of the great cornu with the proximal end of the small cornu (kcrato-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-comual articulation is a diarthrosis formed ])y the junction of each small cornu (kerato-hyal) with the body (basi-hyal). The small cornu has a con- cave facet which articulates with the convex facet on either end of the dorsal sur- face 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 imion 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-humcral 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 arc: (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, THE ELBOW JOINT 181 which arise on the scapular tuberosity and end on the Hps 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: ex- ternally, 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 fiexion 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). Olecrniiou fossa THE ELBOW JOINT " This, the cubital articulation (Articu- latio cubiti), is a ginglymus formed be- tween the distal extremity of the humerus and the proximal ends of the bones of the forearm. The articular surfaces are: (1) A trochlear surface formed by the condyles of the humerus and the groove between them; (2) the corresponding glenoid cavi- ties 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 semilimar notch and the adjacent part of the ridge on the radius are synovial foss£e. The joint capsule is extremely thin behind, where it forms a pouch in the ole- cranon fossa under the anconeus muscle and a pad of fat. In front it is strength- ened 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.) External lateral ligament 43. — Left Elbow Joint of Horse, Poste- rior View. The CAPsrLE is Removed. C.\fter Schmaltz, .\tlas d. .\nat. d. Pferdes.) 182 THE ARTICULATIONS OF THE HORSE The external lateral ligament (Ligament um collaterale ulnare) is short and strong. It is attaclicil 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 ex- tension 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.) External dis- tal tuberosity of radius External metacarpal bone Internal dis- tal tuberosity of radius Internal lateral ligajncnt Metacarpal^ tuberosity' .External dis- tal tuberosity of radius External lateral ligament .External metacarpal bone Fig. 144. — Left Carpal Joints of Horse, Exter- Fk;. 145. — Left Carpal Joints of Horse, .\\terior NAL \'iEW View. i been removeil. The smaller liga- (After Ellenberger-Baum, Anat. The capsule has been removed, g, Radius; 1£, large metacarpal bone. (After Ellenberger-Baum, Anat. f. Kunstler.) The capsule h£ ments are shown. f, Kunstler.) 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 ulna^ ct radii) consist of fibers which pass aliove the interosseous space from either ijorder 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 consider- ation. The distal extremity of the ulna fuses early with the radius, and is, there- fore, regarded usually as a part of the latter. Movement. — This is inappreciable, the forearm being fixed in the position of pronation. THE CARPAL JOINTS 183 THE CARPAL JOINTS These joints taken together eonstitvite the composite articulatio carpi, or what is popularly termed the "knee-joint" in animals.' 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) tlic 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 interosseae). 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 articu- lar 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 tlie fil:)rous canals for the extensor tendons. Its jiosterior 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. The synovial membrane forms three sacs corresponding to the three joints. The radio-carpal sac is the most volum- inous; it includes the joints formed by the accessory carpal bone, and also those be- tween 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 e.xternal 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, ' 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 hkely to persist m- definitely in the absence of a convenient popular equivalent. Fig. 146. — Froxt.vi. Section of Carpal Joints of Horse (Right Side). /.»., External, I.r., internal, lateral ligament; Cr, radial carpal; Ci", intermediate carpal; Cu. ulnar carpal; CB, second carpal; CS, third carpal; C'i, fourth carpal; McB, second (internal) metacarpal; Mc3, third (large) metacarpal; Mc4, fourth (exter- nal) metacarpal. 184 THE ARTICULATIONS OF THE HORSE - Internal lat- eral ligament 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 carjii collateralc 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 antl inner small metacarpal bones. Deep fasciculi are detached to the radial and second carpal bones. The first carpal bone, when pres- ent, is usually embedded in the posterior part of the distal end of the ligament. The posterior part of the ligament is fusetl with the posterior annular ligament (Ligamentum carpi transversum), and concurs in the formation of a canal for the tendon of the flexor carpi in- ternus. 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 con- nected with adjacent bones by three liga- ments (Fig. 444). The pro.ximal one is a short band which extends from the acces- sory 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 in- serted into the accessory carpal bone. The other bones of the proximal row are connected by two anterior or dorsal liga- ments, which are trans\erse in direction, and two interosseous ligaments. An ob- lique ligament passes from an eminence on the posterior surface of the radial car- pal bone to a small depression on the radius internal to the facet for the acces- sory carpal bone. Two ligaments connect the proximal and distal rows posteriorly. Tlie 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 trans\erse anterior or dorsal liga- ments 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 inter- osseous ligaments of the distal row to end in depressions in the interstices between the proximal ends of the metacarpal bones. 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 ]iart of the capsule is, of course, tense during flexion, the posterior part in extension. The movement practically .all occurs at the radio-carpal and intercarp.al joints, the articular surfaces of which are widely separatcil 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 intero-sseous ligaments connecting these bones become tense .and oblique in direction. Internal distal tuberosity of radius Accessory car- pal bone Inferior liga- ments of acces- sory carpal Internal (second) meta- carpal bone Fig. 147. — Left Carpal Joints of Horse (7, Radius; 12, large (third) metacarpal bone. berger-Iiaum, .\nat. fur Kunstler.) Mrlnciirpal tuberosity (After Ellen- THE FETLOCK JOINT 185 THE FETLOCK JOINT This, the metacarpo-phalangeal articulation (Articulatio metucarpo-phalangea), is a ginglymus formed by the junction of the distal end of the large (third) meta- carpal hone, tlie proximal end of the first phalanx, and the proximal sesamoid bones. Articular Surfaces. — The surface on the large metacarpal lione is approxi- mately cylindrical in curvature, l)ut is divided into two slightly uneciual 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 be- hind. 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. The joint capsule is attached around the margin of the articular surfaces. It Branches of suspensory ligament Fig. 148 . Sectiox of Dist.\ OF Horse. /, Large metacarpal bone; 3, fetlock joint; 4, proximal sesamoid bone; 5, first phalanx; 6, pastern joint; 7, second phalanx; S, coffin joint; 9, third phal- anx; 10. distal .sesamoid (navicular bone); 12, sus[)en- sory ligament; 14, deep flexor tendon; Id, superficial flexor tendon: 16, posterior annular ligament of fetlock; SO, inferior sesamoidean ligaments: 21, extensor tendon; S4, plantar cushion; £5, periople; 2S, wall of hoof; 29, sole of hoof: -1 , navicular bursa, proximal part. (After Ellenberger-Baum, Anat. fiir Kiinstler.) OF Limb Fig. 149. — .\hticui,ar Surfaces of First Phalanx AND Sesamoids at Fetlock, with Intersesa- moid .\ND Suspensory Ligaments. (After Schmaltz, .\tlas d. Anat. d. Pferdes.) is thick and ample in front; here a bursa is interposed Ijetween it and the extensor tendons, but the tendons are also attached to the capsule. Pos- teriorly it forms a thin-walled pouch which extends upward bet^\een 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 collateralo 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 lione. 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 he inserted into the outer surface of the sesamoid and the proxi- mal end of the first phalanx. 186 THE ARTICULATIONS OF THE HORSE The capsule is further strengthened by a layer of obUque fibers which pass o\er the lateral ligament on either side and end on the extensor tendon and the proximal extremit\- of the first phalanx. It may properly be regarded as fascia rather than ligament. Movements. — These are of the nature of flexion and extension, the axis of motion ]:assins through the upper attachments of tlie lateral ligaments. In the ordinary standing position the joint is in a state of partial dorsal flexion, the articu- lar angle (in front) being about 140° to 150°. (In the hind liinl) it is about 5° greater.) Diminution of this angle (sometimes ternietl "overextension") is nor- ExtensoT temhm Upper end of capsuU- of fdUick joint Bursa Lalcrnl ligament of fetlock joint Fascia — !*— Superficial flexor tendon Deep flexor tendon Suspensory ligament Lateral interrosseous tendon Upper end of digital sheath Ring of superficial flexor tendon iilersrsatnoidean ligament Posterior annidar ligament (cut) Lateral sesamoidean ligament Snp outer side and aliove, THE STIFLE JOINT 195 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 inferiority 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 feraoro-tibial joint cavity by a sht-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 over- looked 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 2.5 per cent, of cases, according to Baum. It is instructive to distend this capsule and thus obtain an idea of its potential capa- city and relations (Fig. laOj. Accessory cartilage of patella- Inlernal ridge of trochlea of femur - Middle patellar ligament Internal semilunar cartilage - Internal patellar ligament- Tuberosity of tibia _ External fcmoro-patcllnr ligament - External patellar ligament - External femoro-tibial ligament - External semilunar cartilage - External condyle of tibia Fig. 157. — Left Stifle Joint of Horse, Front View, in Extension. I are removed. iS, Femur; 20, patella; 2/, tibia, (.\fter EUenberger-Baum, -\naf . fiir Kiinstle 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 ari.ses from the external epicondyle of the femur just above the lateral femoro-tibial ligament, and ends on the external l)order 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 (Ligamcnta patellse), also called the straight ligaments of the patella, are three very strong l)ands 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 tulicrosity. It receives a strong tendon from the liiceps femoris muscle. The middle patellar ligament extends from the front of the apex of the patella to the lower part of 196 THE ARTICULATIONS OF THE HORSE the groove on the tuhciHjsity of the tibia, a bursa l)eins interposed between the Hgament and the upper i)art 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 fenioris nuiscle, and transmit the action of the latter to the tibia; they also func- l-nirrii,r crtirial tiou similarly for the other muscles attached to them as noted above. It will lie notico-le of the femur, and below to a rough area below the margin of the internal condyle of the tibia. The external lateral ligament (Ligamentuni 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. 'In this figure the patella is pushed up above the trochlea— a position which it does not occupy normally. 198 THE ARTICULATION'S OF THE HORSE 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 tlie u]iper jiart 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 an- terior part of the intercondyloid fossa of the femur. Vastus inlcrmedius Semimemlirnnosii.'s ' Terr, on ^ 4Km^ * y^J J lector ^eiri- Fio. Ifil rPa Stifle Joint of Horse; Sagittal Section Passing Throtjg OF Trochlea and Intercondyloid Fossa. 1, .-Vnterior crucial lic.irnetit; 2, posterior crucial ligament; 3, posterior cornu of internal semilu 4, femoral ligament of external semilunar cartilage; 5, articular artery; G, part of vastus int 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 slacliens 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 up- ward in extension, downward in flexion. Extension is checked mainly by tension of the crucial and lateral hgaments. In extreme extension, which is accoinpaniod In- .sHfiht outward rotation of tlie leg, (lie patella can l>e pusliod upward and inw;ird so tlial its filiro-cartilase lioolis over the upper end of the inner ridge of the trochlea, but it will not iciiKiin there unless held in position. When pressure is removed, the base of the patella tips forward ;uid the cartilage lies upon the most prominent part of the trochlear TIBIO-FIBULAR ARTICULATION — THE HOCK JOINT 199 riilgo. During flexion, whit-h is accompanied by sliglit inward rotation of the leg, the condyles of tlie femur and the srniilunar cartilages glide backward on the tibia; the movement of the" ex- ternal condyle ami carlilagc is grcalei- than that of the inner one. In extreme flexion the patellar and posterior crucial ligauiciils arc 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 heail of the filiula artirulates with a erescentie facet just lielow the outer mai-gui of the external condyle of the tibia. The joint capsule is .strong and close. The shaft of the fibula is attached to the external Ijorder of the tibia by the inter- osseous membrane of the leg (Membrana interossea criu'is); 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. Fig. 162. — IvEFT Hock Joi.nt of Horse, Extern' Fic. 163. — Left Hock Joint of Horse, In View. .Tibia; ^.j, tuber ealcis; 3.5, large metatarsal bone; ^(7, long externallateral ligament; 5/, long internal lateral ligament, (After EUenberger-Baum, .\nat. fur KuQstler.) 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 articula- tions; (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 cor- responding surface of the distal end of the tibia. The ridges and grooves of these surfaces are directed oliliquely 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 200 THE ARTICULATIONS OF THE HORSE 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 practicallj', 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. Su- periorly, it pouches upward behind the distal end of the tibia for a distance of about Short internal lateral ligament -US' f^i^^K Long internal lateral ligament -Bk (* ^^^'1 ~"- 1 »n \W^/^S _.-\ Extirnal lateral ligament I nternal small metatarsal bone ■■■ -- r < i n , , > j, « ■I hxternal small metatarsal bone Fir,. 164. — Left Hock Joint of Horse, Anterior View. SI, Tibia; S2, trochlea of tibial tarsal bone; 35, large metatarsal bone: 50, dorsal or oblique ligament. (After Ellenberger-Baum, Anat. fur Kiinstler.) two inches (ca. .'i cm.). Inferiorly, it is continued downward, forming the sub- tarsal or check ligament, which unites with the perforans tendon about the middle of the metatarsus. 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 lielow; 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 liy the third tarsal with the bones on either sifle. Common Ligaments. — The external lateral ligament (Ligamentum coUaterale THE HOCK JOINT 201 filiularc longuin ct breve) consists of two distinct hands which cross eacli 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. 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 External lateral ligament Plantar ligament Stnall metatarsal bones Large metatarsal bone - Long internal lateral ligament Short internal lateral ligament Suspensory ligament Fig. 165. — Left Hock Joint of Horse, Posterior View. et. Tibia; S4, tuber calcis. (After Ellenberger-Baum, Anat. ftir Kiinstler.) 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 liand 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 arc difficult to isolate. Most of them are not of sufficient importance to justify detailed description. 202 THE ARTICULATIONS OF THE HORSE (1) The tibial and fibular tarsal bones are united bj- four bands (astragalo-calcaneal liga- ments). The internal ligament" extends from the .sustentaculum tah to tlie adjacent part of the tibia tarsal, Ijlending with the short hitcral ligament. The external ligament extencis from the anterior process of tlie 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 roii^jh area> nl tlio oppo.sed surfaces. (2) Tlie siiiallei- liunes 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 Supi-TJicial Jtrxor tendon Gastrocncniius tendon Tarsal tendon of biceps femoris Calcanean bursa Gastrocnemius bursa Upper pouch of joint capsule Tibial tarsal hone Interosseous liijtuncnt Plantar ligament Fourth tarsal bone Interosseous liijament Large metatarsal bone Suspensory ligament Check ligament Tibialis anterior Pcroneus tertius Tibio-tarsal joint carity Joint capsule Central tarsal bone Third tarsal hone Distal annular ligament Fig. 166. — Sagittal Section of Hock of Horbe (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-scaphoid) 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 (fu.sed) first and second tarsals are connected with the fibular tarsal by a posterior (calcaneo-cunean) ligament. (4) The lower tarsal bones are coimected 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. Movements. — These are flexion and extension, which take place at the tibio- tarsal joint. The movements between the tarsal bones, and lietween the latter and the metatarsus, are so limited as to be negligible so far as tlie action of the joint as a whole is concerned. In the standing position the articular angle (in front) is about 1.50° to 160°. Complete extension is prevented b.v tension of the lateral ligaments. P'lexion is checked only by contact of the metatarsus with the leg, JOINTS AND LIGAMENTS OF THE VERTEBRA 203 provided the stifle joint is also flexed. Owins to the fact that the axis of motion is shghtly obli(iue, the lower jiart of the linih deviates somewhat outward during flexion. The movements of the hock joint must correspond witli 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 limh. COMPARATIVE ARTHROLOGY' JOINTS AND LIGAMENTS OF THE VERTEBRA Ox. — The ligaineutum nuchte is better developed than in the horse. The funicular part is clearly divided into two lateral halves, which are round at their occipital attachment, l>ut 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 , Funicular part; b, wide porti* Fig. 167. — Ligamentum Nuch.e op Ox. c. d, lamellar part; e, interspinous ligaments; 1, spin : 1. axis. (EllenherKer-Baum, .\nat. il. llaustiere. i process of first thoracic 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 pos- terior 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. 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. 'This section consists necessarily only of a brief statement of the most important differences in the joints of the other animals. 204 COMPARATIVE ARTHROLOGY There are no intertransverse joints in the lumljar region. Pig. — The ligamentuni nuchse is represented by a fibrous raph6 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 arc clastic. Dog. — The ligamentum nuchae 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 raphe 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 b}' distinct elastic ligaments (Ligamenta intercostalia). The first pair of chondro-sternal joints are separate from each other; inter- crossing 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 intra-articular 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 sur- faces 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 — THE CARPAL JOINTS 205 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. — Xo 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 In-achialis 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 bj- 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 prona- tion: outward rotation is supination.' 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 articu- lar 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 'These movements are best seen in man, in whom the back of the hand may be turned for- ward (pronation) or backward (supination). 206 COMPARATIVE ARTHROLOGY the accessory carpal with the distal end of the ulna, and strong bands connect the distal bones with the metacarpus. The interosseous and in- terordinal 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 ex- tends from its distal part to the side of the large metacar- pal. There is also an inter- osseous ligament, which is per- manent and allows a small amount of movement. The chief metacarpal bones of the pig, and the second to the fifth of the dog, articu- late with each other at their proximal ends, and are connect- ed by interosseous ligaments, which do not, however, unite them closely, as in the horse. METACARPO-PHALANGEAL JOINTS Ox. — There are two joints, one for each digit. The two capsules communicate posteriorly. The two inter- digital lateral ligaments (Liga- menta collatcralia interdigi- talia) result from the bifurca- tion of a band which arises in the furrow between the divi- sions of the distal end of the large metacarpal bone; they spread out and end on the ])roximal ends of the first l)halangos. A strong superior consisting of short intercrossing es of the first jihalanges. —Distal Part of Limb of Ox, Showing AND Tkndons. One Digit and Corresponding Articu- lar Part of Metacarpal Bone are Removed. a, Suspensory liEament; a', branch of a to superficial flexor tendon; a", o'", lateral and central branches of a; b, deep flexor tendon; 6', branch of b to digit removed; c, c, superficial flexor tendon; d, d' , intersesamoid ligament (cut); e, interdigital lateral ligament of fetlock joint; /. tendon of common extensor; o, pro.xi- mal interdigital ligament; A, digital annular ligament; i, posterior annular ligament of fetlock; A*, lateral ligament of pastern joint; I, distal interdigital ligament; m, crucial interdigital ligament (cut); m', 7«", attachments of m to second phalanx and distal sesamoid bone; h. suspensory ligament of distal sesamoid; o, an- terior elastic ligament; p, lateral volar ligament of pastern joint; 1, metacarjJus, sawn off at /'; 2, first phalanx; 3. second phalanx; 4, third phalanx. (Ellenberger-Baum, .\nat. d- Haustiere.) interdigital ligament (I^igamentum interdigitale), fillers, unites the middles of the interdigital surfac METACARPO-PHALANGEAL JOINTS 207 Crucial ligaments (Ligamenta phalango-sesamoideae) 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 midclle 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. Fig. 169. — Ligamknts and Tendons of Digits of Pig, Volar View. a. Superficial flexor tendon; b, deep flexor tendon; b', branches of 6 to accessory digits; c, c' , annular ligaments; d-d'", ligaments of accessory digits; e, cruciate interdigital ligaments; /, /', si>iral band around the flexor tendons of the accessory- digits: g, abductor of accessory digit. (Ellen- berger-Baum, .\nat. d. Haustiere.) Fig. 170. — Ligaments a.nd Tendons of Paw of Dog, Hind Limb, Volar View. a, a'. Superficial flexor tendon; 6, tendon to large pad; c, lumbricales muscles; d, interossei muscles; e, f, annular ligaments at metatarso- phalangeal joints; ff, suspensory Ugament of large pad; h, digital annular ligaments; i. deep flexor tendon; k, distal sesamoid; /, suspensory ligament of k; m, suspensory Ugament of digital pad; n, digital pads. (Ellenberger-Baum, .\nat. d. Haus- tiere.) 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 208 COMPARATnE ARTHROLOGY wliicli join the tendons of the proper extensors of the digits; it sends fibers also to the interdigital hiteral Hgaments 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 ])lialanx 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 inter- osseous 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 ca]isule, 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 arc largely fused to form a strong hand. The lateral ones extenil 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 phal- anges 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 ]iroccss of the tiiird jilialanx. 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 arrange- ment of ligaments which connect the small digits with each other and with the chief digits. This nprLiratus is somewhat complox, hut its chief features are as follows: A superior iiiter- (linilal li«ariic-nl is altaelieil on cither side to the third phalanges of tlie small digits, wliili' centrally it liicn com- missure of the lips. Action. — (1) To elevate the upper lip and the connnissure; (2) to dilate the nostril. MUSCLES OF THE LIPS AND CHEEKS 215 Slnicture. — The muscle arises by a thin a]5oneurosis. 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 com- missure with the orliicularis and i)uc- cinator. Relations. — Superficially, the skin, fascia, and lateral dilator (in part); deepl.y, the levator labii superioris pro- prius, lateral dilator (in part), buccin- ator, branches of the facial vessels and nerve, and the infraorbital arterj- and nerve. Blood-supply. — Facial and palato- labial arteries. Xerve-supply. — Facial nerve. 3. Levator labii superioris pro- prius. — This lies on the dorso-lateral aspect of the face, partly covered bj' 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 be- comes narrower and thicker, then tapers over the false nostril, to termin- ate in a tendon. The tendons of the two muscles unite over the alar car- tilages of the nostrils, forming an ex- pansion which spreads out in the sub- stance of the upper lip. iJeZaiions.-^uperficially, the skin, the levator nasolabialis, and the angu- lar vessels of the eye; deeply, the superior and transverse dilators of the nostril and the infraorbital artery and nerve. Blood-supply. — Facial artery. Neri'e-supphj. — 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. Fig. 173. — Muscles of Head of Horse, Dorsal View. The Pax.mcclus is Removed. a. Levator labii superioris proprius; a', common tendon of a with opposite muscle; 6, levator nasolabialis; /, dilatator naris lateralis; a, zygomaticus; /, dilatator nans superior; ii, parotido-auricularis; o" , scutulo-auricu- laris superficialis superior; p. interscutularis; p', fronto- scutularis, pars temporalis; r, cer\'ico-auricularis superfici- alis; u, corrugator supercilii; x, trausversus nasi; 2, poste- rior, 3, anterior, border of external ear; 8, scutiform carti- lage; 9, zygomatic arch; /O, suijraorbital depression; .:J.5, inner wing of nostril, containing lamina of alar cartilage; 39. facial vein. (After EUeuberger-Baum, Anat. fiir Kunstler.) 216 FASCIA AND MUSCLES OF THE HORSE 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 ])rominence 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 dis- tinct 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 jiarotid duct; deeply, the mandible and inferior laliial 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-mandib- ular 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 buc- calis) extends from the angle of the mouth to the masseter. It is incompletely pennate, having a longitudinal raph6 on which most of tlie muscle-fibers converge. The upper fibers are directed chiefly downward and backward, the lower ones up- ward 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 zygomaticiis, levator naso- labialis, lateral dilator of the nostril, the superior Ijuccal glands, thi^ parotid duct, MUSCLES OF THE NOSTRILS 217 the facial vessels, and branches of the facial nerve; deeply, the mucous membrane of the mouth and the inferior buccal glands. Blood-supplij. — 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. Fig. 174. — Nasal and Superior Labial Mcscles of Horse. a, a'. Dilatator naris transversus; b, levator labii superioris proprius; b', tendon of b; b" , common temion of two levatores labii superioris proprii; c, d . dilatator naris inferior; d, e. dilatator naris superior; /, orbicularis oris; g, levator nasolabialis. a portion of which is removed; li. dilatator naris lateralis fcut); i, cornu of alar cartilage: i-, nostril; t', false nostril; (, nasal diverticulum; m, nasal bone, (.\fter Ellenberger-Baum, Top. .\nat. d. Pferdes.) Action. — To dilate the nostril. Structure. — The muscle lias a flat tendon of origin, passes between the two branches of the levator nasolabialis, and si)reads out in the external wing of the nostril. The lower fibers blend with the orbicularis oris. Relations. — Superficially, the skin, fascia, and tlie labial branch of the levator nasolabialis; deeply, the maxilla and the nasal branch of the levator nasolabialis. Blood-supply. — Facial artery. Nerve-supply. — Facial ner^•e. 3. Dilatator naris transversus (M. transversus nasi). — This is an unpaired, cjuadrilateral muscle, which lies between the nostrils. It consists of two layers. Attachments. — Superficial laj-er, the superficial faces of the laminsE of the alar cartilages; deep layer, the convex edges of the cornua of the same. Action. — To dilate the nostrils. 218 FASCIA AND MUSCLES OF THE HORSE 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 arterj'. Blood-.suppli/. — Palato-labial artery. Nerve-xupply. — 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. Nerre-.'nipply. — 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 ])rocess 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 sub- jects. 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-sup])ly from the facial, transverse facial, supraorbital, and infraorbital arteries; the nerve-supply is derived from the facial nerve. MUSCLES OF MASTICATION 219 4. Levator palpebrae superioris. — This slender, flat inusclo is almost entirely within the orbital cavity. It arises on the pterygoiil crest, passes forward above the rectus oculi sui)eri()r and below the lacrimal gland, and terminates in a thin tendon in the uii]iin- lid. Actiiin. — To elevate the U])per 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 man- dible. 1. Masseter. — This muscle extends from the zygomatic arch ami facial crest over the broad part of the mandibular ramus. It is semi-elliptical in outline. Origin. — B,y 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 jiart is covered liy 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 ^"ill lie noted that a small part, near the temporo-maxillary joint, is not covered by the superficial layer. The two laj'ers are separable onlj' 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 mitldle of the border and leaves the muscle. Blood-supply. — Transverse facial and masseteric arteries. A'erre-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 \dth the masseter. Relations. — Superficially, the scutiform cartilage and anterior muscles of the external ear and the orbital fat; deeply, the temporal fossa antl the tleep temporal vessels and nerves. Blood-supply. — Superficial and deep temporal, and mastoid arteries. Nerve-supply. — ^Mandibular nerve. 3. Pterygoideus intemus (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. 220 FASCI.E AND MUSCLES OF THE HORSE 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 direc- tion. It contains much tendinous tissue (septa). The smaller portion is external to the foregoing, and its fibers are directed downward and backward. 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- Ethmo- Septum of turbinals frontal sinuses Superior meatus Superior turbinal Middle meatus Inferior turbinal Inferior meatus Fin. Section of He OF Horse, Showing Deep Pterygo-maxillary AND Cranial Cavities. 1, Cerebral compartment of cranial cavity; 5, cerebellar compartment of same; 4. tentorium cerebelli; 6, sphenoidal sinus; 6, hamulus of pterygoid bone-tendon of tensor anterior border of hamulus; 7, mylo-glossus. The olfactory mucous membrane is shadetl. 3, tentorium osseum; palati cut off short at pharyngeus, palato-pharyngeus, mylo-hyoideus, digastricus, and stylo-hyoideus muscles, the guttural jiouch, 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-supphj. — Internal maxillary, masseteric, and inferior alveolar arteries. Nervf-supph/. — Mandibular nerve. ■i. Pterygoideus extemus (s. lateralis). — This muscle is consideraljly 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 iimer surface of the neck and the inner jiart of the anterior border of the cond.yle of the mandible. Action. — Acting together, to draw the lower jaw forward: acting singly, to move the jaw laterally, ('. e., toward the side opposite to the muscle acting. The MUSCLES OF MASTICATION 221 latter action is due to the I'aet that the origin is nearer to the median plane than the insertion. Structure. — The muscle is almost entirely fleshy, and the fibers are almost Fig. 176. — Submaxillary and Laryngeal Regions of Hor.se, after Re.moval op Skin and Pannii c, Mastoiflo-humeralis; d, sterno-cephalicus; e, oniO-hyoicieus and sterno-hyoideus; h, buccinator; i, depressor labii inferioris; m, masseter; r, stylo-maxillaris; w, mylo-hyoideus; ^, posterior, S, anterior, border of external ear; 50', angle of jaw; 36, submaxillary lymph-glands; rf7, external maxillary vein; ci9, facial continua- tion of 37: 40, parotid duct; 44, parotid gland; 4S, prominence of chin; x, wing of atlas. (.■Vfter Ellenberger- liaum, Anat. fiir Kunstler.) longitudinal in direction. Some of them are inserted into the edge of the inter- articular meniscus. Relations. — Externally, the temporo-maxillary articulation and the temporalis muscle; internally, the internal pterygoid and tensor palati muscles. The internal 222 FASCIA AND MUSCLES OF THE HORSE 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. Nerre-suppb/. — 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 ])aramastoid 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 stcrno-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-supphj. — Facial nerve. 6. Digastricus. — This muscle is composed of two fusiform, flattened l>ellies, 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 do^^^lward and forward, and is succeeded by a small rounded tendon. The latter perforates the tendon of in- sertion of the stylo-hyoideus, and is provided with a synovial sheath. The anterior belly is larger and terminates by thin tendinous bimdles. 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 (>xternal 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 l)order of the mandible. Insertion. — (1) A median fibrous raphe extending from the symphysis to the hyoid bone; (2) the lingual process and body of th(^ 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 raphd. It is THE inoiD MUSCLES 223 chiefly fleshy, and is thickest hchiiul. The anterior superficial part of the muscle is termeil the mylo-glossus. Relations. — On the superficial surface of the muscles are the ramus, the in- ternal 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 ami vessels, the submaxillary duct, and the lingual and hypo-glossal nerves. Blood -sup ply. — Sublingual artery. \erve-.mpply. — 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. 43G). Origi)}. — 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 up- ward. 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.— Be\o\\; 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 larjTix. 224 FASCIA AND MUSCLES OF THE HORSE Relaiium. — The muscle is crossed outwardly by the lingual artery. Bloods up ply. — 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. .4/toc/(wen^s.— 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-snpphj. — Lingual artery. Nerrr-.'iiipj)!!/. — Glosso-iiharyngeal nerve. 7. Stemo-thyro-hyoideus, and 8. Omo-hyoideus. — These are described with the muscles on the ventral surface of the neck. The Fasci.(E and Muscles of the Neck It is convenient to divide the muscles of the neck into ventral and lateral groups, the two lateral grou]3s being separated from each other by the ligamentum nuchse. THE FASCIA OF THE NECK The superficial fascia is in part two-layered, and contains the cervical portion of the panniculus. The fascice of the right and left sides are attached along the dorsal line of the neck to the ligamentum nuchte, while along the ventral line they meet in a fibrous raphe. 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 sepa- rates to pass under the cervical trapezius, and become attached to the ligamentum nuchae. 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. An- teriorly 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 CEsophagus. 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 tulailar sheath around the trachea, inclosing also the recurrent nerves. VENTRAL MUSCLES This group consists of eleven ]iairs of muscles which lie almost entirely ventral to the Ycrtebne. 1. Panniculus carnosus. — The cervical panniculus (platysma myoides of man) has a fleshy origin on the cariniform cartilage (manubrium) of the sternum. VENTRAL MUSCLES OF NECK 225 It passes forward, outward, and upward, crossing over the storno-cephalicus and jugular furrow obliquely. On reaching the surface of the mastoido-hunieralis 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 Fig. 177. — Antero-latkrai. View of Musci-f.s axd Skeleton of Horse. a. Trapezius; c, mastoido-humeralis; d, sterno-cephaliciLs; /, long head of triceps; /'. external liead of triceps; g, anterior superficial pectoral muscle; g' , posterior superficial pectoral: k', anterior deep pectoral: r, cervical panniculus: z, supraspinalus: 39. omo-hyoideus: SO, slerno-thyro-hyoideus; 31, jugular vein; 32, cephalic vein; I, scapula; 1', cartilage of scapula: 3, spine of scapula: 4. shaft of humerus; 4', external epi- condyle; 5, external tuberosity of humerus; 5, deltoid tuberosity: /4, ventral border ("keel ") of sternum; 14', cariniform cartilage: I.E., first rib. C.\fter Ellenberger-Baum, Anat. fiir Kilnstler.) the facial portion. The right and left muscles meet at a ventral median raph^ in peanate fashion. 2. Mastoido-humeralis. — This is described on p. 2.52. 3. Stemo-cephalicus (Sterno-maxillaris s.-mandibularis).' — This is a long, nar- 'This mu.scle is probably the homologue of the sternal portion of the .^terno-cleido-mastoid of man. On account of the differences in its insertion in the various animals, it seems desirable to adopt the name stemo-cephalicus. 1.5 22G FASCIiE AND MUSCLES OF THE HORSE row 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 fiat tendon. Relations. — Superficially, the cervical panniculus; deeply, the stcrno-thjTO- hyoideus and omo-hyoideus muscles. The uiijxn- 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, hav- ing the submaxillary gland and stylo-maxillaris muscle on its inner side. Blood-supply. — -Carotid artery. Nerve-supphj. ^Ventral branches of the spinal accessory and first cervical nerves. 4. Stemo-thyro-hyoideus (Sterno-thyroideus et sterno-hyoidcus). — 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 sternmii. Insertion. — (1) The external surface of the thjroid 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 lione 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 l)elly has the sterno-ce]ihalicus 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-supphj. — -Carotid artery. A^e?'(ic-s(//j/)///. -Ventral branch of the first cervical nerve. 5. Omo-hyoideus (vSubscapulo-hyoideus). — This is a thin, riMion-like muscle, almost entirely fleshy, which crosses the trachea very obli(iuel\- 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 bono. Structure. — The muscle is composed of iwralU-l fleshy fibers, exce])t at its iirigin, 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, VENTRAL MUSCLES OF NECK 227 on the left side, the oesophagus. In its anterior part the muscle blends with the hyoid part of the stcrno-thyro-hj-oideus, the two covering the thyroid portion of the latter muscle, the thyroid glaml, and the ventral face of the larj-nx. Blood-supply. — Carotid and inferior cervical arteries. Nerrc-siipphj. — Ventral branches of the cervical nerves. 0. Scalenus (M. scalenus primse costae). — 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 liorder and outer surface of the first rib. Insertion. — (1) The dorsal (smaller) portion is attached to the transverse process of the seventh cervical verteljra; (2) the ventral portion is attached to the transverse processes of the sixth, fifth, and fourth cervical vertebrae. Action. — The neck is flexed or inclined laterally, according as the muscles act together or singly. If the neck l)e the fixed point, the muscle may have a respira- tory action by pulling forward or fixing the first rib. Structure. — The dorsal portion is composed of three or four fleshy bundles.' 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 vertebrte, the longus colli and intertransvcrsales muscles, the oesophagus (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 vertebrae and the base of the cranium. Origin. — The transverse processes of the fifth, fourth, and third cervical ver- tebrae. 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 singlj', to incline it to the same side also. Structure. — The origin of the muscle is ])y fleshy digitations. The belly in- creases 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 arterj- (which lies along the lower border), the occipital and internal carotid arteries, and the tenth, eleventh, and sympathetic nerves; deeply, the vertebrae, the longus colli, intertransvcrsales, and the small straight muscle. The terminal part of the muscle lies in contact with its fellow at)ove the pharynx and between the guttural pouches. Blood-supply. — Carotid, verteliral, and occipital arteries. Nerve-supply. — Ventral branches of the cervical nerves. 8. Rectus capitis anterior minor (AI. rectus capitis ventralis). — This is a small muscle which lies under cover of the preceding one. Origin. — The ventral arcli of the atlas. ' The upper part of this may be separated from the scalenus proper, and is then termed the cervicaUs ascendcns or iho-costalis cervicis — a continuation in the neck of the transversalis cos- tarum. 228 FASCI.E AND MUSCLES OF THE HORSE Insertion. — The liasilar process, close to the preceding muscle. Action. — To flex the occipito-atlantal articulation. Structure. — Flesh j-. Relations. — Below, to the preceding muscle; above, to the atlas, occipito- atlantal articulation, and the liasilar process; externally, to the rectus capitis lateralis and the guttural pouch. Blood-supply. — Occipital artery. Nerve-supphj. — ^'entral 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-supphj . — Occipital artery. Nerve-supply. — Ventral branch of the first cervical nerve. 10. Longus colli. — This muscle covers the ventral surface of the vertebrae, 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 vertebrae; (2) cervical portion, the transverse processes of the cervical vertebra;. Insertion. — (1) Thoracic portion, the bodies and transverse processes of the last two cervical vertebrae; (2) cervical portion, the bodies of the cervical vertebrae 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 in- serted into the last two cervical vertebrae. A bursa is interposed between the tendon and the spine at the first cost o- vertebral articulation. The cervical portion con- sists of a number of smaller bundles, each of which passes from its origin on the transverse process of one vertebra forward antl 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 oesophagus; dorsally, the vertebrae 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 a?sophagus, the carotid artery, the vagus, sympathetic and recurrent nerves; dorsally, the vertebrae and, in the middle third of the neck, the iutcrtransversales 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 cesophagus, which is here median in position. Blood-supply. — Subcostal and vertebral arteries. Nerve-supply. — Ventral liranches of the spinal nerves. 11. Intertransversales colli (Mm. intertransversarii cervicis). — These are six fasciculi which occu])y the spaces between the lateral aspects of the vertebrae and the transvers(! and articular processes. There is thus a bundle for each inter- vertel)ral 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 l)undlcs extend between adjacent transverse processes. LATERAL MUSCLES OF NECK 229 Action. — To bend the neck laterally. Structure. — They contain strong tendinous intersections. Relation.'!. — Superficially, the mastoido-humeralis, rectus capitis anterior major, complexus, trachelo-mastoideus, splenius, scalenus, and longissimus muscles; deeply, the vertebrae, 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. 2.50. 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 nuchse. Insertion. — The occipital crest, the mastoid process, the wing of the atlas, and the transverse processes of the third, fourth, and fifth cervical vertebra. 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, fiat tendon, also in common with these muscles. The remaining insertions are fleshy digitations. Relations. — Superficially, the skin and fascia, the trapezius rhomboideus, cer\ncalis, serratus magnus, and posterior auricular muscles; deeply, the com- plexus, 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 Ijetween the deep face of the splenius and the ventral part of the complexus. Origin.— (!) The transverse processes of the first two thoracic vertebra; (2) the articular processes of the cervical vertebrie. Insertion.— {I ) The mastoid process; (2) the wing of the atlas. 230 FASCI.E AND MUSCLES OF THE HORSE u ?* n ■» ^4.S ■=- LATERAL MUSCLES OF NECK 231 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 vertebrae is by aponeurotic slips which blend with the complexus. The suc- ceeding fleshy portion, in passing along the neck, receives fasciculi from each of the cervical vertebrae 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 vertebrae. Blood-S}ipphj . — Vertebral and superior cervical arteries. Nerve-supply. — Dorsal branches of the last six cervical nerves. 6. Complexus (jM. semispinalis capitis). — This is a large triangular muscle which lies chiefly on the ligamentum nuchse, 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 vertebrae; (3) the articular processes of the cer\'ical vertebrae. Insertion. — The posterior surface of the occipital bone, external to the funicular portion of the Hgamentum nuchae. Action. — It is the chief extensor of the head and neck. Act- ing singly, the muscle inclines the head to the same side. Structure. — The origin of the muscle at the withers is apo- neurotic. 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 hy a strong tendon. Relations. — Superficially, the rhomboideus, serratus magnus, splenius, and trachelo-mastoideus muscles; deeply, the liga- mentum nuchae, 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 {'SI. semispinalis colli; transverse spinous muscle of neck). — This muscle lies on the arches of the last five cervical vertebrae. It consists of five or six segments. Origin. — The articular processes of the last five (or four) cervical and the first thoracic vertebrae. Insertion. — The spinous processes of the cervical vertebrae. 232 FASCIA AND MUSCLES OF THE HORSE a t - ■§ LATERAL MUSCLES OF NECK 233 I s ■°' I 2 3 Action. — Acting together, to extend the neck; acting singly, g I ^' I ° I to flex and rotate the neck to the opposite side. ^ g §• ft Ss I Structure. — The muscle is composed of two sets of Innidles. S i -^ 5 I f The superficial bundles arc directed obliciuely forward and g £• 2 J I I inward, each passing from an articular process to the spine >»" § & ^- ~ I of the preceding vertebra. The deep bundles are shorter and I" I '^^ I o run straight from an articular process to that of the preceding o "■ 3 ;! I 2 vertebra. S»&2|| Relations. — Superficially, the complexus, longissimus, tra- il ■3.2 ""I chelo-mastoideus, and great oblique muscles; deeply, the y I a I' ^- ^. spinalis muscle, the ligamentum nuchse, and the arches of the vertebrae. Blood-supply. — Deep cervical and vertebral arteries. Nerve-supply. — Dorsal branches of the last six cervical nerves. 8. Spinalis. — DcscrilDed 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 oliliquely forward and outward. /2c?ai)'ons.— 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. .■Ic^io/).— 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.— SuperhciaWy, 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. i:i~^-3|%! o J; * — S a 2P ■= ■^ -^ 3 t: 234 FASCLE AND MUSCLES OF THE HORSE Blood-supply. — Occipital artery. N^erre-suppli/. — 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 nuchae. Origin. — The edge of the spinous process of the axis. Iihscrtion. — The occipital bone, below and external to the complexus and ligamentum nuchse. Action. — To extend the head. Structure. — The muscle is fleshy and may be divided into two parallel portions, YiG. 180. — Deepest Later of Muscles of Neck of Horse. a, Obliciuus capitis anterior; b, obliquus capitis posterior; c, rectus capitis lateralis; d, rectus capitis anterior minor; c, rectus capitis anterior major; /. longus colli; g, g' , scalenus: h, transversalis costarum; j, longissinius dorsi; k, spinalis et semispinalis; /, multifitius dorsi; m, multifirficial and deep. The former blends somewhat with the terminal part of the complexus. The tleep portion may be termed the rectus capitis posterior medius. Relations. — Superficially, the anterior oblique, splenius, and complexus; internally, the ligamentum nuchae; deeply, the atlas, the occipito-atlantal articula- tion, 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. THE FASCIiE AND MUSCLES OF THE BACK AND LOINS 235 Oritjin. — The dorsal surface of the atlas. Insertion. — The occipital bone beneath the ])rececling 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.' On the other hand, it is sometimes double. Relations. — Superficially, the preceding muscle and the small ol)liciue; deeply, the atlas and the occipito-atlantal articulation. Blood-supply. — Occipital artery. Nerve-supply. — Dorsal branch of the first cervical nerve. The FascijE and Muscles of the Back and Loins The superficial fascia ]iresents 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 vertebraj; 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 ex- ternus abdominis, the transversus abdominis, and the retractor costae. 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 lamellte which intersect the scapular part of the serratus and are at- tached with it to the scapula. Three lamella? 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 vertebrae; it gives attachment to the complexus. The middle one dips in between the longis- simus 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). ■i. Serratus anticus (M. serratus dorsalis inspiratorius). — This is a thin quadri- lateral muscle, named from its toothed ventral border. It lies beneath the rhom- boideus, 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. 'This seems due to pressure produced liy pathological changes in the supra-atloid bursa, which are frequently extensive in dissecting-room subjects. 236 FASCIAE AND MUSCLES OF THE HORSE Stntciure. — The muscle arises by means of a thin aponeurosis which iilends 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, ex- ternal intercostal muscles, and the ribs. Blood-supply. — Intercostal arteries. Nerve-supply. — Thoracic nerves. 5. Serratus posticus (M. serratus dorsalis cxspiratorius). — Tliis muscle re- semliles the preceding one, which it partly covers. Origin. — The lumbo-florsal 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 latissi- mus dorsi. Relations. — Superficially, the latissinms dorsi and external oblique; d(>eply, the longissimus dorsi, transversalis costarum, external intercostals, serratus anti- cus, and the ribs. Blood-supply. — Intercostal and lumljar arteries. Nerve-supply. — Thoracic nerves. Third Layer G. 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 verte- bra ancl the deep layer of the lumbo-dorsal fascia. (2) The anterior liordcrs and external surface of the last fifteen ribs.' Insertion. — The posterior borders of tlie ribs and the transverse processes of the last two or three cervical vertebrae. 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 superficitd tendons spring from the outer edge of the muscle. They are flat anil are about lialf an iuch 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 bursse may be found between the ribs and tendons. Relations. — Superficially, the dorsal serrati and the complexus; deeply, the ex- ternal 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. ' The liiml);ir part of this muscle i.s subject to variation. It may, in quite exceptional cases, extend as far as tlie ilium. THE FASCIA AND MUSCLES OF THE BACK AND LOINS 237 Blood-suppbj. — Intercostal arteries. Merve-supply. — Dorsal branches of the thoracic nerves. 7. Longissimus.' — This is the largest antl longest nuiscle in the body. It extends from the sacrum and ilium to the neck, filling up the space between the spinous processes mediall.v and the lumljar transverse jiroccsses and the upper ends of the ribs below; consequently it has the form of a three-sided prism. Origin.— (I) 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 jirocesses; (2) the thoracic transverse processes; (3) the spinous and transverse processes of the last four cervical vertebrae ; (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. Structure. — This is quite complex. The posterior part of the muscle is greatly de- veloped and constitutes the common mass of the loins. This is covered by a strong aponeurosis which blends with the supra- spinous 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 lum- bar portion of the middle gluteus. In its course further forward the muscle receives fasciculi from the lumbar and thoracic spines, but diminishes somewhat in vol- ume. At the withers it divides into two parts. The dorsal division (spinalis et semispinalis), reinforced by bundles from the first four thoracic spines, passes for- ward under the complexus to be inserted into the spines of the last four cervical vertebrae. 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 vertebrce. 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. i?eia- and ner\'e; s, skin. The fascia? are indicated liy dotted lines. CAfter Ellenberger, in Leisering's Atlas.) 238 FASCI.E AND MUSCLES OF THE HORSE 8. Multifidus dorsi (scniispinalis of the back and loins). — This is a long segmental muscle whicli covers the siiles of the spinous processes of the vertebrtB from the sacrum to the neck. Origin. — (1) The lateral portion of the sacrum; (2) the articular processes of the lumbar vertebnr; (3) the transverse processes of the thoracic vertelira^. Insertion. — The spinous processes of the first two .sacral, the lumbar, thoracic, and last cervical vertebrae. 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 liundles which are directed obliquely forward and upward. Each fasciculus passes over several vertebrae to its insertion. In the posterior part of the series the bundles cross two or three vertebrae and are inserted into the summits of the spines. Anteriorly, the bundles have a more horizontal direction, cross three to five vertebrae, 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 vertel)ral sjjines. Blood-supply. — Intercostal and lumbar arteries. Nerve-supply. — Dorsal branches of the thoracic and lumbar nerves. 9. Intertransversales lumbonun. — These are very thin muscular and tendin- ous strata, which occupy the spaces between the transverse processes of the lumbar vertebrae except the fifth and sixth. Action. — To assist in flexing the loins laterally. Relations. — Superficially, the longissimus; deeply, the cjuadratus 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 de- tached septa which pass between the muscles to become attached to the vertebrae. 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 vertebrae 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 vertebrae, 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. sacrococcygeus 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. THE FASCLE AND MUSCLES OF THE TAIL 239 Insertion. — Tlie dorsal surface of the eoecyseal vertehni'. Action. — Acting together, to elevate (extend) the tail; acting singly, to elevate and incline it laterally. Structure. — The muscle has a strong rounded l)elly. It is inserted by means of short tendons wliich fuse with those of the next muscle. RcldtionK. — Superficially, the coccygeal fascia; internally, its fellow; later- ally, the sacro-corcygeus lateralis; deeply, the vertehra\ 3. Sacro-coccygeus lateralis (M. sacro-eoccygeus dorsalis lateralis; curvator coccygis). — This muscle lies im- mediately lateral to the preced- ing. Origin. — The sides of the sacral spines, with the multifi- dus, and the transverse processes of the sacral and coccygeal ver- tebra*. Insertion. — The lateral sur- face of the coccygeal vertebrae, except the first four. Action. — Acting with its fel- low, to assist the preceding mus- cle in elevating the tail; acting singly, to incline it to the same side. Structure. — This muscle ap- pears to be a direct continuation of the multifidus dorsi . The belly Fig. 1S2. — Cross-section' of Tail of H Close to .\xus. 34, Coccygeal vertebra; 35, sacro cygeus superior; 36, intertransversalis; sacro-coccygeus inferior; 3S, coccygeus recto-coccygeus; 40, coccygeal fascia. (.\fti Ellenberger-Baum, Anat. fijr Kiinstler.) 39, Fig. 183. — Muscles of Perinei'm of Horse. a, Coccygeus; b, retractor ani; c, c', spiiincter ani exter- nus; d, recto-coccygeus; e, sacro-coccygeus inferior lateralis; /. retractor penis; g, bulbo-cavernosus; h, iscliio-cavernosus; I. internal puilic artery: k, anus; I, penis, (.\ftcr Ellenberger- Baum, Top. Anat. (1. Pferdes.) 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 vertebra:^ and a branch of the lateral coccygeal artery and accompanying vein and ner\'e. 4. Intertransversales caudse (Mm. intertransversarii cauda>). — These con- sist 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 240 FASCLE AND MUSCLES OF THE HORSE of the sacrum and occupy the spaces between the transverse processes, to which thej- are attached. They are, however, not arranged in a strict segmental manner. Adion. — Acting together, to fix the coccygeal vertebrae; acting singly, to assist in lateral flexion. .5. Sacro-coccygeus inferior (^Im. sacro-coccygei ventrales; depressor coccygis). — This muscle lies on the ventral aspect of the sacrum and coccyx. It is composed of two portions, described bj* Bourgelat and the German anatomists as separate muscles. (a) The outer portion (il. coccygeus ventralis lateralis) is much the larger of the two. It arises from the outer jiart 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 vertebrse. (6) 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 vertebrae, and is inserted into the ventral surfaces of the coccygeal vertebra. 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 vertebrae. The inner por- tion is much smaller and shorter, reaching only about to the middle of the tail. Relations. — Ventrally, the pelvic and coccygeal fasciae; dorsally, the sacrum, coccygeal vertebrae, and the intertransversales ; laterally, the sacro-sciatic liga- ment, the coccygeus, and the coccj'geal 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 intertrans- versales. 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 vertebrae, to the ribs and their cartilages, and to the sternum. Func- tionall}', they are muscles of respiration. 1. Levatores costarum. — These constituteaseriesofsmalhnuscles which occupy and overlie the upper ends of the intercostal spaces. Origin. — The transverse processes of the thoracic vertebrae. Insertion. — The external surfaces of the upper ends of the ribs posterior to the vertebral origin. Action. — ^To draw the rilis forward in inspiration. Structure. — Arising by tendinous fibers, each muscle passes backward and out- ward 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 distin- guished from the external intercostal, of which it is in reality only a specially de- veloped part. Relations. — Superficially, the longissimus dorsi; deeply, the ribs, internal intercostal muscles, and the intercostal vessels and nerves. Blood-supply. — Intercostal arteries. Nerve-s)ipphi. — Intercostal nerves. 2. External intercostals (Mm. intercostales externi). — Each of these oc- cupies 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. THE MUSCLES OF THE THOUAX 241 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. Tlie thickness of the muscles grad- ually diminishes toward the lower ends of the spaces. Seventh cerincal vcrtchra- Firsl thoracic vertebra Section of scapula hitertrarisversalcs Levatorcs coslarum Retractor co^I't: ' ~~-^i' Intertransverse ligaments , Ilio-lumbar ligament.._ ^ Fig. 184.— Dorsal ,ixd Lumbar Regions of Horse, Dorsal View. (After Schni.-iltz, Atlas <1. Anat. d. Pferdes.) Relations. — Superficially, the serratus magnus, latissimus dorsi, serratus anticus and posticus, longissiraus dorsi, transversalis costarum, rectus thoracis, deep pectorals, obliquus abdominis externus. and panniculus; deeply, the internal mter- costals and (in the upper part of the spaces) the intercostal vessels and nerves. Blood-siipphj. — Intercostal and internal thoracic arteries. Xerve-supply. — Intercostal nerves. 16 242 FASCIA AND MUSCLES OF THE HORSE 3. Internal intercostals (Mm. intcrcostali's interni). — These occupy the entire length of the intercostal spaces, including their interchondral portion. Origin. — The anterior borders of the ril)s and their cartilages. Insertion. — The posterior borders of the preceding ribs and cartilages. Action. — To draw the ribs backward in expiration. It seems probable, how- ever, that the intcrcartilaginous portion is inspiratory.' Structure. — The direction of the fibers is oblique downward and forward. There is a smaller amount of tendinous tissvie 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 sulicostals 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 ijart of the intercostal spaces the int(>rcostal 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-supphj. — Intercostal and internal thoracic arteries. Nerrr-siipply. — Intercostal nerves. 4. Retractor costae. — This is a small triangular muscle which lies liehind the last rib, chiefiy under cover of the serratus posticus. Origin. — The transverse processes of the first three or four lumbar vertebrae 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 ajioneurosis. 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. tranisversus costarum; lateralis sterni). — This is a thin muscle which lies under cover of the deep pectoral muscles. It is directed oliliquely 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 rilis. 6. Transversus thoracis (Triangularis sterni). — This is a fiat mu.scle 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 tend- inous tissue. The anterior bundles are directed forward and outward; the poste- rior liackward and outward. • Thp function of tho intorco.stal mu.scles is stil! :i snhjcct of iiiucli ilisciission. The statements made above seem to represent the view most commonly lield in rcgunl to their action. THE MUSCLES OF THE THORAX 243 Relations. — Superiorly, the cndothoracic fascia ami jileura: inferiorly, the costal cartilages, the internal intercostal muscles, and the internal thoracic vessels. Blood-suppb/. — Internal thoracic artery. Nerrc-supplij. — The intercostal nerves. 7. Diaphragm. — This is a broad, unpaired muscle which forms a partition be- tween the thoracic and abdominal cavities.' In outline it has some resemblance to a palm-leaf fan. In form it is dome-shaped, comi^ressed laterally. On a median section it is seen to have a general direction downward and forward from the lumbar vertebrie 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 cms is attached to the inferior common ligament, and by this means to the first four or five lumbar vertebrae. (6) The left crus is attached in a similar fashion to the first and second lumbar vertebrae. Action. — ^It is the principal muscle of inspiration and increases the longi- tudinal 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 inspira- tion 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 finnly 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 ab- dominis; 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 vertebra (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 tend- inous center. The left crus (Crus sinistrum) arises by a thin tendon from the inferior common ligament at the first and second lumbar vertebrae. This is suc- ceeded 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 limibo- 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 par- 1 It should be noted, liowever, th.at in the embryo the diapliragm appears as a paired struc- ture, extending from the lateral walls of the ca?loni to fuse with the septum transversum. 244 FASCI.E AND MUSCLES OF THE HORSE tially ilivided into right and left halves by the tlescent 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 vense cavse, which is encircled by fibers. A strong tendinous layer extends across below the hiatus asophageus. Longusimus dorsi Lumbar iransverae process Coital (trch AsliiiKil mil 1 1/ ahdnniiHis (, lit ulyo Xiphoid cnrldage (diprei^&cd) FlO. ISo. — DiAPMRiCM OF H 1, Inferior common ligament; 3, 2' , tendonsof crura; S, lumbar symj>athetic trunks; Jt, external spermatic nerve; 5, 5, great splanchnic nerves; 6, cisterna chyli (opened); 7, 7, oesophageal continuations of vagus nerves; 8. lymph-gland; 9, coronary ligament of liver (cut); 10. right lateral ligament of liver (cut); /;, left lateral liga- ment of liver (cut); 12, falciform li'^ament of liver (cut); A.L, lumbo-costal arch; .V.('., intercostal nerve; (\d., right crus; C'.s.. left crus; 4, aorta; Co. coeliac artery; Oc, oesophagus; I'. c, posterior vena cava; I'.p., i>hrenic veins, {.\fter Schmaltz, Atl.is d. Anat. d. Pferde.s.) The diaphragm is pierced by three foramina. (1) The hiatus aorticus is an interval between the two crura and below the last thoracic vortelira. It contains the posteridr aorta, vena azygos, and cisterna chyli. (2) The hiatus oesophageus (or foramen sinistrum) perforates the right crus near its junction with the tendinous THE ABDOMINAL MUSCLES 245 center. It is situated a little to the left of the median \i\ane and two or three inches below tiie thirteenth thoracic vertebra (in expiration). It transmits the a?sophagus, the vagus nerves, and the a?sophageal branch of the gastric arterj-. (3) The foramen venae cavse (s. dextruni) 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.' Relations. — The thoracic surface is related to the endothoracic fascia, pleurse, 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, stom- ach, spleen, pancreas, kidneys and adrenals, and the anterior flexures of the colon. The sympathetic and sj^lanchnic 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. Xerre-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 ofthe 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 (^I. cutaneus maxinius) 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 tuber- osity 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 drawii from the fold to a point about a hand-breadth 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 loosel}'- attached to the underlying structures by a ciuantity 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 timic (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 ad- herent to the aponeurosis of the muscle. Laterally it becomes thinner and is more easih' separated, although fibers from it dip in between the muscle-bundles. It is continued for some distance upon the intercostals and serratus magnus. ' 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 sUu. 246 FASCLE AND MUSCLES OF THE HORSE Traced forward, it passes as a thin layer Ijeneath the posterior deep pectoral muscle. Posteriorly it is attached to the external angle of the ilium. In the in- guinal region it forms the deep fascia of the prepuce or of the mammary glands. The linea alba is a median fibrous raphe which extends from the xiphoid cartilage to the .symphysis pubis. It is formed chiefly by the junction of the apo- neuroses of t he ol ilifiue 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 foetus. 1. Obliquus abdominis extemus (great obhque; 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 arc 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 l)y 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 fiank, where they are almost horizontal in direction. The line of junction is a curve (concave above) extending from the upper edge of the po.sterior 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 thai; 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) liga- ment (Ligamentum inguinale). This curves upward and somcwliat forward, be- comes 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,' 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 sur- face of tlic thigii, where it blends with the femoral fascia. A thin iliac layer ( Lamina iliaca) passes over the outer margin of the iliacus to the external liorder 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 obli(iue, the contents of the inguinal canal, and the sartorius and gracilis. '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. THE ABDOMINAL Ml'SCLES Blood-supply.— Intercostal and lumliar arteries. Nerve-supply.— Intercostal aud lumbar nerves. 247 2. ObUquus abdominis interaus fsmall 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. 248 FASCI.E AND MrSCLES OF THE HORSE Origin. — The external angle of the ilium and the adjacent part of the iiiKuiual (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 jiortion 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' (Annulus inguinalis abdominalis), is found here. It is normally a narrow slit, hounded in front by the edge of the internal oblique, and behintl liy tlie in- guinal ligament. The aponeurosis is to a great extent blended with that of the external oblique, being, indeed, consiilerably interwo^'en 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 adja- cent surface of the sternum. Insertion. — The pubis, by means of the jirepubic tendon. Action. — Similar to that of the oblique muscles. It is specially adapted to flex the lumbo-sacral joints and the lumliar 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 tendineae. They strengthen the muscle and serve to prevent separation of its fillers. The width of the nniscle 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 stermmi. The posterior abdominal artery runs along the outer edge of the muscle posteriorly, and the anterior abdominal artery on or in its anterior part. Blooil-siipplj/. — Anterior and posterior abdominal arteries. Nerre-siippli/. -Intercostal and lumbar nerves. 4. Transversus abdominis. — This muscle, named from the general direction of its fibers, is a triangular curved sheet. Its lateral jiart is muscular, its ventral aponeurotic. Origin.— (i) 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 vertebrae, by means of the deep layer of the lumlio-dorsal fascia. Insertion. — The xiphoid cartilage and the linea alba. ' It. must 1)0 admitted that the term "ring" is ratlier misleading as applied to the abdomi- nal opening of the eanal, since normally it is a mere dilatable slit. The ring-like eonstriotion which exists liere in the male is constit'uleil liv the peritoneum, whieh descends into the canal to form the tunica vaginalis. This peritoneal ring is termed the vaginal ring (Annulus vagmalis), and must not be confused with the subperitoneal ring, i. c, the internal inguinal ring. THE ABDOMINAL MISCLES 249 Action. — Similar to tliat of the olilique inusclos. Strufture. — The muscular part is a sheet of parallel liundlcs of fibers, directed downward and inward. It is thickest over the cartilages of the ribs, and from here it thins out srcatly 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 costse, 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 inter- val 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 simi- larly disposed further back. Blood-supply. — Intercostal, lumbar, and asternal arteries. Nervc-supply. — Intercostal and lumbar nerves. 5. Cremaster extemus. — 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.' It passes doum 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 trans- versalis 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 arterj'. 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." 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) liga- ment. 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 ' As might be expected, the cremaster usualh' undergoes more or less atrophy, and is paler in the castrated subject. In the mare tlie muscle is small, and ends in the connective tissue in the lower part of the inguinal canal. ' The term canal is somewhat misleading; it is rather a slit-like passage or space between the two oblique muscles, since the inguinal hgament is that part of the aponeurosis of the exter- nal oblique muscle which stretches between the external angle of the ilium and the prepubic tendon. 250 FASCIA AND MUSCLES OF THE HORSE surface of the ligament here by tlelicate connective tissue, except where structures intervene between the walls of the canal. Conseciucntly 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 tlie length of the canal varies greatly when measured at difTerent 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 dis- tinctly 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.' 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 obliciue muscles are inserted into its abdominal surface, and the inguinal ligaments are attached to and continue across it in arciforra 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 {ride hip joint). Muscles of the Thoracic Limb I. THE MUSCLES OF THE SHOULDER GIRDLE (Figs. 177, 178, 179, 186) Tliis grou]i consists of those muscles Avhich connect the thoracic limb with the head, neck, and trunk. The group naturally falls into two divisions — dorsal and ventral. ■ A. Dorsal Division This division consists of two la>(M-s which overlie the ])ro]ier 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 liy an ai)oneiirotic portion into two divisions: (a) Trapezius cervicalis. — Origin. — The funicular portion of the ligamentum nuchcB, from the second cervical to the third thoracic vertebra. Insertion. — The spine of the scapula and the fascia of the shoulder and arm. 1 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 foetus in obstetrical cases. The slope varies in different subjects. In some ca.ses the tendon forms about a right angle with the pubic bones. •The terms dorsal and ventral are here used in the topographic and not in the morpho- logical sense. All the muscles of the group are ventral in the latter sen.se. THE .MUSCLES OF THE SHOULDER GIRDLE 251 (b) Trapezius thoracalis s. dorsalis.—O?- /ital 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. Blond-supply. — Internal and external thoracic, inferior cervical, anterior circumflex, and intercostal arteries. Nervc-supplij. — Pectoral (or thoracic) nerves, from the brachial plexus. 4. Serratus magnus (AI. 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 scapulae hominis). Origin. — The transverse processes of the last four or five cervical vertebrae. Insertion. — The anterior triangular area on the costal surface of the scapula and the adjacent iiart of the cartilage. (b) Thoracic part (M. serratus thoracis; serratus anterior hom.inis). 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 sus- pended. (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 for- ward 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 THE MUSCLES OF THE SHOULDER — -EXTERNAL GROUP 255 action, however, it seems desirable to distinguish the two portions. The cer- vical 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 1am- elliP derived from the dorso-scapular ligament. Relations. — Superficially, the mastoido-humeralis, trapezius, deep pectoral, subscapularis, teres major, latissimus clorsi, panniculus carnosus, the abdominal tunic, the brachial vessels, and .the long thoracic nerve; deeply, the splenius, eomplexus, 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 carno- sus 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 CSl. cutaneus scapulse et humeri) arises by a thin aponeurosis from the ligamentum nuchae 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 (Fa.scia 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 underly- ing 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. «78, 179^ 1. Deltoid CSl. 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 infra- spinatus. /«.se/-((on.— 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 256 FASCI.B AND MUSCLES OF THE HORSE triceps. The belly of the mviscle lies for the most part in a cavity formed in the triceps. It is widest about its middle. Relations. — Superficially, the skin, fascia, pannieulus, and mastoido-humoralis; 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-supph/. — 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 car- tilage of the scapula. Insertion. — The inner and outer lips of the bicipital groove. Action. — To extend the shoulder joint. It also assists in preventing dis- location. 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 mem- brane 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, pannieulus, trapezius, and mas- toido-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-supphj. — 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.' 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 lione. When the long insertion is cut and reflected, the short insertion, partly tendinous, partly fleshy, is exposed. Relations. — Superficially, the skin, fascia, pannieulus, 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 axillarj^ 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 infra- ' Giinther states that this muscle assists in extension or flexion according to tlie position of the head of the humerus relative to the glenoid cavity. INTERNAL GROUP 257 #/•/ spinous 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 ab- duct the arm; also to assist in outward rotation. Structure. — The muscle is not rounded in the horse and ox, but flat and triangu- lar. Its origin from the pos- terior border of the scapula is by means of an aponeu- rosis 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. — Superfici- ally, the deltoid and infra- spinatus muscles; deejjly, the scapula, the shoulder joint, and the triceps mus- cle. Blood-supphj. — Sub- scapular artery (circumflex branches). Xerve-supphj. — Axil- lary nerve. Coraco-brachialis- Biceps brachii Brack talis ■ Exhnsor carpi radicdis ..Tendon of tensor fascia' antibrachii Flexor carpi me- diiis ..Flexor carpi in- tern us Tendon of extensor carpi — ! obligtius Deep flexor tendon ■ Check ligament Suspensory ligament-..^ Anterior extensor tendon — - Branch of suspensory ligament- Superficial flexor tendon ( B. Internal Group 1. Subscapularis. — This muscle occupies the subscapular fossa, beyond which, however, it extends both before and behind. Origin. — The subscap- ular fossa. Insertion. — The poste- rior eminence of the internal tuberosity of the humerus. Action. — To adduct the humerus. Structure. — The muscle is flat and triangular, with the base upward. The latter is thin and interdigitates with the scapular attach- ments 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 17 Fig. MrscLES OF Thoracic Limb of Horse, Ixtehnai. View. S, 4. Rhomboideus; 5, latissimus dorsi; S, posterior deep pecto- ral; 9, anterior deep pectoral; 11, supraspinatus; 13, subscapularis; 16, teres major; 20. long head of triceps; 33a. 3£b, tensor fascia? antibrachii; 33. internal head of triceps. (After EUenberger, in Leisering's .\tla3.) 258 FASCI.'E AND MUSCLES OF THE HORSE may be regarded as replaeing 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 bra- chial vessels, and the chief branches of the brachial plexus. The subscapular vessels run along or near the posterior edge of the muscle. Blnod-supply. — Subscapular artery. Ncrpc-mipplji. — 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 apo- neurosis which blends with that of the tensor fasciie antibrachii. The insertion is by a flat tendon which fuses with that of the latissimus dorsi. Relations. — Superficially, the triceps, infra.spinatus, and deltoid muscles; deeply, the serratus magnus muscle. The suliscapular vessels lie in a groove between the anterior edge of this muscle and the posterior border of the subscapu- laris; 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 subscap- ular 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 sur- face 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 antl to flex the shoulder joint. Structure. — The long tendon of origin emerges between the subscapularis and the inner branch of the supraspinatus. It ]iasses 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; inter- nally, the deep pectoral and brachialis muscles. The anterior circumflex artery and the nerve to the biceps usually emerge between the two insertions, and the l)rachial vessels lie along the posterior border of the muscle. Blood-supply. — Anterior circumflex artery. A^eri'e-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 ilistance below the head. Action. — It may perhaps tense the capsule of the shoulder joint and prevent its being pinched during flexion. THE MUSCLES OF THE ARM 259 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; deeplj', 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. Spine of scapula External tuberosity of humerus - /' Deltoid tuberosity - Biceps brachii ' Infraspinous fossa ' Brachialis . - Musculo-spiral Olecranon Fig. ISS.— Bi. „,,,,. , »/ " ^ ■ External lateral ligament of clhoic joint Shaft of radius ' " ' " "/'- If -~^ ■ ■ - - Shaft of ulna AND Bhachiaus Misci.ES OF HoHSE. (.\fter Ellenberger-Baum, Anat. fiir Kiinstler.) 1. Biceps brachii (Coraco-radialis; flexor brachii). — This is a strong, some- what rounded muscle, which lies on the anterior surface of the humerus. Origin. — The tuberosity of the scapula. Insertion.— il) The bicipital tuberosity of the radius; (2) the internal lat- eral 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 partlv 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 mternal 2G0 FASCLE AXD MUSCLKS OK THE HORSE lateral ligament. The long tendon (Lacertus fibrosus) is thinner, blonds with the fascia of the forearm, and ends by fusing with the tendon of the extensor carjii radial is. Relations. — Externally, the mastoido-humeralis and brachialis muscles; in- ternally, the posterior deep pectoral and the superficial pectoral muscles; in front, the anterior deep pectoral muscle; liehind, the humerus, the coraco-brachialis mus- cle, 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 nerv(>. 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 verj'- 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 accom- panies the muscle in the distal half of the musculo-spiral groove. Blood-supply. — Brachial artery. Xerve-supply. — Radial nerve. 3. Tensor fasciae antibrachii (Fig. 187)' (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 ajioneurosis which l)lends with those of the caput longum and the latissimus dorsi. The muscular portion is quite thin in its anterior part, somewhat thicker liehind, and is narrower than the aponeurotic origin. It is succeeded by an aponeurotic insertion, which ends chiefly by l)lending with the fascia of the forearm a little below the elbow. There is, how- ever, 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; in- ternall.y, the latissimus dorsi, serratus magnus, and posterior pectoral muscles. Blood-supply. — Subscapular, ulnar, and deep brachial arteries. Nervc-supj)ly. — Radial nerve. 4. Triceps brachii (Figs. 178, 179, 187) (Brachial triceps; triceps extensor cubiti). — This, together with the preceding muscle, constitutes the large muscular '■ M'Fatlycan and ^'auglian term this muscle the sca])ulo-ulnaris, while .^rloing and Lesbre term it "Ancone accessoire du grand dorsal." The above name seems to agree best witli tlie chief insertion and action, although it certainly arises largely from the tendon of insertion of the latissimus dorsi. THE MUSCLES OF THE ARM 261 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 iongum 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 obhquelj-. 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 fasciae 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 circum- flex 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 laterahs 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 bj^ 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 axillarj' 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. N'erve-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 cx-tcrnal head; internally, the posterior deep pectoral, coraco-brachialis, teres major, 262 FASCI.E AND MUSCLES OF THE HORSE latissimus dorsi, and tensor fasciae 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 some- what 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 ad- herent by its deep face to the joint capsule. Relatio7is. — Superfici- ally, the triceps muscle; deeply, the humerus and the elbow joint. Blood-supply. — Deep brachial arter.y. Nerve-supply. — Radial nerve. Deep flexor tendon Distal end of smalt metacarpal bone Suspensory ligament Branch of superficial flexor tendon Di.'ital digital annular ligament - Upper border of lateral cartilage Fig. 1S9. — Digit of Horse, Posterior View. 14. Deep flexor teiuion: 15. superficial flexor tendon; 16, posterior annular ligament of fetlock; 17, proximal annular or vaginal ligament of digit;-//, lateral cartilage; ^.4, plantar cushion. (After EUenberger- Bauni, .\nat. fiir Kiinstler.) IV. FASCIiE AND MUSCLES OF THE FOREARM AND MANUS The forearm is covered on three sides by the mus- cles of this group, leaving the inner surface of the radi- us for the most part subcu- taneous. 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 antl inner part to the tensor fascia; 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 inter- muscular septa, which form sheaths for the muscles and are attached to the under- lying lioiies. The principal septa are: (a) One which passes between the common FASCI.E AND MUSCLES OF THE FOREARM AND MANUS 263 extensor (in front) and the lateral extensor and flexor carpi cxternus (behind); (6) one between the common extensor and the extensor carpi radialis; (c) one be- tween 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 ac- cessory carpal (]iisiform) 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 tlown the extensor tendons and their synovial sheaths. Be- hind it is greatly thickened and forms the posterior annular or transverse liga- ment 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 DrvisioN 1. Extensor carpi radialis (M. extensor carpi radialis s. radialis dorsalis; ex- tensor 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 ktter 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 com- mon extensor; internally, at the elbow, the brachialis and biceps. Blood-supph/. — Anterior radial artery. Nerve-supplij. — Radial nerve. 2. Anterior or common digital extensor (M. extensor digitalis communis; 264 FASCI.E AND MUSCLES OF THE HORSE 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 Brachialis Cephalic nin Flexor carpi internus Anterior or common extensor of digit Extensor carpi obliquus Metacarpal tuberosity Tendon of anterior extensor Tendon of lateral extensor Branch of suspensory ligament to extensor tendon Lateral cartilage Fig. 190. — Muscles of Left Thoracic Limb of Horse, from Elbow downward, Anterior View. a. Extensor carpi radialis; g'. superficial pectoral muscle, (.\fter Ellenberger-Baura, Anat. fur Kiinstler.) 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. 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, EXTENSOR DIVISION 265 together with vestiges of the proper extensors of the digits. Usually at least two heads may be distinguished. The principal or humeral head (Caput iuimerale) 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 pcnnate. The tendon passes downwartl 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 tlie middle of the first phalanx it is joined by the branches of the suspensory liga- ment, 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)' arises from the outer tuberosity and outer border of the radius, and from the lateral ligament of the elbow joint. The fiat 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)- 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 pro- prius; lateral extensor of the phalanges; extensor sufTraginis).— 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 inter- muscular 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 meta- carpus and fetlock to its insertion. Two synovial membranes occur in connection > This is considered to represent the part of the common extensor for the fourth and fifth digits. 2 Martin considers that this muscle represents the extensor indicis proprius and the part of the common extensor for the second digit. 266 FASCLE AND MUSCLES OF THE HORSE with the tendon. A sheath envelops the tendon, beginning about three inches (ca. 6 to 8 em.) 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, hut otherwise the tendon is adherent to the capsule. The tendon becomes flat and Extensor carpi obliqmi Metacarpal tuberosity ~^ Tendon from anterior to lateral extensor External small metacarpal bone Branch of suspensory ligament to extensor tendon Olecranon Ulnar head of deep flexor Lateral extensor Deep flexor {humeral head) Tendon, of flexor carpi externus Acccfsory carpal bone Check liynmrnt Suspensory ligament Flexor tendons Flexor leiulons Ijitiral earlilaye Fig. 191. — Muscles of Left Thoracic T.iMn of Horse from Elbow Downward; External View. a, Extensor carpi radialis; g, brachialis; o\ anterior superficial pectoral: c, anterior or common digital ex- tensor; e, flexor carpi externus. (.\fter Elleiiljerger-Baum, .\nat. fiir Kiinstler.) much larger below the carpus, having received the tendon of the radial head of the anterior e.xtensor and a strong band from the accessory carpal bone. 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-suppiy. — Interosseous artery. FLEXOR DIVISION 267 Nerve-supply. — Radial nerve. 4. Extensor carpi obliquus (M. abductor pollicis longiis et extensor pollicis brevis: ol)lique extrnsor 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 do\^ia to its lower fourth). Insertion. — The head of the inner (secontl) 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. I-IG, 192- — Cross-section of Middle of Right Forearm of Horse a. Accessory cephalic vein; 6, cutaneous branch of median nerve; c, extensor carpi obliquus; rf, posterior radial artery; e, satellite vein; /, median nerve; g, 3', ulnar vessels; h, ulnar nerve; (, cephalic vein; k, tendon of ulnar head of deep flexor; /, 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; ^ flexor carpi medius; u, flexor carpi internus; c, radius; w, skin; x, anterior radial artery. (After Ellenberger. in Leisering's .\tlas.) Relations. — Superficially, the skin and fascia, the lateral extensor, and the common extensor; deeply, the radius, the extensor carpi radiaUs, the carpal cap- sule, 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. radiaUs 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 268 FASCIiE AND MUSCLES OF THE HORSE three inches (ea. 5 to 8 cm.) above the carpus and extends almost to the insertion of the tendon. Relatiojis. — Superficially, the skin and fascia, the posterior superficial pectoral and the tensor fascice 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 liga- ment. This is the pronator teres, which is usually not present or a mere vest iiii' in the liorsi'. It arises by a small, flat tendon from the flexor cpiromlylc of the humerus, and is inserted into the in- ternal lateral ligament of the elbow. On account of its small size and the fact that the forearm is fi.xed in the position of pronation, the muscle can have no appreciable function. It is usually repre- sented by the long portion of the internal lateral Ugament. 2. Flexor carpi medius (M. flexor carpi ulnaris s. ulnaris medialis; oblique or middle flexor of the meta- carpus).— 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 fasciae anti- brachii, 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. 3. Flexor carpi extemus (M. extensor carpi ulnaris' 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. ' In man the muscle is an extensor of the hand. Fig. 193. — Deeper Mdscles of Forearm of Horse, In- ternal View. S3. Internal head of triceps; 30, flexor carpi mediu-s; 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' , tleep flexor tendon: 33" , subcarpal check ligament; ,94. ulnar head of deep flexor; 36, radial head of deep flexor; ,9fi, suspensory ligament, (.^fter Ellenberger. in Leisering's Atlas.) FLEXOR DIVISION 269 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 For tendon of anterior extensor For tendon o/ ex- tensor carpi radialis Joint cavity For tendon of lateral extensor External laternl liga- ment For long tendon of flexor carpi cxternus For tendon of extensor carpi obliquus Internal lateral liga- ment Posterior ligame?d of carpus For tendon of flexor carpi intcrnus Large metacarpal artery Posterior anmdar Internal meta- Internal metacarpal vein ligament carpal nerve in carpal canal Fig. 194. — Cross-section- of Proximal Part of Left Carpus of Horse. The tendons have been removed to show the canals in which the>- lie. The joint cavity is black. By an oversight the can^al 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. pouch lies under the origin of the muscle at the elbow joint, with the cavity of which it communicates. 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. N'erve-supphi. — 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 iuternus 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.~{l} The eminences on the proximal extremity of the second phalanx 270 FASCLE AND MUSCLES OF THE HORSE lieliind 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. f Fio. 195.— Synovi.\l She.kths and Burs.e of Lower Part of Right Fore Limb of Horse, Lvtfr- NAL View. The synovial sheaths (colored yellow) and 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 ten- don; /, capsule of fetlock joint; 1, extensor carpi radialis; 2, tendon of extensor carpi obliriuus; 5, flexor carpi internus; 4. flexor carpi medius; .5, superfi- cial flexor tendon; 6, deep flexor tendon; 7, suspensory ligament; S, small metacarpal bone; 9, large meta- carpal bone; 10, posterior annular ligament of fetlock; i/. proximal digital annular ligament; 12, radius; IS, radiocarpal joint; 14, fetlock joint; 15, lateral cartilage; 16. band from first phalanx to lateral cartilage. (After Ellenberger, in Leisering's Atlas.) Fig. 196.— Synovial Sheaths axi. I5i rs.k of Lower Part of Right Fore Limu of Horse, Exter- nal View. the joint capsules (colored pink) are injected. a. Sheath of extensor carpi radialis; b, sheath of anterior extensor; c, sheath oi lateral extensor; d, sheath of outer tendon of flexor carpi externus; <■, e', carpal sheath; /,/'./", digital sheath; (?, bursa under anterior extensor tendon; h, bur.sa under lateral ex- tensor tendon; /, capsule of fetlock joint; 1^ extensor carpi radialis; 3, anterior digital extensor; S, lateral digital extensor; 4. flexor carpi externus; 4'f 4"' tendons of 4.' ^. superficial flexor tendon; G, deep flexor tendon; 7, suspensory ligament; 5. external metacarpal bone; 9, large metacarpal bone; 10, posterior annular ligament of fetlock; 7 /.digital annular ligament; 12. fetlock joint; IS, lateral cartilage; 14, band from first jjhalanx to lateral cartilage. (After Ellenberger, in Leisering's .\tlas.) Structure. — The fleshy portion nf the musrlo or humeral head takes origin from the humerus. The radial head (( 'a])ut tenilineuni) consists of a strong fihrous band, usually- termed the radial or superior check ligament, v.hieh fuses with the FLEXOR DIVISION 271 tendon near the carpus. The l)elly of the niusele is intersected by toiuHnous strands, and fuses more or less with that of the deep flexor. Near the carpus it is succeeded In- 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 (^'agina carpca) begins three or four inches (8 to 10 cm.) above the cai'ijus, and extends down- ward nearly to the middle of the metacarpus. Below the carpus the tendon be- comes flattened and broader. Near the fetlock it forms a ring through which the tendon of the deep flexor passes (Fig. 1.50). Here the two tendons are bound down in the sesamoid groove by the posterior aimular 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 liranches the tendon of the deep flexor emerges (Fig. 189). A second S5movial sheath, the digital or sesamoidean (Vagina Tendon of lateral extensor Ttndon of anterior extensor Upper pouch of joint capsule Branch of suspensory ligament Interse^amoid ligament Tendon of superficial flexor Tendon of deep flexor Fig. 197. — Cross-section of Dist.vl P\rt of Left Met.\carpus of Horse, Just Above Sesamoids. 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. 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 re- lated superficially to the skin and fascia; deeply to the deep flexor tendon. Blood-supph/. — Posterior radial artery. Xerve-supphj. — ^ledian 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 elbo^v. 272 FASCI.E AND MUSCLES OF THE HORSE Structure. — This muscle consists of throe principal heads. The humeral head (Caput humerale) constitutes the bulk of the muscle. It is marked l)y tendinous intersections, and is separable into three secondary heads. The uhiar head (Caput ulnare, ulnaris accessorius) is much smaller, and is at first superficially situated be- tween 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 pro\-ided with a tendon. The principal tendon— that of the humeral heacl — 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, lieing included in the carpal synovial sheath with the superficial flexor tendon, as previously described. Continuing down- ward, it is joined about the middle of the metacarpus by a strong fibrous band, the so-called inferior or subcarpal check liga- ment (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 perfor- atus, then in succession over the sesamoid groove, the inferior sesamoidean liga- ments, 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 jihalanx it is inclosed in the digital synovial sheath de- scrilied in connection with the perforatus. The navicular bursa or bursa podotroch- learis is found between the tendon and the third sesamoid or navicular l>one. The terminal part of the tendon is bound down by the fibrous sheet described with the fascia. Relations. — The belly of the muscle is related posteriori}^ 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 externa! 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-supphj. — Posterior radial and ulnar arteries. Nerve-supply. — Median and ulnar nerves. Fig. 198. — Digit of Horse, Lateral View. I. Large metacarpal bone; 3, distal end of small metacarpal bone; S^ fetlock joint; 5, first phalanx; G, pastern joint; 7. second phalanx; 5, coffin joint; 9, third phalanx; ii, lateral cartilage: 77', -upper (sub- cutaneous) border of cartilage; 12, suspensory liga- ment; IS, branch of 13 to extensor tendon; 14, deep flexor tendon; 75, superficial flexor tendon; 7.5', branch of lo; W, posterior annular ligament of fetlock; 17, proximal annular or vaginal ligament of digit; 75, distal annular ligament or reinforcing sheath of deep fle.xor 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. fiir Kunstler.) FASCI/E AND MUSCLES OF THE PELVIC LLMB 273 METACARPAL MUSCLES The five muscles of this group are either reduced to vestiges or mcxUfied 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 nmch 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, lieing 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. FASa^ AND MUSCLES OF THE PELVIC LiMB The FAsa^ 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). Laminae 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 jiartly 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, l)ehind 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 bicejis 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 liga- ment and tuber ischii; it furnishes origin for fibers of the long head of the .semi- membranosus. The fascia lata is continuous with the preceding, and covers the muscles on the 18 274 FASCI.E AND MUSCLES OF THE HORSE 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 fasciae lata 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 fur- nishes the following intermuscular septa : (1) One which passes between the vastus externus and biceps femoris to l)e attached to the external trochanter of the femur; (2) two which jiass lietween the three branches of the biceps femoris; (3) a fourth between the biceps femoris and scmitendinosus. The internal femoral fascia (Fascia femoralis niedialis) 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 niaj', therefore, be termed the common fasciae. The superficial layer is a continuation of the fascite of the thigh, while the second layer may be regarded chiefly as a continuation of the tendons of the super- ficial muscles of the hip and thigh (biceps femoris, scmitendinosus, tensor fascice latte, 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 gastroc- nemius 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 scmitendinosus. The third layer forms sheaths for the muscles, furnishing origin in part to their fibers. Two im- portant 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 an- terior 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 liga- ment. This converts the groove at the back of the hock into a canal, in which are the deep flexor tendon with its sj'novial 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 pero- neus 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 in- closes the tendons (and sheaths) of the two extensors of the digit. The metatarsal and digital fasciae 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 arc not confined to the sublumbar region, but ex- tend beyond it both before and behind. Their chief function is to flex the hip joint. Two, however, — the psoas minor and the quadratus lumljorum, — have not this action. THE SUBLUMBAR MUSCLES 275 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 vertebra^. Origin. — The bodies of the last three thoracic and first four or five lumbar vertebrae, 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 diaphragin, 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 s\^npathetic nerves, and the ureters. Dorsallj-, the chief relations are the vertebrae, the psoas major, and lumbar nerves. Near its insertion the tendon is crossed internally by the external iliac artery, and ex- ternally by the femoral nerve. Blood-supply. — Intercostal and lumbar arteries. Nerre-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 vertebrie. 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 ex- tremities 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), be- comes smaller and rounded, and passes downward and backward to terminate by a strong tendon common to it and the iliacus.' Relations. — -Dorsally, the last two ribs and thoracic vertebrae, the lumbar vertebriB, the internal intercostals, quadratus lumborum, longissimus dorsi, and ihacus, and the lumbar vessels and nerves; ventrally, the pleura and peritoneimi, the ihac fascia, inguinal ligament, the diaphragm, psoas minor, and sartorius, the kidneys, the spleen, the intestine (duodenum, caecum, etc.) and the circumflex ihac vessels. Blood-supply. — Lumbar and circumflex iliac arteries. A^erve-supply. — Lumbar and femoral ner\-es. 3. Iliacus.— This muscle covers the ventral surface of the ilium external to the sacro-iliac articulation, and ex-tends outward beyond the ex-ternal border of the bone, underneath the middle gluteus. 0/-i'3(n.— 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. > 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 mcludc the psoas minor also under this term. 276 FASCI.E AND MUSCLES OF THE HORSE 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, be- tween 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 fasciae latse; in front, the alxlominal muscles; behind, the hip joint. Blood -.-f up ply. — Lumbar, circumflex iliac, and deep femoral arteries. A'rrre-supplii. — Lumbar and femoral nerves. 4. Quadratus Inmborum. — 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 vertebrie; 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. Ncrre-suppli/. — Lumbar nerves. 5. Intertransversales lumborum (^L intcrtransversarii 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 tlie order in which thej' may be conveniently examined. 1. Tensor fasciae latae (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. x\ction. — 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 em.) wide, on the antoro-inferior eminence of the external angle of the ilium. Below this the belly spreads out and terminates about midway between the i)oint of the hip and the stifle in the aponeurosis. The belly fuses to a considerable ex- tent with the superficial gluteus. The aponeurosis fuses with the fascia lata, and THE EXTERNAL MUSCLES OF THE HIP AND THIGH 277 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 ohliciuus 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. Xcrrc-supply. — Anterior gluteal nerve. 2. Gluteus superficialis (Figs. 178, 199) (Superficial gluteus; gluteus externus). — This muscle lies behind and partly underneath the tensor fasciae latae. 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 separalile (ex- cept artificially) from the tensor fascite latse. 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 fascise latiE; behind, the biceps femoris. Blood-supply. — Gluteal and iliaco-femoral arteries. Nerre-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 con- tour. 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 (Clluteus accessorius) is smaller, and arises entirely from the ilium be- tween the gluteal line and the external angle (Fig. 455j . It has a strong flat tendon 278 FASCI.E AND MUSCLES OF THE HORSE which passes over the convexity of the trochanter to l)e 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.' Relations. — Superficially, the skin, lunibo-dorsal and gluteal fascia', the tensur fasciae latoe, gluteus superficialis, and biceps fenioris; deeply, the longissimus, the ilium, sacro-iliac and sacro-sciatic ligaments, the gluteus jirofundus, iliacus and rectus femoris, the iliaco-femoral artery, the gluteal and internal pudic vessels and nerves, and the great sciatic nerve. Blood-supply.— Glutesil, ilio-lumbar, lumbar, and iliaco-femoral arteries. Nerve-supply. — Gluteal nerves. 4. Gluteus profvindus (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 iscluatic 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 tentlinous intersections. The fibers are directed ahnost transversely outward over the capsule of the hip joint and converge at the convexit.y 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. paramcro-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 dor.sal sacro-iliac ligament, the gluteal and coccygeal fasciae, and the intermuscular septum lietween this muscle and the semitendinosus; (2) the tuber ischii. Insertion. — (1) A tubercle on the posterior surface of the femur near the ex- ternal 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 comjilex, 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 pro- pelling 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. Structure. — The muscle has two heads of origin:- The long or vertebral head arises chiefly from the dorsal and lateral sacro-iliac ligaments, the coccygeal fascia, ' By some anatomists the portion inserted into the crest is termed the gluteus accessorius, but Lesbro considers this the deep gluteus, homologous \vith the gluteus minimus of man. The portion in.scrted into the trochanteric ridge apparently represents the piriformis of man. ■ .\pparently the muscle represents the biceps, together with part of the gluteus super- ficialis of man. Hence the names gluteo-biceps and paramcro-biceps liave been suggested. THE EXTERNAL MUSCLES OF THE HIP AND THIGH 279 and the intermuscular septum. There is often a large bursa lietween 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 Sacro-coccygui': !>ilt'(it fascia External angle of ilium ^J,~-' Superficial gluteus Gastrocnemius tendon Superficial flexor tendon — Deep flexor -Lateral extensor Deep flexor tendon Superficial flexor tendon Suspeyisory ligament VIC Limb of Horse, Postero-external View. 17, Position of tuber ischii; o". superficial gluteus; q, ci . nous nerves. Second Layer 1. Pectineus (Figs. 186, 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 pul)o-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 cjuadra- tus 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) lirs briiiml and a little internal to the inter- nal inguinal ring and is bounded anteriorly by the iniiuiiuil ligament, posteriorly by the ante- rior border of the pubis, and externally by the tendon of the psoas minor. The canal termi- nates 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' (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 siulace of the pelvis to the internal condyle of the femur. Origin. — The ventral surface of the pul)is 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 ])arallel bundles united rather loosely. It is usually possible to separate from the principal mass a small anterior short portion,- which is inserted into the femur behind the pectineus. The principal mass^ is perforated below its middle by the femoral vessels, and is 1 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. ' This has been termed by various authors the adductor parvus or brevis. ' Termed by various authors the adductor magnus or longus. THE INTERNAL MUSCLES OF THE THIGH 283 thus (livuU'il inti) two hrani'hos. The outer hrancli is inserted into the haek (jf the fonmr with the short portion, while the inner branch is attached to the internal epicondyle and hiteral ligament. There is often a superficial slip which reaches the internal straight patellar ligament. Some fibers pass untler the lateral ligament anil end on the tendon of the semimembranosus. Relations. — Internally, the gracilis, and Ijranches of tlie femoral artery and of the obturator nerve; externally, the femur, the obturator externus, quadratus femoris, biceps femoris, antl 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-siipph/. — 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 semimembrano- sus. 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 out- ward. Structure. — It is composed of parallel bundles of fibers directeil 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. Obtiirator 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.— (l) 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. 284 FASCIA AND MUSCLES OF THE HORSE Structure. — The ischio-pubie head Ucs on tlic pelvic floor and covers the ob- turator 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 fora- men to be inserted into the trochanteric fossa. A synovial bursa facilitates the play of the tendon over the external border of the ischium.' Relations. — The pelvic surface is covered by the pelvic fascia and the perito- neum. 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'" (Fig. 455). — This is a thin, triangidar nuiscle, which extends from the external bonier 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, ciuadriceps femoris, and capsularis. 1. Sartorius. — This is described on p. 281. 2. Quadriceps femoris (Figs. 179, 186, 200) (Crural triceps). — This con- stitutes 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 fur- nishes 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 fascia latiE, glutei, and vastus externus; posteriorly, the hip joint and the vastus intcrmedius; anteriorly, the fascia lata and the skin. The anterior ' The iliac head is described by some authors as a separate muscle, and termed the pyri- formis. This does not seem desirable, especially since it is at least probable that the homo- logue of the pyriformis of man is that portion of the middle gluteus which is inserted into the back of the trochanteric ridge. -The name is based on the arrangement in man, in whom the muscle consists of two fasciculi forming a groove between them for tlie tendon of the obturator internus. In the horse it is undivided, and is grooved for tlie oliturator tendon, so that at first sight it appears to be double. The gemellus may be regarded as the exlrapelvic head of the obturator internus (.Gegenbaur) . ANTERIOR MUSCLES OF THE THIGH 285 femoral artery and branches of the femoral nerve descend into the interspace be- tween 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. Fold of flank Tensor fascia: lalm Fas/ its iniernus Sartorius Saphenuus vein Saphenous nerve Femoral artery Gracilis Adduclnr Vastus externus Vastus intermedins Peroneal nerve ■ Tibial nerve Semimem- branosus Semitendinosu V Fig. 200. — Cross-section of Middle of Right Thigh of Horse. Origin. — The external border and surface of the femur, from the great tro- chanter 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 dowTiward and forward, many being in- serted into the tendinous sheet which covers the side of the rectus. A bursa is often found between the distal end and the patella. 286 FASCIA AND MUSCLES OF THE HOBSE Relations. — Externally, the fascia lata and skin, tensor fasciae latse, 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 intemus (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 carti- lage; (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, how- ever, 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 intermedins, the anterior femoral artery, and branches of the femoral nerve. Blood-supply. — Femoral and anterior femoral arteries. Nervc-.''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. ' While it i.s 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. THE MUSCLES OF THE LEG AND FOOT 287 IV. THE MUSCLES OF THE LEG AND FOOT The muscles of this r(>gioii cuvcr ahnost all of the tiliia except its internal face, which is largely subcutaneous. As in the forearm, the muscles fall into two groups, Crest of tibia Anterior or long extensor - Lateral extensor - Proximal annular ligament External malleolus Middle annular ligament Distal annular ligament Tendon of anterior extensor Tendon of lateral extensor Gastrocnemius, external head Salens Tendon of gastrocnemius Tarsal tendon of biceps femoris Deep flexor Superficial flexor tendon Superficial flexor tendon Deep flexor tendon Suspensory ligament Branch of suspensory ligament to extensor tendon Fig. 201. — MnscLES of Lower P.irt of Thigh. Lf,g, and Foot of Horse, Extebn.ii- View. o', Fa.5cia lata; (j, roprius; b, levator iiasolabialis; /, dilatator naris lateralis: g', malaris; o. zygo- matico-auricularis and scutulo-auricularis superficialis inferior; o" , scutxilo-auricularis superficialia superior; o"\ scutulo-auricularis superficialis accessorius; p, scutularis; u, frontalis; 2, orbicularis oculi: i , concave surface of concha; 3, 2, anterior and posterior borders of concha; S, scutifonn cartilage; 34, parietal cartilage; 39, facial vein; 49, muzzle; oS. internal palpebral ligament. (After Ellenberger-Bamn, Anat. fur Kiinstler.) The stylo-mandibularis is absent. The digastricus has a tendinous origin on the paraniastoid 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 mandibulse). HYOID MUSCLES The mylo-hyoideus is thicker and more extensive than in the horse. The stylo-hyoideus has a long thin tenchnous origin and is not perforated by the digastricus. 298 THE MUSCLES OF THE OX The genio-hyoideus is more clevcloped. The kerato-hyoideus has an additional attachment on the middle cornu of the hyoid bone. The hyoideus transversus is bifid. The stemo-thyro-hyoideus has no intermediate tendon and is thicker. The omo-hyoideus ari.ses as a thin band from the fascia over the third and fourth cervical vertebra'. It blends here with the rectus capitis anterior major. The occipito-hyoideus is thick. Fig. 209. — Muscles of Head of Ox. Ventral View. d, d' , Sterno-cephalicus; f, omo-hyoideus; g, zygomaticus; h, buccinator: /, (lepre.s.sor labii inferioria; k, orbicularis oris; m, masseter; n, parotido-aui'icularis; o' , zygomatico-auricularis; w, mylo-hyoiileus; /, concha, convex surface; 2, anterior border of concha: SO', angle of jaw; 39, facial vein; A4, parotid gland; J,6, lower lip; 48, angle of mouth; 60, 60', submaxillary gland: 59, larynx; x, wing of atla:^. (After Ellenberger-Baum, .\nat. fur Kiinstler.) Muscles of the Neck a. ventral group The sterno-cephalicus consists of two muscles. They arise from the manu- brium 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. There are two scaleni. The scalenus ventralis (s. prima costa>) arises on the first rib and ends on the transverse processes of the third to the seventh cervical VENTRAL GROUP 299 ° 11 1 1 < -2 3 1 s i s I i . 5, extensor digiti quarti proprius, with synovial sheath (5'); 6, 6', flexor carpi e.xternus, with bursa (6"); 7, flexor carpi internus, with synovial sheath: S, deep digital flexor, with synovial sheath (5'); 9, flexor carpi medius; 10, superficial digital flexor, with synovial sheath W; a, radius; 6, carpus; c, metacarpus; d. cut edge of annular ligament, (.\fter Schmidtchen.) forward. At the fetlock joint it divides into two liranrhes, which are inserted into the third phalanges. 2. The internal digital extensor (M. extensor digiti tertii proprius) arises on the extensor eiiicondyle, and is inserted by two branches into the second and third phalanges of the inner digit. The tentlon receives two reinforcing slij^s 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. The extensor carpi obliquus resembles that of the horse. The extensor tentlons are bound down at the carpus by an annular ligament, and are furnished with synovial sheaths (Figs. 215, 21G). METACARPAL MUSCLES 305 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 transvcrsum), 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 temlon divides near the distal end of the metacarpus into two branches which are inserted into the volar surfaces of tlie ,. ^ third phalanges. The synovial sheaths at the carpus present the follow- ing 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. Bursae may occur under the tendons of the proper exten- sors 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. Bursffi occur between the latter and the branches of the deep flexor tendon. 2 1 7. — Cross-section OF Distal Third OF Mf.tacarpus of b, Tendon of exten- sor (ligiti tertii; c. tendon of common extensor; d, tendon of extensor digiti quarti; h, interosseus medi- us or suspensory ligament; i, tendons of digital flexors; ?*', branch of h; 12, meta- carpal bone, (.\fter EUen- berger-Baum, Anat. fiir Kiinstler.) 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 sujicrficial flexor temlon 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. 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 20 306 THE MUSCLES OF THE OX diverge to be inserted into the second and third phalanges, blending with the lateral ligaments. The Muscles of the Pelvic Limb i, the subluhbar muscles The psoas minor begins at the disc between the twelfth and thirteenth thoracic vertebrce. 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 ,^f<^-',~\ \ forward as the l)ody of the tenth or eleventh ^ thoracic vertebra. n. EXTERNAL MUSCLES OF THE HIP AND THIGH The tensor fasciae latse is large, and the fleshy part extentls further down than in the horse. The gluteus supcrficialis is not present as such; apparently its anterior part has fused with the tensor fasciae latse and its posterior with the biceps femoris. The gluteus medius is small, the lumbar portion being insignificant and extending for- wartl 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 exten- sive, arising as far forward as the external angle of the ilium, antl 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 tro- chanter. 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 thicken- ing, 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. Fig. 218. — Gluteal and Femoral Regions OF Ox, After Removal of Super- ficial Muscles. p, Gluteus medius; r, semitendinosus; w, coccygeus; 2S, vastus externus; SS' , rectus femoris; 29, semimembranosus; 30, gastroc- nemius; 31, sacro-sciaticligament; 16, tuber coxse; 17, tuber ischii; 19, trochanter major; SO, patella; ST, external condyle of tibia. (.\fter EUenberger-Baum, ,\nat. fur Kiinst- ler.) ANTERIOR MUSCLES OF THE THIGH 307 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. Bursee occur under the insertions of the internal and external vasti, and often under the end of the biceps in the adult. Fig. 219 — Muscles of Left Leg and Foot of Ox, Anterior View. a, Peroneus tertius; a', tibialis anterior; b, an- terior or long digital extensor; b' , extensor digiti tertii; c, peroneus longus; rf, extensor digiti quarti; i, (.annular ligaments; fc, external lateral ligament of hock joint; I, branch of suspensory- ligament; 20, patella; 31\ external condyle of tibia; 28, tuberosity of tibia. (After Ellen- berger-Baum, Anat. fiir Kiinstler.) Fig. 220. — Muscles of Leg and Foot of Ox, Ex- ternal View. a. Peroneus tertius; a', tibialis anterior; 6, ante- rior or long digital extensor; b', tendon of 6; c, peroneus longus; d, extensor digiti quarti; e, deep digital flexor; c'. tendon of e; e" , branch of interosseus medius or sus- pensory ligament; /, gastrocnemius (the soleus lies just in front of f r, /', tendon of /; g, tendon of superficial digital flexor; h, interosseus medius or suspensory liga- ment; /. i, annular ligaments; 20, patella; 21\ external condyle of tibia; 28. crest of tibia. (After EUenberger- Baum, Anat. fiir Kiinstler.) 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 s\Tiovial membrane. The capsularis is absent. 308 THE MUSCLES OF THE OX IV. INTERNAL MUSCLES OF THE THIGH The sartorius arises by two heads, one from the tendon of the psoas minor and the iUac fascia, the other from the shaft of the ihum. The femoral vessels pass between them. The gracilis is more extensively united with its fellow than in the horse. The pectineus is large, and arises by a single head from the pubic crest and Fig. 221. — I.Ki.T Tarsus of Ox with Syno- vial Sheaths and Burs.e lNji;rTi:iJ. External Vikw. 1, PeronevLS tertius; 1' , tendon of / and its sheath, 1" ; 2, e.Ktensor digiti tei-tii pro- prius; 2' , tendon of 2: 2", common sheath of tendons of extensor digiti tertii aii horse, Init iloes not reach to theinlernal condyle. The quadratus femoris antl obturator externus resemlile those of the horse. The obturator internus arises from the ischium only, and its tentlon passes through the obturator foramen. The gemellus is large. MUSCLES OF THE LEG AND FOOT 309 V. MUSCLES OF THE LEG AND FOOT There are four digital extensors, two of which are fused with each other and the peroneus tcrtius 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 otlier muscles near the middle of the leg. At the distal end of the tibia it termi- 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; /. ga.d. The inner arises from the tendon of the psoas minor, the outer one from tlic 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. MUSCLES OF THE LEG AND FOOT 317 The quadratus femoris is large. The obturator extemus resembles that of the horse. The obturator intemus is extensive and strong; its tendon emerges through the obturator foramen. The gemellus is fused in i)art with the obturator internus. The quadriceps femoris is more clearly divided than in the horse, and its action is transmitted l)y a single patellar ligament. The capsularis is alisent. MUSCLES OF THE LEG AND FOOT The peroneus tertius rescml)les 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, de- taching a strong branch to the first and second tarsal bones. The tibialis anterior arises on the tiliial crest. Its tendon passes over the hock along the inner border of the tendon of the peroneus tertius (both being bound dowTi by an annular ligament), and is inserted into the inner (second) metatarsal and first tarsal bones. 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 per- oneus longus. It divides into three parts. The tendon of the inner division (M. extensor digiti tertii) ends on the inner chief (tliird) 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 ex- tensors of the fourth antl 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 popUteus jiresents 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. Fig. 228. — Muscles of Leg AND Foot of Pig, An- TERO-EXTERXAL VjEW. a. Tibialis anterior; a\ tendon of preceding; 6, pero- neus tertius; h' , ten obUquus abdominis exteraus has an extensive fleshy portion. It arises from the last (>is;ht or nine ribs and the lumbo-dorsal fascia. Th(^ obUquus abdominis interaus arises from the external angle of the ilium and the luinho-dorsal fascia. The fibers have an almost vertical direction, and there is a fiesliv attacliment 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 indis- tinct tcndiiKius inscriptions. The transversus abdominis presents no special features except that the poste- rior part of its aponeurosis i splits into two layers which include the rectus between them. Muscles of the Pelvic Limb The psoas minor arises on the last thoracic antl first four or five lumbar vertebra", and is inserted into the ilio- pectineal line. The psoas major is sliort, arising from the last four lumbar vertebra*. The outer head of the iliacus is small, while the inner head is large and fuses with the psoas major. The quadratus lumbor- um 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 iliiun. The tensor fasciae latae consists of two i)arts. The anterior part is long ami rounded; the posterior is shorter and fan-like. The gluteus superficialis is small. It arises on the sacrum, first coccygeal vertebra, and sacro-sciatic ligament. It is inserted below and behind the tro- chanter 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 forwaril as the gluteal line, and is inserted into the trochanter major below the medius. The pyriformis is not lilended with the gluteus medius. It arises from the border of the sacrum and from the sacro-sciatic ligament, and ends on the tro- chanter 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 Fig. 235. — Moscles of Tail, Anus, and Genital Organs of Doo. 1, Ilium; 3, femur; 3, tuber ischii; 4. sacro-sciatic lig. ; 5, sacral region; 6, tail: 7. penis; 8, anus; 9, rectum; a, sacro-coccygeus supe- rior; b, sacro-coccygeus accessorius; c, coccygeus; d, sacro-coccygeus inferior; c. retractor ani; /, /', spliiocter ani externus; I7, retractor penis; h, bulbo-cavernosus; i, transversus perinei (?); k, ni, ischio- urethrales; /, ischio-oavernosus; n, tendon of obturator internus; o, gemellus; p, uretiiral muscle. C.\fter EUenberger, in Leisering's .\tlas.) MUSCLES OF THE PELVIC LIMB 327 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. Fig. 236. — Muscles or Pki.vic Limb of Don, Internal View. a, Ilio-psoas; b, tendon of psoas minor; c, sacro-coccy- ntralis lateralis; rf, coceygeus; e, pyriformis; /, obtur- g, origin of retractor ani; h, h' , sartorius; i, ree- ls femoris; k, vastus internus; /, pectineus; m, adductor: , gracilis; o, semitendinosus; p, semimembranosus; q, gas- ocnemius. inner head; (/. tendon of gastrocnemius; r, super- (?ial digital fle.vor; r', tendon of r; s, tarsal tendon of biceps ; t. popliteus; u. deep digital flexor, outer head (flexor s longus); u', long digital flexor; u", common tendon of u and It'; v, tendon of tibialis posterior; w, tibialis anterior; T, tendon of anterior or long digital extensor; 1, pelvic sur- face of ilium; S, section of symphysis pelvis; 3, tuber ischii; 4. internal condyle of femur; 6, ligamentum patella*; 6, 7, in- face of tibia; S. tarsus; S', fibular tarsal bone; 9, s (LUenberger-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 contlyle, 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. 328 THE MUSCLES OK THE DOG 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 annuals. The pectineus is long and slender. It arises from the ilio-pectineal eminence and enils 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 jiroximal 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 fir.st tarsal and second metatarsal. There are foiu' extensors of the digits. 1. The anterior or long digital extensor (M. extensor digitalis longus) is fusi- form, 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 CSl. extensor digitalis lateralis) is feeble and semi- pennate. It arises on the fil)ula 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 tmdcr the long extensor. Its delicate tendon accompanies that of the tibialis anterior to the first metatarsal I)one, 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 tligit, which may represent the extensor hallucis brevis. There may Vie 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 MI'SCLES OF THE PELVIC LIMB 329 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 \'esal — which articu- lates with the corresponding condyle of the femur. The tendon comports itself as in the horse. ^ The superficial digital flexor has a large round ^^C belly. It arises in coininon witli the outer head of ^r fw the gastrocnemius from the external rough line and m ai -i \» Vesalian sesamoid bone, and from the aponeurosis of the vastus externus. The tendon winds around that of the gastrocnemius, passes over the tuber WBllJ. 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 lu jt pad. Muscle-fibers often occur in the tendon in the metatarsal region. r. // /J The deep digital flexor has two heads. The large outer head, the flexor hallucis longus, arises from the tibia and fibula, filling the interosseous It' '^/// .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 m\m\\ patl and terminates as in the fore limb. / ^^^\ The tibialis posterior is a small but distinct ">- -^iW^ muscle, which arises on the proximal part of the ^VW' fibula. The thin tendon accompanies that of the Iw^W flexor longus and ends on the internal lateral liga- VVr ment of the tarsus. J»\\ The tendon of the popliteus contains a small sesamoid bone. Tlie adductors of the second and fifth digits, the lumbricales, antl the interossei are arranged as in the ^"=- 237.— Mcscles of Leg and ,, . ,. , Foot of Dog, External thoracic limb. View. The quadratus plantae arises on the outer surface a. Quadriceps femoris; b, gas- of the distal end of the fibular tarsal bone and on the trocnemius. external bead-, c, super- 1,1, IT . I ]!• 1 ficial digital flexor: d, deep digital lateral tarsal ligament, passes downward and inward, g^^„^. I p^„„^„^ i„„g„^. ^ ,^„. and terminates on a thin tendon which fuses with don of lateral extensor; », peroneus that of the deep flexor. •"■«"*■ *• '°"8 °"" an'^ior digital rr.1- 1-j i J- -i- • i- • 11 1 extensor; A', A". A'", tendons of pre- Ihe abductor dlgltl qUintl is a very small muscle ceding; i. tibialis anterior; a. exten- which consists of two parts. One of these is a ten- sorbrevls; (.slips from interossei (m); dinous slip which extends from the posterior surface ^- ^'''er'.ai <:ondyieof femur; «,pa, ' . ' tella; 3. tibia: 4. tuber calcis; 5.5, an- of the proximal part of the fibular tarsal bone to the nuiar ligaments. (.\fterEiienberger, head of the fifth metatarsal bone: the other part in Leiserings Atlas.) 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 tlie food, its passage through the liody, and the expulsion of the un- absorbed 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 com- plete lining of mucous membrane, external to which is an almost continuous muscu- lar coat. The abdominal portion of the tube is largely covered with a serous membrane — the visceral jjeritoneum. The canal consists of the following consecu- tive segments: 1. Mouth. 4. Stomach. 2. Pharynx. 5. Small intestine. .3. (Tvsophagus. 6. Large intestine. The accessory organs are the teeth, tongue, salivary glands, liver, and pancreas. DIGESTIVE SYSTEM OF THE HORSE THE MOUTH The mouth' (Cavum oris) is the first part of tlie 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 mjdo-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 l)y 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, anil the space is practically obliterated. Its existence becomes very evident in facial jiaralysis, 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 pro- prium). When the teeth are in contact, it communicates with the vestibule only by the interdental spaces and the intervals behind the last molar teeth. Poste- riorly 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. commLssurffi 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 ]ire- sents long tactile hairs in addition to the ordinary fine hair. The upper lip shows ' The term "mouth" is commonly used to sifjnify either the oral ravity (Cavum oris) or the entrance to it (Rima oris). 330 THE MOUTH 331 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 papillae 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 frsenula labii 332 DIGESTIVE SYSTEM OF THE HORSE (supcrioris, infcrioris). The free border of the lip is dense and presents short, very stiff hairs. The attached border is continuous with the surrounding struc- tures, and is adherent to the alveolar borders of the bones of the jaws. Structure. — The lips are covered externally by the skin, and are linetl liy mucous membrane; between these are muscular tissue and glands. The skin lies directlj' on the muscles, many fibers of which are inserted into the former. The muscles have been described (page 214). The labial glands (CdanduliP labiales) form a compact mass near the angles; they are numerous in the upper lip, fewer in the lower. The raucous 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 lal)ial and palato-labial arteries. The sensory nerves come from the trigeminus, anil the motor from the facial nerve. The cheeks (Buccte) 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 (Glandulse 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 con- sists 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 papillae above and below indicates the orifices of the small ducts from the buccal glands. Blood-vessels and Nerves. — The blood-supiily is derived from the facial and buccinator arteries. The sensory nerves come from the trigeminus and the motor from the facial nerve. The gums (Gingivae) 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 formeil 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 raphe (Raphe palati) divides the surface into two equal portions. Each of these presents about eighteen transverse curved ridges (Rugae palatini) which have their concavity and their free edges directed backward. They are further apart and mor(> 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 moUo) is a musculo-membranous curtain which separates the cavity of the mouth from that of the pharynx. It slo])es downward and backward from its junction with the hard palate. The oral surface faces THE MOUTH 333 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 ba.se 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 mem- brane, which ]5asses on each side along the lateral wall of the pharynx and unites with its fellow over the beginning of the a\so])hagus; 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 equidse, its length being five to six inches (12 to 15 cm.). Its length and con- tact 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 usualh' through the nasal cavity.' Structure. — The soft palate consists of: (1) The oral mucous membrane, continuous with that of the hard palate; (2) the palatine glands (Glan- dulse palatinie), which form a layer al)out half an inch in thickness; (3) the aponeurotic and mu.s- cular layer; (4) the pharyngeal mucous mem- brane, continuous with that of the nasal cavity. The muscles proper to the soft palate are the azygos uvulte, the levator palati, and the tensor palati. The azygos uvulae (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 pala- tine 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 pharjTigeal 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 tem- poral bone and the Eustachian tube, and passes forward external to the levator. ' The epiglottis may be either in front of or behind the soft palate; most often it is prevelar. Flo. 239. — Hard Palate and Part o; Soft Palate of Horse. 1 , Raphe palati; S, ridges of palate 3, atlterior end of soft palate, showing on fices of ducts of palatine glands. 334 DIGESTIVE SYSTEM OF THE HORSE Its tendon is then reflected around tlie hamulus of the pterygoid bone, being held in position by a fibrous band and lubricated by a bursa. It turns inward and ex- pands 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-pharyna:eal nerves. The floor of the mouth in its anterior part is free and is formed by the body of the mandii)h', covered by mucous membrane. The remainder is concealed by the attacheil portion of the tongue, with the exception of a narrow space on each side Septum nasi Superior meatus Naso-hirrimnl duet Infraorbital nerve and vessels Levator labii superi- oris proprius Superior buceal neri'c Facial artery Superior buccal glands Parotid duct Lnhial r Inferior labial a M ijlo-hijoide Digastricus Suhlmyual orlenj Fig. 240. — Cnoss-SKCTION of Head op Hobse jdst in Front or Facial Crest. /, Cavity of .superior turbinal; 2, cavity of inferior turbinal; 3, cavuni oris; 4. 4, Kenio-glossi; 5, 5. genio-hyoidei; G, hyo-glojisus: 7, upper, 7', lower fourth cheek tooth. Line to facial artery crosse.s zygoiiiaticus. Superior turbinal Common vicatus Moldle meatus Inferior turbinal Inferior meatus Viixiltari/ sinus eth 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 THE TEETH 339 first incisor, and may be conveniently indicated by the notation I'. The tem- porary 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 tlie crown (Corona dcntis), and a portion covered with cement, termed the root (Radix dentis). The line of union of these parts is the neck (CoUum dentis).' 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 atlvanced 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 (Pul]ia 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 com- plex 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 antl alveolus. The blood-supply to the pul]i is derived from the alveolar or dental branches of the internal artery ; the nerve-supply comes from branches of the trigeminus. • 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 objec- tion to the latter statement lies in the fact that it is not capable of general application. Tims the morphological crown of the permanent molars in the horse is extremely long, and is, for the most part, embedded in the Ijone 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 exposetl part of the crown wears down, the embedded part pushes out of the alveolus, thus preventing deficiency of length. On the old ba.sis 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. 340 DIGESTIVE SYSTEM OF THE HORSE The Teeth of the Horse The Permanent Teeth The formula of the permanent teeth of the horse is: (3 1 3or4 :i\ I - C - P M - I = 3 13 3/ 40 or 42 Fig. 24-J. — Upper Teeth of Horse, About Fodr amd One-hai.f Veaks Old. /', /-, /', Incisors; C, cauiiie; 1", P', pa, P\ premolars; M', M^, .IP, molars. Fig. 245. — Lower Teeth of Horse, Four Years of Age. /', /'-, First and second permanent incisors; Di^^ third deciduous incisor. The cheelc teeth are numbered according to popular usage. In the mare the canines u.sually are very small antl do not erupt, reducing the num- ber to 36 or 38.' ' Ellciihorgcr found, as thp result of extensive observations (8000 subjects), that about 2 to 3 per cent, of mares have erupted canines in both jaws; tliat 6 to 7 per cent, have tliem in the upper jaw; wliile 20 to 30 per cent, liave them in the lower jaw. THE TEETH OF THE HORSE 341 Incisor Teeth. — These are twelve in numlter. 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 equidie) of presenting, insteatl of the simjile cap of enamel on the crown, a deep invagination, the infundi- bulum, 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. Tlie cavity becomes darkened l)y dejjosits 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. 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 Fig. 246. — Lower Incisor and CANr Horse, Five Years Old. -Upper Incisor a> Horse, Five Yea Cani.ne Teeth of 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 direc- tion as seen in profile; at the same time the teeth become parallel and finally con- vergent. Canine Teeth. — These are four in number in the male; in the mare they are usually absent or rudimentary.' They interrupt the interdental space, dividing it into two unequal parts. The upper canine is situated at the junction of the pre- maxilla 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 ' It is interesting to notice that vestigial canines are not at all uncommon in mares, espe- cially in the lower jaw. They are very small, and do not usually erupt; their presence is indi- cated 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 equidae. 342 DIGESTIVE SYSTEM OF THE HORSE 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. Cheek Teeth (Premolars and Molars).' — The constant number of these is twenty-four - twelve in each jaw. Infundibulum Cement Peripheral enamel Dentine Central enamel ( Lingua, Puljj-caviiy Cement Labial surface Quite commonly, however, the number is increased by the pres- ence 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 in- definitely. The occurrence of a similar tooth in the lower jaw — which rarely erupts — increases the dental formula to 44, which is considered the tj-jiical number for mammals. Thej' may be regarded as liclonging 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 248. — LONGITUDIXAL SkCTION OF PERMANENT InCISOR Tooth of Horse, .\bout Natural Size. Central enamel Infundibulum :-\d~. Canine tooth Fin. 249. — IxcisoR Tooth of Horse, Lingual Aspect. (After Ellenbcrger-Baum, .-Vnat. fiir Kiinstler.) Fig. 250. — Canine and Incisor Teeth of Horse. The bone has been removed to show the embed- ded parts of the teeth, (.\fter Ellenberger-Baum, .\nat. fiir Kiinstler.) the young horse. As the cxposcil 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.) ' 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. THE TEETH OK THE HORSE 343 is maintaiopil. Tlio root begins to grow at four or five years of age, and is com- plete at twelve to fourteen, althougli the deposition of cement may continue indefinitely. 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, 2.53). Thus the long axis of the first is directed upward and a little forward, 344 DIGESTIVE SYSTEM OF THE HORSE that of the second is ahnost vertical, while in the remainiler 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 colunni, which separates two very shallow grooves. The masticatory or table surface presents two infundibula, an anterior and a posterior. It slopes obliciuely isthmus faucium is situated below and in front. It is clo.sed by the soft palate exceiit during swallowing. The laryngeal orifice (Aditus laryngis) occu])ies the greater part of tlie ventral wall or floor of the pharynx. Behind this is the oesophageal 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 THE PHARYNX 349 attached to the base of the skull, the great cornu of the hyoid bone, and the thyroid cartilage of the larynx. Thej- 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 bj' passing between the iiterygo-pharyngeus and palato-pharyngeus. Its fibers radiate, many passing forward, others inward lieneath the hj-o-pharj-ngeus. It raises and dilates the pharynx to receive the bolus in swallowing. Fig. 254 — Posterior Part Left ' . Section of Head of Horse, Cut about 1 cm. to Median Plane. /, Posterior nares; 2, phar\-ngeal orifice of Eustachian tube; 3, aditus Jaryngis; 4> entrance to cesophagus; 6, posterior pillar of soft palate; o' , junction of -5 with its fellow over entrance to oesophagus; 6, einglottis; 7, body of thyroid cartilage; 5, arytenoid cartilage: 5. 9, cricoid cartilage; 10, true vocal cord; II, false vocal cord; 12, lateral ventricle of larynx; 13, crico-arytenoideus post. s. dorsalis; 14, ce3ophagU':j; 15. external carotid artery; 10, hypoglossal nerve; 77, giosso-phar>-ngeal nerve; 18, great cornu of hyoid bone; 19, Eustachian tube; J?0, body of hyoid bone; 21, hyoideus transversus; 23, 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', supra- occipital; 27, body of sphenoid bone; 2S, pituitary body; 2S, chiasma opticum; 30, corpora quadrigemina; 31 , thalamus; 3^, arachnoid; JJ. oJontoid ligament; 34, posterior auricular muscles. 2. The palato-pharyngeus arises by means of the aponeurosis of the soft palate from the palate and pterygoid hones. 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 raphe. Its action is to shorten the phar^'nx, and to draw the larynx and oesophagus toward the root of the tongue in swallowino;. 3. The pterygo-phar5Tigeus is flat and triangular. It lies on the anterior part of the lateral wall of the pharj-nx. It arises from the pterygoid bone above the 350 DIGESTIVE SYSTEM OF THE HORSE preceding muscle — from which it is not distinctly separated — crosses the levator palati, and is inserted into the median raphe. Its action is similar to the preceding. 4. The hyo-pharyngeus may consist of two portions: (n) 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 hackwaril, turns inward toward the raphe, and spreads out under the next muscle. (h) 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 rajihe. 5. The thyro-pharyngeus arises from the lateral surface of the wing of the thyroid cartilage. Its fil)ers pass forward and inward to the median raphe. 6. The crico-pharyngeus arises from the cricoid cartilage and ends at the raph6. The fibers are directed upward, forward, and inward; they blend behind with the longitudinal fil)crs of the oesophagus. The last three muscles are constrictors of the pharj'nx. The phar3mgeal aponeurosis is attached to the base of the cranium. It is well developetl on the inner face of the palato-pharyngeus muscle and forms a median raphe (Raphe ]ihar.yngis) dorsally, which is wide in its posterior part. The mucous membrane of the pharynx is continuous with that of the several cavities which ojicn 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 guttin-al pouches. From the Eustachian opening a fold of the mucous membrane (Plica salpingo-pharyngea) passes toward but docs not reach the laryngeal opening. Below, a horizontal folil, the posterior pillar of the soft palate (Arcus pharyngo-palatinus), passes along the lateral wall and unites with its fellow over the entrance to the oesophagus. 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 liounject 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 symj^athetic nerves. THE (ESOPHAGUS The oesophagus 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 sitle 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 metliastinum between the lungs backward, upward, and a little to the left, to reach the hiatus a'sophageus of the diaphragm. Passing THE (ESOPHAGUS 351 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. \'ie\ved with reference to the frontal plane, its course is downward and l:)ack ward till it enters the thorax and passes upward to gain the dorsal faceof the trachea. For a short distance {i. e., to the root of the lung) its direction is almost horizontal; Temporal muscle Thyroid cornu of hyoid bone Parotid duct Lynipli gland Coronoid process Transverse fa- cial vessels Transrerse fa- cial nerve External ptery- goid muscle Internal max- illary vein Internal ptery- goid muscle Ramus of miiiidilile Hyo-pliaryn- geus muscle Isthmus fau- ciutn Tmsil Dii/iislrirus {intirmal. ten- don) Anterior end of submaxillary gland Lingual vein External max- illary vein Fig. 255. — Cross-section of Head of Horse. The section passes through the temporo-mandibular articulation, but is slightly oblique. 1. Corpus cal- losum; .?, lateral ventricle of brain; .?, caudate nucleus; ^. internal capsule; .5, lenticular nucleus; 5. 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. 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.' • 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 oesophagus in the strict sense of the term. The stomach here lies directly on the diaphragm, so that the last inch or so of the oesopha- gus is placed obliquely in the liiatus a'sophageiis, and is partly co\'ered by the pleura, but not by peritoneum. In soft subjects the weight of the stomach, or traction on it, draws part of the oesophagus into the abdomen, inclosed in a collar of peritoneum. 352 DIGESTIVE SYSTEM OF THE HORSE The principal relations of the oesophagus 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 oesophageal trunks of the vagus nerves lie above and below it, and the o'sojihageal 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.' The outer fibers are arranged longitudinally, beginning in two bundles attached in the interval be- tween the arytenoid and cricoid cartilages. The inner fibers run in two sjjiral strata to the terminal part of the tulje, where the arrangement is an outer longi- tudinal and an inner circular layer.- 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-oesojihageal, 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 vertebrae, the lumbar muscles, and the lumlmr 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 dia- phragm. 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 con- siderable 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 ' The potential lumen is difficult to determine at all accurately. When distended, its diam- eter (according to RubcH) \-aries from .5.7 cm. at its origin to 4 cm. at its cardiac end. The thickness of tlic wall varies (inversely as the lumen) from 4 mm. to 1.2 cm. or more. - At the origin of the tube muscular bundles arise on the raphe pharyngis and blend with the crico-pharyngcus. Vcntrally fibers come from the depression l)ctween 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. THE PERITONEUM 353 of cont;ict would be aliout 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 cavitie.s. The line of de- marcation here is the terminal line (Linea terminalis) or brim of the pelvis; it is formed by the base of the sacnini, the ilio-pectineai lines, and the anterior borders of the pnbic 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 laminse into the various peritoneal folds. The peritoneum, the serous membrane which lines the cavity, will lie tlescribed later. The abdominal walls are pierced in the adult In' five apertures. These are: the three openings in the diaphragm which transmit the aorta, posterior vena cava, and the oesophagus; the inguinal canals, which contain the spermatic cord or the round ligament (in female carnivora). In the fa'tus there is the umbilical opening also. The cavity contains the greater part of the digestive and urinar\^ organs, part of the internal generative organs, numerous nerves, blood-vessels, lymph vessels and glands, ductless glands (spleen and adrenal bodies), and certain foetal remains. For topographic purposes the abdomen is divided into nine regions by imagin- ary planes.' 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 vertebra, or the lower end of the fifteenth ril) 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 in- dicated in the subjoined table. Left parachondriac Xiphoid Right parachondriac Left lumbar Umbilical Right lumbar Left iliac Prepubic . .'. Right iUac. 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 = 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 con- tained 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 ' This method of di\dsion, although long in use, is of very little value for accurate descrip- tion. It is mentioned here chiefly because agreement on a more useful topographic method has not been arrived at. - Only a general account of the arrangement of the peritoneum is given in this section, since a, detailed tiescription cannot be understood without a knowledge of the viscera concerned. 23 354 DIGESTIVE SYSTEM OF THE HORSE are normally separated only by the thin film of serous fluid (secreted by the mem- brane) 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 en- dothelial 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 jieri- toneum 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, w^e may imagine the abdominal cavity to be empty and lined by a simple layer of perito- neum, termed the parietal layer (Lamina parietalis). We may regard the organs as beginning to develoii 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 con- necting 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 cur\atia'e 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 cxtcn.sive 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 abdom- inal 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 cor- onary 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 vertebrfe. 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 out- let 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 THE PELVIC CAVITY 355 organs, some foetal remnants, muscles, vessel; the fascia pelvis, and in part by the peri- toneum. The pelvic peritoneum is continuous in front witli tiiat of the abdomen. It lines the cavity as far back as the third or fourth sacral vertebra in the horse, where it is re- fleeted on to the viscera, and from one organ to another. We may therefore distinguish an anterior, peritoneal, and a posterior, re- troperitoneal part of the cavity. Along the mid-dorsal line it forms a continuation of the colic mesentery, the mesorectum, which attaches the first or jjeritoneal part of the rectum to the roof. In animals in fair con- dition a considerable quantity of subperi- toneal and retroperitoneal fat is found on the walls and in the various interstices. In the male the general disposition of the peritoneum here is as follows. If traced along the dorsal wall, it is re- flected at the third or fourth sacral verte- bra on to the rectum, forming the visceral peritoneum for the first part of that tube. Laterally it is reflected in a similar fashion. s, and nerves. It is lined by \M OF Sagittal Section of TO SHOW Disposition of a. Pouch between rectum and roof of cavity, continuous laterally with 6, recto-genital pouch; c, vesico-genital pouch; d, pouch below blaiUler and its lateral ligaments. The lateral line of re- flection of the peritoneum is dotted. The area of rectum covered by i)eritoneum 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. If the rectum be raised, it will be seen Fig. 257 Ho [N M.ale; -Schematic Cross-sections to show Arrangement of Pelvic Peritone B, IN Female. .1; 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, S. lateral. 4, median ligaments of bladder; r. d., vas deferens; u m., uterus mascuUnus. B: a, b, recto-genital pouch; c, c, vesico-genital pouch; d, d, pouch below bladder and its lateral ligaments; 7, mesorectum; 2, g, broad ligaments of uterus; S, 3, lateral. .4, median ligaments of bladder. that the peritoneum passes from its ventral surface and forms a transverse fold which hes on the dorsal surface of the bladder (Fig. 272). This is the urogenital 356 DIGESTIVE SYSTEM OF THE HOHSE fold (Plica urogenitalis). Its concave free edge passes on either side into the in- guinal 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 vesiculse seminales, and the uterus masculinus (a fcetal 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 Saccus cwciis {left cxlrcmily) Area of attachment to dia- phragm {non-peritoneal) Fig. 25S. — Stomach of Fixerl in situ when full liut not ilisi P.vRiET.\L Surface, The larger branches of the veins are shown. First Part of Duodenum. anterior gastric artery with two satellite 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 foetus. In the female the arrangement is motlified liy the i)resence of the uterus; the urogenital fold is very large, so as to inclose the uterus and a small jiart of the vagina. It forms two extensive folds, th(> broad ligaments of the uterus (Liga- menta 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-uteriiia), and the vesico-genital jiouch (Excavatio vesico-uterina). Further details will be given in the tlescription of the pelvic viscera. THE STOMACH 357 THE STOMACH The stomach (Ventriculus) is the hir^e dilatation of the ahmentary canal be- tween the a'sophagus antl the small intestine. It is a sharply curved, U-shaped sac, the right branch being, however, much shorter than the left one. The con- vexity is directeil ventrally. When moderately distended, there is often a slight constriction which intlicatcs the division into right and left sacs. It is relatively small, and is situated in the dorsal part of the abdominal cavity behind the dia- phragm and liver, mainly to the left of the median plane. Area of attachment to dia- phragm (non-peritoneal) Fig. 259. — Stomach of Horse, Visceral Surface, with First Part of Duodenum. I situ when full but not distended. The posterior ga.stric artery and its larger branches with two satelUte veins are shown. It presents for description two surfaces, two curvatures, and two extremities. The parietal surface (Fades 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 in- testine. The lesser curvature (Curvatura minor) is very short, extending from the termination of the a'sophagus 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 caecus is a rounded cul-de-sac which lies under the upper ends of the fourteenth, fifteenth. 358 DIGESTIVE SYSTEM OF THE HORSE and sixteenth ribs and the diaphragm.' It is rehited to the pancreas behinfl 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 oesophageal orifice or cardia is situated at the left ex- tremity of the lesser curvature, but aljout eight to ten inches (ca. 20 to 25 cm.) from the left extremity. The oesophagus joins the stomach very obliquely. The opening is closed by the sphincter cardiiE 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 pro- duced by a ring of muscular tissue — the sphincter pylori. The stomach is held in position mainly by the pressure of the surround- ing viscera and by the oesophagus. 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 oesophageal notch and the portal fi.ssure. 3. The gastro-splenic omentum (Lig. gastro-lienale) passes from the left part of the great curvature to the hilus of the spleen. 4. The great or gastro-colic omen- tum (Omentum majus) connects the ventral ]iart of the great curvature and the first curve of the duodenum with the terminal part of the great colon and the initial ])art 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 tlorsally to the liver and vena cava, ventrally to the pancreas. The stomach of the equidse is relatively small, its cajiacity varying from two to four gallons (ca. 8 to 15 liters). The size, form, and po.silion of the .stomach are .subject to considerable variation. When the .stomach is nearly empty the saccus caecus contains only ga.s and is strongly contracted; the middle portion (pliysiolocical fundus) contains the ingesta and preserves its rounded oharacter, wliile the pylorii' ijortion is contracted. Wlien distended the middle portion settles down .some fom- 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 ' This is the position in the expiratory phase a.s usually seen in the dead subject. In inspira- tion the saccus ca;cus lies under the upper parts of the sixteenth and seventeenth ribs. s\\>?S^ Fig. 260. — Everted Stomach op Horse from which THE Mucous Membrane has been Removed. O, Qisophagu.s; D, duoflenum; 6, circular layer; c', internal oblique fibers; c", loop around cardia; r"', transition of internal to external oblique fibers; d, fibers connecting the two branches of the cardiac loop; p, antra! sphincter; p' , pyloric sphincter. (EUenberger- liauin, .\nat. d. Haustiere.) THE STOMACH 359 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 (Timica serosa) covers the greater part of the organ and is closely adherent to the muscular coat except at the curvatures. It partiallj^ 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 longitu- dinal, a middle of circular, and an internal of oblique fibers. The layer of longi- tudinal fibers (Stratum longitudinale) is very thin and exists only along the curva- tures and at the antrum. At the lesser curvature it is continuous w'ith the longi- Saccus cacus (left extremity) (Esophageal region (non-glamhilar) Fundus gland region Duodenal diverticulum Pylorus Pyloric gland region 261. — Froxtal Section' of Stomach an-d First Part of Dcon C, Cardiac orifice. Photograph of specimen fixed in t,ili tudinal fibers of the oesophagus. 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 (Fibrte obliquae) are arranged in two laj'ers: the external stratum covers the left sac and is a continuation (in part) of the longitudinal fibers of the cesophagus; 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 cardise). 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. 360 DIGESTIVE SYSTEM OF THE HORSE The mucous coat is dearly divided into two parts. That which lines the left sac resembles the a^sophageal mucous membrane, and is termed oesophageal 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.' 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 reildish-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 mem- brane has a reddish-gray color and contains branched, tubular, pyloric glands (pyloric gland region); it cor- responds to the pyloric portion of man and the dog. The folding of the stomacli wall at the lesser curvature produces a prominent ridge which projects into the cavity of the stomach. Circular ridges occur at the antral antl pyloric sphincters. Blood-vessels and Nerves. — The stomach receives blood from all the branches of the coeliac artery. The gastric veins drain into the portal vein. The nerves are deriveil from the vagus and sympathetic nerves. -Diagram of Zones of Mucous Memb 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 caecum. Its average length is about seventy feet (ca. 22 meters). When distended Jts 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. - The duodenum is about three to four feet (ca. 1 to 1.25 m.) long. Its shape is somewhat like a horsesiioe, the convexity being directed toward the right. The first part is directed to the right and forms an w -shajied curve. The convexity of the first j)art of the curve is dorsal, of the second ventral. It lies on the middle and right lobes of the liver, and presents two dilatations (Ampullae) with a constric- tion between them. The duodenal angle or head of the pancreas lies in the con- ' This occlusion is usually so complete that distention of the stomach by air or fluid forced in tliiough the pylorus may be carried far enough to rupture tiie stomach without ligating the ccsopliagus. "- Xo natural line of demarcation exists, but there is a marked iiKrcasc of (he thickness of the wall toward the terminal part. Other differences will be noted in thr furl her description. THE SMALL INTESTINE 3G1 cavity of the second curve, and here, five to six inches (ca. 12 to 15 cm.) from the pylorus, the pancreatic duct and the bile duet 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 caecum, 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 ciEcum, crosses the median plane under the third and fourth lumbar vertebra, 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 florsal part of the colon; the remainder is somewhat less closely attached by it to the ca;cum Fig. 26.3. — Topography of Viscera of Horse, Left View. I.R., First thoracic vertebra; I.L., first lumbar vertebra; 3.K., second sacral spine; S., scapula: '1.. humerus; .S^, sternum; i?.. ilium; O., femur; Z... lung in complete expiration; /., dotted line indicating contour of lung in inspiration: H , pericardium; Z, costal part of diaphragm; Z', tendinous center of diaphragm; I.N., left kidney: l.v.C, left ventral colon; v.Q., sternal flexure of colon; d.Q., diaphragmatic flexure of colon; D., small intestine; ^f., small colon; M', rectum; a, coccygeus muscle; b, retractor ani; c, c , sphincter ani externus: d, cnnstrictor vulvce; e, sacro-coccygeus inferior: /. anterior gluteal artery: g, internal pudic artery; h, abdominal wall in section. (After Ellenberger, in Leisering"s .\tlas. reduced.) 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.' 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 (Ansae) 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 ' 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. 362 DIGESTIVE SYSTEM OF THE HORSE caecum at the lesser curvature of its base. The average diameter of the jejuiio- 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 some- what the terminal part of the oesophagus. 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 mesen- teric 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 vertebrae. 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 Pancreatic Diverliculurn duodeni Fig. 264. — Diagram of Section of Diverticulum Duo- deni OF Horse. .Solid line indicates mucous membrane. the latter has a free edge which passes to the caecum. Structure. — The wall consists of four coats — serous, muscular, sub- mucous, and mucous, enumerated from without inward. The serous coat is complete ex- cept 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 con- tracted 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. 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 p^dorus 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. .\t the ileo-ctecal opening the mucous membrane projects slightly into the cavity of the ctEcum, forming the ileo-caecal 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 liasement mem- brane is a layer of unstriped muscle-fibers, the muscularis mucosae. The glands of the small intestine are of three kinds: 1. The intestinal glands (Glandulse intestinales Lieberkuehni) are found throughout. They are simple tubular glands which open between the villi. THE LARGE INTESTINE THE CAECUM 363 2. The duodenal glands (Glandulse duodenales Brunneri) arc 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 mucosa and the mucous membrane. 3. The lymph follicles (Xoiluli 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 (Xoduli 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, anil 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. Vessels and Nerves. — The arteries of the small intestine come from the coeliac 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 m.) in length. It differs from the small intestine in its greater size, in being sacculated, for the most part, possessing longitudinal bands, and ha\nng a more fixed position. It is divided into caecum, great colon, small colon, and rectum. The Caecum The caecum (Intestinum csecum) 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 364 DIGESTIVE SYSTEM OF THE HORSE seven to eight gallons (ca. 25 to 30 liters). Tt 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 ab- dominal 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 bodj', and an apex. The base (Saccus ctecus) extends from about the thirteenth intercostal space l)ackward 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 ciEci) 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 aliout five to six inches (10 to 15 cm.) below it. The apex (Apex caeci) 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 ven- Origin of small colon Sternal flexure AM OF Cecum and Large Colon of Horse. trally to the origin of the great colon. The body is attached dorsally to the first part of the colon by the cseco-colic fold. The apex is free, and consequently may vary in position. The ciEcum has four longitudinal bands (Ttenise), situated on the dorsal, ventral, right, and left surfaces; these cause four rows of sacculations (Haustra). The ventral band is entirely exposed or free (Taenia libera) ; the dorsal band is free on the apex. The csecal arteries are placed on the other two. The right or parietal surface of the caecum 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-caecal orifice (Ostium ileocaecale) 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 o])posite the lower end of the last rib. The end of the ileum is partially telescoped into the caecum, so that the orifice is surrounded by a fold of mucous membrane, forming the ileo-caecal valve (Valvula ileocaecalis). The peritoneum and limgitudinal muscle-fibers do not take part in its formation. The caeco-colic orifice (Ostium caecocolicum) is placed above and external to THE GREAT COLON 365 the preceding one; the interval between tliem is only about two inches (ca. 5 cm.), and they are separated by a distinct ridge which projects into the interior of the caecum. The orifice is slit-like and is small in relation to the size of the cjecum and colon. It has a valvular fold (\'alvula caecocolica) at its lower margin and a Fig. 267. — Topography of Viscera of Horse, Right View. i/?.. First thoracic vertebra; iL., first lumbar vertelara; ;^iv'., second sacral spine; 5., scapula; -l ., humerus; 5(., sternum; 5.. ilium; O., femur; /.., right iung; //.. pericardium; Z., diaphragm (pars costalis); r.v.C, right ventral colon; i\Q., sternal flexure of colon; rf.Q., diaphragmatic flexure of colon; C, body of ca-cum; C, base of csecum: C"., apex of c^cum; D., small intestine: F., pelvic flexure of colon; M., rectum; a., abdominal wall in section; 6, duodenum: c, coccygeus muscle: rf, retractor ani; e. e' , sphincter ani externus; /, anterior gluteal ar- tery; g. internal pudic artery; h, xiphoid cartilage, (.\fter Eilenberger, in Leisering's Atlas.) muscular ring (Sphincter cseci). Large crescentic or semilunar folds (Plicae cieci) project into the cavity of the bowel, and between these are large pouches (Cellulse caeci). Vessels and Nerves. — The csecal 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 The great colon (Colon crassum) begins at the cseco-colic orifice, and terminates by joining the small colon behind the saccus csecus 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 caecum. When removed from the abdomen, it consists of two jjarallcl 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 Fig. 268. — Ileo-cecal Orifice of Horse. a, Mucous membrane of CKCum; b, ileum; c, ileo-ciecal orifice; d, fold of mucous membrane. (.\fter P. .Schumann.) 366 DIGESTIVE SYSTEM OF THE HORSE the flexures. The first, right ventral part (Colon ventrale dextrum), begins at the cseco-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 xijihoid cartilage it bends sharply to the left and backward, forming the sternal flexure (Flcxura diaphragmatica ventralis). The second, left ventral part (Colon ventrale sini.strum), passes backward on the left part of the abdomi- FiG. 269. — Abdo-minal Viscera of Horse, Ventral View. The ventral wall and part of the lateral walls of the abdomen are removed. C, Csecum; r.v.C, right ventral part of colon; v.Q., sternal flexure of colon; l.v C, left ventral pari of colon; d.Q., diaphragmatic flexure of colon; D, small intestine; M, small colon; a, ventral free band of ciccum; b, inner band of CEecum; c, lateral band of ventral part of colon; rf, ventral band of ventral part of colon; c. point of elbow; /, anterior end of sternal region; 0, xiphoid cartilage; h, teats, (.\fter EUenberger-Baum, Top. .\nat. d. Pferdes.) nal 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 dorsalc sinistrum), which passes forward above the left ventral portion. On reaching the stomach, diaphragm, ami left lolje of the liver, it turns to the right, forming the diaphragmatic or gastro-hepatic flexure (Flexura dia- phragmatica dorsalis). The fourth or right dorsal part (Colon tlorsale dextrum) passes backward above the first portion, and on reaching the inner or left surface THE GREAT COLON 367 of the base of the cfficum 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. 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. Fig. 270. — Topography of Viscera of Horse, Right Side, Deeper View. i.iZ., First thoracic vertebra; i.L., first lumbar vertebra; ;?.A'., second sacral spine; 5, 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 caecum: r.v.C, right ventral colon; i-.Q., sternal flexure of colon; d.Q., diaphragmatic fJexure of colon; r.rf.C, right dorsal colon; F., pelvic flexure of colon; D., small intestine; //., urinary bladder; M., rectum; a, left ventricle; a' , right ventricle: b, b' , right coronary artery; c, left atrium; c , right atrium; rf. small (left) coronary vein; c, vena azygos; /, anterior vena cava; 17, posterior vena cava; h, sinus venosus; i, right phrenic nerve: k, right vagus, with its dorsal ik') and ventral {k") divisions; I, aorta; m, oesophagus: n. trachea; 0, diaphragm {median section); p, right lateral ligament of liver; q, duodenum; r, dotted line indi- cating 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; 2, abdominal wall; z*, xiphoid cartilage. (After EUenberger, in Leisering's .\tlas, reduced.) The first part of the great colon is attached to the lesser curvature of the cfecum by two layers of peritoneum which form the caeco-colic fold. The ventral parts of the colon are similarly connected to the dorsal parts of the same side by the meso- colon. 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 caecum exter- nally. It is connected indirectly with the diaphragm and liver by means of a fold derived from the right lateral ligament of the liver. 368 DIGESTIVE SYSTEM OF THE HORSE The relations are coinijlex, liut the more important facts are as follows : The ventral portions (first and second) have extensive contact with the abdominal wail ventrally and laterally. On the right side the colon is almost entirely excluded from contact with the flank by the caecum; on the left side it has no contact with tlie upper part of tlie 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.' Fig. 271. — Topography of Viscera of Horse, Left Deep View. //?., First thoracic vertebra; /L., hrst lumbar vertebra: ;gA'., second sacral spine; tS'., scapula: .1., humerus; /i., ilium: /''..femur; ScA., pubis; Si., ischium; Z,.. liver (left lobe); il/o., stomach, the posterior contour of which is indicated by dotted line x: Mi, spleen; I. N., left kidney, concealed part indicated by dotted Une ; M ., small colon; D., small intestine, parts of which have been removed; I. 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.l, broad ligament M' ., rectum; V ., vagina: H., bladder; a, left ventricle; a', right ventricle: 6, left coronary artery with descending (I)') and circumflex (h") branches; c, left auricle; rf, pulmonary artery (cut); e, aorta; /, ligamentum arteriosum; ff. brachiocephalic trunk (anterior aorta); A, trachea; (', cesophagus; A*, left phrenic nerve; /, 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; /, sphincter ani internus; n, sacro-coccygeus inferior; v, abdominal wall in section; w, xiphoid cartilage. (After EUenberger, in Leisering's Atlas.) The pelvic flexure is variable in position, but usually it is directed to the right across the pelvic inlet. The ventral portions of the colon have four longitudinal muscular bands (Tffiniffi) which produce four rows of sacculations (Haustra). On the first ])art 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 ccecum. 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 ' Abnormal displacement, e. g., torsion of the left parts, is not rare, and is liable to produce death if not promptly reduced. THE SMALL COLON 369 other bands ajipear, so that the flexure has three bands; two of these are dorsal and free, the tliird 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 ciecus of the stomach and lielow 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.). Fig. 272. — Pelvic Ixlf.t 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 ore- master muscle. The subluiubar region is greatl.v foreshortened in this view, a, a'. Kidneys; a", adrenal; b., ureter; c, renal artery; rf, aorta; e, coeliac artery (cut); /, anterior mesenteric artery (cut); (7, posterior mesenteric artery; h, circumflex iliac artery; i, external iliac artery; k, internal iliac artery; /, 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; r, external pudic arter\-; w, rectus abdominis muscle; J, transversus and obliquus internus abdominis: y, ij' , cre- master externas; z, posterior vena cava (cut), (.\fter EUenberger-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 tsenise 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 mesen- tery is narrow at its origin, but soon reaches a width of about three feet (ca. 24 370 DIGESTIVE SYSTEM OF THE HORSE 80 to !)0 cm.). Its parietal Ijorder 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 I'oot of th(^ great mesentery, and behind with the mesorectum. There are two taeniae and two rows of sacculations. Of the taenia?, 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 rectmn (Intestinum rectum) is the terminal part of the bowel; it extends from the pelvic inlet to the anus.' 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 fiask-shaped dilata- tion tennetl the ampulla recti ; it is attached to the surrounding structures by con- nective 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 laterallj' to the pelvic wall, ^'entrally the relations differ in the two sexes. In the male they are the bladder, the ter- minal parts of the vasa deferentia, the vesiculjE seminales, the prostate, the bulbo- urethral (Cowper's) glands, and the urethra. In the female they are the uterus, vagina, and vulva." 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 caecum and colon which are between the layers of the cseco-colic fold and mesocolon; (b) the areas of attachment of the CiEcum 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 fibrse transversiE coli. The nmscular 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 vertebrae. 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 cor- responding to the ext(Tnal constrictions. It has no villi, Brunner's glands, or Peyer's patches. The intestinal glands (of Lieberkiihn) are large antl numerous. Solitary glands are also numerous, especially at the apex of the cajcum ami in the left dorsal j^art 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. ' There is no natural line of demarcation between tlip stnall colon and rectum: the plane of the pelvic inlet is selected for convenience of description. - The .anterior part of the rectum is very variable in position and relations. It is not often median, but may bo dodccted either to right or left. Most often it is pushed to the left by the pelvic flexiire 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 coveretl by peritoneum dorsally and laterally is very variable, and appears to be in inverse proportion to the fullness of the bowel. THE PANCREAS 371 The anus is the terminal orifice of the ahmentary canal. It is situated Ijelow 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, liairlcss, 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 intemus is merely a terminal thickening of the circular coat of the bowel. 2. The sphincter ani extemus is a broad liand of striped muscle-fibers outside the internal sphincter. Some fil:)ers are attached to the coccygeal fascia above, others to the perineal fascia lielow. 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 cocc^'geal vertebra, passes downward over the retractor, and unites with its fellow below the anus. In the male it is largely continued ijy the retractor penis muscle; in the female it blends with the constrictor vulvje. It may act as an accessory sphincter of the anus. Blood-supply. — Internal pudic artery. Nerve-supply. — Hiemorrhoidal and perineal nerves (for the sphincter ani exter- nus 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 mechan plane. Its central part lies under the sixteenth and seventeenth thoracic vertebrae. 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.' The dorsal surface faces upward and forward. It is partially' covered by peritoneum. It is related chiefly to the ventral surface of the right kidne\- and adrenal, the posterior vena cava, the portal vein, the coeliac artery and its divisions, the gastro-phrenic ligament and the saccus caecus of the stomach, the right and caudate lobes of tlie liver, and the gastro-pancreatic fold. There are grooves for the divisions of the ca?liac artery, and a large one for the splenic vein. The ventral surface looks do^\-nward and liackward ; it is in general conca\-e. It presents two impressions, separated b\' an oljlique ridge. The smaller of these (Impressio caecalis) lies to the right, and is caused bj' the pressure of the base of the caecum; the larger one (Impressio colica) indicates the area of con- tact 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 duo- denum and the caudate lobe of the liver. The left border is slightly concave, and is related to the first part of the duode- num, the left sac of the stomach, and the splenic vessels. ' A descriptive method based on that in use in human anatomy cannot be applied with clearness to the organ in the horse. 372 DIGESTIVE SYSTEM OF THE HORSE 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 (Amiulus portarum). The root of the great mesentery is in contact with the border just to the left of the median jjlaiie. The anterior or duodenal angle (Caput pancreatis) is attached to the concavity of the second curve of the duodenum, anil 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 pan- creas in man. It is in contact with the base of the spleen, the left kidney and adrenal body, and the saccus ciECUS of the stomach. Right kr'c/ney Stomach Fig. 273. — Pancreas or Horse with I in duct and its two chief radicles are indicated by gland. ubstance of the 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 tis.sue 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 cijecum and the terminal part of the great colon. There are almost invariably two ducts. The large one is termed the pan- creatic 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 duo- denal angle to end at the duodenal diverticulum alongside of the bile-duct. The THE LIVER 373 duct is noarly half an inch (ca. 1 cm.) wide, and is very thin-walled. It is situated in the .substance of the g.liuu\ near its dorsal surface; none of it is free. The acces- sory pancreatic duct (Ductus pancreaticus accessorius [Santorini]) arises either from the chief duct or its left radicle, and ends on a papilla in the duodenum oppo- site the chief duct. Structure. — The j^ancreas 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 cipliac and anterior mesenteric arteries. The nerves are derived from the coeliac 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.). AVhen 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 stronglj* convex, and lies against the diaphragm. It faces chiefly upward and forward. It presents, just to the right of the mecUan plane, a sagittal groove for the posterior vena cava (Fossa vense cavse). 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 back- ward; 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 de- pression for the great colon (Impressio colica). Dorsal to this is a smaller depres- sion for the blind end of the base of the caecum.' 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 vense cavse; (3) a deep notch (Impressio ' These impressions are not evident on the soft organ. In hanlened material they are clearly mapperl out, although of course variable in size, in conformity with the degree of fullness of the various hollow \'iscera. The caecal impression may not be evident if, as often happens in old horses, the right lobe of the liver is much atrophied. 374 DIGESTIVE SYSTEM OF THE HORSE ocsoi^hagea) wliicli is mainly occupied by the thick margin of the ajsophajical open- ing of the (Haphrafiin. The ventral border is thin, and is marked by two deep interlobar fissures or incisuies (Incisura> intcrloliares), which partially divide the organ into three prin- cipal 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 um- bilicalis); the latter contains the umbilical vein in the fu>tus, 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 th(> middle of the sixteenth rib. The left border is thin and short. It extends backward to a point opposite Right lateral ligament \ Fight lobe Posterior vena cava (Esophageal notch ^'^f^ lateral ligament lobe Falciform ligament Flo. 274.— Liv Round ligament E, H.\RDENED in sUu, Parietai. Surface. the lower part of the ninth or tenth rib. The ventral and lateral borders together constitute the margo acutus. 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 laminEe. The right one is attached to the right of the fossa vense cavse; 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 a-sophageal notch; it detaches a middle fold which extends to the notch and is continuous with the small omentum. The two laminae 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 varial)le tlistance. In its concave free eilge is found THE LIVER 375 3. The round ligament (Lig. teres hepatis), a fibrous cord which extends from the uinliiUcal fissure t6 the unibihcus; it is the vestige of the umbiHcal vein, which hi tiie fcetus 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 IoIm' to the costal part of the diaphragm. Poskriur vena cava Renal iinprexmon AUackment of (/astro-piincreatic fold Portal fissure _ Hepatic artery ; Attachment of lesser omentum Hepatic duct (Esophageal notch Left lateral ligament Umbilical fissure Fig. 275. — Liver of IIonsR, Visceral Surf.\ce. .Specimen from middle-aged subject, hardened in situ. 5. The left lateral ligament (Lig. triangulare sinistrum) attaches the dorsal edge of the left lol)e to the tenilinous center of the diaphragm. 6. The hepato-renal or caudate ligament (Lig. hepatorenale) attaches the caudate process to the right kidney and the Imse of the caecum. 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 376 DIGESTIVE SYSTEM OF THE HORSE 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 tlie midiUe lobe may exceed it in size.' 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 be- tween the two la.ycrs 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 pan- Renal impression Posterior rena cara Portal vein Hepatic artery Hepatic duct (Esop/iagcal notch Middle lobe L'mbilcca! rein 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. creatic 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 jirevents regurgitation from the intestine. There is no gall-bladder. Structure. — The liver is covered by an outer .serous, and an inner fibrous coat. The serous coat covers the gland excejjt 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 laminae into the ligaments, and also ' Flower and Rugo 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 lolies would correspond'to the middle lobe of the foregoing de- scription, and the right ccntial lobe would be the equivalent of the quadrate lobe of man. THE SPLEEN 377 delicate strands into the gland substance. At the portal fissure it is abuntlant 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.' Vessels and Nerves. — The portal vein enters at the portal fissure. It conveys blootl from tlie 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 tlie nutrient vessel. All the l)lood is returnetl from the liver to the posterior vena cava by the hepatic veins. The portal vein and the hepatic artery both divide into interlobular l)ranches, which run together in the portal canals of the interlobular tissue. The branches of the portal vein (Vense intcrlobulares) 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 intcrlobulares) 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 - (Vense hepaticie) 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 lol:)ules and join the sublobular veins (Vente 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 diai^hragm. 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.' 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, de- pending 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, ahhough 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 ' In the young foal the interlobular tis.sue is more abundant and the loljulation correspond- ingly distinct. - The hepatic veins may be recognized on section from the fact that they remain open, being connected closely with the parenchyma. ^ 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 thvroid 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. 378 DIGKSTIVE SYSTEM OF THE HORSE pounds in lior.scs weighing 1000 to 1200 pounds. The chief variation in outhne 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 esecus 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 jjarietalis) is convex, and lies chiefly against the dia])hragin, but is in direct contact with the upper parts of the last two ril)s 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 uneciual 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 liehind the ridge (Facies intestinalis) is Posterior basiil angle Attachment of xiis/x^nsonj \ ligament ) Tmt impression / .1 nterior basal ang Splenic artery Splenic vein Anterior border ^7 — Spleen of Horse arketl intestinal impression is related t much more extiMisive; it is related chiefly to the small colon, the small intestine, and the grctit omcntiiin. It may be marked by one or two fissures. The anterior border (Margo anterior) is concave and thin. The posterior border (\Iargo posterior) is convex and thin. Tlie 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 iti silii, 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 caucus of the stomach and the left kidney; the jiosterior 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 PERITONEUM 379 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 licnis) 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 liga- raentum 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 ma.-ises of splenic tissue may be found in the gastro-splenic omentum. They are termed accessory spleens (Lienes accessoria;). Structure. — The spleen has an almost complete serous coat. Subjacent to this antl intimately united with it is a capsule of fibrous tissue (Tunica albuginea), which contains many elastic fibers and some unstriped muscular tissue. Numerous trabeculae (Trabeculae lienis) are given off from the deep face of the capsule and ramify in the substance of the organ to form a supijorting network. In the inter- stices of this framework is the spleen pulp (Pul]ia lienis), a dark red, soft, grumous material. This is supported by a delicate adenoid reticulum, and contains numer- ous 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 trabeculae. The arteries which enter the pulp have a sheath of lymphoid tissue, which collects on the vessel wall at certain points, form- ing 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 jDin. The blood passes into cavernous sj^aces lined bj' endothelium w'hich 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.' (Figs. 256, 257, 278, 279.) We may consider the peritoneum as consisting of tw-o sacs — a greater and a lesser. The greater sac lines the greater part of the abdominal cavitj^ 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 vis- cera. The two sacs communicate by a relatively narrow passage, termed the epiploic foramen of Winslow (Foramen ei^iploicum) . This opening is situated on the visceral surface of the liver above the jjortal fissure. It can be entered by passing the finger along the caudate lobe of the liver toward its root. Its dorsal (or an- terior) 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 ' The student is strongly recommended to study the peritoneum of a foal or other small subject when the opportunity occurs, a.s in these the viscera are easily handled, and the course of the peritoneum can be followed without difficulty. 380 DIGESTIVE SYSTEM OF THE HORSE extremity, where it is about an inch (ca. 2.5 to 3 cm.) wide.' 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 Ijurste 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 oesophageal notch the fingers can be passed around the border of the liver and the vena cava till the coronary ligament is encountered. Thus the vestiinile is closed except (1) on the right, where it communicates with the cavity Fig. 278. — Diagram of General Arrangement of Peritoneum ( a. Pouch between rectum and roof of pelvis, continuous witli b, recto-genital pouch; d, pouch below blaihier and its lateral Ugaments; /, lesser omentum; Int., small intest to the epiploic foramen (of Winslow). Sagittal Tracing. c, vesico-genital ijouch; The arrow points of the greater .sac by the epiploic foramen; and (2) l)ehind, where it communicates with the cavity of the omentum. 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 b!ends with the suspensory ligament of the latter, and forms a recess (Recessus lienalis) behind the saccus CiECus of the stomach. It now passes along the hilus of the spleen, and is continued to the great curvature of the stomach l)y the gastro-splenic omentum. It is convenient to regard the spleen as being intercal- ' The passage is subject to a good deal of variation in caliber and is sometimes completely occluded. THE PERITONEUM 381 ated in the left part of tlie great omentum; on this basis the gastro-splenic omentum woukl he that part of the great omentum which connects the hilus of the spleen with the great curvature of the stomach. The great omentum is relativelj^ small in the horse, and is usually not visible when the abdomen is opened. It is gc-nerally folded up in the space between the visceral surface of the stomach and the intestine.^ The lesser sac furnishes tlie peritoneal covering for: (1) the visceral surface of tlie 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 ; (8) a small part of the visceral surface of the Uver above the attachment of the lesser omentum anil llic poiial fossa; (4) the posterior vena cava, from the level of the epi- ploic foramen [of Winsldul iiiiN ]i;issage through the diaphragm (in so far as it is not embedded); (n) the part of the parietal surface of the liver between the right and middle di\isions of the cor- onary 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; (j of Head of Cow, Cn a little to the Right of the Median- Plane. i. Cerebral hemisphere; 5. corpus striatum; 3, hippocampus; .{, olfactory bulb; o, corpora quailrigemina; e, optic nerve; 7, pons; S, medulla oblongata; 9. spinal corJ; /O. pituitary body; //, .sphenoid sinus; /5, lateral mass of ethmoid; 13, ventral straight muscles; H, pharyngeal (retropharyngeal) lymph gland; IS, longus colli; 16, soft palate; 17. vallate papilla;; IS, tonsillar sinus; 19, conical papilte of cheek; 20, hyo-epiglotticus mus- cle; «i, epiglottis; ^3, hyo-glossus muscle; C1,C3, atlas, axis. Subject was hardened with mouth open. bro-miish mass which reaches from the angle of the mouth a short distance under' the masseter muscle. The mifldle part consists of loosely arranged yellow lobules. A linear series of large papilla exists on the floor of the mouth on each side of the frenum lingua;. 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 384 DIGESTIVE SYSTEM OF THE OX thick, horny epitheUal covering — forming the so-called dental plate or patl. The palatine ridges extend from this backward about two-thirds of the length of the hard palate. They are nearlj' straight, and, for the most part, are serrated on the free edge. A median furrow extends between the ridges. The posterior thirtl 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 Cai'Uy Superior Superior Septum of superior turbinal meatus nasi turbinal Frontal Middle meatus Inferior turbinal Inferior meatus Maxillary sinus Palatine sinus Palatine artery. Inferior labial Hypoglossal nerve Naso-laerimal duct Infraorbiial nerve Masselcr Sujjerior buc- cal yla/ids Facial artery Facial vein Inferior buccal ylands Subiiiigual (/land Digastrieus Sulmiaxil- Lingual lary duet nerve Vic. 2S2. — Cross-section of Head of Ox. The .section passes through the internal canthi. L.n., Lincual arteries. The arrow indicates the communicatii lietv llary and palatine sinu of the naso-palatine canal. This canal is two inches or more (ca. 5 to 6 cm.) in lengtli ami ojicns on the floor of the nasal cavity; it also communicates by a slit- like opening with the organ of Jacobson. 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 oesophagus. The azygos muscle is much better THE TONGUE 385 developed than in the horse. The fibrous ajioneurosis is for the most part replaced by muscular tissue. The isthmus faucium is wide and dilatable. On either side, b(>hind the an- terior 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. (Esophagus- Apices of aryljnni't. Aditus laryngis Epiylutl Thyroid gland Wall of pharynx reflected Posterior pillar of soft palate Soft palate cut and reflected Vallate papiUce TonsiiL:r sinus Eminence of dorsum Fungiform papilla Tic. 283. — Tongue of Ox, Dohs.\i. Aspect. Pharynx, soft palate, and origin of oesophagus are cut dorsally 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 papillae in front of this prominence are large and horny, with sharp points directed backward. They impart to the tongue its rasp-like roughness. The papillae on the prominence are large, broad and horny; some have a blunt conical form, others are rounded or flattened. Behind the prominence, the papilte are long and soft, ;'. e., not horny. The fungiform pajjillse are numerous and dis- tinct; they are scattered more generally over the dorsum and edges of the free 25 386 DIGESTIVE SYSTEM OF THE OX part. The vallate papillse 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 prominonee of the dorsum. The foliate papillae and the lingual fibrous cortl are absent. The muscles are well developed; the hyo-glo.ssus 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 I-C'-P-M- I = 32 V 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 Fig. 285. — Incisoh Tooth of Ox. 2A' , Lingual surface of crown; 2It'\ masti- cators' surface. The crown is clearly marked off from the rounded root by a neck, (.\fter Ellen- berger-Baum, .\nat, fiir Kimstler.) rounded, and is embeddeil in the jaw in such a manner as to allow a considerable degree of movement. There is a distinct neck. In addition to the simjjle numeri- cal designation, the following terms are commonly applied to the indiviilual teeth: pinchers or central, first intermediate, second intermediate, and corner incisors. It is probaljle 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, how- ever, the gum retracts so that the roots are partly exposed and may come into wear.' The deciduous incisors differ from the permanent set chiefly in being much smaller. The crowns are narrower anil diverge more. The canines are absent (unless the fourth incisors be considered to rejiresent them). 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 ' 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. THE TEETH 387 388 DIGESTIVE SYSTEM OK THE OX progressively increase in size from before liackward. 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 decitluous teeth is: (0 0 3\ Di- De - Dp- I = 20 4 0 3/ T.VBLE OF AVERAGE PERIODS OF ERUPTION OF THE TEETH IX THE OX Teeth Eruption A. Temporary: First incisor (Di 1) Second incisor (Di 2) I n- ii » -y i Third incisor (Di 3). | ^''^^ '° ^ weeks. Fourth incisor (Di 4) J First cheek tootli (Dp 1) Birth to 3 weeks. Second cheek tooth ( Dp 2) 1 „. ,, , , Third cheek tooth (Dp 3) / ^'^th to few days. B. Permanent: First incisor (II) 1 J^ to 2 years. Second incisor (12) 2 to 2J4 years. Third inci.sor (13) 3 years. Fourth incisor (14) 33>^ to 4 years. First cheek tooth (PI) 2 to 2}^ years. Second cheek tooth (P 2) 1 ' 2 to 2}^ years. Third cheek tooth (P 3) 2}^ to 3 years. Fourtli cheek tooth (Ml) 5 to 6 months. Fifth cheek tooth (M2) 1 to 1}^ years. Sixth cheek tooth (M3) 2 to 2^ 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 condi- tions. 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 j^ellow in color. It is covered to a small extent \>y 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 hcrse. The sublingual gland consists of two parts. The dorsal part (Glandula sub- lingualis 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 numer- ous small tortuous ducts (Ductus sublinguales minores), which open between the jjapillae under the side of the tongue. The ventral part is shorter and thicker, and THE PHARYNX — THE CESOPHAGUS 389 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 pharjTix is short and wide. The vault (Fornix pharyngis) is divided into two cul-de-sacs by a median fold of mucous membrane (Septum nasi membrana- ceum), 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 Fir.. 2S7.— Salivary Glands of Ox. a. Parotid gland; b, submaxillary gland; c, inferior, d, midtlle, and e, superior buccal glanils; /, labial glands; ff, buccinator nerve; ft, buccinator vein; /, masseter (cut); 2, ramus of mandible; 5, zygomaticus muscle; 4, conical papili* of lip: 5, buccinator muscle. (After Ellenberger, in Leisering's .\tla3.) The posterior nares are small. The entrance simjile fold of mucous membrane, to the oesophagus is large. 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 CESOPHAGUS 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 390 DIGESTIVE SYSTEM OF THE OX 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 ccsophagus and may, if enlarged, obstruct it (Fig. 289). THE ABDOMINAL CAVITY The abdominal cavity of the ox is very capacious, both absolutely and rela- tively, 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 l)et\veen 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 i)art 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 largeh' 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 he separated by a plane through the lower end of the tenth pair of ribs, or through the last thoracic vertebra. Tlie 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 olilique 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 s])leenj and extends con- siderably over the median plane into the right half. It is compound, lieing composed of four divisions, viz., rumen, reticulum, omasum, and abomasum.' The division is clearly indicated externall>' by furrows or constrictions. The first three divisions may be regarded as provcntriculi or a-sophageal sacculations, the fourth being the stomach proper (in the narrower sense of the term). The oesophagus opens into the stomach on a sort of dome formed by the rumen and reticulum, and is continued through the latter by the ccsophageai 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 diviiled or fluid food. The abomasum joins the small intestine. Capacity. — Th(> 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 arc about half as ' In popular language these are conveniently regarded as so many stomachs, and termed arcordingly "first," "second," etc. Otlier names are in common use, e. g., paimch, honeycomb, manifold or manyijfies, antl rennet or true stomacli. THE STOMACH 391 Iarp;e as the aliomasum; in ten or twelve weeks this ratio is reversed. During tiiis ])erioci the omasum a])])ears to he contracted and functionless. At four months the rumen and reticuhun together are about four times as large as the omasum antl 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., anrl the abomasum 8 or 7 per cent, of the total amount. Exterior and Relations 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 some- what compressed laterally, and may be described as having two surfaces, two curva- tures 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 Fig. 288. — Projection of Viscera of Cow on Body-wall, Left .Side. Oes.. Oesophagus: Ret., reticulum; b.s., anterior blind sac; b.s.', b.s".. posterior blind sacs of rumen; 0, 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. 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 firnilj' attached to the left portion of the crura of the diaphragm and the sublumbar muscles by peri- toneum and connective tissue. The ventral curvature is also com-ex and lies on the floor of the abdomen. The surfaces arc marked by the right and left longitudi- nal furrows (Sulci longitudinales), which indicate externally the division of the rumen into dorsal and ventral sacs.' The reticular (or anterior) extremity (Ex- tremitas 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 ven- trally over the round, blind end of the ventral sac. The former only is continuous ' It has been customary to term the sacs left and right respectively, but these do not repre- sent the relations as they exist in situ and as they are presented on frozen sections. 392 DIGESTIVE SYSTEM OF THE OX with the reticulum, a ventral groove (Sulcus runiino-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 cesophagus terminates. The pelvic (or i)osterior) 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 csecus 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 groo\c by means of the grooves between the dorsal and ventral blind sacs at each enrl. The ventral groove (Sulcus accessorius) curves somewhat vent rally 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 Hes 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.' 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 ahuost entirely to the right of tlic 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 junc- tion 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 nnnen. 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 ' It is important to notice that the reticulum is separated from the pericardium by an interval of about 1 to P-2 inches (ca. 2 to 4 cm.) only, since foreign bodies which are often .swal- lowed by cattle lodge in the reticulum, and not rarely (if sharp) perforate the reticulum and diaphragm. THE STOMACH 393 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 i or ]jvloric) 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 cesophageus backward to about the third or fourth lumbar vertebra. The lesser omentum attaches the right face of the oma.sum and tlie pyloric liortion 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 Ijjind sacs at either extremity; they are termed the chief piUars. The anterior chief pUlar (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 2.5 cm.). It is continued on either side b}' the rela- tively narrow longitudinal pUlars, which connect it with the posterior pillar. The posterior pillar (Pila caudahs) 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 cU\asion 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 alx)ut 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 almo.st vertical fold formed l\v the apposition of the walls of the two compart- ments. 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 rumino- reticulare). 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 ventrical! 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 394 DIGESTIVE SYSTEM OF THE OX beliiiiil the cpsophagoal groove and about four to five inches lower down. Undoubtedly food or water swallowed with a moderate ilegree of force passes first into the rumen. Foreign bodies (which arc 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 ami al«iut 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 papilhe, 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 papilliB 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 wail of the atrium is finely wrinkled and non-])apillated, while above and Fig. 2S9. — 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. .4., 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, ruraino-reticular foM. externally it is papillated. The papillary arrangement also extends over the edge of the rumiiKj-reticular fold an inch or two (ca. 2 to 5 cm.). The oesophageal groove (Sulcus oesophageus) is a semicanal which iiegins 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 finall.v forward. The twist involves chiefly the left lip, and the relative irosi- tions of the lips is reversed at the ventral end. The mucous membrane on the lips of the trsophageal groove is brown and wrinkled, like that of the atrium; in the bottom of the groove it is pale, like that of the (I'sophagus, marked by longitudinal folds, and presents pointed horny iiajiilla* on the lower i)art. The reticulo-omasal orifice (Ostium reticulo-omasicura) is situated in the right THE STOMACH 395 wall of the reticulum aliout five or six inehes above the bottom of the latter. It is rounded, antl is limited below and laterally by the junction of the lijis of the oesophageal groove. In the reticulum the mucous membrane is raised into folds about half an inch high, which inclose four-, five-, or six-sided spaces (Celluloe reticuli) ; this peculiar arrangement suggested the scientific name, and also the popular term "honey- comb." These cells are subdivided by smaller folds, and the bottoms are studded with pointed horny papilla?. The cells grow smaller and gradually disappear near the oesophageal 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. M Fig. 290. — Reticulum of f)x, from Photoghaph. 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 oritice. The spiral twist of the cesophageal groove was of necessity partly undone by reflecting the wall; its lips are drawn apart, showing some of the peculiar birdclaw-like papillse in the lower part. At the reticulo-omasal orifice there are peculiar horny papilla?, which are curved antl- resemble the claws of a small bird. The cavity of the omasum is occupied to a considerable extent by about a hundred longitudinal folds, the laminae (Laminse 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 drawTi apart or a cross-section is made, it will be seen that there is a second order of shorter laminse, 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 laminje (Recessus interlaminares), and reduced to a fine state of division by being ground down by the numerous rounded horny papillse which stud the surfaces of the folds. The ventral wall of the omasum forms a groove (Sulcus omasi), which 396 DIGESTIVE SYSTEM OF THE OX 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 Httle downwartl and to the right. It is free from leaves, but marked usually by slight folds and small papillae; 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 papilhe already mentioned as occurring in the lower part of the oesophageal groove. The omaso-abomasal orifice (Ostium omaso-aljomasicum) 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 (Valvulae terminales), which probably prevent regurgitation of the contents of the aliomasum. The cavity of the abomasum is divided by a constric- tion 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 (Plicae spirales). The second part (pyloric region) is much narrower and re- sembles 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. Structure. — The serous coat invests all of the free sur- face of the stomach. The surface of the rumen which is attached to the dorsal abdominal wall is of course uncoveretl, as well as the adjacent area to which the spleen is attached. The furrows are bridged over by the peritoneum and super- ficial 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 tlic 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 omen- tum is foimed by the peritoneum leaving the stomach along the left longitudinal and ]iosterior transverse furrows and the right surface of the rumen below the longitudinal furrow, also the ventral curvature of the al)omasum. Its superficial (ven- tral) part is attached on the right to the duodenum, while the tleep (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 condi- tion. 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 aljout one-half to one inch (ca. 1 to 2 cm.) thick. Scattered bundles of striped muscle-fibers radiate from the cardia m the wall of the atrium. The muscular coat of the reticulum consists of two chief layers which begin and end at the (csojihageal groove; they pass in a circular or oblique fashion around the sac, the fibers of the two laj'ers crossing each other at an acute angle. The walls of the cells contain a central muscular layer. The lips of the a:'sophageal 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 Fkj. 291. — Mrscni.ATi-nE OF GisOPHAGEAL Groove and .-Vd- jACENT Part of Stomach of Ox, si: FN' from with- in AFTER Removal OF MuCOl'S MtM- URANK. a, U-^sophaKUs; b, in- ner muscular la.\-er of atri- um; f/, reticulo-omasal ori- fice; c, e', muscle of lips of groove; ft, lower end of umscle of larger lip, wliich curves arountl the reticulo- omasal orifice in part ami spreads out in the inner muscular layer of the reti- culum in part; A. lower end of muscle of smaller lip which in part curves around the reticulo-omasal orifice and is in part con- tinuous with theinner mus- cular layer of the oinasal groove and the omasum; (*, inner muscular layer of reticulutn. (Ellenberger- Baum, Anat. d. Haustiere.) THE INTESTINE 397 has two layers of oblique, unstriped muscle-fibers, with a variable outer layer of striped muscle contiuiious with that of the cesophagus. The muscular coat of the omasum consists of a thin external longitudinal laj'er and a thick internal circular layer. At the omasal groove there is an additional inner layer of longitudinal fibers. The lamina 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 mucosa-. 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 -7^ Oesophagus blind Sacs / - , , \ ^ Fig. 292. — Stom 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. 398 DIGESTIVE SYSTEM OF THE OX The small intestine has an average length of about 130 feet (ea. 40 m.) and a tlianieter ui alxjut two inches (ca. 5 to 6 cm.). Tlie duodenum is about three or four feet (ca. 1 m.) in length. It passes for- ward to the visceral surface of the hver; here it forms, ventral to the right kidney, an S-shaped curve. Thence it runs backward ahnost 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 (oa. 60 cm.) from the pylorus. Tlio pancreatic duct opens ai)out a foot (ca. 30 cm.) further back. The remainder of the small intestine is ar- ranged 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 blintl sacs of the rumen to the left side. The orifices of the pancreatic duct and the bile duct are on papillae, no diverticulum being present. There are permanent transverse folds of the mucous membrane (Plicse circulares). , Duodenal glands (of Brunner) occur in the first fe; i c"' ■■■ fifteen feet or more (4 to 5 m.), intestinal glands \>' •' ' iHi tliroughout. 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-esecal valve there is always a patch, and in most cases there is also a patcli on the csecal 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 caecum is about 20 to 30 inches (ca. 50 to 60 cm.) long, 4 to 5 inches (ca. 10 to 12 cm.) Fig. 293— Pkyebs rAT.nis,,! sm m i In- wide, and has a capacity of about 2J^ gallons TKSTiNKoi-ox (aboiii ; „Miu,;,i M^e-). (g^. 9 to 10 Htcrs) . It begins opposite the lower part of the eleventh rili, and extentls upward and backward against the right flank; its rounded blind end is free, and lies near or in the pelvic inlet. The colon is about 35 feet (ca. 10 m.) long; its diameter is at first about the same as that of the caecum, 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 centripetalcs et centrifugales). The first part (Ansa proximalis) is market! off from the caecum only by the ileo-ctccal opening; it forms an S-shaped THE LIVER 399 Fig. 294. — Projection of Viscer.\ of Bull ox Body-wall, Right Side. P., Pylorus; G.b., gall-bladder; R.K., right kidney; L.K., left kidney; P., (above duodenum) pancreas; i?/., urinary bladder; F. s., ve.sicula seminalis; if. {/., buJbo-urethral (Cowper's; gland. Costal attachment and median line of diaphragm are indicated by dotted lines. Gall-bladder Falciform ligament (cui Coronanj ligament (cut) Poslcriar nna cava Hepatic veins (E.foj)liage(d notch Fig. 295 — Liver of Ox, Pvrif.tal .Surface; Hard 400 DIGESTIVE SYSTEM OF THE OX curve and is continueil 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 grailually diminishes in cahber, 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 usuall.v 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. Caudate lobe Area of attachment to dia- phragm {nonperitoncal) Renal im prea^tion (irij lir/nment ncT vena cava hayec.t notch ^ Fig 296.— Liv Hardf.ned m situ. The serous coat is of course absent on the adherent surfaces of the spiral i)art of the colon. There is a large amount of fat in the mesentery. The longitudinal muscular coat is evenly distrilnited, consequently there is no sacculation of the bowel. There is a valvular mucous fold at the ileo-ca^cal orifice. A Peyer's patch occurs in the beginning of the cajcum and one in the first jiart of the colon. THE LIVER The liver lies almost entirely to the right of tlie median plane. Its long axis is directed obliquely downward anil 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.). THE LIVEK 401 In .small subjects the weight (aoconiing to Schmaltz) varies from (j'2 to 10 pounds (ra. 3 to 4.0 kg.), in large subjects from 11 to 13 pounds (ca. 5 to (1 kg.). According to Schneider, the average weight is alxnit 13 pounds (ca. 6 kg.) — a little over 1 per cent, of the live weight ami about 2 per cent, of the ilrcssed carcass. When hardened in situ, its configuration adapts it accurately to tlie structures with which it is in contact. The parietal surface is convex and is for the most part applied to the right ]iart of the diaphragm, hut a small part of it is in direct contact with the last two ribs and with the tlaiik at the lumho-costal angle. It faces ujiward, forwartl, and to the right. The curvature of the parietal surface is not regular. It is marked, except in its \entral liart, by a blunt oblique ridge wliich corresponds to the basal border of the right lung. This prominence divides the sui'face into two areas. Of these, the external one is directed outward, Renal impression Hepatic aricry Portal vein — Bile-duct Lesser omentum (cut) (Esophageal notch I' ml, ilical fissure Fig. 297. — Liver of Young Ox, Visceral Surface; Hardened j'n fj'tu. is only slightly convex, and often shows impressions of the last three ribs. The inner area pre- sents 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 resophageal notch to the umbilical fissure. 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 speci- mens: (1) The omasal impression ilmpressio omasica) is a deep central cavity l>clow the portal fissui'c. (2) The reticular impression Ilmpressio reticularis) is a smaller marginal depression below the oesophageal notch and the inner part of the preceding, from which it is separated l)y a rounded ridge. (3) The abomasal impression (Impressio abom.a.sica ) , 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 sep- arated bv ridges from the preceding impressions. It disappears as the omasum and reticulum '26 402 DIGESTIVE SYSTEM OF THE OX increase in size and displace tlie abomasum from contact with the liver. (4) Shallow grooves for the S-shapod portion of (he duodenum (Irapressio duodenalis) may be found above and external to the portal fissure. (5) The fossa of the gall-bladder (Fossa vesica; fellece) 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 duet, several large hepatic lymph glands. Above and external to it a part of the pancreas is attached. The dorsal border is short and thick; it extentls backward a short distance :e Drawixu of Liver of Ox, Visceral SrRF L.ci/^ac ofFi^"'"^ Fig. 301.— Stomach of Sufkp, Left View. From photograph of specimen hardened ?>i si(«. The reticulum is somewhat contracted. Arrow points to posle rior furrow between blind sac8. Pylorus Fig, 302 — SToMArn or Shfep, Rh:ht \'ikw From photoRraph of specimen h.lrdeued in siUi. Dotted line in*licates position of sple 406 DIGESTIVE SYSTEM OF THE SHEEP 407 The salivary glands resemble those of the ox in general, but the parotid cluet 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 verj- narrow tonsillar sinuses on either side. Fig. 303. — Cross-sectiojj of Sheep, throt-c-h Ninth Thoracic Vertebra, Anterior View. i. Cardiac orifice; 5. crsophageal groove; 3, rumiuo-relicular orifice; 4, rumino-reticuiar foid; 5, dorsal sar 6, body of ninth thoracic vertebra; 7, vena hemiazygos; S, aorta; 9, posterior mediastinal Ij-inph gland; 70, /O. crura of diaphragm; i/. posterior vena cava; / 2. portal vein; fl./.. right lung; L.(.. left lung; S, spleen (cut very obliquely); L, liver; R, reticulum (posterior wall). Arrow points to reticulo-omasal orifice. f The fornix of the pharynx presents a median plicated fold which is a continua- tion 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 Ijmph glands and a number of hfemolymph glands above the pharynx. The oesophagus has a lumen of about an inch when moderately distended; otherwise it resembles that of the ox. 408 DIGESTIVE SYSTEM OF THE SHEEP 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 e.\tends 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 papilla; 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 back- ward and less to the right than in the ox. The parietal surface extends forward as Fig. .304— Ann far as the sixth rib or intercostal space, and is related to the diaphragm anil liver. The fundus lies on the sternal part of the diaphragm and in contact with the abo- masum. The oesophageal 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 ])int. It is oval and compre.s.sed laterally. It is situated almost entirely to the right of the median plane, opposite to the ninth and tenth ril)s, 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 lielow to the abomasum. The lamina^ are less numerous than in the ox; in the neck which connects the omasum with the reticulum they have DIGESTIVE SYSTEM OF THE SHEEP 409 the form of low thick ridges, and bear long, pointed, horny papillae. 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 laminae of the omasum are large, pointed, horny papillae. The number of laminae is less than in the ox. The general arrangement of the intestine is like that of the ox. The small Posterior rena cava Portal vein Hepatic artery Omasal impres- sion Lesser omentum Reticular impres- sion Abomasal ivipression Fig. 305. — Liver of Sh 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 e.xtensive Peyer's patch is found. The caecum 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 caecum, but diminishes to about the width of the small intestine. The Uver 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 410 DIGESTIVE SYSTEM OF THE PIG two chief lobes. The caudate lobe is prismatic and l)lunt-])oiiited. The neck of the gall-bladder is long. The bile-duct joins the pancreatic duct to form a common duct (Ductus choletlochus 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 tlorsal end or base is attached Umbilical fissure Posterior pena to the left crus of the diaphragm under the last two or three ribs. The hilus is at the ijosterior basal angle. The ventral end is narrower and thinner than the base; it is situated opposite the ninth and tenth ribs above their middles. DIGESTIVE SYSTEM OF THE PIG THE MOUTH The rima oris is extensive, the angles of the mouth being situated far liack. 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. Tlie mucous membrane of the cheeks is smooth. The buccal glands are THE MOUTH 411 compaftly arranged in two rows opposite the cheek teeth. The parotid duct opens opposite the fourth or fifth clieek tooth. The hard palate is long ami narrow; it is marked by a median furrow, on eacli side of which are twenty or more ridges. On its anterior part there is a triangular incisive ]5a]iilla, 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.' 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, Fig. 307,— Tovr.nE of Pig. J, Apex; g, dorsum; S, root; a, orifices of ducts of lingual glands; b, papillae of root; c, vallate papilla (not really so distinct as in figure); d. foliate papilla; p, fungiform papilto; /. epiglottis (pulled back); g, median glosso-epiglottic fold. (EUenberger-Baum, .\nat. d. Haustiere.) marked by numerous crypts; these elevations are the tonsils. Tonsillar ti.ssue also occurs in the lateral walls of the fauces. The tongue is long and narrow and the apex is thin. Two or three vallate papillae are present. The fungiform papillce are small and are most numerous laterally. The filiform papillte are soft and very small. On the root there are soft, long, pointed papilUe, directed backward. Foliate papillae are also present. There is a well-marked median glosso-epiglottic fold, on either side of which is a depression (^'allecula epiglottica). The frenum linguae is double. The dental formula of the pig is: (.314 3\ I - C - P - M - ) 3 14 3/ ' The epiglottis in the pig seems to be constantly retrovelar. Tlie 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. 412 DIGESTIVE SYSTEM OF THE PIG The formula for the temporary teeth is: / 3 1 4\ 2 I Di - Dc - Dp - I =32 V 3 1 4/ The upper incisors are small ; they are separated from each other by spaces, and from the eaiiines l)y 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, arc flattened laterally, and have three small eminences on the crown. The lower incisors are almost horizontal and are convergent and close to- gether. The first and secontl are about equal in size, prismatic, and deeply im- FlG. 308.— Sk Half Old, SccLprrRED to THE Teeth. es; Pl-4, premolars; Ml-S, l)lanted in the jaw. The labial surface is slightly convex, the lingual concave and marked near its extremity lay a ridge. The third incisor is much smaller and has a short narrow crown and a distinct neck. 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.' 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. The cheek teeth increase in size from before backward. They have (with ' The canines of the pig are "permanent pulp" tooth and thcrcfoio growth, and are without roots in the strict sense. ipable of continued THE MOUTH 413 certain exceptions noted below) complex tuberculate crowns; the term hunodont is applied to this condition, as distinguished from the selenodont structure in horses and cattle, in which there are prominent ridges of enamel. Thej- are short-cro^\Tied 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 jireceding ones, while the upper one is much wider and is tuberculate. Fig. 309. — Superfici.\l Glands of Head of Pig. a. Parotid gland; a', a", cenical and submaxillary angles of a; b, c, ventral and dorsal buccal glands; d, labial glands; e, masseter muscle; /./'.Ij-mph glands; g, dotted line indicating outline of submaxillary gland, which is concealed. (Eiienberger-Baum, .\nat. d. Haustiere.) The average periods of eruption of the teeth are given in the subjoined table. Tooth I,.. I,.. Iv C . . Pi.. P,.. P.,.. m;. Eruptiox Ch.axge 2 to 4 weeks 12 months / upper 2 to 3 months \ lower 1 } .; to 2 months 16 to 20 months Before birth S to 10 months Before birth 9 to 10 months .5 mont hs 5 to 7 weeks / upper 4 to 8 days. . . \ lower 2 to 4 weeks . . / upper 4 to S days . . \ lower 2 to 4 weeks 4 to 6 months 8 to 12 months 18 to 20 months 1 I }■ 12 to 15 months I 414 DIGESTIVE SYSTEM OF THE PIG The parotid gland is large and trirailiate. It extends very little on to the mas- seter 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 onlj' partially Fig. 310. — Dissection of Mouth and Pharyngeal Region Pio /, Ilaril piilate; 2, tongue showing distinctly fungiform papilla;; 5, foliate papilla; ^, lymph nodulea of soft palate; 5, stylo-gio.ssus muscle, out of which a portion has been cut; G, hyo-glossus; 7, genio-glossus; 8, genio- hyoiid process. (Elleti- berger-Baum, .\nat. d. Haustiere.) 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 (Glandulte parotideaj accessorise) may be found along the course of the duct. THE MOUTH 415 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 Fig. 311. — Sagitt.\l Section of Ph.\ryngeal Region of Pig, Partly Schematic. ;, Palate bone; 2. sphenoid bone; 3' , sphenoidal sinus; 2" , occipital bone; S, epiglottis; J,, arytenoid carti- lage; o, thyroid cartilage; 6, root of tongue; 7, mouth cavity; 8, isthmus faucium; 9, hard palate; 10, septum nasi; ii, ventral muscles of head; a, soft palate; a', free edge of a; b, dorsal wall of pharynx; c, forni.x of pharynx; d, cavity of laryn.x; c, y, naso-phary nx ; /, oro-pharyn.x; h, posterior pillar of soft palate; i, dotted line indicating lateral boundary between nasal cavity and pharynx; k, aditus laryngis; /, entrance to oesophagus; 7«, Eustachian orifice; n, pharyngeal recess; o, posterior naris. (-\fter Ellenberger, in Leisering's Atlas.) three inches (ca. 5 to 7.5 cm.) beneath the mylo-hj'oideus muscle along with the duct. The latter opens near the frenum linguae, but there is no papilla. The sublingual gland has an arrangement similar to that of the ox. The pos- Pylurus Fig. 312. — Stomach of Pig, Parietal Surface. The organ contained a rather small amount of ingesta and hence is somewhat contracted. CEsvphcigus Diiode nuin Pylorus Fig. 313. — Stomach of Pig, Visceral Scrface. Organ was fixed in situ and is somewhat contracted. terior 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 416 DIGESTIVE SYSTEM OK THE PIG larg:er, licing two or three inches (ca. 5 to 7 cm.) long and about twice the wicUh and thickness of the posterior part. All or most of the ducts from the posterior part unite to form the ductus sublingualis major, A\hich opens near the ductus suljmaxillaris. Eight or ten ductus sublinguales minores convey the secretion from the anterior part through the floor of the mouth. Fig. ai5. — Visceral Surface of Stomach of Pig, StJF COA Kkmovkd. O, Gisophagus; D, diiotlenum; Di, diverticuluii external oblique libers; r', internal obliiiue fibers; c", ( loop; /, fold at entrance to diverticulum; p, pyloric spbii d. Haustiere.) Fig. 316. — Everted Stomach of Pig, from which the Mucous Membrane has been Removed. a, a', a", a'", longitutlinal fibers; b, circular fibers; c. rdiac loop; d, fibers which connect branches of cardiac ter; p' , pyloric prominence. (Ellenberger-Bauni, .\nat. 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 opsophagus. Its lower margin is formed by the junction of the posterior pillars of the soft palate, which contain muscu- THE (ESOPHAGUS — THE STOMACH 417 lar tissue derived from the ])alatinus and iialato-pharyngeus. The vault of the jiharynx (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 in- funilihvilum in which the Eustacliian tube opens. THE (ESOPHAGUS The oesophagus is short and nearly straiglit. It has (according to Rubeli) a potential caliber of nearly 3 inches (ca. 7 cm.) at either end, and about 1^ inches (ca. 4.2 cm.) in its middle part.' The miuscular coat, except near the cardia, is striated. There are mucous glands in the submucosa to about the middle of the tube. 317. — Abdominal Viscera of Young Piu, Ventral ,\spect. The stomach was very large in this subject. THE STOMACH The stomach is large and pjTiform. Its average capacity is about 1^^ to 2 gallons (ca. 5.7 to 8 liters). When full it extends backward to the last left inter- ' It is usually stated that the cardiac end is funnel-.sliaped, but it is not so in formalin hardened cadavers nor in frozen sections. The hiatus oesophagus is a long slit in the right crus of the diaphragm, and the terminal part of the oesophagus, which lies in it, is flattened transversely. 418 DKJESTIVE SYSTEM OF THE PIG costal space laterally and the uiubilicu.s veiitrally. The left portion is large and rounded, while the right portion (Pars pylorica) is small, and bends sharjily upward to join the small intestine. The parietal surface is related to the liver, gall-bladder, centrifugal Fig. 318. — Dlvgram of Cecum and Colox of Pig. C^oils of colon have been pulled apart somewhat. 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 V ■ 310. — Solitary Nodplks from Large Intestine V 1*1G. (Elleuberger-Baum, Auat. d. Haustiere.) Fig. 320. — Ileo-c.*:cal Openinc and Adjacent Part OF C-ECUM AND CoLON OF PlG. a, Mucous membrane of colon; 6, mucous mem- brane of fipcum; f, Peyer's patch; rf, ileo-ca'cal oi>en- ing; e, end of ileum; /, folds (frenula) of ileum. (After P. Schumann.) left extremity presents a flattened conical l)lin(l pouch, the diverticulum ventriculi, the apex of which projects backward. Tlie oesophagus joins the stomach very obliquely, almost in the median plane, and about three or four inches (ca. 8 to 10 THE INTESTINE 410 cm.) below the twelfth thoraeie vertel)ra. The cardiac opening is plit-Hke and is bounded al)ove 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 cartha; it is transversely oval, and i.s bounded (except externally) l)y a thick fold which contains spirally arranged muscular fibers. The mucous membrane may be divided into four regions. Over a quadri- lateral area around the cardia (about one inch on the right and two or three inches on the left siile of the orifice) it is oesophageal 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.' The fourth or pj'loric region is pale, thinner than the preceding, and presents a number of irregular folds. At the ]5ylorus 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 (ea. 3 to 4 cm.) long and nearly half an inch (ca. 1 cm.) high. Sometimes it is grooveil; in other cases it has the form of a rounded eminence attached by a pedicle to the wall. Fibers from the circular muscular coat exteinl into it. THE INTESTINE The small intestine is 50 to 65 feet (ea. 15 to 20 m.) long. The mesen- tery 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 tiie 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 ' It will be noted that the fundus gland region does not extend up to the lesser curvature; here the cardiac mucosa joins the pyloric. 420 DIGESTIVE SYSTEM OF THE PIG patches and solitary glands aro numerous and very distinct ; the patches are usually l)and-Hke and prominent; the solitary glands form projecting nodules marked l)y crypts. 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 connectetl by a mesentery with the dorsal alxlominal wall between the kidneys. The caecum is cylindrical, aI)out 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 Islind end reaching to within about two inches (ca. 5 cm.) of the pelvic inlet. The ileum joins the caecum obliquely and projects somewhat into its lumen. The colon has at first about the Hepiilic arlcry He/Milic duel (Esophageal notch ••. 322. — Liver of Pio, Visceral Sui Photograph of specimen hardened in si same caliber as the CiBcum, 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 si)iral labyrinth, it passes forward to the stomach and pancreas antl 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 ciuantity of fat. The caecum has three longitudinal muscular bands and three rowjs of sacculations, which are continued a short distance on the colon. The sjiiral colon has two bands and two series of sacculations, which, however, gradually disappear in the centrifugal part. THK LIVER 421 THE LIVER The liver is relatively large, its average weight being about 4 to i}4 pounds (ca. 2 kg.). It is thick and very strongly curved.' It i.s tlividcd l)y three deep interlobar incisures into four principal lobes — right lateral, right central, left central, left lateral; the la.st 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 \\'ith 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 Umbilical Jiss ure •phageal iiuich Hejiatic reins Fig. 323.— Livkr ok Pk.. Parietal SntrACE. Photograph of specimen hardened in situ. visceral surface is deeplj- 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, emerg- ing only at its passage through the diaphragm. The CESophageal notch is large and is occupied mainly by the large right eras of the diaphragm. The right ' The description here given is based mainly on the appearance of the organ as hardened in silii, which differs radically from that of the soft organ, as is seen on comparison of the annexed figure (Fig. 321). 422 DIGESTIVE SYSTEM OF THE PTG lateral l^ordcr pxtonds backward to the upper part of the twelfth intercostal space or thirteenth rib. The k>ft lateral l)order is opposite the eighth rib and intercostal space. The ventral border extends backward about as far as the umbihcus. There are no lateral ligaments and the falciform ligament disappears early. The gall-bladder is attached in the fossa vesicae felleae on the right central lobe, at a considerable distance from the ventral border. The cystic duct joins the hepa- tic duct at an acute angle immediately after the emergence of the latter from the l)ortaI 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. Owing to the large amount of interlobular tissue, the lobules are map]3ed out sharply; they are polyhedral in form and are 1 to 2. .5 mm. in diameter. For the same reason the gland ti.ssue is much less friable than that of the other animals, from which it is easily di.stinguished. Fig. 324. — Projection of Viscera of Pig on Body-wall, Left Side. D, Costal line of diaphragm; t/, ureter; V. S., vesicula seminalis; B. c, bulbourethral gland; P, penia Fig. 325. — Projection op V'ihcera or Pig on Bon £*, Costal attachment of iliaphragin; O, DIGESTIVE SYSTEM OF THE DOG — THE MOUTH 423 THE PANCREAS The pancreas is elongated, and is situated transversely on the dorsal abdominal ■nail, A^-ith 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 lolies; the posterior lobe bends around the great mesenteric artery and the portal vein; the anterior one is pointed, extends dowTiward 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 fxtremity 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 in- testinal areas. The spleen is attached so loosely to the stomach that it may be regarded as being inter- calated 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 Fig. 326. — Tongue of Dog. a, Tonsil; b, vallate papil- Ise; c, foliate papilla; d. fungiform papilla": *'. median groove of dor- sum; /. epiglottis; g, soft papilUe of root; k, middle glosso-epi- glottic fold; 7, tip: B, root. (Ellen- berger-Baum. Anat.d. Haustiere.) 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 oppo- site 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 bull-dog) 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. The cheeks are loose and capacious, and their mucous lining is smooth antl 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 424 DIGESTIVE SYSTEM OF THE DOG eight to ten curved ridges on either side of the raphe. Behind the first pair of ineisor t(H>th is the triangular incisiv^e pai)illa, at wliieh the naso-palatine (hiets open. The mucous membrane i.s 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 ]:)igmented, but has a bright red color. The upper surface is marked by a median groove (Sulcus metli- anus linguie), and is thickly beset with short, pointed, filiform papillae, the free ends of which are directed backward. On the root the jjapillte are long and .scift: similar jiapillae occur on the lateral walls of the isthmus faucium. The fungiform papilkc 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 papilhr on either side. Small foliate pa])illae are also present. In the inferior part of the tip of the tongue is the lyssa, a fusiform cortl, composed of fibrous tissue, muscular tissue, and fat. In large dogs it is about two inches (ca. 4 to 5 cm.) long. '. — Skull of .Viu-lt St. Bkrnard Dog, Sculptured to Snow the EMiiKDnr. Il-S^ Inciaors; C, caQines; Pl-4, premolars; Ml-S, molara. THE TEETH The formula for the permanent teeth is: / :5 1 4 2\ I I-C'-P- M - I V :5 1 4 3/ THE TEETH 425 All of tho teeth have short crowns and distinct necks; they erupt rapiilly. 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 trituberculatc, the central projection Ijeing 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. 32S.— Bask of I , premolar.s; MIS, account of the shortn anfl ijremolars on 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.' 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 arc typically j, but in brachycephalic breeds they are com- monly reduced to i, and in extreme cases even to *. The reduction occurs at either ' In the bull-dog, which is very prognathic ("undershot"), the lower canines are opposite to or sUghtly 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. 426 DIGESTIVE SYSTEM OF THE DOG end or at both ends of the series.' The first tooth appears only onoc. The fourth tooth of the upper row and the fifth of the lower row are much larger than the rest, and termed sectorial or camassial teeth. From these the teeth diminish in size Ijoth forwarfl 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, /. <>., 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 w-ide, 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 Fig. .329. — Dissection or Head of Dog, Showing Salivary Glands, etc. ". Ocular muscles; 6, pterygoideus internus (cut); c, stylo-glossus; rf, digfLstricus (cut); e, genio-glossus; /, getiiu-hyoideus; g, hyo-glossus; h, thyro-pharyngeus; ;', crico-pharyngeus; k, thyro-h.voideus; /, zygomatic process of temporal (.sawn off); 1, parotid gland; 3, 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: .¥, ducts of 7; 5, lacrimal gland. (Ducts colorefl red.) (.\fter EUenberger, in Leisering's Atlas.) 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. The average periods of eruption are given below. Tooth Eruption Chance I, 4 to 5 weeks ] Ij 4 to 5 weeks )• 4 to .^ months I3 4 weeks J C 3 to 4 weeks 4 to .'i months Pi 4 to 5 months 1 Pj 4 to 5 weeks . , ,. .1 P' 3 to 4 weeks -^ '° '' "'°"'*'^ P, 3 to 4 weeks J M, 4 months »j / upper 5 to 6 months ' \ lower 4J^ to 5 months Mj 6 to 7 months ' Increase in number also occurs, the supernumerary teeth being at either end of the series. THE SALIVARY (ILANDS — THE PHARYNX 427 THE SALIVARY GLANDS The parotid gland is small. Its uj^iier part is wide and is divided into twc lobes by a deep noteh into whii'h 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 ((ilandulo" parotidae acces- sorise) are .sometimes found along the cour.se 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 linguie on a very indistinct papilla. The sublingual gland is divided into two parts. The posterior part (Glandula sublingualis grandicanalaris) lies on the digastricus muscle in intimate relation with Fig. 330. — Sagittal Section- of Pharyngeal and Laryngeal Regions of Dog. 1, OSsophagus; 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; /. origin of cEsophagus; g, vestibule of larynx; A, isthmus faucium; i, Eustachian opening; k, posterior naris. (.\fter EUen- berger, in Leisering's .\tlas.) 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 428 DIGESTIVE SYSTEM OF THE DOG (T(irus tuharius). The esophageal opening is rehitively small and is encircled l)y a fold of the mucous membrane. The hyo-pharyngeus muscle is clearly ilivided into a kerato-pharyngeus and a chondro-pharyngeus. THE (ESOPHAGUS The oesophagus is relatively wide and dilatable except at its origin. The constriction at its origin is termed the isthmus oesophagi. 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 con- sists mainly of two layers of spiral fibers which cross each other; near the cardia, however, the fillers are longitudinal and circular. There are mucous glands ami lymph glands in the submucosa throughout. (Esophagus Lesser curvature Bile-duct Pylorus Fig. 331. — Stomach of Dog, Pariictat. .Surface. Organ fixed in situ wlien 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 al)out 3 liters (ca. ()!2 pints), with a range between 0.6 and 8 liters (ca. Ik to 17 J 2 pints). Neumayer gives the capacity as 100 to 250 c.c.per kilogram of Ijody-weight (ca. 2.7 ounces per pound). The average capacity of the human stomacli is esti- mated at 3.5 to 40 ounces — only al)Out 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 chieHy 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 pjdoric part is directed sharply forward and upward. THE STOMACH 429 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 xiphoiel cartilage to the pubis. (Esophngus Lesser curvature Pylorus Bile-duct Fig. 332. — Stomach Organ fixed i Dog, Visceral Surface. u 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 Fig. 333. — Everted Stomach of Dog from which THE Mucous Membrane is Removed. O, CEsophagus; D, duodenum; b, circular fibers; spond to the ascending, transverse, and descend- ing colon of man. The first or right part (Colon ascendens) is very short. It begins at the junction of the ileum and csecum, 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.- The caliber of the colon is about the same throughout. It has no bands nor sacculations. The mucous membrane of the caecum 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 peri- (From Leisering's Atlas.) Fig. 33S.— Termination or Ilevm op Dog. 0, Colon; 6, ca'cum; c, ileum; d, ileo-ctpcal open- ing: r. circular depression around end of ileum, {.\fter P. Schu toneal reflection being under the second or third coccygeal vertebra. At the junc- tion of the rectum antl anus the mucous memltrane 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 hazel- nut, and contain a dirt}' gray, fatty substance, which has a jieculiar and very unpleasant odor. The skin which lines these pouches contains coil-glaiuls. Fur- ther 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 vertebrte 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 ' Rll(!iil)orKor and Baiiin state that the ca>cum may reach a length of 20 cm. in very large dogs. - When the stomach is very full, it pushes the left portion of the colon over to the right, l)roducing an acute angle in place of a transverse branch. The terminal p.art of the colon is thus oblifiue in direction. THE LIVER 433 is much smaller and is prismatic. The right central lobe is second in size, and i)re- sents a somewhat tongue-shaped quadrate lohc, markeil 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 poit. i/eiuz cai/a LeduLct /Jmiilical fissure Fig. 339. — Liver of Doo. Soft specimen sketched with lobes drawn apart. Hepatic (Esophageal notch artery Posterior tcna cava Left lateral ligament Right lateral lobe Gnll-bladder {not visible) Right central lobe Fig. 340. — Liver of Dog. Visceral Sdrf.\ce; H.\rdf.n-ed m situ. Left central lobe, gall-bladder, and great part of right central lobe not visible. — on the right, the caudate process; on the left, the papillary process or lobe, both often being subdivided by fissures. 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 28 434 DIGESTIVE SYSTEM OF THE DOG the lesser curvature of the stomach), which separates two deep cavities. The depression to the left of the ridge is occupied bj' 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 duotlenum, 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 hver 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 bountled 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 com- pletely 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 embed- ded in the parietal surface of the right lateral lobe; it receives two large hepatic veins just before piercing the diaphragm. The oesophageal notch is large, and is occupied on the right by the thick margin of the hiatus ocsophageus. The left liorder 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 kidnej- and the right branch of the pancreas. The ventral border lies on the ventral abdominal wall a variable distance behind the xiphoid cartilage. The gall-bladder lies in the fossa vesics fellea?, between the two parts of tlio riglit central lobe; it does not reach to the ven- tral 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. Fig. 341.— Splk Doo .SlRFACE. a, a. Ridge; 6, ventral end: c, dorsal end. (.\fter Ellen- berger, in Leisering's Atlas.) 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 extemis 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 behiiul 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 liile duct, while the smaller one enters the duodenum an inch or two (ca. 3 to 5 cm.) further back. THE SPLEEN 435 THE SPLEEN 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 tlie 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 Fig. 342. — Projectiox of ViscEn.i of Dog (Male) ox Body Wall, Left Side. A, C, D, Apical, cardiac, aud diaphragmatic lobes of lung: P, pericardium; Pr, prostate. Costal attachment metiiaa line of diaphragm are dotted. Fig. 34.3.— ProjeC] A, C, D, .\pical, cardiac. Pan., right branch of pancreas; ( are dotted; also posterior contou IN of Viscera of Dor, (Female) on Body Wall, Right Side. nd diaphragmatic lobes of right lung: P., pericardium: L. K., right kidney; ovary; U, cornu of uterus. Costal attachment and median line of diaphragm 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 dia- phragm. 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,' the pharynx, tlie larynx, the trachea, the bronchi, and the lungs. The kings are the central organs in whieh tlie 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 communi- cates behind with the jjharynx through the posterior nares (C'hoanse) ; 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 larj'nx is a complex valvular apparatus which regulates the volume of air pass- ing 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 thjToid and the thymus, are usually described in this section, although they are in no sense a part of the respira- tory 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 placetl obliquely, so that they are closer together below than above. They are bounded by two alae or wings (AIje 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, w Inch leads backward to a blind cutaneous pouch. This cul-de-sac, the diverticulum nasi, extends backward to the angle of junction of the nasal l)one 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 alae and lines the vestibule. In the ' An external nose (Nasus cxternus), such .is exists in man, forming a projection distinctly marked ofT from the rest of the face, does not exist in the domesticated animals. THE NASAL CAVITY 437 posterior part of the diverticuluin the skin is thin and usually l)Iack, and is covered with exceedingly fine hairs; it is iirovided with numerous sebaceous glands. The inner wing is supported by the alar cartilage (Cartilago alaris), which is shaped somewhat like a connna, the convex margin being direct medially. The cartilages are attached by filirous tissue to the extremity of the septal cartilage. Each consists of an upper, ciuadrilateral curved plate, the lamina, and a narrow comu which curves downwartl and outward, supporting the inner wing and the lower com- missure, but not entering into the formation of the outer wing. The lamina causes the projection of the upper jiart 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 Fig. 344. — Nostrils of Horse. a, Diverticulum nasi (shown as if distended): b. philtrura; c. false nostril; d, true nostril; e', prominence caused by lamina of alar cartilage; e", prominence over cornu of same: /, external wing of nostril; g. internal wing; h. lower commissure; /. orifice of naso-lacrimal duct. {EUen- berger-Baum, .\nat. d. Haustiere.) Fig. 345. — Cross-section of N.\ri.\l Region of Horse. 1, Nasal bone; 2, tendon of levator labii su- perioris proprius; 3, external nasal nerve; 4. nasal diverticulum; 5, outer wall of 4' ^i dilatator naris inferior; 7, levator nasolabialis •+■ dilatator naris lateralis; S, maxilla and premaxiUa; 9, naso-lacrimal duct; 10, II , chief branches of superior labial ner\'e, with superior labial artery at their inner side; 13, nasal cavity; 13, superior turbinal fold; i.^, inferior turbinal fold, inclosing cartilaginous prolongation of inferior turbinal bone: 15, venous plexus; 16, sep- tum nasi: 16', parietal cartilage: 17, vomero-nasal organ (of Jacobson): IS, venous plexus of palate; 19, buccinator; SO. skin; S3, anterior nasal nerve; 24, palatine process of premaxilla. (After Ellen- berger-Baum. Top. .\nat. d. Pferdes.) projection of the skin a short distance behind and below the lower commissure. 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, how- ever, is formed by the septal cartilage (Cartilago septi nasi). The surfaces of the cartilage are marked l)y 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 no.strils these plates are somewhat wider, partially making good the defect in the bony roof of the cavity 438 RESPIRATORY SYSTEM OF THE HORSE in this situation groove of the v Fio. 34r,.— Nasai Dorsal ViKW. liauni, Anat. fi tend back so far Tlie ventral border is thick and rounded; it Hes chiefly in the omer, but anteriorly it occupies the sjjace lietween the premax- illary bones. The posterior border is continuous with the perpendicular p\aW of the ethnioiti bone.' The alar cartilages are attached to the anterior extremity l>y 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 aliout 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. The two turbinal bones (C'onclise nasales) project from the lateral wall, and divide the outer part of the cavity into three meatuses — superior, midille, 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. The middle meatus (Meatus nasi medius) is rKiinsiier.) bctwcen tlic two turbiual bones. It is somewhat larger than the superior meatus, and does not ex- ; it ends near the great ethmoturbinal and the ethmoidal meatuses. iES OF Horse (After Ellenberger- InJerioT meatus Superior I'lferwr turbinal „ . Ethmo- Septum between turbinal Middle /superior lurbmals fronlal sinuses meatus ^ ^,.^nt„^ Fici. .'MT.— Nasal Cavity of Hohsf,, Sa. /, Superior turliinal fold; 3, alar fold, containing cartilaginoi pointing to na-so-inaxillary fissure; 4. cranial cavity; 5, sphenoidal olfactory mucous membrane is shaded. Dotted lines indicate antei which inclose parts of frontal and maxillar,\' siruises. Sf-ction with Septum Removed. prolongation of inferior turbinal; S, arrow nus; 6. hamulus of pterygoiii bone. The r limit of uncoiled parts of turbinal bones. In its posterior part is found the extremely narrow, slit-like interval by which the ' Tlie septal oartilage is to be regarded as an unossified part of the mesethmoid. It will be noteil that the line of doinarculion between the bone and the cartilage is irregular and varies \yith age; extensive ossilieat ion (or ealcifiealionlof the cartilage is commonly found in old animals. 'I'he process often results in the formation of calcareous islands in the cartilage. THE NASAL CAVITY 439 maxillary f^imis conmiunicates with the nasal cavity — the naso-maxillary fissure (Aditus naso-maxillaris). The fissure is not visible from the nasal side, being con- cealed by the overhanging superior turbinal. A fine flexible probe, passed outward and somewhat backward between the turbinal bones, enters the maxillary sinus; if in- troduceil a little further in the same direction, it usually passes through the orifice of communication between th(> maxillary and the frontal sinus and enters the latter. Superior in Hcptuni nasi Lacrimal sac Transverse facial resscls Palatine artery Vena reflexa Palatine vein Biirrinator and Dr/i. liibii inf. Btin-inator vessels and nerve Lingual nerve Lingual artery Lingual vein Submaxillary duct Hypoglossal nerve Digastricus {ant. belly) Fig. 348. — Cross-sectiom of Head of Horse. The Section P.tssES Thhocgh the Internal Canthi. 7, Mylo-hyoideus; 2, stylo-glossus; 3, hyo-glossus; 4. geoio-glossus; 5, lingual process of hyoid bone. An arrow points to the naso-raaxillary fissure. 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 sinu.s-meatus, but it also conducts air to the olfactory region. The inferior meatus (^leatus nasi ventralis) is situated between the inferior 440 RESPIRATORY SYSTEM OF THE HORSE turbinal and the floor of the cavity. It is much larger than the other two, anil 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 (Choanie) 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 vas- cular, and is, in general, firmly attacheil to the underlying periosteum and peri- chondrium. 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 y^,^ 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 (Glandulae 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 e])ithelium. In it are numerous olfactory glands (Glandulae olfactorite) ; 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 j^harynx and trachea. It is a complex valvular apparatus, which regulates the volume of air in respiration, prevents aspiration of foreign bodies, ami is the chief organ of voice. It is situatetl partly between the internal ];)terygoid muscles, partly in the neck CARTILAGES OF THE LARYNX 441 between the parotid glands.' 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 oesophagus. Ven- trally it is covered by the skin, fascia, antl sterno-hyoid anil 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 thyroitl cornua of the hyoid bone, and thus in- directly 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. ■■ m ^^H^^H[^^^^H ■■■■ ^V! ll^%JWf ^ ^^^^H^^l ^^ ^^ ^^^B|^v ^^^^^B P^^% ll^ '■ -.-c: >f°.'s'^ i=tfeo^3!^S i^^ s. V L ^ ^ -- ^^' "cVico- raehzai\ Obiiqut Crico'-rth^roid Fig. 349. — Larynueal Cartilages oe Horse, Right View. The cricoid cartilage (Cartilago cricoidea) is shaped like a signet ring. The dorsal part is a broatl, 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 articu- lares arytsenoidese) are placed at the anterior border, are oval and convex, and articulate ^vith the arytenoid cartilages. The posterior facets (Facies articulares thyreoideffi) 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 ' In the ordinar)' 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 licliiiid 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. 442 RESPIRATORY SYSTEM OF THE HORSE Posterior border Arch Fig. 350. — Cricoid C.\rti OF Horse. Left L.\teb.\l lamina is thick and slislitly 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-aryten- Median ridge Lamina oideus lateralis muscle. The pos- terior border is attached to the first ring of the trachea by an elastic membrane. The inner sur- face is smooth and is covered with mucous membrane. The thyroid cartilage (Cartilago thyreoidea) consists of a median thickened portion, termed the body, and two lateral laminae or wings. The body forms ventrally a slight prominence (Prominentia laryngea), which can be felt, but is not visible in the living sub- ject; it supports the base of the epiglottis, which is attached to it by an elastic ligament. The wings or laminae 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 Body pharyngeal fascia and the palato- pharyngeus muscle, and bears a cornu at each end. The anterior comu (Cornu orale) is attached to the thyroid cornu of the hyoid bone; below it is a notch, which is con- verted into a foramen (Foramen thy- reoideum) by a fibrous band, and transmits the superior laryngeal nerve to the interior of the larynx. The posterior comu (Cornu caudale) articu- lates 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 liy the crico-thyroid membrane. The anterior border is slightly convex, and is attached to the hyoid bone by the thyro-hyoid mem- brane. The posterior border overlaps p,,. 351.— thyroid c.^RTiLAni.. of Horse. Ven-th.^l the arch of the cricoid cartilage, and view gives attachment to the crico-thyroid muscle. The inner surface is concave, and is covered by mucous memlirane to a small extent. The epiglottis (Cartilago epiglottica) is situated above the body of the t hyroid Thyroid notch Wiiifj Anterior cornu ofiterior cornu surface for articu- lation with cricoid CARTILAGES OF THE LARYNX 443 cartilage and curves toward the root of the tongue. It is shaped somewhat like a pointed ovate leaf, and presi'uts two surfaces, two borders, a base, and an apex. The oral lor anterior) surface is concave in its length, convex transverseh- ; the pharyngeal (or jiosterior) surface has the reverse configuration. The borders are thin, ilenticulatetl, and somewhat everted. The base is thick, and is attached to the dorsal surface of the body of the thjToid cartilage by elastic tissue. From each side of it a cartilaginous bar projects backward; these processes Pharyngeal surface correspond to the cuneiform car- tilages of man. The apex is pointed and curved ventrally. Nearly all of the epiglottis is covered mth mucous membrane. It lies sometimes in front of, sometimes behind, the soft palate. The arytenoid cartilages (Car- tilagines arytenoide;p) are situated on either side, in front of the cri- coid, and partly betw-een the alse of the thyroid cartilage. They are somewhat pjTamidal in form, and may be described as ha\ang 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 di\'ided by a ridge into two areas: the lower flat area faces outward, and is covered I:)y the th>To-arytenoid and lateral crico-ar}i:enoid muscles; the upper concave area faces chiefly forward, and is covered by the traasverse arji;enoid muscle. The anterior border is convex, and at the base of the cartilage forms a projection termed the vocal process ( Proces- sus vocalis) ; it is so named because Cuneiform process 352. — Epiglottis of Horse Right Lateral Vie Muscular process Apex it gives attachment to the vocal or thjTO-arj-tenoid ligament, which forms the basis of the true vocal cord. The posterior border is straight, and exlends from the vocal process to the facet on the base. The dorsal border forms a deep notch with the ajjex. 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 pro- cess (Processus muscularis), which gives attachment to the crico- arj-tenoid muscles. The internal angle is attached to its fellow by the transverse arj-tenoid ligament. The apex (Cartilago corniculata) curves upward and back- ward, forming vrtth its fellow the pitcher-shaped lip, from which the cartilages derive their name. The cricoid and thyroid cartilages, and the greater part of the arytenoid cartilages, consist of hyaline cartilage. The apices and vocal processes of the arjienoid cartilages and the epiglottis (^including the cuneiform processes) consist Fig. 353. — Left .-Vrttenc Vocal process Cartilage of Horse, Inner 444 RESriRATORY SYSTEM OF THE HORSE 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 bodj- of the thyroid, and often involves the greater part uf the cartilage. Joints, Ligaments, and Membranes of the Lar'nyx The crico-thyroid joints (Articulationes crico-thyreoidese) 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 car- tilage. The capsule is thin, but is strengthened by accessory bands dorsally, externally, and internally. The movements arc chiefly rotation around a trans- verse axis passing through the centers of the two joints. The crico-arytenoid joints (Articulationes crico-arytsenoidea) are also diar- throdial. 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-thyreoidese) are formed by the anterior coruua of tiie thyroid cartilage and the extremities of the thjToid coi'nua of the hyoitl bone. They permit rotation around a transverse axis passing through the two joints. The crico-thjToid 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 largelj- of elastic tissue. It is reinforced ventrally by longitudinal fibers, dorsally bj' fibers which stretch across the thyroid notch. The th5rro-hyoid membrane (Membrana hjo-thyreoidea) connects the an- terior 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 Ijlends with the thyro-hyoid membrane, and dorsally it is not well defined. The th5no-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 laminae of the thyroid cartilage. Other fibers attach the cuneiform processes somewhat loosely to the thyroid laminae. The transverse arytenoid ligament (Ligamentum aryta^noideum transversum) is a slender Ijand which connects the inner angles of the liases 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 ventri- culare) 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. MUSCLES OF THE LARYNX 445 The crico-tracheal membrane (Ligamentum crico-trachealc) comiects the cricoid cartih^ge witli the first ring of the trachea. Muscles of the Larynx A. Extrinsic Muscles The stemo-thyro-hyoideus is tlescribed on p. 226. The thyro-hyoideus ( AI. hyo-thjTeoideus) is a fiat, quadrilateral muscle, which lies on the outer surface of the thyroid lamina and the lateral jjart of the thj-ro- 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 laryiLY toward the root of the tongue. The hyo-epiglotticus (M. hyo-epiglotticus) is a feeble muscle which occupies a median position al)ove the central ])art of the thyro-hyoid membrane, inclosed by an elastic sheath, the hyo-epiglottic ligament. It arises from the l)ody of the hyoid Fig. 354. — Larynge.\l Muscles of Horse, Seen from Left Side After Remov.^l of M.^jor P.\rt of L.^min-\ OF Thyroid Cartilage. a, Kerato-hyoideus; b, thyro-hyoideus; c, crico-thyroideus; d, sterno-thyroideus; f, ventricularis; /, vocalis; g, crico-arytenoideus lateralis; h, crico-arytenoideus post. s. dorsahs; (, arytenoideus transversus; 1, lingual process; 2, small cornu; S, thyroid cornu, of hyoid bone; 4. thyroid cartilage; S, cricoid cartilage; 6. epi- glottis; 7. apex of arytenoitu, their surfaces present impressions and elevations Fig. 361. — Lkft Lung of Horse, Costal Surfac Specimen hardened /" situ. corresponding exactly to the structures with which they are in contact. Each lung presents two surfaces, two borders, a base, and an apex. 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 oesophagus (Sulcus ocsophageus), which is deepest on the left lung. A groove for the aorta (Sulcus aortic) curves upwanl 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 ' 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. THE LUNGS 455 are grooves for the traehea, the anterior aorta, the anterior vena cava, and other vessels. Ligament of lunij (rut] or d p r Groove for ^ ? for oesophagus fA.r^-tenoideus muscle is not divided; it is fan- shaped, thick, and narrow dorsally; ventrally, it is attached to the base of the Fig. 364. — Muzzle of Ox. 49, Nasolabial region; 4S, lower lip. (.4fterEllen- berger-Baum, Anat. fiir Kunstler.) 460 RESPIRATORY SYSTEM OF THE OX epiglottis, the angle of the union of the thyroid lamina, and the crico-thjToid 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 sep- Frontal eminence Great ethmo-lurhiiml Superior turhinal Superior maitiis Middle meatus Inferior turhinal Inferior mealaf: Naso- labial glands Gcnio- Mylo-hy- Genio- glossu^ oideus hyoideus Thyroid cartilage Body of mandible Fig. 365. — Sagittal Section of Head of Cow. ;, Cerebral hemisphere; S, lateral ventricle; S, thalamus; .(, corpora quadrigemina; 5, optic chiasmal e, pituitary body; 7, pons; S, medulla oblongata; 9, cerebellum; JO, spinal cord; 17, ventral straight muscles; /a, pharyngeal lymph gland; 75, arytenoid cartilage; i4, epiglottis; JS, cricoid cartilage; / 6, vocal cord; 17, palatine sinus; 18, soft palate; 19. Eustachian opening; Ci, Cj, C'a, first, second, and third cervical vertebrae; B.o.. basioccipital; Sp., presphenoid. arated by a varying interval, so that the tube is flattened and membranous dor- sally. 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. THE BRONCHI There are three chief bronchi. The l)ron(hus for the apical and the anterior cardiac lobe of the right lung is detached from the trachea at a considerable dis- tance anterior to the bifurcation. THE THORACIC CAVITY AND PLEURA 461 THE THORACIC CAVITY AND PLEURA The thoracic cavity i;s relativelj' 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 Fig. 366. — Choss-section of Thorax of Sheep. Passing THROunH Middle op Fifth Pair of Ribs, Posterior View. /,;', Lungs; S, 3', bronchi; S, 3', pulmonary arteries; 4, tlioracic aorta; 5, oesophagus; ff, lymph gland; 7, vena hemiazygos; 8, posterior vena cava; 9, large pulmonary vein; 10, left atrium, //, vena hemiazygos; 2.2, left ventricle; icS, right ventricle; /4, sternum; /5, internal thoracic vessels; iff, six' n joracic vertebra. 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 pericar- dium it lies for the most part on the left wall of the chest. 462 RESPIRATORY SYSTEM OF THE OX 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 harrlrr- FlG. 3G7- — Right Lung of Ox, Costal Surfack. Organ hardened in situ. lobe Fig. 368. — -Right Lung of Ox, Mkdiastixal .\spect. hardened in situ, i, Left bronchus; 3, pulmonary veins; S, pulmonary artery. of the lungs is about 7}4 pounds (ca. 3 to 4 kg.); they form about j]-^ of the body weight. They are divided into lol)os liy dccj) fissures (Incisurse interlobares). The left lung is divided into three lobes, named from before backward apical, THE LUXGS 463 cardiac, and diaphragmatic. The right lung has four or five lobes; the apical lobe is much largiT than that of tlie loft hing, and occupies the s|)acc in front of the pericardium, pushing the mediastinum against the left wall;' 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 broncluis from the trachea opposite the third rib. The right lung is adherent to the trachea from the second rib backward. Apical lobe , Cardiac lobe Alediaslinal lobe Diaphragmatic lobe linnl lymph gland Fig. 369. — Lungs and He.^rt of Sheep, Ventral View. Specimen hardened in situ. Space between heart and lungs was occupied by pericardium and fat. The interlobar iissures begin at the ventral margin of the lung and pass toward the root. Those of the left lung he opposite to the fourth and sixth ribs. The diaphragmatic lobe is the largest, and has the form of a thrcc-siilcd p\r:imid with its base resting on the diaphragm. The cardiac lobe is prismatic and forms thr iidstciior margin of the cardiac notch; its long a.xis corre- sponds to the fifth rib. The apical Inl.r 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. ' It is therefore often termed the precardiac lobe. 464 RESPIRATORY SYSTEM OF THE PIG 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 glantl are more extensive and paler in color than in the horse; they extend further forward, overlajiping the crico-pharyngeus muscle to a small extent, and come in contact dorsally with the oesophagus. They are flattened, and have an irregular, lol)ulated surface. In the young subject the isth- mus 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 pos- terior extremity or inner surface of the lateral lobes of the thjroid. A pical lobe JlorS^ I border "^'^^^--^c ^,^ oesophagus ■""- Diaphragmatic surface Apex \ I Cardiac notch Fig. 370. — Rlonx Lung of Sheep, Mediastinal Aspect. Hardened in situ. B, Bronchus; P.a., pulmonary artery; P.v., pulmonary vein; T'.c, posterior vena cava; L.g., bronchial lymph-gland. THE THYMUS GLAND The thjTBus 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 GOO 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 ,^n()ut (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 LARYNX 465 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 ])art of the bone in the outer wing of the nostril. The notch between the nasal bone and the prcmaxilla is closetl in by jjarietal 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 jiart of the sejitum 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 diviiles posteriorly into two branches; one of these extends upward and back- ward Isetween the lateral mass of the ethmoid bone and the superior turbinal; the other widens and joins the inferior meatus. The opening l)etween 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 in- ferior turbinal and with the cavitj' of the superior turbinal. The dorsal division of the middle meatus presents several opening.? into the frontal sinus. The in- ferior meatus is relatively roomy; it communicates with the space inclosed by tlie 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 remarkaljle 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 comi^ressed laterally; its lamina is long and narrow; its arch is tlirected obliquely downward and backward. Tiie thyroid cartilage is very long; its laminae are unitefl ventrally and form a median ridge. The anterior cornua being absent, there are no joints formed with the hyoid bone. The po.?- terior cornua are broad, bent inward, and articulate with the cricoid cartilage. The epiglottis is relatively very large, and is more closely attached to tlie 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-e]iiglottic ligament and the strong hyo-epiglottic muscle.' The apex of the arytenoid cartilage is very large, and is divided into two parts at its extremity; the inner jiart 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 liackwartl; and each is pierced by a long, slit-like opening, which leads into the large laryngeal saccule. The thjTO-arytenoid or vocal ligament is similarly divided into a larger anterior and a smaller posterior part. There is a middle ventricle near the jja.se 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 super- ficial layer corresponds to the muscle of the other animals; the deep part consists of transverse fibers. ' 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 tlie thyro-hyoid membrane are inelastic, while the posterior part of the membrane is thin and elastic and allows the epiglottis to lie separated by a considerable interval from the thyroid cartilage. Morever, the borders of the epiglottis are "connected with the thyroid cornua of the hyoid bone by lateral hyo-epiglottic ligaments. 30 466 RESPIRATORY SYSTEM OF THE DOG 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 sub- divided or not. The left lung reseml)lcs that of the ox in form and loliation. The lobulation is distinct, but the interlolmlar septa are thinner than in the ox. Groove for resophagua Dorsal border Trachea _ Apical lobe Cardiac lobe Mediastinal lobe Fig. 371. — Right Lung of Pig, Mediastinal .\p Hardened m situ. B, Left bronchus; V'., pulmonary veins; .1.. pulinon pkragniatic lube (base) artery; /. Uinpli plands THE THYROID GLAND The two lobes of the thyroid are long ami 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 LARYNX 467 the two parietal cartilages, which curve laterally and toward each other. A grooved plate extends outwartl from the septal cartilage in the floor of the nostril, and another lamina supports the alar fold of the inferior turbinal Ijone. The length of the nasal cavity varies greatly in tlifferent breetls, correspond- ing, 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 ethmoiil 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 ]3art, owing to the great development here of the inferior turbinal. The posterior jjart of the nasal cavity is divided by a hori- zontal plate, the lamina transversalis, into an upper olfactory part and a lower respiratory part. The sinuses have been described (vide Osteology). Cartilages of 6, lower cartilage Leiserin Upper parietal cartilage; parietal cartilage: c, alar . (.\fter EUenberger, in c's Alias) The laminae of the thyroid THE LARYNX The larynx is relatively short. The lamina of the cricoid cartilage is wide; the arch is grooved laterally, cartilage are high, but short; they unite ventrally to form the liody, 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 jiosterior coi-nu is strong, and has a rounded surface for articulation with Fig. .37.3.— Sagittal Section op Nasal Region op Dog. /.Skin; 2, parietal cartilage; .i, floor of nasal cavity; 4, lamina transversalis; 5, mucous membrane of hard palate; 6. upper lip; 7, frontal bone; S, frontal sinus; 9. cranial plate of front-al bone; /O, cranial cavity; II, dotted line indicating anterior limit of olfactory region; a. superior turbinal; b, inferior turbinal; h', b", inferior turbinal fold: c, e. ethmoturbinals; d, cribriform plate of ethmoid; /, superior meatus; », middle meatus: h, inferior meatus; i, naso-pharyngeal meatus, (.\fter EUenberger, in Leisering's .\tlas.) the cricoid cartilage. The arytenoid cartilages are relatively small, and have between them a small interarytenoid cartilage. The epiglottis is ciuadrilateral : 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. The false vocal cords extend from the cuneiform cartilages to the thyroid. 468 RESPIRATORY SYSTEM OF THE DOG The true vocal cords arc large and prominent. The entrance to the large lateral ventricle and saccule is a long slit parallel with th(> 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 flatteneil 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 intotwo 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 tiie right lung. The anterior branch of the left bronchus crosses under the pulmonary artery. THE LUNGS The lungs (Figs. 342, 343) dift'er 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 co.stal surface of the lungs is corresjiondingly convex. There is no cardiac notch on the left lung, although a small jjart of the jioricardiura 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 lolje 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 maj- be found. On account of the small amount of interlobular tissue the lobulation is not distinct. THE THYROID GLAND Th(^ lateral lobes of the thyroid gland are long and narrow, and have a flat- tened, eiliijsoiilai form; they are placed on the lateral surfaces of the trachea near the larynx. The extremities are .small, the posterior one often Ix'ing pointed. The isthmus is inconstant and varialjle; in large dogs it usually has the form of a glandu- lar Ijand which may l)e nearly half an inch (ca. 1 cm.) wide; in small dogs it is usually absent. Accessory thyroids are frequently present; thre(> or four may be found on eith(^r side, as well as a median one near the hyoid lionc. The parathyroids, al)Out the size of millet or hem]) seed, are four in number usually. Two are ])laced on the deep face of the thyroid loljcs; 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 lol)e is much larger than the right, and extends back as far as the sixth rib at the time of its greatest size. Accortling to Baum tlie gland increases in size during the first two weeks after birth, and atroi)hies 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 (Apjiaratvis urogenitalis) includes two groups of organs, the uri- narj- and the genital. The urinary organs elaborate and remove the chief excretory fluid, the urine. The genital organs siTve for the formation, development, and expul- sion of the products of the reproductive glands. In the higher vertebrates the two apparatus are independent except at the terminal part, which constitutes a urogeni- tal 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 uropoie- tica) 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 pjTiform sac, situated on the pelvic floor when empty or nearly so; it is a reservoir for the urine. The urine ac- cumulates in the bladder until that organ is full, and is then expelled through the urethra. Fig. 374. — General Dorsal View of Ubisary Organs of Horse. 1, Right kidney; V , left kidney; 2. «'. ad- renal bodies; S. S' , 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; S, S, internal iliac arteries; 9, 9, umbilical arteries, (.\fter Leisering's Atlas.) THE URINARY ORGANS OF THE HORSE THE KIDNEYS Each kidney (Ren) presents two sur- faces, 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.' 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 ' 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. 469 470 THE URINARY ORGANS OF THE HORSE 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, caecum, 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 ves- /'"■'^ L.I. J 0 i CJ L.IT — _ 0 0 Gh ^^"^^^^z.izr, i Fit:. .375. — DiAf.RAM of Position and Dorsal Relations of Kidni:ys of Horse. Areas of direct relations are inclosed by continuous lines; parts of skeleton which overlie the kidneys but are i contact with them are indicated by dotted lines. L.I-IU, lumbar transverse processes. sels and nerves reach the kidney at the hilus, and the sinus contains the ]K'lvis 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. 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 extremitj- of the right one. It lies usually under the upper ])art of the last ril) and the fir.st two or three lumbar transverse processes. The dorsal surface is convex, and is THE KIDNEYS 47] 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 liiyht adrenal Left, adrenal Left ureter Fig. 376 — Kidnevs and Adren.\ls of Horse, Dors.\l View. Hardened in situ. Impression of seventeenth rib on right kidney is indicated by small cross. Anterior mesenteric artery (stump) Renal arteries Fig. ."ir?. — KiDNETs .\n-d .\drex.4i.5 of Horse, Ventral View. Hardened in situ. Left renal vein (not marked) is seen curving round posterior end of left adrenal. terminal part of the duodenum, the left adrenal, and the left extremity of tlie pancreas. The internal border is longer, straighter, and thicker than that of the right 472 THE URINARY ORGANS OF THE HORSE kidney. It is related to the ])ostcrior aorta, the adrenal, and the ureter. The external border is related chiefly to the ba.se of the spleen. The anterior extremity extends almost to the saccus CiECUs 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 dis- tinct. The psoas area is flat, parallel with the inner border, and widens behind. The diaphrag- matic 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 antl 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 sub- peritoneal 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. Renal crest Cortical substance Medullary substance Renal artery Fig. 378. — Frontal (Horizontal) Section of Kid.n-ey of Horse. removed. \ large accessory renal artery entered the posterior pole. Sectii liiiiitiiig layer between cortical and medullary substance are white in figure. pancreas, and the base of the ctecum, 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 jjole may be found ventral to the third or fourth lumbar transverse process. The position of the right kidnej' seems to be very constant, excluding its movements during respiration. 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, antl 710 grams for the left. Ellenlierger and Baum (24 cases) give the right kidney as varying between 430 and 840 grams; and the left between 42.5 and 780; this is an average of 635 grams (about 22'.) ounces) for the right kidney, and ()02.5 grams (about 21 'o oimces) for the left. They give the relation of the weight of both kidneys to the body-weight as 1: 25.5-344. In a Percheron mare weigliing about 2000 pounds the right kidney weighed 4 potmds 3 ounces, and the left one 4 potmds. 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. IS 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. THE KIDNEYS 473 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 healtiiy ki(hiey. It is continued along the hilus and lines the renal sinus. Sections through tiie kidney show it to consist of an external cortical substance and an internal metlullary substance.' 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 tlistinct 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 arci- form vessels, which are taken to represent the demarcation between the jirimitive lobes.- Between the vessels the medulla is prolonged somewhat toward the per- iphery, forming the bases of the renal (or Malpighian) p3n"amids. These are not very pronounced in the kidney of the horse, especially as the gland is not papillated. Renal crest Peleis lUmil Branches Ureter vein of renal artery Fig. 379. — Traxsverse .Sectiox of Right Kidxey of Horse Through thf- Hii.us. Posterior portion of organ hardened in situ. Note cur\-ature of dorsal surface. Between the leases of tlie pyramids processes of the cortex dip in toward the sinus, forming the renal columns.^ The inner central part of the medulla forms a concave ridge or cre.st which projects into the pelvis of the kidney; the crest is marked by numerous small openings at which the renal tubules terminate. 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 bj' a convoluted part (Pars convoluta). The former (formerly termed pyramids of Ferrein) a])])ear as ray-like prolongations from the bases of the pyramids (hence also termed medullary raj's), and consist largely of narrow, straight or slightl.v flexuous, tubules (limbs of the loops of Henle). The convoluted part (formerly termed the labyrinth) is granular in appearance, and consists lurgel}- of the renal corpuscles and convoluted tubules. The pelvis of the kidney (Pelvis renalis) is the dilated origin of the excretory ' The most instructive sections are those made in the horizontal and transverse planes, through the pelvis in each case. - The foetal kidney is divided bj' 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. ' In the kidney of the horse the renal columns dip in between the pyramids very super- ficially as compared ^\'ith the arrangement in the human kidney. Breuer states that the pyra- mids are 40 to 64 in number, and are arranged in four rows. Only the middle ones are distinct. 474 THE URINARY ORGANS OF THE HORSE duct. It lies in the sinus of the kidney, and it is funnel-shaped, l)ut flattened dorso- ventrally. The renal crest' (Pai)illa 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 (Rcces- sus 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. Tlie muscular coat consists of longitudinal and circular fibers. The mucous coat does not cover the renal crest, nor is it continued Arched collecting tubule Siriiight colhcl- ing liihiilc Distal coiiro- liUed tubule Renal (Malpig- hinri) corpuscle Proximal convo- luted tubule Loup of Henle Collecting tubule Arteria arci- . formis Large collecting tubule Papillary duct Artery of capsule Interlobvlar artery Capillary net- irork. Vas afferens Artcriola recta apuria .M Glomerulus Vetia arciformis "Z_J: Fig. 380. — Dhorammatic Scheme of Uriniferou.s Tubules and Blood-vessels of Kidney. Drawn in part from the desrriptions of Golubew (Bohm. Davidoff. ami Huber). into the diverticula of the pelvis. It has a yellowish tinge, and presents numerous folds. It contains glands (Cdandulse pelvis renalis) which secrete the thick mucus always found in the pelvis. Renal Tubules— The parenchyma or proper substance of the kichiey i.s eoniposed of the small renal or uriniferous tubules ('rnlmli renalcs), which are very close together ami have a complicated course. Each tubule begins in a thin-walled, spherical dilatation or capsule, which is invajiinated 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 th:; 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 antl nearly straight, it descends for a variable distance into the medul- lary 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 ' The crest is the result of fu.sion of the papilla; or apices of the pyramids in the embryo. THE URETERS ^THE URINARY BLADDER 475 and liccomes tortuous, I'onstituting 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. Stioma. — The interstitial tissue forms a reticulum throughout which supports the tubules and blood- ve.s.sels. It is very scanty in the cortex, much more abundant in the medulla, in which it incrc:iscs in amount toward the pelvis. Blood-supply. — The kidneys receive a large amount of lilood 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 lArteriae arciformes). P'rom these arciform arteries branches pass into the cortex and medulla. The cortical branches (Arterise 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 liy a smaller efferent vessel, which breaks up im- meiliately into capillaries which form networks around the tubules. The medul- lary branches descend in the pyramids, forming in them bundles of straight twigs (Arteriolae rectae). The veins correspond in general to the arteries. In the superficial part of the cortex the veins form star-like figures (\'enre stellatte) by the convergence of several small radicles to a common trimk. Lymph Vessels. — These maj^ be divided into two sets, capsular or superficial, and parenchymatous or deep. Nerve-supply. — The nerves are derived from the renal plexus of the sym- pathetic, and form a plexus around the vessels. THE URETERS The ureters are the narrow part of the excretory ducts of the kidneys. Each l)egins at the renal pelvis and terminates at the bladder. It is about ^ to ^ inch (ca. ()to8 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 towartl 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, tiu-ns 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 cour-se 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 composctl of loose fibrous tissue. The muscular coat (Tunica muscularis) consists of inner and outer layers of longitudinal fil)ers, with a stratum of circular fibers between them. The mucous membrane (Tunica mucosa) is covered with transitional epithelium; glands (Glandulffi mucosa ureteris) resembling those of the renal pelvis occur in the first three or four inches of the ureter. THE URINARY BLADDER The urinary bladder (\esica 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 cavit}', and does not reach to the inlet. AVhen moderately filled, it is ovoid 476 THE URINARY ORGAN'S OF THE HORSE in form, and extends a variable distance along the ventral al)(Iominal 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 ; ' on its middle is a mass of cicatricial tissue (Centrum verticis), a vestige of the urachus, which in the foetus forms a tubular connection between the bladder and the allantois. The body or middle part (Corpus vesicae) is rountled, 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 en- trance of the ureters." The posterior narrow extremity, the neck (Collum vesicse), 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 vcsiculae 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 bj- three iioritoneal folds, termerl the middle and lateral ligaments (Figs. 257, 272). The middle liga- ment (Plica umbilicalis media) is a median triangular fold, formed by the reflection of the peritoneum from the ventral surface of the bladiler on to the ventral wall of the pelvis and alidomen. In the new-born animal it is extensive and reaches to the um- bilicus; in the adult it is usually much reduced in length relatively. It contains ela.s- tic and muscular fillers in its posterior part. The lateral ligaments (Plica- uniliilicales laterales) stretch from the lateral aspects of the l)ladder to the lateral jjchir walls. Each contains in its free edge a round, firm banil. the round or umbilical ligament (Lig. umbilicale s. teres); this is the remnant of the large Uv\a\ umbilical artery, the lumen of which in the adult is verj' small. The retroperitoneal jiart 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 movatile. Structure. — The wall of the bladder consists of a partial ])criton(>al 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 fokl; in the female it passes on to the vagina, forming the vesico-genital pouch. \'entrally the peri- toneum covers only the anterior half or less of the Isladtler, and is reflected posteri- orly on to the ]ielvic 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 sur- faces, but laterally they become oblique and decussate with each other. A dis- tinctly circ'ular arrangement is found at the neck, where the fibers form a sphincter (Annulus urethralis). The mucous coat (Tunica nuicosa) 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 motlified dorsally in the vicinity of the neck over a triangular area, termed the trigonum vesicae ; the angles of this space lie at the orifices of the two ureters and the urethra, which are close together. ' This is commonly termed the fundus by veterinarians, but is not the homologue of tlie fundus of tlie human Ijladdcr. ' This would correspond to the fundus vesicae of man. THE ADRENAL BODIES 477 Here the mucous membrane is closely attacheil and does not form fokls. From each ureteral oriiice (Orificium ureteris) a fokl of mucous membrane (Plica urctcr- ica) 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 arc a little more than one inch (ca. 3 cm.) apart. The terminal part of the ureter, after pierc- ing 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 tlie 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 urethrse 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 transi- tional epithelium like that of the ureter and renal pelvis. It contains lymph nodules. Blood-supply. — This is derived chiefiy 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 i^osteriorl.y. 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). Thej' form a plexus in the submucosa which presents microscopic ganglia. In the foetus and new-born animal the bladder is situated chiefly in the abdomen. It is long, narrow, and fusiform. Its aljdominal end lies at the umbilicus, through which it is con- tinued by the urachus to the extra-embryonic part of the allantois. As the pelvis increases in size and tlie large intestine grows, the bladder retract.s 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 (Glandulfe suprarenales)' are two small, flattenetl organs, which lie in contact with the anterior part of the inner border of the kidneys (Figs. 376, 377). Thej' 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 abotit half an inch or more ( ca. 1 to 5 cm.) in thickness. The weight varies from one to two ounces (ca. 28 to oG gm.). The right adrenal is related internally to the posterior vena cava, to which it is atlherent. 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 ciecum. dorsally, to the right renal vessels. The anterior extremity is con- cealed 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 coeliaco-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 mlu tlie adrenals present se\-eral features not e\'ident in the soft organs. The anterior part of the riglit adrenal is tmsted upward and outward over the inner margin of the kidney, so tliat 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 tlie liver, ■From the standpoint of comparative anatomy the term "adrenal" seems decidedly preferable to "suprarenal." 478 URINARY ORGANS OF THE OX 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-fibcr.s. From it trabecular pass radially into the substance, blending with the fine supporting reti- culum. The parenchyma consists of a cortical and a medullary portion. The cortical substance (Sul)stantia corticalis) is red-brown in color, and is clearly distinguishable from the yellow medullary substance (Substantia medullaris). A large central vein ( N'ena centralis) is visible on cross- sections. The cells of the corte.x are arranged in chains of one or two rows. In the peripheral portion the cells are of high cylinilrical shape, and the chains form connecting loops; Giinther has pro- posed 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 con- tain 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 chromaf- fin cells; they share this peculiarity with certain cells of the sym- pathetic 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 receiv(> a rela- tively large bloixl-siipply 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 hinjih glands. The numerous nerves are derived from the sympathetic system through the solar and renal plexuses. Tlie fillers form a rich interlacement, especially in the medullary sub.stance. Ganglion cells are fountl chiefly in the medulla, but also occur in the deeper part of the cortex. Fig. 381. — .\dhenal Body of Horse; Horizont.\l Sec- tion, Reduced. /, Capsule; £, 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 vari- able depth. The lobes vary in size, and are commonly about twentj' to twenty- five in nuniljer. 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 hnubar transverse processes. The dorsal surface is rounded, and is in contact chiefly with the sub- lumbar 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 ])osterior vena cava. The external liorder is convex. The anterior extremity occupies the renal impression of the liver, and is capped l)y 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 VRIXARY ORGANS OF THE OX 479 side, behind and at a lower level than the right kidney. It then lies usuallj- under the third, fourth, and fifth hnnbar vertehrie. 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 External border Anterior extremity Ureter Renal artery Fill. 382. — Right Kidney of Ox, Ventral Face. Organ hanienetl in situ. Fat has been removed from fisvures herween lobes. is often more or less flattened by contact with the rumen, and may be termetl the ruminal surface. The anterior extremity is small, the posterior large and rounded. The preceding stateraent.s 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. The kidneys are embedded in a large amount of perirenal fat. The weight Renal artery Fig. 383. — Frontal Section op Kidnet of Ox. L, Lobes of cortex: P. papillse; C, calyx major; c*, calyces minores. of a kidney is about 20 to 2.5 ounces (ca. 570 to 700 gm.), the left one being usuallj' an oimce or more the heavier. The two form about 34 P^r cent, of the laody-weight. The right kidney measures about S to 10 inches (ca.-20 to 25 cm.) in length, 4 to .5 inches (ca. 10 to 12 cm.) in width, and 2I2 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 kidnej' 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, 480 URINARY ORGANS OF THE OX thiii-wallod tulies, the calyces majores ; tho anterior cal>-x is usually the larger. Each calyx major sivcs 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 tlie calyces and vessels is filled with fat. On .section through the kidney tlio 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 calj-x. The renal columns are much more distinct than in the horse. At the hilus the renal artery is dorsal, the vein in tlie middle, and the ureter ventral; a quantity of fat surrounds these structures in the hilus. The kidneys of the sheep are bean-shaped antl smooth, without any superficial lobation. The soft organ is regularly elliptical in form, with convex dorsal and ventral surfaces and rounded e.xtremities; its length is about 2J/2 to 3 inches (ca. 5 to 8 cm.), its width about 13^2 to 2 inches (ca. 4 to 5 cm.), and its thickness a little Fig. 385.— Kidney oi -ii /, Cortical substanc S, renal crest; It, renal pelv ing's .\tla.s. reduced.) 2, ineLluUary substance; 5, ureter. (From Leiser- more tlian 1 inch (ca. 3 cm.). In ])osition tliey resemble those of the ox, excejit that the right one is usually a little further back, and lies under the first three huubar 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. When tho rumen is full, the left kidney (which is attuehed by a short nie.sentery) usually lies entirely to tlic right of tho median plane, under the third, fourth, and fifth lumbar trans- verso processes. The primitive dorsal surface has become ventro-m.edial, and is sonienh:U flattened by contact with the rumen. The ureters are, in general, like those of the horse, except in regartl to tlie first part of the left one, which has a peculiar course, in conformity with the remark- al)le position of the kidney. It l)egins at the ventral part of the hilus (which faces toward the right), cinves 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 extenils further forward on the abdominal floor. The peritoneal coat extends backward further than in the horse. URINARY ORGANS OF THE PIG 481 THE ADRENAL BODIES The right adrenal lies again.st 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 sur- face is convex and lies in the renal impression of the liver. The ventral surface is grooved for the po.sterior 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 liorder 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 Posterior pole Groove for vena cava J Anterior pole Fig. 386. — Left .\drenal of Ox. Ventral View: Hardened in situ. _ Anterior pole Fig. 387. — Right .\drenal of Ox, Ventral View: 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. 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.) ^^ide. 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. 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 sjonmetrically placed 31 482 URINARY ORGANS OF THE PIG pKrag tiki A •' Fig. 3sS. — KinKETS OF Pin m sidi, Vicntrai C.a., Hepatic artery: Ma., gastro-splenic ai Cortical s^tbslance Medullary substance Papilla: ^ Calyces minores Via. 3Sa — Ibontal Section oi Kidney of Pig. DRINARY ORGANS OF THE DOG 483 on either side of the first four lumbar vertebrae. (Variations in position are not rare, and involve the left kidnej^ oftener tlian 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 mid- way between the last rib and the external angle of the ilium. The anterior ex- tremity of the right kidney usually extends as far forward as the last rib, liut has no contact with the liver. The weight of the kidney of a medium-sized pig is about seven to nine ounces (200 to 2.30 grams). The ratio of their combined weight to that of the body is about 1 : 1.50-200. Structure. — The hilus is about in the middle of the inner border. The pelvis is funnel-shapetl, anil diviilcs into two calyces niajores, which pass in a curve for- ward and backward respectively, and give off some eight to twelve short calyces minorcs; each of the latter contains a papilla Some papillse are narrow and coni- cal, and correspond to a single pyramid; others are wide and flattened, and result from the fusion of two or more pjTamids; 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. c, 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 fir.st relatively wide and gradually tliminishes in caliber. The bladder is relatively very large; when full, it lies chiefly in the abdomi- nal cavity. It is almost completely covered with peritoneum. URINARY ORGANS OF THE DOG The kidneys are relatively large, forming about j^jt to ^^^ 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 ven- tral 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 aiTected by the de- gree 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 vertebrje, 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 les.s 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 484 URINARY ORGANS OF THE DOG 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 papillse, 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 e.xist. The ureters i)resent no special features. The bladder is abdominal in position, the neck lying at the anterior I)order of the pubic bones. It is relativelj' 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 kid- ney 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 vesiculae seminales; (4) the prostate, a musculo-glandular organ; (5) the two bulbo-urethral (or Cow- per's) glands; (ti) the male urethra, a canal which transmits the generative and urinary secretions; (7) the penis, the male copulatory organ. The vesicula 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 diverti- culum of the abdomen termed the scrotum. Their long axes are nearly longitu- dinal. They are ovoid in form, but considerably compre.ssed from side to side. Each presents two surfaces, two borders, and two extremities. The internal and external surfaces (Fades medialis, lateralis) are convex and smooth. The free or ventral border (Margo liber) is convex in both directions. The attached or dorsal border (iVIargo epididymidis) is nearly straight, and is the one by which the gland is suspended in the scrotum by the spermatic cord; the epididj'mis is at- tached 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 ^Nlullerian duct of the embryo. A testicle of average size of an adult stallion is aliout 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 commonh' of un- equal size, the left one being more often the larger. The epididymis is adherent to the attached border of the testicle, and overlaps somewhat the e.xternal surface. Its anterior enlarged end is termed the head or globus major (Caput epididymidis), and its posterior, slightly enlarged end is the tail or glolius 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 memlirane. The body is less closely attached bj- 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. epididjTiiidis), 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 485 486 THE MALE GENITAL ORGANS OF THE HORSE 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-filiers. From the deep surface of this tunic delicate mem- branous septa (Septula testis) pass into the glantl, dividing it into pjTamidal spaces, the bases of which are peripheral. At the anterior part of the attached border of the testicle connective tissue and smooth muscle-fibers jiass into the substance of the glantl, forming the mediastinum testis; from this the septa radiate. The mediastinum contains a network of fine canals, the rete testis; / ^Vs.^ Fir,. 390. — Ingtinal Reoion of Stallion, with Testicles Exposed. a. a'. Testicles; 6, scrotum, opened and reflected; c. tunica vaginalis communis, opened and reflected; rf, ligament of epididymis; e, tunica vaginalis propria (mesorchium); /, vas deferens; {7,(7', tail of epididymis; /t, body of same; i, head of same; k, digital fossa or sinus epididymidis; /, spermatic vessels showing through tunica vaginalis propria; m, spermatic artery; n, prepuce; n', raph6; o, preputial orifice. (After EUenberger-Baum, Toi). .\nat. d. Pferdes.) 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), su])ported by loose intertubular connective tissue. The tubules are collected into small masses or lobules (Lobuli testis). They arc at first very tortuous (Tubuli contorti); to- wartl the a])ex 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 (^'asa efferent ia) ])iercc the albuginea and enter the head of the epiflidymis. The epididymis is covered by the tunica vaginalis propria and a thin albuginea. THE SCROTUM 487 Its head consists of lobules iLdhuli cpididymidis), each of which consists of a coiled tubule or conus vasculosus, wliich succeeds a vas efferens. By the union of these tubules is formed a siuolc tulie, tiic duct of the epididymis (Ductus ei^ididy- midis), which, by its coiu])lex coils, forms tlic body and tail of the epididymis antl terminates in the vas deferens. The tubules and the coils of the duct of the epididymis are held together by connective tissue and unstriped musclc-fil)ers. The tubules and duct are lined with ciliated epithelium, and the duct has a mus- cular coat which consists of longitudinal and circular fibers. Vessels and Nerves. — The testicle is richly supplied with blood by the sper- matic artery, a l)ran(h 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, Fig. 391. — Right Testicle axd Spermatic Cord of Horse, Inclosed in Tcnic.\ Vaginalis. c. Tunica vagioalis communis; g, prominence caused by tail of epididymis; p, cremaster externus mus- cle. (.A.fter Ellenberger-Baura, Top. .\nat. d Pferdes.) Fig. 392. — Right Testicle and Sperm.vtic Cord of Horse, E.xposed. a'. External surface of testicle; c. tunica vagin- alis, cut and reflected; d, ligament of epididymis; e, mesorchium; g, tail, A, body, f', head of epididymis; k, digital fossa or sinus epididymidis; I. spermatic vessels showing through tunica vaginalis propria; m, end of spermatic artery. Dotted line indicates position of vas deferens on other side of mesorchitun. (After EUen- berger-Baum, Top. Anat. d. Pferdes.) and runs forward on the free border to the anterior extremity. It is partially embedded in the tunica albuginea, and detaches lateral branches \\hich ascend in a tortuous fashion on each surface of the testicle; these give off small branches which enter the gland on the septa. 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 SCROTUH The scrotum, in which the testicles and the lower parts of the spermatic cords are situated, is somewhat globular in form, but is commonly a.symimetrical, since 488 THE MALE GENITAL ORGANS OF THE HORSE 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 sub- cutaneous muscular tissue. The latter contracts on exposure to cold, so that the scrotum is drawn up and becomes thicker and \\Tinkled; 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 longitu- dinal furrow, in which is a line, the raphe 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 raphe 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.' Elsewhere the dartos is loosely connected with the underlying tunic liy 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-boolis of human anatomy. Tlie.se 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 jiarietal peritoneum of the abdomen at the internal inguinal ring. It is thin above, but is thick in its scrotal part, where it is strength- ened by fibrous tissue (Lamina fibrosa) derived from the transversalis fascia. It will be described further under the caption tunica vaginalis." 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 de- tached from the inner surface of the mesorchium, near the posterior (attached) border of the latter. At the vaginal ring it separates from tlie other constituents of the spermatic cord, and turns back\\ard 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 liladder) 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 bj^ the necks of the vesiculse 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 Ijy the ejaculatory ducts. The latter are formed in the urethral wall by the union of the ' This is a remnant of the gubernaculum testis of the foetus. ■ 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. THE SPERMATIC CORD — THE TINICA VAGINALIS 489 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 ciuarter 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. Bej'ond 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 peri- toneum, 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 tulmlo-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 ea^^ty to the scrotum. It begins at the internal inguinal ring, where its constituent parts come together, extends obliciuely 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, inter- spersed 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 \asible externallj'. 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 vaginahs is sht 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 pre- sents posteriorly the deferential fold (Plica ductus deferentis). Between the two lajers of the mesorchium are bundles of imstriped muscle (cremaster internus) and small vessels. THE TUNICA VAGINALIS The tunica vaginalis is a somewhat pjTiform serous sac which extends from the internal inguinal ring through the inguinal canal to the bottom of the scrotum. 490 THE MALE GENITAL ORGANS OF THE HORSE Like the abdominal peritoneum, of which it is an cvagination, it consists of two layers — parietal and visceral. The parietal layer, or tunica vaginalis communis (s. refliexa), 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 (C'avum vaginale) is a diverticulum of the general peritoneal cavity, with which it communicates through the vaginal ring (Annulus vaginalis). It contains normally a small quan- tity of serous fluid. The jwrietal layer is reflected from the posterior wall of the inguinal canal arountl the structures of the cord, forming tlie 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 tlie inguinal canal, but it is also applied to the upper opening of the cavity of tlie tunica vaginalis. It should Spermatic vessels and nerves Parietal layer of tunica vaginalis Visceral layer of tunica vagiiialis or mesorchium Cremaster inlernus Vas deferens Fig. 393.— Di ' Cross-section 4l,is: Latter Rkpre only bf applied to the abdominal opening of the canal, the subperitoneal ring. The peritoneal ring at which tlir i-avily of the tunica vaginalis opens into the general peritoneal sac is distin- gui.slird li\ I lie iiauLc vaginal ring. It is placed about four or five inches (ca. 10 to 12 cm.) from the liiica allia, and about two or three inches (ca. 6 to S 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. DESCENT OF THE TESTICLES During early fatal 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 jiroceeds 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 hordcT. In its po.sterior edge is the elongated tail of the epididymis, and two cords of filirous tissue and unstriped muscle. One of these cortls is short and connects the tail of the epididymis with the testicle ; later it becomes shorter, THE VESICUL^ SEMINALES 491 and is termed the ligament of the epididymis. The other cord, the gubemaculum testis, extends from the tail of the epididymis to the sul)))eritoneal 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 I)osteriorl}-. The body of the epididymis at this time lies in the edge of an ohlique fold formed bj' the outer layer of the mesorchium. After the middle of fo'tal life, a pouch or diverticulum of the peritoneum, the processus vaginalis, grows ilowmvard through the inguinal canal, carrying with it cremaster fibers derived from the internal oblique muscle and a layer from the transversalis fascia. It is accom- panied 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 tlie migration of the testicle are matters on which much uncertainty still exists. That the gul)ernaculum exerts sufficient traction to guide the epididymis and testicle to the inguinal canal seems plausible. The internal inguinal ring may constitute a locus minoris resistentia; 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 fre- quently happens that one testicle or both may be retained in the inguinal canal or in the abdonten 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 crj-ptorchism 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 mesorchium 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 2.5 cm.) long, and the ligament of the epididymis much elongated (10 to 1.5 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 oestrum, 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 vesiculae seminales ( Fig. 394 ) arc two elongated and somewhat pyriform sacs, which lie on either side of the posterior part of the dorsal surface of the blad- der. They are partly inclosed in the urogenital fold, and are related to the rectum dorsally. Their long axes are parallel with the vas defercntia and converge pos- teriorly. Each consists of a rounded l)lind 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.l5to20cm.) long, and their greatest diameter is about two inches (ca. 5 cm.); in the gelding they are usually much smaller.' ' 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 re- sembled the urinary bladder in appearance and contained about a quart of thick, amber-colored secretion. 492 THE MALE GENITAL ORGANS OF THE HORSE The vesiculse are, for the most part, retroperitoneal, but the fundus extends forward into the urogenital fokl anil hence has a serous covering. The neck or duct (Ductus excretorius) dips untler the prostate, and usually unites with the end of the vas deferens to form the ejaculatory duct. Structure. — The wall, exclusive of the partial serous coat, consists of a fibrous Bulbo-uretliral (Cowpcr's) gland — On left aide urethriil 304. — Internal Genital Organs of Stallion. Dorsal View. cle has been removed over bulbo-urethral gland. Corriua of uterus masculinus dicated in urogenital fold. adventitia, a mirldle 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 open- ings of tubulo-alveolar glands. The epithelium is columnar. The blood-supply is derived from the internal pudic artery. THE PROSTATE — THE BULBO-URETHRAL GLANDS 493 THE PROSTATE The prostate (Prostata) is a musculo-glaiuhilar organ which lies on the neck of the blacldcr and the beginning of the uretlira, 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 cor- responding 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 mascu- linus, the terminal parts of the vasa deferentia, and the necks of the vesiculse 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 trabeculse into the gland substance, dividing it into spheroidal or ovoid lobules. Tlie 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 vari- able 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 Miiller and the homologue of the uterus and vagina. THE BULBO-URETHRAL GLANDS The bulbo-urethral (or Cowper's) glands (Glandulae 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 494 THE MALE GENITAL ORGANS OF THE HORSE about two inches (ca. 5 cm.) in lengtli, antl an inch or more (ca. 3 cm.) in width. In the geliUns they are aliout the size of an average hazel nut. Structure. — They resemble the prostate in general structure, but the inter- stitial tissue is much less abundant, especially in regard to its muscular elements. In the peri]iheral ])art 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 i^apiihe liehind 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 Deep arU'rij (Jro/n internal pudic) Dorsal artery (from Corona glandis external pudic) Collum (ihinrlis Proc. doriiuli.^ :/hnr!i.. i.^^ ^ 4B Ure- thral proems Retractor penis muscle BODY Fig. 395. — Penis of Horse, L-\ter-kl View. in a cutaneous pouch, the prepuce or sheath. It is cylindrical in form, but much compressed laterally in the greater part of its extent. In the quiescent state it is about 20 inches (ca. 50 cm.) long; of thi.s, about 6 to S inches (ca. 1.5 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 incorpor- ated 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 jienis is flattened laterally for the most part, but becomes rounded and smaller anteriorh'. 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, embeddeil 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 PENIS 495 The glans penis is tlio culargod free einl of the organ. It is marked off from the bod}' liy a faintlj- iiiarl^cd neck iColhini glandis). In front of this is a promi- nent circular ridge, tlie corona glandis, which is notched below. The base of the glans is rounded and extentls further backward dorsally than vontrally; it i.s 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 tul)e, the urethral process (Processus urethra>), covered by a thin integument. The urethra is thus surroundeil by a circular fossa, which opens superiorly into the urethral sinus, a bilocular diverticulum lined bj- thin black skin. This diverticulum is filled some- times with a caseous mass of sebaceous matter and epithelial debris. Structure. — The penis consists essentially of two erectile Ixxlies, the corpus cavernosum penis and the corpus spongiosum. The corpus cavernosum penis forms the greater part of the Inilk of the penis except at its free extremity. It arises from each side of the ischial arch bj- a cms, which is embedded in the ischio-cavernosus muscle. Belowthe ischial archthe crura fuse completelj' to form the laterally compressed bodj' of the corpus cavernosum; this presents ventralh' the urethral groove (Sulcus urethralis), which contains the urethra and corpus spongiosum. An- Dorsum penis Corpus cavernosum Corpus spongiosum Trabecules Tunica albuginea — Bulhn- carcrnosus m uscle Retractor penis muscle Fig. 396. — Cross-section of Boi>i or Pf.nis of Ho teriorly, the corpus cavernosmn divides into three processes, a long central one, which is capped by the glans penis, and tw-o 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 trabeculae pass inward from the tunic and form a sponge-like framework in the in- terior of the corpus cavernosum, which is thus di\nded into numerous spaces (Cavernse). These spaces may be regarded as greatly enlarged capil- laries; they contain blood, are lined with flat endothelial cells, antl 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. 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 trabecular, be- tween which are slit-like intervals; through the latter the blood-spaces of the two corpora caver- nosa communicate. In the horse no distinct septum exists except near the root, but m the pro.xi- mal and distal parts of the corpus cavernosum there are vertical trabecute. The corpus spongiosum or corpus cavernosum urethrae forms a tube around the urethra, and is inucli enlargetl at its free end to form the bulk of the glans penis; throughout the remainder of its cour.se it is practically uniform in size, and does not form any very distinct bulb (Bulbus urethra?) 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 mches (ca. 10 cm.) on the middle process of the corpus cavernosum penis, forming the processus dorsalis glantlis. The urethral process is covered by a thin layer of corpus spongiosum. 496 THE MALE GENITAL ORGANS OF THE HORSE In structure the corpus spongiosum has a general resemblance to the corpus cavernosum, but the trabeculse are finer and more clastic. In the glans the trabe- culffi 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 jilexus 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 liiiiihar 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-cavemosus (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 some- what 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 sur- face of the first two or three coccygeal vertebrae. It chvides 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 form- ing 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 arc 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 (Prseputium), popularly calleil the "sheath," is a doul)le in- vagination 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 pripputiale) ; dorsally it is directly continu- ous with the integument of the abdominal wall. It is marked by a median raphe praeputii, a continuation of the scrotal raphe. At the lower margin of the pre- putial orifice there are often in the stallion two papilla*, which arc 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 ex- ternal 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 sec- ondary tubular invagination, the prepuce proper, in which the anterior part of THE MALE URETHRA 497 the penis lies. Tliis tuljular cavity is closed behind by the reflection of the internal layer on to the penis to form the jx'nilc layer of the prepuce. Its orifice is sur- rounded by a thick margin, the preputial ring (Annulus pra^putialis), which is connected ventrally with the outer part of the sheath by the preputial frenum (Frenulum pnejiutii). The arrangement differs from that found in man in the fact that the inner part of the pre- puce as described above is equivalent to the entire human prepuce. Thi.s part, tlie prepuce projier, is well seen on .sagittal sections, and can be demonstrated by pulling the penis, inclosed ill tliis 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 tlie preputial i-ing.) 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 pig- mented; they form irregular folds, and are supplied with numerous large sebaceous glamls anel coil glands, which reach their greatest size at the preputial ring. Be- FiG. 397. — .Saoittal 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.O-t fossa glandis; D, diverticulum of fossa glandis: p.w., processus urethra?. yond this the glands are absent, and the skin resembles a non-glandular mucous membrane. The secretion of the preputial glands (Cdanduhr pra?])iitiales), to- gether with desquamated epithelial cells, forms the fatty smegma prseputii, 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 laj'er of elastic tissue, derived from the abdominal tunic, and termerl the stispensory ligament. Vessels and Nerves. — The arteries are branches of the external pudic artery, antl the veins go chiefly to the external pudic vein. The lymphatics go to the sujicr- ficial inguinal and lumbar lymph glands. The nerves are derivetl 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 32 498 THE MALE GENITAL ORGANS OF THE HORSE the pelvis, turns around the ischial arch, forming an acute angle, and passes forward inclosed in the corpus spongiosum. It may, therefore, he iliviiled into two seg- ments, 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 distinguishablefromthe neck of the bladder in size or structure; in fact no line of tlcniarcation 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 urethras. It is related dorsally to the rectum and the prostate, ventrally to the internal obturator muscles, and laterally to the bulbo-urethral Lateral lobe of prostate Orifice of vierus mascvlinus Ducts of urethral glands Collie 111 us seininalis Duets of h^dho-urethral (Cowper's) glands Fig. 398. — Pelvic Urethra Posterior Part op Bladder i e.d., Ejaculatory ilucts Slit Ventrally and Laid Open. glands. It is inclosed, except at its origin, by the urethral (^^'ilson's) muscle. Beneath this is a rich venous plexus, forming a sort of erectile tissue." 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 aliout an inch in the fossa glandis as a free tube, the processus urethrse; this jiart is covered by a delicate integument, under which there is a thin layer of erectile tissue. ' It has been customary to divide the pelvic part of the urethra into prostatic and mem- branous parts. These terms apply well in human anatomy, but have no special value in com- parative 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 wliich that term is used in regard to man. THE MALE URETHRA 499 The himon of tho tulio is liirfjely 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 al)0Ut 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 cros.s-seetion 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 tmiform to the glans penis. Here there is a .slight fu.siform dilatation (Fo.ssa navicularis), beyond which the tube contracts. The opening from the bladder into the urethra is termed the internal urethral orifice (Orificium urethrse internum); it is closed except during urination. The terminal ojiening is the external urethral orifice (Orificium urethrje externum) or meatus urinarius. The t\vo orifices of the ejaculatory ducts are situated dorsally on either side of the collieulus seminalis, about two inches (ca. 5 cm.) behind the internal urethral orifice; they are slit-like antl close together. The small orifice of the uterus masculinus is placed centrally on the collictdus; it is inconstant. The orifices of the prostatic ducts are on two groups of small jiapillte, 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 papillae, about an inch (ca. 2.5 cm.) further back and close to the median line. The small orifices of tlie urethral glands are situated laterally in the wide pelvic portion. Structure. — The mucous membrane contains an unusually large amount of fine elastic fibers, ami in its pelvic jiart there are alveolar glands (Glandulse ure- thrales). 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 aliout two inches from the internal urethral orifice in a rounded elevation, the collieulus 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 outsitle of the mucous coat. Beyond this the latter is inclosed ]>y a layer of erectile tissue, composed of plexuses of veins supported by traboculse 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 ure- thra, 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 contrac- tion it plays an important role in the ejaculation of the seminal fluid, and also in evacuating the last of the urine in micturition.' (2) The bulbo-cavernosus muscle (or accelerator urinse) 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 spongio.sum and the urethra. Beyond this it diminishes very gradually in thickness, and consists of fibers which arise on a median ventral raphe 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. ' 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. 500 MALE GENITAL ORGANS OF THE OX HALE 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-col- ored, Ijut in some breeds is more or less pigmented; it is sparselj' 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 elon- gated, 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 Vesicula seminalis Body of prostate External vrctlirtil orifice Tail Fig. 399. — Genebat, View of Genital Ourans of Bull. width is about two and a half to throe inches (ca. 0 to S cm.), and the antero-postcrior diam- eter about the same. The weight is about nine or ten ounces (ca. 250 to 300 grams). 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 closelj' 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 pos- terior border of the testicle, to which it is attached by a narrow peritoneal fold. The tail is larg(> 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 i)art of the cord is about eight toten inches (20to 25 cm.) in length. The cremaster externus is well developed, and almost completely incloses the tunic to the neck 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 MALE GENITAL ORGANS OF THE OX SOI relatively very small, ami is about four inches (ca. 10 cm.) from the linea alha. The cremaster internus is feeble. The spermatic cords emerge tlirough tlie outer angles of the external inguinal ring.s, and curve downward and inward to the neck of the scrotum. The e.\ternal rings arc about four inches (ca. It) 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 Vesicula seminalis Urethra (covered by urethral muscle) Bulho-urethral {Cowper's) gland Fig. 400. — Lvternal Gknital Org.ans The right vesicula i.s sectioned frontally. The dutteJ line indicate te (body) iti.l; Dors-al View. he Ijaclvward extension of the peritoneum. cords. The me.sorchium extends to the bottom of the tunica vaginalis, forming a narrow fold (ca. 1 cm. wide) which attaclics 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 outw^ard, 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 tlie 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 po.sterior part of the bladder they are in apposition for a distance of about four inches 502 MALE GENITAL ORGANS OF THE OX (10 cm.), flanked and overlapped by the vesiculse seminales. They form ampullae 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. The.y then pass under the body of the prostate and unite with the ducts of the vesiculie seminales to form the ejaculatory ducts. The latter liave slit-like openings on either side of the colliculus seminalis The vesiculae seminales are not bladder-like sacs, as in the horse, but are compact glandular organs- with a lobulated surface. In the adult thej' 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 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 commonlj' unsymmetrical in size and shape. Short branches are often given off from the chief tube. partially covered with peritoneum. Fig. 401.— An OF Penis of Bull, Bohm.) Fig. 402. — Cross-section of Pelvic Urethra of Bull. 7 , Prostate gland (pars disseminata); 5, urethra: S, urethral muscle; 4, aponeurosis. The lumen of the urethra is black. The excretory duct or neck joins the outer side of the vas deferens at an acute angle to form the ejaculatory duct. The structure of the vesicula is masked liy a tliick capsule of fibrous tissue and uiisfripod muscle, which maintains it in its bent condition antl also sends trabecular 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 glanduUe ve.siculares is preferred by some anatomists. The prostate is pale yellow in color, and consists of two parts. The body (Corpus prostatte) is a mass which stretches across the dorsal surface of the neck of the bhidiler and the origin of the urethra. It measurers about an inch and a half (ca. 3.5 to -1 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 ojien into the urethra in rows between two folds of the mucous membrane which proceed. backward from the colliculus seminalis. MALE GENITAL ORGANS OF THE OX 503 The uterus masculinus appears to be absent fieciueiitly. Ellenberger states tliat it opens between the ejaculatory ducts, while Martin says that it usually has two orifices at the collieulus, but that it often unites with the vasa deferent ia. The bulbo-urethral (Cowper's) glands arc 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 buhbo-cavernosus muscle. Each has a single tluct which opens into the urethra under cover of a fold of the mucous memlirane. The penis is cylindrical, and is longer and of very much smaller diameter than in th(> 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-vcntrally, 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 remarkalily 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 trabeculse 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 JDody is somewhat flattened dorso-vent rally beyond the iirst 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-cavemosus 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 raphe into two lateral halves except at its origin. It dim- inishes in size from behind forward, and its anterior extremity is pointed. The ischio-cavemosus 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 arc 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 liy 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 epithe- lium, 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 pannicu- lus carnosus. The anterior pair, the protractors of the prepuce (Mm. prseputiales 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 thej' 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 504 MALE GENITAL ORGANS OF THE PIG the prepuce {Mm. prteputiales eaudales), arise in the inguinal, region and converge on the anterior part of the prepuce. They draw the prepuce backward. These muscles are subjeet to a good deal of variation. The retractor may be absent . Many fibers come in from the pannieulu? on either side, dip under the protractor, and are inserted into the skin just behind tlic preputial opening. The homologuc 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 (AVilson'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 di-sseminata of the prostate surrounds the urethra as far back as the bulbo-urethral glands. The colliculus seminalis is short, but prominent; frotn it the urethral crest extends forward to the trigonum vesicae. The extrapelvic part has an enlargement, the bulb, at its origin; it then gradually Processus urethrm Galea glandis Corona (jlandis Collum glandis Prepuce Processus urethrm Galea glandis Corona glandis Tuhrrcnl'im Colhiin ijhnxHs Prepuce Raphe yraputii Fig. 403. — -Interior Part of Penis of Ram. -1. Right side; B, leftside. (After Bohm.) diminishes in diameter, and is relatively very small at its termination. Other features have been mentioned in preceding paragraphs. 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. bej'ond the glans penis, forming a twisted processus urethrse. 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 epidiflymis is closely attached to the testicle anil the tunica vaginalis; the tail is specially large. The spermatic cord is necessarily very long (20 to 25 cm. in a boar of meditmi size). The vas deferens in its testicular part is flexuous, and is closely attached to the tunica vaginalis; it forms no ampullae. The cremaster extemus is well developed, and extends to about the middle of the scrotal part of th.e tunic. MALE GEN'ITAL ORGAN'S OF THE PIG 505 The vesiculae seminales are exceedingly large, and extend into tlie abdominal cavity. They are three-sided pjTamidal 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 jiink 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 frequentlj- unite. In the adult boar the vesiculae are about five to six inches (ca. 12 to lo cm.) long, two to three inches (ca. .5 to S cm.) wide, and one and a half to two inches (ca. 4 to 5 cm.) thick; they weigh about 6 to S ounces each. The prostate consists of two jiarts. as in the ox. The body is about an inch (2.5 cm.) ^-ide, and embraces the neck of the bladder and the urethra at their junction dor- sally and laterally. It is con- cealed by the vesiculir sem- inales. The pars disseminata forms a layer which surrountls the pelvic part of the urethra, and is covered l\v the urethral muscle. The uterus masculinus is small. The bulbo-urethral (Cow- jjer's) glands are very large and dense. They are somewhat cyliuchical, and lie on either side of and upon the pos- terior 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. Thej' are partially covered with a layer of stri- ated muscle (^I. ischio-glandu- laris), and have a lobulated surface. Each gland has a large excretory duct which leaves at the posterior ex- tremity, 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. It is to be noted that these accessorj' glands are very small in animals which have been castrated eady. The penis resembles in general that of the ox. The sigmoid flexure is, how- ever, 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 extfemity. 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. Fig. 404— Gi .Testicle; 6, epididjT Organs of Boar. 35 deferens: d. spermatic artery f , vesicula seminalis reflected to show the body of the prostate, /; e' excretory ducts of vesiculse; (/, bulbo-urethral (Cowper's) gland; h urinary bladder; i', urethral muscle; k. bulbo-cavernosus muscle; i penis; /'. sigmoid flexure of penis; /", spiral anterior part of penis, ex posed by slitting open prepuce; m. orifice of preputial pouch; n. re tractor penis muscle. (Ellenberger-Batim, Anat. d. Haustiere.) 506 MALE GENITAL ORGANS OF THE DOG 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, 12 '2 cm. in breadth, and 6 cm. in height. The opening into the pre- puce 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 raphe 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 ]iart of the dorsal border of the testicle. The spermatic cord and the tunica vaginalis are long; they cross the side of the penis very obliciuely. The upper entl of the tunic is sometimes closed, so that there is then no vaginal ring. The vasa deferentia have very narrow ampullae. The vesiculse 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 unstripcd 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 jiart 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; ilorsally 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 MALE GENITAL ORGANS OF THE DOG 507 forms a rounded enlargement, the bulbus glandis; anteriorly it is cylindrical, smaller, and pointed at the extremity. Just in front of tlie l)ull)\is glandis there is a thick circular layer of glands, forming the annulus glandularis (Schmaltz). The two dorsal veins arise from the Ijulbus glandis, pass Ijackward on the dorsum penis, and unite at the ischial arch. A small muscle (M. compressor vense dorsalis penis) arises from the tutjer 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 slieath around the anterior ])art of the penis. The outer la3-er is ordinary integument. The inner layer has the character of a Fig. 405. — External Genital Organs of Male Dog, Ventro- lateral View of Preparatio.v. i, Scrotum; 1\ tunica vaginalis; 2, epididymis; 3, vascular part of spermatic cord; 4. vas deferens; 5, prepuce; 6, glans penis; &, corpus cavemosum penis; 7. bulbus glandis; 7', contour of bul- bus in erection; S, ischio-cavernosus muscle: a, acetabulum; 6, ob- turator foramen. lAfter Ellenberger, in Leisering's Atlas.) Fig 1, Urinary bladder; 2. ureter; 3, vas deferens; 4. prostate; 5. urethral muscle; ff, bulb of urethra; a, abdominal wall; 6. ilium; c, ischium, (.\fter Ellenberger, in Leisering's Atlas.) glandular mucous membrane; it is thin and reddish in color. The penile layer is glandless. In the fundus of the praeputial cavity there are numerous Ij-mph follicles. The protractor muscles arise in the xiphoid region antl decussate pos- teriorly around the extremity of the penis. The pehdc part of the urethra is relatively long. Its first part is inclosed in the prostate.' At the ischial arch the urethra has a well-developed biloljed bulb, formed by an enlargement here of the corpus spongiosum. It is covered by the strong but short bun30-caverno.sus muscle. The other erectile bodies have been described. The urethral (Wilson's) muscle is very strong; it encircler the urethra and has a median raphe dorsally. ' Tliis is clinically important, since enlargement of the prostate may interfere with mic- THE FEMALE GENITAL ORGANS The female genital organs (Organa genitalia feminina) are: (1) The two ovaries, the essential re]iroiluctive glands, in which the ova are produced; (2) the uterine or Fallopian tubes, which convey the ova to the uterus; (3) the uterus, in whicii the ovum tlevelops; (4) the vagina, a dilatable passage through which the fcetus 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 functionaUy with the generative organs proper as to be described with them. GENITAL ORGANS OF THE MARE THE OVARIES The ovaries (Ovaria) of the mare are bean-shapetl, and are much smaller than the testicles. Their size varies much in different subjects, and they are Fifi. 407. — Lateral View of Genital Okgans and Adjacent Strttcti'res of Mare. The removal of the ulher ahilominul viscera has allowe i the ovarie.s and uterus to sink down, whereas they are normall.v in contact with the roof of the cavity in the non-pregnant subject. /, Left ovary; S. Fallopian tube: S, left cornu uteri; 4. right cornu uteri; 5, corpus uteri; 5', portio vaginalis uteri, and 5", os uteri, seen through window cut in vagina; S, broad ligament of uterus; 6', round ligament; 7, vagina; S, labia vulva'; 9, rima vulvsp; 9*, superior commissure, and 0" , inferior commissure of vulva; JO, constrictor vulvae; //, position of vestibular bulb: /S, ventral wall of abdomen; i3, left kidney; /4, left ureter; 7.5, urinary bladder; ;C, urethra; /7, rectum; is, anus; 19, 19', unpaired and paired parts of sphincter ani externus; SO, retractor ani cut at disappearance under sphincter; 21, sui?pensory ligament of anus; 32, longitudinal muscular layer of rectum; 22' , recto-coccj'geus; S3, constrictor vaginie; a, utero-ovarian artery, with ovarian (a') and uterine (n") branches; b, uterine artery ; c. umbilical artery; rf, ischium; c, imbis; /.ilium. (.After Ellenberger, in Leisering's .\tlas.) 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 508 THE OVARIES 509 and a lialf (ca. 3 to 4 cm.) thick. The weight is about two and a half to tiirce ounces (ca. 70 to 80 grams). Eacii presents for description two surfaces, two borders, and two extremities or poles. The surfaces are termed internal and external (Facies medialis, lateralis); thej' are both smooth and rounded.' 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 depres.sion, the ovulation fossa. The tubal or anterior extremity (Extremitastubaria) is rounded, and is relateil to the fimbriated end of the uterine or Fallopian tube. The uterine or posterior ex- tremity (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 alidominal cavity, about a handbreadth be- hind the corresponding kidnej'. Thcj' are in contact with the lumbar wall of the abdomen, and are com- monly 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 at- tached (mesovarial) border is commonly directed toward the median plane, the free border laterally and somewhat ventrallv. The position of the ovaries is not constant, but is sub- ject 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 v-entrally. 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 correspond- ing 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 con- tact with it. The right ovary commonly lies a little (ca. 2. .5 cm.) further forward than the left one. Except during preg- nancy, they are normally in contact with the lumljar ab- dominal wall, and do not hang down among the adjacent viscera. Fig. 408. — Eight Ov.\rt of Mare, WITH .\djacext Structures. The extremity of the cornu uteri is opened. /, Ovary; 2. Fal- lopian tube, with its ostium abdom- inale (2'), fimbrire iS"), and ostium i2"'); 3, cornu uteri, with its lining (3'); 4> ovarian liga- ment: 4\ mesosalpinx. (After Ell- enberger. in I.eisering's .\tlas, re- duced.) The ovary is attached to the sublumbar region by the anterior part of the broatl liga- ment; this part of the ligament, the mesovarium, is about three or four inches (ca. 8 to 10 cm.) wdde, 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 o\'ary has a covering of peritoneum. The peritoneal investment is absent at the attached border where ' 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 tlorsal 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. 510 GENITAL ORGANS OF THE MARE the vessels and nerves enter; this area is termeil the hilus. The ovulation fossa is covered liy a layer of columnar cells, a remnant of the ])rimitive germinal epithe- lium. 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 occupieil 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 condensa- tion of the stroma termed the theca f olliculi ; within the theca is a quantity of fluid, the liquor f olliculi. These constitute the Graafian follicles (Folliculi oojihori), 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 super- ficially 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 oestrum. 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 enlarKcnient and fatty changes, the follicle cells are transformed into lutein cells, form- ing a yellow mass known as a cor- pus 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 ex- tends 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 filjrous tissue, in which there are often cj'sts of various sizes. The ova, present in enormous num- ber at birth, have then been extruded, or destroyed by phagocytic action or de- generation. Vessels and Nerves. — The arteries of the ovary are derived from the ovarian artery. The artery is relatively large and is fle.xuous; it reaches the attached i)order 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. Fig. 409. — Schematic Represent.ation of Change.s in Ovary of Mare fro.m Fcetal to .\dult State, (.\fter Born.) The changes alTect chiefly the free border (upper in figure) and the extent and form of the area covered by germinal epithelium (4). /, Peritoneum (broad ligament); S. ligament of ovary; S, fimbria of Fallopian tube: 4, germinal eijitheliuin; 5. vessels, which reach the ovary at the attached border (ff). The latter represents the hilus, while the deep ilepression at the free border is the ovulation fossa. (EUenberger. in Leisering's .\tlas.) THE UTERINE OR FALLOPIAN TUBES — THE UTERUS 511 THE UTERINE OR FALLOPIAN TUBES The uterine or Fallopian tubes (Tubts uterinse) act as excretory ducts of the ovaries, since they convey tlie ova from the repiochictive glands to the uterus. They are not, however, in tlirect continuity with the glands, hut rather partly in contiguity with, and partly attached to, thcni.' 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 laj'er of the broad ligament, and termed the mesosalpinx. This largely covers the outer aspect of the ovary, and forms with it and the broad liga- ment a pouch called the bursa ovarica. The uterine extremity of the tube com- municates with the cavity of the cornu bj' 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 fimbriae, some of which, the fimbriae ovaricae, are attached in the ovulation fossa. In the center of the fimbriated extremity is a small opening, the ostium abdominale, lij- which the tube communicates with the peritoneal cavity. The tube ajipears normally to be applied to the ovary, so that the extrudetl ova pass into it and are conveyed to the uterus.' Pedunculated cysts, the hydatids of Morgagni, are often found on one or more of the fimbriiE. In the mesosalpinx are bUnd flexuous tuljules, which constitute the paroophoron, a remnant of the Wolffian body. They are most evident in the young adult, and tend to disappern- 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 memljrane is continued on the fimbria^, and meets the mucous lining on them. The fibrous coat or adventitia is continuous with the filjrous lamina of the broad ligament. The muscular coat consists chiefly of circu- lar fil)ers, although longitudinal fibers occur externally. The mucous coat is thin and is much plicated. The folds (Plicse tubarite) are chiefly longitinlinal, but in the wide part of the tube (Ampullse tuba?) they are very complex, .so that on cross-sections the spaces between the folds may be mistaken for brancheil tubular glands. The folds are continued on to the findiria. 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 scjuamous 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 posteriorh'. It is situated chieflj' in the ab- dominal cavity, Ijut extends a short distance into the pelvic cavity. It is attached to the lumljar 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 aljdomen. They appear to varj- considerably in position; commonly thej- ' The Fallopian tubes may be regarded, both in structure and morphology, as prolongations of the uterus (McMurrieh). - The arrangement is the only exception to the general rule that the serous cavities are closed. In this case the mucous memlirane of the fiml)riated extremity is continuous with the adjacent peritoneum, a persistence of the embryonic relations of the Miillerian duct. 512 GENITAL ORGANS OF THE MARE are pressed up against the sublumhar muscles by the intestine (left portions of large colon, small colon, and small intestine). They are cj'lindrical, 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 some- what in caliber, converge, ami 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. Fio. 410.— Gkn-itai. ORnAN-s OF Maff. Dobsal View. The left cornu and adjacent jjart of the botly of the uterus and the vagina and vulva are opened up. U Ovary; 2. Fallopian tube, with S' , its timbriated end; S, cavity of corpus uteri; J,, cavity of left cornu; 5, right cornu, with 5', its communication with the body; (7, portio vaginalis uteri; 6', os uteri; 7, broad ligament of uterus; 8, ligament of ovary; 9, vagina; 10, vulva; /O', glandula- vestibulares majores; 10". glandulte vestibulares niinores; 11, transverse fold; 12, external urethral opening; IS, 13', labia vulva?: 14, glans clitoridis; 14', jtmction of crura to form corpus clitoridis indicated by tlotteil lines: 15, urinary bladder: a, utero-ovarian artery with ovarian (a') antl uterine (a") branches; 6 ute'"'"" '""*°'"'' t xftar v\\at\\^arrrar ',„ r Qico,-i,^.T't Atloc^ irtery. (.\fter EUenberger, in Leisering's When a soft utori;,s is distpndeil, the cornua are strongly curved, but this does not represent tlie natiu-al form. Wlien fixed in .litii tlie liorns are eitlier sliglitly curved or nearly straight. The two horns are commonly unsymmetrical in length and diameter in mares which hiive borne young. The body of the uterus (Corpus uteri) is situated partly in tin- abdomen, partly in the pelvic cavity. It is cylindrical, but considerably flattened dorso- vcntrally, 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 rcctalis) is related to the small colon and rec- THE UTERUS 513 turn. 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 liody 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 1 3.5 to 4 cm.) in diameter. Attachments. — The body and cornua are attached to the abrlominal and pelvic walls by two extensive peritoneal folds, the broad ligaments (Ligamenta lata). These extend on either side from the sulihmibar region and the lateral pelvic walls to the dorsal border of the cornua and the lateral margins of the bod.y 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 extremitj' 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 (C'avum 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 o])ens into the vagina by the os uteri externum, and into the liody by t he 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 essential^ 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 tubu- lar uterine glands (Glandula? utcrinse). 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; tliere is also a branch from the internal pudic artery. The veins form pam- jjiniform plexuses and accompany the arteries. The lymphatics are numerous and go to the internal iliac and lumbar glands. The nerves are derived from the sjTnpathetic through the uterine and peh-ic plexuses. The foregoing statements refer to the non-g^a^^d uterus. In the pregnant state it under- goes 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. SO to 90 cm.), and a corresponding diameter; intliis process it extends much bevond the ovarv, and the broad ligament. The gravid uterus is entirely abdominal in position, and extends alongthe ventral wall, chiefly to the left of the median plane. It weighs about nine pounds (ca. -1 kg.), according to Ellenberger. The broad ligaments increase greatly 33 514 GENITAL ORGANS OF THE MARE in size and contain more muscular tissue. Tlie 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 be- comes non-ciliated and stratified. THE VAGINA The vagina i.s tlie i);issage 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, vcntrally to the liladder 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 jiouch passes backward somewhat less between the vagina and bladder. Thus most of the vagina is retroperitoneal and is sur- rounded 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 jiroj^er 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 laj'er 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 u.sual 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 vaginae. The posterior part is directly continuous with the vulva without anj' 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 vaginte).' Vessels and Nerves. — The l)lood-supply is derived from the branches of the internal pudic arteries. The veins form a jjJexus which is drained bj- the internal pudic veins. The lymphatics pass to the internal iliac lymph glands. The nerves are derivetl from the symitathetic through the pelvic plexus. THE VULVA The vulva or urogenital sinus is the terminal part of the genital tract.- 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 vuIvsb) has the form of a vertical slit, about four to six inches (ca. 10 to 15 cm.) high, and is margined ' In formalin-hardened subjects there is frequently a pronounced ring-like constriction at the beginning of the vulva. - The term vulva is used here in the sen.se in which it is understood generally by English and French veterinarians. In the (lerman works it is applied only to the labia and other struc- tures around the external orifice of the urogenital sinus, while the sinus itself is termed the vestibule of the vagina (Vestibulum vagina>). THE FEMALE URETHRA 515 by two prominent roundwl folds, the labia. The labia of the vulva (Labia vul- vae) meet above at an acute angle, forming the superior commissure {C'ommissura dorsalis), which is about two inches (ca. 5 cm.) below the anus. Below they unite to form the thick rountled inferior commissure (C'ommissura 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 in- ferior commissure; this is the glans clitoridis, the homologue of the glans penis. Overlying it is a thin fold, the prepuce of the clitoris (Prceputium clitoridis). At the anterior extremity of the ventral wall of the vulva, /. c, about four or five inches (ca. 10 to 12 cm.) from the inferior commissure, is the external urethral orifice or meatus urinarius (Orificium urethrae 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 seliaceous 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 nuicous membrane. Between these is a layer of striped muscle, the constrictor vulvae; 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 ele- vates the clitoris. The constrictor vestibuli muscle embraces the vulva in front of the preceding; it is joined on either side bj' a band of unstriped muscle which arises from the first and secontl coccygeal vertebrae, 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 urethrae 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 supi)lied with blood bj' 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 papilhe which converge toward the inferior commissure; these mark the orifices of the ducts of the glandulae vestibulares minores. On either side of the dorsal wall is a grou]i of eight to ten larger prominences on which the ducts of the glandulae vestibulares majores (of Bartholin) open. Quite exceptionally there may be found on either side of the urethral orifice tlic opening of the canals of Gartner (Ductus epoophori 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 bj^ a small rounded glans. The organ is composed of erectile tissue similar to the corpus cavernosum penis. The ischio-cavemosus (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 bullous vestibuli. THE FEMALE URETHRA The female urethra (Urethra ferainina) 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. 516 GENITAL ORGANS OF THE MARE Structure. — The intrinsic muscular coat consists of longitudinal and circular layers of unstri]^ed fibers. Between these is a laj-er 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 epithe- lium. The urethral muscle {M. compressor urethrte) embraces the urethra and is continued backwartl for some distance under the constrictor vestibuli. It is covered by a fibro-elastic membrane. THE MAMMARY GLANDS The mammary glands (Glanduhr lactifera>) are motlifietl cutaneous glands which are so closely associated functionallj' with the genital organs as to be con- sidered accessory to them. In the mare they are two in numl)er, and are placed on either side of the median plane in the inguinal region. Each gland has the form of a short cone, much com- pressed transversely, and having a flat inner surface. It consists of the glandular mass or body of the gland (Corpus mammae) and the teat or nipple { Papilla mam- mse). The base is related to the abdominal wall, to which it is attached by areolar tissue, which contains a venous plexus, the superficial inguinal Ij'mph 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, ehieflj- hairless, and supplietl 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 lamina? detached from the abdominal tunic which ilescend on either side of the median plane, forming a septum between the two glands, and constituting their ligamentum suspensorium. These lamina? 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 parench5rma is jiinkish 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 capside which sends inward numerous tralieeulse; these form the interstitial tissue, and ilivide the gland into lobes antl 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 memlirane, and from it t^^'0 (or three) lactiferous ducts (Ductus lactiferi) pass through the extremity of the nipple. Tliese ducts are lined with a non-glandular mucous membrane, which is covered with stratified scjuamous epithelium. They are surrounded by unstriped nuisctdar 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 tlic .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 GENITAL ORGANS OF THE COW 517 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 i lyinpli 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 tliose of the marc, 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. -10 to 45 cm.) from the vulva in a cow of medium size. Fig. 411. — Ovart of Cow. i. Broad ligament of uterus; 2, ligament of ovar>'; 5, fimbria ovarica; 4. attachment of broad ligament; 5, surface of ovarj' covered with ger- minal epithelixmi; 6, corpora lutea; 7, Graafian follicle. (From Leisering's Atlas.) Fig. 412. — Uterus of Cow, Contr.\cted, Dors.^l View. a, Body of uterus; 6, fc', horn of uterus; c. ovar>-; rf, d', triangular folds connecting horns of uterus (Lig. intercomu- alia). (.\fter Zieger.) 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 cor- pora 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.). The Fallopian or uterine tubes are long and less fiexuous than in the mare. The junction witli 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 fimbrise 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 pos- terior 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 gratlually 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; 518 GENITAL ORGANS OF THE COW its wall is rcnuirkahly dense, and may he nearly an inch (ca. 2 em.) in thickness. Its lumen, the cervical canal, is sjiiral, 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 uterinse). ^tflPife z^V The.se are oval prominences, about a hun- OSlCQI^f^kli ' dred 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 al)out }4 to ?4 inch (ca. 1.5 to IS mm.) in length, j inch (ca. S mm.) in width, and ' s inch (ca. 2 to 4 mm.) in thickness. During pregnancy they become greatly enlarged and pedunculated. The larger one.s then measure about 4 to .5 inches (10 to 12 cm.) in length, 1 to 1 Jo inches (3 to 4 cm.) in \\-idth, 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 scries which obliterate the lumen. At the ex- ternal orifice (os uteri) the folds (Plicae palmata?) form rounded prominences ar- ranged 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. Fig. 414 ITAL Organs of Cow. Dorsal Fig. 41^. — Uterine Cotyledon of Cow. The figure repre.seiits a cotyledon of medium size. (Afte Ellenberger, in Leisering's .\tlaa.) The right uterine cornu and the vagina and vulva are opened up: /, Labium vulvae; $, ventral commissure: S, glans clitoridis; 4, glandula vesti- bularis major, exposed by slit in mucous mem- brane; 5, opening of duct of preceding; 6, sub- urethral diverticulum; 7. external urethral open- ing; 8, openings of canals of Ciartner; 9, os uteri; 10, corpus uteri: //, cornu uteri; 13, cotyledons: 13, Fallopian tube; 14, oslimn abdominale tubic; 15, ovary (FroTU Leisering's Atlas, reduced.) The broad ligaments are not attached in the sulilumbar region as in the mare, but to the u]ip('r part of the flanks, aliout 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 tleveloped, and can he traced distinctly to the vicinity of the internal inguinal ring. The vagina is somewhat longer and more roomy than that of the mare; its GENITAL ORGANS OF THE COW 519 wall is also thicker. Its average length in the non-pregnant animal is at)out eight inches (ca. 20 cm.); liut 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 forni.\ vagina; in oophorectomy. In the ventral wall of the vagina, between the muscular and mucous coats, there are frequentl.v present the two canals of Gartner (Ductus epoophori longitu- dinales). 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 uretliral orifice. These tubes are remnants of the Wolffian ducts, and, like other foetal vestiges, are very variable. Roder 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 hgaments for a variable distance toward the ovary. They are of clinical interest in that cy.sts frequently form along their course. \L Section of Part of Urogexita DrVERTICCLUM. Cow, Showing Scbcrethral 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 cni.i 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 reailily 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 glandulae vestibulares majores (or glands of Bartholin) are situated on the lateral walls of the vulva, under the constrictor vulva". 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 vagina^ 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 520 GKXITAL ORGANS OF THE COW somewhat ellipsoidal in form, hut flattened transversely. The base (or dorsal surface) of each gland is slightly concave and slopes obliquely downward and for- ward in adaptation to the alxlominal 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 aliout three inches (ca. 7 to 8 cm.) in length. It is customary a, Body of Klarid; b, Lactiferous — Cross-section op Mammary Glands of Cow. Ills; c, cavity of teat; J, duct of teat; r, intennammary groove; /.septum between glands; {/, supramammary fat. 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, in- jections of fluids of different colors into the two teats of the gland demonstrate that the cavities drained by them do not communicate. The size and form of the glands vary greatly; in the highly .^specialized dairy breeds (p. g., Holsteins) they often attain enormmis 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 inter- stitial 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 suljstancc (polymastia). Sanson described a case in which there were seven teats, all giving milk. GENITAL ORGANS OF THE SOW 521 Each teat has a single duct which widens superiuriy and opens free!}- into a roomy lactiferous sinus or milk cistern (Sinus lactiferusj. 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 drainetl by three trunks, viz., the very large subcutaneous abdominal ("milk vein"), the external pudic, and the perineal vein. Tlie lymphatics are numerous, and [Dass to the supramammary glands chictly. The nerves are derived from the inguinal nerves and the posterior mesenteric plexus of the sympathetic. GENITAL ORGANS OF THE SOW 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. Fig. 417. — Genital Organs of Sow, Dorsal View. The Vagina and Cervix Uteri are Slit Open. 1, Labia vulva?; 2, glans clitoridis; 3, vulva; 4, external urethral orifice; 3, vagina: 5', cervix uteri; 6, corpus uteri; 7, cornua uteri, one of which is opened at 7' to show folds of mucous membrane; S, Fallopian tube; 5^, abdominal opening of tube; P. ovaries; 70, ovarian bursa; ii, broad ligaments of uterus; 75, urinary bladder, (From Leisering's .\tlas.) 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 promi- 522 GENITAL ORGANS OF THE BITCH nences, so t!mt soinetinK's tlu' filand lias an irregulai', nuiUicrry-like aspect; this is due to tlie fact that there is veiy Httle stroma and the hirger Graafian follicles project from the surface. The Fallopian or uterine tubes are long ( ca. 15 to 80 cm.), and less flexuous than in the mare. The fimbriated extremity forms an amjjulla anil has a large abdominal opening. The uterine end shatles inseusiblj- into the small extremity of the cormi 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.' 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. Tlie changes in form and position of the uterus during pregnancy are similar to those men- tioned 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 jiointed and dejien- dent. The mucous lining is plicatetl. There is a small suburethral diverticulum. The vestibular glands are small and variable in number. The vestibular bullis 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, anil 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 l)itch. Each teat has commonly two excretorj- ducts. GENITAL ORGANS OF THE BITCH The ovaries (Fig. 33(5) are small, elongated-oval in outline, and flattened. Each ovary is situated clo.se to or in contact with the posterior pole of the corre- sponding kidney, and thus lies ventral to the third or fourth lumbar vertebrijp, 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 Ugament. The surface of the ovary presents ])rominences caused by projecting tiraafian 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 jiasses at first forward and then turns backward, hav- ing a straight or only slightly flexuous cour.se. The fimbriated extremity lies in the bursa ovarii, and has a rather large ojiening. 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 ' Lesbre states that the cornua may attain a length of 45 to 50 cm. GENITAL ORt5ANS OF THE BITCH 523 inches (ca. 12 to 15 cm.) long. The horns are of viniform diameter, are nearly straight, and lie entirely within the abdomen. They diverge from the bodj' in the form of a V toward each kichiej". Their posterior parts are united by the peri- toneum. The neck i.s very short and is fused dorsally with the vagina. It has a thick muscular coat. The mucous mem- brane of the uterus has long uterine glands and also short tubular crypts. The broad ligaments contain fat and imstriped nuisfje. They are much longer in the mitldle than at either enil. The posterior part is attached tn the anterior part of the vagina. The roiind ligaments are very long, extending through the inguinal canals, and traceable almost to the vulva. The horns of the graviil uterus present dilata- tions or ampullae, which contain the fa?tuseS| and are separated by constrictions. The gravid uterus lie.s 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 nar- row anteriorly, and has no distinct fornix. The muscular coat is thick and consists chiefly of circular fibers. The mucous mem- brane forms longitudinal folds. The canals of Gartner are usually absent. The vulva has thick labia which form a pointed inferior commissure. The mucous lining is smooth. On either side of the ure- thral orifice there is a small depression. The glandulse vestibulares majores are absent, but the smaller glands are present, and their ducts open ventrallj- on either side of a mechan ridge. The vestibular bulbs are relatively large and join dorsally. The clitoris has a small pointed glans, beneath which is a diverticulum. The corpus caver- nosum is a little more than an inch (ca. 3 to 4 cm.) long in a subject of medium size, and is infiltratetl 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. Fig. 418. — GE^^TAL Org.a Vulva, vagina, and uteri open, a. Ovarian bursa; b, sar the right o OF Bitch. iin part) are slit opened to show rf.rf, horns of uterus; e.e'.body of uterus; /, neck of uterus; /', OS uteri; g, vagina; h, hymen; i, vulva; k. e.xterna! urethral orifice; I, urinary bladder; m, urethra: rt, n, labia vulva-; o, fossa clitoridis; p, clitoris. .(After Ellenberger, in Leisering's Atlas.) 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 lieart to the tissues; (2) the capillaries, microscopic tubes in the tissues which ]5ermit 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 lilood from the left ventricle all over the body, whence it is returned by the venje cavae 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 (Arteriae), 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, ?'. 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 (Kami connnuni- cantes) occur in certain places; they may be transverse or in tlie form of arclies. Wide-meshed networks of A'essels are termed Retia vasculosa. Terminal or end ar- teries are such as form isolated networks, /. c, do not anastomose with adjacent ar- teries. 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 (Venae) 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 sateUite vein ; in many places two veins accompany a single artery. The primi- tive venous trunks do not run with the arteries, and most of the superficial veins (VeniE cutanea?) 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 524 THE PERICARDirM 525 in bony grooves are termed (venous) sinuses; examples of tills are tiie sinuses of tiie dura mater of the brain. Structure of Arteries.— Tlie wall consists of three coats. The external coat (Tunica externa) consi.sts 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 onh' 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 (\'agina vasis) is a condensation of the surrounding con- nective tis>ue, 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 com- pletely when empt.v, while arteries do not. The middle coat is very thin and con- sists to a large extent of ordinar\' 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 cUrected 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 bj- numerous small arteries, called vasa vasorum. These arise from branches of the arterj- 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-meduUated fibers. They form plexuses around the vessels, from which fibers pass mainh' to the muscu- lar tissue of the middle coat. BLOOD-VASCULAR SYSTEM OF THE HORSE THE PERICARDIUM 1 The pericardium is the fibro-serous sac which sui'rounds 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 inela.stic. 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. \'entrally 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 invag- inated liy 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, jiarietal 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 epicardiimi. The serous pericardium is composed of a connective-tissue membrane, rich in elastic fibers, and covered on its free surface by a laj'er of flat endothelial cells. The pericardium is covered by the mediastinal jjleura (Pleura pericardica) and is crossed laterallj' by the phrenic nerves. Its lateral surfaces are related chieflj' 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 ' The pericardium is described before the heart since it must be examined first in the labor- atory. 526 BLOOD-VASCULAR SYSTEM OF THE HORSE ribs. The anterior border of the base is opposite to the second intercostal space, and the posterior l)ordcr is opposite to the sixth rib or space. The base is related to the great vessels, the trachea and its bifurcation, the bronchial lyni])li glands, the cesophagus, and the vagus, left recurrent, and cardiac nerves. The two parts of the serous pericardium are, of course, continuous with each other at the hne of reflection on to the great vessels. The latter are covered in varying degree by the \'isceral layer. The aorta and pulmonary arterv are inclosed in a complete common sheath as far as the bifurcation of the latter. A pouch paiises inward lietweon tlie 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 riglit ami below for a distance of an inch or a little more (ca. 3 cm.). The pulmonary veins receive practicallv 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 antl somewhat flattened cone. It is attached at Brachiocephalic trunk / Pulmonary reins Lift nur,rlr ,/i.r) Ventricle _Coronary 'groiirc Posterior border Left longitudinal groove Fig. 419. — He,\bt of Horsi:, Left View. Hardened in situ The dotted line indipjitcs the line of reflection of the serous pericardium. The epicardii have not been removed from the heart. id subepicardial fat 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. In position the heart is decidedly asymmetrical, about two-fifths being to the THE HEART 527 right of till' median iilanc and three-fifths to the left. The long axis (from the middle of th(> hase to the apex) is directed downward, Ijackward, and somewhat to the left. The base (Basis cordis) is directed dorsally and lies a little above the middle of the ilorso-ventral diameter of the thorax. It is opposite to the riijs 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 ol>liquely downward and backward; its lower part is parallel with the sternum. The posterior border (Margo caudalis) is much shorter, nearly vertical, Pulmonary ( right branch Pulmonar,/ reins '"''"^ Heft branch \ vna iizygos Line of reflecti' Fig. 420. — He.\rt of Horse, Right View. H.\rdened in situ. :rous pericardium dotted. Epicardium and subepicardial fat have not been removed from heart. Left ventricle is considerably contracted. and is opposite to the sixth rib or intercostal space. The surfaces, right and left (Fades dextra, sinistra), are convex and are marked by grooves which indicate the division of the heart into four chambers, the two atria al>ove and two ven- tricles below. The left surface (covered by the pericardium) is in contact wdth 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 riljs. The coronary or atrio-ventricular groove (Sulcus coronarius) indicates the division between the atria and tlie ventricles. It almost completely encircles the 528 BLOOD-VASCULAR SYSTEM OF THE HORSE heart, but is interrupted liy 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.) 'Honary veins fe. — Pulmonary veins Fig. 421.— Base of Hkart of Horse Posterior vena eara Left atrium (sinus venosus) Large Vessels, Dorsal View. Specimen Hardened in situ. above the apex. The grooves are occupied by the coronary vessel ami a variable quantity of fat. Size and Weight. — In horses of meflium size the heart usually weighs about seven or eight jjounds (ca. 3.5 kg.), or about 0.7 per cent, of the body-weight. There is, liouever, great range of variation in apparently normal specimens. The following measurements were obtained in medium-sized hearts in diastole: Sagittal diameter of base 2.5 cm. Greatest width of base IS to 20 em. Cireumference at coronary groove 6.5 to 70 cm. Distance between origin of puhiionary artery and apex 2.5 cm. Distance between termination of posterior vena cava and apex 18 to 20 cm. THE RIGHT ATRIUM 529 The Right Atrium The right atrium (Atrium dcxtrum) or auricle forms the right-anterior part of the base of the heart, aiul lies above the right ventricle. It consists of a sinus venosus, into which the veins open, anil an auricle or auricular appendix. The latter is a conical diverticulum which curves around the right and anterior surfaces [iilirior vena cava Orifice of vena azygos Pulmonary I'dn": Fossa ovalii Right ventri- cle {septal wall) Fig. 422. — Right Side of He.\rt of Horse Open-ed up b Hardened in situ. The right ventricle wa^ in diastole, r, Intervenous crest; v, v, tricuspid valve; p. p, papill moderator bands. Arrow points into origin of pulmonary artery. Part of Right W.\ll. Organ of the aorta, its blind end appearing on the left side in front of the origin of the pulmonary artery. There are five chief openings in the right atrium. The opening of the anterior vena cava (Ostium vente cavte cranialis) is in the upper and fore part. The opening of the posterior vena cava (O.stium vense cava? 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 34 530 BLOOD-VASCILAR SYSTEM OF THE HORSE posterior vena cava; the orifice is jirovidcd with a small semilunar valve or valve of Thebesius (Valvula sinus coronarii). The middle coronary vein has a scjiarate 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 venae cordis parva^i these arc concealed in the depressions between the musculi pectinati. The atrium is linetl with a glistening membrane, the endocardium. Its walls are smooth except on the right and in the auricle (or apjx'ndi.x), 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 venae cavse are without valves. A ridge, the intervenous crest,' 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 tliick margin (Limlnis fossae ovalis). The fossa is the remains of an opening, the foramen ovale, through which the two atria communicate in the fo'tus. 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 antl above the left ventricle. The auricle (or appendix) extends outward and forward on the left side, anfl 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 cavit.y 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 sejital wall op])osite the fossa ovalis, bounded above by a fold which is the remnant of the valve of the foramen ovale of the fcetus. The atrio-ventricular opening is situatetl 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 bj' the musculi pectinati. The number and the arrangement of tlie pulmonary veins are \-ariable. They may be five to nine in number. The large.st oriiiee is posterior. I'sually three vein.s of considerable size enter close together on the right above th(> posterior vena cava, and three or four open close to tlie ridge wliich projects from the roof at tlic liase 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 jiart projects higher and forms the conus arteriosus, from which the iiulmonary 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). ' This is termed the tubercle of Lower in human anatomy and the tuberculum intervenosum by German veterinary anatomists. THE RIGHT VENTRICLE 531 The axis of the cavity, taken from this ridge to the apex forms a spiral curve down- ward and to the right. The septal wall is convex and faces obliquely forward and to the right. The right atrio-ventricular orifice (Ostium venosum dextrum) is oval and is situated opposite to the lower jjarts of the third and fourth ribs. It is guarded by a tricuspid valve (\'alvula trieuspidalis); 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 Anterior j'ena cara — Right coronary ' 9^ artery Modcmtu, band Right venlriclc— Rigid coronary urkr'j Great coronary -^( ^ vein U'" Left coronary ■---.^_ _;)*>'—.._ artery {circuni- ■'V''--^^ flex branch) /' " Bicuspid valve Chordw tendinecE Musculu^ papillaris ^'^ Moderator band Left ventricle Specimen hardened i Fig. 423. — Section op Heart of Horse. n'lii and cut nearly at right angles to the ventricular septum. The left ventricle is contracted. but not ad maxin V . a., Segmeot of aortic valve. into the ventricle; they give attachment to chordre tendinea?. The auricular surfaces are smooth. The ventricular surfaces are rough and furnish attachment to interlacing branches of the chordae tendines. The valves are folds of the endo- cardium, strengthened by fibrous tissue and at the periphery liy muscular fibers also. The chordae tendineae are attached below to the three musculi papillares, which project from the ventricular wall; .superiorh- they divide into branches which are inserted into the ventricular surfaces and the free edges of the valves. Each segment of the valve receives chordae tendineae 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 (O.-^tium arteria^ pulmonalis) is circular and is situated 532 BLOOD-VASCULAR SYSTEM OF THE HORSE 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 semi- lunar cusps (Valvulae semilunares arteria- pulmoiialis) ; 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 Musculi peclinati Pulmonary artery ^^ Musculi ^^ ■peclinati '\ Aortic valve -- Great coronary vein Left coronary artery Bicuspid valve Chorda: tenrtincw Papillary muscle ^S-— Right coronary > j artery '"'--Tricuspid valve — ^__ Papillary m uscle Trahecula: ' carnecE Fig. 424. — Section of Heart of Horse. Specimen Ha ; is cut nearly at right angles to the ventricular septum, and is viewed from the right and posteriorly. artery forms opposite each cusp a pouch, the sinus of the pulmonary artery (or of Valsalva). The walls of the ventricle (except in the conus arteriosus) bear muscular ridges and bands, termed trabeculse cameae. These are of three kinds, viz., (1) ridges or columns in relief; (2) musculi ]iapill:ires, somewhat conical flattened projections, continuous at the base with the wall and giving off the chordtp tendinea; to the tricuspid valve; (3) moderator bands (Musculi transversi cordis) which extend from the septum to the opposite wall. The latter arc partly nuiscular, partly tendinous, and vary in different subjects. The strongest one is usually about midway between the Ijase and apex and extends from the septum to the base of the anterior musculus papillaris. It is considered that they tenil to prevent overdistention. THE LEFT VENTKICLE 533 The Left Ventricle The left ventricle (\'entriculus sinister) forms the left posterior part of the ventricuhxr 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 anil 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 con- traction of its wall. It is almost circular in cross-section. The left atrio-ventricular orifice (Ostium venosum sinistrum) is opposite to the fifth rib and intercostal si)ace. It is almost circular and is guarded by the Origin of right coronary urttj-/ Conus arteriosus Pulmonary opening Origin of left coram iry artery Left atrio-ventricular opening. Fig. 425.— 1 ! been removed : [E Bases of the Ventricles of the Heaht of the Horse. \d the aorta and pulmonary artery cut off sfiort. The left ventricle V.V., Pulmonary valve; a. v., aortic valve. 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 (Valvute semilunares aortae) ; 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 valvulsp semilunaris). The chordae tendineae are fewer but larger than those of the right ven- tricle. There are two large musculi papillares, one on each side; they are usually 534 BLOOD-VASCULAR SYSTEM OF THE HORSE compound. The moderator hands 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 trabeculip are fewer and less prominent than in the right ventricle. The interventricular septum (Septum ventriculorum) is the musculo-memliran- ous partition which separates the cavities of the two ventricles. It is placet! ol)- liquely. 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 con- cave 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 compli- cated 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 Ijands fall naturally into two groups — superficial and deep. The former aic 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, wliile 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 l)e jjroper to each ventricle, have been shown by MacCallum to be in reality almost all conunon 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 attachetl 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. Tho.se which surround the origins of the pulmonary artery and aorta are festooned in confoi'mity with the attached borders of the valves. The aortic ring contains on the right .side a ])late 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 THE PVLMOXARY ARTERY THE SYSTEMIC ARTERIES 535 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 subenilocardial 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. IMost of the blood is returned by the coronary veins, which open into the right atrium by the coronarj- sinus.' 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 suliepicardial 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 ac- company the l)lood-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 ijase of the right ventricle. It curves upward, backward, and inward, and tlivides 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 pulmonarj- artery to the aorta in the foetus. 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 arterj' is about seven inches (ca. 17 to IS 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 arterj' 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 sj'stemic arterial trunk. It begins at the base of the left ventricle and is practically median at its origin. It pa.sses upward and slightly forward between the pulmonary artery on the left and right atrium on the right. It then curves sharply l)ackward and upward and inclines somewhat to the left, forming the arch of the aorta ( Arcus aortse), 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 vertebrte between the lungs it traverses the hiatus ' These vessels will be described later in their systematic order. 536 BLOOD-VASCULAR SYSTEM OF THE HORSE 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 aortae. Here it forms three pouch-like dilatations, the sinuses of the aorta (or uf Valsalva). These correspond to the cusps of the aortic valve, and the coronary arteries arise from the left posterior and anterior sinuse.s. At the arch the Ri(,hl Pidmnyiari/ rcitis pulntonari/ artery Great coronary rein Small corumiry vein l!ig}d coronary artery Fig. 426. — Cahdiac Vessels of Horse, Right Side. Veins are black, arteries white. diameter is about two inches (ca. 5 cm.), and beyond this it diminishes gradually in width. 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 attach- ment of the ligamentum artcriosum, 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 l)y the ocsophagits 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 v('rt('i)r;p, 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. COMMON BRACHIOCEPHALIC THUXK OR ANTERIOR AORTA 537 BRANCHES OF THE THORACIC AORTA I. CORONARY ARTERIES The two coronary arteries, riglit 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 back- ward. It then descends in the right ventricular groove almost to the apex of the heart. The left coronary artery (A. coronaria sinistra) arises from the left posterior Pulmonary veins Great coronary rein Left coronary artery, circumflex brancli. Descending branch of left coronary artery Great coronary vein Fig. 427. — C.^rdiac Vessels of Horse, Left Side. The dotteti lines indicate part of the left coronary artery which is concealed by the left auricle. sinus of the aorta, passes to the left lieliind tlie 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 f)r anterior aorta (Truncus brachiocephali- cus 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 bj- the left vagus and cardiac nerves, and the left recurrent nerve runs between it and 538 BLOOD-VASCVLAR SYSTEM OF THE HORSE the trachea. It divides opposite to the second intercostal space or tiiird ril) into the lirachiocephalir and left brachial arteries. The brachiocephalic artery (A. Ijrachiocephalica) is directed forward and a little iii)\vard in the anterior media.stinum, beneath the trachea. Opposite the first ril) 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 he described with the vessels of the thoracic linil). The left brachial artery (A. subclavia sinistra) is longer than the right one and ri.ses to a higher level. It forms an almost semicircular curve, the concavity being Fio. 428. — TopoGRAPnT of Thoracic Cavity of Horse, Xept Side, after Removal of Left Li'ng. The ninth, fifteenth, and eighteenth ribs are retained, a, Pericardium; h, thoracic aorta; c. brachio- cephalic trunk; rf, rf", dorsal artery; rf', subcostal artery; e, e', superior or deep cervical artery; /, vertebral artery; 0, (/', left brachial artery; h, inferior cervical artery; i, internal thoracic artery; k, common carotid artery; I, jURular vein; m, brachial vein; m', inferior cervical vein; n, anterior vena cava; o. thoracic duct; ;), rrsophagus; Q, costal part of diaphragm; (/, tendinous center of same; q", left crus of same; r, anterior mediastinal lymph- glands; ». trachea; /, bronchial lymph-glands; u, root of left lung; r, anterior mediastinum; v' , posterior medi- astinum; w, longus colli; x, sterno-cephalicus; 't, scalenus; z, transversalis costarum; /, longissimus; 2. splenius: B, spinalis et semispinalis; 4. 4'. rhomboideus; 5, left i>hrenic nerve: 6, left vagus; 6' , 6", oesophageal continuations of vagi; 7, dorsivl branch of right vagus; <9, cardiac nerve; 9, left recurrent nerve; 10, cervical trunk of sympathetic; //, first thoracic ganglion of sympathetic; IS, thoracic trunk of sympathetic; IS, brachial plexus, (.\fter Ellen- berger-liauin. Tojj. .\iiat. d. Pferdes.) ventral. It is related internally to the oesophagus, 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 iDeyond tliis their course and distribution are similar. The brachial and brachioce])halic 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 anil oesophagus toward the second intercostal sjiace. The right artery arises usually by a common trunk with the COMMON BRACHIOCEPHALIC TRUNK OR ANTERIOR AORTA 539 superior cervical, crosses the right face of the trachea and has no contact with the oesophagus. 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 inter- costal 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 Fig. 429. — Topography of TiioRAnr Cavity of Horsf, Right View. The ninth, fifteenth, ami eighteenth ribs are retained, a, Pericardium; 6, posterior vena cava; c, vena azygos; c'. oesophageal vein; rf, e, anterior vena cava; /, brachial vein; g, inferior cervical vein; h, jugular vein; I, vertebral vein; k, superior cervical vein; I, dorsal vein; 7?i. trachea; n, root of right lung; o, trsophagus; p, mediastinal lobe of right lung; g, mediastinum; r, bronchial Ijmph glands; s, mediastinal lymph glands; (, costal part of (liaphragm; i', tendinous center of same; w, intercostal muscle; r, longus colli; u', po.sterior deep pectoral muscle; w' , anterior deep pectoral muscle; i, superficial pectoral muscle; y, sterno-cephalicus; z, scalenus; /, 6, right brachial artery; 2, dorso-cer\-ical trunk; 3', superior or deep cer\-ical artery; 3, dorsal artery (cut); 3', subcostal artery: 4. internal thoracic artery; 6, external thoracic artery; 7. inferior cervical artery; S, bicarotid trunk; 10, aorta; 11, oesophageal artery; 12, thoracic duct; 13, right phrenic nerve; 14, brachial plexus; 15, right vagus; 15', IS", esophageal continuations of vagi; IB, right recurrent nerve; 17, cervical trunk of sympa- thetic; l,i. thoracic trunk of sympathetic; SO, inferior cervical ganglion; SI, first thoracic ganglion of sympathetic; S3, right cardiac nerve; 23, longissimus; 24, transversalis costarura; 2d, spinaUs; 26, multifidus; 27, ligamentum nuciia?. (After EUenberger-Baum, Top. Anat. d. Pferdes.) the second intercostal space, passes across the transversalis costarum and longissi- mus toward the withers, and divides into several diverging branches. An anterior branch passes upward and forward Ijetween the splenius and complexus and anas- tomoses with branches of the superior cervical artery; the others are directed upward under the serratus magnus and rhomlioideus to the withers, supplying the muscles and skin of this region. 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 ar- teries. 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. 540 BLOOD-VASCULAR SYSTEM OF THE HORSE 2. TliP superior or deep cervical artery (A. cervicalis profunda) arises in front of the dorsal or liy a common trunk with it. It crosses the cesophgaus (left side), the trachea (right side), and the longus colli, and emerges from the thoracic cavity l)y passing through the space behind the first cost o-trans verse articulation. In the thorax it gives off a small branch (A. mediastini cranialis) to the mediastinum and the pericardium; also the first intercostal arterj' (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 nuchiB, 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 nuclue, anil the skin, and anastomoses occur with the dorsal artery above and the vertebral artery below. The artery sometimes emerges throush the seeond intercostal space. 3. The vertebral artery (A. vertebralis) arises from the brachial for brachio- cephalic) opposite the first intercostal space and passes upward and forward. On the left side it crosses the oesophagus, 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 Verlebral arterij Fig. 430. — Vertebr 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 occi- pital artery under cover of the great oblique muscle of the head. At each inter- vertebral foramen a spinal branch ( Ramus spinalis) is given off which enters the vertebral canal and reinforces tlic \cntral spinal artery. It also gives off series of dorsal and ventral muscular branches 'Rami nuisculares). The dorsal branches are the larger; they supply the deep exten.sor muscles of the head and neck, and anastomose with the deep cervical and occipital arteries. The ventral liranches supply chiefly the scalenus, longus colli, intertransversales, and rectus capitis anterior major. The artery is accompanied by the vertebral vein and a sym- ])athetic nerve trunk. In some oases the last cervical transverse process has a foramen transversarium, through whicli the artery [Kusses. 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 trans- versus thoracis muscle. It runs backward tmder 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 THE COMMON CAROTID ARTERY 541 branches arc dctachod. The intercostal branches (Rami intorrostales) pass upward in tlio intercostal sjiaces and anastomose witii liomonymous descending arteries. Tlie lower branches detach small twigs to the transvers\is thoracis, ])lcura, 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. thymicse) 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 anas- tomose 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 be- tween the ninth costal cartilage and the xiphoid cartilage, runs backward on the abdominal sia-face 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 alxlominal 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 witli 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 cUvides 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 jjrescapular lymph- glands; it gives branches to these muscles and the prepectoral and prescapular lymph glands. The descending branch (A. transversa scapulae) 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 (Arteriae carotides communes) arise from the brachio- cephalic 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 rih 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, anrl laterally to the vagus and recurrent nerves. It is commonly 542 BLOOD-VASCULAR SYSTEM OF THE HORSE two or three inches (ca. 5 to 7 cm.) in length, liut it may varj- between one and eight inches (ca. 2.5 to 20 cm.). The right common carotid artery passes obhquely 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 Fig. 431. — Vessels and Nerves of Neck of Horse. a, Mastoido-huraeralis; 6, sterno-cephalicus; c, omo-hyoideus; d, sterno-thyro-hyoideua; c, trachea; /, posi- tion of cariniform cartilage: fl. anterior superficial pectoral muscle; A, scalenus; i', intertransversales; A:, insertion of serratus cervicis; /. origin of trapezius; m, rhomboideus; n, splenius; o, complexus; p. i^, trachelo-mastoideus: p', ^, tendons of same; r, longissimus; s, obliquus capitis posterior; (, wing of atlas; u, parotid gland; v, supra- spinatus; w, anterior deep pectoral; j, spine of scapula; .y, prescapular lymph glands; /, external maxillary vein; S. S, jugular vein; 4, carotid arter.v, exposed by drawing jugular vein aside; 5. 6, ascending anil descending branches of inferior cervical artery; T, cephalic vein; S, branches of superior or deep cervical arter.v; 9-14. ventral branches of second to seventh cervical nerves; to, branches of dorsal divisions of cervical nerves. (Ellenberger-Baum, Top. Anat. rl. 1'ferde.s.) nerves, ventrally by the recurrent nerve. At the last two cervical vertebrae it is in contact superficially with the jugular vein, but further forward the omo-hyoideus muscle intervenes between the artery and vein. Near its ter- mination the artery becomes more deeply placed and is related externally to the submaxillary and parotid glands, internally to the oesophagus. In some cases it is in contact ventrally with the thyroid gland, especially when the latter is larger than usual. THE COMMON CAROTID ARTERY 543 Tlir left common carotid artery diftVrs from the right one in that it is related deeply to the a'sophagus, 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 com- prise: 1. Muscular branches (Rami muscu- lares) of variable size, which go to the ventral mnscles of the neck and the skin. 2. (Esophageal and tracheal branches (Rami ocsophagei et trachoales). Small twigs go to the cervical lymi:)h 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. thy- reoidea cranialis). This, the largest col- lateral branch of the carotid, arises from the latter two or three inches before it divides. It curves over the anterior end of the thjToid gland, into which it sends several branches. It gi\es off a lar3mgeal branch (A. laryngea), which sends tAxigs to the external muscles of the larynx and the constrictors of the pharynx, passes between the cricoid and thyroid cartilages, and sup- plies the internal muscles and the mucous membrane of the larynx. A small phar3ni- geal branch (A. pharyngea ascendens) runs upward antl forward to the crico-pharyn- geus, and supplies twigs to the posterior part of the pharynx and the origin of the oesophagus. Small innominate twigs are given off to the trachea, the oesophagus, and the sterno-thyro-hyoideus anil omo- hyoideus muscles. In some cases the thxroid anil 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 larj-nx with the superior laryngeal nerve. The pharyngeal branch frequently comes directly from the carotiil. 5. The accessory thyroid artery (A. thjTeoidea caudalis) is an inconstant vessel which arises from the carotid at a vari- able distance liehind the thyro-laryngeal — sometimes from the latter or from the i)aro- tid arterJ^ 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. Fig. 432. — Choss-section of Neck of Horse, Passing through Fifth Cervic.\l A'er- TEBR.\; .\nterior View. a. Branches of cer\'ical nen'es; a', nuchal fat; b, intertransversalis muscle; c, longissimus muscle; d, vertebral artery; e, vertebral vein; /, vertebral nerve; g, spinal accc-s-^ory nerve (upper division); h, recurrent nerve; /, vago-sympa- thetic trunk; ^^ tracheal lymph duct; /, body of fifth cervical vertebra; /', transverse process of same; m, carotid artery; n, jugular vein; o, superior cer\'ical arterj-; o' , satellite vein of o, p, spinal cord; q. dura mater; r, spinal vein; s ligamentum nuchte; /, rhomboideus muscle u, splenius; v, complexus; w, niultifidus; x serratus cervicis; y, mastoido-humeralis; z sterno-cephalicus; 1, rectus capitis ant. major; ■2, omo-hyoideus; S, panniculus; 4. sterno- thyro-hyoideus; 5, longus colli; 6, 7, trachelo- mastoideus; S, trapezius; 9. spinalis; 10, cesophagus; //, trachea, with cartilaginous ring {II'), mucous membrane ill"), and mus- cular layer {il'"). (After Ellenberger. in Leiser- ing's Atlas.) 544 BLOOD-VASCULAU SYSTEM OF THE HORSE THE OCCIPITAL ARTERY 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 Fig. 433. — Deep Dissection op Neck op Horse. a, a, Ends of sterno-cephalicus; 6, anterior part of omo-hyoideus; c, sterno-thyro-hyoideus; d, trachea; c, OESophaRUs; /, cariniform cartilage; g, rectus cap. ant. major; h, stump of trachelo-mastoideus; i, iotertraris- versales; /.-, multifidus; f, m, scalenus; n, serratus cer\icis; o, o, stumps of splenius, j?, longissimus. g, complexus (most of which is removed) ; r, rhomboideus; s, trapezius; (, spinalis et semispinalis; u, lamellar part of lig. nuchip; V, mastoido-humeralis; w, anterior deep pectoral; x, supraspinatus; y, anterior superficial pectoral; z, scapular tuberosity; /, /, articular processes of cervical vertebrse; 2, 2, transverse processes of same; ^, atlas; 5', axis; 4, A. jugular vein (remainder removed;; 5. common carotid artery, from which a piece is removed to show the ac- companying nerves; 6, vago-sympathetic trunk; 7, 7, tracheal and muscular branches of carotid artery; S, re- current ner\-e; 10, left tracheal lymph-duct; //, 12, ascending and descemling branches of inferior cervical artery (/3); 14, cephalic vein; 13-20, ventral branches of second to seventh cervical ner\'es; 21, roots of phrenic nerve; 22, thoracic or pectoral nerves; 22' , nerve to serratus magnus; 2S, musculo-cutaneous nerve; 24, median nerve; 25, ulnar nerve; 26, radial nerve; 27, axillary nerve; 2S, dorsal branches of cervical nerves; 28' , accessory nerve (cut); 29, superior or deep cervical artery; SO, muscular branch of vertebral artery; 31, posterior (anastomotic) branch of occipital artery; 32, vertebral artery; 55, 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.) with that artery by a common trunk of variable length. It pursues a somewhat fiexuous 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 THE OCCIPITAL ARTERY 545 major.' Tlie internal carotid artery, the inferior cerebral vein, and the accessory, vagus, and sympathetic nerves cross its deep face. It gives twigs to the sub- maxillary gland, the anterior straight muscles, the guttural pouch and the adjacent lymph glands, and two named collateral branches. The condyloid or pre- vertebral artery (A. condyloidea) is a small vessel which passes up- ward and forward on the guttural pouch, and divides into muscular and meningeal branches. The latter enter the cranium through the foramen lacerum and hj'po- glossal foramen and are dis- tributed to the dura mater. This artery is very variable in its origin. The posterior meningeal or mastoid artery (A. nieningea caudalis) is a much larger vessel which runs upward and forward between the small olilique muscle and the paramastoid process, passes through the mastoid fora- men into the parieto-temporal canal, enters the cranial cavity, and is distributed to the dura mater. The posterior or retrograde branch (Ramus dcscendens) 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 occipitalisj passes through the alar (antero-ex- ternal) foramen of the atlas and supplies the muscles and skin of the poll, anastomosing with the deep cer\'ical artery and its fellow of the opposite side. In the alar furrow it gives off the cerebrospinal artery, which en- ters the s]iinal canal through the intervertebral (antero-in- ternal) 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 . 434. — Vessels t iNe OF Base of Brain of Horse. IS, 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; Bl , stump of internal carotid artery; 22, anterior choroid artery; 23, anterior menin- geal artery; 24, middle cerebral artery; 25, artery of corpus callosum; 26, anterior communicating artery; /, /', 1", ol- factory tracts; 1'" , olfactory peduncle; 2-12, cranial nerves; a, olfactory bulb; b, trigonum olfactorium; c, lamina perforata anterior; d, fossa transversa; e, pyriform lobe; /. cerebral peduncle; g, tractus transversus; h, corpus mammillare; i, tuber cinereum; k, lateral fissure (of .Sylvius); /, presylvian fissure; m. pons; o. pyramid; p, facial eminence; q, corpus restifornie; r, cerebellum; s, middle peduncle of cerebellum, (.\fter Ellen- berger Baum. Top. .\nat. d. Pferdes.) ^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. 3.5 546 BLOOD-VASCULAR SYSTEM OF THE HORSE 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. ]\Iedullarj' branches (Rami medullares), ten or twelve in numlier, dis- tributed 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 car. It often arises from the posterior cerebellar. 4. Anterior cerebellar arteries (Aa. cerebelli nasales). These are very variable in immbcr and origin. There are often two or three on either side and they fre- quentlj' 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. conimunicantes caudales) diverge at an acute angle and join the posterior communicating branches of the internal carotid arteries on the inferior surface of the cereliral 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 lacerimi. 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 conimiuiicating 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 jiostcrior) turns back- ward and joins the posterior cerel)ral. It gives off the deep cerebral artery (A. cerebri profunda) which winds around the cerebral peduncle and is distriluited 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 tho 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 pro- ceeds 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) jiasses outward in the lateral fissure (of Sylvius) and divides into branches on the outer surface of the hemisphere. The arterial circle of AVillis (Circulus arteriosus) (Fig. 434) is formed at the THE EXTERNAL CAROTID ARTERY 547 interpeduncular space of the base of the brain by the union of the anterior cere- liral arteries in front, l)y the diverging posterior cerebral arteries behind, and is completed laterally by the junction of the latter with the posterior communi- cating arteries and by the internal carotid. It is irregularly polygonal in out- line. The ci'reliral arteriog are vory variable in arrangement, and the foregoing account is a brief statement of the more usual disposition of the larger vessels. Tlie 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 con- tinuation 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 stj'lo-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 termin- ates about two inches (ca. 5 cm. ) below the temporo-maxillary articulation by divid- ing 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, ex- ternal maxillary, and posterior auricular. It also furnishes variable branches to the submaxillary and parotid glands, the guttural pouch, and the pharyngeal h'mph glands, as well as twigs to some adjacent muscles. 1. The inferior masseteric or maxillo-muscular artery fA. masset erica inferior) is given off from the external carotid at its emergence from beneath the stylo- hj'oideus. It passes do'maward 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 ])arotid gland. 2. The external maxillary, facial, or submaxillary artery ( A. maxillaris externa)' arises from the external carotid on the inner surface of the posterior belh- of the di- gastricus (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 hj-- poglossal 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 for- ward in the submaxillary space. Here it lies on the lower part of the internal pterygoid muscle, and is related internallj' 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." 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 zj'gomaticus, and are crossed superficially by branches ' By some authors the term facial is applied to the artery only after it turns aroimd the lower border of the jaw. - The artery is conveniently placed at its inflection for taking the pulse, .since it is super- ficial and lies directly on the bone. 548 BLOOD-VASCULAR SYSTEM OF THE HORSE of the facial nerve and deeply l)y the parotid duct. The artery terminates over thelevtaorlabii j'uperioris proprius by dividing into the dorsal nasal and the angu- lar 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 for- ward on the lateral wall of the pharynx under the elastic pharyngeal fascia. It is distributed to the soft i)alate, pharynx, and tonsil. (2) The lingual artery (A. lingualis) is a large branch which diverges from the parent tnuik'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 Fig. 435. — Superficiai. DissKmoN of Head of Horse. Most of the Panniculus is Removed. a. Dilatator naris superior; 6, levator labii superioris proprius; c, levator naso-labialis; d, dilatator iiaris lateralis; c, buccinator; /, zygomaticus; g, depressor labii inferioris; h, stump of retractor anguli oris; )', nias- seter; k, k, scutularis; /, 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; /, corrugator supercilii; u, orbicularis oris; v, parotid gland; w, z.vgomatic arch; x, scutiform cartilage; l/, upper commissure of nostril; 1, facial nerve; 2, superior buccal nerve; rf, 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; S, infratrochlear nerve; 9, frontal nerve; 10, lacrimal nerve; W, end of auriculo-pali)ebral nerve; Jl, inferior masseteric artery and vein; 13, transverse facial artery and vein; 13, facial artery; 14, inferior labial artery; IS, superior labial artery; 16, lateral nasal artery; 17, dorsal nasal artery; IS, angvilar artery of the eye; / 9, posterior auricular artery; ^0. ;?/, jugular vein; ;?.g, external ma.xillary vein; 55, great auricular vein; 2.<. parotid duct; 24', origin of same. (After Ellenberger-Baum, Top. Anat. d. Pferdes.) the kerato-hyoideus, turns inward under tlie intercornual joint of the h>oid bone, and runs forward in the tongue between the hyo-glo.ssus and genio-glo.ssus. This l)art (A. jirofunda linguie) is flexuous and is accompanied by branches of the hypo- glossal and lingual nerves. It is the chief artery of the tongue, and anastomoses with the opposite artery aiul the sublingual. (3) The sublingual artery (A. sublingualis) is a smaller vessel w Inch 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. THE EXTERNAL CAROTID ARTERY 549 It detaches branches to the muscles and skin in the sulmiaxillary space, the sub- maxillary 1} inph glands, antl 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 mvlo-hvoideus. Fig. 436. — Parotid. Masseteric, and Lingual Regions of Horse: Deep Di.ssectiox. Third Layer. a, Mylo-hyoideus, anterior part, reflected: 6, genio-hyoideus; c, genio-glossus: d, sublingual gland; c, ramus of mandible, the greater part of which is removed: e', stump of masseter; /, maxillary tuberosity; 7, great cornu of hyoid bone; A. wing of atlas; (, intermediate tendon of digastrieus; i"', anterior belly, i", posterior belly of digastricus; k, posterior part of mylo-hyoideus; /, hyo-glossus; m, pterygoideus internus (cut); n, stylo-hyoideus; o, stylo-maxillaris (cut); p, crico-pharyngeus; q, obliquus capitis ant.; r, tendon of trachelo-raastoideus; 8, rectus cap. ant. major; t, mastoido-humeralis (cut); u, sterno-cephalicus (cut); r. sterno-thyroideus (cut);u', sterno-hyoideus (cut); x, omo-hyoideus; i/, obliquus cap. post.; z, splenius (cut); l-J,, upper cheek teeth; 4', last cheek tooth; 5, stump of facial nerve; 6, stump of buccinator nerve; 7, lingual ner\'e: /'.superficial branch. 7", deep branch of lingual nerve; 5, stumps of inferior alveolar artery, vein and ner\'e; S, mylo-hyoid nerve (cut); 10, glosso-pharyngeal nerve; //, hypoglossal nerve; 12, superior laryngeal nerve: i5, 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; i5, submaxillary duct; ^5, common carotid artery; ^0, parotid branch; 31, 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; 2S, posterior palatine artery; 29, lingual artery: 30, sub- lingual artery; 32, internal maxillary artery; S3, internal maxillary vein (origin): 34, remnant of parotiri gland; 35, thyroid gland; 36, jugular vein; 37, pharj-ngeal lymph glands, (.\fter 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 subhngual remains on the external face of tlie mylo-hyoideus — thus resembling the submental of man — and the sublingual gland is supplied by a special branch of the Ungual. 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 mem- brane of the cheek, and the lower lip, anastomosing with the mental artery and the corresponding vessels of the oppo.site side. It detaches a branch (A. anguli oris) to the angle of the mouth, which anastomoses with the superior labial. 550 BLOOD-VASCULAR SYSTEM OF THE HORSE (5) The superior labial artery (A. laliialis superior) arises from the facial in front of the facial crest (Fig. 435). It pa.sses forward under the dilatator naris lat- eralis and levator nasoIaljiaUs to the upper lij), 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 tlic jialato-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 lal)ial at the point of hifuroation of tlie facial or with the dorsal nasal from the infraorbital artery (as in the ox). In some cases it gives olT a dorsal nasal l)ranch. (7) The dorsal nasal artery (A. dorsalis nasi) arises on the levator labii superi- oris proprius and passes forwartl under the levator nasolabialis to the tlorsum 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 adtlition to the preceding, unnamed branches are supplied to the submaxil- lary 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 intermedins) passes up the convex surface of the extei^nal ear to the apex, while the other (Ramus medialis) winds around to the anterior (inner) border, and forms an arch with the inter- mediate 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 (.\. auricularis profunda) enters the interval between the exter- nal 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 stylomastoid artery, which passes through the stylomastoid foramen into the tym- panum, forms an arch arouiul 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 bonier of the ramus of the mandible under cover of the parotid glanil, and diviiles below the level of the condyle into the anterior aiu'icular and transverse facial arteries. It is crossed superficially by the facial nerve. The anterior auricular artery (A. auricularis anterior) passes upward behind the temp(jro-ni:uidil Hilar 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-i)alpebral branch of the facial nerve. It is distributed to the skin and the temporal and anterior auricular muscles, and sends a liranch through the conchal cartilage to the skin which lines it. Collateral twigs are detached to the jiarotid gland, and an anterior branch anastomoses with the supraorbital artery. A branch sometimes passes into the parieto-temporal canal ami anasto- moses with the jiosterior meningeal (mastoid) artery. The transverse facial artery (A. transversa faciei) is larger than the preceding. THE INTERNAL MAXILLARY ARTERY 551 It turns around the neck below the condyle of the nian(Uble and emerges from be- neath the parotid j»;land (Fig. 435), It then passes forward a short distance on the masset(*r about half an inch below^ the zygomatic arch and plunges into the muscle, in which it commonly divides into two chief branches. It is accom- panied by a vein and a branch of the superficial temporal nerve. It supplies the 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 styloglossus; b, genio-glossus; c, genio-hyoideus; d, omo-hyoideus; e, kerato-hyoideus; /, thyro-hyoideus; g, thyro- pharyngeus; h. crico-thyroideus; (, sterno-thyroideus; A:, thyroid gland; m, crico-pharyngeus; n, palatinus and palato-pharyngeus; t», pterygoideus externus; p, tensor palati; g, levator palati; r, temporalis; s, rectus cap. ant. major; (, obliquus cap. ant.; u, guttural pouch; v, great cornu of hyoid bone, posterior extremity of which is removed and indicated by dotted line; U', position of small cornu, dotted line; x, thyroid cornu; y, tongue; z. anterior pillar of soft palate; 1 , superficial temporal nerve; $, chorda tympani; S, stump of inferior alveolar ner\'e; 4- 4, Ungual nerve, intermediate part removed; 5, deep temporal ner\'e; 6, masseteric nerve; 7, buccinator nerve; 8, great palatine nerve; 9, infraorbital nerve; 10, sphenopalatine and posterior nasal ner\'es; 11, spinal accessory ner\*e; 12, vagus; 13, pharyngeal branch of vagus; 14, superior laryngeal ner\'e; Id, vago-sympathetic trunk; 16, .sympathetic, with superior cervical ganglion a little further back; 17, glosso-pharyngeal nerve; IS, phar>'ngeal and 19, lingual branches of glosso-pharyngeal; 20, hypoglossal nerve; SI , left recurrent ner\-e; £2, common carotid arterj-; 23, parotid branch; 24, thyro-laryngeal artery; 24', laryngeal artery; 25, occipital artery; 26, internal carotid artery; 27, external carotid artery; 2S-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; -jff, dottetlhne indicating outline of submaxillary gland; ^7, lacrimal gland. (After EIlenherger-Baum, Top. Anat. d. Pferdes.) masseter and the skin of this region, and anastomoses with the external maxil- lary and posterior deep temporal arteries. The pulse may usually be felt in this artery as it passes below the arti<'uIation 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 552 BLOOD-VASCULAR SYSTEM OF THE HORSE 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 iiaferior 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 mandibulir s. in- ferior) 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 downwartl and forward in the mandibular canal, and terminates at the mental fora- men by tlividing into mental and incisor branches. The mental branch (A. nien- talis) emerges through the mental fora- men and anastomoses in the lower lip with the opposite artery and the inferior lal)ial. The incisor branch continues for- ward in the bone, supplies twigs to the canine and incisor teeth, and anastomoses with its fellow of the opposite side. Col- lateral branches are detached to the ptery- goid 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. 4. The middle meningeal artery (A. mcningea media) arises beneath the buc- cinator nerve where the internal maxillary turns forward. It passes backward across the temporal wing of the .sphenoid to the antero-e.xternal 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 tliis artery is variable, and is in inverse ratio to that of the posterior meningeal. 5. The posterior deep temporal artery (A. temporalis profunda aboralis) Fig. 438. — Right Eve of Horse. a. Remnants of periorbita; b, levator palpe- brse superioris; c, obliquus oculi inferior; d, rectus oculi inferior; e, rectus oculi externus; /, rectus oculi superior; g, sclera; {/.' cornea; h, lacrimal gland; /, frontal nerve; k, frontal arterv; I, branch of lacrimal ner\'e to gland; in, lacrimal artery; n, zygomatic nerve; o, branch of ophthalmic artery; p, branch of oculomotor ner\'e to obliquus oculi inferior; (j, maxillary nerve; r, infraorbital nerve; 8, posterior nasal nerve; t, great palatine nerve; «, small palatine nerve; r, internal maxillary artery; w, buccinator artery (cut); x, infraorbital artery; j:', malar artery; y, sphenopalatine artery; s, great palatine artery; /, small palatine (or staphyline) artery; /, posterior deep temporal artery; 5, S, stumps of orbital margin; .{.facial crest; 5, temporal fossa; 6. foramen lacerum orbitale; 7, anterior end of alar canal; S, posterior opening of same. (After Ellenberger, in Leisering's .\tlas.) THE INTERNAL MAXILLAKY ARTERY 553 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 ana.*tonioses with the superficial temporal and middle men- ingeal arteries. In some cai?rs 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 liranches — 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, Fir,, 439. — Left Eye of Horse, Deeper Dissectiox. The outer plate of bone has been removed behind the pterygoid crest to expose the vessels and nerves. a, a. Remnants of periorbita; 6, stump of rectus ocuh superior; c, obliquus oculi inferior; d, rectus oculi inferior; e, rectus oculi lateralis; f', retractor oculi; /, rectus oculi internus; g, g, obliquus oculi superior; /(. eyeball; i, trochlear ner\-e; k. ophthalmic ner\'e; k' , nasal nerve; k", infratrochlear nerve; k'", ethmoidal nerve; I, optic ner\-e; m. frontal nerve; n, lacrimal ner\'e; o, zygomatic ner\'e; p. nei^'e to obliquus inferior (from oculomotor); q, maxillary nerve; r, infraorbital nerve; s, sphenopalatine nerve; ^ great palatine nerve; », small palatine nerve; V, internal maxillary artery: w, buccinator artery (cut off); x, infraorbital artery; a-', malar artery; y, spheno- palatine artery; s, great palatine artery; z' , small palatine (or staphyline) artery; 1 , 2, stumps of zygomatic arch; ,:?, stump of supraorbital process; 4, facial crest; 5, temporal fossa; 6, ophthalmic artery; 7, muscular branch of 5; ,•?, lacrimal arter>' (cut); 9, frontal artery; 10, anterior deep temporal artery; 11, ethmoidal artery, (.\fter EUenberger-Baum, Top. .\nat. d. Pferdes ) in which it is chiefly distributed. It gives twigs to the orbital fat and the skin of the frontal region, 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 b.y the ethmoidal artery. Its branches are as follows: (a) The supraorbital or frontal artery (A. supraorbitalis)' is a small vessel which often arises from the anterior deep temporal or the internal maxillarj-. 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. (6) The lacrimal artery (A. lacrimalis) runs upward and forward within the ' This vessel appears to represent both the supraorbital and frontal of man. 554 BLOOD-VASCULAR SYSTEM OF THE HORSE periorbita along the outer edge of the loviitor palpebrae superioris to the lacrimal gland, in which it is chiofly distrilDuted. It also sends twigs to the upper eyelid. (f) Muscular branches (Rami musculares) supply the orbital nuisdos, the periorbita, the third cyclitl, and the conjunctiva. (f/) 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. ciliaries 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 Fig. 440.— S. Section of He Horse, Cut a Littli Ri. Mediax Plane. 1, Skin; 2, nasal bone; 3, frontal bone; 4, parietal bone; 4', tentorium osseum; 6, occipital bone; 6, sphenoid bone: 7, hard palate; 5, premaxilla; 5, mandible; iO, hyoid bone; i/, septum between frontal sinuses; IS, alar cartilage; 13, dilatator naris transversus; 14, septum nasi with venous plexuses, 16, palato-labial artery JG, 16', upper and lower septal branches of 16; 17, septal branch of sphenopalatine artery and satellite vein IS, septal branch of ethmoidal artery; 13, sphenoidal sinus; 30, guttural pouch; 21, pharynx; 22, pharyiigea! orifice of Eustachian tube; 23, posterior naris; 24, soft palate; 26, palatinus muscle; 26, pharyngeal muscles 27, oesophagus; 2S, dotted line indicating position of posterior pillar of soft palate; 29, lamina; ^9', arch of cricoid cartilage; 60, arytenoideus transversus muscle; SI, ejjigiottis; S2, body of thyroid cartilage; SS, vocal process and cord; 5.{, arytenoid cartilage; 55, lateral ventricle of larynx; 3G, trachea; rf7, ventral straight muscles of head; 38, longus colli; 39, atlas; 40, axis; ^/, lig. nuchce; 42, dorsal spinal muscles; 43, muscles of external ear; 44, omo- and sterno-hyoideus; ^5, tongue; .45, mylo-hyoideus; ^T*. genio-hyoideus; 4'?. genio-glossus; 45, longitudinalis inferior; 60, longitud. superior; 61, hyo-ei)iglotticus; S2, chin and mentalis muscle; 63, venous plexus of hard palate; 64, corpus callosum; 66, septum pellucidum; 66, fornix; 67, thalamus; 6S, pineal body; 69, corpora quadrigemina; 60, cerebral peduncle; GI, corpus mammillare; 62, pituitary body; 63, chiasma opticum; 64. inter- carotid artery; 65, medulla oblongata; 66, interventricular foramen; 67, infundibulum; 6S, third ventricle; 69, cerebral aqueduct ; 70, anterior medullary velum; 7/, fourth ventricle; 73, posterior medullary velum; 7.J, basilar artery; 74, spinal cord; 76, ethmoitlal nerve; 76, septal branch of posterior nasal nerve; 76', branch of same to organ of Jacobson; 77, olf.actory nerve to organ of Jacobson; 75, nasal branches of palatine artery, (.\fter Ellen- berger, in Leisering's .\tlas.) arteries, run forward, one on each side, between the sclera and choroid to the perii)hery of the iris. Here they divide into branches which anastomose and form a circle (C'irculus iridis major). From this secondary branches arc detached which form a .secoml circle around the ptij^il (Circulus iriilis minor). (e) The central artery of the retina (Arteria centralis retinae) is a small vessel which arises from the ojihthalmic or from a posterior ciliary artery. It pierces the optic nerve a short distance liehind 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 antl radiate in the posterior part of the retina. (/) The ethmoidal artery (\. ethmoidalis) is the continuation of the oph- THE INTERNAL MAXILLARY ARTERY 555 thalmic. It enters the cranial cavity through the ethmoidal foramen, passes inward on the cril^riform 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 ami the adjacent part of the septum nasi, and runs forward on the superior turbinal. The third part passes forward in the pterygo-palatine fossa, accomi:)anied 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. 437j. It turns around the max- illary tuberosity, accompanied liy 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 maxil- lary 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 groo\'e at the inner side of the maxillary tuber- ositj' 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 iJterygo-palatine fossa and passes into the nasal cavity, where it divides into internal and external liranches. 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 infraorljital. (5) The palatine or palato-labial artery (A. palatina major) is the direct con- tinuation of the internal maxillary. It passes through the palatine canal to the roof of the mouth, accompanied by the palatine nerve, and rims forward in the palatine groove, where it is joined l^j' the vein. A little behind the plane of the corner incisor teeth it curves inward over a bar of cartilage to the foramen in- cisivum, 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 anasto- mose 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. Com- monly 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. 556 BLOOD-VASCULAR SYSTEM OF THE HORSE Arteries of the Thoracic Limb THE brachial ARTERY The brachial artery, after turning around the lower liorder 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 sub- scapular arter}', 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.' It is related internally to the serratus magnus and the posterior deep pectoral muscles, and the cut)ital 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 ve-;-;?l, which arises near the anterior liorder of the subscapularis, runs upward, and dips in between that muscle antl the supraspinatus. It gives ])ranches 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 infeiior 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 inter- stice between that muscle and the teres major on the inner surface of the long head of the triceps, turns aroimd 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 fasciae 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 v(>ssel 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 scapula?) arises about two or three inches (ca. ."> to 7..') cm.) above the shoulder joint, passes forwaril to the posterior bortler of the scapula, and divides into two liranches. 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 supjilies branches to the subscapularis. ' The term axillary is often applicj to the artery from the (irst rib to the point of origin of the subscapular branch. THE BRACHIAL ARTERY 557 Posterior deep pecto- ral muscle Tendon of panniculus Neroe to biceps Anterior circumflex artery Anterior superficial pectoral muscle Extensor carpi radiahs Radius Accessory cephalic letn Fig. 441. — Dissection of Shoulder % '•■:■• Mi- I Sirimk. A, Brachial artery; B, .subscapular artery; C, thoracico-dor.sai artery; D. deep brachial artery; E, ulnar artery; F, anterior radial artery; G, posterior radial (or median) artery; H, brachial vein; /. external thoracic (or ".spur") vein; J, brachial vein; K, K, K, posterior radial veins; L. cephalic vein; L\ contmunicating vein; M, brachialis muscle; -V, internal epicondyle of humerus; O, prescapular lymph glands; F, position of axillary lymph glands: 0, position of cubital lymph glands; /, suprascapular nerve; S. subscapular nerves; 3, thoraco- dorsal ner\-e; 4. musculo-cutaneous nerve; 4'. cutaneous branch of musculo-cutaneous nerve; o. median iier\'e: tf, a.xillary nerve; 7. ulnar nerve; 5, radial nerve; 9, thoracic nerves. (After Schmaltz, .\tlas d. .\nat. d. Pferdes.) 558 BLOOD-VASCULAR SYSTEM OF THE HORSE 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 I'l/tar rurre Brachial vessels Median nerve Cephalic vein Anastomotic l)i-anch Ciitnncous briinrli of imilian nerve Extensor carpi radialis Median nerve Accessory cephalic vein Cephalic vein Post, radial (or median) artery Flexor carpi inlernus (cut) Internal lateral ligament of carpus Tendon of extensor carpi obiiquus Metacarpal tuberosity Dorsal interosseous artery and nerve Fic. •)42.- C-b.. Coraco-brat'hial t'Tiox OF Right Forearm and Carpi's B.m., internal epicondyle of humerus; R, ^ Schmaltz, Atlas d. Anat. d. Pfcrile Long licad of triceps Internal head of triceps Ulnar vessels Tensor fasciiF antibrachii {cut) Inar head of flexor carpi medius Humeral origin of flex, carpi med. Origin of flexor carpi inlernus Common i7iterosseous artery Superficial flexor of digit Ulnar head of deep flexor Fascia, cut and reflected Deep flexor of digit Ulnar vessels and nerve Outer branch \ of median Inner branch j nerve Tendon of flexor carpi internus Flexor carpi medius (cut) E.tt. volar met. artery E.H. met. nerve E.rt. met. vein Int. met. nerve Large met. artery Int. volar met. artery Branch to deep volar arch Superficial flexor tendon Check ligament Internal metacarpal vein Internal Sirface. bcutaneous surface of ratlins. antl the humerus. It givps branches to the coraco-bracliialis and deep ])ectoral and ends in the upjier part of the biceps and in the mastoido-lunucralis. It anastomoses with the posterior circumflex. THE POSTERIOR RADIAL ARTERY 559 Not rarely it arises below the middle of the humerus and passes upward between the biceps and coraco-brachialis. In those 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 hut short trunk which arises usually about the niidiUe of the humerus. It passes backward and divitles into several branches which supply the triceps, tensor fasciae antibrachii, anconeus, and l)rachialis. A liranch runs in the musculo-spiral groove with the radial nerve to the front of the elliow joint and anastomoses with the anterior ratlial. A slender branch passes down along the external border of the extensor carpi and supplies cutaneous twigs. Anastomoses occur with the ulnar and recur- rent interosseous arteries. The point of origin is inconstant and it is not uncommon to find two arteries instead. Often a large branch for tlie 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 foramt'u 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 ten.sor fascia antibrachii. It gives branches to these muscles, the posterior superficial pectoral, the cubital lymph glands, panniculus, and skin. At the inter- nal epicondyle of tlie 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 lietween 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 carjji externus) with a Ijranch of the radial artery, with which it forms the supra- carpal arch. It detaches small collaterals to the muscles along which it passes and terminal twdgs to the outer surface of the carpus. 7. The nutrient artery of the humerus (A. nutritia humeri) is a short vessel which enters tlie nutrient furanuMi i)f the humerus. It often arises from the ulnar. 8. The anterior radial artery l.\. collateralis radialis inferior) passes downward and a little outwartl on the anterior face of the humerus under cover of the liiceps 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 cUgit 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 elliow joint, under cover of the posterior superficial pectoral muscle.' 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 tendin- eum) of the superficial flexor of the digit and is continued by the large metacarpal artery. ' The pulse can be taken where the artery lies on the lateral ligament, since the pectoral muscle is thin here. 560 BLOOD-VASCULAR SYSTEM OF THE HORSE 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 bchinil and partly upon the artery; lower down there Deltoid Maslniihi-huiiicrnli.t Exiininl In, 1. 1 of tnapx { Cutaneous branch of axillary neri'c Anterior radial artery Anterior extensor Brachialia Extensor carpi radialis Extensor erir/ii ohlifjiiiis Tendon of rxlensm- earpi radialis Ext. liitir(d liy. of carpns Rete earpi dorsalc Tendon of ant. extensor Briincli to liiteral extensor Tensor fascia antibrachii Lonij head of triceps Branch of radial tierre to exi. and int. heads of triceps and anconeus Deep brachial artery Raili(d nerre Long head of triceps Inlirnol head of triceps Anconeii.'i External head of triceps {cut off) Olecranon • Ulnar head of deep flexor — Cutaneous branch of nlnnr nerve — ■ External lateral lig. of elbow Flexor carpi extern us (cut and reflected) Interosseous artery Ulna Ulnar head of anterior extetisor — Deep flexor of digit — Lateral extensor of digit — I'lnar nerve and vein -- Flexor carpi extern us — Dors(d interos.ieous artery — Superficied Ijranch of nui:-r nerre Cur pal .fheath (opened) U liter tendon of flex, carpi ext. Accessory carpal hone Accessorio-mitacarpid ligaments Blind friini iieiissiiri/ carpal to hilinil ,.i:l, i,^,,r lendon Lateral extensor lendon Fic. 44.3. — Dissection of Left Forearm of Uohse, Kxtkrnal Surfack. (.\tter Srhmaltz, .\tlas d. .\nat. d. Pferdes.) arc usually two satellite veins, anterior and posterior. The chief collateral branches are as follows: 1. Articular branches for the elbow joint. THK PO.STEKIOU RADIAL ARTERY 561 2. Muscular branches to the flexors of the carpus and digit. The hirgcst of these arise at the ]iroxiinal third of the forearm. 3. The common interosseous artery (A. interossea eommunis) is a vessel of Artery of rcte carpi mlnre Oblique liganu nt Internal lateral liq First carpal boiic Deep volar metacarpal arlcrii Int. metacarpal bout Radius A ccessorio-radial lig. Accessorio-ulttar lig. External lateral lig. Check ligament A cccssorio-imlacarpal lig. Deep volar arch Suspensory ligament E.rt. imtacarpal bone Fig. 444. — Deep Dissection gp Right C-\rpus of Horse, Po.«tkrior ^'IEw. 7, Raiiial carpal bone; 2, accessory carpal bone; J, second carpal bone. (After Schmaltz, Atlas d. .\nat. d. Pferdes.) considerable size which arises at the level of the interosseous space, through which it passes. Before entering the space it gives off a small Ijranch, the volar interos- seous (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 Cutaneous branch of inw^cidn- cutanroiis nu i r Tendon of exlensur carpi uhln/ m^ Lateral liyaniLut Tendon of extensor carpi radialis Tendon of anterior dig. extensor Skin Lateral ligament Tendon of lateral dig. extensor Tendon of deep dig. flexor Tendon of superficial dig. flexor Long tendon of flex, carpal extcrnus — Superficial branch of ulnar nerve. Tendon of flex, carpi intirnus Int. metacarpal vein Int. volar or small met. arterii Common dig. or large met. at tin/ Posterior annular ligament Internal metacarpal ntric External metacarpal vein External metacarpal nerve External volar met. artery Fig. 445. — Cross-sectio.n of Right Carpus of Horse. The soft structure.s are cut at the level of the radio-carpal articulation, exposing the proximal row of carpal bone-^. Cr. Radial carpal bone: Ci, intermediate carpal bone; Cu, ulnar carpal bone: Ca, accessory carpal bone. (.\ftei- Schmaltz, .\tlas d. .Anat. d. Pferdes.) from the space it gives off branches to the flexor carpi extcrnus, 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 36 562 BLOOD-VASCULAR SYSTEM OF THE HORSE as the dorsal interosseous artery. This vessel (A. interossea dorsalis) passes down hctwccii the anterior and hiteral extensors of the digit and concurs with the anterior radial in forming a network on the anterior surface of the carpus, the rate carpi dorsale. P'roni the latter arise two small vessels, the internal and external dorsal metacarpal arteries (A. metaearpea dorsalis medialis, lateralis), which run distally in tlie grooves ix'tween 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 carjji volare. 5. The external volar metacarpal artery (A. metaearpea volaris lateralis) is a small vessel which arises just above the carj^us 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 bor- der of the accessory carpal bone, and arrives at the head of the external metacarpal Ijone. Here it is connected with the internal volar metacarpal artery, usuallj' l)y two transverse branches, thus forming the deep volar or subcarpal arch (Arcus volaris profundus). Onv of these l)ranehes lies between the sub- carpal check ligament and the suspensory ligament; the other (not always present) lies beneath the latter on the large meta- carpal bone. A small branch descends to the fetlock with the external metacarpal nerve. Below the arch the artery pur- sues a flexuous course downward on the posterior face of the large metacarjaal l^one alongside of the external small metacarpal and under cover of the suspensory liga- ment. At the distal third of the meta- carpus it commonl}' unites with the cor- responding vessel of the inner side to form a short trunk which passes backward through the angle of divergence of the branches of tlie suspensory ligament and joins the external digital or the common digital artery. 6. The internal volar or small metacarpal artery (A. metaearpea \'olaris meilialis) is given off from the posterior radial at an acute angle, usually a little abo\-e 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 i)osterior annular ligament. Arriving at the proximal end of the inner meta- carpal 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 suijplies the nutrient artery to the large metacarpal bone. Fig. 446. — Cross-section of Middle of Right Met.\carpu8 of Horse. a. Common digital (or large metacarpal) artery; b, internal metacarpal vein; c, internal metacarpal nerve; d, e-xternal metacarpal nerve; e, branch of external volar metacarpal artery; /, external metacarpal vein; g, fj, tl, deep volar or interosseous metacarpal arteries; h, tendon of anterior extensor; i, tendon of lateral extensor; k. anastomotic branch connecting metacarpal nerves; /. deej) flexor tendon; m, check ligament; n, superficial flexor tendon; o, suspensory liga- ment; p, large metacarpal bone; (j, q, small metacarpal bones; r, skin, (.\fter Ellenberger, in Leisering's .\tlas.) The foregoing account describes the most common arrangement of the dorsal and volar metacarpal arteries. Variations in their origin and connections are common, hut have no great surgical importance. Collateral brandies are omitted for the same reason. In some cases the THE COMMON DIGITAL ARTERY 563 internal volar metacarpal is connected with the common digital or large metacarpal artery a little below the carpus by a branch passing obliciuely across the inner border of the deep flexor tendon; this forms a superficial volar arch. THE COMMON DIGITAL ARTERY The common digital or large metacarpal artery' is the direct continuation of the posterior radial. It tlescentls in tlie carpal canal along the inner side of Internal lateral ligament of carpus Tendon of cxtcnfior carpi, radialis Tendon of extensor carpi obliijuus Lateral ligament of fetlock joint Ant. extensor tendon Extensor branch of suspensori/ ligament Dorsal artery of first phalanx Lateral ligament of pastern joint External metacarpal vein Internal metacarpal vein Piislirior atinular ligament of carpus Sujierficial flexor tendon Internal metacarpal nerve Communicating branch Large metacarpal artery Internal metacarpal vein Suspensory ligament Lumbricalis inuscle Anterior digital nerve Posterior digital nerve Digital artery Digital vein Ligament of ergot Deep flexor tendon Lateral cartilage Coronary plexus Coronary matrix Laminar matrix Fig. 447. — Dissection of Right C.\rpus, MHTACARprs, and Digit of Horse, Inner View, (.\fter Schmaltz, Atlas d. Anat. d. Pferdes.) 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. ' This vessel is also termed the A. metacarpea volaris superficialis or the palmar metacarpal artery. 564 BLOOD-VASCULAR SYSTEM OF THE HORSE THE DIGITAL ARTERIES The internal and external digital arteries (A. digitalis medialis, lateralis) are formed by the bifurcution of the foninioii digital at the distal third of the meta- carpus. 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 })ranches emerge through the foramina at the lower border, where they anastomo.'^e with each other in arciform fashion. These branches were named by Spooner the inferior connnunicating arteries, and the anastomotic arch formed by them is termetl the circmnfiex artery of the third phalanx (Chauveau) or the artery of the lower border of the third jihalanx (Leisering). Each artery is accomjianied by a vein and by the digital nerves. Above the fetlock the artery is most ileeply 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 b}^ 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, tentlons and synovial sheath, ergot, and skin, the digital arteries give off: 1. The artery of the first phalanx or perpendicular artery (A. phalangis primae), a short trunk which arises at a right angle about the middle of the first phalanx, and divides into dorsal and volar Ijranches (Rami dorsalcs 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 sesa- moidean ligaments and anastomoses with the opposite artery. 2. The artery of the plantar cushion (A. toricae phalangis tertisp) arises at the ])roximal border of tlie lateral cartilage and passes backward and downward to ramify in the ])lantar cushion and tlic matrix of the heels and frog. 3. The dorsal artery of the second phalanx (Ramus dorsalis phalangis secun(hr) 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 jihalanx, 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 secundae) is smaller than tlie 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 Cliauveau tlie coronary circle. The dorsal (anterior) part of the cirfle g:i\'es off commonly an artery (A. coronalis phalangis tertice) near either side of the extensor tendon, which divides into two branches. The central Inanch 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 de- scending branches of the arteries of the first phalanx concur in tlie formation of the arch. 5. The dorsal artery of the third phalanx or jireplantar artery (A. dorsalis phal- angis tertiie) arises at the dee]) face of the wing of the third phalanx, passes outward through the notch or foramen there, and rims forward in the groove on the wall surface. It gives off ascending and descending branches, which ramify in the matrix BRAN'CHES OF THE THORACIC AORTA 565 of the wall of the hoof, anastomosiiig above with the circumflex artery of the cor- onarj- cushion and hclow with the circumflex artery of the third ])halanx. Before jiassing through the wing it detaches a retrograde branch to Ihe plantar cushion, and after emerging one which ramifies on the outer aspect of the lateral cartilage. The terminal part of tlie ctigital 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 sjiinal cord and its membranes. The visceral branches (Rami viscerales) are the bronchial and oesophageal, which arise by a broncho-tt'sophageal trunk. The parietal branches (Rami parietales) are the intercostal and phrenic arteries. 1. The broncho-oesophageal (Truncus broncho-oesophageus) is a short, usually liulboiis, 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 tra- chea and divides into bronchial and CESophageal branches. (a) The bronchial artery (A. bronchialis) crosses the left face of the a-sophagus to the liifurcation of the trachea, where it divides into right and left branches. Each enters the hilus of the corresjwntling lung al)ove the bronchus, which it accompanies in its ramification. It supjilies the lung tissue and also detaches twigs to the bronchial lymph glands and the mediastinum. (6) The oesophageal artery (A. cesophagea) (Fig. 429) is a small vessel which ]3asses backward above the oesophagus in the posterior mediastinum and anasto- moses with the oesophageal branch of the gastric artery. It detaches twig.s to the oesophagus 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 back- ward ventral to the oesophagus. In some cases there is no broncho-cesophageal trunk, the bronchial and oesopliageal 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 sulicostal 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 bodj' of a vertebra to the corresponding intercostal space, detaches twigs to the vertebra* and the pleura, antl divides into dorsal and ventral branches. The dorsal branch (Ramus dorsalis) gives off a spinal branch (Ramus spinalis) which passes through the inter- vertebral foramen, gives twigs to the memliranes 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 jjosterior border of the rib and is subpleural. Each is accompanied by a vein and nerve, the artery being in the middle and tliC 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 ])leura, and gives off perforating branches which pass out to the serratus magnus, the abdominal muscles, and the skin. 3. Tlie phrenic arteries (Aa. phrenica?) are two or three .small vessels which arise at the hiatus aorticus from the ventral aspect of the aorta, often by a common 5G6 BLOOD-VASCULAR SYSTEM OF THE HORSE trunk. They supply the crura of tlie diaphragm. common with an intercostal artery. In some cases thev arise in BRANCHES OF THE ABDOMINAL AORTA The collateral liranchcs of the alxlominal 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 anil to the scrotum. The visceral branches are the cocliac, anterior mesenteric, renal, posterior mesenteric, and the spermatic or utero-ovarian. The parietal branches are the lumbar arteries. ■Plan of Branches of Celiac .\rtkry of Horse. artery; 3, hepatic artery; 4, splenic artery; 6, posterior gastric artery; 6, an- FiG. 448 /, Cccliac artery; 2, gastri _... , _, .„, , , ,, ., ., . ., ^ tenor gastric artery; 7, cesophageal branch; S, gastro-duodenal artery; 9. pancreat gastro-epiploic artery; ;;, pyloric artery; IS, left gastro-epiploic artery; IS, short gastric branches of spier >-duodenal artery; W, right I. The coeliac artery or axis (A. coeliaca) 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 ilorsal surface of the pancreas into three l)ranches — the gastric, hepatic, antl splenic. 1. The gastric artery (A. gastrica sinistra) passes downward and forwanl in the gastro-phrenic ligament, gives off cesophageal 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 i)ranclies pursue a flexuous course toward the greater curvature and anastomose with the short gastric arteries and the gastric branch of the hepatic artery. (h) The posterior branch (Ramus caudalis) is distributed in a similar fashion on the visceral surface. BRANCHES OF THE ABDOMINAL AORTA 567 (c) The oesophageal branch (Ramus cesophageus) passes through the hiatus cpsophageus into the tliorafic cavity above the cesophagus and anastomoses with the CESophageal Ijraach of the broncho-ccsophageal artery. Fig. 449.— Pi.ax of Chief Branches of .\xterior Mesenteric Artery of Horse. / Stump of anterior mesenteric artery; 2, stumps of arteries of small intestine; 3, e-vternal ca-cal artery; i, internal cxcal arterj-; 5. ileal artery; 6, ventral colic artery; 7, dorsal colic artery: 8, middle coUc or first artery of small colon. The gastric artery often arises bv a common trunk with the splenic. The two terminal branches may arise separately, or the anterior from tlie splenic and the posterior from the hepatic. The ccsophageal branch often arises from the splenic or the posterior gastric. 2. The hepatic artery (A. hepatica) is larger than the gastric. It passes for- ward to the right and ventrally on the dorsal surface of the pancreas, covered by BLOOD-VASCTLAR SYSTEM OF THE HORSE p 3 "d '^ « -= £; '^ - <,' i 5 I -■ i g 6 ^ & " 2 o o "^ ' s'^ g 1^ duodenum and divides into the right gastro- 8'c3i^s|'^^ ejjiploic and the pancreatico-duodenal. The -»l9sii ill right gastro-epiploic artery (A. gastroepiploica §*«i=-°s°-t dextra) crosses over the po.sterior surface of the '■a I c^-7il— :'IZ duodenum and enters the great omentum, in ^«- i t-^-|l I S which it runs to the left, parallel with the z il-^. ■«■ I ■^- 1 1" I I It " greater curvature of the stomach. It gives 2^^' lli'sli°eS branches to the latter and to the omentum and forms an anastomotic arch with the left gastro- epiploic artery. The pancreatico-duodenal artery oJgHs 5J*-|3" -3^ -^ (A. pancreaticoduodenalis) divides into pancreatic ««1 a*7. i^°--§ and duodenal branches. The former (Ramus pan- ■2" I °^' * £ 1 i-f' i J I creaticus) supplies the middle part of the pancreas I. ■^- -S" 4 = I 3 ° I J := 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 |i=°|-3i^"' branch of the anterior mesenteric artery. I S «" = :^' I H ^ i 3. The splenic artery (A. lienalis) is the J 'I ■-'! " i .i i 3 largest branch of the cccliac. It passes to the left i* alS-l ||E|£2||z-= (with the large satellite vein) on the left extremity of the pancreas and across the saccus csecus of the stomach. Entering the suspensory ligament of ^ 'I I u I d E I X 1 "i I "3 I the spleen, it runs in the hilus of the spleen to o-s"'- ■S = 2's3 = '5oj1- the apex, bevond which it is continued as the «""S'» -S9fH3°H'"3-f left gastro-epiploic. It gives off the following a § i I -: I r. 1 .1 I ]^- S i ^ branches : (fl) Pancreatic branches (Rami j-ancreatici) to the left extremity of the jjancreas. (b) Splenic branches (Rami lienalcs), which plunge into the sul)stance of the spleen. (c) Gastric branches (Aa. gastricse breves), which pass in tlie gastro-splenic omentum to the greater curvature of tlie stomach, where they bi- furcate and anastomose with the gastric arteries. ^ ■-■■BB E-Hc ?:-gr 5-^== _; j= !3 • - £ ^ S ig-gs > Z =3 S * ' - > -a "s .2 - I — -3 d '5 „ i = ^. -r •= ^ ^ 570 BLOOD-VASCULAR SYSTEM OF THE HORSE (d) The left gastro-epiploic artery (A. gastroopiploica siiiitr}' (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 caecal artery (Ramus csecalis lateralis) passes be- tween the CEecum and the origin of the colon and runs on the external muscular band of the caecum to the apex, where it anastomoses with the internal artery. Besides numerous collaterals to the csecum, it gives off the arterj' of the arch, which passes along the lesser curvature of the base of the ciecum and runs on the outer face of the origin of the great colon. (3) The internal or superior caecal artery (Ramus ca'calis medialis) passes along the inner band to the apex of the csecum, where it anastomoses with the external caecal artery. (4) The ventral, right, (jr 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 caecum. 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 jiasses to the origin of th(> 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 anasto- motic branch to the dorsal colic artery. ' 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 Selerostomum armatum. In the author's experience an entirely normal specimen is quite exceptional in adult horses. • 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. BRANCHES OF THE ABDOMINAL AORTA 571 III. The renal arteries (Aa. renalesl, 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 hack; it passes directly outward to the kidney and is then disposetl 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 fre(iiient. 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 htemorrhoidal artery (A. haemor- rhoidalis 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. spermaticfe interns), 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 l)road ligament of the uterus and divides into ovarian and uterine branches. The ovarian branch (A. ovarica) pursues a flexuous cour.se 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. \T. 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 corre- sponding branch of an aortic intercostal artery. The ventral branch (Ramus 572 BLOOD-VASCLLAR SYSTEM OF THE HORSE Internal iliac lymph glands Circumflex iliac rf.s.fcii External iliac lymph glands Inguinal ligaments Posterior branch of circum- flex iliac artery External cutaneous nerve External spermatic nerre Tensor fascia: lata: Femoral nerre and ante- rior femoral vessels Femoral artery Precrural lymph glan'ls Deep inguinal lymph glands Fascia lata Saphenous nerves Saphenous vessels Jjilernal patellar ligament Middle patellar ligament Fic. 451. — DissEcnox of Pelvis. Thigh, and Cpper Part of Leg of Horse, Internal View. /-.Lumbar vessels; V'.c, posterior vena cava; --l, aorta (termination); C, sympathetic trunk; /, internal iliac arter>-* 3. lateral sacral arterj-; 3, mitidle coccygeal arter>-; 4. lateral coccygeal arter>-; $, umbilical artery icut off); 0, internal pudic arterj-; 5', vesico-prostatic artery; 7. obturator arter>-; 8, a. profunda penis (from left obturator); P, posterior gluteal (or ischiatic) vessels; iO. external iliac artery; //,//', deep femoral artery; 13, prepubic arter>-; /3. branch of deep femoral arter>'; /4, great sciatic nerve; ;5, posterior gluteal ner^-e; /ff (above), internal pudic ner\*e; 16 (below near |>elvic outlet), suburethral venous plexas; 77, sacro-coccygeus inferior; 18, coccygeus; /S, recto-coccygeus; 50. retractor ani; 5/, 3/'. two headsof obturator intemiLs; 52, symphysis pelvis; 8S, prepubic tendon; 24 suspensor>* ligament of penis; 2.5, retractor penis muscle; SO, bulbo-cavernosus muscle; 27, urethra (cross-section); 23, cms ijenis (cross-section); 29. suspenj*or>- ligaments of anus (= upper part of retractor penis muscle) ; 3L\i.e). 1, Bulbo-urethral (Cowper's) gland; ;?, transversus perinei muscle (?): 5, ischio-urethral muscle: .f, retractor penis muscle; o, bulbo<»vernosu3 muscle. (.4fter Schmaltz, Atlas d. Anat. d. Pferdes.) 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 : 1. The last pair of lumbar arteries jiass up through the foramina at the junction of the last lumbar vertebra and the sacrum. 2. The internal pudic artery (A. pudentla interna) arises near the origin of the internal iliac. It passes backward and somewhat do^\-nward, 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 e.Nternal face. It then re-enters the peh-ic cavity, passes backward on the retractor ani to the ischial arch, and divides 574 BLOOD-VASCULAR SYSTEM OF THE HORSE into the perineal and the artery of the Inilb 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 aliout an inch (ca. 2 to 3 cm.) from the origin of that vessel. It is a very large artery in the foetus, 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 fa'tal 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.' It Coccygcus jnuscle Anal lymph glands Branch of posterior gluteal artery Posterior hcEmorrhoidal nerve \ uliar branch of pudic nirvc li I rnal pudic t 'J J I ch of pu- I I cm- to I t ris Obluralor arltry Fig. 453 — Dissection Mare :IXEUM /, Sacro-coccygeus superior; 3, sacro-coccygeua lateralis; 3, intertransversales; 4. sacro-coccygeus inferior; 5. recto-coccygeus; 6, sphincter ani externus; S', branch connecting sphincter ani with constrictor vulva-; ?■ vestibular bulb; S, tuber ischii; 9. sacro-scL-itic lig.inent. (After Schmiiltz, .\tlas d. .\nat. d. Pferdes.) gives off small vesical branches (Aa. vesicales craniales) to the blaildcr, and twigs to the prostate and vasa deferens in the male. In the mare a small brancli runs forward along the ureter into the broad ligament of the uterus. (2) The middle haemorrhoidal or vesico-prostatic artery (A. haniiorrhoidalis media) in the male arises usually near the jjrostate and runs backward lateral to the n>ctum. It svij)])lies liranches to the rectum, l)ladder, 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 i)asses ' Tlic obliteration in the adult extends a variable distance from the vesical end toward the origin, but usually involves only a small part. THE INTERNAL ILIAC ARTERY 575 upward at the side of the anus, which it supplies, and gives twigs to the bulho- 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 urethrae) may be regarded as the direct continuation of the internal putlic in the male. It lies at the side of the urethra above the ischial arch, dijis uniler 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. (4a) The artery of the clitoris (.\. 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. 3. The lateral sacral artery (A. sacralis lateralis) arises at the hunbo-sacral Fig. 454. — Cross-section of Tail of Horse. 1, Dorso-Iateral coccygeal vessels ami nerve; 2, ventrolateral coccygeal artery and nerve; S, middle coccygeal artery; 4. sacro-coccygeus superior; J,', sacro-coccygeus lateralis; S. 6'. inteitransversales; 6. saero- coccygeus inferior; 7, recto-coccygeus; S. coccygeal fascia; 9, fibro-cartilage between fourth and fifth coccjgeal vertebrae. The veins are black. 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 for- amen between the last lumbar vertebra and the sacrum and through the ventral sacral foramina. They give off liranches to the spinal cord and its membranes which reinforce the ventral spinal artery, and others which emerge through the dorsal sacral foramina and sujijily 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 con- tinues in that position along the tail between the depressor muscles, supplying these and the skin. (.3) The posterior gluteal or ischiatic artery (A. glutea caudalis) emerges 576 BLOOD-VASCULAR SYSTEM OF THE HORSE Internal nrcum- JICX VCSKlh Pironenl nerve Tibial nerre Posterior femoral artery N . cutaneus sura; Popliteal lymph glands Gastroenemius Reevrrenl tarsal vessels Tc.rscl or acces- ticry tendon of biceps femcris Deep flexor of diffit Gastrocnemius tendon Superficial flextr tendon c . , , <^^_. ^_ >^_ «. M i Tuber calcis Superficial peroneal nciit Dcep peroneal neru Proximal annular lujnn Middle annular ligament External lateral ligament Distal annular lir/nment ■ Fio. 455. — DissKCTioN OK Pelvis, Thigh, and Le<: of Hohm . 1 xtti:\m. Vikw. 1, Dorsal branches of last intercostal and first three lumbar nerves; ii, (.ulaneous branch of fourth lumbar nerve; d. ventral branches of last intercostal nerve; 4. branches of ilio-hyijogastric nerve; 6, superficial branch of ilio-inguinal nerve; 6, great sciatic nerve; 7, 8, nerves to biceps femoris (from posteiior gluteal nerve); 9, nerve to semitendinosus (from same); 10, posterior cutaneous nerve of thigh; II, internal pudic nerve; IS, anterior gluteal vessels and nerves; IS, posterior gluteal (or ischiatic) vessels; 14, branches of obturator vessels; IB, proximal muscular branches of great sciatic nerve to biceps femoris. semitendinosus, and semimelTibranosus; 16, nerve to tensor fascia- latx (from anterior gluteal nerve); /~, gluteus profundus; ;S, stump of gluteus medius; i9. gemellus; M, trochanter major; 21, stump of biceps femoris; SS. sacro-coccygeus superior; SS", sacro-coccygeus lateralis; £f, coccygeus; 24, sacro-coccygeus inferior; $5, line of fusion of aponeuroses of internal and external oblique muscles of abdomen; 25'. aponeurosis of external oblitjue muscle (lamina iliaca); S6, branches of iliaco-femoral vessels; 27. ilio-lumbar vessels; SS, ilio-ltimbar lif rii:tnt or deep layer of lumbo-dorsal fascia; 29, external angle of ilium; SO, internal angle of ilium; S;, lateial sacio-iliac ligament; as, sacro-sciatic ligament. (After Schmahz, Atlas ' and small satellite vein; 2, anastomosis between external pudic and internal cir- cumflex veins; 5, accessor>' ligament: 4. round ligament; 5, transverse ligament; ff, head of femur; 7, obturator externus (stumps); 5, inner margin of obturator foramen; 9, origin of gracilis; /O. origin of adductor; 11, hulho- cavernosus; 13, retractor penis; 13, suspensory ligament of penis, (-\fter Schmaltz, .\tlas d. .\naf . d. Pferdes.) ilium a little behind the external angle, giving branches to the gluteus medius and tensor fasciae latse (Fig. 45.5). 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. circumflexa 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 anil vastus externus. It is accompanied by two satellite veins. It gives collateral branches to the iliopsoas, the glutei, and the tensor fasciae latae, 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 37 578 BLOOD-VASCVLAR SYSTEM OK THE HORSE the ilium along the ventral border of the iliac head of the obturator internus, ac- companied 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 obliciuely through the foramen. In this part of its course it gives off a vesical branch and twigs to the obturator internus and the hijvjoint. After its emergence from the pelvic cavity it runs b.ickward on the ventral face of the ischium, passes through the semimemliranosus and, ill the male, enters the crus penis, forming the arteria profunda ])cnis. It anastomoses with the internal pudic, and usually with the external jiudic liy a branch which runs forward on the dorsum penis. Large collateral liranches are detached to the adductors of the thigh, the biceps femoris and semit(>ndinosus, forming anastomoses with the deej) femoral and jiosterior 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 vertelira, 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 perito- neum and fascia, and is related behind to the corresponding vein. Its branches are as follows: 1. The circxmiflex iliac artery (A. circumfiexa 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 accom])anied 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 fascise latae to the fold of the flank, supplying branches to that muscle, the jianniculus, 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 sjirings 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 jnuscle to the inguinal canal, supplies twigs to that muscle, the tunica vaginalis, and other constituents of the sjiermatic cord (Fig. 450l. 2a. 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 579 The Femoral Artery Figs. 450, 45 d 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 se]Ku-iite(l 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. Fig. 457. — Disskction of iNorixAL Regiox .4nd Inner SrRFACE op Thigh of Horse. 1 External pudic arter>'; 2, anterior branches of /; S, posterior branches of 1; 4, transverse anastomosis between external pudic veins; 4' venous plexus of dorsum penis: 5, femoral arterj" 6, saphenous ner^'e: 7. an- terior border of external inguinal ring; S. obliquus abdominis inlernus; 9, posterior border of external inguinal ring; W, tunica vaginalis; II. vas deferens: IJ, cremaster muscle; 13. prepuce; 14> glans penis; 13. external urethral orifice: 16, posterior branches of circumflex iliac vessels; 17. saphenous vessels; IS. fold of flank; /5, penis (cut); A, superficial inguinal lymph glands; B, precrural lymph glands; C, ileep inguinal lymph glands. (After Schmaltz, .Atlas d. .Anat. d. Pferdas.) It is related at its origin to the sartorius in front, the femoral vein beliiiul (which separates it from the pectineus), and the iliacus externally. Lower down it is related superficially to the deep inguinal lymph glands, and deeph' 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: 1. The prepubic artery (Truncus pudendo-epigastricus) arist s from the femoral artery at its origin, usually Ijy 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 olilique muscle into the posterior at>dnminal and external pudic arteries. (1) The posterior abdominal artery (A. epigastrica caudalis) passes along the 580 BLOOD-VASCULAR SYSTEM OF THE HORSE external border of the rectus abdominis and anastomoses in the umbilical region with the anterior alKloiiiiual artery (Figs. 272). It supplies branches to the rectus and ol)liquus interiius 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 liranclies to the superficial inguinal Ij-mph 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 anasto- moses 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 Ijase of tlie mammary gland. 2. The deep femoral artery (A. profunda femoris) arises either by a common trunk with the preinibic or a little distal to it (Fig. 451). It passes backward and downward across the inner face of the femoral vein, then below the puliis in the space between the hip joint and the pectineus muscle. On reaching the obtura- tor externus it inclines more ventrally and outward, passes out between the inter- nal border of the femur and the quadratus femoris, and ramifies in the biceps femoris and semitendinosus. It supplies large collateral branches to the adduc- tor muscles and twigs to tlie deeji inguinal lymi)h 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 doe\) face of the sartorius, and dips in between the rectus femoris and vastus internus (Fig. 451). It is related extern- ally 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 Ijetween 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 ilivides above the hock into two branches, which accom- pany 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 THE POPLITEAL ARTERY — POSTERIOR TIBIAL ARTERY 581 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 be- tween 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 gas- trocnemius, gives branches to that muscle and the flexor perforans, and is con- tinued by a slender artery which accompanies the tibial nerve and unites with the recurrent tibial arterj-. A branch ascends alongside of the sciatic nerve be- tween 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 C/D-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 tibise). 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 recur- rent 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. inetatarsea plan- taris superficialis medialis, lateralis) descend on cither side of the deep flexor tendon with the plantar nerves and unite with the great metatarsal or with the corre- sponding 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 582 BLOOD-VASCULAU SYSTEM OF THE HORSE 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 Tibial iiiserlion of srnii- \ tfn(liii(isi(!< Saphenous vein Poplileus Flexor dig. longus (s. acceissoriuli) Posterior tibial vesach Anterior extensor Internal lateral tii/dimnl of tinck Pi-roncus terlius ■ — Inner {citncon) tendon of libialis (inlirior Outline of bursa Great nielalarsal Ftg. 458. — DissF.rTiON- oi- Lr.r, and H Tendon of semiten- dinosus Gaslrncnemiux {internal head) Tendon of (jaalroc- Teiidon ofsujierlicidl fliror Tiirsal bndaii of s,llllh,nllln,.:' Tibial ,„nr I'leurrent libiiU I'ssels Deep flexor tendon Internal tarsal iirlerij Tendon of flexor dig. lon- gus (s. aecessorius) ■r E.rl( mid plantar rein lull nidi plantar arleru — I nil mat plantar nerre Del p flexor tendon Internid planiiir meta- tarsal ressels (.\fl,T Si-hnialtz, Atlas il. Anat. ,1. Tfcides.) the direct continuation of the infernal plantar artcrj', the external artery only uniting with the perforating tarsal. ANTERIOR TIBIAL ARTERY 583 ANTERIOR TIBIAL ARTERY The anterior tibial artery (A. tibialis anterior) is much the larger of the two terminal branches of the iiopliteal. It passes forward through the upper part of Vaslus r.c/r/-/,».s- Gaslrocncmiiis, (xlrnml Superficial flexor Articular rcsscl. Joint capsule External condyle of femur Popliteuf! Joint capsule, opened External lateral ligament Recurrent tibial vessels Salens Tibialis posterior Lateral extensor tendon Recurrent tarsal vein External plantar vein External tarsal rein External tarsal artery Trochlea of tibial tarsal bone ji J — \B External lateral ligament _JL,A Fibular tarsal ban Femoral ressels Posterior femoral artery Popliteal artery Adductor dastrocnemius, internal head Tibial nerve Flexor dig. longus s. accessor- ius Flexor hallucis longus Recurrent tibial artery External tarsal artery Internal tarsal artery Upper end of tarsal sheath Deep flexor tendon Long flexor tendon Plantar nerves Plantar arteries Joint capsule, opened Fic. 459. — Deep Dissection- of Right Stifle, Leg, and Hock of Horse, Posterior View. The hock is flexed at a right angle, and the tulier calcis is sawn off. The tibial nerve is drawn inward to show its musQular branches. Branches of tibial nerve: /, Z. to gastrocnemius; d. 4. to superficial flexor; S, to popliteus; 6, to flexor longus or accessorius; 7, to deep flexor. (After Schmaltz, Atlas d. Anat. d. Pferdes.) 584 BLOOD-VASCULAR SYSTEM OF THE HORSE 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 PahU Tendon of liiceps fcniDri-t External patellar ligament Gastrocnemius External condyle of tibia External lateral ligament Peroneal nerve Superficial peroneal nerve Lateral extensor Anterior extensor Peroneus tertius Loop of outer tendon of peroneus tertius Perforating tarsal artery Slump of extensor breiris Great metatarsal artery Lateral extensor tendon Anterior extensor tendon 1 astiis internus . 1 rcessory cartilage of patella Gracilis Sartorius Trochlea of femur Jiilinus coronarius) is a very short bulbous trunk which receives most of the blood from the wall of the heart. It is situated just ' Most of the veins are depicted in the illustrations of the section on the arteries, to which reference is to be made. 586 THE VEINS below the termiiuitioii of the po.sterior vena cava and is eoviTed in part l)y a thin \a\vr of ventricular niusclc-fihcrs. It opens into the right atrium just l.elow the posterior vena cava. It is formed by the union of two tributaries. The great cardiac or left coronary vein (\. 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 (\'. cordis media) begins on the right side of the apex, ascends in the right longitu- dinal 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 (^'v. cordis minores), three to five in number, are small vessels which return some blood from the riglit ventricle and atrium; they open into the latter near the coronary groove^ in sjiaces between the musculi pectinati. THE ANTERIOR VENA CAVA (Fig. 429) The anterior vena cava (V. cava cranialis) returns to the heart the })lood 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 jugu- lar and two brachial veins. Its origin is attached to the first pair of ribs. It passes l)ackward 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 l^etween 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 brachio- cephalic 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 nearlj' always a conmion trunk for all three. 4. The dorsal vein (Y. 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 verte- bral 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 vertebrae, in contact usually with the VEINS OF THE HEAD AND NECK 587 thoracic duct, which separates the vein from the aorta. At the seventh vertehra it leaves the spine, curves downward and forward over the right side of the tiioracic duct, trachea, and oesophagus, and opens into the right atrium opposite the third intercostal space. Its tributaries are: 1. The last fourteen intercostal veins (Vv. intercostalcs) 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 oesophageal vein (V. oesophagea), satellite of the oesophageal artery, joins the vena azygos as it inclines downward. 3. The bronchial vein (\'ena bronchialis) unites with the jireceding to form a short common trunk (Ellenlierger-Baum), or empties into the great coronary vein (Chauveau).' 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 teinporo-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." 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 maxillarj'. It may he 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 pter^'goid 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 lingute), which is a satellite of the lingual nerve. (2) The inferior alveolar or dental vein (V. alveolaris mandibulae), a satellite of the corresponding artery. It often unites with the jireceding. (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 ' Chauveau says "the bronchial veins, which ramifj' on the bronchi lil^e the arteries of which they are satellites, open into tlie great coronary vein very near its moutli, after liaving uuitcil to form a single vessel, which sometimes opens directly into the atrium." Ellenberger and Haum state that the bronchial and a'sophageal veins open into the vena azygos separately or l)y a com- mon trunk. Martin describes a short broncho-ocsophageal trunk, but the vein which lie 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 oesophageal vein. Iiut no distinct bronchial vein in the horse. ■ M'Fadyean records a case in which the vein lay on the deep face of the omo-hyoideus with the carotid artery. 588 THE VEINS 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 (\'. cereliralis dorsalis), whicli is the emissary of the transverse sinus of the dura mater; it emerges from tlie parieto-temporal canal behind the postglenoid process. The transverse facial vein (^'. 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 (^^ masseterica) joins the jugular at the upper border of the sterno-ceiihalicus tendon. It is a short trunk formed by the confluence at the posterior border of the jaw of masseteric and Fig. 401. — .Superficial Vessels and Nerves of Head axd .Interior Part of Neck of Horse. a, Masseter; 6. parotid gland; c, parotido-auricularis; i, masseteric artery; 5, parotid branch; ^.transverse facial artery; .4. facial artery; 5. 5. inferior labial artery; 7, superior labial artery; 5. lateral nasal artery; 5, in- fraorbital artery; iO dorsal nasal artery; 7i, angular artery of eye; /.?, /3, jugular vein; i .4. great auricular vein; 16, masseteric vein; 16, superficial temporal vein« 17, transverse facial vein; 17', deep temporal vein; IS, external maxillary vein; i5; facial vein; .50. labial vein; j?7, dorsal nasal vein; 22, lateral nasal vein; 33, angular vein of e.ve; 34, 25, facia\ nerve; 55', 5.5", superior and inferior buccal nerves; 26, transverse facial ner\'e; 27, auriculo- palpebral nerve; 55, anterior auricular nerve; 29, cervical branch of facial nerve; 30, ventral branch of second cervical nerve; 30', 30", S&", auricular and cutaneous branches of 30: 31 , branches of dorsal division of first and .second cervical nerves; 33, dor.sal branch of spinal accessory nerve, (.\fter l.eisering's .\tlas.1 pterygoid veins. The former is usually connected by a large branch with the l)uc- cinator vein. 4. The great auricular vein (\. auricularis magna) is a satellite of the posterior auricular artery above, but joins the jugular a variable distance below and liehind the point of origin of the artery. 5. The inferior cerebral vein (V. cereliralis ventralis) is an emissary of the cavernous sinus of the dura. It is a satellite of the internal carotid arterj', receives the condyloid vein, and joins the jugular near the occipital vein or by a common trunk with it. (i. The occipital vein {\ . occipitalis) arises in the fossa atlantis by the union of muscular and cerebrosjiinal 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 {\. maxillaris externa) arises by radicles which correspond in general to the branches of the arterj' of like name. It passes JUGULAR VEINS 589 do^^^l over the cheek along the anterior border of the masseter muscle behind the arterj', crossing over the parotid (hict. 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 liackward along the lo\\ei' border of the parotid gland, and opens into the jugular vein at the posterior angle of the gland.' The chief differences in the tributaries of the vein as compared with the branches of the corrts]iond- ing artery are as follows: The labial veins (\'v. labiales) form a plexus in the submucous tissue of the cheek from which two veins emerge. The upper one i)asses back and joins the buccinator vein. The lower one (V. labialis communis) joins the external maxillary vein. Three veins connect with the ex- ternal maxillary at the anterior border of the masseter. The upper one is the transverse facial, which unites close to the enil of the facial crest. A little lower is the large valve- less vena reflexa or alveolar vein. This passes liack under the upjier part of the masseter on the maxilla, turns around the tuber maxillare, j^er- forates 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: («) The palatine vein (V. palatina major), which separates from the palatine artery at the anterior palatine fora- men and passes in the groove lietween 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 an- teriorly, (b) The sphenopalatine vein (V. spheno-palatina) 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. The venous plexuses are remarkably developed in certain parts of the nasal mucosa. On the septum a httle below its middle and on the turbinals the veins are in several lavers. The olfactory region does not share in this arrangement and the veins here are small and join the eth- moidal vein. ' The venous angle formed by this junction indicates the position of the thyroid gland. Fio. 462. — Dissection of Adjacent P.\rt c a, Ramus of mandibl c, c' , onio-hyoidei and sterE right side): d, hyoid bone: SrBMAXILLAHY SpACE AND Neck of Horse. b, sterno-cephalicus muscle; -hyoidei (portion removed on anterior belly of digastriciis; /. g, raylo-hyoideus: h. submaxillary lymph gland.s (por- tion removed on right side): i. parotid gland: A;, submaxil- lary gland: ;. chin: m. stylo-maxillaris; /. parotid duct: 3, facial vein: S, facial artery: 4. external maxillary vein: 5, sublingual vein; 6, sublingual artery: 7. ventral branch of first cervical ner\e: S. mylo-hyoid nerve. (.After Ellenberger, in Leisering's -Atlas.) 590 THE VEINS (c) The ophthalmic vein (\. oiilitlialmica) is a short trunk, connected in front with the vena refit'xa and behind with the cavernous sinus through the foramen hicerum orbitale. It receives veins which correspond to the arterial branches. The buccinator vein {\. buccinatoriu) extends backward from tlie external maxiUary 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 maxillaro 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 laliial jjlexus, and is usually connected with the masseteric vein. Fin. 463. — Deeper V AND Nerves of Head of Horse. The parotid f;lancl, most of the masseter muscle, and a portion of the ramus of the tnaiidible are remove.!. a. Remnant of nias-seter muscle; 6, internal pterygoid muscle: c, stylo-mandibularis; d, d\ levator labii superioris proprius (portion removed); e, periorbita; i, ma.sseteric artery; /', parotid branch; ;?, trunk for anterior (.:*) and posterior {4) auricular arteries; 5, 5', superficial temporal artery; 6" , transverse facial artery; 6, inferior alveolar (or dental) artery; 6' , mental continuation of 6; 7, buccinator artery; 6'. infraorbital artery; 9, II, jugular vein; 10, external maxillary vein; 12, inferior cerebral vein; IS, facial vein; t/,, angular vein of eye; 16, dorsal nasal vein; 16, lateral nasal vein; 17, superior labial vein; IS, 19, inferior labial veins; 20, labial jjlexus; 21, 22, emer- gent veins of plexus; 23, vena reHexa; 2^, trunk of sphenopalatine and infraorbital veins; 2S, palatine vein; 3G, great auricular vein; 27, 28, superficial temporal vein; 29, transverse facial vein; SO, buccinator vein; 31, dorsal lingual vein; 5.?, inferior alveolar or dental vein; 5.^, pterygoid vein; 54. deep temporal vein; 55. superior cerebral vein; SG, external nasal nerve; S7, anterior nasal nerve; 38, superior labial ner\-e; .•i9, ma.sseteric nerve; 39' , end branches of 39; 40, buccinator nerve; 4h pterygoid ner\'e; 4/a, inferior alveolar or dental nerve; 4tb, mylo-hyoid nerve; 42, posterior auricular nerve; 43, auricular branch of vagus; 44, internal auricular nerve; 46, auriculo-palpebral nerve (cut); 4e, digastric nerve, (.\fter Leisering's .\tlas.) The lingual vein (V. lingualis) is not a satellite of the artery. It is formed at the side of the lintjual 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 jiartly in the sub.stance 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 lymjih glands, and joins the external maxillary near the posterior liorder of the jaw. Near its termina- tion it receives the sublingual vein, or the hitter may open into the external maxil- lary directly. 8. The thyroid vein {\. thyreoitlea) 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. THE SINUSES OF THE DURA MATER 591 9. Muscular, tracheal, and oesophageal veins. 10. Tho cephalic vein (Vena cephalica) enters the jugular near its termination. It will l)e (l(>srril)e(| with the veins of the thoracic limb. 1 1 . The inferior cervical vein (V. ccrvicalis ascendens) accompanies the artery. It may open into the brachial vein. The Sinuses of the Dura Mater These (Sinus durae matris) are blood-spaces between the meningeal anene(l by sawing off the arches. The ner\'e- roots are cut on one side and the spinal cord turned over to right. 7, Ventral or middle spina! artery; 2. reinforcing branches from vertebral, intercostal, or lumbar arteries (according to region): ^, longitudinal vertebral sinuses; a. ventral surface of spinal cord; 6, dura mater (cut); f. nerve-roots; d. superior common liga- ment. (.\fter Ellenberge--, in Leisering's .\tlas.) 594 THE VEINS corvical panniculus, and opens into the terminal part of the jugular or the brachial vein. It receives an accessory cephalic vein (^^ cephalica accessoria), which arises from the carpal network, runs upward along the inner border of the extensor carpi, Fifi. 460 — l)lS.Sl.f TiON OF PliCTORAL ReGION AND ANTtRIOR TaRT OF AUUOMINAL WaI.L OF lloRSE. 1, Jugular vein; S, loose connective tissue of axillary space; S, ascending branch of inferior cervical artery; 4, descendiuK branch of same; 6. cephalic vein; 6. median nerve; 7. ulnar nerve; 8, brachial artery; 0, brachial vein; 10, external thoracic or "spur" vein; 11, anterior abdominal artery and vein; IS, branches of sixth cervical nerve; IS, cutaneous branch of axillary nerve; 14, cutaneous branch of musculo-cutaneous nerve; IB, cervical panniculus; W. sterno-cephalicus; 17, scalenus; IS, mastoido-humeralis; 19, anterior superficial pectoral; SO, posterior superficial pectoral: 2/, anterior deep pectoral; 23. posterior deep pectoral; .85, abdominal panniculus; 94, obliquus abdominis externus; 5.5, rectus abdominis: SB, coraco-brachialis; 27, tensor fascise antibrachii; a, preacapular lymph glands; b, prepectoral lymph glands; r. axillary lymph glands; d, cubital lymph glanda; ex., xiphoid carlilage. (.\fter Schmaltz, .Vtlas d. .\nat. d. Pferdes.) turns along the lower border of ttie l)rachialis, passes under the superficial tendon of the biceps and joins the cephalic. THE POSTERIOR VENA CAVA 595 The deep veins of the fore;inn are variable. Commonly two posterior radial veins (^'enae medianoradiales) accompan.y the artery of like name, one in front and one behind. A thirtl vein arises by ratlicles 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 bracliial vein. The conunon interosseous vein joins the posterior satellite. The anterior radial vein (\'. coUateralis radialis) is a satellite of the artery. The ulnar vein is usually double at its proximal part, and communicates with the deep l>rachial vein. There are three chief metacarpal veins. The internal metacarpal vein {\. metacarpea volaris superficialis nicdialis) arises from the volar ^•(■nous arch above the fetlock. It is the largest vein of the region and lies in front of the large meta- carpal 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 alcove the fetlock and passes upward behind the external border of the suspensory ligament in front of the external branch of the median ner^■e and accompanied by a small artery. At the proximal end of the metacarpus it is connected with the deej) meta- carpal vein by two transverse anastomoses which pass across the suspensory liga- ment. It then passes upward as a satellite of the external volar metacarjaal artery and concurs in the origin of the ulnar and posterior radial veins. The deep meta- carpal vein (V. metacarpea volaris profunda medialis) arises from the venous arch, passes forward between the two branches of the suspensory ligauient, 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 susjiensorj- 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 ])art 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 cir- cumflex vein of the third phalanx or vein of the distal border of the third jihalanx, 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 596 THE VEINS anil left fonmiou iliac veins at the fifth lumbar vertebra, above the terminal part of the aorta and ehiefiy to the right of the median plane. The moJe of origin is variable. In some cases there is a common trunk formed hy 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 diaiihragm and the pancreas till it reaches the liver. Here it inclines downward along the inner border of the right lobe antl the parietal surface of the liver, largely emliedded in the gland substance, and passes through the foramen veme cavtt of the diaphragm. It then runs for- ward 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, accom- panied by the right phrenic nerve, and opens into the posterior part of the right atriinn. 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 commoii trunk. The first communicate with the vena azygos. 2. The spermatic veins (Vv. spermatica? internee) (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 com- monly 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«. The utero-ovarian veins are much larger than the jjreceding 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 calilier and thin-walled. The right veiii 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. hepaticae) 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. phrenicse), 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 mejiia), 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. portse) is a large tnmk which returns the blood carried to the viscera by the gastric, splenic, and mesenteric arteries. Its peripheral tribu- taries correspond closely with the branches of the arteries, but the terminal trunks do not. The vein is formed Ijehind the ixuicreas and below the posterior vena cava by the confluence of the anterior and posterior mesenteric and splenic veins. It passes forward, traverses the iiosterior part of the pancreas very obliquely, inclines THE COMMON ILIAC VEINS — THE VEINS OF THE PELVIC LIMB 597 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 blooil 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 in- testinal 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. mesent erica 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. Usuallj' a single colic vein corresponds to the two arteries of the right portions of the colon. 2. The posterior mesenteric vein (V. mesentcrica 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 (\'. lienalis) is the very large satellite of the splenic arterj'. 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 ciBcus of the stomach and above the left end of the pancreas, receives commonly the posterior gastric vein (^'. 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) Tiie gastro-duodenal vein (^'. gastroduodenalis) corresponds mainly to the extrahepatic Ijranchcs of the hepatic artery. (3) The anterior gastric vein (\'. gastrica cranialis) joins the portal at the portal fissure. THE COMMON ILIAC VEINS (Fig. 456) These (V. iliacse communes) are two very large but short trunlcs which result from the union of the internal and external iliac v-eins 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 (A'v. circumflexEe ilium profundae) 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 (^^ 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 (\\\ h\-pogastricie), 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 interna! pudic veins receive affluents from the venous plexuses of the prepuce and penis in the male; of the mammarj' gland, vulva, vagina, and vestibular bulb in the female. THE VEINS OF THE PELVIC LIMB The external iliac vein (V. iliaca ex-terna) (Figs. 4.50. 4.51) lies behind the cor- responding 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: 598 THE VEINS 1. The obturator vein (V. obturatoria) is a satellite of the artery and usually opens into the external iliae at the insertion of the psoas minor. Its radicles anastomose with those of tlie internal and external pudie veins (Figs. 451, 455). 2. The iliaco-femoral or external circumflex veins {\v. circumflexse 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 suljpubic groove behind the pectineus to unite with the deep femoral vein. The right and left veins are connected M' a large transverse anasto- mosis and each has a large connection with the obturator vein. Each receives the posterior abdominal vein {V. e]iigastrica 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 w-all, anastomoses with the internal and external thoracic and deep abdominal veins, and joins the external pudic or posterior al)dominal vein. A small vein accom])anies 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, 400) 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 betw'een that muscle and the sartorius, and joins the femoral or the external pudic vein.' 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 tlu^ recurrent tibial vein, which it ac- companies on the leg. It receives the recurrent tibial vein {V. recurrens tibialis)- 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 for- ward 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 lioek, ascends on the deep fascia of the external surface of the leg in front of the tentlo Achillis, passes between the biceps femoris and semitendinosus, and joins the posterior femoral vein. It is connected with the recurrent tibial vein bj^ a large anastomotic branch which crosses in front of the tuber calcis. I'sually a branch from it ascends along the great sciatic nerve and anastomoses with the obturator vein. 'The placo and mode of termination is quite variable. It may disappear from the surface of Ihe thisli at any point above the distal third. In some cases it'pa-sscs through the anterior pari of the gracilis instead of dipping in between that muscle and the sartorius. • This often joins the posterior femoral or the popliteal vein. THE LYMPHATIC SYSTEM 599 The popliteal vein (\'. poplitea) lies along the inner side of. the artery (Fig. 459). It is fornu'd liy the confluence of anterior and posterior tibial veins. Two anterior tibial veins (\'v. tibiales anteriores) usually accompany the artery of like name; tlie 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 titiial vein. It is a satellite of the artery The internal or great metatarsal vein {\. 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 aliove 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 jilantar 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 liga- ment, and ascends on the posterior face of the large metatarsal bone. At the proxi- mal end of the metatarsus it is connected with the external metatarsal vein b}^ 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 Ij-mphaticum) 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 l.ymph, which contains numerous lymphocytes.' The}' 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 IjTiiph 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 (Lymphoglandulse) are intercalated in the course of the lymph' vessels. They vary widely in size, some being microscopic, others ' 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 600 THE ^'EINS several inclics in length. In form tliey may bo 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 im- portant. 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 gra>- 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 arc 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 fe\\er. Each gland has a depression, the hilus, at which the blood-vessels enter and the cfTerent 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 thp 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. Smroiuiding this i.s a rich plexus of lymph vessels, forming the so-called sinus, iiicldsr.l in soiiio cases by a fibrous capsule. The gland consists of a mass of follicles, inclosed in a lihrous capsule, from which trabeculae pass in and unite the follicles. Be- neath the capsule i> llir peripheral sinus, wliich consists of a very rich plexus of lymph vessels; to this the afferent vessels pa.ss 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 cor- tex, since it is more vascular; it contains the central lymph sinuses, which have a similar structure to the peripheral sinu.s. The haemolymph glands dift'cr from the lymjah 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 trabeculae 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, nmch fewer in the dog, and apparently are alisent in the horse. The^^ occur along the course of the aorta, in the perineal fat, at the portal fissure, and with the gastric anil mesenteric lymph glands. In the ox they are also found under the trapezius muscle, under the skin of the ujjpcr 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 bj' the veins and lyiniih vessels. The large serous sacs are often included in this category-. The exact relationship be tween the lymphatic capillaries and the tissue spaces is still a matter of controversy. It is held by some that the lymph-ves.sels are in direct communication with the tissue spaces, while others maintain that the lymphatics are complete closed tubes. Communi- cation between I he s|i:n is and \ csscls is in general very free. Mall has shown that granules in- jected into till- liipaii.' .iitiiv ill-.' Kiurned by the lymphatics as well as by the veins, and intra- muscular injeetiuiis will enter I he 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 tlioracicus)is the chief collecting trunk of the lymi)h- atic .s.ystem. It l>egins as an elongated irregular dilatation, the cistema or recepta- culumchyli, which is situated between the right side of the aorta ami the right itus THE LYMPH GLANDS AND VESSELS OF THE HEAD AND NECK GOl of the diaphragm at the first and second huiil)ar vcitihne. The ihict enters the thorax through the hiatus aorticus and runs forward on the riglit 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 obliciucly over the left face of the esophagus, 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 ilistance (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 ujijier part of the origin of the anterior vena cava just liehind the angle of junction of the jugular veins. The terminal bend is ampuUate 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 tfie cisterna or at a varialile point from the right duct, runs across the left intercostal arteries parallel to tlie latter, and unites with it over the base of the heart or further forward. The two are connected bj 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 liy 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 Ij'mph glands of the intestine, stomach, liver, and spleen.' 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 bj- ducts from the prepectoral and right axillarj' glands, and by the left tracheal duct. The duct is provided v/ith several pairs of valves; the best developed are at its termination. THE RIGHT LYMPHATIC DUCT This vessel (Ductus lymphaticus dexter) — when present — collects the lymi)h 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 aiTerents. 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 fiu-ther 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 Ijackward about four or five inches (ca. 10 to 12 cm.). They are covered by the skin and a ' The lymph vessels of these organs appear to vary considerably in their mode of termina- tion, and the arrangement needs further study. Some ducts from the stomach, liver, and spleen open directly into the cistern. 602 THE VEINS thin layer of fascia and panniculus. and arc therefore palpable. Anteriorly they are firmly attached to the niylo-hyoidci, 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 liorder 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 w^th the subdural and subarachnoid spaces and send efferents to the pharyngeal anti anterior cervical glands. 2. The phaiyngeal lymph glands (Figs. 4.36, 437, 569) may consist of two groups. One lies on the lateral surface of the pharynx along the course of the ex- ternal carotid artery. These glands are related externally to the stylo-maxillaris and digastricus ancl 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 sulimaxillary 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 ])arotid 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 cesophagus; below to the external maxillary vein and the outer border of the omo-hyoideus.' 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 pharyn- geal glands. Their efferent vessels go to the middle and posterior cervical glands. 4. The middle cervical lymph glands (Lg. cervicales mediae) 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 tlie 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 lymjihatic duct on the right, or open directly into the vena cava. 6. The prescapular or superficial cervical lymph glands (Lg. cervicales ' Abscess here can be reached readily by an incision between the vein and the omo-hyoideus. THE LYMPH GLANDS AND VESSELS OF THE THORAX 603 supcrficiales) lie on the anterior border of the anterior deep pectoral muscle, in relation to the omo-hyoideus internally and the mastoido-humcralis externally (Figs. 431, 441, 46(3). They are on the course of the ascending branch of the in- ferior 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 col- lecting trunks for tlie lymph of the head and neck. Thej' 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 LYIVIPH 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 vertebrae, 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 tliere 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 oesophagus 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 thj'mus or its remains, the trachea, and the oesopha- gus. 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 pig- mented in dissecting-room subjects. The left recurrent ner\e hes above them on the ventral face of the trachea. 3. The bronchial Ijrmph 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 oesophagus (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. pul- monales). They receive the deep and most of the superficial lymph vessels of the lungs, and the efferents from the posterior mediastinal glands. Their efferent ves.sels 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 inilurated. 4. The posterior mediastinal lymph glands (Lg. mediastinales caudales) are usually small and are scattered along the posterior mediastinum above the oesopha- gus. They receive afferent vessels from the oesophagus, mediastinum, diaphragm, and liver. The efferents go to the bronchial and anterior mediastinal lymph glands, partly to the thoracic duct directly. 604 THE VEINS Sometimes one or two small glands are situated in the aeute 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 nutin grouiis, ])arietal antl visceral. The parietal glands lie in the subperitoneal or subcutaneous tissue; they receive the lymph \essels 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 atljacent 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 limibar lymph glands (Lg. lumbales) lie along the course of the abdom- inal aorta and ]iosterior 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 Imnbar trunks of origin of that vessel. 2. The internal iliac lymph glands (Lg. iliacae internffi) are grouped about the terminal part of the aorta and tlie 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. iliacie externa') form a group on either side on the iliac fascia at the i)ifurcation 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 (I^g. sacrales) are small nodes situated along the border's 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 mannnary glands in the female. The efferent vessels ascend through the inguinal canal and go to the deep inguinal and lumbar glands. G. The ischiatic Ijrmph 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. gastricije) 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 THE LYMPH GLANDS AND VESSELS OF THE THORACIC LLMB GOo 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 coeliac radicle of the thoracic duct, hut along the left part of the great curvature they go to the splenic glands. 2. The hepatic lymph glands (Lg. hepaticae) lie along the portal vein and hepa- tic artery and in the lesser omentum. Their efferent vessels go to the cceliac 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 whic-h 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 eiTerents jiass to the cceliac radicle of the thoracic duct. 4. The mesenteric lymph glands (Lg. mesentericse) 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 in- testinal radicles of the cisterna chyli. The lymph vessels of the intestine form three sets of capillary plexuses, ^^z., in the subserosa, submucosa, and mucosa. The lymph follicles, solitar}- 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 caecum are numerous and arc distributed along the course of the ctecal blood-vessels. Their efferents enter into the formation of an intestinal radicle of tlie cisterna chyli. G. The lymph glands of the great colon are extremely numerous and are placed close together along the colic Ijlood-vessels. Their efferent vessels are large and numerous. They converge to two large trunks which concur with those of the ctecum 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, pa-sses between that vessel and the coeliac artery, turns sharply backward across the right renal vessels and opens into the cisterna. It is formed by the union of the coeliac trunk with efferents from the glands of the small intestine, caecum 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 attaclunent of the mesentery, in part between the layers of the latter along the course of the l)lood-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 ihac glands. 5. The anal lymph glands (Lg. anales) form a small group on either side of the sphincter ani externus (Figs. 451, 453). They receive aflerents from the anus, perineum, and tail. Their efferents go to the internal iliac glands. THE LYIVIPH GLANDS AND VESSELS OF THE THORACIC LIMB 1. The axillary lymph glands (Lg. axillares), some ten to twelve in number, are grouped on the iimer 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 GOG THE VEINS veins with the brachial (Fig. 466). Their effercnts 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 cov(>red by the deep fascia and the posterior superficial pectoral muscle. They receive as affercnts most of the vessels from the limb below this point. Their efferents pass chiefly to the axillary glanrls, but in part to the prescapular glands also. A number of superficial lymph vessels ascend with or near the suljcutaneous veins (cephalic and accessorj' 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 j^lexus which drains into the prepectoral and prescapular glands by a number of vessels which accompany the cephalic vein. The deep lymph vessels of the pec- toral region run with the external thoracic vein to the axillary glands. THE LYMPH GLANDS AND VESSELS OF THE PELVIC LIMB i. The precrural or subiliac lymph glands (Lg. sul)iliaca?) are situated in tlie fold of the groin on the anterior liorder of the tensor fasciae lattB, 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 lymj^h 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 l.ymph glands. 2. The deep inguinal lymph glands (Lg. inguinales profunda) form a large group situated in the upjx-r 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. Tlieir efferent vessels ascend to the internal iliac glands. 3. The popliteal lymph glands (Lg. poplitese), usually four to six in number, lie behind the origin of the gastrocnemius and between the biceps femoris and semi- tendinosus at the division of the posterior femoral artery into its primary Ijranches (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 ac- companies 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 Fcetal Circulation The blood of the fa>tus 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 THE FCETAL CIRCULATION 607 internul iliac arteries and pass downward and forwartl in the uml)ilical folds of peri- toneum on either sitle of the bladder to the umbilicus. Here they are incorporated with the umbilical vein and the urachus in the umbilical cord, ramify in the allan- tois, and end as the capillaries of the fcctal placenta. They conduct the impure blood to the placenta. After birth these vessels retract with the l)ladder to the pelvic cavity; their lumen becomes greatly reduced and the wall thickened so that they arc cord-like and are termed the round ligaments of the bladder. The umbilical vein receives the oxygenatetl 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 cortl on entering the abdomen and passes for- ward 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 imibilical vein is conveyed directlj- 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 l)etween the atria, by wliich the latter communicate with each other. It is guarded by a valve (Valvula foraminis ovalis) which prevents the Ijlood from passing from the left atrium to the right. After birth the foramen soon closes, but this part of the septum remains membran- ous, and there is a deep fossa ovalis in the right atrium which indicates the posi- tion 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 1 mited in the foetus, 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 circula- tion undergoes promptly an enormous increase and the ductus is rapidly trans- formed into a fibrous cord — the ligamentum arteriosum. The only arterial blood in the fictus 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 car- ried into the right atrium by the posterior vena cava passes largely, if not entirely, through the foranaen 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 lilood passes into the left ventricle ami 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. 608 THE BLOOD-VASCULAR SYSTEM OF THE OX THE BLOOD-VASCULAR SYSTEM OF THE OX The Pericardium and Heart The pericardium is attached by two fibrous bands (Ligamenta sterno-peri- ('ar(Haca) to the .sternum opposite the facets for the sixth costal cartilages; these Hganients, right and loft, are embedded in the mass of fat which separates the apex of the pericardium from the floor of the thorax. Ai(liru}r nrm cava Brachiocr plialtL trunk Riijhl auricle I'ubnonary arUrij Lignmrnlum arkriosum Left branch of pulmonary artery Pulmonary rcht.t / \\ Po^hrior rcna cava Vena hiiniazyyos I.( ft auricle Right ventricle Left coronary art( rt/ Poxtrrior branch of left cnriiiiiirii artery in ill/, mil iliiile rp-oove Left nnlricle Tlie heart of the a(hdt ox has an average weight of about .'')} 2 to fi 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 (liameters. A shallow intermediate groove (Sulcus intermediiis) extends from the coronary groove down the left side of the po.sterior border, but tloes not reach the apex. The amovmt 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 exten- THE ARTERIES (509 sive contact with the lateral wall of the thorax on the left side, but none on the right side, where a consideraMo thickness of lung covers the pericardium.' Two bones, the ossa cordis, (h>velo]) in the aortic fibrous ring. The right one is in apposition witli tlie atrio-ventricular rings and is irregularly triangular in form. Its left face is concave anil 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 separatetl 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 = 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 wliich descends in the intermediate groove, and terminates l>y 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 liranches 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 lengtli. The brachial arteries give off in tlie thorax the following branches: 1. A common trunk for the suljcostal, dorsal, superior or deep cervical, and vertebral arteries. (1) The subcostal artery commonly arises separately, but may 1 c given off as in the liorse. It sui)iilics the first three intercostal arteries. (2) The dorsal artery is relatively small. It usually ascends in front of the first costo-vertehral 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 vertebra or be- tween the sixth and seventh cervical and is distributed as in the horse. (-4) The vertebral artery i)asses along the neck as in the horse to the inter- vertebral foramen between the second and third cervical vertebra;, 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 anas- tomoses—and divides in the atlas into two branches. The smaller internal division (cerebrospinal artery) passes forwartl 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 intervcrteljral foramen of the atlas and ramifies in the muscles of the neck in that region, com- pensating 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 mus- cles are large and compensate for the small size of the deep cervical artery. The collateral spinal branches of the vertebrals pass through the intervertebral for- amina, 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. ' It is, of course, only the pcricanliuin wliich comes in contact with the wall, but it is cus- tomary as a matter of convenience to speak of the relation of the heart as tlioUKh it were direct. - Only the most important differential features of the arrangement of the vessels as compared with those of the horse will be considered. 39 610 THE BLOOD-VASCULAR SYSTEM OF THE OX 3. The inferior cervical artery corresponds usually to the ascending branch of that vessel in tlic horse. 4. The external thoracic artery is large and usually gives off a branch which is equivalent to the desceniling branch of the inferior cervical artery of the horse. THE COMMON CAROTID ARTERY The carotid arteries usually arise from a common trunlc about two inches (ca. 5 cm.) in length, but in exceptional cases are given off separately from the brachio- FiG. 46S.— Schema of Chief Arteries op Head of Cow. 1, Common carotid artery; S, thyro-laryngeal; S, thyroid; 4, laryngeal; 6, pharyngeal; 6. occipital; 7, condyloid; S, middle meningeal; 9, pharyngeal; /O. external maxillary; I/, Ungual; J2, sublingual; /d. superior labial; H, internal maxillary; IS. masseteric; 16, inferior alveolar; 17, buccinator; IS. great palatine; 19. sphenopalatine: 20, posterior auricular; «/, superficial temporal; 2^. posterior meningeal; 23, anterior auricular; S.^, artery to matrix of horn; 35, deep temporal; SS, arteries to rete mirabile; a?, frontal; aS, malar; 2S', dorsal na.sal continuation of malar; 39, infraorbital; 39' , lateral nasal continuation of 29. cephalic. Each jiursues 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, (rso])liageal, :md muscular branches, it gives off the thyroid and laryngeal arteries. The thyroid artery (A. thyreoidea cranialis) bends around the anterior end of the thyroid giantl, in which it ramifies. The accessory tliyroid artery is usually absent. The laryngeal artery may arise with the thyroiil. THE COMMON CAROTID ARTERY 611 1. The occipital artery is relatively small. It gives off: (1) The pharyngeal artery, which, however, may arise from the external carotid. (2) Several l)ranehes to the muscles (chiefly the flexors) and to the atlanto- occipital joint. (3) The condyloid artery jiasses 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 i)asscs 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. 2. The external maxillary artery is smaller than that of the horse, but pursues Fig. 469. — Floor of Cranium and .\nterior Part of Vertebral Canal of Ox. 1, Vertebral artery; 2, muscular branches of /; 3, branches of / to the rete mirabile, 4; 5, branches of in- ternal maxillary artery to rete; 6. branch of internal maxillary artery entering cranium through foramen ovale; 7, condyloid artery; S, emergent artery from rete, distributed like internal carotid artery of horse; 9. 9' , longitu- dinal vertebral sinuses; a, cribriform plate; 6, optic foramina; c, for. lacerum orbitale + rotundum; d, foramen ovale; e, occipital condyle; /, g, h, first, second, and third cervical vertebrae. (After Leisering's Atlas.) a similar course. The lingual artery is large, and often arises separately from the common carotid; it gives ofl" 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 latge; it usually gives off a branch which runs forward almost parallel with the lateral na-sal. The angular artery is absent or rudinientary, 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. G12 THE BLOOD-VASCULAR SYSTEM OF THE OX (4) The masseteric artery rcsombles 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 masse- ter. (2) It gives off a Ijranch which corresponds to the posterior meningeal artery of the horse, enters the temporal canal, and ramifies in the dura mater, giving oft" 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 umscle and the eyelids. (5) A large branch passes around the outer side of the ba.se of the horn-core, supplies the matrix of the horn, and anastomoses across the back of the frontal emincnice 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 comnion triuik with the infra- orbital and gives ofi the dorsal nasal and the angular artery of the eye. (4) The infraorbital artery is large and emerges from the infraorbital foramen to form tlie 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 nasopalatine canal and terminates in the mucous membrane of the anterior part of the nasal cavity. ARTERIES OF THE THORACIC LIMB Tiie brachial artery pursues the same course in the arm as that of the horse. At the elbow it becomes the median.' The chief differential features in its branches are as follows: 1. Tli(> 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 supjilies 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. Tlie superior collateral ulnar artery is often doulilc, and does not extend to the carjius. The median artery (jjosterior railial 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 bra- ciiial, passes through the ])roxinuil interosseous space, and descends (as the dorsal interosseous) in the groove between the radius and ulna, and concurs in the forma- tion of the rete carpi dorsale. At the distal end of the forearm it sends a branch ' The homologie.s of tlie vessels of the lower parts of the limbs are still unoortain. The account given here is mainly based on the views of Sussdorf and Baum. ARTERIES OF THE THORACIC LIMB 613 tlirough 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. 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 Fig. 470. — Artfhiks of Di6t.\i- Part of Right Fore Limb of Ox, -\.NTtRioB Vikw. a. Interosseous arter>'; b, dorsal branch of radial arter>" c, rete carpi dorsale; rf, dorsal meta- carpal arterj-; e, dorsal common digital arterj-; /, /, dorsal proper digital arteries. Fig- 471.' — .\rteries of Distal Part of Right Fore Limb of Ox. Posterior View. ff, L'lnar artery; h, radial arterj-; i, volar branch of common interosseous arterj'; k, /. m, deep volar metacarpal arteries: .4. r., volar arches; n, volar com- mon digital arterj-; o, o', p, volar proper digital arteries. proximalis) runs outward between the suspensory ligament and the large meta- carpal 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 arterv, 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 614 THE BLOOD-VASCULAR SYSTEM OF THE OX cover of the flexor carpi internus without giving ofi" any large branches in the fore- arm. 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 iirancli from the internal deep volar meta- cari)al 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 l)ranch from the arch pa.sses forward through the inferior foramen of the metacarpal bone and joins the dorsal metacarjjal artery which descends from the rete carpi dorsale in the anterior metacarpal groove. The volar common digital artery (A. metacarpea volaris su])(rficialis III.) passes into tlie 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 correspond- ing vessels in the horse. The volar common digital detaches a branch (A. inter- digitalis 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 eommon 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 chgital artorios, 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 rctc car])i ilorsale, descends in the groove on the anterior face of the metacarpal lione, and is joined l)y the inferior perforating metacarpal artery from the deep volar arch to constitute the dorsal common digital artery. This vessel (A. digitalis commimis dorsalis III.) divides into two dorsal proper digital arteries. The internal digital artery (A. digiti III. medialis) is the continuation of the internal dec]) 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 oesophageal arteries often arise separately. Ten pairs of intercostal arteries usually arise from the aorta. The other three come from the sulx'ostal artery. The two phrenic arteries are very variable in origin. They may come from the aorta, the co'liac, left ruminal, or an intercostal or lumbar artery. BRANCHES OF THE ABDOMINAL AORTA The cceliac artery is aljout 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 th(> posterior vena cava on the right. It gives off five chief liranches. 1. The hepatic artery arises from the convex side of the curve of the ca-liac artery as it crosses the jjosterior vena cava. It passes downward, forward, and to BRANCHES OF THE ABDOMINAL AORTA 015 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 arter_y, 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. (.'■!) The cystic artery supplies the gall-bladder. (4) The gastro-duodenal artery divides into right gastro-epiploic and pan- creatico-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 rum(>n. 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 Ijottom 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 continua- tion of the ca?liac. 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. gastro-epiploica 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 aboma- sum, 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 Ijranch 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 coeliac, 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. 616 THE BLOOD-VASCULAR SYSTEM OF THE OX Fig. 472. — Gastric Ahteries of Ox, Right View (Partly Schematic). 1, Coeliac artery; S, right ruminal ; S, splenic; 4. reticular; 5, left ruminal; 6, omaso-abomasal; 7, dorsal branch of 6: S, ventral branch oi 6 (= left gastro-epiploic); A, dorsal sac of rumen; B, ventral sac of rumen; C, C, posterior blind sacs; D, a?sophagus; E, reticulum; F. omasum; G, abomasum; H, duodenum; /, right loogitudinal furrow of rumen. By an oversight the reticular artery is shown as arising from the omaso-abomasal. Fig. 473. — Gastric Ar /. Left ruminal artery; S, continual nimino-reticular groove; .1, dorsal sac of rumen; a. ventral sac ot rumen; f. (. . po gus; £, reticulum; F, rumino-reticular groove; G, left longitudinal furrow of rumen ii:s OF Ox, Left Virw (Partly Schematic). of right ruminal artery; 3, reticular artery, which disappe rumen; C, T. posterior blind sacs; />, ccsopha- BRANCHES OF THE ABDOMINAL AORTA 617 2. The ileo-cseco-colic artery ramifies on the right face of the spiral part of the colon. It gives off the iieo-cjeeai artery, which divides into ileal and caecal 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 mesen- teric pursues a course in the mesentery corresponding to the series of mesenteric lymph glands. The two preceding vessels are essentially the arteries of the small intestine, Small Fig. 474. — Plan of Br.\nches of A.nterior Mesexteric .\rtert of Ox. /, .\nterior mesenteric arterj" ^. middle colic arter>-; 3, ileo-cseco-colic artery; 4, ramus collateralis; 6, continuation of anterior mesenteric artery, giving off branches to small intestine; 6, csecal artery; 7, colic branch of posterior mesenteric arterj-; .4. termination of duodenum. 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 coeliac artery. Both arteries give branches to the lymph glands.' ' 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. 618 THE BLOOD-VASCULAR SYSTEM OF THE OX The posterior mesenteric artery arises from the aorta near its termination. It is small and su])i)ii('s 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 liackward. but necessarily varies in direction in conformity with the position of the kidney {q. i'.). The spermatic arteries resemble those of the horse. The utero-ovarian arteries are small. The five ]Kurs of lumbar arteries derived from the aorta are distributed much as in the horse. Tlie sixth usually comes from the internal iliac artery. The middle sacral artery is a vessel about 3 mm. in diameter which continues Fig. 475. — Pelvic Arteries of Cow. Part of the right wall of the uterus and vagina is removeti and the cervix uteri is shown in sagittal section, a, .\orta; 6, utero-ovarian artery; 6', ovarian, and t", uterine branch of 6; c. external iliac artery; rf, right internal iliac artery; e, conunon trunk of umbilical artery (c') and middle uterine artery (/); g, ilio-lumbar artery; h, anterior gluteal arteries: /, middle ha-morrhoidal artery; /:, posterior uterine artery; /, perineal artery; 7h, posterior gluteal artery; n, obturator arteries; o, artery of clitoris; p, posterior mesenteric arterj-; r. anterior ha-mor- rhoidal artery; «, middle sacral artery; i, ovary; 5, apparent body of uterus, really apposed horns; 2', cornu; 3, vagina: 4, cervix uteri; 4' , vaginal part of uterus Cos uteri); 5, 6' , broad ligaments, large part of right one re- moved; 6, urinary bladder; 7, rectum; 5, sacrum; p, symphysis pelvis, (.\fter Zieger.) 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 (htemal) arches of the coccygeal vertebra;. 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 ARTERIES OF THE PELVIC LIMB 619 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. urcterica) and the deferential artery (A. defcrentialis), 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-ovanan artery. (2) The ilio-limibar artery is relatively small and is distributetl chiefly to the subluml)ar muscles. It is sometimes rejilaced tiy branches of the circumflex iliac and gluteal arteries. (3) The anterior gluteal artery is commonly re])resented by several vessels. (4) The obturator artery is represented by several small branches which supply the obturator and adductor muscles. (5) The iliaco-femoral anil lateral sacral arteries are alisent. 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 notcli ami 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 liranches 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 ]3enis; the a. dorsalis penis runs along the dorsum penis to the glans and gives twigs to the j^repuce; the a. profunda penis gives off a perineal branch and enters the corpus cavcrnosum penis. In the female it gives off a large posterior uterine artery, which supplies tlie 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 Ijase of the mammarj' 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 sujjply the oljturator internus and compensates otherwise for the at).sence of the obturator artery. .3. The anterior femoral artery is large. It often gives off the external cir- cumflex artery of the thigh, which perforates the proximal end of the ciuadriceps, gives branches to that muscle, tlie iliacus, glutei, and tensor fasciie lata'. 4. The saphenous artery is large. It descends in front of the homonymous vein to the postcro-internal surface of the hock, where it divides into two plantar branches. The internal plantar artery (A. plantaris medialis) is the direct continua- tion 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 witli the perforating meta- tarsal 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 620 THE BLOOD-VASCULAR SYSTEM OF THE OX digital artery. Tlie external plantar artery (A. plantaris lateralis) is small. It descends along the outer Iwrder 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 -$" Fit;. 476. — AnTKRiFs 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. Fig. 477. — Arteries of Distal Part of Right Hind Limb of Ox, Posterior View. f. Saphenous artery; /,/', 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; /, /', internal and external plantar digital arteries. superficial plantar metatarsal artery, it assists in forininii; the distal plantar arch and heconies the external digital artery. The posterior tibial artery is relatively small and is distributed chiefly to the muscles on tlie posterior surface of the tibia. Lower down it is replaced by the saphenous artery as descrilxMl 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 thr(nigh the proximal foramen of the metatarsal bone and concurs with the superficial plantar THE VEINS G21 arteries in forming the proximal plantar arch. Near the distal end of the metatarsal bone it gives off the distal perforating metatarsal artery vvhirh passes hack through the distal metatarsal foramen and assists in forming the distal i)lautar arch. The two arches are connected by the small deep plantar metatarsal artery which lies in the groove on the jiosterior 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 arterj^ 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 ' The vena hemiazygos usually takes the jjlace of the vena azygos. It lies along the left side of the aorta and the bodies of the thoracic vertebrae, turns down across the left face of the aorta and left pidmonary artery, runs liack over the left auricle and opens into the great coronarj* vein or the right atrium. It receives the intercostal veins. Two jugular veins occur on either side. The internal jugular vein (V. jugu- laris interna) is a relatively small vessel which accompanies the carotid artery. It arises by occipital, laryngeal, and thyroid radicles, receives tracheal, a'sophageal, 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 sternocephalicus and omo-hj-oideus 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 cereliral vein. It is also drained bj- 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 di.u;ital 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 ' Most of the differences in the veins of the ox are correlated with thc-ie 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. 622 THE BLOOD-VASCULAR SYSTEM OF THE OX 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 meta- carpus 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 meta- carpal 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 tleserve special notice. They converge to a venous circle at tlie base of the udder, which is drained chiefly l)v two pairs of veins. The subcutaneous abdominal vein (anterior mammary or "milk" vein) is very large in animals of the dairy lireeds 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 manmiary 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 Iiorder 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 anil 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 u])ward 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 Ijranch from the venous arch above the sesamoids. It ascends super- ficially 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 liorder 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 THE LYMPH VESSELS AND GLANDS 623 metatarsal vein is larger than the preceding. It passes superficially over the outer face oi 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 formetl by the confluence of three radicles; it usually receives the small posterior mesenteric vein. The portal tributaries are in general satellites of the correspond- ing arteries. The Lyhph Vessels and Glands The thoracic duct arises from a small cisterna cliyli 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 Ij'mph 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 l)ifurcates or divides into three or four branches, which are often connected by plexiforna anastomoses. The efferent vessels from the intestine converge to a large trunk which ac- comjianies 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 stom- ach, 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 sali- vary gland and the sterno-cephalicus muscle. Usually one or two hremol.vmph 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 hsemolymph glands lie on its deep face. The pharyngeal lymph glands number two or three on each side. Of these, two large suprapharyngeal glands (Lg. retropharj-ngeales) 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 se\-eral hifimolymph glands. An atlantal gland is situated below the wing of the atlas on the spinal accessory nerve. It is iliscoid, 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 (('. 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. 624 THE BLOOD-VASCULAR SYSTEM OF THE OX 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 effeicnts lo tlie prescapular gland. The prescapular or superficial cervical lymph gland i.s situated at the anterior border of the sujiraspinatus under cover of the niastoido-humeralis and omo-trans- versarius. It is elongated and may be an inch or more in width and four or five inches long. Two occur in exceptional cases. \ chain of ha'molymph 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-trans- versarius at the point whore it passe.-; under the niastoido-huiucralis (Forgeot). 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 Fig. 478. — Superficial Lymph Gi,.^n-i)S of Cow Projected on SrRF.\CE of Body. i. Submaxillary: 3, subparotid: d, atlantal: 4, parapharyngeal: S, anterior cervical: 6, midiUe cer%-ical: 7, pre- scai>ular; S, precrural. (With u.se of tig. in EUenberger-Baum, .\nat. f. KUnstler.) brachial vein at the first ril), and one at tlic junction of the common trunk of tlie external and subcutaneous thoracic veins with the brachial. The intercostal lymph glands are situated, as in the horse, at the uj^jjcr iJurts of the intercostal sjiaces. Associated with them are hsemolymph glands. The sternal lymph glands are situated along the course of the internal thoracic artcrj' 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 oesophagus and the trachea." Hiemolyni|ili glands occur here also. Usually three large bronchial lymph glands are present (Fig. 289). One is situated at the origin of each chit'f l)r(inclius anil the third is under the trachea at the origin of the special bronchus of the ajsical lolie of the right lung. Another ' The upper series is continuous with the posterior mediastinal ((esophageal) glands and the lower or tracheal glands with the bronchial. Hence we might well designate the mediastinal glands as ccsophageal (anterior and posterior) and tracheo-bronchial. THE LYMPH VESSELS AND GLANDS 625 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 cesophagus. There may be a single gland about eight inches (ca. 20 cm.) long, the anterior half of which lies on the (rsoph- agus (Fig. 289).' 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 l3Tnph glands form an irregular series scattered along the abdom- inal aorta and posterior vena. A bean-shaped renal lymph gland occurs at the hilus of each kidney. Hiemolymph glands occur along the course of the aorta. Fig. 479. — Ixtestine of Ox, Sprea Ca, Ciecum; C, colon; D, duodenum: //, ileum; J , jejunum; R, rectu nteric Ij-mph glands. (.A.fter The internal iliac lymph glands comj^rise a group of five or six at the termi- nation 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 diver- gence 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 l)etween 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 ' When enlarged, as is often the case in tuberculosis, tliis gland frequently causes difficulty in swallowing and in rumination and produces chronic or recurrent bloating. 40 626 CIRCULATORY SYSTEM OF THE PIG of tlie 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 diam- eter, is situatcil on the lower jiart of the sacro-sciatic ligament near the lesser sciatic notch under cover of the bicejis 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 runiinal 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 aliomasum at the attachment of the great omentum. Two or three large hepatic or portal lymph glands are found at the upper part of the ])ortal 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 coeliac artery. A large discoid cceliaclymph gland lies on the pancreas and the coeliac artery, covering the latter as it gives olt" its primary branches. The mesenteric lymph glands are large and numerous. Thej' 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 fasciae latae a short distance above the stifle. It is elongated like the prescapular gland and may be six inches (ca. 15 cm.) long. Several subcutaneous hiemolym])h 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 fascise latae, and one or more small ones occur on the surface of the latter nuisrle. 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 oiijiosite to the third rib as far as the xijihoid cartilage, and also to the sternal part of the diaphragm. The heart is small in i)roportion to the body-weight, especially in fat animals. It is relatively short and wide. The apex is blunt and is marked by a notch (In- cisura apicis). Its long axis is more oblique, but it is less asynunetrical 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 THE ARTERIES 627 right one. The right longitudinal groove is placed far back and there is no pos- terior 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 ])asscs 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 liy 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 brachio- cephalic. 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. Thej' 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 supphes 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 pharj-ngeal 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 jiursues a flexuous course between the ramus of the mandible and the jitiTygoid nniscles. 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 uifra- orbital 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 (Esophageal arteries usually arise separately. The coeliac 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 l)ranches, 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 pancre- 628 CIRCULATORY SYSTEM OF THE PIG atico-duodonal ami right gastro-epiploic. The anterior gastric usually supplies the cesopluiKcal artery. The continuing trunk (A. hepatica propria) gives off a cystic })ranch and divides in the portal fissure into four branches which supply the liver. The splenic artery gives off the ])osterior gastric (usually), branches to the stomach above the cardia, twigs to the pancreas, short gastric arteries to the left part of the great curvatur(>, and sjilenic liranches, and is continued as the left gastro- epiploic artery. The postorior gastric may uri.sc from tlie gastro-liepatic or in tlic angle of divergence of the two primary divisions of the cochac. The a?sophageal l>ranch may come from the splenic. J""ii;, 4,S0. — Artehiks of DmTAL Part ok Kic-.ht Fore Fig. 4S1. — Arteries of Dis , Part of Kk:ht Fore Limb ok Pig, A.vterior Vii:w. a. Terminal part of volar interosseous artery; b. ilorsal interosseous artery; c, rete carpi tlorsale: f/. dorsal metacarpal arteries; e, dorsal coniinoii dig- ital arteries; /, dorsal projjer iligital arterie.s. Limb of Pig, Posterior View. 0, Ulnar artery; h, superficial branch of radial artery; /, collateral ulnar artery; j, volar interosseous arterj-; h, deep branch of radial artery; k\ deep volar metacarpal arteries: /, superficial volar metacarpal arteries; iii, 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 i)ancreas, the ilio-ca'cal 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 liranches 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. .\ phrenico-abdominal artery arises on either side a little in front of the renals. It divides into braiiclics which go to the costal part of the dia])liragm and the abdom- inal muscles. The renal and spermatic arteries present no special characters. THE ARTERIES 629 The posterior mesenteric artery arises near the termination of the aorta. It is small and is clistrilnUcd 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. 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 Fig. 482. — .\rteries of Dist.\l Part of Right Hind Limb of Pig, .\nterior View. a, .\nterior tibial artery, continued on tarsus as the dorsalis pedis; b, perforating tarsal arterj"; c, dorsal metatarsal arteries; d, common digital ar- teries; e, proper digital arteries. Fig. 483. — -Arteries of Dist.il Part of Right Hind Limb of Pig, Posterior View. /. Saphenous artery, continued as internal tarsal artery; g, external tarsal artery; h, internal plantar artery; h' , external plantar artery; i, per- forating tarsal artery; j, deep plantar metatarsal arteries; k, common digital arter\-; /, proper digital arteries. the corresponding interosseous spaces and unite with branches of the volar meta- carpals 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 tlie 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. 630 CIRCULATORY SYSTEM OF THE PIG 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 jjostcrior abdominal artery, which otherwise arises from the deep femoral. The deep femoral artery is given off above the level of the pubis. The pos- terior abdominal and external pudic arteries may arise from it by a short common trunk or separately. The external pudic gives branches to the i)reinice but not to the penis. Tiie popliteal artery gives off the peroneal. The femoral artery gives off a short trunk which divides into anterior femoral and external circuniflex 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 \\ ith the perforating tarsal arterj- in forming the proximal plantar arch. The posterior tibial artery is small, being replaced distally by the saphenous. It gives branches to the nuiscles on the posterior face of the tibia and supplies the nutrient artery of that bone. The anterior tibial artery is continued as the dorsalis jiedis on the flexion sur- face 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 jilantar 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 ami)ulla. The latter suddenly contracts and opens into the termi- nal ])art 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 suliniaxillary 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 pos^^erior border of the masseter, partly covered by the parotid gland. Another large subparotid gland lies below the liase 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 i)liarynx aliove the external carotid artery and below and THE LYMPH VESSELS AND GLANDS 631 behind the paramastoitl 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 ju^uhir vein. The prescapular lymph glands are situated at the anterior border of the anterior deep pectoral muscle under cover 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 tlie trachea; the others are situated on the brachial vessels as they turn around the first rib. Tlie axillary lymph glands are usually absent, but very small nodes may l)e found near the insertion of the latissimus dorsi. Cubital glands are not present. Fig. 484. — Stomach and Part ok Lvtestixe of P:g, Spread Out. a, Pyloric portion of stomach; 6, duodenum; c, jejunum; d, caecum; e, /, colon; ff, pancreas; A, epiploi foramen {ol Winslow); i, portal vein; t, hepatic lymph glands; /, gastric lymph glands; m, oesophagus. (Afte 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 Iimibar 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 cir- cumflex iliac and the external and internal iliac arteries; (2) a gland in the angle of divergence of the internal iliac arteries. 632 CIRCULATORY SYSTEM OF THE DOG The external iliac lymph glands are small, two or three in number, and lie in front of the cirruniflcx iliac vessels near the point of the hip. The visceral lyiniili 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 ou 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 caecal lymph glands situated along the first part of the csecal 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 (if the ilium. The superficial inguinal lymph glands are situated behind the external ingui- nal ring. No deeji inguinal lymph glands are present. The popliteal lymph glands are small normallj- and may escape notice. A few nodules occur in front of the chstal 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 ape.x 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.' 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 peri- cardium is in direct contact with the chest-wall over a narrow triangular area (l)ase 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 tnmk. 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 cor- onary 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 relative weight is subject to wide variation. It is large in hunting dogs and such as are trained for speed or worked. THE ARTERIES 633 The Arteries There is no common brachiocephalic trunk (anterior aorta). Two hirgc ves- sels arise from the convexity of the aortic arch; these are the brachiocephalic and left brachial arteries. The brachiocephalic gives oE the two carotid arteries, no common trunk being present. It freciuently also sup]5lies the posterior tliyroid artery. The intrathoracic branches of the lirachial 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 ril), and the superior cervical through the first intercostal space. The latter is relatively small. 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 Fig. 485. — .\rteries of Thoracic Cavity and Part of Neck of Dog. a. Aortic arch; a', thoracic aorta; b. bracliiocephaUc arterj'; c, left brachial artery; rf. rf, common carotid arteries; e, vertebral artery; /. dorsal artery; tj, deep or superior cervical artery (usually given off from a com- mon trunk with /': h. extrathoracic part of /; i, subcostal artery; k, inferior cer\ucal artery; I. descending branch of k: m. ascending branch of k: n, internal scapular; o, acromial; p, superficial cer\'ical; q. s. extrathoracic part of left brachial; r. external thoracic; t, internal thoracic; t' , asternal; (". anterior abdominal; u, perforating branch of (; r, anterior mediastinal (thymic); u', ventral intercostals; x. bronchial; t/, oesophageal; 2/. dorsal intercostals; z, descending branch of left coronary artery; z*. circumiiex branch of same; 1, cesophagus; 2, trachea; 3^, bronchi; 3, first rib (sawn off); 4. right ventricle; 5, left ventricle; -5'. left auricle; 5", pulmonary artery (cut off); (?, diaphragm; 7, S, 9, last three cervical vertebrae; 10, thymus. (.\fter EUenberger, in Leisenng's Atlas.) 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 vertebra^ into the vertebral canal and unites with the opposite artery and a branch of the occipital arterj- 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. 634 CIRCULATORY SYSTEM OF THE DOG The external thoracic artery arises outside of the thorax and sends Ijranches to the mammary ghinds. 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 oesophagus. Collateral branches arc the posterior thjToid (which may, however, arise from the right or left brachial or the inferior cervical), pharyngeal, thryo- laryngeal, muscular, tracheal, and glandular (to the submaxillary gland). Each carotid divides under the wing of the atlas into occipital and internal and ex- ternal carotid branches. The occipital artery is small. It gives off condyloid and posterior meningeal branches, jjasscs up through the notch on the anterior margin of the wing of the atlas, and is tlistributed to the muscles of this region. Its cerebrospinal branch Fir,. 486.— SuPERFicuL Vkssels of Head of Dog. /, Facial artery; S. inferior labial artery; 3, artery of angle of mouth; 4. superior labial artery; 6, lateral nasal artery; e, dorsal na.sal artery; ?•, superficial temporal artery; S, transverse facial artery; S, anterior auricular artery; 10, zygomatico-orbital artery; /;, satellite vein of 10; 12. ant. auricular vein; IS, superficial temporal vein; H, internal ma.\illary vein; Id, post, auricular vein; 16. 17, external jugular vein; 18, external maxillary vein; i9, J?ij, facial vein; «0, inf. labial vein; «/, buccinator vein; 2^, vena refiexa; 2.<, superior labial vein; 25, vena angularis oculi; ^ff, dorsal nasal vein; a, concha; 6, parotid gland; c submaxillary gland; (/.submaxillary lymph glands; <•. mylo-hyoideus; /, digastricus; i;, masseter; h. zygomaticus; i. scutularis; A-. tejnporalis; /, or- bicularis oculi; m, zygnmatic arch; n, retractor angnli oris; o. buccinator. (EUeiiberger-Baum, .\nat. d. Ihmdes.) 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 [)osterius, enters the carotid canal and forms a bend before entering the cranium through the carotid foramen. It forms a plexus which is connectetl by liranches 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 tiie ihrect continuation of the common carotid. It passes along the lateral wall of the pharynx, emerges from beneath the digastricus. and divides into suiierficial temijoral and internal maxillary arteries. It gives off the large fiexuous lingual artery which has a course similar to that of the horse. THE ARTERIES 635 The external maxillary, smaller than the lingual, passes along the upper border of the digastrieus, gives off the sul)lingual, 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 digastrieus and continues between the mylo-hyoideus and the ramus of the mandible. The posterior auricular artery arises at the anterior border of the digastrieus, gives branches to the salivary glands and the adjacent muscles, and ascends on the convex face of the concha. It divitles 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 tenijioral fascia toward the eye, and dividt'S 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 gi\'cs off the middle meningeal, which sends a branch to the carotid ple.xus. 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 ophthal- mic and gives off the artcria centralis retinae. 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 railial 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 supra- spinatus, deltoid, trapezius, and mastoido-humeralis. In about half the cases it gives off the anterior circumflex, Avhich 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 aliout a third of the way clown the arm. (4) The bicipital artery (for the liiceps) is given off at the lower part of the arm. (.j) 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 tlie 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 f|uadratus, gives off a branch to the rete carpi dorsale and the fifth volar metacarpal artery, antl terminates by joining the volar liranch 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. 636 CIRCULATORY SYSTEM OF THE DOG The dorsal branch assists in forming the rete carpi dorsale. The larger volar branch descends l)ehind the inner border of the carpus and joins the end of the volar interosseous in forming the deep volar arch. From this areh three deep volar Fig. 487. — Vessels and Nerves of Inner Surface OF Shoulder and Arm of Dog. a, b. Brachial artery; c, subscapular ves.sels; d, thoracico-dorbal vessels; e, deep brachial vessels; /, sup- erior collateral ulnar vessels; g, brachial vein; h, h", cephalic vein; h', mediano-radial vein; (, anterior thoracic nerves; k, musculo-cutaneous nerve; /, median nerve; m, ulnar ner\'e; «, radial nerve; o, thoracico- dorsal nerve; 1, subscapularis muscle; 2. supraspinatus muscle; S, teres major, 4, latissimus dorsi; 5, deep pectoral muscle; 6, biceps brachii; 7, lonfi head of tri- ceps; S, tensor fascitp antibrarhii; 9, internal head of triceps; 10, pronator teres. (Ellenberger-Baum, .\nat. d. Hunde**.) Fig. 4S8. — Arteries of Forearm of Dog, Inner View. a, Brachial; a', median; c, common interos- seous; d, volar antibrachial; e, radial; *•', e", dorsal and volar branches of e; f,f', cutaneous branches of e; (7, ulnar; /, biceps brachii; 2. extensor carpi radialis; 3, pronator teres; 4. deep digital flexor; 6, radius; 6, superficial digital flexor; 7, flexor carpi radialis; S. flexor carpi medius; 9, humerus. (Ellenberger-Baum, Anat. d. Hundes.) 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. THE ARTEKIES 637 The ulnar artery descends on the deep flexor of the digit, and sends a connecting branch to the radial ahove 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 cor- responding 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 Fig. 489. — .\rteries of Distal Part of Right Fore Limb of Dog, .Interior View. a, Branch of volar interosseous artery: b, proximal collateral radial arter>' (external branch); c, radial artery (dorsal branch); d, rete carpi dorsale; e, deep dorsal metacarpal arteries; /. superficial dorsal metacarpal arteries; g, common digital arteries; k, proper digital arteries. Fig. 490. i. Radial artery; ;. ulnar artery; k. volar in- terosseous arterj-; /.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. 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. 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 oesophageal branches, in 638 CIRCULATORY SYSTEM OF THE DOG addition to the broncho-oesophageal, which arises close to or with the sixth inter- costal and ramifies in the usual manner. The abdominal aorta, after giving off the external iliac arteries, continues about half an inch tu an inch (ca. 1 to 3 cm.) under the last lumbar vertebrsB, gives off the internal iliacs, and is continued by the middle sacral artery. This small vessel runs backward under the sacrum and coccygeal vertebrae and gives off branches in segmental fashion. The coeliac 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, anasto- moses with the (left) gastric artery, and is continued by the gastro-duodenal. This Fig. 491. — End Branches of Aorta and Radiclp;!? of rosTERioR Vena Cava or Dog. o, .\bdominal aorta; 6, posterior mesenteric artery; c, lumbar arteries; d, circumflex iliac artery; e, ex- ternal iliac artery; /, deep femoral artery; g, posterior abdominal artery; h, external pudic artery; a, femoral artery; i, i, internal iliac arteries; t, visceral branch of iV /, parietal branch of iV m, iUo-lumbar artery; n, anterior gluteal artery; o, lateral coccygeal artery; p, posterior gluteal artery; q, umbilical artery; r, middle h:i-mor- rhoidal artery; 3, posterior hajmorrhoidal artery; s, perineal artery; (, art. profunda penis; n, art. bulhi urethra; i", art. dorsalis penis; u), middle sacral artery, a', posterior vena cava; other veins are satellites of arteries and correspondingly named; i, ilio-psoas muscle; 5, tendon of psoas minor; 3, abdominal mu.icles; i, sartorius; 5, rectus femoris; B' , vastus internus; 6, pectineus; S', adductor; 7, gracilis; 8, symphysi-s pelvis; 9, ilium; ;0, pyriformis; //.gluteus superficialis; 12. obturator internus; /rf, penis; H, lumbar vertebr.T. (After Ellenberger, in Leisering's .\tla3.) divides near the jiylorus 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 liranch 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. Th"^ anterior mesenteric artery arises close behind the coeliac. It gives off a connnon trunk for two colic arteries and the ileo-c?eco-colic. The former supply the transverse and the anterior part of the left or descending colon, while the latter divides into liranches for the ileum, caecum, and first part of the colon. The trunk is continued as the artery of the small intestine, giving off fourteen to sixteen THE AHTEKIES 639 branches (Aa. jpjiinales), which form a series of anastomotic arches in the mesentery near tlic howcl. Two phrenico-abdominal arteries (Aa. phreniciE 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 ab- dominal surface of the corresponding crus of the diaj^hragm to the sternal part. The inner branches anastomose with those of the opposite artery, the outer branches with intercostal arteries chiefly. The ab- dominal arteries give branches to the lum- bar muscles, the renal fat and capsules, and ramify in the oblicjue abdominal muscles. The renal and spermatic arteries offer no special featui'cs. The utero-ovarian artery divides near the ovary into three or four branches which supplj' 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. 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 ex- ternal pudic divides into anterior and posterior branches; the former runs for- ward, supplies branches to the inguinal lym]:)h glands, the mammary- glands and skin, and anastomoses with the mam- mary Ijranch 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, ac- companied by the anterior branch of the Dternal Fig. 492. — Arteries of Pelvic Li.MB Of Dog, Internal View. a. Abdominal aorta; b, fe- moral: c, c', deep femoral; d, pos- terior abdominal; e, external pudic; /, cuniflex; (/, anterior femoral (accompanied by terior branch of femoral nerve); h, external flex; /, k, muscular branches; /, articular blanch; 7/(, saphenous; n, o, plantar and dorsal branches of sai>henous; q, saphenous nerve; r, obturator nerve; /.ilio-psoas; .2, ilium; 5, gracilis; 4< semitendinosus; 5, adductor raagnus; G, adductor longus; 7, quadri- ceps femoris; 8, sartorius; 9, semimembranosus; 10, gastrocnemius; 1 1 , tibialis anterior; IS, tibia. (EUen- berger-Baum, Anat. d. Hundes.) 640 CIRCULATORY SYSTEM OF THE DOG femoral nerve, dips in between the rectus femoris and vastus inteinus. The ex- ternal circumflex arterj^ passes forward between the sartorius internally and the rectus femoris and tensor fasciae lata; 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 oiiliquely Fig. 493. — .\rterie8 of Distal Part of Right Hind Limb of Dog, Anterior View. a, E.xternal branch of anterior tibial artery; b, anterior tibial artery; c, saphenous artery (anterior branch): d, perforating metatarsal artery; e, dorsal metatarsal arteri&s: /. deep dorsal metatarsal arteries: (7, superficial dorsal metatarsal arteries: h, anasto between dorsal and plantar arteries; digital arteries: j. proper digital arteries. Fig. 494. — .\rtehies of Distal Part of Right Hixn Limb of Dog, Posterior View. k, Saphenous artery (posterior branch); I, V, internal and external plantar arteries; in, perforating metatarsal artery; n, deep plantar metatarsal arterie;': o, superficial plantar metatarsal arteries; p, common digital artery; q, proper digital arteries. 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 poste- rior 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 deej) flexor tendon and unite with the perforating metatarsal artery to form the proximal i)laiitar arch. The artery continues down the middle of the plantar surface of the metatarsus and divides near the metacarpo-phalangeal joints into THE VEINS 641 three superficial plantar metatarsal arteries. These vessels unite with throe deep plantar metatarsal arteries which ilescend from the proximal ])lantar arch and witii Ijranehes 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 bj- the saphenous. It supplies twigs to the tlext)r nmsdes 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 u]i]ier 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 tiliial supplies the external or fifth dorsal metatarsal artery for the outer side of the fifth digit. At the proximal ixirt of the metatarsus it gives off three deep dorsal metatarsal arteries which descend in the intervals between the metatarsal bones and concur with the sujier- ficial 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 suppl.y the muscles in this region like the posterior gluteal (or ischiatic) artery of the horse. It gives off the following branches: (1) The ilio-lmnbar 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 fasciae lat£p; 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 liranch on the lateral face of the rectum, retractor ani, and coccygeus. Its chief collateral branches are: (1) The imibilical 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 chieflj- in the body and neck of the uteius and the vagina and anastomoses with the utero-ovarian. (2) The middle haemor- rhoidal 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 isc'hial arch as the artery of the penis (A. ])enis). This vessel, after giving off the deep artery of the penis (A. profunda penis), which supplies the artery of the bulb (.\. bulhi urethra') 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 con- fluence of jugular and brachial veins. 41 042 CIRCULATOKY SYSTEM OF THE DOG The vena azygos roscmlilcs that of the horse, and receives at the ninth or tenth thoracic vertelira a vena hemiazygos. Two jugular veins are present on each side. The external jugular vein is formed by tiie union of external and internal maxillarj' 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 witii 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 mandiljle 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, liut 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 tribu- taries. It receives the sujierior 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 b(>low. 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, wliile the first digit has one. The posterior vena cava, its collateral affluents, and common iliac radicles present no s])cciai features of importance. The internal iliac vein corresponds in regard to its tributaries with the liranches of the artery, except tiiat it is not di\-i(ied into dorsal anil ventral branches. The external iliac, femoral, and popliteal veins with tiieir 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 ]ilantar metatarsal vein. It comnmnicates 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 imion of dorsal and external plantar metatarsal veins, crosses the outer surface of the leg obliquely upward and back- ward, ascends behind the gastrocnemius and joins the posterior femoral vein. THE LYMPH VESSELS AND GLANDS 643 The metatarsal and digital veins rosoinl)le in general the corresponding vessels of the fore Hinl). The Lymph Vessels and glands The cistema chyli is hxrge and fusiform. The thoracic duct may be single throughout, hut often tlivides anteriorly into two branches, which may then unite and form a tlilatation 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 th(> right l)racliioc('])halic vein. The submaxillary lymph glands (Fig. 48G) are commonly three in number on each side. They are situated in the angle between the masseter and the submaxil- lary salivarj' 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 be- tween the upper part of the posterior border of the masseter and the parotid gland. Tlie pharyngeal (or retropharj'ngeal) lymph glands, one or two in numlser 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 ijordcr of the supraspinatus, embedded in a mass of fat. Usually two or three are present on each side, Ijut 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 h(>ad 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 ves- sels 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 chiefiy 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 uniciue, 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 coordinated. For purposes of gross description it is divided primarily into two parts, central and peripheral. The central nervous system (Systema nervorum cent rale) comprises (a) the spinal cord (McMhilia spinalis), and {!>) the brain (Encephalon). The peripheral nervous system (.'-Systema nervorum periphericum) includes (*)) 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 aiisc or end witliin the central system, and therefore constitute an integral part of the latter. Tlie structural and funclidiial unit of the nervous system is the neurone, which consists of the cell-body, usually termel the nerve-cell, and all its processes. The processes arise as out- growths from the cell-liody 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 t lie distal end of a limb. A nerve is composed of such processes, usually inclosed in a protecting and insulating shea I h, an 1 iinilid intcj liundles l)y connective tissue. The neurones are embedded in a in'ciiliar suppiirtin^j; li^^uc ii'iincd neuroglia. This consists of a very intricate feltwork of gliu-libers, many of wind; arc 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.' To the naked eye the central nervous system apjiears to he 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 larg(>ly of medullated nerve-fibers, packed closely together and arrangerl 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 sul)stance and much more vascular. It is composed chiefly of cell-bodies and iion-medulhited processes. In some situations it is modified to form the gelatinous substance (Substantia gelatinosa), which is pale vellowish-gray and jelly-like. Ganglia are gray masses found on the dorsal roots of the s]iinal ner\'es 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 ])roperly to the central system, but it is customary to include them with the peripheral ]iart 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 connec- tions as cranial or cerebral, spinal, and sympathetic. Th(> 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 periijheral or central direc- tion. On the same basis the nerve-fibers are designated efferent and afferent ' Limitations of space and the purpose of this work preclude consideration of the finer structure of the nervous system, for which amjjlc literature is available. 644 THE MENINGES — THE DURA MATER 645 respectively. A Imnille of fillers which passes from one nerve-trunk to another is called an anastomotic branch (Ramus anastomoticus). In some situations the exchanse of branches between adjacent nerves is so free as to constitute a nerve- plexus (Plexus nervorum). The term ramus commimicans is proi)erly 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 (Xervi 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 arach- noidea, and (3) the pia mater. THE DURA MATER The dura mater is a dense resistant memlirane of white fibrous tissue; in the fresh state it is bluish-white in color. On account of the difference in its arrange- ment within the cranium from that in the spinal canal it is customary to describe it as consisting of two parts, cereljral 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 lie 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 l)lood-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 sutiu'es 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 tlie 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 gro.ss subdivisions of the brain. These septa are; (1 ) the falx cerebri; (2) the tentorium cerebelli; and (3) the diaphragma sellse. The fabc 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. 646 NEUROLOGY 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 ])osterior poles of the cerebral hemispheres. It is attached al)ove to the tentorium osseuin and laterally to the petrosal crests. Its lower border is thin, concave, and free; it forms the upper and lateral lioundaries of an opening (Incisura tentorii) which incloses the mid-brain. The diaphragma sellae is a small circular fold which roofs over the sella turcica and the pituitary body. It is perforated centrally by an opening (Foramen dia- phragmatis) for the infundibuluiu. 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 magiuun to the second or third segment of the sacrum. It is separated from the periosteum of the spinal canal by a considerable epidural space (Cavuni ejjidurale) 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 inplos(>s the delicate filum terminale of the spinal cord. The subdural space (Cavum subdurale) is the cavity between the inner surface of the dura luater and the arachnoidea. It is a mere capillary space which contains just sufficient fluid to moisten its surfaces; this fluid is usually regarded as Ij-niph, 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 diijiosed surface of the dura mater. Between it and the pia mater is tlie subarachnoid space (Cavum subarachnoideale) which contains the cerebrospinal fluid. An inner sur- face 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 super- ficial 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 (CistcrniB 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. PIA MATER 647 The chief cisternal are: (1) the cisterna magna, which is at the angle formed between the posterior face of tlie cerebellum and the upper surfa<-e of the medulla oblongata. It communi- cates with the fourth ventricle through the foramen of Magendie (in man); and behind with the wide subarachnoid s[)ace of the spinal cord; (2) the cisterna pontis on the ventral surface of the pons; (o) tlic cisterna basalis, which lies at the base of the cerebrum and is divided by the optic chiasma into two parts (cisterna chiasniatis, cisterna interpeduncularis); (4) the cisterna fossae lateralis, situated at the lower part of the lateral fissure (,of Sylvius), and continuous with the cisterna basalis. Along the u]iper honlcr of the falx cerebri the arachnoidea bears bulbous excrescences, the arachnoid granulations or Pacchionian bodies. These are in- closed in thin cvaginations 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 jiressure on the bone and produce in it depressions of variable deptli. The spinal arachnoidea (Arachnoidea spinalis) is directly continuous with that of the brain at the foramen magnum. It forms a relativcl.y witle tube around the spinal cord, so that the latter (inclosed in the pia) is surrounded by a very consider- able quantity of cerebrospinal fluid. The spinal subarachnoid space is traversed by fewer arachnoid trabeculse than is the case in the cranium. It is partially sub- divided 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 memlirane 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 bj' a la.yer of endothelium. From its deep face numerous trabecular are given off which penetrate into the sub- stance 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 witiiin 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 thej- 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 telae chorioideae 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 l)rain. 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 ligamentmn denticulattim, 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 denticu- 648 NERVOX'S SYSTEM OF THE HORSE lated 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 s])iiialis) 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 19.5 cm.), and its weight about 8}^ 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 prac- tical ])urposes 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 meduUaris. 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 I6J-2 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 corres]3ondence 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 vertebrae, so that the roots of the last lumbar nerve must run backward the length of the last lumbar vertebra to reach the interverte- bral 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 lengtlis; the longest are the third to tlie sixth rcrvical. wliicli measure 11, 10, 10, and 8.5 cm. respectively. Tlie spinal nerves are in general ilesignated accord- ing to tlie vertebra; behind which lliey emerge from the \-ertcbral canal. In tlie neclc, however, tliore are eight pairs of nerves and only seven vertebra'; here tlic first nerve emerges through tlic intervertebral foramen of tlie atlas and the eightli lietvveen tlie last cervical and tlie 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 vcrtebi-a and sub- sides in the second thoracic. Its maximum transverse diameter is about an inch (ca. 25 nnn.) and its dorso-ventral nearly half an inch (ca. 12 mm.). The lumbar enlargement (Intumescentia lumbalis) is situated in the fourth and fifth lumliar vertebra;. It is a little narrower than the cervical enlargement, and its dorso- THE SPINAL CORD ()49 ventral dianu^tcr is also slightly smaller. Behind this the cord tapers rapidly to form the conus meduUaris. The tip of the latter is continued by a delicate glisten- ing strand, tiif filum terminale, which is composed largely of fibrous tissue con- tinuetl from the pia mater, covered by arachnoid. The surface of the spinal cord is divided into two similar halves by a dorsal median groove (Sulcus nudianus dorsalis) and a ventral median fissure (Fissura mediana ventralis). On citlicr side of the former is the dorso-lateral groove (Sulcus dorsalis lateralis) at which the fibers of the dorsal nerve- -KX Fig. 495. — Ventral Vikw of Mkdulla Oblongata AND First and Second Segments of Spinal Cord of Horse; the Membranes are CrT AND Reflected. i, Lig. suspensorium arachnoideale; 2, right cerebrospinal artery; S. 5, digitations of lig. denticu- latum; 4. free border of lig. denticulatum; 6, middle spinal arter.v; 7, basilar artery; S, pons; 9, arach- noidea; 10, dura mater; //, 12. ventral root-bundles of first and second segments of spinal cord; 1"/., N. abducens; IX. X. glosso-pharyngeus and vagus; XI, accessory, medullary part; XT. accessory, spinal part; a. line between medulla oblongata and spinal cord. (Dexler, in EUenberger-Baum, .\nat. d. Haustiere.) Fig. 496.— Cauda Equina. 1 . Dura and arachnoidea divided and reflected; 2. spinal cord; 3, nerve-roots. (From Leisering's .\tlas, reduced.) 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 ven- tralis) 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 650 NERVOUS SYSTEM OF THE HORSE groove. These grooves indicate the division of the white matter of the cord into columns to be described later. Examination of cro.ss-sections of the P]iinal cord shows that it is a bilaterally sj-mmctrical structure, incompletely divided into ri^dit antl left halves by a ventral fissure antl a dorsal septum. The ventral median fissure (Fissura mediana ven- tralis) 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 neu- roglia with an admixture of pial tissue. The two halves (if the cord are connected by commissures of gray and white matter. ' The gray commissure (Commissura grisea) is a transverse band of gra.y 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 Ftg. 497. — Cross-section of Spinal Cord in situ, tx Part SrHF:MATir. /, Dorsal column; ^, lateral column: .^, ventral column; 4. dorsal horn; 5, ventral horn; (7, gray ( sure; 7, white commissure; 8, central canal; 9, dorsal septum; 10, ventral fissure; //, tlorsal nerve-root; 12, ventral nerve-root; 13, .spinal ganglion; / 4, nerve; i5, intervertebral foramen; 75, arch of vertebra; /7, epidural space; IS, dura mater (represented a little too thick); 19, ligamentum denticulatum; 20. 20, longitudinal venous sinuses; 21, middle spinal artery. The subdural and subarachnoid si>aces (black) are traversed by delicate trabe- cula?. The outer part of the arachnoid and the pia mater are not shown. white commissure (Commissura alba) is a l)ridge of white matter which connects the ventral columns of the cord over the dorsal end of the ventral median fi.ssure, and constitutes a conducting path from one side to the other. The central canal of the cord (C'analis 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 i)art is considered as consisting of dorsal and ventral gray columns or horns (Columna grisea dorsalis, ventralis). In the greater part of the cord the THE SPIXAL CORD 651 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 sepa- rated 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 ]iass. From the middle of the cervical region to the lumliar region there is a medial ]iruj(>ction of gray matter on the lower part of the dorsal colunm; this is the nucleus dorsalis or Clarke's column. In the anterior jiart of the cord there is an outward projection of the gray matter at the base of the ventral horn; this is termed the lateral colimin 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 followinn; gross regional characters: (1) The cervical cord near the medulla is compressed dorso-Aentrally. Its width is about IS mm. and its greatest tliickness about 8 mm. It has dorsallj' 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 Ijhmt 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 gracihs 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 ha\-e pointeil ends and turn decitledly outward. The ventral cornua are short and tliick and are directeil ve;'y 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 cer\'ical enlargement measures aljout 25 nmi. transversely and 12 mm. vertically. The dorsal cornua are smaller than the ^•entral 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 traasverse 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 tlorsal 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 hunl)ar enlargement is much flattened, especially dorsally. The transverse diameter is about 22 mm. and the tlorso-ventral 9 to 10 mm. The cornua are very large. The ventral cornua are thick and rouniled and turn sharplj- 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 out- ward. (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 colimms (Funiculi ventrales) are situated on either side between the median fissure and the ventral gray coliunns. Tliey 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 652 NERVOUS SYSTEM OF THE HORSE groove (where present) indicates a suhtlivision of the dorsal column into two fasci- culi or tracts; the inner of these is the fasciculus gracilis (Cioll's column); the outer, the fasciculus cuneatus (Burdach's column). The anKHints of gray and white matter vary greatly in difTcrent 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 enlarge- ment backwani. Iiivc'stisialidiis h.nc sliown that in man the cohimns of white matter are subdivided into fa.sriculi or tr;iri>, winch constitute definite conducting paths of greater or less length. Our knowledge of tlic I racis in I he domesticated animals is very limited, and it is quite unsafe to make inferences from tin' ananiiciiicnt in man. As evidence of this it may be noted that the ventral cerebrospinal oi' direci |i\ laiiii^lal tract of man cannot be recognized as such. The dorsal white ciihinju- i-i)nsist 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 lascending) branches form the direct sensory path to the brain and extend in the fa.sciculus 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 colunm. 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 cliiefly 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 cerebcUo.spinal fasciculus (direct cerebellar tract of Flech.sig) extends along the periphery of t lie lateral column. It contains ilic axones of the cells of the nuclei is dmsalis (Clarke's column), whii'h pniceeil to the medulla oliliiiii;ai a and enter the ecu liclhiin liy I lie restiform body. The rubrospinal tract of Monakou appears lo take the place of I he laleial ccreliro.spinal fasciculus or ciii..>e.l p\ laiiiidal tract of man. It lies at the inner side of the cer iHlld-pInal fasciculus. Its tiliei- H I c 111 the nucleus ruber of the mid-brain, cross the median ]ila iccussation of Forel), ami |i:i— li ickward in the tegmentum and medulla oblongata to the laieial cnhimn of the cord. It is a p.iili for motor impulses coining from the cerebral cortex and the cerebellum. The lateral fasciculus ])roprius or ground-bundle is deeply situated at the side of the gray columns. The bulk of ils libers 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 \'entral colunm. It extends to the middle of the thoracic region. It consists of intersegmental fibers, and contains in the anterior part of the cer\ical 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 cer\ical region it occupies a semilunar area which reaches almost to the surface ventro-laterally. Scattered libers 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 th(> 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 al)out 23 ounces (ca. 650 gm.), and forms about ' of 1 per cent, of the body-weight. It is clesirable to examine the general external configuration of the lirain before studying its various parts in detail.' When divested of its membranes and vessels (Figs. 499, 500), its ventral ' 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 ^•essels and membranes which must be ex- amined first have been described. THE BRAIX 653 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 jiart of the cerebral hemispheres. The area between them is the interpedimcular space. It is largely covered by the pituitary body nr hypophysis, a yellowish-t)rown, discoid structure, which is connected with the base of the cerebrum by a delicate tube called the infimdibulum. ' On dra^\"ing the pituitary body gently aside, the infundil)ulum 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 jierforated 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, wliich is continued behind by two diver- gent bands, the olfactory tracts or striae. 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 striie. Behind this is a depression, the fossa transversa," which is continued across the external stria and sharply limits the second and much larger eminence, the pjrriform 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 shagg>- ajipearance 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, ami the eleventh or spinal ' Unle.ss care is used in remo\dng the brain the infundibulurn 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. - The fossa corre.sponds in position to the locus perforatus anticus of the human brain, but is not pierced by numerous openings for vessels in the horse. 654 NERVOUS SYSTEM OF THE HORSE accessory nerves are connected by a linear series of roots with the lateral aspect of the vt'ntral surface of the medulla. The spinal part of the accessory nerve comes forward alonf;- the etlge 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. 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 Transverse fissure Olfactory bidh Frontal pule of hemisphere ^ Cerebrum Fig. 498. — Braix of HonsE, Dorsal Vie /, Entoniarginal fissure; 2, marginal fissure; S, ectom ^ ^ . Occipital pole hemisphere of 1 1 1 P '., rbell im .1/ dulla Ohio, (jiita V \ llOVT . Nai URAL Size. rgii al fi.ssi re; J, suprasylvia 11 fts sure. hemispheres fonn 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 !)>• tliick 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 occiiiital ])oles of the hemispheres overlie the anterior part of the cerebellum, from which they are separatetl l)y 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 THE UHOMHENt'EPIIALON 655 lobe, tho vermis, and two lateral hemispheres. It is marked by numerous gyri and narrow sulri which have in general a transverse direction. The posterior third of the medulla oblongata is not covered by the cerebellum. 'riie liiuin is developed from the expanded cephalic part of the neural tul)e of the eml)ryo. The process comprises a series of thickenings, fiexures, and unequal growth and expansion of various parts of the tube. In the hifilier 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 conni'ctcd by narrow passages. The tube is first subdivided by two constrictions into three biaiii vesicles, termed respectively the hind-brain or rhoinbcnrephalon, the mid-brain or mesencephalon, and the fore-brain or prosencephalon. The hinil-brain gives rise to three secon- dary 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 Cavities. BRAIN Secoxdarv .Segments. Derivatives. Myelencephalon .Medulla oblongata. . . Metencephalon J J."^"^" ',; ( ( erebellum Isthmus rhombencephali . . . J .\nterior cerelDt Mesencephalon . -pe,h. [ Anterior medullary velu: [ Corpora quadrifremina . : Cerebral peduncles ' Optic thaiami Subthalamic tegmenta . . Pineal body ' Pituitary body Optic nerves and retinae. . . Cerebral hemispheres Olfactory tracts and bulb.. Fourth ventricle Cerebral aqueduct Anterior part of third ventricle. Lateral ventricles and olfac- tory continuations. 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 (lorso-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 (Kissura 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 caecum) behind the central part of a transverse Ijand, 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 intermedins ventralis). The pyramids join the pons in front; behind they become narrower and disappear into the sub- stance of the medulla, in which their fibers intercross, forming the decussation of the pyramids (Decussatio pyraniidum).' The superficial origin of the sixth cranial nerve (N. oculoniotorius) is just lateral to the anterior end of the pyramid. The corpus trapezoideum is a trans- verse 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 trajiezoideum there is a variably developed rounded eminence, the tuberculiun faciale. The root-fibers of the twelfth or hjpoglossal nerve form an oblique linear series lateral to the posterior part of the pyramid. 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 ' 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. 656 NERVOUS SYSTEM OF THE HORSE cord, extends forward to about the middle of the surface. Here the restiform bodies, which constitute the hps of the fissure, diverge to form the lateral lx)un- dariesof 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 tlic 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 ])art of the lateral column, termefl the tuberculum cinereum. The central canal of the cord is continued in the posterior part of the medulla, THE RHOMBEXCEPHALON 657 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 dor.sal aspect of the latter, which is concealed at present, will he considered later in the ilescriptiou of the fourth ventricle. The lateral surface is narrow hehinil, 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 strise which curve obliciuely downward and liackward from the surface of the r(>stiform body LoiKjUiiilhial fissure Olfiidonj bulb _ Olfacturij jwilinide I nkriiiil (AfiuioTij Intel External olfaclory tract —\- — Trigonum olfadorium ^\~ Fossa transversa Cerebral peduncle Tractus pelt, transrersus Tuberculum facial _^tJ^_- Interpeduncular space — Pons Corpus trapezoideum Pijraniid Medulla ~'~-— Chorioiil plexus of fourth nnlnele' ' Median Jissure and de- cussation of pyramids — Spinal cord Fig. 500.— L: toward the hypoglossal root-fibers; these are the external arcuate fibers (Fibrse arcuatffi externa). The recess between the lateral aspect of the medulla and the cerebellum is occupied by an irregular mass of villous projections of tlie ])ia 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 liere the wall of the fourth ventricle; also that the restiform body terminates in front by entering the Ijase of the cerebellum, forming its pos- terior 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 42 658 NERVOUS SYSTEM OF THE HORSE tlio 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 aiTerent 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 ohvaris 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 whicli is folded on itself so as to inclose a mass of white matter. It is about 2 era. 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 con- nected with the opposite side of the cerebrllum by the ccrebello-olivary fibers. At its inner side are two small accessory olivary nuclei. The pyramidal tracts, which are small in ungulates, send mo.st of thi'ir 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 conl. anil otliiTs arc connected with the nuclei of the motor nerve-roots. From the nu- cleus gracilis and nucleus cimeatus fibers arise which are traceable forward to the thalamus. Transverse fissure Vermis Hemisplie of cere- bel- lum Basilar (irlery Fic. 501. — Brain of Horse, Left Lateral View. The larger arterie-s are .shown. The nerve-roots are indicated by Roman numerals. P.c. Chorioid plexu.s of fourth ventricle: B.p., middle peduncle of cerebellum; P, pons; //, pituitary body; L.p., pyriform lobe; A. p., trigonum olfactorium; li.u, olfactory bulb; iS'.r.a., sulcus rhinalLs anterior; S.r.p., .sulcus rhinalis posterior; /''./., lateral fissure (of Sylvius) ; F./.a., anterior branch of lateral fissure; iS.p., presylvian fissure; S.p.n., anterior presyl- vian fissure; S.s., suprasyivian fissure: .S.e., ectomarginal fissure. These are the internal arcuate fibers (Fibra? arcuata- interns'), which curve across the median plane below the central gray matter and form with those of the opposite side the decussation of the fillet iDecussatio lemniscorum). Beyond the decussation the fibers form an iiii]>()rtant longitudinal tract which extends forw-ard in the mid-brain. This is the fillet or lemniscus, the chief continuation of the sensory conducting path from the donsal 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 (Fibr;e dorsales) pass directly to the dorsal aspect of the restiform body of the s;une side; others (Fibrae ventrales) cross to the opposite side, descend clo.se to the ventral fi.ssurc, and then curve upward and forward to the restiform body. The dccii.^sation of the arcuate fibers forms the distinct median raphe seen on cross-sections of the nu'dulhi anterior to (he pynunidal (h-cu.ssation. The restiform body, silu:ilrd dorso-latcrally, contains, in addi- tion to the :ircuate fibers, the cerebello-olivary fasciculus bcfnrr nuntiDiicd, and the cerebello- spinal fasciculus or direct cerebellar tract. Tiic dorsal longitudinal fasciculus corresponds to the ventral ground-btmdle of the spinal cord, displaced dorsally by the decussation of the pyra- mids and fillet. In the posterior part of the medulla it is not marked off from the fillet, along the dorsal e Ige of which it lies. From the level of the hypoglossal nucleus forward it is di.stinct 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 bimdle of longitud- inal fibers, the spinal root (Tractus spinalis) of the fifth nerve; internal to it is the terminal nu- cleus of the sensory root of the nerve. THE PONS 659 THE PONS The pons (Varolii) is that part of the brain stem which Hes between the medulla and the cerel)ral peduncles; it is marked off from these ventrally by anterior and (ir Fig. 502. — Cross-section of Medulla Oblong.i.ta of Horse, Passing through Facial Nicleus. Cr, Corpus restiforme; D, dorsal longitudinal fasciculus; Fa, ascending part of facial nerve: L, fillet; .V7. nucleus of facial nerve; iVS, triangular nucleus of vestibular root of eighth nerve; .VS' , spinal root of eighth nerve; Pi), pyramid; Ra, raphe; R7, radicular part of facial nerve; RS, vestibular root of eighth nerve; Sg, substantia gelatinosa; Ta, posterior end of tuberculuni acusticum; V, spinal root of trigeminus. (Ellenberger- Baum, Anat. d. Haustiere.) posterior grooves. Viewed from below it is elongated transversely, convex in both directions, and presents a wide shallow median groove (Sulcus basilaris), which Fig. 503 — Cross-sectiom 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; fl7, root of facial nen-e; i. fillet; .U, central white matter of cerebellum; N6, abducens nucleus; X8, triangular nucleus; .VS'. nucleus of Deiters; A'S". tuberculum acusticum; Oo, anterior ohve; Pi/, pyramid; R6, root of abducens nerve; R7, root of facial nerve; Re. cochlear nerve; if r. vestibular nerve; .Sff, substantia gelatinosa; T. corpus trapezoideum; V, spinal root of trigeminus. (Ellenberger-Baum, .\nat. d. Haustiere.) 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 660 NERVOtS SYSTEM OF THE HORSE lateral limit of the ventral surfaee. Transverse striations indicate the course of its sujierficial (ventral) fibers which connect the two sides of the cerebellum. The dorsal surface is blended on either side with the overlying anterior i)eduncles 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 tlip pons is seen to 1)6 composed of dorsal and central parts. The dorsal part (Pars dorsalis pontis) consists superficially of a layer of gray matter co\ered by the epen- clyma of the fourth ventricle, lieneath this the median raphe 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, latcmlisl; tin- 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 raphe under the gray matter of the floor of the fourth \entricle. In cross-section the fonnatio reticularis forms a large area below the superficial gray matter and the longitudinal bundles. Dorso-laterally is the la'rge 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 tlic motor nucleus of the same nerve, exter- nal to whicli is its motor root. Tlie ventral part of the pons (Pars basilaris pontis) is composed of transverse and longitudinal filx'rs, and a Uu-gc auiount of gray matter which is broken up into small masses (Xuclei i)i>iilis) by the iiitrrsci'iioii of the fibers. The transverse fibers are gath- ered laterally into a com])act mass wliich turns upward and backward and enters tlie central white matter of tlie cerebellum, forming the middle cerebellar pedtincle. Centrally the fibers are ar- ranged in bundles which intercross. The transverse fibers are chiefly of two kinds. Some arise from the Piu-kinje cells of the cerebellar cortex and pass either to the opposite side of the cere- bellum or turn at the raphe and run forward and backward in the brain-stem. (Jthers are ax- ones of cells of the nuclei ponti.s, and pass to the hemispheres of the cerebellum. The corpus trapezoideum is mainly the central continuation of the cochlear division of the auditory ner\-e. Above it is the small anterior olivary nucleus (Nucleus olivaris nasalis). The longitudin.al 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, intersperseil among the deep transverse fibers in the anterior part of the pons. Toward the poste- rior 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 cortlco- pontile fibers. THE CEREBELLUM Tlie cerebellum is situated in the jxtsterior fossa of the cranium, and is sep- arated from the cerebral hemispheres bj- the trans\'erse 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 approximatel.v globular but very irregular. It is somewhat comj^ressed dorso-vont rally and its transverse diameter is the greatest. The anterior surface faces ujiward and forward and is co\-ered 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 jiairs of peduncles with the medulla, pons, and mid-brain. It is customary to recognize three gro.ss 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 meduUary velum, a thin lamina which forms the anterior part of the roof of the fourth ven- tricle. The posterior extremity, the nodulus, gives attachment to the posterior medullary velum which covers the posterior recess of the fourth ventricle. The hemispheres (Ilemisplueria cerebelli) are clearly sejiarated from the vermis by two deep ]mramedian fis.sures. They lie in the lateral depressions of the cereliellar compartment of the cranium. In tracing the fi.ssures 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 \ermis forms all of the fore part of the cerebellum. THK CEREBELLUM 661 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 arc more j)ronounced than the others, and l)y 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, (o) 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 cohmins of the cord. Near the middle of the medulla it inclines outward, forms the lateral wall of the fourth v(MitricIe, and ends bj' 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 siu'face of the pons, forming the lateral boimdary 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 meduUare), which is joined by the peduncles, and gives off primary laminae to the lobules; from these secondary and tertiary laminiE arise, the latter entering the gjTi. The arrangement on sagittal section is tree-like, hence the classical term "arbor vitse" which is applied to it. The central gray matter consists of groups of cells which form small nuclei embedded in the central white substance. .\s 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 cerebelhmi are as follows: The posterior pedimcle (Corpus restiforme) is composed of afferent and efferent fibers which connect the cerebellum with the medulla and spinal cord. The cerebello-spinal fascicu- lus or direct cerebellar tract, which arises from the cells of the nucleus dorsalis i( larkc's column) of the cord, ends in the cortex of the vermis; many of its fibers cro.*s to the cippusite side. Numerous arcuate fibers from the nucleus gracilis and nucleus cuneatus of the .-amc and op- posite sides estabUsli connections \\ith cells of the cerebellar cortex. Clivo-cerebellar fibers (chiefly afferent ) connect with the olivary nucleus of the same and of the opposite side of the me- dulla oblongata. The nucleo-cerebellar fasciculus comprises fillers derived from the nuclei of the fifth, eighth, and tenth cranial nerves (Edinger). The descending cerebello-spinal fascicu- lus consists of fibers wliich terminate in relation witli 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 for- ward to the tegmentum of the cerebral peduncle, the subthalamic region, and the thalamus. After the peduncles disappear under the corpora quaihigeniina, they converge and many of their fibers intercross, forming the decussation of the superior peduncle. A considerable numljer 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 rubro-spinal tract through the braiii-sfrni unci lateral columns of the cord to the ventral horn cells. The ventro-latcral cere- licllijspinal fasciculus (Gowers' tract) is an ill-defined tract wliich connects the spinal cord with the cerebeUum. Its fibers appear to be axones of cells of the posterior horns of the cord; they pa.ss in the lateral column of the cord, become scattered in passing through the reticular forma- tion of the medulla and pons, and enter the cerebellum by waj- of the anterior medullary velum. 662 NERVOUS SYSTEM OF THE HOHSE The Fourth Ventricle The fourth ventricle (\'entriculus quartus) is the cavity of the rhombencepha- lon; it coniniunicatcts witli the central canal of the spinal cord behind, and through the aqueduct with tlie third ventricle in front. It is somewhat rhomboid in out- line, elongated from l)efore backward and narrowest behind. It is lined complete!}' by an cijitlieliuui (Ependyma) and contains a small amount of fluid. Its floor (Fossa rhomboidea) is formed by tiie medulla and pons and is marked by tln-ee longitudinal furrows whicli converge l^ehind. It is widest and deepest a little in front of its middle. The i)osterior 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 FaciuL eminence -' Columns of fornix Corpus striatum Chorioid plexus of lateral ventricle SIriii / white matter of the cereliellum. A thin lamina of white matter, the posterior medullary velum, l)acked l)y pia mater, completes the roof posteriorly. After removal of the cerebellum the line of attachment (Twnia 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, ancl turns outward behind the brachium pontis. The thick part which stretches over the posterior angle of the ventricle is termed the obex. The pos- terior part of the ventricle forms three recesses, of which two are lateral and the third median and posterior. The lateral recesses communicate with the sub- FiG. 50.5. — Brain Stem and Basal Ganglia of Hohse, Right View. F.a., External arcuate fibers; Cr., corpus restiforrae; P, pyramid; T, corpus trapezoideum; B.p., middle peduncle of cerebellum; P.c, cerebral peduncle; S. sulcus lateralis; T.t., tractus transversus; /,, trigonum lem- nisci; Ca., corpus quad, ant.; f.p., corpu.s quad, post.; i?, commissure of Cp.; G, corpus geniculatum internum; T.O., olfactorj- peduncle; B.o., olfactory bulb. arachnoid space by distinct openings (Aperturse laterales). The layer of pia which strengthens the roof here is named the tela chorioideaof the fourtli 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 ajipear to lie within the ventricle, but are really excluded from the cavity by the epithelial lining, which they invaginate. THE MESENCEPHALON The mesencephalon or mid-brain connects the rhomliencephalon with the fore-brain. In the undissected Itrain it is covered dorsally by the cerebral hemi- spheres. 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 tra- versed longitudinally by a narrow canal, the cerebral aqueduct, which connects the fourth ventricle with the third. The corpora quadrigemina' 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 ' In the new nomemclature the term lamina quadrigemina is applie-] to the dorsal mass of the n.id-brain, and the four eminences which it bears are the corpora qua.aiscmina. 664 NERVOUS SYSTEM OF THE HORSE higher than the posterior pair. They are gray in color, almost hemispherical, and are separated by a narrow furrow which leads forward to the suhpineal fovea. A wide groove intervenes between them and the optic thalami. The posterior pair (CoUiculi caudales) are relatively small and are paler than the anterior iwir. They are marked liy a wide median dcjiression, and are limited below by a transverse furrow (Sulcus postquadrigeminus), at cither side of which the trochlear (fourth) nerve emerges. Laterally each is jjrolonged to the inner geniculate botly by a band of white matter termed the inferior brachium.' The cerebral peduncles or (Tura cerebri (Pedunculi cereljri) appear on the base of the brain as two large roix'-like stalks which emerge from the pons close together and di\-crge as they extend forward to enter the cerebrum. At the point of disajiiiearance the optic tract winds obliquely across the peduncle. About half an inch further back a small tract (Tractus peduncularistransversus) 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 tlie pituitary body, a discoid brown mass which is connected with the base of the l>rain by a hollow stalk, the infundibulum. The posterior part of the space is pierced by numerous minute openings wliicii transmit blood- vessels, and is therefore termed the locus perforatus posticus. The objects in the space belong to the dicncephalon, and will be dcscrilx'd later. The lateral asjiect of the peduncle is marked by a groove (Sulcus lateralis mcsence]ihali) which indi- cates the division into a dorsal part, the tegmentum, and a ventral part the basis pedunculi; these are separated by a hyn- of dark gray matter, the substantia nigra. Tiie triangular area (Trigonum lemnisci) above the lateral groove is faintly marked by fibers passing obliquely upwaril 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 (Aquseductus cerebri) is the canal which extends through the mid-brain from the fourth to the thirtl 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 aljout the third ventricle, the cavity of this division of the brain.-' 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 ])rincipal body in this jjart of tiie lirain. 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 th(>y 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 interpcsitum). Laterally it is sep- ' In man a distinot superior brachium eonnocts the superior pair with the lateral geniculate body, liut in the (lonicsticatol animals the union with I he optic thalamus is too direct to allow of any definite arm hcinfj rocojfiiized. = 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 telen- cephalon, but will be considered here as a matter of convenience. THE DIENCEPHALON 665 arated from the nucleus caudatus l)y an oblique groove in which there is a band of white matter termed the stria terminalis or tienia semicircularis. Internallj' it is bounded by a narrow band, the stria meduUaris, on which is a delicate ridge of ependyma termed the taenia thalami. The striie unite posteriorly and blend with the stalk of the pituitary i)ody. Near this point they present a small enlargement caused by the nucleus habenulie. 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 laterallj with the optic tract.' 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, au important mass of white matter compo.sed of fibers pa.ssing to and from the (■ciclinil cortex. These fillers go to form a large part of the ventral portion (basis) of the cerebral ]ie(linu-le. 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, ^'entral to the thalamus proper is the subthalamic tegmental region. This is the continuation of the tegmental part of the cerebral peilunclc inlo the clicmcphalun. It contains the red nucleus ( Nucleus ruber) an important ganglion on the coin-se of tlie 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 oppo.site 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 cro.ss-.sections of the subthalamic region; this is the subthalamic nucleus (Xucleus hypothalamicus s. corpus Luysi), which consists of pigmented nerve-cells scattered throughaden.se network of fine medul- lated fibers, and is riclily supplied with capillary blood-vessels. The two nuclei are connected by a transverse commissure (( 'onnnisstu'a hypothalamica), which crosses the floor of the third ventricle above the maminillary liody. The pineal body or epiphysis is a small ovoid or fusiform red Inown mass situated in a deep central depression l)etween the thalami and corpora (juadrigemina. 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 striae medullares of the thalamus. Immediately under the posterior part of the stalk is a short transverse band of white matter, the posterior commis- sure. The pineal body is inclosed in a fibrous capsule from which numerous trabecule pass inward, dividing the organ into spaces occupied by round epithelial cells of the same origin as the epen- dyma of the ventricle. The mammillary body (( 'orpus manunillare) 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 inter- jicduncular 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 infundi- bulum, 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. ' This backward projection of the thalamus is equivalent to the pulvinar and lateral genicu- late body of man, which are not superficially divided in the domestic animals. 666 NERVOUS SYSTEM OF THE HORSE It is glandular in character and there is good ground for tlie view that it is an organ of internal secretion. Besides the chief cells which stain lightly, it contains large deeply staining chromophile colls. 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 arrange- ment. It is almost entirely inclosed by the glandular part. It arises as an outgrowth from the I)rimitive diencephalon, but loses most of its earlier ner\-ous character. The optic chiasm and tracts form the anterior boundary of the interpeduncular space. The optic chiasm or commissure (C'hiasma opticuin) 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 ojjticus) curves over the cerebral jXHUincle outward, l>ack- Djitic tract Fiu. 506. — Cross-section of Brain of Horse, N.^tirai. Size. Section passes through posterior part of third ventricle an<.i is viewed from behind. 1 .. Longitudinal fissure; 2, hippocampus; 2', fimbria; 3, septum pellucidum; 4, lateral ventricle; 5, thalamus; 6, habenula; 7, third ven- tricle; 8, cerebral peduncle; S', hypothalamus; 9, mammillary body; 10, pituitary body; //, pyriform lobe; 12, ventral end of hippocampus; l.i, amygdaloid nucleus. Between the upper parts of the ta?nia! thalami is the chorioid plexus of the third ventricle, and above this are the internal cerebral veins ward, and upward to the posterior part of the thalamus and the internal geniculate body; some fibers reach the anterior quadrigeminal body. 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 genicti- late bodies; this, bundle is called Cludden'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 thahuiii. It conniiunicates by means of the aqueduct with the fourth ven- tricle behinil, and in front it is continuous with the lateral ventricle on each side through the interventricular foramen. Its floor is formed by the structtires of the interpeduncular space and to a small extent 1)V the tegmentum of the cerebral peduncles. The roof is formed in the strict sense only by the epcndyma, 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 dcliratc chorioid plexuses THE TELENCEPHALON 6(37 which appear to lie within the ventricle, although they are excluded from the cavity Ijy 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 tajnia 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 (Commis- sura caudalis) crosses the posterior wall above the entrance to the acjueduct; 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 \i'ntricle 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 infundibu- lum 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 oi)tic part of the hypothalamus. The latter has been con- sidered as a matter of convenience in the ilescription of the diencephalon. The Cerebral Hemispheres The cerebral hemispheres (Hemisphteria) form the greater part of the fully develo]>ed 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 l)ehind the middle. The two hemispheres arc 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 apjiears 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 cerelielli. The convex or dorso-lateral surface' conforms closely to the cranial wall. The medial or internal siuiace 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 de- pression, 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 ' In order to study the configuration of the hemi.sphere it should be separated from its fellow by median section ami from the brain stem by cutting across the mid-brain. Material for this purpose should be hardened in sita. 668 NEKVOUS SYSTEM OV THE HORSE bj- numerous openings for the passage of small l)lood-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 up- ward 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 adaiJted to tlie corpora quadrigemina and the pineal Iwdy. The frontal pole or anterior extremity (exclusive of tlie olfactory bulb) is compressed laterally, and the occipital pole or posterior extremity forms a blunt point. 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 Fui. 507. — Left Cerebral Hemisphere of Horse, L.^ter.^i. View. The Olfactory Bulb is Ci't Off. /. Lateral fissure (of Sylvius); 2, 3, 4, middle, posterior, and anterior branches of /," 5, presylvian fissure; 6, 6,' sulcus rhinalis, anterior et posterior; 7, suprasylvian fissure; S, ectomarginal fissure; 9, & , ectosylvian fissure. of white matter (Centrum semiovale); (2) the rhinencephalon or olfactory ]X)rtion of the brain; (;5) the corpus callosum and fornix, the great commissural white masses; (4) the lateral ventricle and certain ini])ortant structures associated there- with. The pallium is tiu-own into numerous folds, the gyri cerebri, which are seji- arated l)y sulci or fissures of varying ilei)tli. The general pattern of the gyri antl 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 hemisj)here 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 pass(>s ujiward, one runs oblitiuely forward and upward, and the third is directed upward and backward. 2. The suprasylvian fissure (F. suprasylvia)' is long and divides a large ])art ' Termed by l^esljre tlie parietal fissure ami by M'Fadyean the great oblique fis.sure. THE CEREBRAL HEMISPHERES 669 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 graduallj- downward, passes back to end on reaching the tentorial surface. It is continuous intemallj' with the transverse fissure usually and in front with the presj'lvian fissure. 3. The presylvian fissure (F. prasylvia) is the continuation forward of the preceding. It i)asscs forward, outward, and downward almost to the frontal pole, and then inclines backward to end at the groove which marks the u])per limit of the rhinenccphalon (Sulcus rhinalis). 4. The marginal fissure (F. marginalis) extends along the dor.so-mcdial Iwrder. 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 docs not extend quite as far forward as the marginal fissure, from which it is si'iiarated 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 (rhinenccphalon) from the rest of the hemisphere. It is undulating and is highest where it is crossed by the lateral fissure (of Sylvius).' On the medial surface (Fig. 50S) the main fissures and sulci are as follows: 1. The calloso-marginal fissure (F. calloso-marginalis) is extensive and well- defined. It is a]iproximately parallel to the dorso-medial border of the hemisphere, from which it is aliout 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." 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 pjTiform 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 hippo- campal 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 ' Just .above this point is a lobe which is homologous with the insula of man. When the overhanging gyri which partly conceal it — forming tlie operculum — are removed, there are dis- closed several short, deeply placed gj'ri (Gyri breves). - 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. 070 NERVOUS SYSTEM OF THE HORSE is tlierpfore continuous with the fimliria. The two hippocampi are connected at their highest parts by transverse fibers wliieh constitute the hippocampal commis- sure. The interval lietween tlie 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 Gyruti fornicaliis Transverse Calloso-mar- jissare ginal Jia Marginal fissure Entomarginal fissure Lamina Chiasma termmabs opticum Posterior , commissure \ ^\^^^.^^ Pituitary Cerebral niedul- body aqueduct lary velum Fourth ventricle The membranes and ^ P.r., cerebral peduncle; (\q,. r. optic recess; r', infundibuli C, genu of corpus callosuni; Fig. 508. — Medi.vn Section of Brain of Horse. essels are removed. C, Central white matter (corpus corpora quadrigemina; P, pineal body; 7Vi., thalam ir recess; C.tti., mammillary body; s, subcallosal gj-ru; >S', splenium of same; /, callosal sulcus; 2, interventrii medydlare> of cerebellum; is; V.lll., thir.l ventricle; ; A. p., area parolfactoria; lular foramen; S, olfactory bulb. The cerebral lobe of the pituitary body is distinguished by its lighter colo been seen (Fig. 500). The lateral borders will be seen on the floor of the lateral ventricles, where they form thick roundt'd bands containing convolutions of blood-ve,s.sels, known as the chorioid plexuses of the lateral ventricles (Fig. 511). When the tela is pulled out one may easily get the impression that the lateral \eiitriele communieates with the exterior by means of the ehorioid fis.sure. Sueh is not the ease, sinee the chorioid plexus is eovered liy the epithelial hninfc of tlie ventricle, which has been torn away. The rhinencephalon or olfactory jiart of the brain comprises the olfactory bulb, peduncle and tracts or roots, the trigonum olfactoriuin, the area parolfactoria, and the pyriform lobe.' ' From the morphological point of view other structures should be included, but in descriptive anatomy it is usual to limit the appHcation of the term to the parts enumerated above. THE CEREBRAL HEMISPHERES G71 The olfactory bulb (Bulhus olfactorius) is an oval enlargement which curves upward in front of the frontal pole of the hemisphere. Its convex superficial face tits into the ethmoidal fossa and receives numerous olfactory nerve-fihers through the cribriform plate; hence it is very difficult to remove the Ijulb intact. It con- tains 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 filjers which are the axones of the mitral cells of the deep layer of the gray substance and go to form the peduncle and stria-. 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 tile olfactory tracts. The olfactory tracts or striae (.Striie olfactorii) are three in number. The Inkri'cntricular Jura Gyrus fornicalu Sublimbic fissxtre (ant. pari) Transverse fissure ( ' alloso-marginal fissure Sublimbic fissure (post, part) Entomarginal fissure Marginal fissure Sulcus rhinalis anterior Ectomarginal fissure Hippocampal fissure ^,^^^^ ^^^^^^ posterior Fig. 509. — Medio-vextr.<.l .\spect of Right Cerebr.^l Hemisphere of Horse. The olfactory bulb is cut off. T.ol.. Olfactory peduncle; A.p.. area parolfactoria ; Tr.O., facforium; T.op., optic tract; Co., chiasm pellucidum; F, fornix; G.c, callosal gyn L p., pyrifonn lobe; G.k., hippocampal gy; I opticum; G.s.. subcallosal gyr s; T, cut surface of thalamus c, corpus callo tirabria; G.d., trigonum ol- .S.p., septum gyr external tract (Stria lateralis) is much the largest and most distinct. It passes Imckwanl, upward, and outward, widens out and joins the pyrifonn lolje. 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 striae. 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. 672 NERVOUS SYSTEM OF THE HORSE The pyriform lobe (Lobus piriformis) is the well-marked prominence on the base lateral to tlic 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. Tlie fibers of the olfactory tract.s go to the pyriform lobe and hippocampus, the trigonum olfactorium, the area parolfactoria, the Mil.call.i-^al sjynis, and part of the gyrus fornicatus. The central connections of the olfactory apparni ii- mv complex and are not yet fully understood. The anterior cerel)ral commissure contains lil.n-^ «liirh pass from the olfactory bulb of one side by way of the inner tracts to the bulb of the uppn>iic side; also fibers ulii.li cni-^s in it from the uiner tract of one side to the pyriform lobe of i lir opimMlc side. Many lil.n- |ki- l.y \yay of the septum pellucidum, fornix, and fimbria to th.' InppocaTiipus. Otlier til.c'i.- p.i>s m ilie anterior pillar of tlie fornix to the mammillary body and thence to the thalamus l)y the tlialamo-mamniillary bundle. The corpus callostun is the great transverse commissure which connects the two cerebral hcniisplicrcs through about half of their length. On median section (Fig. 508) it is seen to be arched from before backward, white in color, and coin- Fir,. .510. — Laterai. View of Cast of Cavities of Brain of Horsk. Bo, Cavity of olfactory, which communicates through the canal / with a lateral ventricle; Ca, anterior hum. Cm, boily, Ci', ventral horn of lateral ventricle; M, isthmus which connects lateral ami third ventricles Ep, suprapineal rece.ss, below which is the small infrapineal recess; Ro, optic recess; Rh . infuiulibular and jjitnitary 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.) po.sed substantially of transverse fibers. The middle part or truncus (Trunctis corporis callosi) slopes downward and forward and is thinner than the (>nds. The anterior thickened end, the genu, bentls downward and backward and thins out to form the rostrum ; tlie latter is continuous with the lamina terminalis. The pos- terior end, tlic 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 (Indus;'um griseum), in which are strands of longitudinal fibers (Striaj longitudinales) ; the latter are arranged in median and lateral bundles (.Str>a mcdialis, striic laterales).' 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 tlie iongitudintil striie) run transversely and spread out laterally in all directions in the central wiiite matter of the hemispheres to the cortex, forming the radiation of the corpus callosum (Radiatio corporis callosi). ' It is generally lielieyetl that these constitute an oKactory path. THE CEREBRAL HEMISPHERES 673 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 an- terior 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 (Columnae fornicis) (Fig. 512) are two slender round Ijundles which emerge from the bodj^ in front of the interventricular foramen Olfactory bulb Corjyus viedullnre Caudate nucleus ^ r" Chorioiil plexus --W - Fornix II ippocampus Fig. 511. — Brain of Horse, with L- ;ntricles Opened by Remova Hemispheres. OF Upper Part of Cerf.bral and diverge slightlj- as they curve downward and backward to the mammillary body. From the mammillary body the greater part of these fornix fibers are continued to the thalamus by the thalamo-mammillary fa.sciculus (or bundle of Vicq d'.\zyr). Others pas,s 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 tlie 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 43 674 NERVOIS SYSTEM OF THE HORSE give off fibers to form the alveus or white matter which covers the ventricular face of the hippocampi, and tjetween them are transverse fibers which constitute the hippocampal coniniissiin'. The septum pellucidum is the mechan partition lietween the two lateral ven- tricles. 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 (Laminze scpti pellucidi) which are in direct contact with each other. They consist of nerve-filiers and gray matter. The latter exists in considerable amount in the thicker part of tlic 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. 512.— Cross- Section passes through cliiasni:] pellucidum; S, columns (anterior pill: (centra! white matter) of hemisphere: capsule: //, insula. 1 tihrreiitricular foramen Anterior coininissure SECTION OF Brain- of Horse, about Natura opticum, and is viewed from in front, i, Longitudinal fissure: S, septum irs) of fornix; 4. lateral ventricle; 5, chorioid plexus: 6, corpus meduUare 7, caudate nucleus; S, lenticular nucleus; 9, internal capsule; 10, external The lateral ventricle (^'entriculus lateralis) is the irregular cavity in the interior of each ccrel^ral hemisphere.' Each communicates with the third ventricle through till" interventricular foramen (of ]\Ionro), 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 ]mrt 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 siilenium of the corpus callcsum. 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) ' It is hardly po.ssible 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. THE CEREBRAL HEMISPHERES 675 curves downward and forward into the pyriform lobe. The roof of the ventricle is formed by the corpus callosuni 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 jiyriform lobe. The two bodies are separated by an ol)lique groove which is occupied l)y the chorioid plexus of the lateral ven- tricle. This is the thickened edge of a fold of pia mater, tiie tela chorioidea (or velum interpositum), which lies l)etween the hippocam]nis and the thalamus. It contains convolutions of small l)lood-vessels and in old sut)jects 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 Fig. 513. — S.\gitt.\l 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; Cm., central white matter (corpus meduUare) of cerebellum and of cere- brum; P. c. tin front of P), cerebral peduncle; //.hippocampus; V, lateral ventricle; T, thalamus; A'. c, caudate nucleus; C'.i., internal capsule; .V.^, lenticular nucleus; B.o., olfactory bulb. white band, the stria terminalis (or taenia semicircularis), is seen along the margin of the caudate nucleus, where it bounds the intermediate groove. The plexus partiallj' covers a wider white band whicli is blended with the white substance of the hippocampus; this is the posterior pillar of the fornix and its continuation, the fimbria. The corpus striatum' 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 knowni 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 knowni as the claustrum. The two nuclei are fused in front, and ' The term arose from the striated appearance of the mas.s in sections cut in certain planes, the gray matter being cut up into strands by tracts of white fibers. G7G NERVOUS SYSTEM OF THE HORSE further back they are connected by strands of gray matter which intersect the in- ternal capsule. The amygdaloid nucleus (Nucleus amygdalae) (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 (C'apsula 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 liasis 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 thala- mus. 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 pelluci- dum and trigonum olfaetorium. It is therefore probably part of the complex comiections be- tween the primary and secondary olfactory centers. The Cranial Nerves The cranial or cerebral nerves (Nn. cerebralcs) 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: 1. Olfactory Sensory (Smell) II. Optic . .'- Sen.sory (Sight) III. Oculomotor Motor IV. Trochlear Motor V. Trigeminal Mixed VI. Abducent Motor VII, Facial Mixed VIII. Auditory Sen.sory (Hearing and Equihbration) IX. Glosso-pliaryngeal Mixed X. Vagus or Pneumogastric Mixed XI. Spinal accessory Motor XII. Hj'poglossal IMotor THE FIRST OR OLFACTORY NERVE The olfactory nerve (X. olfactorius) is peculiar in that its fibers are not aggre- gated 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 corre- sponding 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 pro- cesses of the ganglion cells of the retina. The fibers converge within the eyeball to THE FIFTH, TRIGEMINAL, OR TRIFACIAL NERVE 677 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 pos- terior part of the eyeball, and passes backward and inward to the optic foramen. After traversing the latter it decussates with its fellow of the oiiposite 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 bj- i)rolongations 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 oppo- site side. In the tract the fibers proceed to (1) the internal geniculate liody, (2) the |)()stciior 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 non- visual 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 interior 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. Fillers 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 con- tinues above the maxillarj- nerve and iii company with the ophthalmic nerve to the foramen lacerum orbitale. It emerges through the foramen with the latter nerve and the abducens ami divides into two branches. The superior branch is short and divides into twigs wliich sup])ly the rectus superior, retractor, and levator palpebrs superioris. The inferior branch (Figs. 438, 439) is larger and much longer. It supplies the motor fibers to the ciliary ganglion (which lies directl.v 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 obliciue 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 (X. 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 oblicjue muscle of the ej'eball (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 onlj' nerve which is connected with the dorsal aspect of the brain. THE FIFTH, TRIGEMINAL. OR TRIFACIAL NERVE The trigeminal nerve (X. 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). 678 NERVOUS SYSTEM OF THE HORSE The sensory root (Portio major) extends forward through a notch on the lower part of the jietrosal 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 celts, and the fibers of the nerve? whicli oxtentl pcriphrrally from the gangHon are dendrites of the I'clls. The sensory root-fibers cuicr i he ti'i;iiiiiii iim cf ilic pons and cH vide into anterior and posterior branches, which terminate alioiil iIh' rclls uf llir sensory nucleus of termination of the trigeminus. This nucleus extends frum llu- pons tn Ihr sixtli cervical segment of the spinal cord (Dexler). The posterior liranchcs of the Hliers arc collected into a compact bundle, the spinal tract or root of the trigeminus, which lie< lateral to the sul)stantia gclatinosa in the medulla. The centr.al connections of till' sensory |i:irt of the trigemiiuis are very extensive. The most impnrtriiit paths are: (1) Axone- (if .ell- nf the sensory nucleus and the ~ul'-i,inii:i gelatinosa pass eliiell\ ;i~ arcuate fibers across I lie raphe to the thalamus, whence impuNes aie transmitted by i lialaiim-eiirtical fibers to the cerebral cortex. In ungulates a distinei i raei extends from the anterior jiai I of the sensory nucleus to the thalamus of the same side (\\ allenhernl. It is probable that cnllaterals of the arcuate fibers go to the motor nuclei of the lillli, sexenth, ninth, and tenth cranial nerves. (2) Axones of cells of the sensory nucleus enter the jjustciior cerebellar pciluncle of the same sirle 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 raphe. 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. ojihthalmicus) (Figs. 438, 439, 440) is purely sensory and is tlie 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 dis- tance. It enters the foramen lacerum orltitale 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 i)alix'l)r;e superioris and ramifies chiefly in the lacrimal gland and the upper eyelid. A Ijranch (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-palpehral ;uid 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 su])erior oblique muscle, at first within, then outside of, the ])eriorbita. 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 :uid atu-iculo-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. ethmoi- THE FIFTH, TRIGEMIXAL, OR TRIFACIAL NERVE G79 dalis) is the continuation of the parent trunk. It accompanies the ethmoidal artery through the foramen of lilve 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 in- fratrochlear nerve (N. infratrochlearis) runs forward to the inner canthus and rami- fies in the skin in this region; it detaches twigs to the conjunctiva and caruncula lacrimalis, and a long branch which supjilics the third eyelid and the lacrimal ducts and sac. The naso-ciliary nerve furnishes the sensory or long root (Radix longa) of the ciliary ganglido. The ciliary ganglion is placed on the inferior branch of the cjculomotor nerve. It is usually not larger than a millet-seed, and is liest 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; (6) motor fibers from the oculomotor nerve; and ((■) S)mipathetic 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 lietween 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 (X. maxillaris), also termed the superior maxillary, is purely sensory and is mucli 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 v/ing of the sphenoid. It is related internally to the cavernous sinus and superiorly to the ojihthalmic nerve, with which it is blended for some distance. It emerges through the foramen rotuudum, passes forward in the pterygo-palatine fossa above the internal maxillary arterj- and embetlded in fat, and is continued in the infraorbital canal as the infraorbital nerve (Fig. 439). Its branches are as follows : 1. The zygomatic nerve (X. zygomaticus s. subcutaneus malae), 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 chieflj- in the lower lid and the adjacent skin. Anastomoses are formed with branches of the lacrimal nerve. 2. The sphenopalatine nerve (X'^. sphenopalatinus) is given ofT in the pterygo- palatine fossa from tin- lower l)order of the maxillary nerve (Fig. 439). It is broad and flat and forms a jilexus in which several small sphenopalatine ganglia are inter- posed. It divides into posterior nasal, and greater anil lesser palatine nerves. (1) The posterior nasal nerve (X. nasalis aboralis) passes through the sphenopala- tine 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 (X. 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 (X. palatinus major s. anterior) (Figs. 680 NERVOUS SYSTEM OF THE HORSE 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 jialatine fora- mina to supply the mucous membrane of the inferior meatus. The branclie.s of tlie two nerves anastomose in the hard palate and form a plcxii.s about the branches of the palatine arteries. Fig. 514. — Di.ssEmoN of Head of Horse. The masseter and superficial muscles and the parotid gland are in great part removed, a, a. Levator labii superioris proprius; h, b. levator nasolabialis; c, dilatator naris inferior; d, buccinator; e, common mass of buc- cinator and depressor labii inferioris; /, depressor labii inferioris; g, masseter; h, orbicularis oculi; ?', temporalis; k, occipito-hyoideus; k', stylo-maxillaris; /, sterno-cephalicus; /'. tendon of same; m, omo-hyoideus; n, crico-pharyngeus; o, mastoid tendon of mastoido-humeralis; p, splenius; i/, inferior buccal and labial glands; r, superior buccal glands; s, remnant of parotid gland; t, submaxillary gland; u, anterior cervical (subparotid) lymph glands; i', probe passed into diverticulum nasi; w, cornu of alar cartilage; x. internal palpebral ligament; H, wing of atlas; z, scutiform cartilage of ear; /, external nasal nerve; 5, anterior nasal nerve; S, 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; S, facial nerve (cut); 9, superficial temporal nerve; W, anastomosis between 9 and S; II, internal auricular nerve; J£, posterior auricular nerve; 13, digastric nerve; 14, cervical branch of facial nerve (cut) ; /S, auriculo-palpebral nerve; /S lacrimal nerve; /7, frontal nerve; AS, infratroch- lear nerve; 19, n. zygomaticus s. subcutaneus malcp; 30, spinal accessory nerve; SI, ventral branch of spinal ac- cessory nerve (to sterno-cephalicus); S3, ventral end branch of first cervical nerve; 23, thyro-laryngeal artery; Si, internal maxillary artery; 3S, masseteric artery; S9, great (posterior) auricular artery; 27, external branch of eS; 5S, deep auricular artery; 29, superficial temporal artery; SO, transverse f.acial artery; 31, facial artery; S3, inferior labial artery; 55, superior labial artery; 3.4, lateral nasal artery; 35, dorsal nasal artery; SS, angular.artery of eye; 37, labial twigs of palato-labial artery— loft uncolored by oversight: 33, branch of buccinator artery; 39, buccinator vein; 40, vena reflexa; 41 , 43, jugular vein; 43. external maxillary vein; 44. inferior cerebral vein; 4S, stump of great auricular vein; 46, ramus of mandible; 47, facial crest; 4S. zygomatic arch; 49, parotid duct. (.\ftcr Kllenberger-Baum, Top. .\nat. d. Pferdes.) (3) The lesser or posterior palatine nerve (N. ])alatinus minor s. posterior), also termed the stapiiylinc is much tlic 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. ,51.5) lie on the perpendicular part of the palate bone and the pterygoid process under cover of the maxillary nerve. The afferent fibers of the THE FIFTH, TRIGEMINAL, OU TRIFACIAL NERVE 681 plexus and ganglia come chiefly from tlie branches of the sphenopahitine 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 (X. canalis pterygoidei) is formed by the union of sympathetic til)ers with the superficial petrcsal branch of the facial nerve. It pa.sses forward at first l)etween 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 tliat 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 maxil- lary nerve, around whicli they have a plexiforni arrangement. 3. The infraorbital nerve (X. infraorbitalis) is the continuation of the maxillary trunk. It traverses the infraorbital canal, emerges through the infraorlntai fora- men, and divides into nasal and superior labial branches. Along its course it gives off superior alveolar or dental branches (Rami alveolares maxillse), 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 ma.xillare, and supply the posterior molar teeth and the raa.xillary sinus. The middle alveolar branches are given off in the infraorbital canal, and consti- tute 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 termi- nals 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 (X. mandibularis), also termed the inferior maxil- lary branch, is formed tjy 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 fora- men lacerum, between the temporal wing of the sphenoid bone and the muscular process of the petrous temporal, and gives off the following Ijranches: 1. The masseteric nerve (X. 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 (Xn. tcmporales profundi) (Fig. 437), two or three in number, arise by a common trunk mth the masseteric. They supply the temporal muscle. 3. The buccinator nerve (X. buccinatorius) passes obliquely forward through the anterior part of tlie external pterygoid muscle, then between the internal pterygoid and the tuber maxillare (Fig. 514). It continues forward in the sub- mucous tissue of the cheek along the lower border of the buccinator and divides into Ijranches which ramify in the mucous meml^rane 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 mem- brane of the cheek and to the buccal glands. It also communicates with the in- ferior buccal branch of the facial nerve. 4. The pterygoid nerve (X. 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 682 NERVOUS SYSTEM OF THE HORSE buccinator nerves, and is related internally to the tensor palati and the Eustachian tube. It receives motor fibers from the pterygoid nerve and sensorj- fibers by the small superficial petrosal nerve from the tympanic plexus, through which communi- cations are made with the facial and glosso-pharyngeal nerves. Sympathetic fibers are derived from the plexus on the internal maxillary artery. Efferent fila- ments go to the tensor palati, tensor tympani, and pterygoid muscles, and to the Eustachian tube. The Ranglion is .small and sonipwhat difficult to demonstratt'. In many cases it is replaced by a number of minute sanslia 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 di- vides into two branches. The upper branch (Ramus transversus faciei) accom- FiG. 515. — Deep Dissection of Bask of Cranittm, Viewed from the Right and Below. The tympanic cavity is opened and the paramastoid process is sawn off. a. Occipital condyle; h, body of sphenoid; c, external auditory meatus (part removed); d, malleus; c, incus; 1, stump of ophthalmic nerve; £, ina?dllary nerve (cut off); S, sphenopalatine plexus; 4> Vitlian nerve; 4, deep petrosal nerve; 4" • branch to tympanic plexus; 4'". superficial petrosal nerve; o, superficial temporal nerve (cut otT) ; 6, masseteric nerve (cut off); 7, mandibular nerve (raised) ; S, lingual nerve (cut otT); 9. pterygoid ner\'e (cut); /O. nerve to tensor tympani; 77, otic ganglion; /^, facial nerve; i.^, stapedial nerve; 14, chorda tympani; 16, glosso-jjliaryngeal nerve (cut); 76, tympanic nerve; 77, vagus (cut off); 7 in the formation of tlie auricular plexus. 6. The inferior alveolar or dental nerve (N. alveolaris mandibuhr) (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 l)ranches, which ramify in the lower lip and chin. Before entering the bone, the nerve detaches the mylo-hyoid nerve (N. mylohyoideus), which runs tlownward 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 submaxillar^' space. The dental THE SIXTH OR ABDUCENT NERVE G83 and gingival branches detached from the nerve within the inaiuHhle are arranged lilve the corresponding nerves of the ujiper jaw. 7. The lingual nerve (X. lingualis) arises by a common trunk with the inferior alveolar or dental nerve (Figs. 430, 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 super- ficial branch (Ramus superficialis) runs forward on the stylo-glossus and accom- panies 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 connnunicates with the lingual branch of the glosso-pharyngeal nerve. The larger deep branch (Ramus profundus) turns around the lower edge of the hyo-glossus, jjasses ujiward and forward Isetween that muscle and the genio-glossus, and continues forward on tlie latter to the tip of the tongue. It gives branches to the mucous membrane and the fungiform papillse of the tongue, and anastomoses with branches of the hypo- & .a^^-oci^^ Fig. 516. — Part of Branch op Lower Jaw of Horse. Internal Vi The bone has been removed to show the vessels and nerves. /, i', Inferior alveolar branches to cheek teeth and gums; 2' , branch to canine and incisor teeth; S^ 3\ 4, satellite vein. (After Leisering's .\tlas.) ntal nerv'e; S, 2, ferjor alveolar or dental artery: glossal 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. THE SIXTH OR ABDUCENT NERVE The abducent nerve (N. abducens) emerges from the brain behind the ]X)ns and just external to the pyramid (Fig. 499). It passes forward across the pons, jMcrces the dura mater, and accompanies the third and ophthahnic 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 sup- plies 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 ot the abducent nerve are axones of the large muUipolar 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 (n) the anterior olive; ib) the oculomotor nucleus of the oppasite side; (c) the motor area of the cerebral corte.x bj- means of the pyramidal tract of the opposite side. 684 NERVOUS SYSTEM OF THE HORSE THE SEVENTH OR FACIAL NERVE The facial nerve (X. facialis) has its suiierficial origin at the lateral part of the corpus trapfzoidcuni. immediately behind the j^ons (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 lietween the vestibule and the cochlea, then curve backward and downward in the jjosterior wall of the tympanum to end at the stylo-mastoid foramen. The bend formed by the nerve is called the knee (Cleniculum n. facialis) and liears at its highest point the round geniculate ganglion (G. geniculij. The nerve consists of two parts, motor and sensory. The motor part constitutes the bulk ofjthe nerve. Its deep origin is from the cells of the facial nucleus, which is situated in the medulla aliove the facial tubercle. On lea\ing the nucleus the root-fibers pass upward and inward, in- cline forward close to the median plane, and then bend sharply downward to the point of emer- gence. The highest point of the bend is subjacent to the gray matter of the erainentia teres in the floor of the fourth ventricle, and the abducent nucleus lies in the concavity of the curve. The small sensory part iX. intermedins) consists of axones of cells of the geniculate ganglion, which i,< interp(jsed 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 tympaiii. 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 raiiius 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 j^arotid gland upon the masseter muscle, it receives the lower branch of the superficial temporal nerve, and divides into supe- rior 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.' 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 antl tmites with a filament issuing from the tympanic plexus to form the small superficial petrosal nerve (N. petrosus superficialis minor); this ends in the (itir ganglion. 3. The stapedial nerve (N. stapedius) (Fig. 515) is a short filament tletached from the facial nei\c as it turns down in the facial canal. It innervates the sta]ie- dius muscle. 4. The chorda tympani (Fig. 515) is a small nerve which arises a little l)elow 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 petrotymjianic 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. ' Although this nerve springs directlj- from the ganglion, it contains motor as well as sensory fibers. THE SEVENTH OR FACIAL NERVE 685 5. Anastomotic tilanu'iits unit(> with tlie auricular t)rancli of the vagus near the stylomastoid foramen. 6. The posterior auricular nerve (X. auricularis posterior) arises from the -facial at its emergence from the facial canal (Fig. 514). It runs upward and l)ack- ward with the posterior auricular artery under cover of the parotid gland and sup- plies 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 (X. auricularis internus) springs from the facial close to or in common with the preceding (Fig. 514). It ascends in the paro- tid gland just Ijchind 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-hyoidcus. At its origin it gives off a small branch which forms a loop around the great auricular arter.v or its posterior branch and rejoins the tnnik. 9. The auriculo-palpebral nerve (X'. 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 distril.iuted to the orbicularis oculi, corrugatur supercilii, anil levator naso- labialis. 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 liranches (Figs. 435, 461). 1. The superior buccal nerve (X. 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 (X". buccalis ventralis) crosses the masseter obliciuely 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, anastomose.s, 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. 686 NERVOUS SYSTEM OF THE HORSE THE EIGHTH OR AUDITORY NERVE The auditory nerve (X. acusticus) is connected with the lateral aspect of the medulla just hchind and external to the facial (Fig. 499). It has two roots, vesti- bular 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 saccu- lus, and to the ampullae of the semicircular canals, of the internal ear. In the in- ternal 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. cochleae) 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 \'estibiilar ner\-e arise from the vestibular ganglion as central processes (axones) of the bipolar colls of the f;anglion. Tlic peripheral processes (rlendrites) of the cells form arborizations about the (Icrp ends of the hair-cells of the macuke and iiiiiiiiriicular canals. The fibers enter the iiu-dulla, iki-> between the re.stiform body and the spinal tract of the trigeminus, and spread out tu end m the vestibular nucleus in the floor of the fourth ventricle. Among the central connections of tlie vestibular nerve are: (1) fibers vi'hich connect its nucleus with centers in the cerebellum (chiefly of the oppo- site side); (2) the vestibulo-spinal tract, which convej-s 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 antl 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 \-entricle. From the ventral nucleus fillers pass in the corpus trapezoideinn 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 quadrincriiiiial binly ;ind llic inh rnal geniculate body. The axones of the cells of the dorsal nucleus jiass largely i:iN llic sirur arn-^lica') over the restiform body and acro.ss the floor of the fourth ventricle toward tlie inedian plane. They then turn ventrally, cross to the opposite side, and are continued by the lateral fillet. From the mid-l)rain a tract proceeds to the cortex of the temporal lobe of the hemisphere. THE NINTH OR GLOSSOPHARYNGEAL 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 bodj-; 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 ])er- forates 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).' It then curves downward and forward over the guttural pouch and behind the great coriui of the hyoid l)one, 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. tymjianicus) (Fig. 515) arises from the petrous ' This ganglion appears to be equivalent to the jugular or superior and petrous ganglia of man. THE TENTH, VAGIJS, OR PNEUMOGASTRIC NERVE 687 ganglion and passes upward between the petrous and tympanic parts of the temporal hone 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 tym- panic plexus. From the jilexus 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 \'agus nerve and with the superior cervical ganglion of the sympathetic. 2. A consideralile branch runs backward on the guttural pouch, contributes filaments to the ])haryngeal 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 V)ranches. 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 sym- pathetic filaments in forming the pharj'ngeal plexus; from this liranches 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 ])osterior 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 gusta- tory fibers to the vallate papillae. A considerable branch unites with a twig from the lingual nerve. The glosso-pharyngeal is a mixed nerve, containing both motor and sensory fil)ers. 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 pmi'isx^ nf ihc ganglion cells enter the medulla, pass upward and inward through the formatio retiiiilaris, and end in the nucleus of termination in the floor of the fourth ventricle. The motor fibers arise fruin 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 dis- tributed 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 con- verge to form a trunk which passes outward, pierces the dura mater, and emerges from the cranium through the foramen lacerum posterius (Fig. 51.5). In the foramen the nerve bears on its lateral aspect the elongated flattened jugular gang- lion (G. jugulare). The ganglion communicates with (a) the tympanic nerve, (h) the petrous ganglion of the nintli nerve, (c) the spinal acce.s.sory, and (rf) the hypoglo-ssal. 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 hlamcnts 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 688 NERVOUS SYSTEM OF THE HORSE internal carotid artery and crosses tiie 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 sym- Lig. nucha Splenius^ Nuchal fal Branch oj occipital artery Corn-plexus Complexus tendon Intertransversalis Rectus capitis posterior major Spinal accessory nerte (dorsal branch) Mantoido- hiimiralis 'ayus accessory nerte (dorsal branch) Rectus capitis ante- rior major Jugular vein Thyro-laryngeal artery Anterior cervical lymph glands Extrninl nia.r- illury nin Sterno-ccphiilic Omo-hyoideus and sterttu-hyoidcu Tliyroid gland SUriio-lliyroideus Fig. 517. — Cross-section of Neck of Horse, Passing throdoh Posterior Part of Atlas. The head and neck were extended, i, Dorsal arch of atlas; 2, odontoid process; S, odontoid ligament; 4, vertebral siniises; 6, dura mater; 6, spinal cord; 7. vertebral artery; 8, wing of atlas; 9, atlanto-axial joint cavity; 10. ccsophagus; 11, 11, recurrent nerves: 12, 12, ventral branches of spinal accessory nerves. By an oversight the ubliquus cai). i>ost. (above wing of atlas) is unmarked. pathetic, and from this point backward the relations of the right and left vagi differ somewhat and must be described separately. The right vagus (Fig. 429) enters the thorax in the angle of divergence of the right l)rachial artery and the truncus bicaroticus. It then passes backward and slightly upward, crossing oblitiuely 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 TENTH, VAGUS, OR PNEUMOGASTRIC NERVE 689 The left vagus (Fig. 428) enters the thorax on the ventral face of the crsophagus, crosses obliquely under the left brachial artery, and passes back on the external surface of that vessel in company with a large cardiac nerve.' 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 oesophageal trunks (Truncus ocsophageus dorsalis, ventralis). These run backward in the posterior mediastinum, above and below the oesophagus resjDeetively, and enter the abdominal cavity through the hiatus cesophageus; they supply branches to the oesophagus 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 celiac and subsidiary plexuses. The ventral trunk passes to the lesser curva- ture 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 liranches of the vagus are as follows: 1. The pharyngeal branch (R. pharyngeus) is given off in relation to the supe- rior 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 l^asses along the side of the oesophagus and ramifies in its cervical part. According to Ellenberger and Baum the pliaryngeal plexus receives filaments also from the digastric, superior laryngeal, hypoglossal, and first cervical nerves. The branches of the plexus form secondary intermuscular and submucous ple.xuses, 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 jjharynx, and the entrance to the oesophagus; 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. .\t 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 gangUon 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 ' 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. 44 CM NERVOUS SYSTEM OF THE HORSE arteriosum, winds aimind tlic 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 wortliy of note that the left nerve passes beneath the bronchial lympli 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. Tlic 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 tesophagus in the neck. The right recurrent is given off from or in common with a consiJcrable trunk which connects the vagus witli the first thoracic ganghon 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 eachnerve (Fig. 517) lies on the dorsal surface of thetrachea, in relation to the oesophagus internally and the carotid artery above.' It passes hetween the crico-arytenoideus posterior and the crico-pharyngeus ; the terminal branches supply all the muscles of the larj^nx except the crico-thyroid, and communi- cate with branches of the superior laryngeal nerve. Collateral branches are given off to the cardiac plexus (Rr. cardiaci), to the trachea (Hr. tradieales), to the rcsophagus (Rr. a-sophagei), 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 sj'mpathetic and recurrent nerves to form the cardiac plexus, which innervates the heart and great vessels. 5. Small tracheal and oesophageal branches (Rr. tracheales et cesophagei) 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 oesophageal plexuses, from which twigs go to tlu' trachea, ffsophagus, 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 pulmonar^ 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 re.spect. 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 sjiimd nerves. Most of the fibers end in arborizations about the cells of the v:ig(i-t;losso-]ilmryni;i-:il iiUfli-iH nf 1 rrniiii;ilion, which consists of two parts. Of these the dorsal sensory nucleus (XihI.iik ,iI;c ciiH-n;!! is -ituated in the posterior part of the floor of the fourth ventricle and in the adjaci'iit part uf llic rlosed portion of the medulla near the me- dian plane. The other part is termed the nucleus of the solitary tract, and is so named lnrauM' its cells are grouped about the bundle (Tracius solilariiis) foniicii by the posterior diN i-mn- nl' the afferent nerve-fibers. It ends about th<> lc\ el of the pyramidal decussation. Tlic si'iuiidui y central connccticms are siinil;ir to those of the sensory part of the trigeminus. The motor fibers land those of the nuMlulIary part of the acce.s.sory) arise from the dor- sal motor nucleus and the ventral motor nucleus. The cells of the former lie in groups along the ventro-medial side of the tlorsal sensory nucleus. The latter, also termed the nucleus am- biguus, 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 ]3urely 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 ' The nerve lies here about a finger's breadth aliove the thyroid gland. If. however, the gland is enlarged it may come in contjvct with the nerve. The same is true in regard to the rela- tion to the anterior cervical lymph glands. THE ELEVENTH OR SPINAL ACCESSORY NERVE 691 which emerge between the dorsal antl ventral roots. The bundles unite to ft)rm a trunk which is very small at its origin at the fifth segment of the cord, but in- creases 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 antl ninth nerves and emerges through the foramen laccrum posterius. It then runs backwaril and down- FiG. 31S. — Neck of Horse, after Removal of Part of Panxicttlcs asd Trapezits. a, a', Ma^toiUo-humeraUs; 6. anterior superficial pectoral imigcie; c, cer\*ical pannicultis; d, sterno-cephal- icils; e, omo-hyoideus; /. sterao-thyro-hyoideus; {/, trachea; h, h' , h", teadons of splenitis, mastoido-humeralis, and trachelo-ma^toideus; i, trapezius cenicalis: t.supraspinatus; /, anterior deep pectoral muscle; m, rhomboideus cer\-icalis; n, serratus cer\-icis; o, splenitis, upper and lower borders of which are indicated by dotted lines; p, parotid gland; y the sixth cervical nerve is quite small. Each of the three chief roots, /. 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:' 1. The large suprascapular nerve (N. suprascapularis) turns outward and for- ward and disappears between the su]iras])inatus and subscapularis. 2. The much smaller subscapular nerves (Nn. subscapulares), usually two primary trunks, arise close behind the suprascapular, run backward a short dis- tance, and divide into several branches which enter the lower third of the subscap- ularis. 3. The anterior thoracic or pectoral nerves (N. pectorales craniales), three or four in numt)cr, arise from the anterior jiart 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 u.sually to the posterior deep muscle. The latter receives one or two other nerves. 4. The musculo-cutaneous nerve (N. musculocutaneus) arises from the an- terior part of the ]ilexus and passes over the outer face of the brachial artery, below which it is connected by a large l:>ut short branch with the median nerve, thus form- ing 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 bra- chial plexus. It lies at first above the brachial artery, then passes between the arterj' 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 liehind the brachial artery and is accompanied a short distance by the radial nerve. 7 The radial nerve (X. 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 ' In orflor to examine the plexus and the oriRins of its chief brandies eonveniently and with as Httle disturbance of relation as possil)lo, the suliject should be suspended in imitation of the natural position and tlie fore limb abducted as much as is necessary. SUPRASCAPILAR NERVE — AXILLARY NERVE 697 dips into the interstice between that muscle and the long and internal heads of the triceps. 8. The axillary or circximflex nerve (X. axillaris) arises behind the musculo- cutaneous. It passes downward and backward on the inner face of the sub.scapu- laris and disajijiears between that muscle and the subscapular artery. 9. The long thoracic nerve (X. thoracalis longus) is wide and thin. It passes backward across the surface of the serratus magnus. to which it is di.stributed. The branches which enter the muscle are given off both upward and dowiiward in fairly regular fashion. 10. The thoraco-dorsal nerve (X. thoracodorsalis) passes upward and back- ward across the subscapularis nuisclc to ramify in the teres major and tlie latissimus (.lorsi. 11. The external (or subcutaneous) thoracic nerve arises by a common trunk with the ulnar. It runs liackward and downward across the inner face of the tensor fasciae 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 dor.si 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 CSn. pectorales caudales) may be used to include S, 9, and 10. Suprascapular Nerve The suprascapular (Fig. 441) is a large nerve derived chiefly, if not exclusively, from the si.xth and seventh cervical components of the brachial plexus. It passes lietween the supraspinatus and subscapularis muscles and turns around the distal fourth of the anterior border of the scapula to reach the supraspinous fcssa. 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 supphed by it. HUSCULO-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 liranch 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 ex- ternal heads of the triceps, it reaches the deep face of the deltoid and divides into G98 NERVOUS SYSTEM OF THE HORSE several divergent branches. The muscular branches supplj- the teres major, cap- sularis, teres minor, infraspinatus, deltoid, and niastoido-humeralis. The cutane- ous branch (X. 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-spira!, 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 arterj- 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 fasciae 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 down- ward and outwartl 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 anti- brachii dorsalis); brandies 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 sup- plies 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 ex- ternus, 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.' Fig. 520. — Cit Nf.rves of Right Fore Limb op Hor.se, External Face. a. Cutaneous branch of axillary nerve: b, cu- taneous branches of radial nerve; c, posterior cutane- ous branch of ulnar nerve; fl, cutaneous branch of me- dian nerve; e, superficial branch of ulnar nerve; /, external metacarpal nerve; ff, anastomotic branch con- necting internal and exter- nal metacarpal nerves; 1, external head of triceps; 2, extensor carpi radialis; 3, anterior extensor; .(, flexor carpi extertms. C.\ftcr El- lenberger, in Leisering's Atlaa.) 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 fasciae 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 ' 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. MEDIAN NERVE 699 ppicondyle of the humenis. In the fort-arm it crosses obliquely the deep faee of the ulnar head of the flexor carpi ineilius and descends under the deep fascia with the vessels, at first on the ulnar head of the perforans, and then between the midtUe and external flexors of the carpus. Near the level of the accessory carpal bone it divides into two terminal branches, su])erficial and deep. It gives off two i)rinci]ial col- lateral branches. The cutaneous branch (Ramus cutaneus palnuiris) is detached just before the nerve passes under the tensor fasciae 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 Jij.li uxor carpi rudiulis Inlenntiscular septum Anlcrior extensor of digit Intermuscular septum Lateral extensor of dii/it Iniermusndar septum Flexor carpi externus Flexor perforans. {humeral head) Flexor perforatum Flexor perforans {ulnar head) Ulnar rein j Ulnar nerve Ulnar artery 21. — Cross-section of Forearm of Horse about Three ] The rleep fa.scia is flesignateil by re^l line. .V, .1 V , Accessory cephalic vein Vein Cephalic vein Intiriinl lateral ligament of elbow Median nerre Posterior radial reins Puslerior radial artery Flexor carpi intemus Fl'xor carpi medius I.) BELOW 1 essels and i : Elbow Joint. 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 meta- carpal or volar 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 700 NERVOUS SYSTEM OF THE HORSE 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 int(>rnal lateral ligament. .\t the elbow the nerve is covered by the posterior superficial pectoral muscle and is crossed by the large oblique connection between the cephalic and Ijrachial veins. The ^■arial3le and often piexiform venous arrangement renders approach to the nerve here undesirable. It can be reached hdcrnnl mdacarpal vein MdaciiriHil or rolar nerve Digital artery Dorsal or anterior digital branch Volar or posterior digital branch Distal end of cxtcrned small meta- carpal bone Large metacarpal hone Suspensory ligament Superficial flexor tendon Posterior annular ligament of fetlock Exlensiir branch of suspensory lii/ainent Olilii/ue or middle inferior scxdnidiilean lig. I 'ular lig, of paslem joint Proximal annular lig. of digit Deep flexor tendon Distal annular lig. of digit 2.— Dissection or Dibta . Part ui- Ku. IT Im.KK .JMi. >,K Ho rtil;igc; 2, .i, 4. ligaments rom first phala nx to thin sesamoi.l, 1 (.\fte Schmaltz, .\tla s d, Anat. d. Pferdes.) ulli of heel, and la best liy an incision just l)eliinil the lower part of the long internal lateral ligament: here the nerve lies umlcr the deep fascia in the furrow between the radius anil 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, apd 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 corresponiling external nerve. At the proximal part of the forearm tlic nerve nms almost straiglit downward along the posterior border of tlie 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 MEDIAN NERVE 701 interval between the internal and mifliile 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 niicUUe of the arm, passes beneath the lower liart of the biceps, and divides into muscular and cutaneous branches. The mus- cular branch enters the lirachialis. 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 jxisses 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 maj' go to the extensor muscles. The metacarpal or volar nerves,' 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 (X. 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 super- ficial 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 metacar- pus, 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 metacar- pus 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 hocjf on the dorsal (anterior) face of the digit. 2. The volar or posterior digital branch (Ramus volaris) is the direct continua- tion of the tnmk. It tlescends liehind 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 cress very obliquely over the artery and anastomose in a variable manner with each other and with the anterior branch. The external metacarpal or volar nerve (X. 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 l^y a small artery from the volar subcarpal arch. Toward the distal end of the metacarpus it is joined by the oblique laranch from the internal nerve, and beyond this is arranged like the lat- ter. 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. ' In veterinary works these arc frequently termed plantar nerves, which is an unfortunate misnomer. The writer inclines to the use of tlie old term metacarpal or common digital to desig- nate the nerves as far as their divisions, and the term digital beyond this. 702 NERVOUS SYSTEM OF THE HORSE THE THORACIC NERVES The thoracic nerves (Xn. thorucalos) number eighteen on either side in the horse. They are designated numerically according to the vertebrae behind which they emerge. Most of them are arranged in a very similar manner and therefore tlo 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 trans- versalis 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 the}' 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 nucha> and the scapular cartilage. The ventral branches or intercostal nerves (Nn. intercostales) are mucli larger than the preceding, and are conne<'ted with the sympathetic by rami communi- cantes. The first goes almost entirelj' to the Israchial plexus, but sends a fine branch downward in the first intercostal space which is expended in the muscle there with- out 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 ril), 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 supph'ing 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 la.st 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 ab- dominis, 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 (Xn. 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. fe H s 703 704 NERVOUS SYSTEM OF THE HORSE Their dorsal branches are small in comparison with the ventral ones. They are distrilxitcd 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 communicautes, anil give branches to the sublumbar muscles. Those of the first two nerves are arranged in a manner analogous to the corresponding brancli 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 cjuadratus lum- borum 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 antl the external oblique, perforates the latter, and runs downward and back- ward 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 back- Crura of ti'mphragm Diaphragm Last intercostal ne Ilio-hypngnxtric nerve - Ilin-inguinal nerve- Exlernal spermatic nerve External cutaneous^ ,// nerve Sympathetic trunks Insertion of quad- ratus lumhorum' Anterior part of j^ lumbosacral plexus [Z Obturator nerve Femoral nerve Splanchnic nerve Last intercostal arteries First lumbar arteries Attachments of psoas major — Body of vertebra External spermatic nerve Trunk of lumbar arteries I'Es OF Horse, Ven' Sixth lumbar artery Ventral sacro-iliac ligament (After Schmaltz, .\tlas d. .\nat. d. Pferdes.) ward beneath the pcritoneimi to the outer ])order of the rectus abdominis, gives branches to the internal oblique, and terminates in the rectus abdominis. The ventral l:(ranch of the second lumbar nerve is comiected 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 <'anal along the outer border of the cremaster (to which it detaches filaments) and ends suhcutaneously in the scrotum and prepuce in the male, the mammary gland in tlie female. The ilio-inguinal nerve (N. ilioinguinalis) may be regarded as the con- tinuation of the ventral branch. It runs ]iarall('l with tlie iho-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 LUMBO-SACRAL PLEXUS 705 ilio-hypogastricus, detaches branches to the internal obhciue muscle, and descends the inguinal canal with the inguinal l)ranch, 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 Ijy a small anasto- motic branch with the second nerve and furnishes a root of the lumlio-sacral plexus. It gives off a branch to the psoas muscles, an inguinal branch, and is continued as the external cutaneous nerve. The inguinal btanch (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 ex- ternal to and parallel with the external iliac artery and de- scends in the inner part of the inguinal canal. It emerges at the external ring with the ex- ternal pudic artery and rami- fies in the external genital organs and the skin of the inguinal region. The external cutaneous nerve of the thigh (X. cutaneus femoris lateralis) runs backward in the sub- stance of the psoas muscles and emerges at the outer bor- der of the psoas minor. It then passes outward and back- ward 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 ex- ternal oblique and the iliacus a short distance below the point of the hip, and descends on the inner face of the tensor fasciae latae (near its anterior border) and ramifies subcuta- neously in the region of the stifle. Pig. 525. — Soperficiai. Nerves of Pel- vic Limb and Posterior Part op Trunk of Horse. a. Cutaneous branches of sixteenth and seventeenth thoracic nerves, b. cuta- neous branches of lumbar ner\'es, c, cu- taneous branches of sacral nerves; d, cutaneous branches of coccygeal ner%'es, e. /. (7, cutaneous branches of last inter- costal, iUo-hypogastric, and ilio-inguinal nerves; *;'. end of external cutaneous nerve of thigh; k, posterior cutaneous nerve of thigh; i, i, cutaneous branches of great ____^ sciatic nerve; t, posterior cutaneous nerve The origin and disposition of of the leg; I. superficial peroneal nerve, some of the foregoing nerves arc „|^ terminal part of deep peroneal nerve; n external plantar nerve, variable. In some cases the ilio- ;^ obliquus abdominis externus; 2, tensor fasci.-E lat£e; 3 gluteus inguinal nerve ends in the psoas superficialis; i. biceps femoris; b, semitendinosus. 6, ante major, and appears then to be ab- tensor; 7, lateral extensor; S, flexor tendo sent. The mode of formation of artery. (After EUenberger, in Leisering'a Atlas ) the inguinal nerves is very incon- stant. The inner nerve mav arise m. • • i i i, ^\-ith one of the outer ones from a common trunk, or they may anastomose. Ihe 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 great metatarsal 706 NERVOrS SYSTEM OF THE HORSE 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 be- tween the psoas major and minor, then crosses the deep face of the tendon of in- sertion 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. ol)turatorius) is derived from the ventral liranches 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 liranches which innervate the obturator externus, pectineus, adductor, and gracilis muscles (Fig. 456). Anterior Gluteal Nerve This nerve (N. glutanis cranialis) is derived chiefly from the last lumbar and first sacral nerves. It divides into four or five liranches which emerge through the great sacro-sciatic foramen with the divisions of the anterior gluteal artery and supply the gluteal and tensor fascia latie muscles. The nerve to the latter and the anterior part of the superfic'ial gluteus passes l:)etween the deeji jiart of the glu- teus 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. glutceus 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 supjilies 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 GREAT SCIATIC NERVE 707 posterior head of the superficial gkitcus. The inferior nerve runs downward and backward on the sacro-sciatic Hgainent 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). Great Sciatic Nerve The great sciatic nerve (N. ischiadicus) (Figs. 451, 455, 526), the largest in the body, is deriveil cliieHy 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 CoCCIIQKll i; rt, hr.r Sacral spines Lateral sacro- / iliac ligament \ "^111 t ^^vr^>^-=itftt!s:-izi TuhlT ischii^ Gemel- Anastomosis' lus between ob- turator and internal pudic \\. Obturator artery \ Obturator internus Obturator vein Lesser sciatic foramen Fig. 526. — Vessels and Nerves on Pelvic Wall of Horse. Ner\'U9 ischiadicus = great sciatic nerve: n. glut. inf. = anterior gluteal nerve; n. pudendus = internal pudic ner\'e. (After Schmaltz, Atlaa d. Anat. d. Pferdes.) 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 deej) 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 quad- ratus femoris. In its descent in the thigh it lies between the biceps femoris ex- ternally 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: 708 NERVOUS SYSTEM OF THE HORSE 1. In the pelvic part of its course the sciatic nerve supphes small branches to the obturator internus, gemellus, and quadratus femoris; the branch to the obtura- tor internus reaches the muscle bj' 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 proxinialis) which divides to supply the semimembran- osus and the short heads of the l)iceps femoris and semitcndinnsns. 3. The posterior cutaneous nerve of the leg or external saphenous nerve (X. cutaneus surae 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. peronseus) (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 inchule a twig to the biceps femoris, the reinforcing fasci- culus detached about the middle of the thigh to the posterior cutaneous nerve, and, lower down, the external cutaneous nerve of the leg (Ramus cutaneus sura> later- alis). The latter, also known as the jieroneal cutaneous nerve, emerges between the middle and posterior divisions of the bice]is femoris at the level of the stifle joint and ramifies under the skin. The superficial peroneal or musculo-cutaneous nerve (N. peronteus 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. perona^us profundus) is the direct continuation in i)oint of siz(> of the peroneal trunk. It dips in between the lateral and anterior extensors of the digit, gives Ijranches 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 anlrrior til)ial vessels by the tibiahs anterior (muscular part of the flexor metatarsi). It should he noted that the outer of the two veins which almost always accompany the artery here is fre- cus. 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 (Apcrtura mediana) with the subarachnoid space. ' Only the most salient differences as compared with the horse will be mentioned. Fig. 528. — Br.\in of Cow, Dorsal View. J, Sulcus transversus; B, longitudinal fissure; 3. antero- internal frontal gyrus; 4. olfactory bulb; 6, marginal or sagittal pole of hemisphere; S, lateral fissure (of Sylvius); 7, hemisphere of cerebellum; S, vermis of same; 9, accessory nerve; 10. dorsal root of first cervical nerve. (EUenberger-Baum, .\nat. d. Haus- 716 THE NEUVOUS SYSTEM OF THE OX to the pineal body: The pons is smaller, l)oth transversely and longitudinally, than that of the horse. It is stroniiJA' 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 tal dilations. The anterior peduncles are very short. The cerebral peduncles are short. A small eminence in the locus jierforatus posticus is caused by the presence of the interpeduncular ganglion. The internal geniculate body is iirominent. The pineal body is long and fusiform, and is dften pigmented in spots. The third ventricle forms two considerable recesses in relation one (R. pinealis) extends up into the body; the other (R. supra]5inealis) is a long tuliular prolongation in front of it. The optic tracts cross the cerebral pedun- cles 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 reiati\-ely wider than in the horse. The frontal jjoles 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). An- terior 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 iiattern of the fissures and gyri of the ]iallium is somewhat simpler than in the horse. 1. The lateral fissure (of Sylvius) is very deep. It.s middle branch extends almost ver- tically upward on tlie iniildle of the lalei-al surface of the hemisphere, and is separated by a gyrus of varialile widtli frorii tlie 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 baek 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 .''orwanl. Its form is very variable. 4. The transverse fissure cuts obliquely into the dorsal border in front of the sagittal pole. It is short ami di'cp 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 tlie postcTior part of the preceding. 7. The ectomarginal fissure is lateral and parallel to the marginal fissure. It does not ex- tend so far in either direction as the latter and is often more or h-ss broken up by annectcnt gyri. S. The sulcus rhinalis is more open than in the horse, since it is not overlapped by the gyri above it. 9. The calloso-marginal fi.ssure is flexuous and not .so regular as in the horse. It is often Fig. 529. — Cerebral Hemispheres of Dorsal View. a, Transverse fissure; b. lateral fissure (of Sylvius); c, coronal fissure: rf, diagonal fissure; c, entomarginal fissure; /, marginal fissure; g, ectomarginal fissure; h, suprasylvian fissure. (After Ellenherger, in Leisering's .\tlas.) THE NERVOUS SYSTEM OF THE OX 717 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 iu front of the transverse fissure and commonly joins the calloso-marginal fissure below. 11. Short and variable fissures occur in front of and liehind the middle branch of the lateral fissure (F. ectosylvia anterior, posterior). The olfactory bulb is much smaller than in the horse. The external olfactorj- 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, ophtlialmic, 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 mem- brane of the frontal sinus: tlie large outer branch runs backward and supplies the matrix of the horn. The frontal nerve emerges from the orbit below the supraor- bital process. The naso-ciUary 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 divi-sion of the oculomotor nerve bj- several short filaments. In consequence of the absence of the canine and upper incisor teeth the corresponding branch of the infraorbital nerve is naturahy wanting. The mandibular nerve emerges through the foramen ovale. The superficial temporal nerve gi\es 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 ^loussu 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 for- ward along the depressor labii inferioris. At the point where it crosses the facial vein and parotid duct it gives off an ana,stomotic 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 oesophageal trunk communicates with the splanchnic nerve, contri- butes t'\\'igs to the hepatic plexus, and ramifies chiefly on the riglit surface of the rumen and the adjacent surface of the abomasum. The inferior oesophageal 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 liy 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 arrange- ment. The thoracic nerves number thirteen pairs. The more important differ- ences in the limb-plexuses and their branches are as follows: The brachial plexus is formed by the ventral branches of the last three cervical 718 THE NERVOUS SYSTEM OF THE OX and first thoracic nerves; the second thoracic nerve furnishes no root, but the ven- tral 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 exter- Median lurve- 'Ulnar nerve Anastomotic branch Fig. 530. — Nerves of Distal Part op Right Fore Limb ok Ox, Anterior View (Schematic). p. Dorsal digital nerves. Fig. 531. — Nerves of Distal Part of Right Fore Limb of Ox, Posterior View (Schematic). p, Volar digital nerve.s. nal head of the triceps and descends on the dorsal aspect of the limb. It commu- nicates 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. The ulnar nerve divides at a variable distance down the forearm into two branches. The dorsal or superficial branch emerges lietween 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 tlescends along the superficial digital flexor, gives a branch to the suspensory ligament below the carpus, THE NERVOUS SYSTEM OF THE OX 719 and unites with the external l)ranch of the nietUan nerve to form the external volar digital nerve. Tlie median nerve is much larger than the uhiar. It passes beneath the prona- tor teres, descends the forearm as in the horse, and divides in the distal part of the metacarpus into two branches. Tlie 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, Superficial peroneal nerve Deep peronealy-- nerce ,-■ Internal sa-/ phenous nerve Tibial nerve Internal planiar nerve Kitcrnal saphen- ous nerve External plantar nerve ' — Deep branch Fig. 532. — Nerves of Distal Part of Right Hind Limb of Ox, Anterior View (Schematic). p, Dorsal digital nerves. Fig. 533. — Nerves of Distal Part op Right Hind Limb of Ox, Posterior View (Schematic). p, Plantar digital nerves. 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 (X. 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). 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 720 THE NERVOUS SYSTEM OF THE PIG bi'iu'iitli llie jjcroiicus loiisins it passes down on the front of the tarsus and meta- tarsus and divides into three l)ranehes. Tlie internal and external branches descend as the internal and external dorsal digital nerves on the chief digits. The larger middle branch joins a l)ranch 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 cliief digits. The deep peroneal nerve descends in the leg as in the horse and continues down the anterior groove of tlie metatarsus with the dorsal metatarsal artery. Its terminal branches concur with brandies from the superficial peroneal nerve in the formation of the two axial dorsal digital nerves (N. dig. dors. lat. dig. Ill et dig. dors. med. dig. I\' i)edis), and with a branch of the internal ijlantar nerve in the formation of corresi)onding 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 (X. dig. plant, med. dig. Ill) along the inner side of the fle.xor tendons of the inner chief digit; the outer branch turns around the flexor tendons to reach the interdigital space, where it concurs with a brancli of tlie deep peroneal nerve in the formation of two axial plantar digital nerves (N. dig. plant, lat. dig. Ill et dig. jilant. med. dig. IX) 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 liga- ment and to the external small digit, and continues along the outer face of the ex- ternal digit as the external plantar digital nerve (X. dig. jilant. lat. dig. IV). The sympathetic system closelj- 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 con- nection is formed with the spinal accessory nerve. The cervical trunk is smaller than in the hor.se, and arises by two or three bundles from the su]ierior cervical ganglion behind its middle. The inferior cervical ganglion is distinctly sejiarable from the first thoracic; the latter is large. There are thirteen pairs of thoracic ganglia. The cceliaco-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 (KUenberger-Baum). It is almost circular in cross-section, except at the enlargements, where it is somewhat flattened dorsoventrally. The conus medullaris extends to the anterior part of the third sacral segment. The epidural space is occujiied by a large (juantity of fat. The brain in adults of medium size weighs about 125 grams (ca. 4 to 4^2 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 liroad. The cuneatc 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 i^resents 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 quadri- THE NERVOUS SYSTEM OF THE PIG 721 geraiiia are wide apart, rounded, and relatively large. The internal geniculate bod}- 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 bat kward on the depressed part of the lateral surface of the hemi- sphere: it appears unliranched on superficial examination, but when the gyrus which almost completely conceals the insula is raised, an anterior branch is exposed which forms the dorsal lidundary of the insula. 2. The suprasylvian fissure pursues a curved course approximately parallel with the dorso-medial l)order 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, antl 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. 6. The marginal fissure Ijegins behind the cruci- ate fissure close to the dorsoniedial border and ex- tends in a gentle curve backward almost to the occi- pital pole. 7. The ectomarginal fissure lies above and nearly parallel to the posterior part of the supra- sylvian fissure. 8. The entomarginal fissure lies along the pos- terior part of the dorso-medial liorder. 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 liroati anrl short. The trigonum olfactorium is so prominent as to be termed the tuberculiun olfac- torium. 46 Fig. 534. — Cerebral Hemispheres OF Pig, Dors.\l View. a, Upper part of lateral fissure (of Sylvius); 6, cruciate fissure; c, suprasylvian fissure, with its anterior branch ((f) and upper branch (c"); d, diagonal fissure; e, coronal fissure; /, presylvian fissure; g, marginal fissure; k, ectomarginal fissure; i, entomarginal fissure, (.\fter Ellen- berger, in Leisering's .-Vtlas.) 722 THE NERVOUS SYSTEM OF THE PIG The cranial nerves present the following special features: The third, fourth, sixth, and the ophthalmic and maxillary divisions of tlio fifth nerve, cmcriic tosetiier as in tlie ox. The lacrimal nerve resenil)les that of the horse, the frontal that of the ox. The naso-ciliary nerve is rehitively large and sends numerous filaments to the ocular muscles. The maxillary nerve has a very short course in the pterygo-palatinc fossa. The infraorbital nerve is large in correlation with the development of the snout which receives numerous Ijranches. The mandibular nerve emerges through the foramen lacerum anterius. The superficial temporal nerve is small; according to Moussu it furnishes the c-xcito-secretory fibers to the ujij^er ])art of the ])arotid gland, wiiile those going to the lower jjart are derived from tlie mylo-hyoid nerve. The inferior buccal nerve jiasses downward and forward under cover of the Median Ulnar inrre 1 \ \ Radial nerve {dorsal branch) -~ \ \ -\— nerve \ {ridaneuus \ branch) L- Ulmir ncm- f Dor!i(d branch Diip branch Fig. .535. — Nerves of Distal Part of Riout Fore Limb op Pig, Anterior View (Schematk). c, Dorsal common digital nerves; p, dorsal proper digital nerves. Fig. 536. — Nerves of Distal Part of Right Fore Limb of Pig, Posterior View (Schematic). p, \'oIar proper digital nerves. parotid gland and accomi)anies tlie 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 gangUon 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 comjionent. The cesophageal trunks form a posterior cpsophageal 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 jilexus. The hypoglossal nerve may present a small dorsal root, on which there is a minute hjiiogiossal ganglion (of Froriep). THE NERVOUS SYSTEM OF THE PIG 723 The spinal nerves numlier 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 Dap pcruntat nerve Superficia, peroneal nerix Internal plantar nerve Fig. 537. — Nerves of Distal Part of Right Hikd Limb of Pig, .\nterior View (.Schem.itic). p. Dorsal proi>er digital nerves. Fig. 53S.— Nerv Limb o Right Hind of the ulnar nerve. The formation and arrangement of the digital nerves are indicated in the annexed schematic figures. 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 ])lexus differs chiefiy 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 divitle to form the plantar digital nerves, two for each digit. In addi- tion, 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. 724 THE NERVOUS SYSTEM OF THE DOG Tile sympathetic system of tlip pig has received wry little attention from anatomist.s. The superior cervical ganglion is long and fusiform. It gives off filaments which jtjin the vagus n(^ar the ganglion nodosum. The cervical tnmk is short and relatively larger tiiau 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 lum})ar enlargements, where it is compressed dorso-vent rally. The conus medullaris lies over the junction of the sixth and seventh lumbar vertebrae. Fig. 539— Basi: of Brain of Dog. a, Olfactory bulb; a,' a", external and internal olfactory tracts; 6, optic nerve; c, oculomotor ner\'e d, trochlear nerve; c, trigeminua; /, abducens; n, facial h, auditory; i, gloaso-pharyngeal; k, vaRUs; /, spinal accessory; m, hypoglossal; 2, trigonum olfactorium; 5, anterior perforate*! substance; 4» tuber cinereuin and infumlibulum; 4', mamniillary body; 6, pyriform lobe; G, temporal lobe; 7, parietal lobe; S, frontal lobe; 9 pons; iO, medulla oblongata; //, cerebellum; 13,' bral pcdxmcle; 75, occipital lobe. (EUenberger-Baum Anat. d. Hundes.) Fig. 540.— Bra Stkm of Dog, Dorsal Vi a, Spinal cord; />, dorsal median groove; c, c\ funiculus gracilis; c", clava; d, d' , funiculus cuneatus; d", tuberctilum cuneatum; e, funiculus lateralis; e' , tuber- culum Rolandi; /.medulla oblongata; /,//,///, floor of fourth ventricle (fossa rhomboidea) ; y, limiting groove; h, median fissure; i, eminentia medialis; k, ala cinerea; /, /'.pons; m, posterior peduncle, and n, middle peduncle of cerebellum (cut); o, anterior peduncle of cerebellum; ;j,/y,corporaquadrigemina, anterior and posterior; q, proxiniately concentric with the preceding. It also consists of three parts — anterior, middle, and pos- terior. 4. The ectomarginal or collateral fissure runs forward on the dorsal aspect of the hemis])here almost parallel with the dorso-medial border. A little in front of the middle of the surface it gives oiT a short ansate fissure (F. ansata) which runs obliciuely inward and forward, and is continued bv the coronal fissure. Fig. 542. — CF.REBRtr.M of Dog, Dorsal ViKW. a. End of lateral fissure (of S\l- vius); 6, ectosylvian fissure; c, c', r", suprasyKnan fissure: d, fissura ansata minor; e, ectolateral fissure; /, ectomar- ginal or collateral fissure; o, fissura an- sata; h, coronal fissure; /, meflilateral fissure; /:, entomar^nal fissure; /.post- cruciate fissure; m, cruciate fissure; o, presyhnan fissure; p. fissura prorea. (.\fler Ellenherger, in I.eisering's .\tlas.) Fig. 54.1.— Fisscrks of L.mf.r.m. Sirf;\ck or Ckrk- BRU.M OF Dog, Right .Sidk, a, Fissura prorea; b, frontal fissure; c, ol- factory fissure; d, d' , sulcus rhinalis; e, presylvian fissure; /. precruciate fissure; g, postcruciate fissure; A, cruciate fissure; i, lateral fis. nmzzle. The infratrochlear nerve runs forward between the internal Fic. r)4fi. — Nerves of Fate oi- Dor,. FAnoTin fJt.ANn is Removed. a, Facial nerve; b, posterior auricular nerve; c, internal auricular nerve; d, digastric nerve; e, inferior buccal nerve; /, cervical branch of facial; ti, auriculo-palpebral; h, superior buccal nerve; /, temporal branch; k, k', k", zygomatic branch; I, auriculo-temporal; m, malar branch of /,- n, buccinator nerve; o, mylo-hyoiil branch; p, subcutaneu.s malai; q, lacrimal nerve; r, frontal nerve; s, infratrochlear nerve; /. infraorbit.il nerve; 1, i>aramastoi(l process; 2, fligastricus muscle; S, base of concha; 4, masseter; 6, zygomaticns; (>, scutularis; 7, zygomatic arch; S, maxilla. (Ellcnberger-Baum, .\nat. d. Huntles.) straight and the superior oliliciue muscles of the eye and ramifies on the face in the vicinity (if the inner canthu.s. Tlie maxillary nerve, after giving off the zygomatic, divides into infraorbital and sphenopalatine branches. The zygomatic nerve emerges through an opening in the ui)per part of the orbital ligiunent and ramifies in tlie lower lid and on the adjaciMit surface of the face. The infraorbital nerves, two in number, tlivide within the infra()rl)ital canal and ;tfter their emergence upon the face, thus forming seviMi or eight external nasal and superior labial branches. The sphenopalatine nerve gives off lesser ;uii! greater palatine ami posterior nasal nerves. Tlie mandibular nerve jiasses 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, ' The origin of tlic lurrimal ncrvo is .sucli that Kllenberger-Baum and Martin describe it as a branch of tlie maxillary nerve. THE NERVOUS SYSTEM OF THE DOG 729 and ramifies on the lateral surface of the face. The inferior alveolar nerve arises by a common trunk with the mylo-hyoid; it gives oft' dental branches and term- inates in mental and inferior labial branches. The lingual nerve supplies vaso- dilator and excito-secretory filaments to the submaxillary and sublingual salivar}' glands; these fibers are derived from the chorda tympani. The facial nerve divides near the iiosterior 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 ac- companies 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 lie about half an inch (ca. 1 to 1.0 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 ^-entrally to the common carotid artery. The formation of dorsal and ventral oesophageal trunks by the union of the dorsal and ventral divisions of the two nerves takes place at the hiatus oesophageus. 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 jiarietal 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 jiharynx to end in the crico-thyroid muscle. It furnishes a root of the inferior pharyngeal branch, and comnmnicates 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 fila- ments 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 cesophagus. It contributes filaments to the pharyn- geal plexus, communicates with the recurrent nerve, and supplies twigs to the thy- roid 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 meml)rane of the pharynx. The superior laryngeal nerve arises from the ganglion nodosiun and descends over the side of the phar\'nx. crossing beneath the carotid artery and the superior laryn- geal nerve. It passes through the thyroid notch and ramifies in the mucous mem- brane 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 bortler of the thyroid cartilage, gives a branch to the crico-arytenoideus posterior as it pa.sses over that muscle, and con- 730 THE NERVOUS SYSTEM OF THE DOG tiiiue« 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 supi)ly the trachea and concur with the inferior pharyngeal branch in forming a ]ilexus on the cervical ])art of the cesophagus which innervates that tube.' The depressor nerve is a very delicate filament which arises usually from the supe- rior laryngeal nerve and accompanies the vago-s^^npathetic trvudc to the tliorax; its fii)ers reach the heart through the cardiac nerves. The pulmonary and pos- terior oesophageal plexuses are highl.v developed. The hypoglossal nerve gives off a long branch (R. descendens) which rvms 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 com- prise 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 anil 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 ex- tensors of tiie eU)ow, dips in between the internal head of the triceps and the ac- cessory head of the anconeus, winds around the arm, and divides between the brach- ialis 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 liranches 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 carjjus, 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 nniscle and divides into sui)erficial antl dee|) 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 (X. dig. vol. lat. dig. V), and a branch (X. met. vol. IV) which descends in the space between the fourth and fifth metacarpal bones and unites with the deep l)ranch. The deep ' Lesbre terms this the tracheo-cesophagcal branch, and considers that it mu.st bo regarded as an accessory or internal recurrent nerve. THE NERVOUS SYSTEM OF THE DOG 731 branch (R. profuiulus) descends in the carpal canal and di\ides under the deep Hexor tentlon into its terminal Ijranchcs. The smaller of these supply the volar metacariial nmscles. 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, sul)divide, and concur with the volar metacarpal branches of the median nerve in forming the volar proper digital nerves (Xn. clig. vol. proprii). The median nerve descends behind the brachial arterj', 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 l)ranches below the elbow Branches o/^tTl" radial nerve Median nerve Fig. 547. — Nkrvks of Distal Part of Right Fore Limb of Dog, -\xterior View (Schematic). p, Dorsal proper digital nerves. Es OF Distal Part of Right Fore Dog, Posterior View (Schematic). n, \'olar proper digital nerv'es. 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 super- ficial 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 intermeta- carpal 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. 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 J32 THE NERVOUS SYSTEM OF THE DOG considered as the eontimuition 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 cutani'ous twigs from the stifle to the metatarsus. The peroneal nerve separates from the tibial above the origin of the gastrocne- mius, runs downward and forward across the outer head of that muscle, passes between the ileep flexor of the digit and the peroneus longus, and divides into super- ficial 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. cutan- eus dorsalis inedialis), and divides at the proximal part of the metatarsus into three Inlcrnal idanlar nerve Dorsal common . digilal nerves Plantar common digilal Fig. 549.— Nerves of Distal Part of Right Hin Limb of Doc, .\nterior View (Schematic). p, Dorsal proper digital nerves. Fig. 550. — Nerves of Distal Part of Right Hixn Limb of Dog. Posterior View (Schematic). V, Plantar projier digital nerves. 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 n(>rve 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 corresixjiiding arteries along the intermetatarsal spaces ami unite with the dorsal common digital nerves in supplying the dorsal 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 THE NERVOUS SYSTEM OF THE DOG 733 divides near tlie iniildle 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 descentis cm the sujierfieial flexor tendon and divides into three plantar metatarsal nerves (Xn. met. plant. II. Ill, l\), which unite with the plantar common digital nerves. The external plantar nerve passes down between the flexor tendons, sends twigs to the imi.-^cles on the jilantar surface of the metatar- sus, and divides into three plantar common digital nerves (Xn. 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 sjmipathetic 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 cer\'ical nerves. The cervical trunk unites with the vagus so intimately as to form a vago-s\-mpathetic 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. /ESTHESIOLOGY THE SENSE ORGANS AND COMMON INTEGUMENT The organs of the senses (Organa sensuum) receive external stimuh 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-epithe- lium, and a conduction path which is simple in the more generalized sense organs, elaborate in those which are highly specialized — the eye and the car. 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 Upper eyelid Third eyelid • Caruncula \ j lacrimalis \ i Inner canthvs l^uirer eyelid Fk;. 551. — Lkpt Eye" op Horsk. 9, ZyKOiiiatic arch; 10. .supraorhKal depression; 12. supraorbital procRss; 27. facial cresl. (Afler Ellenberger- Haum. Anat. fiir Kiinstler.) organs associated therewith. The accessory organs (Organa oculi accessoria) are the orbital fascia; 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 fascise. 734 THE EYELIDS AND CONJUNCTIVA r35 THE EYELIDS AND CONJUNCTIVA The eyelids, uiiper and lower (Paliiehra sujierior et inferior), are movable folds of integument situated in front of the eyeball. When closed, thej' 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 palpelirarum). When the ej'e is closed, it is an oblique slit about two inches (ca. 5 cm. ) in length ; when open, it is bicon- vex in outline. The ends of the fissure are the angles or canthi, and are dis- tinguished 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 ^ -shainMl bay or recess, termed the lacrimal lake (Lacus lacrimalis). In this there is a rounded, pigmented prominence known as the lacrimal canmcle (C'aruncula 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 (C'onunissiu'a palpebrarum medialis, lateralis). The anterior surface of the lids (Facies anterior palpebrarum) is convex and presents a varialjle num- ber of long tactile hairs in addition to the ordinary but verj' 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 infrapal- pebral depression (Sulcus infrapalpe- bralis) indicates somewhat indistinctly the limit of the lower lid. The upper lid is marked by tw'o furrows when raised. The posterior svirface (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 pos- terior), 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 verj' 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 Fig. '7 3 —Vertical Section of Antehior Part of Eye of Horse, with Lids Half Closed. 1, Tarsal gland of upper lid; 2, palpebral con- junctiva; 3, fornix conjunctiva'; -J. levator palpebra* superioris; 5, orbicularis oculi; 6, cornea; 7, anterior chamber; 8, iris; 9, 9\ granula iridis, 10, posterior chamber; 11, ciliary process; 12, ciliary muscle; IS, ciliarj' zone or suspensorj' lig. of lens; 1^, chorioid; 15^ sclera; 16, lens; 17, root of tactile hair. (After Bayer, Augenheilkunde.) 736 THE SENSE ORGANS AND SKIN OF THE HORSE iniiiutc. slit-like ojioniiiK, the punctum lacrimalis, which is the entrance to the lacrimal duct or canaliculus. Structure of the Eyelids. — The skin of the eyehds 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 chieflj- of the elliptical bundles of the orbicularis oculi, with which are associated fibers of tlie 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 com- missure 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 i)alpebral raphe 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 nniscle (of ]\liiller). The tarsal glands (CJlandulse 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 tulnilar duct beset with numerous alveoli, in which a Findon which pa.sses between the rectus superior and the eyeball, and is inserted into the sclera between the superior and ext(>rnal recti, about lialf an inch behind the margin of the cornea. The obliquus oculi inferior (M. oblicums bulbi ventralis s. inferior) is wide and • This belongs to the upper eyelid, but is described here on account of its position. THE EYEBALL 739 much shorter than tlio recti. It arises from the inner wall of the orbit in the small depression (Fossa muscularis) Ijehind 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. Simi- larly the internal and external recti rotate the eyeball al)Out 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 correspond- ing recti. Also the four recti acting together will retract the eyeball. v-&-»^;- Fig. 555. — Vertical Axiai. Section of Orbit op Horse. a. Eyelids; b, bulbar fascia (Tenon's capsule); c. c', retractor bulbi; d, rectus oculi inferior; e. obliquus oculi inferior (in cross-section); /, rectus oculi superior; g, levator palpebrie superioris; h, obliquus oculi superior (in cross-section); i, lacrimal gland; k. k' , periorbita; /, superficial fascia; m.deep fascia; n. akin; o, retrobulbar fat; p, extraorbital fat; (/, temporalis muscle; r, supraorbital process; s, cranial wall; i, cornea; 2, sclera; 3, chorioidea; 4. ciliary muscle; S, iris; 6, granula iridis; 7, retina; 7', optic papilla; S, optic ner\'e; 9, crys- talline lens; 10. capsule of lens; 11. ciliary zone; IS. posterior chamber; IS anterior chamber; 14, conjunctiva bulbi; 15, vitreous body. (After EUenberger, 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 coordinated actions of several muscles, involving combinations which are quite comple.x 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. 740 THE SENSE OUGANS AND SKIN OF THE HORSE It has the form approximately of an oblate spheroid, liut is composed of the segments of two spheres of different sizes. The anterior, transparent, corneal segment has a radius of curvature of alwut 17 mm., and the po.sterior, 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 sclerse. The central points of the anterior and posterior curvatures of the eyeball are termed respectively the anterior and pos- terior poles (Pohis 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 (.'Equator) is an imaginary line drawn around the eye- ball midway between its poles, anil meridians (Meridiani) are lines drawn around it through the poles. Thp avorago transverse diameter of the eyeball is about .'J cm., the ^■ertical about 4.5 cm., ami the axial about 4.2.5 cm. The distance from the anterior pole to the point of entrance of the optic nerve is about 3 cm. Letis seen through cornea Cornco-Kchrdl junctioiu Third cyclitl^ / \ Caruncula iacriinalis ^ \ ^^^A'^'^"' \ "Pupil Fig. 5.56. — Left Etebai.i. of Horse, in aim. after Removal of Upper and Lower Lids. 9. Zygomatic arch; IS, supraorbital process; 19, orbital fat; S7 . facial crest. (After Ellenberger-Baum, Anat. fiir Kiinstler.) 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 compo.sed of a posterior oi)a(iue part, the sclera, and a transparent anterior part, the cornea. The sclera, popularly termetl the "white of the eye," is a dense fibrous mem- brane 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 sclersB in its anterior part. The episcleral tissue, which is richly supplietl 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 THE FIBROUS TUNIC 741 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 ple.xus, the plexus s. sinus venosus sclerae, formerly called the canal of Schlemm. The optic nerve passes through the jiosterior part of the sclera a little below and external to the posterior pole. The ojiening t\)r the nerve is crossed by interlacing fibrous strands, forming the lamina cribrosa sclerae. 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 laj-ers. The very limited blood-supply is derived from the ciliary arteries, and the veins open into the vense vorticosse and ciliarj- veins. Sclera Reflection of conjunctiva Iris Granula iridis Cornea Lens Anterior cha^nber Rectus oculi inferior Ciliary processes — \'ertical Sectiox of Eyeball of Horse, about ?. The contour of the crystalline lens is dotted. The lymphatics are represented by intercommunicating cell spaces. The nerves are derived from the ciliary nerves. 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 corneae. The posterior surface (Facies posterior) is concave; it forms the anterior boundary of the anterior cliamber, and is in contact with the aqueous humor. The margin (limbus cornea>) 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 laj^rs: (1) The epithelium corneae is continuous with that of the conjunctiva sclera?, and is of the stratified squamous type. (2) The lamina limitans anterior is merely a condensa- 742 THE SENSE ORGANS AND SKIN OF THE HORSE tioii of the next layer. (3) Tlie substantia propria forms the bulk of the cornea and is conii)osed of interlacing bundles of connective tissue, arranged in part in lamellae disposed parallel with the surface. In the amorphous cement substance l)etween the lamella; are fiatteneil connective-tissue cells, the corneal corpuscles. These have branching processes which unite with those of other cells, thus form- ing a protoplasmic network.' (4) The lamina elastica posterior, also termed the membrane of Descemet or Demours, is a thin and iiractiially homogeneous mem- brane which is less intimately attached to the sul)stantia ]iro])ria than the anterior lamina. It is dear, glistening, and elastic. At the periphery the lamina divides into tliree sets of fil)crs. The anterior fibers join the sclera, the middle give attach- iiiciit to tlie ciiiaPN- niusck-, while the posterior i)ass into the iris and form the ligamentum pectinatum iridis. (.5) The endothelium (camerae anterioris) consists of a layer of flattened i)()lygonal 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 (Pl(>xus annularis), from which fibers pass into the substantia projiria, become non- medullated, and form the fundamental or stroma plexus. From this perforating branches pass through the anterior linuting layer antl form a subepithelial plexus, from which filaments ascend between the epithelial cells. Other liranches from the plexuses in the suljstantia propria end as fibrils which are in close relation with the corneal corpuscles. Fig. 5.^S. — Tapetum of Horse a, Optic papilla; 6, lowei border of tapetum. (After Ellen- berger, in Leisering's .\tlas.) The Vascular Tunic The vascular tunic (Tunica vasculosa oculi) lies in- ternal 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 oj)tic nerve and less closely in ))!aces 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 paijilla has a remarkable metallic luster, and is termed the tapetum of the chorioid (Tapetum chorioidea"). The apjiearance here varies in different individuals, l)ut the jirevailing colors in most cases are iridescent blue and green in various nuances shading into yellow. Posteriorly the chorioid is perforated by the o[)tic 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 lamelUe of filirous tissue, each containing a network of elastic tissue. Among these are large-branched, pig- mented, connective-tissue cells. The spaces l)etwe(>n the lamelhe are lined with endothelium, and form a system of lymph-clefts whirh together form the pericho- rioiil space (Spatium perichorioideale). (2) The lamina vasculosa is the outer part ' According to Piersol the sy.stom of spaces and ranaliculi in the substMiitia propria is com- |)letely filled by the cells and their processes, upon which tlie nutrition of the cornea largely de- pends. The lamina ehistica anterior, formerly described as a distinct Laver between tlie corneal epithelium and the substantia propria, does not exi.st a,s such, but there "is a condensation of the Bupcrfieial part of the latter, which Rollett termed the anterior limiting Layer; it is not elastic. THE VASCULAR TUNIC 743 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 chorio- capillaris consists of an extremely rich network of capillaries embedded in an almost homogeneous matrix. Between it and the lamina vasculosa is a layer of filjro- 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, con- nects 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 (Orl)icularis ciliaris) is the posterior zone, which is distinguished from the chor- ioid mainly bj' its greater thickness and the absence of the chorio-capil- laris. Its inner face presents numer- ous 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 liga- ment of the latter. They are small at their origin on the ciliary ring and become much thicker and higher toward their inner ends. The \\-idth of the circle formed by them is narrower at the inner side than elsew'here. Their bases ex- tend 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 cov- ered by a continuation of the lamina basalis of the chorioid, on which there are two layers of epi- thelial cells which constitute the pars ciliaris retinae. Thej' consist of a rich network of tortuous vessels supported in pigmented connective tissue. The ciliary muscle (:\I. 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. In man the muscle ha.s 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 fabers. Fig. 559. — Vascul Horse, Front The cornea is removed and the sclera is reflected in flaps. 1, Sclera; /', lamina fusca; 2, chorioidea; 2' , ciliary veins; S, ciliary muscle; 4, iris; o, S' , granula iridis; 6. pupil, through which the lens is visible. (After EUenberger, in Leisering's Atlas.) 744 THE SENSE ORGANS AND SKIN OF THE HORSE 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 arrange- ment 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 vif^ililc through the cornea. It is pierced centrally liy 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 Hght the vertical diameter of the pu])il 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 liga- mentum 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 com- nnmicate with the anterior chamber. The pupillary border (Margo ])ui)illaris) surrounds the pupil. Its u]i]ier part bears in its middle several black masses of variable size, termed the granula iridis or corpora nigra; similar, l)ut much smaller, projections may be seen on the lower margin of the pupil. The anterior surface (F^acics anterior) determines the color of the eye, which is dark brown usually. It is marked by delicate concentric lines (Plicje 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 .sjjhincter and a dilator of the pu]iil. The sphincter pupillae lies in the posterior jiart around the pupil, with which the fibers are largely concentric. The dilatator pupillae 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.' There appear to be minute clefts here by which the lymph-spaces of the stroma comnumicate with the anterior chamber. The posterior surface is covered bj- a ])ignicute(l 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 oph- thalmic artery. The arteries of the chorioidea are derived chiefly from the short post(>rior 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, th(> circulus arteriosus major. From this branches go to the ciliary muscle and processes anil 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 sup]ily 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 ' In albinos the pigment is absent here, as elsewhere, and the iris is pinkish in color. THE RETINA 745 trunks, the venae vorticosae, 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 vena> vorticosa- perforate the sclera about at the ecjuator 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 jDupillae is supplied by fibers derived from the oculomotor nerve, while the dilatator pupill» is innervated by the sym- pathetic. THE RETINA 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 'II 6. Fig. 560. — Inner SuRFArE of .\nterior Part of Eyeball of Horse (Equatorial Section). /, Sclera; 3, chorioidea; S, retina (drawn away from chorioidea): 4^ ciliary processes; 3, crystalline lens, through which the pupil (6) is seen, (.\fter Elienberger, in Leisering's .\tlas.) -Fundus TION o Equatorial Sec- Eyeball of Ho I, Sclera; S, chorioidea; 3, retii 4, tapetum; 3, optic papilla; 6, optic i Elienberger, in Leisering's .^tlas.) three parts. The large posterior part, which alone contains the nervous elements, including the s]3ecial neuro-epithelium and the optic nerve-fibers, is termed the pars optica retinae. It extends forward to the ciliary body, where it terminates at an irregular line called the era 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 liy two laj'ers of epithelial cells. In the pars ciliaris retinae the inner stratum is non-pigmented, while the outer layer is a direct con- tinuation of the stratum pigmenti of the pars optica. In the pars iridica retinae both are pigmented. In the dead subject the pars optica is an (ipa(|ue, 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 epi- thelium, and the reddish appearance of the fundus as viewed by the ophthalmoscope is caused by the l)lood 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. ex- ternal to the vertical meridian. The central part of the papilla is slightly depressed (Excavatio papillfe n. optici). 746 THE SENSE ORGANS AND SKIN OF THE HORSE 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 httle. In inspec- tion of the fundus with the ophthalmoscope numeious fine branches of the arteria centralis retina are seen radiating from the periphery of the papilla. The optic nerve fibers converge from all iiarts 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 retinae 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 differen- tiated than th(> 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 sujjported in a peculiar sustentacular tissue, and are covered externally by a layer of pigmented epithelium (Stratum pigmenti retinse). The nervous ele- ments 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.' The arteries of the retina are derived from the arteria centralis retinte and anastomotic branches from the short ciliar.y arteries. The arteria centralis enters the optic nerve a short distance behind the eyel:)all 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 dichoto- mously into end-arteries. The anterior part of the retina is non-vascular. The veins accomjiany 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 ]iupil with the posterior chamber (Camera oculi posterior); this is a small aimular space, triangular in cross-section, which is bounded in front by the iris, behind by the peripheral part of the lens and its ligami^nt, and externally by the ciliary processes. The chambers are filled by the aqueous humor (Humor aqueus), a clear fluid which consi-sts 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 sclerae. 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 liiconvex, transparent body, situated in front of the vitreous body and in ])artial contact with the posterior surface of the iris. Its ])erii)hery, the aequator 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 hmnor 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 ' For the minute structure of the retina reference must be niatie to histological works. THE EXTERNAL EAR 747 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 Icntis). The transverse diameter of tlie lens is about 2 cm., the vertical diameter is shghtly 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 \-ision. The zonula ciliaris (of Zinn) or suspensory ligament of the lens (Fig. 552) consists of delicate fibers (FibriE 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; the}' 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 cap- sule is thickest on the anterior surface, and here it is lined In' a layer of flat poh'- gonal cells, the epithelium of the lens capstile. The lens substance, when hardened, is seen to consist of concentric laminae arranged somewhat like the layers of an onion, and united by an amorphous cement substance. The laminse 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 stibstance which unite the groups of lens fibers. These lines, the radii lentis, are three in number in the foetus 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 foetus the lens is nearly globular, and is soft and pinkish in color. During part of foetal life it is surrounded by a vascular network, the tunica vasculosa lentis. This is derived chief!}- from a temporary vessel, the hyaloid artery, which is a continuation forward of the arteria centralis retince through the hyaloid canal that traverses the \'itreous 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 auriculae) faces inward and is widest in its middle part ; its lower part is almost circular in cur^'ature, 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 748 THE SENSE ORGANS AND SKIN OK THE HORSE parts (crura helicis). The posterior border is eonvex. The apex is flattened, jjointed, and curved a little forward. The base is strongly convex. It is attached to the external auditory process of the petrous tenii)oral hone, 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 comiilicated arrangement of muscles. The conchal or auricular cartilage (( 'artilago auricula") determines the shape of the ear; its form can be maile 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 conchce). This part is funnel-shaped and curves outward and a little backward. Its internal (medial) siH'face is strongly convex, forming a prominence termed the eminentia conchae. The lowest part of the internal margin bears a narrow, jiointed prolongation, the styloid process. This jirocess is about an inch long and projects downward externally over the an- nular cartilage; the guttural pouch is attached to its free end. Behind its base there is a foramen through S which the auricular branch of the vagus passes. The liasal part of tlir posterior border is cut into liy a notch, whicli wpanilcs two . irregular quadrilateral plates. The upper plate (Tragus) is overlapped by the an- terior border, and is separated fz-om the ad.iacent part of the posterior border (Antitragus) by a notch (Incisura inter- tragica). The lower plate is curved to form a half ring and partly o\'erlaps 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. Fio. 562. — Conchal and Annular Cartilages of Ear of HousF., E,\tkrnal Vikw. i, Base of concha: 5, posterior border, ,^, anterior bor- der of concha; 4, intertrapc notch; 5, eminentia concha; ff, styloid process; 7, annular cartilage; 9, zygomatic arch. (After EllenberKer-Havim, Anat. fiir Kiinstler.) The annular cartilage (Cartil- ago 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 em- braces the external auditory jirocess 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 sui)erficial 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 th:- underlying parts. The external auditory canal or meatus leads from the cavum concha; to the tympanic menihrane. It does not contimie the general direction of the cavity of the concha, but extends inward, downwaril, 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 tem- THE AURICULAR MUSCLES 749 poral t)one. Those are unitetl liy elastic membranes to form a complete tube. Its caliber diminishes from \vithout inward, so that the lumen of tlie inner end is al)out 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 liy a considerable amount of subcutaneous tissue except at the ajiex. The integument which lines the concave surface is intimately ad- herent 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 conchae. 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 ((ilandulse ceruminosae) 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 sulxlivided into two sets, viz., (a) extrinsic muscles, which arise on the head and adjacent part of the neck, and move the ex- ternal 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 subcutancously 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, w^hich arise from the zygomatic arch and the frontal crest, and arc inserted into the outer and anterior borders of the scutiform cartilage respectively. (h) The interscutularis arises from the sagittal crest, over which it is in part continuous with the nuiscle 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 l)ase of the conchal cartilage under cover of the parotido-auricularis. (5) 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 w-hich is de- tached from the interscutularis over the inner border of the scutiform cartilage. It ends on the anterior aspect of the lower jiart of the dorsum of the conchal car- tilage. 3. The superior auricular muscles (Mm. auriculares dorsales) are two in number. (a) The scutulo-auricularis superficialis accessorius is a narrow band which is 750 THE SENSE ORGANS AND SKIN OF THE HORSE largely covored by the proeeding muscle. It arises from the posterior prolongation and the adjacent part of the superficial face of the scutiform cartilage, and is inserted into the conv'ex surface of the conchal cartilage internal to the preceding muscle, the two crossing each other at an acute angle. (6) The parieto-auricularis is flat and triangular; it arises from the sagittal crest under cover of the cer\ico-scutularis, runs outward and a little backward, and is inserted liy a flat tendon into the lower part of the convex surface of the concha untler cover of the cervico-auricularis superficialis. 4. The posterior auricular muscles (Mm. auriculares caudales) are three in number. (a) The cervico-auricularis superficialis is a thin triangular sheet. It is witle at its origin from the occipital crest and the adjacent part of the ligamentum nuchse. Fig. 563. — External E.\r op Horsk and it.s Muscles, L.^teral View. 2, Posterior border, 3, anterior border of auricula: 8, scutiform cartilage; 5, zygomatic arch; n, parotido- auricularis; o, zygomatico-auricularis; o', scutulo-auricularis superficialis inferior; o" , scutulo-auricularis super- ficialis raedius et superior; p, interscutularis; p', fronto-.scutularis (pars temporalis): q, cervico-auricularis profundus major; «. small (or anterior) oblique muscle of head; (, splenius; ?/. tendon of majstoido-humerulis; c, mastoido-humeralis; x, wing of atlas. (.■Vfter Ellenberger-Baum, Anat. fijr Kiinstler.) and becomes narrower as it jxissos outward to be inserted into the inner side of the convex surfac(> of the concha. (6) The cervico-auricularis profundus major arises from the ligamentum nuchje, partly beneatli antl partly beliind the preceding muscle. It is directeil outward and is inserted into the postero-external aspect of the base of the ear, partly under cover of the ])arotido-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 conclia, partly under cover of the parotid gland. 5. The parotido-auricularis (s. M. auricularis inferior) is a ribbon-like muscle which lies on the ])ar()tid gland. It is thin ami wide at its origin from the fascia on the lower ])art of tlie parotid gland and becomes somewhat narrower and thicker as it passes upward. It is inserted into the conchal cartilage just lielow the angle of junction of its borders. THE AURICULAR MUSCLES 751 G. The deep auricular ur rotator muscles (M. auriculares profundi s. rotatores auricula-), two in nuinlier, are situated under the scutiform cartilage and the base of the concha and cross eacli other. (a) The scutulo-auricularis profundus major is the strongest of tlie auricular muscles. It is flat and is about an inch wide. It arises from the deep face of the scutiform cartilage and passes liackward to end on and below the most ])rominent part of the base of the concha (cniinentia conclue). (6) The scutulo-auricularis profundus minor lies between the base of tlie con- cha and the preceding muscle, and is best seen when the latter is cut and reflected. Fig. 564. — Muscles of Externai. Ear of Horse, Viewed from Above. On the riglit si(ie parts of the superficial muscles have been removed and the scutiform cartilage turned back to di.spiay the deeper muscle.s. a, Frontal part, a', temporal part of fronto-scutularis; b, interscutularis; c, cervico-scutularis; rf, e, scutulo-auricularis superficialis superior and medius; /, zygomatico-auricularis; 3, scutulo- auricularis superficialis acce-ssorius; o, cervico-auricularis superficialis; q, scutulo-auricularis superficialis inferior; (, scutiform cartilage; «, parieto-auricular!.«: v, cervico-auricularis profundus major; u\ cervico-auricularis prof, minor; j, x', scutulo-auricularis prof, major et minor; y, temporalis. (Ellenberger-Baum, .\nat. d. Hau^tiere.) 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 down- ward, backward, and outward to be inserted into the base of the concha under cover of the preceding muscle. 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 arc as follows : 1. The antitragicus consists of a few bundles which are attached to the conchal 752 THE SENSE ORGANS AND SKIN OF THE HORSE cartilage behind tlie junction of its two borders, and are partially l)lended with the insertion of the parotido-auriciilaris. 2. The helicis is a small muscle attached in a position opposite to the preceding on the anterior hordiT 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 auriculae' is a thin stratum of muscular and tendinous fillers which extends upward on the posterior surface of the concha from the eminentia conchae. Actions. — The base of the concha is rounded and rests in a pad of fat (Corpus adi])osum auricula;), 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 coordinated actions of several muscles which are verj' 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 aiu'icular muscles in general erect the ear and turn the opening forward. The interseutularis concurs in this action, causing adduction and a symmetrical position of the ears; it also acts directl.y on the conchal cartilage, .since the scutulo-auricularis superficialis superior is in reality a conchal insertion of the interseutularis. 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 profunrlus minor tends to direct the opening downward and outward. The parotido-auricidaris draws the ear downward and backward, and acts with the cervico-auricularis i)rofuntlus 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-palpe- bral 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 mandibu- lar 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 temjioral Ijone situated between the mem- brana 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 'EUenberger and Raum regard this as the honiologue of !lie transversus and obliquus auriculte of man. THE MIDDLE EAR 753 and the greater part of the incus; (3) a relatively large ventral recess in the bulla ossea. The external wall (Paries menibranacea) is formed largely by the thin mem- brana tympani, which closes the inner end of the external auditory canal, and thus forms the septum between the external anil middle parts of the ear. The membrane is an oval tlisc, 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 tj'mpanicus) 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, prodvicing 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 Fig. 565. — Right PcTRors Tempor.^l Bone of Horse, Antero-internal View. /, External auditory meatus; 2, annulus tym- panicus; S, lamina? radiating from 2; 4, niembrana timpani; 5, malleus; 6, incus; 7, stapes; S, fenestra cochlea; (s. rotundum); 9, facial canal; II, It", semicir- cular canals; //', vestibule; 12 cochlea. (After Ellenberger. in Leisering's Atlas ) Fig. 566. — Right Auditory Ossicleg and Mem- BRAN.v TvMP.\Ni. Enlarged and Viewed erom Inner Side and Below. J, Malleus; 2, incus; 2', 2", short and long processes of 2; 3, stapes; 4. tensor tympani; 5, ligament attaching long process of malleus; 6, stape- dius muscle; 7, fenestra cochlete (s. rotundum). (.\fter Ellenberger. in Leisering's .\tlas.) 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 com- posed 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 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 cochleae (s. rotundum) is situated below and behind the preceding; it is an irregu- larly oval opening and is closed by a thin membrane (Membrana tympani secund- aria), 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 48 754 THE SENSE ORGANS AND SKIN OF THE HOKSE tympanic o]ieiiing of llic luistat'hian tulic. Ahovo this and incompletely separated from it by a tliin ])iatc of hone is tlic semicanal for the tensor tympani muscle. The superior wall or roof (Paries tcgmentalis) is crossed in its inner part by the facial nerxc: liere the facial canal is more or less deficient ventrally, and the nerve is covered b}' the nmcous membrane of the tj'mpanum. The posterior wall (Paries mastoidea) presents nothing of importance; a tympanic antrum and mastoid cells, such as are found behind the tympanic cavity proi)er 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. Tlie auditory ossicles (Ossicula auditus) form a cliain which extends from the outer to tile inner wall of tlie cavity. They are named, from without inward, the malleus, tlie incus, the os lenticulare, and the stapes. The first is attached to the inner surface of the tyni]ianic membrane and tlie last is fixed in the fenestra vestibuli. The malleus or hammer, the largest of the ossicles, consists of a head, neck, handle, and two processes. The head (("apitulum mallei) is situated in the epitynii)anic recess. It is smooth and convex above and in front, and presents Fig. 567. — .\L-mTORY Ossicles and Membrani TyMPAXI, I.NNER ViEW, ENLARGED. ^,.\nnulu3 tympanicus; ;2, niembrana tym- pani; 3, malleus; 4. incus; S, stapes, (.\fter Ellen- berger, in Leisering's .\tlas.) Fi<;. .'ifiS. — Ric;ht .-VuDiTORY Ossicles, Enlarged as In- iiir,\Ti'.i> HY Li.N-Es Giving their Actual Length. a, Malleus; /, head; 2, neck; 3, handle; 4, long pro- cess; 5, muscular process, b, Incus; I, body; S. short branch; 5, long branch; c, os lenticulare. c. Stapes; i.head; £, crus; 3, base; 4. attachment of stapedius, (.\fter Ellen- berger, in Leisering's .\tlas.) on its postero-internal aspect a concave facet for articulation with the body of the incus. The neck (( -ollum 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 situatcfl 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 (I'rus longum) projects downward from the body and then curves inwanl; 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 liackward, and is attached to the wall of the recess by a small ligament. The stapes or stirrup consists of a heail, two crura, and a base. The head THE EUSTACHIAN TUBE 755 (Capitiilum 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) oecujiies the fenestra vestil)uli, to which it is attached. The space be- tween the crura and tlic base is closed l)y a membrane. The articulations and ligaments of the auditory ossicles comprise: (1) A diarthrodial joint between the heail of the malleus and the body of the incus (Articu- latio incudonialleolaris), 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, ("i) 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 tjTn- pani 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 tjTnjiani; 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 ]iosterior 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 jjart of the facial canal. It contains minute lymph nodules and small mucous glands (Glandulce tympanicse). The epithelium is in general colunmar 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 stylomastoid foramen, and forms a circle around the tym- panic membrane. The nerves of the mucous membrane come from the tymjianic plexus. The Eustachian Tube The Eustachian or auditory tube (Tuba auditiva [Eustachii]) extends from the tympanic cavity t(j the ])harynx; 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 comnnmicates with the anterior part of the tympanic cavity by the small slit-like tympanic opening (Ostium tympanicum tubse auditive). For a distance of about a quarter of an inch (ca. G 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 tubff audi- tivse) is situated on the postero-superior part of the lateral wall of the pharjiix just 75G THE SENSE ORGANS AND SKIN OF THE HORSE below the level of the jjosterior iiares. It is a slit, an iiicli 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 tli(> lower part of w^hich 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 boun- dary of the opening is the lateral wall of the pharynx. The liasis of the tube is a plate of fibro-cartilage (Cartilago tuba' auditivte) wliich is firmly attached dorsally to the fibrous tissue which closes the foramen laccrum basis cranii, the temporal wing of the sphenoid, and the pterygoid bone.' On cross-section the cartilage (except at its tympanic end) is seen to consist of two laminae which are continuous witli each other above. The internal lamina (Lamina medialis) gradually W'idens toward the pharyngeal end, where it forms a broad valvular flap. This is convex internall}', and its thin anterior edge forms the inner margin of the pharyngeal opening. Behind this the lamina has a thick free edge which projects vcntrally 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 ])alati muscles, which are in part attached to it; it does not exist at the pharyngeal entl of the tube. The mucous memtjrane of the tube is continuous behind with that of the tympanum and in front with that of the pharj-nx. On either side it is reflected to form a large diverticulum, the guttural pouch. It is covered with ciliated e]iithelium, and con- tains mucous glands and lymph nodules. The pharyngeal opening appears to be closed ortlinarilv, but the tube opens during degluti- tion. This action is apparently produced by tlie part of tlie 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 tubse auditivse); they are not present in the domesticated animals other than the equida;. 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 presi^henoid 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 l)ase of the cranium, the atlanto-occipital joint capsule, and the ventral straight muscles. Ventrally it lies on the pharynx and the origin of the oesophagus. Laterally the relations are numerous and coni])lex. 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, hyjioglossal, and sujierior 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 th(> 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 at- tached to the styloid process of the conchal cartilage. ' There is, strictly speaking, no osseous part of the tube such as occurs in man. In I lie horse the cartilage extends to the tympanic orifice. THE GUTTURAL POUCHES 757 Each pouch communicates witli the ]iharynx through the pharyngeal orifice of the Eustachian tube, and is in direct continuity with the mucous memhrane of the latter. The wall of the ])ouch is a delicate nuicous membrane which is in general rather loosely attached to the surrounding structures. It is covered with ciliated epithelium and is supplied with mucous glands. Scutifiirm airliUuje, posterior process ('Li)ichal cartilage Mastoido-humcralis tendon Nerves IX, X, XI Inferior cerebral rein Internal carotid artery Guttural pouch Occijnto-h yoideus inuscle ugular vein Int. maxillary artery Ext. maxillary artery Pharyngeal lymph glands Stylo-maxillaris muscle Sterno-ccphalicus tendon ■S^ibniiixillnry gland Thyroid cartilage Ext. maxillary rein Omo-hyoidei Fig. 569. — Cross-section of He.\d of Horse. The section passes through the base of the external ear and just behind the posterior border of the lower jaw. /, Rectus capitis anterior minor; 2. rectus capitis anterior major; S. inner walls of guttural pouches in .,n- position; 4, 4. arytenoid cartilage, upper piece apex; ventricle of larynx; .9, tr . posterior pillar of soft palate; 6. false vocal cord; ; vocal cord; 9. vocal muscle; 10. thyro-hyoideus muscle. . lateral It is worthy of note that the pharyngeal orifire of the Eustachian tube is at such u level as to provide (in the ordinary position of the head) only an overflow outlet for the escape ot tluul which may accumulate in the pouch. The two pouches are often unequal in size, and variations in regard to the distance which thev extend backward are not uncommon In one case a small aged horse, the right pouch extended along the oesophagus about five inches (ca. 1_ cm.) behind the ventral tubercle of the atlas, and the left one a little more than two inches (ca. *> cm.). iNo pathological changes were apparent, and the condition was not recognizable externally. Lases of extreme size— so-called tympanites— of the pouches occur, antl are apparently congemtal 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. 758 THE SENSE ORGANS AND SKIN OF THE HORSE 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 (Auri.s intprna s. Laliyrinthus) oonsists 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 teniixiral Ihhic, which inclose the membranous ]iart. The first is called the membranous labyrinth, and contains a fluid, the endolymph. The second is the osseous labyrinth. The two are se]iarated by the perilymphatic space, which is occupieil by a fluid termed the perilymph. The Osseous Labyrinth The osseous labyrinth (I^abyrintlius osseus) (Fig. 565) is excavated in the petrous tein|ioral Ixjuc 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 (Vestil)uluin) is the central part of the osseous laljyrinth, 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 tlie fenestra vestibuli, which is occupied by the base of the stapes. The inner wall corrcsjionds 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 sphaericus, which lodges the saccule of the membranous labyrinth. In its lower jtart there are about a dozen minute foramina which transmit filaments of the vestiliular nerve to the saccule. The posterior and larger depression is the recessus ellipticus, which lodges the utricle of the membranous labyrinth. The crista vestiljuli divides below into two divergent branches, wliich 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 tran.sinit nerve filaments to the utricle and the ampulliB 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 aquseductus vestibuli is a small slit behind the lower part of the crista vestibuli. The afiuicductus ])asses backward in the jietrous temporal bone, and opens on the inner surface of tlie latter near the middle of its posterior border; it contains the ductus endolyiujihaticus. 2. The osseous semicircular canals (Canales seniicirculares ossei), three in number, are situated behind and a]10^'e the vc^stibule. They are at right angles to each other, and arc 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 ex- ternal canals have a common orifice. Each canal forms aliout two-thirds of a circle, one end of which is (>nlarged 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 ain]nilla and ojx'iis 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 cdininune, which opens into the supero-internal part of the vestibule. The posterior canal (Canalis semicircularis posterior) is THE MEMBRANOUS LABYRINTH 759 also nearly vertical. Its ampulla is below, and opens into the vestilnilc (liroctly, while the non-dilated end joins that of the superior canal. The external canal (Canalis semicircularis lateralis) is nearlj' 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 Ijlunt cone, the base of which (Basis cochleae) 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 nun. acToss the base and about 4 mm. from base to apex. It consists of a spiral canal (Canalis sjiiralis cochlea'), which forms two and a half turns around a central cohunn termed the modiolus. The modiolus diminishes rajiidly in diameter from base to apex. Its l)ase (Basis modioli) corresponds to the area cochlea 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 fenestrse and ends near the cujiola as a hook-like process (Hamulus lamina> 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 tlic outer wall of the cochlea and completes the sejjtum between the two scala-, but the_y com- municate 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 t\nnpani is the inner orifice of the aquaeductus cochleae, a small canal which opens behind the internal auditory meatus, and establi.^hes a conniiunication between the scala tympani and the subarachnoid space. The internal auditory meatus has been described in part {vide Osteologj')- 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 jjassage of nerves to the utricle and the ampulUe of the superior and external membranous semicircular canals. The anterior part of the inferior depression (Area cochleje) 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 tra- beculte 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 vestiljule, largely in the recessus ellipticus. It receives the openings of the membranous semicircular canals, and the small ductus utriculo- saccularis leatls from its lower part to the ductus endol3'mphaticus. 2. The saccule (Sacculus) is situated in the recessus sphsericus of the vestibule. From its lower part the ductus rexmiens 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 aquaeductus vestibuli, and term- 760 THE SENSE ORGANS AND SKIN OF THK HORSE inatcs uiulor tlie duni inatcr on the jiDstcrior part of the internal surface of tlie petrous teniiioral lionc in a dilated lilind end, the saccus endolymphatieus. 3. The membranous semicircular canals (Ductus semicirculares) correspond in general to the osseous canals alreaily described, but it may be noted that while the ampuUiP 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 (Cscum vestibulare) in the cochlear recess of the vestibule, and ends by a second blind end (Cscum 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 Keissner), which extends obliquely from the lamina spiralis ossca to the outer wall of the cochlea. The tympanic wall or floor intervenes between the cochl(>ar duct and the scala tympani; it is formed by the periosteum of the mar- ginal part of the lamina spiralis and the membrana basilaris, which stretches be- Fio. 570. — Left Membranovs Labyrinth (Es- I.ARGHD). /. Cochlea; 2, fenestra vestibuli; J, fenestra cochlea;; 4. ductus, endolymphatieus; 6, superior, 6, external, 7, inferior semicircular canal, (.\fter Ellenberger. in Leisering's Atlas.) Fig. 57!. — Schem.atic Sectional View of L.vbyrinth (Enlarged). 1, 2, S, Superior, external, and inferior semi- circular canals: 4< utricle: 6, saccule: 6, cochlea: 7, auditory nerve. (After EllenberRer, in Leisering's Atlas.) tween the fre(> edge of tlie lamina and the outer wall of the cochlea. The outer wall consists of tlie fibrous lining of the cochlea, which is greatly thickened to form the ligamentum spirale cochleae. Structure.' — 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 s]iecial and remarkable structures occur, among which are the following: (1) The maculae acusticae ajipcar 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 maculae are fine crystals of lime salts, embedded in a mucoid substance, and termed otoconia. (2) The cristae acusticae are linear thickenings of the w-all of each ampulla of the membranous semicircular canals. Their structure is similar to that of the macule. (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 ' For the finer structure reference is to be made to the histological literature. THE SKIN 7G1 essentially of remarkable supporting cells and hair cells. Fibers of the cochlear nerve ramify about the Itasal 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 distributetl to the utricle, saccule, and membranous semicircular canals, and mediati's eiiuilibration. 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 s]iiralis 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 commime) is the jirotective covering of the liody, and is continuous at the natural openings with the mucous membranes of the digestive, respiratory, and urogenital tracts. It contains per- ipheral 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 tht> body of the same animal, and also with the breed, sex, and age. The color also varies greatly, l)ut 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 (Plica^ 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 liy 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 consideralile part of the body the subcutis con- tains striped nuiscle, the panniculus camosus (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. ^ The amount of subcutaneous tissue varies widely; in some places it is abundant, so that the skin can be raised consideralily; in other situations it is practically absent and the skin is closely adherent to the subjacent structures. Subcutaneous bursae 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 epider- mal 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 connec- tive-tissue layer, the coriimi. 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.- It is divisible into a superficial, harder, drier part, the stratum comeum, and a deeper, softer, moister part, the stratum germin- ativum. The cells of the latter contain pigment, and liy their proliferation com- pensate the loss bj' desquamation of the superficial ]5art of the stratum corneum. ' This muscle has been described in the Myology. ^ To prevent a possible misapprehension, it may be stated that the epidermis primarily molds the corium, and that tlie glands and hair-follicles are invaginations of the epidermis. 762 THE SENSE ORGANS AND SKIN OF THE HORSE In many i)laccs further subdivision into strata is evident on properly jirepared cross-sections. The coriiun 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 papillae, which are received into corresponding depressions of the epidermis. They contain vascular loops and nerves, or, in certain situations, special nerve-endings. The papilla; are host developed where the epidermis i.s 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 (Glandulae cutis) are chiefly of two kinds, sudoriferous and sebaceous. The sudoriferous or sweat glands (Glandule sudorifera?) consist of a tube, the lower, secretory part of which is coiled in the deep part of the corium or in the sub- cutis to form a round or oval ball (Corpus glanduUe sudoriferEe). The excretory duct (Ductus sudoriferus) passes almost straight up through the corium, but pur- sues a more or less flexuous course through the epidermis, and opens into a hair- follicle or by a fininel-shaped pore (Porus sudoriferus) on tlie surface of the skin. The sebaceous glands (Glandulae sebaceae) 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 Ijodies. In certain situations {c. cj., the labia vulvae, 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 (l)y 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 sprcial type-s occur. Some of these are to be regarded as modified sweat glands, e. g., the nasd-laliial glands of the ox, the glands of the snout of the pig, and the glands of the plantar cushion of the horse. Others, c. 3., the tarsal (or Meibomian) glands of the eyelids, are modified sebaceous. Still others are not yet d.-issilicd satisfactorily. Some of these .spi^cial types have been referred to in previous chai)tiis, and dtlieis will receive attention in the special descriptions which follow. The mammary glands arc liiglily modihed 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 papillse. Small vessels from the deep plexus go to the fat and sweat glands, and the subpapillary plexus sends fine branches to the papillae, hair-follicles, and sebaceous glands. The veins form two plexuses, one beneath the jiapillte, and another at the junction of the corium and subcutis. The lymph vessels form subpapillary and subcutaneotis plexuses. The nerves vary widely in number in different parts of the skin. The terminal fibers either (>nd free in the epidermis and in certain parts of the coritnn, 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 THE APPENDAGES OF THE SKIN 7G3 inanimals, and some parts which appear at first sight to be l)are are found on close inspection to be provided with sparse and very fine liair. 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 vibrissae 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 (Plumina pilorum), and at certain points these converge to form vortices (Vortices pilorum). 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-foUicle (After EIlenberger-Baum, .^iiat. (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 704 THE SENSE OKGANS AND SKIN OF THE HORSE together and contain ])igment. The medulla is the central core of softer, cubical or polyhedral cells; it contains some ])igment 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 lietween their outer and inner layers; in ungulates the sinuses are crossefl by trabeculae 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 comi)arcd to hairs matted together liy 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 si^eciallj- developed on the lips, the prepuce, mammarj- 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, L'ut 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) sj^rings from the dorsal border of the neck and the adjacent part of the withers; its anterior part, which covers the forehead to a varialile extent, is termed the foretop (Cirrus capitis). The tail, with the excejition of its ventral surface, bears verj' large and long hairs (Cirrus caudae). 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 wiilfly, and is in general much greater in the draft breed.s than in others. In Shire and < IxdcxLilc Ih.ix-, for instance, the hair on the volar aspect of the metacarpus and metatarsus and I'ltlnck In (ilicii so long and abundant as to account for the term "feather," which is commonly aiiphnl tu ii I'V hur.scmen. THE HOOF The hoof (Unguis) is the horny covering of the distal end of the digit. It is convenient to tlivide it for description into three parts, termed the wall, sole, and frog. 1. The wall is defined as the jiart of the hoof which is visible when the foot is placed on the ground.- It covers the front and sides of the foot, and is reflected posteriorly at an acute angle to form the bars. The latter (Pars inflcxa medialis, lateralis) appear on the ground surface of the hoof as convergent ridges, which sub- side 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 ungulaj dorsalis), lateral parts or "quarters" (Pars ungula» medialis, later- alis), 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 obli- the junction of the frog with the bar and sole. Tliis surface presents fine stria; and openings for the papillae of the frog matrix. The inferior or ground surface presents a central furrow (Sulcus intercruralis), which is bounded by two ridges or crura (Crura furcse ungula^) ; 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 7(58 THE SENSE ORGANS AND SKIN OF THE HORSE sides, where it unites with the angles of the walls; the junction here is covered by the expiiniled jjeriojile and constitutes the bull) of the hoof. Fig. 577.— Hoof ok Horse, Richt Fore Foot, Ohound Surf.\ce. a?, Inner (juarter; ^5, outer quarter; iS9, ground border of wall (toe); 40, white line; 41, sole; 4S, apex of froK; 4'^, lateral ridge of frog; 44, central furrow of frog; 4i, lateral furrow be- tween frog and bar; 46, bar. (After Ellenberger- Baum, .\nat. fur Kiinstler.) Fig. .'J7S. — Horizontal SErxioN of Hoof of Horse. The section i.s cut just above the ridges of the frog and bars and parallel with the ground surface, i. Wall; ^, sole; d, median ridge of frog; 4, lateral ridge formed b,^■ junction of frog and bar; 5, median furrow over apex of frog: G, lamina' of wall; 7, lamina? of bar. The apex occupies the central angle of the concave border of the sole, and forms a blunt, round prominence a /•w, little in front of the middle of the ground surface of the hoof. Structure of the Hoof. — The hoof is comjiosed of epithelial cell.s wliich are more or less com- jiletely keratinized except in its deepest ]iart, the stratum ger- minativum; 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 intertulnilar epithelium, and inclose medullary cells and air-spaces. The wall may be regarded as consi.sting of three layers. The external layer consists of the jieri- opl(! and the stratum vitreum. The periople is composed of soft, non-pigmented tubular horn. It is con- tinuous with the epidermis above, and extends downward a variable distance. Fig. 579.— Fhoxtai. I'.VUT /, Wall; S, s frog; 0, lateral lamina- of bar; periople of heel of Horse Front. , sole; S, bar; .{, frog; ige formed by jtinction 5, median ridge of of frog and bar; 7, ironary groove: /O, THE MATRIX OF THE HOOF 769 Usually it forms a distinct haiul somewhat less than an inch wide, except at the heels, where it is much wider, ami 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 ])eri()])le its smooth, glossy ai)i)earance. 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 laminae and is non-pigmented. The laminse 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 laminae becomes fully keratinized. They are composed of non-tubular horn in the normal state. The sole consists of tubular and intertubular horn. The tutjes run parallel with those of the wall and vary much in size. The frog is composerl 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 ungula?) 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 correspond- ing parts of the hoof. 1. The perioplic matrix or ring (Margo matricis unguis) is a band 5 to 6 mm. in width which lies in a groove between the perioi^le 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 papillae which curve downward and are received in depressions of the periople, to which it supplies nutrition. 2. The coronary matrix or cushion (Corona matricis ungulse) 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 ujiper border of the bar it is not very clearly defined from the matrix of the frog. The convex superficial surface is thickly covered with papillie 4 to ft mm. in length, which are received into the funnel-like openings of the coronary groove. At the heels and along the bars the papillte 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 unguis) — also termed the sensitive laminse — bears primary and secondary laminae which are interleaved with the horny laminae 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 laminae are small at their origin above, become wider below, and end in several papillae 4 to 5 mm. in length. The sensitive laminae supply nutrition to the horny laminae and to the interlaminar horn of the white line. 4. The sole matrix (Latus volare matricis ungula>) — 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 papillae, which are specially large along the r70 THE SENSE ORGANS AND SKIN OF THE HORSE 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 bj- a modified and highly vascular periosteum. Cut edge of skin Ptnophc mull 1 1 Cornnnri/ mnli 1 1 — -j Laminar iiialri t Outline nf hoof Fig. 5S0. — Lateral View of Foot of Horse after Removal of Hoof and Part of Skin, (.\fter Schmaltz, Atlas d. Anat. d. Pferdes.) 5. The frog matrix (Furca matricis unguis) — also called the sensitive frog — is moulded on the deep surface of the frog and bears small papillae. Its deep face is Perioplic matrix Coronary matrix Laminar matrix Frog matrix Position of navicular lionc Sole matrix Aj)ex of frog White line Ground border of wall Fio. 581 . — Ground Sl-rfack of Foot Pcriople of heel or hnlb TKK KkMOVAT .\na(, il. Pfer.les.) HnoF. (After Schmtvltz, Atlas d. blended with the plantar cushion. The germinal cells of the frog derive their nutrition from this part of the matrix. THE MATRIX OF THE HOOF 771 Tho digital or plantar cushion (Torus digitalis) is an important part of the elastic apparatus of the foot. It is a wedge-shaped mass whieh 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; interiorly the cushion is closely attached to the cartilages, but higher up a rich venous jilexus intervenes. The base, situated posteriorly, is partly sul)cutaneous, 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 ves- sels. It consists of a feltwork of fibrous trabecular 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 secre- tion contains fat. Vessels and Nerves. — The matrix is richly supplied with blood by the digital arteries. The veins are valve- less, and form remarkable plexuses which communicate freely with each other and are drained by the digital veins. The lymph vessels form sub- papillary 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 laminse. 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 equida>, 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 l)elow 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 tho finene.ss or coarseness of the integument in general. The supracarpal chestnut is about 1 J 2 to 2 1 2 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 Fig. 5S2. — Cross-section of Digit op Horse, throit.h Dlstal End op Second Phalanx. a. Second phalanx; b, deep flexor tendon; b' , digital synovial shealh; c, plantar cushion; d, lateral cartilage; e, skin; /, hoof; g, anterior extensor tendon; h, cavity of coffin joint; i, suspensory ligament of navi- cular bone; k, lateral ligament of cotfin joint; /, digital artery; m. digital ner\-e. (.\fter Ellenberger, in Leiser- ing's Atlas.) 772 SENSE ORGANS AND SKIN OF THE OX hock. When well developed it is about 2 to 2>2 inches long, broad below and produced above to form a long pointed end, with a short blunt anterior process. The}' are composed of horn somewhat like that of the frog. Organ of Smell The peripheral part of the olfactor.y 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 ethmo-turbinals and the adjacent part of the superior turbinal and the septum nasi, in which the fibers of the olfactorj' nerve ramify. It is dis- tinguished by its yellow-brown color, thickness, and softness. It contains charac- teristic tubular olfactory glands (of Bowinan), which arc lined by a single layer of pigmented cells, and a neuro-epithelium, the olfactory cells, the central processes of which extend as non-meduUated fibers to the olfactory bulb. The epitheUum 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 liranch, 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 l)order 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 papilla?, 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 occupj' 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 tlie gustatory pore; the central end is produced to form a fine process which is often branched. The taste buds are innervated by fit)ers of the glosso-pharj^ngeal 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 tjTDe. The superficial part of the cartilage of the third eyelid is leaf or shovel-shaped and thicker than in the horse; the edge Ijears a narrower process, on which there is a transverse bar, giving the arrangement THE EYE 773 some resemblance to an anchor. The gland of the thinl eyelid is very large — an inch or more in length — anil may he divided into two parts. The deep part is pink and consists of loose lobules, but the much larger superficial part is more com- pact. There are two large and several smaller cxcretorj- ducts. The subconjunc- tival tissue of the third eyelid contains lymph nodules, which are specially numer- ous on the bulbar side. Upper eyelid^ Third eyelid Caruuculn lacrimalis. Internal canth Lower eyelid Fig. .583.— Eye of Ox. (.\fter EllenberKer-Baum, .\nat. fiir KUnsller.) The lacrimal gland is thick and di.stinctly loliulated. It is more or less clearly divided into a thick upper and a thinner lower part (Glandula lacrimalis superior, inferior't. Tliere 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 easilv found. Conjunctim bulbi Third eyelid Caruncula Incrimali^ Cornea Pupil Fig. 584. — Left Eyeball of Ox m situ, Exterx.\l View. 19, Orbital fat. (.\fter Ellenberger-Baum, .\nat. fiir Kunstler.i The eyeball resembles that of the horse in sha])e, 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 thickne.ss 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. 774 SENSE ORGANS AND SKIN OF THE OX 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 ophthal- moscopic 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 artcria centralis retina? arises from a posterior ciliary artery and divides close to the optic papilla into three brandies 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 fiuid 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 ciuadrilateral 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 ver>- 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-scutuhiris arises from the posterior surface of the cranium below the frontal eminence, and receives slips from the parieto-auricularis and cervico-auricularis supcrficialis. (3) The zygomatico- auricularis and scutulo-auricularis supcrficialis 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 supcr- ficialis arises from the ligamentum nuchas 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 ligamentimi nucha; 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 car- tilage. (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 nuchse; the outer, wider part is pale, and arises beneath the cervico-auricularis sui)erficialis, 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. COMMON INTEGUMENT 775 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 promi- nence 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 pharyn- geal 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 com- posed of coarse fibrous trabcculse and fat. The cutaneous glands arc fewer and less developed than in the horse. Except about the natural openings, at the point of tlie hock, and the flexion surface of the fet- lock, 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 laj-er 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 caudse). 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 con- cave 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 con- tinuous 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; 5S5. — Claws of Ox, Volar Aspect, (.\fter Ellenberger-Baum, Anat. fiir Kunstler.) 776 SENSE ORGANS AND SKIN OF THE OX it is continuous without demarcation with the periople of the Ijull). The periophc matrix bears relatively long papilla-. The coronary matrix is much less developed than in the horse and its papillae are short. The sensitive laminae are much nar- rower and are more numerous than in the horse; secondary laminae are not jiresent. The matrix of the sole is not marked off behind from that of the perio]ile; its papillae 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 papillae here arc long and often compound. The accessory digits hea.T 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 obliciuely Lateral extensor tendon Metacarpal bone ^I et war po- phalangeal articulation First phalanx Lateral extensor tendon Common extensor tendon Proximal interphalangeal join Second phalanx Perioph Coronary matrix Third phalanx Wall of hoo. Annular liijament 5: ^Plantar cushion I /'/"'" pouch of capsule nf distal inter phalangeal J, nut — A'lineular hone on tlie volar asjiect of each chief digit and is attached below t(i the distal iihalanx and sesamoid bones, sending fibers also to the clastic pail of the heel. The horns (C'ornua) inclose the horn processes of the frontal bones (except in the polled breeds). They vary very greatly in size, form, and curvature. Tlie root or base of the horn (Radix eornus) 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 hor.se. Near the root the horn is encircled by variable rings. Toward the apex (Apex eornus) the thickness of the horn increa,ses till it becomes jiractically 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 eornus) 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 SENSE ORGANS AND INTEGUMENT OF THE PIG 777 long, slencU'r iia]iilla'; in the body of tlio horn it becomes thin and tli(> papillae are smaller, bvit increase in size apically. Rudimentary papillated laminae also occur. The skin of the sheep varies in thickness from 0.5 to 3 nun., liut 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 infra- orbitalis) is an invagination about half an inch in tlepth, 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 o])en; coil glands are also present. The secretion of the glands is fatty anil forms a yellow sticky covering on the skin when dry. The inguinal (or mammary) pouch (Sinus cutaneus inguinalis) is much more extensive, anil is situated in the inguinal region in both sexes. The skin of the pouch bears scattered fine hairs and contains well-develoiied sebaceous glands and exceedingly large coil glands. Tlie interdigital pouch (Sinus cutaneus interdigi- talis) is a peculiar tubular invagination of the integument which opens at the an- terior 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 liackward, 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 gands. 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 formeil chiefly by the orbital liga- ment, 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 sur- rounds the deep part of the cartilage, there is a deeper gland of Harder (Glandula palpebrse tertia; 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. 778 SENSE ORGANS AND INTEGUMENT OF THE PIG The canmcula lacrimalis has the form of a ritlgo; it (Uvides 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 i)ass through sejiarate ojienings at the infraorbital margin. The naso-lacrimal iluct is usually short and opens into the inferior meatus at the pos- terior end of the inferior turbinal.' 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 grajash- brown or yellowish-brown, but sometimes has a blue tinge. The pupil is a trans- verse 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 arterv 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 jiart, and divides into two branches, one of which passes almost horizontally backward in the cavum concha;, 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 cavitj' 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 l)ehin(l the posterior nares. It is somewhat infundibular, and is bounded internally l\v 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 ac- cumulates 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 pre- putial diverticulum. The hairs are sparsely scattereil in improved breeds — indeed, in some cases the skin is almost bare. The long hairs or bristles are arranged usually in groups 'The lowrr punplvim hiorimalp is frpqupiitly absent and the corro.'iponding duct therefore bhnd. There is often a duct or its remnant wliich opens below the inferior turbinal foki, but is not connected beliind with the functional duct. SENSE ORGANS AND INTEGUAIENT OF THE DOG 779 of three. They are most developed on the neck and back. The liristles 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 lietter 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 arrange- ment and may differ on the two sides. It may open into the inferior meatus im- mediately 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 780 SENSE ORGAN'S AND INTEGUMENT OF THE DOG border forms a pouch below its middle, and is thick and rounded in its basal part. Here the conchal cartilage bears a jiointcd process (Processus uncinatus), which pro- jects upward and backward. The outer wall of the cavuni conchse is supported by a quadrilateral plate (Tragus) above and a somiannular cartilage below. The concave surface presents several cutaneous folds, and in the cavum conchse there arc 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 conchte 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 ilivisible 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 parotiilo-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 mantlible above the angular process. The helicis and the verticalis auricula? are well developed. The tympanic cavity is very roomy, extending ventrally into the large but simple cavity of the bulla ossea. The tj'mpanic membrane is extensive and oval. The promontory is verj' pronounced. The auditorj' 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 tliffcrent breeils. 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 nmnerous 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 i)erincinn, 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 anil distal to the accessory carpal bone. The metacarpal and metatarsal pads (Torus metacarpalis, meta- tarsalis) are the largest and are situated Ijehind the distal ends of the metacarpal or metatarsal bones and the greater part of the first phalanges. They are somewhat heart-shaped, with two uneciual lateral lobes, and the apex distal. The metapodio- phalangeal joints rest on them wh(>n 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 trabeculic with the bones and tendons. The epidermis is thick and largely keratinized, and is studded with numerous rounded papilla which are readily seen with the naked eye. The coritnn has large papillae, and contains sweat glands and lamellar corpuscles. OLFACTORY AND CU.STATOKY ORGANS rsi The claws (Ungues) correspond in form to the ungual part of the distal pha- langes which they inclose. The horn of the claw consists of a body or wall anil 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 phalan.\ and is covered by skin. The lateral borders converge and inclose the sole anteriorly. The matrix presents a coronary part which bears papillse only near the coronary Ixirder. 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 matri.x of the sides of the wall bears small lamina^ which converge to the matrix of the sole. The latter is papil- lated. When the flexor muscles are inactive, the distal phalanges and the claws are Fig. 587.— Pads of Paw of Dog. , Cari>al pad; b, metacarpal pad; c^-c^, digital pads (From Leisering's .\tlas.) Fig. 588. — Half of Cl.aw of Dog, Inner Surface. a, a'. Coronary part, fc, volar part of wall; c, sole; d, section of c; e, section of wall; 1 , coronary border; 2, apex; S, dorsal surface. (From Leisering's Atlas.) 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 iihalanx. OLFACTORY AND GUSTATORY ORGANS The olfactory region lies above the lamina transversa, which separates it from the naso-pharyng(>al 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. ^ NDEX 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, 59S Abducent nerve, 683 Abduction of joints, 172 Abductor cruris posterior mus- cle, 327 digiti quinti muscle, 324, 329 hallucis muscle, 329 pollicis brevis et opponens poUicis muscle, 324 Abomasum of ox, 390, 392 cavity of, 396 of sheep, 409 Accelerator urinte, 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 ^■Equator lentis, 746 iEsthesiology, 734 Air-cells of lungs, 457 Ala; 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, .5.87 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 7S3 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 fis.sure 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 vertebra? 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 ca%ity, 353 pharyngeal, of horse, 447 Apex ca?ci, 364 784 INDEX Apical lobe of lungs of ox, 462, 463 Aponeuroses, 211 Aponeurosis of external ob- lique muscle, 246 of internal oblique muscle, 248 of transversus abdominis nuiscle, 249 pharyngeal, 350 Appendages of skin, 762 Appendix testis, 485 ventrieuli larjTigis, 447 Aquanluctus cochlea?, 759 vestibuli, 758 A(nieihK't of cerebrum, 664 of Sylvius, 664 Aqueous humor, 746 Arachnoid granulations, 047 Arachnoidea, 646 spinal, 647 Arch, alveolar, superior, of horse, 69 of aorta, .535 of cricoid cartilage, 441 plantar, 581 venous, 595 zygomatic, 56, 67 Arciforin 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 retinae, 746 ccclilea-, 759 pardU'actoria, 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 jilantaris 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 antibraehial, of dog, 635 asternal, .541 auricular, 5.50 of dog, 635 of ox, 611 of pig, 627 posterior, 550 axillary, 5.56 basilar, 546 bicipital, of dog, 635 brachial, .538, 556 deep, 559 of dog, 633, 635 Arteries, brachial, 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-oesophageal, 565 buccinator, 555 of pig, 627 cscal, 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 cerN-ieal, 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 eoeliac, 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-intereostal, 538 end, 524 ethmoid, 5.54 Arteries, 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 gastrohepatic, of pig, 627 gastrosplenic, of dog, 638 gluteal, anterior, 577 of dog, 641 of ox, 619 posterior, 575 ha>morrhoidal, 594 of dog, 641 hepatic, 377, 567 of dog, 638 of ox, 614 hypogastric, 573 ideal, 570 ileocEecal, 570 ileo-ca>co-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, 580 785 Arteries, mammary, 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 pis, 627 maxillo-musoular, 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, 62S, 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 plan- tar, 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 oesophageal, 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 cUtoris, 575 of conjunctiva, 737 of corpus callosum, 546 of dog, 633 of external ear, 752 of eyeUds, 737 of Fallopian tubes of mare, 511 of first phalanx, 564 of hoof, 771 of internal ear, 761 of ox, 609 of pehdc limb of ox, 619 of penis, 496 50 Arteries of penis, 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 popUteal, 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 Arteries, spermatic, of ox, 618 of pig, 627 sphenopalatine, 555 splenic, 569 of dog, 638 of ox, 615 of pig, 628 staphyline, 555 structure of, .525 stylomastoid, 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 thjTO-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 umbiUcal. 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 vesicoprostatic, 574 volar, deep, 562 of second phalanx, 564 Arthrodia, 172 Arthrology, 169 comparative, 203 786 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, 170 biisi-cornual, ISO capsule, 170 carpal, 183 of dog, 205 of ox, 205 of pig, 205 carpo-mctacarpal, 183 cavity of. 170 chondro-sternal, 17S circumduction of, 171 classification of, 169 coccvgeal, 175 coffin, 189 costo-central, 177 costo-chondral, 178 costo-transverse, 177 cost o- vertebral, 177 crico-arytenoid, 4-14 crico-thyroitl, 444 dorsal flexion of, 171 elbow, ISl 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 interccntnil, 173 intercornual, 180 intermetacarpal, of dog, 206 of ox, 206 of pig, 206 JntcnK'ural, 173 inten)lia!angeal, distal, 1S9 of dog, 209 of ox, 208 of pig, 208 proximal, 188 intertransverse, 175 knee, i83 metacarpo-phalangeal, 185 of dog, 2()S 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-liyoid, 180 temporo-inandibular, 179 of dog, 204 of ox, 204 of pig, 204 thyro-liyoid, 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 \-illi of, 170 volar flexion of, 171 Arytenoid cartilages of larynx, 443 of dog, 467 of ox, 4.59 of pig, 465 ligament, transverse, of lar- ynx, 444 Arytenoideus transversus mus- cle of larynx of horse, 446 Asternal artery, 541 ribs, 25 of horse, 43 Astragalo-calcaneal ligaments, 202 Astragalo-scaphoid ligaments, 202 Atlanta! 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 ventricuH of ox, 393 Auditory canal, external, 747, 748 meatus, external, 56, 748 internal, 56, 7.59 nerve, 686 ossicles, 7.54 process, external, 56, 67 tube, 7.55 Auricle of horse, 747 Auricular artery, anterior, 550 of dog, 635 of pig, 627 posterior, .5.50 of ox, 611 I'jranch of vagus, 687 cartilage, 748 lympli 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 Helniholtz, 755 lymph glands, 605 of dog, 643 of ox, 625 of pig, 631 nerve of horse, 697 Axis, 34 development of, 3.5 lentis, 747 of dog, 1.50 of ox, 112 of pelvis, 97 of ox, 133 of pig, 137 optic, 740 Azygos uvula', muscle of, 333 Back, fascia- of, 235 superficial, 235 muscles of, 235 of dog, muscles of, .325 of ox, muscles of, 300 INDEX 787 Back of pig, muscles of, 313 Ball-and-socket joint, 172 Bands, longitudinal, of c;pcum, 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. 6154 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 tibiaUs, 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 trigoniim 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 ca\'ities, 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 diploe, 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, hvoid, 64 of (log, 1.59 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 Umb, 27, 74 of dog, 162 788 Bones, of thoracic limb of ox, 127 of pig, 146 of thorax, 27, 47 of dog, 153 of ox, 115 of pig, 139 OS coxa?, 29, 92 of pig, 148 palatine, 60 of ox, 120 of pig, 142 parietal, 54 of ilog, 155 of ox, 117 of Dig, 140 patella, 29, 104 of dog, 168 of ox, 134 of pig, 149 pelvic, 93 of dog, 167 of ox, 132 of pig, 148 perforations, 23 periosteal arteries, 21 periosteum, 21 pliacoid, of cat, 164 phalanges, 29, 89, HI 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, 25, 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, 146 sesamoid, 29, 92, 111 developing in tendon tis- sue, 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 vertebra;, 24, 31 anticlinal, 42 caudal, 24 cervical, 24 coccygeal, 24, 41 diaphragmatic, 42 knnbar, 24, 38 of dog, 150 of ox, 112 of pig, 136 sacral, 24 thoracic, 24, 35 vessels, 21 vomer, 63 of dog, 1.58 of ox, 122 of pig, 143 yellow marrow, 21 zygomatic, of horse, 62 Brachia conjunctiva, 661 Brachial artery, 538, 556 deep, 5.59 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-oesophageal 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, 506 789 Bulbo - urethral glands of horse, VXi structure of, 49-i of ox, 503 of pig, 505 Bulbus aortse, 536 oculi, 739 Bulla, lacrimal, of ox, 121 ossea, 57 Burdach's column, 1552 Bursa, bicipital, 259 na\'icular, of deep digital flexor muscle, 272 of biceps femoris muscle, 279, 280 of flexor pedis perforatus muscle, 293 of gastrocn('niiu> nuiscle, 290 of rectus fen inri> n nitric, 284 of semiteniliiiDsus muscle, 280 ovarica of mare, 511 ovarii of bitch, 522 podotroclilearis, 272 supra-atloid, 174 supra-spinous, of horse, 175 of anterior digital exten- sor muscle, 265 synovial, of infraspinatus muscle, 256 of lateral digital extensor muscle, 266 of teres minor muscle, 257 Bursal synovial membrane, 211 Cecal artery, 570 lymph glands of pig, 632 Cseco-colic fold, 367 orifice, 364 Ca'cum, 363 of dog, 431 of ox, 398 of pig, 420 of sheep, 409 cupulare, 760 vestibulare, 760 Caleaneo-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 C'allosomarginal fissure, 660 of dog, 727 of ox, 716 of pig, 721 Calyces majores, 480 minoras, 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 l)one 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 articula- tion, 194 of femoro-tibial articula- tion, 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 ar- ticulation, 179 of tenon, 738 of tibio-fibular articulation, 199 splenic, 379 Caput laterale tricipitis, 261 Caput longum tricipitis, 261 medialc tricipitis, 261 Cartliac bronchus of \agus, 690 glands of stomach of liorse, 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, 3.59 veins, 586 Cariniform cartilage, 46 Carnassial teeth of dog, 426 Carotid artery, common, 541 h'ft, 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, 1.56 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, 74S 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, 441 790 Cartilage, cricoid, of ox, 459 of pig, 4(j5 eiisiform, of liorsc, 46 epiglottic', of dog, 467 of horse, 442 of ox, 459_ of pis, 465 epipliyseal, 22 iiitcnirytonoid, of dog, 467 of pig, 465 liitcnil, of third phalanx of liorsp, 1)1 marginal, 171 of larynx of horse, 441 of nasal septum of horse, 437 of nost rils of ox, 459 parietal, of nasal cavity of horse, 437 scapular, of horse, 75 scutiform, 74S 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 gleiioitl, 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 riiouth of horse, 330 of onuusum 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 Cavura concha; of dog, 780 epidurale, 646 subdurale, 646 tympani, 752 of dog, 780 of ox, 775 Cavum tjmpani of pig, 778 Cells, air, of lungs of horse, 457 ethmoidal, of horse, 52 gustatory, 772 Cement of "teeth, 339 Center, tendinous, of dia- phragm 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 Cerebrospinal 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 Ivniph 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 vertebra;, 24 of (log, 1.50 of horse, 32 Cervical vertebrte of ox, 112 of pig, 136 Cervicahs ascendens muscle, 225 CerV'ico-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 Choana^, posterior, of horse, 68 Chondro - pharyngeus muscle of horse, 350 Chondro-sternal articulations of horse, 178 Chorda tympani, 683, 684 Chorda" tendineie, 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, fa?tal, 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, 171 791 Circumflex artery, anterior, 558 external, 577 of ox, 019 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 Cisternse suharachnoidales, 6-46 Clarke's column, 651 Claustrum, 675 Clavicle, 27 of dog, 102 Claws of dog, 781 of ox, 775 of pig, 779 Cleft, palatine, of horse, 60, 69, 71 \'ulvar, of mare, 514 Cleido-cervicaiis 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, 52"3 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 gangUon, 713 nerves of horse, 710 vertebrae, 24 of dog, 152 of horse, 41 of ox, 114 of pig, 138 Coccygeus muscle of dog, 325 of horse, 238 ventraUs lateralis muscle of horse, 240 Cochlea, 759 of dog, 780 Cochlear nerve, 686, 761 Ca'liac arterv, 566 of dog, 638 of ox, 614 of pig, 627 Ij'mph gland of ox, 626 plexus, 714 CceUaco-mesenteric ganglia, 714 Coffin bone of horse, 90 joint, 189 Cofliin joint, capsule of, 189 lateral hgaments 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 seminahs 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 tsni;p of, 370 Column of Burclach, 652 of GoU, 652 of spinal cord, 651 renal, of horse, 473 Columna grisea of cord, 650 Columnar fornieis, 673 Comma-shaped tract, 652 Commissura grisea, 650 hypothalamiea, 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, pos- terior, 546 Compact substance of bone, 20 Complexus muscle of dog, 325 of horse, 231 of pig, 312 Compressor coccvgis 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 liorse, 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 Ugament of horse, 177 Conjugate diameter of pehns of horse, 97 of ox, 132 Conjunctiva, 736 of ox, 772 Conjunctival sac, 736 Constrictor vestibuli muscle of mare, 515 vuh'se 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 car- tilage of horse, 442 of nostrils of horse, 437 posterior, of thyroid car- tilage 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 Coronarv 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 fornieis, 673 geniculatum mediale, 665 luteura of mare, 510 Luvsi, 665 792 INDEX Corpus mctUillarc of cprchcl- luin, 661 |):i|)ill:ir(', 762 Mihniin of maif, .510 s|)()iitjii)suin of horse, 495 striatiiin, 675 irapi'zoideum, 655 of .loK, 725 of ox, 715 of pig, 720 vitreuin, 746 Corpuscles, Malpighian, of horse, 379, 473 renal, of horse, 473, 474 Corrugator superoilii muscle of horse, 2 IS Cortex of thymus gland of horse, 45S Corticopontile fibers, (MiO Costal arcli, 23 <-urtiIag<'s, 25, 26 (if hurse. 45 facets (if tlioracic vertelira', 36, 37 groove, 26 pleura of horse, 451 Costo-centnil articulations of horse, 177 Costo-eiiondral articulations of horse, 178 Costo-sternal ligament, supe- rior, of horse, 178 Costo-transverse articulations of horse, 177 Costo-\ertebral 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, 1.39 cavity of dog, 161 of horse, 69 of ox, 124 of pig, 145 nerves of clog, 728 of horse, 676 of ox, 717 of pig, 722 roots of, 6.56 superKcial origins of, 653 region of lior.se, 67, 68 sutures of horse, 179 Cranio-faoial index of dog, 1,59 CreiTiaster, external, of horse, 249, 490 of ox, .500 of pig, 313 of testicle of pig, 504 Creiniusteric artery, 578 Crest, facial, of horse, 58, 62, 68 frontal, of horse. 55, 66 na.sal, of horse, 71 Crest, occipital, of horse, .50, 69 of fcmiu- 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 liorse, 473 sagittal, of horse, 54, 6(i seniihinar, of third phalanx of horse, 91 splicno-occipital, of horse, 51 sublingual, of horse, 348 suiiracondyloid, of femur of liorse, 97 tiliial, 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 ethmoid of horse, 52 Crico-arvtenoid joints of hor.se, '444 Crico-arytcnoideus lateralis muscle of horse, 445, 446 Cricoid cartilage of dog, 467 of horse, 441 of ox, 4.59 of pig, 465 Crico-pharyngeus muscle of horse, 350 Crico-thyroid joints of liorse, 444 membrane of liorse, 444 Crico-thyroi(^leus muscle of horse, 445 Crico-tracheal membrane of horse, 445 Crista galli of horse, 52, 70 terminales of horse, 530 vestibuli, 7.58 Cristas a('ustica>, 760 unguhe, 765 Crown of tooth, 339 Crucial fissure of ox, 717 ligaments of femoro-tibial articulation of hor.se, 198 Cruciate fissure of dog, 727 of pig, 721 Crura cerebri, 664 fornicis, 673 helicis, 74S of dog. 779 of diaphragm of hor.sc, 243 Crural fascia of hor,se, 274 nerve, anterior, of horse, 706 triceps muscle of horse, 284 Crureus muscle of horse, 286 Crystalline lens, 746 Cubital Ivniph glands, 606 of dog, t;43 Cuboido-cunean ligaments of horse, 202 Cuboido-seaplioid ligament of horse, 202 Cuneate tubercle of pig, 720 Cuneiform cartilage of larynx of dog, 467 Cupola, 759 Curvator coccygis muscle of liorse, 239 Cushion of hoof, 769 plantar, 771 Cutaneous glands of ox, 775 nerve of leg of horse, 70S of neck, 695 Cutaneus maximus muscle of abdomen. 245 scapula' et humeri muscle, Cuticular ridge of stomach, 360 Cystic duct of ox. 403 Dartos of scrotuni of horse, 488 Deciduous canine teeth, .346 cheek teeth, 346 incisor teeth, .346 of ox, 386 teeth, 346 Decusisalio lemniscorum. 6.58 Deeus.saliciii of fillet, 6.5S of iiyramids, 655 of superior peduncle of cerebellum, 661 pyramidal, 6.5s 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 liorse, 213 of neck of horse, 224 of shoulder of horse, 255 fle.xor imiscle of ox, 311 gluteus muscle, 278 pectoral muscle, 253 254 of dog, 320 of ox, 302 of pig, 314 se,samoidean 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, 6S1, 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, 18 793 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 Diapliragma sellir, 6-16 Diaphragmatic flexure, 366 lobe of lung of ox, 463 pleura, 451 vertebra, 42 Diarthroses, 170 Diencephalon, 664 Digastric muscles, 213 ner\-e, 6S5 Digastricus muscle, 222 of dog, 319 of ox, 297 of pig, 311 Digestive svstem, 330 of dog," 423 of ox, 3S2 of pig, 410 of sheep, 405 Digit or digits, 2S 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, 920 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 pupilla^, 744 Diploe, 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 tuba; auditivEe, 756 ventriculi of stomach of pig, 418 Dolichocephalic breed of dogs, 1.59 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 duets, alveolar, of lungs, 457 Barthohn'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 Ductsofbulbo-iucthral 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 liorse, 372 Ductus arteriosus, 535, 607 endolympliaticus. 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 liorse, 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 Eotosyhian fissure of dog. 726 Ectoturbinals of ethmoid of liorse, 52 Eighth nerve, 686 Ejaculatorv 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, 118 794 INDEX Eminence, iliopectineal, puljis, 95 intcrcondyloid, of tibia, olivary, of dog, 72.') Eminent ia fonclia>, 748 medialis, 662 pyrainidalis, 755 Emissary \cins, 591 Enaniel'of teeth, 339 Enarthrosis, 172 Enceplialon of horse, 652 End arteries, 524 End-brain, 667 Endocardium, 530, 534 Endothoracic fascia, 450 Endoturbiiuils of ethmoid, Ensiforra cartilage, 46 Entomarsjinal fissure of ( Of!. of horse, 689 of o\, 716 of pig, 721 Epicardium, 525, 534 Epicondvle, 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, corneae, 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. SeeCEsopluKjiis. Ethmoid artery, 554 bone of dog, 1.57 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 njusal 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 pupilla? 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 digit! 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 epicoiulyle of femur, 100 of himierus, 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 of femoro-tibial articu- lation, 197 of fetlock joint, 1S5 of hock joint, 200 of pastern joint, 188 ligament of temporo-man- dibular articulation, 179 malleolus of tibia, 101 metatarsal bone. 111 oblif|ue muscle of abdomen, 246 occipital protuberance, 50 patellar Ugament, 195 pterygoideus muscle, 220 sagittal crest, 54, 66 supracondyloid crest of hu- merus, SO 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 vertebra;, 36, 37 of tibia, 102 of ulna, 83 posterior, of larynx, 441 Facial artery, 547 of dog, 635 transverse, 550 bones, 27 canal, .50 crest, 58, 62, 68 nerve, 684 of dog, 729 of ox, 717 nucleus, 684 paimiculus of pig, 311 tuberosity of ox, 120 veins, 5.SS of pig, 630 Facies articulares aryta>noidea;, 441 INDEX 795 Facies articulares thyreoide®, 441 cost alls, 454 diaphragraatica, 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. 4 i vertebra", 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 criu-al, 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, 2.52 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, 681 cerebrospinal, 660 cuneatus, 652 dorsal longitudinal, 658, 660 gracilis, 652 intracommissuralis ventralis, 6.52 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, 59S Feraoro-tiliial articulation, 196 Femur, 29, 97 development of, 100 of dog, 167 of ox, 1.33 of pig, 148 Fenestra cochlea, 7.53 ovalis, 753 rotundum, 753 vestibuU, 7,53, 758 Ferrein's pvramid, 473 Fetlock joint, 185, 764 Fibers of heart, 534 of stomach, 359 Fibrse arcuata; externa, 657 zonvilares, 747 Fibro-cartilagp, 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 eve, 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 papillse of tongue of horse, 336 Fillet, 658 lateral, 660 medial, 660 terminale of horse, 648, 649 Fimbria of brain, 669 of Fallopian tubes, 511 ovaricae of mare, 511 First carpal bone, 85 intertarsal sac, 200 nerve of horse, 676 phalanges of dog, 165 First phalanges of horse, 89, 1 1 1 development of, 89 of ox, 130 tarsal bone, 109 of ox, 135 Fissura callosn-marginalis, 669 ectouKUfiiiKilis, (i()9 entoinarginulis, (i69 lateralis .Sylvii, 668 marginalis, 669 mediana ventralis, 649 sublimbica, 669 thyreoidea of dog, 467 transvensa, 669 Fissure, ansate, of dog, 726 callosomarginal, 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 cerebrimi, 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 ]5ig, 721 naso-maxillarv, 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-tj'mpanic, 57 portal, of dog, 433 of horse, 373 of ox, 402 prsesylvian, 669 of dog, 727 of horse, 669 of pig, 721 splenial, of pig, 721 subUmbic, 669 suprasplenial, of dog, 727 suprasylvian, of dog, 726 of horse, 668 796 INDEX Fissure, suprasvlviaii. of ox, 716 of pig, 721 transverse, 669 of ox, 71(5 uinl)ilic;il. 37-i ventral iiicdiari, 249 P^ixcil vfrteljnr. 24 Flat nmsclcs, 211 Flexion of joints, 171 Flexor brachii muscle of liorse, 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, 321 hallucis brevis muscle, 329 longus muscle. 329 musi-lc, deep, of ox, 311 suiK-rticial, of ox, 311 of carpus of ox, 305 pel lis [jcrforatus muscle of horse, 271, 292, 293 perforans muscle, 271 perforatus muscle, 269 pollicis brovis 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 Fnetal circulfUion, 606 lung of horse, 454 Fold, alar, 437 cicco-colic, 367 deferential, of testicles, 491 gastro-pancreatic, 3.5S of articulations, 170 ruiniiiii-icticular, 393 ■sagittal, of pleura, 4.52 turbinal, inferior, 440 superior, 440 urogenital, 355 vahular, of c.erum, 365 Folia cerebelU, (ill! Foliate papdUe of tongue, 336 Follicle, (Jraafian, of mare, 510 hair, 763 lymph, 600 of small intestine of horse, 363 of thyroid gland of horse, 4.5S Foot of horse, muscles of, 287 of ox, muscles of, 309 of pig, muscles of, 317 Foramen, alar, 68 alare, 34 ca;cum of medulla, 655 carotid, of dog, 1.56 ethmoidal, 51, 52, 67, 70 Foramen, hypoglossal, 48, 68, 71 incisix'e. .59, 69 infraorbital, .5S, OS interxentricular, (i67, 674 intervertebral, of horse, 33 of ox, 112 lacerum basis cranii, 57, 68, 71 of horse, 49 orbitale of horse, 51, 67 niagmnn of horse, 48, 68 mandibular, 64 maxillary, 58, 67 mental, 63 mitrient, 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-mast oid, 57 supraorbital, of horse, 55, 66 of ox, 119 supratrochlear, of humerus of dog, 163 temporal, of hor.se, 51, 67 thyreoideum, 442 transversarium of axis of ox, 112 venic cav;p, of horse, 245 volar, of third phalanx, 91 Winslow's, of horse, 379 of ox, 396 Foramina papilloma of kidnev of ox, 480 Forearm, bones of, 28 i of horse, fascia" of, 262 I deep, 262 j superficial, 262 muscles of, 262 of ox, muscles of, 304 of pig, muscles of, 315 Forefoot, bones of, 28 Foretop, 764 Formatio reticularis. 651, 6()0 Fornix, 673 conjunctiva', 73() vagina; of mare, 514 Fossa, acetabular, 96 anterior, of skull, 70 j atlantis of, 34 condyloid, of horse, 48, 68 coronoid, of honse, 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 hypophy.seal. .50 infraspinous, 75 infratemporal, 68 intercondyloid, anterior, of tibia,' 102 of femur, 99 posterior, of tibia, 102 interi;eduncularis, 664 ma.sscteric, of mandible of dog, 1.59 middle, of skull, 71 ovulation, of mare, 509 ovalis, 607 of horse, 530 of Sylvius. 667 olecranon. SO olfactory. 52. 70 pituitary. 50 post<'riiir, of skull, 71 post-glenoid, ,56 pterygo-palatine. 60. ()7 .subscai}ular, 75 su])raci)ndyloid. of fenuir of horse, 99 supraspinous, 75 synovial, of tibial tarsal bone, 105 temporal, 67 transverse, 658 trochanteric, of femur. 99 synovial, 170 vagina' 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 Fraenula labii of horse, 331 Frenum linguie of horse, 334, 335 of pig, 411 preputial, of horse, 497 Frog matrix, 770 of hoof, 767 sen.sitive. 770 structure of, 769 Frog-stai,-, 767 Frontal artery, 553 bone of dog, 1,55 of horse, 55 of ox, lis 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, 73 797 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 liorse, 73 Fronto-scutularis, 749 Fundus glands of stomach of horse, 360 Fungiform papilla; of tongue of horse, 336 Funiculi dorsales, 651 ventrales, 651 Furoa ungula?, 767 Gall-bladder of dog, 434 of ox, 403 of pig, 422 Ganglia, cervical, of ox, 720 ca'liaco-mesenteric, 714 definition of, 644 sacral, of ox, 720 thoracic, of ox, 720 GangHon, cervical, 711 of dog, 733 of pig, 724 ciUary, 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, 63S 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-coiic omentum of horse, 358 Gastro-duodenal artery, 569 Gastro-duodenal vein, 597 (jastro-epiploic artery, 569, 570 Gastro-hepatic artery of pig, 627 flexure of liorse, 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 liorse, 363 fundus, of stomach of horse, 360 hsemolymph, 600 labial, of horse, 332 lacrimal, of dog, 779 of horse, 737 Glands, lacrimal, of ox, 773 lingual, of horse, 336 Ivmph, 599 bn.ncl.ial, of horse, 457 of ox, 623 1)1' pig, 630 mammary, of bitcli, 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 liorse, 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, 457 798 INDEX Glands, thyroid, of ox, 464 of pig, 4G6 urotliral, of horse, 499 uterine, of cow, 518 of mure, 513 zygomatic, of dog, 427 Glandula laryngeal of liorse, 4-18 palpeljrx tertia; profunda, 779 tympanica", 755 vestibulares majores of cow, 519 of mare, 515 minores of mare, 515 Ghins clitoridis of dog, 519 of mare, 515 penis of dog, 506 of horse, 495 of ox, 503 Glasserian fissure of horse, 57 Glenoid cav-ity of horse, 67, 68, 76 fossa of horse, 56 notch of horse, 76 Ghding joint, 172 movement of joints, 171 Glomerulus of kidney of horse, 474 Glossopliaryngeal nerve, 686 Glottis of liorse, 447 vocalis of horse, 448 Gluteal artery, anterior, 577 of dog, 641 of ox, 619 posterior, 575 fascia of liorse, 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 profunilus 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 Gompluisis, 169 Ciraahan follicles of mare, 510 Gracilis muscle of dog, 328 of horse, 2S1 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 ab- domen of horse, 246 omentum of horse, 354, 358 of ox, 396 sciatic foramen of horse, 94 trochanter of femur of horse, 99 Ciroove, bicipital, of humerus of horse, 79 carpal, of horse, S6 coronarv, of heart of horse, 527 of rumen of ox, 392 dorsal median, in horse, 649 of tliird phalanx of horse, 91 dorsolateral, in horse, 649 lacrimal, of horse, 58 longitudinal, of heart of horse, 528 musculo-spiral, of horse, 77 oesophageal, 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 lU'ethral, 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 H^MAL arches of coccygeal vertebra; of dog, 152 spine, 25 Hxmolymph glands, 600 Ha'inorrhoidal 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, 77S tactile, 763 Hamulus of horse, 61 Hand. See Manna. 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, fascia; of, 213 muscles of, 213 of pig, muscles of, 311 Heart, 524 of dog, 632 of horse, 526 structure of, 534 of ox, 60S of pig, 62(j veins of, 585 Heels, 764 Hehcis muscle, 752 HeUcotrema, 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 hor.se, 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 cesophageus 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 Histologv, 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, 76S Horn-cores of ox, 118 Horner's muscle, 736 Horns of lateral ventricle, 674 of ox, 776 Humefalis obliquus muscle of horse, 260 Humerus, 28 of dog, 162 of horse. 77 development of, SO of ox, 127 of pig. 146 Humor, aqueous, 746 Humor, vitreous, 746 Hydatid of Morgagni of Fal- lopian tubes of mare, 511 of testicles of horse, 485 Hymen of mare, 514 Hyo-epislottic ligament, 444 Hyo-epitilot til-US muscle, 44c 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-thyreoitleus 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-csecal artery, 570 orifice, 364 value of dog, 431 of horse, 362, 364 Ileo-ca-co-coUc 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 Ilio-costalis cervicis muscle of horse, 227 muscle of horse, 236 of ox, 300 INDEX Iliohvpogastric 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 lUo-psoas muscle of horse, 275 Iliopectineal 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, 3S6 of pig, 412 of sheep, 405 Incisura intertragica, 748 thyreoidea caudalis, 442 Incus, 754 Index, cephahc, 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 conmiissure 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 maxiUary foramen, 64 sinus, 73 meatus of nasal cavity of dog, 467 of horse, 439 of pig, 465 of nose, 62, 72 navicular hgament, 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, 440 799 Infraorbital artery, 555 of dog, 635 of pig, 627 canal, 59 foramen, 58, 68 nerve of dog, 728 of horse, 6S1 of pig, 722 poucli, 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 tendinea- of rec- tus 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 vertebrae, 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, inferior, of ox, 208 800 Interdigital ligaments, suiio- rior, of ox, 20G pouch, 777 Intcrlolmhir bronchi of liorsc, 457 tissue of lungs, 4o7 Intcrniccliate carpal bone of iiorsc, 83 zone of kidney, 473 Intermetacarpal joints of dog, •JOt) of ox, 200 of pig, 206 Intermuscular septa, 212 of forearm, 262 of gluteal region, 273, 274 of leg, 274 of shoulder, 255 Internal angle of ilimn, 94 of pubis, 95 auditory meatus, 56 capsule, 065, 676 condyle 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, 1S4 of cotfin joint, 189 of elbow joint, 181 of femoro-tibial articu- lation, 197 of fetlock joint, 185 of hock joint, 201 of pastern joint, 188 malleolus of tibia, 103 metatarsal bone, 111 musclesof thighofox, 308 oblique muscle of abdomen, 247 occipital protuberance, 54 orbital foramen, 67, 70 patellar ligament, 196 pterygoiileus 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 Intcrneural articulations of vertebra;, 173 Interosseous artery, common, .561 dorsal, 562 of dog, ()35 of ox, 012 recurrent, 561 ligami'nt of radio-ulnar ar- ticulation, 1,S2 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, 1,89 proximal, 188 joints of dog, 209 of ox, 208 of pig, 208 ^ Interscutularis, 749 of dog, 780 of ox, 774 Intersesamoidean ligament, 1S7 Interspinales muscles of dog, 325 of ox, 300 of pig, 313 Interspinous 1 i g a m e n t s of horse, 175, 176 Interstitial tissue of mammary glands, 516 Intertarsal sac, first, 200 second, 200 Inter! nrisvrrsales caudff, 239 colli iniis,-l<., 228 luniboruni muscle, 2.38, 276 muscle of dog, 324, 325 of ox, 300 of pig, 312, 313 Intertransverse articulations, 175 ligaments, 175 Intertubercular groove of hu- merus, 79 Interventricular foramen, 667, 674 grooves of heart, 528 septum of left ventricle, .534 Inter\ertebral 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, 410 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 Intumescontia 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, 019" lymph glands, 604 of ox, 020 of pig, 632 spine, inferior, of horse, 95 superior, of horse, 94, 95 Ischio-cavernosus muscle of clitoris, 515 of penis, 490 of ox, 503 Ischio-coccygois muscle, 238 Ischio-femoralis muscle, 283 Iscluo-urethr;d muscles of horse, 499 Ischium, 29 of dog, 105 of horse, 95 of ox, 131 of pig, 148 Isthmus faucium of horse, 335, 348 of ox, 385 oesophagi of dog, 428 of prostate, 493 of thvroid gland, 457 of dog, 408 of urethra masculina, 498 pharyngeal, 350 Jacobson's organ of horse, 440 Jejuno-ileum, 361 Jejunum, 361 Joint, 109. See also Arliculu- lions. Jugular ganglion, 087 of dog, 729 of ox, 717 of pig, 722 veins, 587 of dog, 042 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, 3.50 Kidneys, 409 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 Kidnevs of horse, mucous coat "of, 474 muscvihir coat of, 474 papilla of, 474 pelvis of, 473 right, 409 stroma of, 475 structure of, 473 tubules of, 474 veins of, 47o vessels and nerves of, 754 weight and size of, 472 of ox, 478 of pig, 481 of sheep, 480 Labia of vulva, 515 \ocalis of horse, 448 Labial arterv, 549 of ox, 611 superior, 550 glands of horse, 332 ner\-e 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 sclene, 741 elastica posterior, 742 fusca, 740 limitans anterior, 741 of hoof, 765 of nostrils, 437 of omasimi of ox, 305 of thyroid cartilage. 442 papyracea, 52 spiralis ossea, 759 suprachorioidea, 742 terminahs of third ventricle, 667 51 Lamina, transverse, of ethmoid bone of dog, 157 vasculosa, 742 Laminar matrix, 769 Laryngeal arterj' of ox, 610 nerve of dog, 729 recurrent, 689 superior, 689 orifice, 34S saccule, 447 Larynx of dog, arytenoid car- tilage 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 dor- salis muscle of, 445 laterahs 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 liga- ment of, 444 ventricular Ugament, 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, ot carpal joints, 183 of coffin joint, 189 of elliow joint, 182 of femoro-tibial articu- lation, 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, 181 801 Lateral ligament, internal, of femoro-tibial articu- lation, 197 of fetlock joint, 185 of hock joint, 201 of pastern joint, 188 left, of fiver, 375 of atlanto-occipital articu- lation, 177 of l)laddcr, 476 of liorse, 3.56 right, of liver, 375 ma.sses of ethmoid, 52 muscles of neck, 229 pterygoidcus muscle, 220 rectus capitis, 228 sacro-coccygcus muscle, 239 sacro-iliac ligament, 190 sesamoidciui ligaments, 187 surface of skull of dog, 160 of horse, 66 of ox, 123 of pig, 144 \entricle, 674 of larj-nx of hor.se, 447 of ox, 459 Laterahs sterni nuiscle 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 iUac, of external oblique muscle, 246 muscular, of trachea, 450 serous, of pericardium, 525 sjTiovial, of articulations, 170 \-isceral, 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, 6.58 lateralis. 660 medialis. 600 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 hor.se, 333 palpel)ra> superioris, 219, 73S rostri muscle of pig, 311 scapula; hominis, 254 802 Ligainont or ligaments, annu- lar, 212 anterior, of horse, 263 of manus of horse, 263 of pelvic limb of horse, 274 posterior, of parpus of horse, 263 arciform, of radio-iilnar ar- ticulation (if horse, 182 arytenoid, transverse, of larvnx of horse, 444 astra(jalo-i-alr:ineal, 202 ast ranalii-sraphoid, 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 ealeaneo-raetatarsal, 201 ealeaneo-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 liorse, 173 superior, of horse, 173 conjugal, of horse, 177 coronary, of horse, 374 coslo-sternal, superior, 178 costo-trans\erse, superior, 177 cotyloid, of horse, 192 crucial, of femoro-tibial ar- ticulation of horse, 198 cul)oido-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 articu- lation of horse, 197 of fetlock joint, 185 of hock joint, 200 of pastern joint, 188 of t emporo-niandiljular ar- ticulation, 179 falciform, of horse, 374 femoro-natellar, lateral, 195 gastro-phrenic, of horse, 358 hepa to-renal, of horse, 375 hyo-epiglottic, of horse, 444 ilio-lumbar, of horse, 191 inguinal, of horse, 246 intcrchondral, of horse, 178 Ligament, interdigital, infe- rior, 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 articu- lation 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 ar- ticulation, 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 phal- anges 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 scroliini ..f hiiVM'. 4SS of tilii:il I:iism1 Ihiiic, 202 of vcrtchnc of dog, 204 of horse, 172 of ox, 203 of pig, 204 ovarian, of bitch, ,522 of mare, 509 l)alpebral, 736 patellar, of horse, 195 periarticular, 171 plantar, of hock joint, 201 posterior, of pastern joint, 188 of temporo-mandibular ar- ticulation, 179 Poupart's, of horse, 246 pulio-fcnioral, 193, 2.50 radiate, of horse, 177 round, of bladder, 476 of hip joint of horse, 193 of horse, 356 of li\er of hor.se, 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 Ligament, sesamoidean, of horse, 186, 187, 188 of ox, 207 short, of hock joint. 201 sternal, of horse, 17S 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-arvtenoiil. inferior, 444" superior. 444 tliyro-eiiiglottic. 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'liorse. ISS Y-.shapcd, uf horse, ISS Ligament;! annularia of tra- chea, 450 fiava, 174 sternopericardiaca of ox, 608 Liganientum arteriosum, 535, 607 crico-thyreoideum, 444 denticulatum, 647 nucha', 174 pectinatuin iriilis, 742 spiralc cc>clilc:c, 760 Limbus palpeliralis, 735 Line, curved, superior, of skull, 69 gluteal, 93 ilio-pectineal, 93 popliteal, of tiliia, 100 terminal, 353 Linea alba, 246 Lingu.al 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 luorse, 330 muscles of, 213 of ox. 382 of pig, 410 of sheep, 405 Liquor folliculi of mare, 510 pericardii of horse, 525 pleura' of horse, 453 Liver of dog, 432 of horse, 373 structure of, 376 of ox, 400 of pig, 421 INDEX 803 Liver of shopp, 400 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 iiu'diastinal, of lung of horse, 456 of ox, 463 of liver of dog, 432 of horse, 374 of pig, 421 of lungs of dog, 46S 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 pvriform, 66S 'of dog, 72S Lol>ular 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 jjrostate of horse. 493 of testicles of horse, 4S6 of thymus gland, 458 of thyroid gland, 458 Lobus piriformis, 672 Locus perforatus posticus, 664 Loins of dog, muscles of, 325 of horse, fascia; 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 caecum of hor.se, 364 fissure of cerebrum, 607 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 wins, 596, 597 viTlcbra-, 24 c.t .log, 151 of liorse, 38 of ox, 112 of pig, 138 Lumbo-dorsal fascia, 235 Lumbo-sacral plexus of dog, 731 of horse, 705 of o.x, 719 of pig, 723 Lumbricales muscles of dog, 324, 329 of horae, 273, 295 of ox, 305 of pig, 316 Lung, foetal, of horse, 454 of dog, 468 lobes of, 468 of horse, 453 air-cells of, 457 alveolar duct.s of, 457 alveoli of, 457 apex of, 456 l)asal border of, 456 base of, 4.56 bronchial branches of, 456 carcUac 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 lolies of, 4.56 lobulation of, 456 IcjlHile of, 457 lymph vessels of, 456, 457 liiediastinal lobe of, 456 surface of, 454 precardiac lobe of, 463 root of, 456 ventral border of, 4.54 ^■esscls and nerves of, 457 of ox, 462 apical lobe of, 462, 463 cardiac lobe of, 463 diaphragmatic lolie, 463 fissures of, 462 lobes of, 462, 463 lobulation of, 463 mediastinal lobe of, 463 of pig, 463 lobes of, 466 of sheep, lobulation of, 464 Luvs's bodv, 665 Lvmph, 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 ca-cal, of pig, 632 cervical, 601 of ilog, 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, 6()4 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 jiig, 632 of ca'cum, 605 of colon, ()05 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, 632 804 INDEX Lymph glands, sternal, of ox, 624 subiliac, 606 submnxillarv, 601 of iloti. 643 of ox, 623 of pig, 630 subparotid, of ox, 623 thoracic, of pig, 631 nodes, 599. See Lymph (/lands. no'diilps, 600 of siilccn of horse, 379 spaces, 600 Lymphatic duct, right, (iOl system, 599 Lymphocytes, 599, 600 Lymjih-vessels, 524, 599 of adrenal bodies, 478 of tlog, 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 iSIacula- acusticae, 760 ^Lalar 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 tiljia, 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 Ij'mph glands, 604 yein of ox, (i22 Mammillary body, 653, 665 of ,!,,«.■ 726 processes, 25, 43 Mandiljle 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 Manas, bones of, 28 of horse, fascia> of, 262 Manus of horse, muscles of, 262 Marginal cartilage, 171 fissure of horse, 669 of ox, 716 of jiig, 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 rficial, 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 popUteus, 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 psoiis 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 plantar, 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 oeuli, 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 eosta>, of horse, 242 of pig, 313 oculi, 73S 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 thonicalis, of dog, 320 of horse, 251 ring-like, 21 1 rotator, 757 sacro-coecygei, 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 semitcndinosus, of dog, 327 of horse, 280 of ox, 30f) 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 INDEX 80!) Muscle, serratus posticus, of ox, 300 thoracis, of horse, 254 vcntralis, 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 pupilte, 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, 29S 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 stvlo-mandibularis, 222 "of ox, 297 stylo-niaxillaris, 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 fasciae antibrachii, of dog, 322 of horse, 260 of ox, 303 of pig, 315 lata>, of dog, 326 of horse, 276 of ox, 306 of pig, 316 palati, of horse, 333 tyrnpani, 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 th>To-arytenoideus, 446 thyro-hyoideus, 445 thjTO-pharyngeus, 350 tibiaUs 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, 7.ol transversaUs 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 cerv'icalis, 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 surse, of horse, 292 ulnaris laterahs, 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 intermedins, of horse, 286 of ox, 307 Muscle, vastus internus, of horse, 286 veiitricularis et vocalis, 446 vocalis, of horse, 446 volar, of pig, 315 Wilson's, of dog, 509 of ox, 504 zygoinatico-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 asophagus, 352 layer of trachea of horse, 450 process of arytenoid car- tilages of larynx, 443 of .temporal bone, 57 ring of ca'cum of horse, 365 system, 211 Muscularis mucosa- of small intestine, 362 Musculi papillares of left ven- tricle, 533 of right ventricle, 531 pectinati, in right atrium, 530 Musculo-outaneous n e r v e s, 696 of dog, 730 of horse, 697 of leg of horse, 708 Musculo-spiral groove, 77 nerve of horse, 698 Myenteric plexus, 714 Mj'lohyoid nerve, 682 of dog, 728 Mylo-hvoideus muscle of dog, .319 of horse, 222 of ox, 297 Myocardium, 534 Myology, 211 X.\RES, 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, 4.36 common meatus of, 440 ethmoidal meatuses, 440 inferior meatus of, 439 middle meatus of. 438 parietal cartilage, 437 superior meatus of, 438 vessels and ner\'es, 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, 679 810 INDEX Nasal process of horso, GO region of horse, 66 .septum, 71, 72, 73, 437 vein of ox, 621 of i)ig, 630 Naso-ciliarj' nerve, 678 of ox, 717 of pig, 722 Nasofrontal suture, o/i, 61 of ox, 1 19 Naso-labial glands of ox, 77") Naso-lacrinial duet 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-turbiiial liones, 62 Navicular bone, 92, 1 1 1 bursa of deep digital flexor muscle, 272 ligaments, inferior, 190 suspensory, of horse, 189 Neck of dog, muscles of, 324 of horse, fivscia 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. 6S6 auricular, 6S.3 posterior, 69.5 auriculopalpebral, 6S5 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 cla.ssitication 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, 69.') dental, (iM, 682 depressor, of dog, 730 diga.stric, 68,5 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 glossopharyngeal, (iSii ghiteal, of hor.se, 706 hemorrhoidal, of horse, 710 hvpoglossal, 692 "of dog, 730 of ox, 717 of pig, 722 ilio-hypogastric, 704 iUo-inguinal, of horse, 704 infra-orbital, of dog, 728 of horse, 681 of pig, 722 infra-trochlear, 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 larvngeal. of dog, 729 recurrent, 689 superior, 689 lingual, ()S3 of dog, 729 lumbar, of horse, 702 mandibidar, 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 nnisculocutaneous, 696 of dog, 730 of horse, 697, 698 of leg of horse, 708 musculospiral, of horse, 098 mvlohvoid, t)82 of dog, 728 nasal, of dog, 728 of horse, 697, 681 nasociliary, 678 of ox, 717 of pig, 722 ninth, 686 oculomotor, of horse, 677 of ox, 717 Nerve, obturator, of horse, 706 a'sophageal, 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 ptervgoid canal, 681 of skin^ 7(i2 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 hnrsc. 7116 sciatic. i, 29 of horse, 92 of pig, 148 pedis of dog, 506 of horse, 90 rostri of pig, 143, 464 sufTraginis 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 vertebra;, 25 Osteoblasts, 22 Osteoclasts, 22 Osteogenesis, 22 Osteology, 19 Ostium abdominale of mare, 511 uterinum of mare, 51 1 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, 50S of sow, .521 Overextended joints, 171 Overshot dog, 425 Ovulation fossa of mare, 509 in mare, 510 Pacchionian liodies, 647 Pad, dental, of ox, 384 Pads of dog, 780 Palate, hard, of dog, 423 of horse, 69, 332 of ox, 3S3 of pig, 411 of sheep, 405 soft, of dog, 424 of horse, 332 of ox, 3S4 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 maxilla of horse, 58 of premaxilla> 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-pharvngeus 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 testi- cles 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 arter\-, 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 kidnev, 474 filiform, of tongue, 336 foliate, of tongue, 336 fungiform, of tongue, 330 hair, 763 of dieeks 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, 27S Paranasal sinuses of horse, 72 Parapharvngcal Ivmph ghiiid of ox, &2S Paratliyroid gland of clog, 4t)S of horse, -158 of ox, -le-i Parenchyma of adrenal bodies, 478" of liver, 377 of mammary glands, 51G testis, 486 Parietal hones 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, O'j 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 Parol ido-auricularis, 750 of dog, 780 of ox, 774 Pars liasilaris pontis, 660 ciliaris retinie, 745 dorsalis pontis, 660 intercartilaginea of larvnx, 448 intermembranacea of larvnx, 44S iridica retinae, 745 optica retina>, 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 INDEX Pectoral muscle, deep, poste- rior, of pig, 314 of horse, 2.52 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 fascise 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 kidnev of horse, 473 of ox, 13"2 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 Ijody of, 494 corona glandis of, 495 corpus cavernosum, 495 spongiosum, 495 fossa glandis of, 495 glans, 495 813 Penis of horse, ischio-caverno- sus 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, 49t) 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 tem- poral bone of dog, 1.56 Petrosal crest of horse, 57, 70 nerve, 684 sinus, inferior, 592 superior, 591 Petro-tympanic fissure, 57 Petrous ganglion, ()S6 temporal bone, 56 of ox, 120 Pever's patches of horse, 363 of ox, 398 814 INDEX Peyer's patches of pig, 419 Phacoid bone of cat, 164 Phulanges, 29 distal, 29 first, 29 of dog, 16.5 of liorse, 89, 111 of ox, 130 middle, 29 of dog, 165 of horse, 89 1 1 1 ligaments of lateral car- tilages of, 190 of ox, 130, 136 of pig, 148, 1.50 proximal, 29 second, 29 of dog, 16.5 of horse, 89, 111 of ox, 130 tliird, 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 (log, 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, 014 nerve, 695 vein, 596 Phrenieo-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, 3.50 Pilomotor fibers, 711 Pinchers, 339 Pineal body, 665 of ox, 716 recess, 667 Pinna of horse, 747 Pituitary body, 653, 664, 665 of (log, 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 pulmonarv, 452 sagittal fold of, 452 visceral, 452 of ox, 461 of thoracic ca^^ty, 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 coeliac, 714 coronary, 595 dorsal, 595 gangliosus ciliaris, 745 gastric, 714 of dog, 729 hepatic, 714 of horse, 377 hypogastric, 715 interosseous, 595 lumbosacral, of dog, 731 of horse, 705 of ox, 719 of pig, 723 mesenteric, 714 myenteric, 714 oesophageal, 713 of dog, 730 of ISIeissner, 714 pampiniform, of testicle, 487 pelvic, 715 pharyngeal, of dog, 729 pulmonarv, 690, 712 of (l(jg, "730 renal, 714 solar, 713 spermatic, 487, 714 splenic, 714 submucous, 714 tympanic, 687 utero-ovarian, 714 venosi, 524 venosus sclera", 741 venous, of urethra, 516 Plexus, volar, 595 Plica iridis, 744 salpingo-pharyngea, 756 vena' cavje 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 PopUteal 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 cla\ncularis, 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, 44 1 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-extemal angle of ischium of horse, 95 Post-glenoid fossa, 56 process, 67 INDEX 815 Pouch, cutaneous, of sheep, 777 recto-genital, of horse, 350 recto-V'e.sical, of horse, 356 vesico-gonital, of horse, 356 Poupart's Ugamont, 246 Precrural lymph glands, 606 of ox, 626 of pig, 632 Premaxilla of dog, 157 of horse, 59 of ox, 120 of pig, 1-12 Premaxillarv region, 66 Premolars, 33S, 342 Prenasal bone of pig, 143 Preorbital region of horse, 68 Prepectoral Ivmph glands of ox, 6"24 of pig, 631 Preplantar artery, 564 Prepubic artery, 579 tendon of horse, 250 Prepuce of chtoris of mare, 515 of dog, 507 of horse, 496 raphe of, 498 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 horee, 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 sphen- oid 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 Ungual, of horse, 65 mammillary, 25 of horse, 43 mastoid, of horse, 67 maxillary, of dog, 158 muscular, of arytenoid car- tilages 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 maxilliP of horse, 58 of premaxilla;, 60 paramastoid, 48, 68, 69 post-glenoid, of horse, 67 pterygoid, of horse, 51 retrossal, of horse, 91 spinous, of axis of horse, 34 of ox, 112 of cervical vertebrae of ox, 112 of lumbar vertebra; of horse, 39 of ox, 114 of thoracic vertebra? of horse, 36 of ox, 112 of vertebra^ 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 anconaeus 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, ex- ternal, 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, 6.SI processes of horse, 51 veins, .587 Pterygoideus externus muscle of horse, 220 intorniis muscle of horse, 219 lateralis muscle of horse, 220 muscle of ox, 297 Pterygo-palatine fossa, 60 of horse, 67 Ptervgo-pharvngeus muscle of "horse, 349 Pubis, 29 of dog, 167 of horse, 95 of ox, 131 of pig, 148 Pubo-femoral ligament of horse, 193, 2,50 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 cavitv 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 Fer- rein, 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, 728 816 INDEX Pyriforniis muscle of ilog, '.i'M of horse, 284 sinus of horse, 350 Qiadhatis femoris muscle of (log, 328 of horse, 283 of ox, 308 of pig, 317 lumboruiii muscle of dog, 326 of horse, 276 of ox, 306 of pig, 316 plauta; muscle of dog, 329 Quadriceps femoris muscle of horse, 284 of ox, 307 of pig, 317 Quarters, 764 Radial artery, anterior, fir^d of dog, 635 of ox, 613 posterior, 559 of ox, 612 carpal lione, 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 Radid-carpal joint, 183 sac of horse, 183 Raiho-ulnar articulation, 182 Radius, 2S of dog, lli:> of horse, 80 development of, 82 of ox, 127 of pig, 147 Radix pulmonalis of horse, 45() Rami communicantes, 711 of lower jaw of liorse, 6:5 Ramus communicans, 693 Raphe palati of horse, 233 lii'a'putii of horse, 406 scroti of linrse, ISS Rece|)lacuhnn chyli, 600 Recess, pharvngeal, 350 Reccssus ,-(i.'lilcaris, 7.58 elhplicus, 758 infundil)uli, 667 lieiialis of horse, 380 opticyis, 667 l)inealis, 667 spha-ricus, 758 te<-ti 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 mus- cle 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 ocuh, 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, 4,80 sinus of horse, 470 tubules of horse, 474 \'eins, 596 of ox, 621 Respiratory bronchioles, 457 svstem, 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 mem- brane 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 costiE 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 hor.se, 177 asternal, 25 of horse, 43 costal cartilage, 25 groove, 26 devcloinnent, 26 extremities. 25 exIiTiKil .surface, 26 of horse, 43 floating, 25 head, 26 intercostal spaces, 25 internal .surface, 26 neck, 26 of dog, 1.53 of horse, 43 articulations of, 177 de\-elopment, 44 of ox, 114 of pig, 13S posterior Ijorders, 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 trochanteric, 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 INDEX 817 RiiiK--^ <)i' ring, til nous, of iiilcr- viTtebral tiljiiwart Hani's, 173 inguinal, external, 24G, 2ij0 internal, 248, 249 muscular, of ca-cum, 365 of trachea, 45',) peritoneal, 491) [jortal, 372 preputial, 497 subperitoneal, 490 vaginal, 2 IS, 290 of ox, 500 Ring-like musfles, 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 liladder of horse, 47G of hip joint of horse, 193 of horse, 356 of Uver of horse, 375 of uterus of bitch, 523 of cow, 51S of mare, 513 Rubrospinal tract, 661 of Monakow, 652 Rugae palatini of horse, 332 Rumen of ox, 390, .391 blind sacs of, 392 cardiac orifice of, 394 cavity of, 393 coronarj' grooves, 392 dorsal curvature of, 391 longitudinal furrows, 391 mucous membrane of, 394, 397 nmscular coat of, 30G pillars of, 393 ventral curvature of, 391 of sheep, 40S of stomach, serous coat, 396 Ruminal artery of ox, 615 Rumino-rcticular 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, 2(H) tibio-tarsal, of horse, 200 Sacculations of ca-cum, 364 Saccule, 759 laryngeal, of horse, 447 Saccus caucus 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 52 Sacral lyni|)h glands, 604 ncrN cs of horse, 710 vertebne, 24 of dog, 151 of hoi-se, 39 articulations of, 175 development, 41 ot ox, 114 of pig, 138 Sacro-ooccj geus acccssorius 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 ventraUs mediates muscle of horse, 240 Sacro-iliac joint of dog, 209 of horse, 190 (if 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, 70S of horse, 706 vein, .59.8 of dog, 642 of ox, 622 Sartorius nuiscle of dog, 328 of horse, 281 of ox, 308 of pig, 316 Satellite vein, 524 Scala tympani, 759 vestibuli, 759 Scalenus clorsalis 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 .'fcansorius muscle of liorse, 278 J^caiiha of auricle, 747 Scaphoido-cunean hgaments of horse, 202 scapula, li of dog, 162 of horse, 74 of ox, 127 of pig, 146 Scapular cartilage of horse, 75 Scapulo-hiuiieral portion of |)anniculus, 255 Scai)ulo - humcralis posticus muscle, 2.58 Scapulo-ulnaris mas^cle, 2(i0 Schlitz, 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, 500 of horse, 487 of ox, .500 of pig, 504 Scutiform cartilage, 748 Scutularis, 749 cf dog, 780 of ox, 774 Scutulo-auricularis, 749, 751 of dog, 7.'-() 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, 1.30 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, mem- branous, 760 osseous, 7.58 Semilunar canal of third phal- anx, 91 cartilages of femoro-tiliial articulation, 196 crest of third phalanx, 91 ganglion, 678 notch of ulna, 82 Semimembranosus nuiscle of dog, 2.S0 of horse, 280 of ox, 306 of pig, 316 Seminal ve-sides of dog, 5t)t) of horse, 491 of ox, 502 of pig, 505 Seminiferous tubules of testi- cles of horse, 486 Semispinalis capitis muscle, 231 colli muscle, 231 Semitendinosus muscle of dog, 327 of horse, 280 818 INDEX Semitendinosu.s muscle of ox, 300 of pig, 310 Sense organs of dog, 779 of horse, 734 of ox, 772 of pig, 777 Sensitive, frog, 770 .sole, 709 Septum, interalvcolar, 58 intermuscular, 212 of forearm, 262 of gluteal region, 273, 274 of leg, 274 of shoulder, 2.35 interventricular, of left ven- tricle, 534 incdiainnn dorsale, 050 mediastinum, 450 nasi, 71, 72, 73, 437 of testicles of horse, 486 of thoracic cavity, 450 pelhicidum, 074 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, 3(32 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 tis- sue, 211 distal, 29 of dog, 165 of horse, 92, 111 of ox, 131, 130 of pig, 14S proxitiial, 29 Sesamoidean ligaments, ISO, 273 of ox, 207 Seventh nerve, 084 Sexual differences of pelvis of horse, 97 Shaft of hair, 763 Sheath, car()al, of deep digital flexor muscle, 272 of superficial digital flexor muscle, 271 ocular, of horse, 738 of arteries, 525 svnovial. See Synoriiil ' shnilli. tarsal, of flexor pedis iier- forans muscle, 294 tendon, 211 Short ligament of hock joint of horse, 201 muscles, 211 sesamoidean ligament, 188 Shoulder girdle. 27 of horse, nuisdes 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 vilna of horse, 82 flexure of ox, 503 notch of horse, 04 Sinus or sinuses, cavernous, 592 coronary, 585 opening of, 529 cutis, 761 ethmoid, of horse, 74 frontal, of dog, 101 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, 101 of horse, 72 ! of ox, 126 j of pig, 140 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, 120 paranales of dog, 432 paranasal, of horse, 72 petrosal, inferior, 592 superior, 591 phrenico-costalis, 4.50 pyriform, of horse, 3.50 rectus, 5S1 renal, of horse, 470 sagittal, .591 sphenoidal, of horse, 50 of ox, 127 of pig, 140 .spheno-palatine, 00 of horse, 50, 74 straight, .591 tarsi of horse, 105 tonsillaris of ox, 385 transverse, 591 urogenital, of mare, 514 venosus sclerie, 741 Sixth nerve, 083 Skeletal muscle, 211 Skeleton, 19 appendicidar, 19 axial, 19 flat bones, 19 irregular, bones 19 .Skeleton, long bones, 19 medullary cavity, 19 number of bones, 19 of dog, 1.50 of horse, 31 of ox, 112 of pig, 130 short bones, 19 .splanchnic, 19 Skin, appendages of, 762 of dog, 780 of horse, 701, 704 of mammarv glands of mare, 510 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, 05 apex of, 69 articulations of, 179 cranial region, 68 frontal region of, 66 guttuial legion, 68 middle fossa of, 71 palatine region, 68 parietal region of, 06 posterior fossa of, 71 superior curved lines, 69 sutures of, 179 synarthroses of, 179 synchondroses of, 1.80 of ox, 115, 123 of pig, 144 Smegma prsputii of horse. 497 Smell, organ of. of horse, 772 Snout of pig, 404 Soft palate of dog, 424 of horse. 332 of ox, 384 of pig, 411 Solar plexus, 713 Sole matrix, 769 of horse, 765 sensitive, 709 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, 09 intcrclenlal, of horse, 5S interosseous, of forearm, 80 suliniaxillary, of horse, 02 Spatia anguli iridis, 744 zonularia, 747 Spatium perichorioideale, 742 Special anatomy. 17 Spermatic arterv, 571 of dog, 639 of horse, 487, 489 of ox, 618 of pig, 628 cord, lymph.atics of, 489 of dog, .506 of horse, 489 INDEX 819 Spermatic cord of ox, 500 of pig, .504 nerve, external, of horse, 704 plexus. 714 of horse, 487 veins, 596 of horse, 487, 4.S0 ^^pheno-frontal suture, 55 Sphenoid bone of dog, 150 of liorse, 50 of ox, 115 of pig, 141 Sphenoitlal notch of liorse, 55 sinus of horse, 50 of ox, 127 of pig, 146 ."^pheno-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, 3.59 of bladder of horse, 476 of mammarv gland of cow, 521 ot mare. 516 of uterus of mare, 513 pupillie. 744 pylori of horse, 358, 359 Spina furca> ungute, 767 helicis of dog, 779 Spinal accessory nerve, 690 of ox, 717 araclmoidea, 647 cord of dog. 724 of horse, 648 of ox, 715 of pig, 720 tracts of, 6.52 ganglion, 692 nerves of dog, 730 of horse, 692 of ox, 717 of pig, 723 root of fifth ner\-e, 658 veins, 543 Spinalis et semispinalis muscle of pig, 313 muscle of horse, 233 Spine, hiemal, 25 ischiatic, of horse, 94, 95 of hoof, 767 of scapula of horse, 74 of tibia of horse, 101 ventral, 25 of cer\-ical vertebra- 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 vertebrae of ox, 112 of lumbar vertebrae of horse, 39 Spinous process of lumbar vertebra; of ox, 114 of thoracic vertebrae of horse, 36 of ox. 112 of vertebnr 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 pul|) of horse, 379 Splenial fissure of dog, 727 of pig, 721 Splenic angle of horse, 372 arterv, 569 of "dog, 638 of ox, 615 of pig. 628 lymph glands, 005 of pig, 632 plexus, 714 vein, 59G Splenium, 672 Splenius muscle of dog, 324 of horse, 229 of ox. 300 of pig. 312 Spongy substance of bone, 21 Spur \ein. 593 Squamous part of occipital bone of horse, 49 tempKjral 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 Stemo-mandibularis muscle, 225 Sterno-maxillaris muscle, 225 Sterno-thyro-hvoideus muscle of dog, 319 of horse, 224, 226 of ox 298 of pig, 312 Sterno-thjToideus et stemo- hyoideus muscle, 226 Sternum, 26 of dog, 1.53 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, 3.58 coats of, 359 fibers of, 3.59 greater curvature of, 357 lesser curvature of. 357 mucous coat of, 360 muscular coat of, 3.59 asopliMgcal orifice of, 3.58 pyloric extremity, 358 orifice of, 3.58 serous coat of, 359 structure of, 359 submucous coat of, 3.59 ves.sels and nerves of, 360 of ox, 390 of pig, 417 of sheep, 408 Stop of face of dog, 160 Straight mu.'^cles of head of . pig. 312 sinus, .591 Stratum corneum, 761 germinativum, 761 of hoof. 768 periosteale of hoof, 769 \'itreum of body, 769 Stria lateralis, 671 medullaris, 665 terminalis, 665 Stria- acusticae, 662 olfactorii, 671 Striated muscle, 211 Stroma iridis, 744 of kidney of liorse. 475 of ovary of marc, 510 vitreuni, 746 Stylo-glossus muscle. 337 Stvlo-hvoideus muscle, 223 of ox, 297 Stylohyoids of horse, 65 Stvloid process, 748 of horse, 68, 69 of radius of dog, 161 of temporal bone, 57 of ulna of horse, 82 of ox, 129 Stvlo-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 Subcallos.al gjTUs, 671 Suljcarpal arcli. 562 check ligament of horse, 272 ligament of horse, 183 Subcostal artery, 539 of dog, 6.33 of ox, 600 Subcutaneous bursa-, 761 Subrutis. 761 Sulxlural space, 646 Subiliac lyiiipli glands, 606 Sul)liiiil>ic ti^^sure. 069 ."^uljlingual artery. .548 of dog, 635 crest of horse, 348 ducts of dog, 427 820 ■274 547 Siil)linsiial ducts of horse, 348 (jland of (log, 427 of horse, 347 of ox, 388 of pip, 41.") vein, o9(1 of ox, (l_n Sulihiinl)ar Illu^ of ox, 300 of pis. 316 Siil>ni:ixillarv artery duel of d(')K. 427 of hoise, 3 IS ghmd of dog, 427 of horse, 347 of ox, 388 of pig, 41.5 Ivinpli glands, (iOl of dog, 043 of i)ig, 630 space of horse, 63 Submental artery, .54f) Submucous plexus, 714 Subperitoneal ring, 490 Subpubic groove of horse, 9.5 Subscapular artery, .5.56 of dog, 63.5 of ox, 612 fossa of iiorse. 7.5 nerve, 69(') Subscapularis nuisclc of dog, .321 of horse, 2.57 of ox, 302 of pig, 314 Subscapvdo-hyoideus muscle of horse, 220 Subsphenoidal canal, 51 confluents, .592 Substantia alba, 644 corticalis of lens, 747 gelatinosa. 644 of cord, 6.51 grisea, 641 of corf!, 6.50 Subtarsal ligament, 200 Subtiialaniic nucleus, 66.5 Icgmenlal region, 06.5 Subuielhi-al diverticulum cow, .519 of sow, .522 Sudoriferous glands, 762 Sulcus aorta' of horse, 454 basilaris of pons, 659 callns.d, i\'V) con.Mi.li^ nu-'nh: 76,5 of ill-, 7(i' 649 ■(i7 )rsalis, 649 f ol)lf)ngata, cniio| dorsahs lalcMal inlcn-nu.ilis, 7( internicdius of ox, (iOS ventralis 655 limitantcs, 6lj2 niedianus dorsalis, 649 o.>;opliagus of horse, 4.54 of l)rain. 0.54 rhinalis. ()69 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, 30.5 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 nuisclc of ox, 311 gluteus muscle of horse, 277 muscl<'s of head of horse, 213 pectoral muscle of dog, 320 of horse, 2.53 of ox, 302 sesamoidean ligament, 188 Superior alveolar arch, 69 atlanto-axial ligament, 176 allanto-occipital membrane of horse, 176 border of mandible, 64 clieck ligament of superficial digital flexor muscle, 270 commissure of vulva, .515 conunon vertebral ligament coslo--iiiii,il ligament, 178 cost(i-ir.uis\( Tsc ligament of horse, 177 ciu'ved lines of skull, 69 dental canal of horse, 59 dilal.iior ii.nis muscle, 218 in.-i>i\ii- iMU-rl.., 216 intcrdmiial liuament of ox, 206 ischiatic spine, 94, 95 levator palpebr;p muscle, 219 maxillaiy 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, 1.58 of horse, 62 of ox, 122 crest of nasal hones, 01 fold of horse, 440 Supinator muscle of dog, 323 of jiig, 315 Supra-ulloid bursa, 174 Supracondyloid crest, exter- nal, of humerus, SO of femur, 97 fo.ssa of fennir of horse, 99 Supra-orbital artery, 553 canal of ox, 119 foramen of liorse, 55, 66 of ox, 119 groove of ox, 119 process of horse, 55, 66 of ox, 119 Suprarenal glands, 477 Suprascapular artery, 550 nerve, 696, 697 Suprasiiinatus muscle of dog. 321 Supraspinal us muscle of horse, 256 of ox, 302 of pig, 31 1 Suimispinovis bursa, 175 fossa of horse, 75 ligament of horse, 174 Suprasplenial fissure of dog, Siipi:is\l\ian fi.ssure of dog, 720 of horse, 668 of ox, 716 of pig, 721 Supratrochlear foramen of humerus of dog, 163 Su-spensorv ligament of penis of horse, 494 of spleen of horse, 379 navicular ligaments, 1S9 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 nasofrontal, of horse, 55, 61 of ox, 119 na.so-lacrimal, of horse, (H naso-maxillary, of horse, 61 palatine, median, 69 transverse, of horse, 69 parieto-frontal, 54, 55 parieto-occipital, 54 parieto-temporal, 50 sagittal, of horse, .54 spheno-frontal, of horse, 55 spheno-squamous, 56 Sweat glands, 762 of dog, 780 of ox, 775 of i)ig, 778 Svmpalhetic svsleni, 710 of dog, 733 of ox, 720 of pig, 724 trunk, 711 Sym])hysis, 109 of lower jaw of horse, ISO pelvis of hor.se, 191 Synarthroses, 169 of .skull of horse, 179 Svnchondroses of skull, ISO Svnchondrosis, 109 Synovia, 170 Synovial bursa of anterior digital extensor muscle of horse, 265 of infra.spinatus muscle of hoi'se, 256 of lateral digital exten.'-'or muscle of horse, 26() of teres minor muscle of hor.se, 2.57 fo,>isa, 170 of tibial tarsal bone, 105 layer of articulations, 170 INDEX 821 Synovial membrane, 211 bursal, 211 of anterior digital ox- tensor muscle, 2()0 of rarpal 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, 201) sheath at carpus of ox. 305 of anterior digital ex- tensor muscle, 2t)5 of coraco-brachialis mus- cle of horse, 258 of deep digital flexor nuis- cle 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, 52-1 Tactile hairs, 763 Tienia of small colon, 370 semicircularis, 685 thalami, 665 Tail of dog, miLscles of, 325 of horse, 764 fasciae of, 238 muscles of, 238 of ox, muscles of, 300 of pig, muscles of. 314 Tapetum cellulosum, 779 filirosum, 743 of ehorioid, 742 of ox, 774 Tarsal artery, external, 5S1 of pig, 630 perforating, 585 bones, 29 central, of horse, 107 of ox, 134 fibular, of horse, 106 Ugaments 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 per- forans muscle, 294 sinus of horse, 105 Tarsal vein of ox. 622 recurrent, 598 Tarso-metatarsal hgaments, 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, 340 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 cavitv 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. 6.57. ()63 of Ihinl ventricle, 666, 670 Telencephalon, (>('7 Temporal artery. anterior deep, 553 of dog, 635 of ox, 612 posterior deep, 552 superficial, .5.50 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 ner\'e. 682 of dog. 728 of horse, 681 of ox, 717 of pig, 722 jirocess of maxillary bone of horse, .58 vein, .587, 588 wings of horse, .51 Temporalis muscle of dog. 318 of hor.se, 219 of ox, 297 Temporary teeth of horse, 346 Temporo-hyoid articulation, 180 Temporo-mandibular art icula- tion of dog, 204 of horse. 179 of ox, 204 of pig. 204 Tendinous center of dia- phragm of horse, 243 Tendo femorotarseus muscle of horse. 289 Tendon, prepubic. 2.50 sheath, 211 Tendons, 211 Tenon, capsule of, 738 Tensor fascia; antibracliii muscle of dog, 322 of horse, 260 of ox, 303 of pig, 315 lata' 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, 2.56 of ox, 302 of pig. 314 tubercle of humerus, 77 Terminal arch of digital ai- teries, .564 arteries, 524 line of horse, 353 nuclei, 658 822 INDEX Testicles of dog, 506 opididyinis of, 506 tunica vaginalis of, 506 of luirse, 485 appendix of, 4S5 delei-entiul fold of, 4'.ll descent of, 490 guliei'naouliim testis, 4!tl hydatid of Morgagni, 45S l6l)nles of. 486 niediastiiuiin testis, 486 pampiniform plexus, 489 parenchyma of, 486 rete testis, 486 seminiferous tubules, 481) septa of. 486 structure of, 485 tubules of, 486 tunica afliuginea of, 486 vaginalis propria of, 485 \asculosa of, 486 vas deferens of, 488 vessels and nerves of, 487 of ox, 500 (•remaster externus mus- cle of, 500 epididymis of, .-)(I0 tunica vajiiiKdis of, .'■>()ll vas defcn-ns of, ."".01 of pig, .51)4 cremaster externus muscle of, .504 epididvmis of, .-|()4 vas d<.fenMis of, .-)()4 Thalamocortical hbers, 661 Thalamus, optic, 664 Theca folliculi of mare, 510 Thigh, 29 of horse, muscles of, '2iiK 281, 284 of ox, muscles of, 306, oOi, 808 of pig, mu.sdes of, 316 Third carpal bone of horse, 86 eyelid, 736 ■ of ox, 772 of pig, 777 metatar.salboneof horse, 1 10 nerve of lior.se, 677 phalanges of dog, 165 of horse, 90, 111 of ox, 130 sesamoid bone, 92, 111 tar.sal bone of hor.se, 109 of ox, 135 trochanter of femur, 99 ventricle, 666 TlKjraeic aorta, 536 branches of, 565 artery external, 541 internal, 540 of dog, 633 of ox, 609 of pig, ()27 cavity, 27 of liorse, 4.50 of ox, 461 duct of dog, 643 of horse, 600 of ox, ()23 of pig, 630 ganglia, 712 of ox, 720 limb, bones of, 27 I Thoracic liml) of dog, ar(icul.-i- ! tions of, 205 bones of, 162 nuiseles of, 319 of horse, articulations of, 180 bones of, 74 muscles of, 2.50 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 ner\es, anterior, 696 of horse, 697, 702 portion of panniculus, 255 of sympathetic system, 712 ^ein, 586, 593 vertebriE, 24 of dog, 1.50 of horse, 35, 36, 37 of ox, 112 of pig, 137 Thoiacico-dor.sal artery, .5.56 Thoraco-dorsal nerve, 697 \ein, 593 Thorax, articulations of, of dog, 204 of horse, 177 of ox. 204 of pig, 204 bones of. 27 of dog. 1.53 of hor.se, 47 of ox, 115 of pig, 139 nuiscies of, of <'og, .325 of horse, 240 of ox, 300 of jiig, 313 Thvnuis gland of dog, 468 of horse, 458 of ox, 464 of pig, 466 Thyro-arytenoid ligament, 444 Thyro-arytenoideus muscle of horse, 446 Thyro-epiglottie ligament, 444 Thyro-hyoid joints, 444 Thyro-hyoideus muscle, 445 Thyrohyoiils of horse, 6.5 Thyroid artery, accessory, 543 ■ of ox, 610 of pig, 627 cartilage of dog, 46)7 of hor.se, 442 of ox, 4.59 of pig, 465 cornua of lior.se, 65 glaiul of dog, 4(i8 accessory, 4(i8 of liorse, 457 accessory, 4.58 of ox, 464 accessory, 464 of pig, 466 vein, .590 Thyro-laryngeal artery, 543 Thvi-o-pharvngeus muscle, 350 Tibia, 29 Tibia of dog. 167 of hor.se, 100, 102, 103 of ox, 134 of pig, 149 Tibial arterv, anterior, .583 of dog, 641 of ox, 620 of pig, 630 posterior, .581 recurrent, .581 lioncs, 29 crest of horse, 100 nerve, anterior, of horse, 70S of dog, 732 of horse, 708 of ox, 720 tansal bone of horse, 105 ligaments of, 202 syno\'ial fossa of, 105 trochlea of, 105 of ox, 134 vein, anterior, .599 of dog, 042 posterior. 599 recurrent, 598 Tibialis ant erior nmscle of dog, 32S 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, 3S5 of pig, 411 of shecji, 405 Tonsil, faucial, of horse, .'!33 of pig, 411 of sheep. 407 Topograi)hic anatomy. 17, IS Torus carpalis, 780 metacarpalis, 780 tubarius, 778 TrabecuUe earneip of right ventricle, .532 of corpus eavernosum jjcnis, 495 of prostate, 493 of thyroid gland, 458 splenic, of horse, 379 Trachea of dog, 468 of horse, 448 of ox, 460 of i)ig, 466 Tracheal duets, fi03 of dog, 1)43 Tracliclo-mastoideus nuuscle of dog, 325 of horse, 229 of pig, 312 Tract of spiral cord, 6.52 olfactory. (;71 optic. 666 of ox, 716 pyramidal, ()58 Tract us centralis of thymus gland, 458 823 Tractus olfactorins, 071 Tnmcus bicaroticus, 541 rina of o\. r2S opticus, ()()(') Tuber calcis of fibular tarsal .of pig, 147 Tragicus muscle. 751 bone of horse, 106 Ulnar artery, .5.59 Tragus, 7-lS cinereimi, 653, 665 of dog, 637 of dog, 7.S!) of dog, 72() of ox, 613 TransvcTsalis cost arum muscle ischii of horse, 95 superior collateral, of ox. of dog, :ii5 scapula' of horse, 77 612 of horse, 2'M> Tubercle, cuneate, of pig, 720 carpal bone of lujise, 84 of ox, 301) internal, of humerus, 78 nerve of dog, 730 of pig, 313 lacrimal, of horse, 61 of horse, (j96, 698 fascia of horse, 21i) of Lower, 530 of ox, 718 Transverse arytenoid ligament of scapida of horse, 75 of pig, 723 of larynx; 444 psoas, of horse, 93 vein, .595 diameter of pelvis, 97 teres, of humerus, 77 of dog, 642 fissure, 039 Tubcrculum cinereum, 656 I'lnaris lateralis muscle of dog. of ox, 716 facialc, 6.55 323 fossa of Ijrain, 667 inter\('nosimi of horse, 530 medialis muscle of dog, 323 liyoideus muscle, 224 olfactorium of pig, 721 Umbilical artery, 574, 606 himina, ethmoid bone of ilo>;, Tuberosity, alveolar, 69 of dog, 641" 1.57 bicipital, of raduis. 81 of ox, 619 ligament of carpus, 263 of scapula. 77 fissure of horse, 374 of hip joint of horse, 192 deltoid, of horse, 78 ligament of bladder, 47() of radio-ulnar articula- external, of humcius, 78 vein, 607 tion of horse, 182 of radius of horse, 81 Undershot dog. 425 palatine suture of horse, 69 facial, of ox, 120 Ungual phalanx of hor.si'. 90 sinuses, 591 internal, of humerus, 79 Unipcnnale muscle. 212 spinous muscle of neck, 231 of radius nf horse. Si Unstripcd muscle, 211 Transversus abdominis muscle in.-i\ill,-u-y, nf horse. 5S Ureters, 469 of dog, 326 metacarpal, of hor.sc, 88 of bladder, fundus of, 47() of horse, 248 of atlas of ox, 112 of dog, 484 of ox, 302 of 1 ibia of horse, 102 of heart, pelvic part, 475 of pig, 313 Tubules of testicles, 486 of horse, 475 costarum muscle, 242 renal, of horse, 474 abdominal part, 475 thoracis muscle of horse. 2 12 seminiferous, of testicles, 486 of ox, 480 of pig, 313 uriniferous, of horse, 474 of pig, 483 Trapezius cervicalis muscle, 250 Tunic, abdominal, 245 Urethra, 409 muscle of dog, 319 of pig, 313 masculina of dog, 507 of horse, 250 fibrous, of ape, 740 of horse, 497, 498, 499 of ox, 302 Tunica allmginea, 4.86, 495 of ox, 504 of pig, 314 fibrosa of kiilney, 473 of pig, 506 thoracalis muscle, 251 mucosa laryngis, 448 of cow, 519 Triangularis sterni muscle, 242 propria of skin, 762 of mare, 515 Triceps brachii, 260, 261 vaginalis communis, 490 of sow, 522 extensor cubiti of hor.se, 230 of dog, 506 Urethral crest of horse, 499 muscle of do?, 322 of horse, 4.89 glands of horse, 499 of ox, 303 of ox, 500 groove of horse, 495 of pig, 315 propria of horse, 485, 490 muscle of dog, 507 surse muscle of horse, 292 vascuiosa of testicles, 486 of horse, 499 Trifacial nerve of horse, 677 Turbinal bones of dog, 1.58 of mare, 516 Trigeminal nerve of horse, 677 of horse, 62, 438 of ox, .504 Tiigonum lemnisci, 634 of ox, 122 of pig, 506 olfactorium, 653, 637, 671 of pig, 143, 465 orifice, external, of cow, 519 ^■esicae of horse, 476 crest, inferior, of horse, 58 of male horse, 499 Trochanter, external, of femur superior, of nasal bones of of mare, 515 of horse, 99 horse, 61 of ox, 503 great, of femur of horse, 99 fold, inferior, of horse, 440 internal, of horse, 477, 499 internal, of femur, 97 superior, of horse, 440 of horse, 477 Trochanteric fossa of femur of Twelfth nerve, 692 of pig, .505 horse, 99 Tympanic artery, 552 process of horse, 495 ridge of femur of horse, 99 cavity of dog, 780 sinus of horse, 495 Trochlea of femiu- of horse, 99 of horse, 7.52 Urinary bladder. See Bliid- of tibial tarsal bone of of ox, 775 der. horse. 105 of pig, 778 organs, 469 Trochlear foramen of horse. 51. memfjrane, 753 of dog, 483 67 n(>rve, 686 of horse, 469 nerve of horse. 677 opening of Eustachian tube, of ox, 478 origin of, 664 755 of pig, 481 Trochoid, 172 plexus, 687 Uriniferous tubules, 474 True joints, 170 Urogenital fold of horse, 355 ribs, 25 sinus of mare, 514 of horse, 43 Udder of cow, 519 system, 469 vertebrie, 24 Ulna, 28 Uterine artery, 571 vocal cords of dog, 468 of dog, 163 middle, 578 of horse, 448 of horse, 82 of dog, 641 824 INDEX Uterine artery of ox, 019 posterior, 57-1 cotyledons of cow, 518 glands of cow, 518 of niaro, 513 tubes of bitch, 522 of cow, 517 of inaro, 511 of sow, 522 Utero-ovarian artcrv, 571 of dos, 639 of ox, 618 plexus, 714 veins, 596 Uterus inasculinus of dog oO:! of horse, 493 of ox, 503 of pig, 505 of l)itch, 522 of cow, 517, 5)8 of horse, Ijroad ligaments,356 of mare, 511, 512, 513 of sow, 522 Utricle, 759 prostatic, of horse, 493 Uvula of pig, 411 V.\(ii.\A of l)itch, 523 of cow, 518 of mare, 514 of sow, 522 tendinis, 211 \aginal ligaments, 212 ring of horse, 248, 490 of ox, 500 svnovial membrane, 211 Vagus, 687 of dog, 729 of ox, 717 of pig, 722 Vallate papillc of tongue, 33(> Vallecula of Sylvius, W>7 Valve, bicusi>i'..'!) tibial, anterior, .599 of dog, 642 posterior, 599 reciu'rent, .598 ulnar, .595 of dog, 642 umbilical, 007 utero-ovarian, 596 valves of, .525 vas vasorum of. 525 vertebral, 580 Velum interpositum of (lord ventricle. 060 medullarv. 000, 603 825 Vena azygos. 5S6 of (log, 642 of horse, oponiiig of, 529 cava. .524 anterior. .580 opening of. 529 of (log. 641. 642 of ox. 622 posterior, 595 opening of, 529 coraitans, .524 hemiazygos. 5.S7 of (log, 642 of ox, 621 jugularis of ox, 621 reflexa, 589 of ox, 621 Vena^ vorticosa", 745 \'enous arch, 595 plexus of lu'ethra of mare, 516 Venter of scapula of horse, 75 ^"entral 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 vertebne of ox. 112 Ventricle, fourth, of horse, 662 lateral. 674 of larynx of horse. 447 of ox. 4.59 middle, of larynx. 447 of heart of horse, k^ft, 533 right, .530 third, 666 \'entricular ligament of larynx of hor.se. 444 Ventricularis et vocahs muscle of horse, 446 Ventriculus bulbi olfactorii, 671 larvngis medianus of horse, 447 lateralis, 674 larjTigis of horse. 447 quartus. 662 tertius, 666 Vermis, 660 of dog, 725 ^'ertebra;, 24 accessory processes, 25 anticlinal, of horse, 42 arch. 24 articular processes, 25 body. 24 caudal. 24. 25 centrimi. 24 cervical, 24 of dog. 1.50 of horse, 32 of ox. 112 of pig, 1.36 coccygeal, 24 of dog, 1.52 of horse. 41 of ox, 114 of pig. 138 development. 25 diaphragmatic, of horse, 42 \'erlcl)ne. false. 24 tixed, 24 foramen, 25 ha-mal 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 0.x, 112 of pig, 138 mammillary processes, 25 movable, 24 notches, 25 of horse, intercentral articu- lations of, 173 interneural articulations of, 173 ossification of, 25 primary centers of ossifica- tion, 25 sacral, 24 of dog, 151 of horse, 39 articulations of, 175 development, 41 of ox, 114 of pig, 138 secondary centers of ossifi- cation, 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 ^'ertebral artery, 540 of dog. 633 of ox. 609 of pig. 627 canal, 25 of horse. 42 cohmm. 24 of d(jg. l.'iO 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 comesp, 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, 3.56 Vesico-prostatic artery. 574 Vestibular ganglion. 686 ner\-e. 686. 761 Vestibule of ear, 758 Vestibule of larvnx of horse, 447 of omental cavity, 380 Veterinary anatomy, 17 Vibriss;!', 763 Vidian canal of horse. 51. 61 nerve, 6.81 Villi of articulations, 170 Visceral layer of pericardium, 525 pleura of horse. 4.52 Vitreous body. 74() of ox, 774 ^'ocal cords, false, of dog, 467 of horse, 447 of ox, 459 of pig. 465 true, of dog, 468 of horse. 44S ligament of horse, 444 process of horse. 443 ^"ocalis muscle of horse, 446 Volar arch, .562 artery, deep. .562 of .second phalanx. 564 common digital arter\' of ox, 614 digital nerves of (log. 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 \"omer of dog, 1-58 of horse. ()3. 431 of ox, 122 of pig, 143 Vomero-nasal organ. 772 of horse. 440 Vortex cordis of horse. 534 V-shaped ligament. 188 \'ulva of bitch. 523 of cow, 519 of mare, 514 of sow, 522 A"ulvar 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 Win.slow's foramen. 379 of ox, 396 Wirsung's duct of hor.se, 372 Wolf tooth. .3.39 of horse. oS. 64 Wool, 777 Xiphoid cartilage. 26 of horse. 46 Y-.sH.\rKD ligament, 188 826 Zone, epigastric, of horse, 353 hypogastrii-, of liorse, 353 intermeilialc. of kidney, 473 inesogastric, of horse, 353 Zonula ciliaris, 743, 747 of Zinn, 747 Zygoniatii- arcli of liorse, .56, 07 hones of horse, 62 erest of horse, 58, 62 gland of dog, 427 nerv'e of dog, 72S of liorse, 67(1 proee.ss of frontal hone, 55 of maxillary hone, 58 Zygomatic process of t(m[ oral hone, 56 Zygomatico-auricularis. 74'.» of ox, 747 Zvgomaticus muscle of dog, 318 of horse, 215 of ox, 295 of pig, 311 /