Part 93

The accessory digits bear short conical horn capsules which resemble in a general way those of the chief digits, and have a similar matrix, which covers one or two nodular vestigial phalanges. From these a fibrous band descends obliquely on the volar aspect of each chief digit and is attached below to the distal phalanx and sesamoid bones, sending fibers also to the elastic pad of the heel.

The =horns= (Cornua) inclose the horn processes of the frontal bones (except in the polled breeds). They vary very greatly in size, form, and curvature. The root or base of the horn (Radix cornus) has a thin edge which is continuous with the epidermis. It is covered by a thin layer of soft horn similar to the periople of the hoof of the horse. Near the root the horn is encircled by variable rings. Toward the apex (Apex cornus) the thickness of the horn increases till it becomes practically a solid mass. The horn consists mainly of tubes which are very close together, except at the rings, where there is more intertubular horn. The =matrix= of the horn (Matrix cornus) is united to the horn process by periosteum which is traversed by numerous blood-vessels. The matrix at the root of the horn is thick and bears long, slender papillæ; in the body of the horn it becomes thin and the papillæ are smaller, but increase in size apically. Rudimentary papillated laminæ also occur.

The =skin= of the =sheep= varies in thickness from 0.5 to 3 mm., but differs greatly in fineness and in other respects in various breeds. In Merinos considerable folds occur on the neck. Cutaneous pouches (Sinus cutis) are constantly present in certain situations. The =infraorbital= or =lacrimal pouch= (Sinus cutaneus infraorbitalis) is an invagination about half an inch in depth, which is situated in front of the inner angle of the eye. It bears scattered fine hairs, into the follicles of which large compound sebaceous glands open; coil glands are also present. The secretion of the glands is fatty and forms a yellow sticky covering on the skin when dry. The =inguinal= (or mammary) =pouch= (Sinus cutaneus inguinalis) is much more extensive, and is situated in the inguinal region in both sexes. The skin of the pouch bears scattered fine hairs and contains well-developed sebaceous glands and exceedingly large coil glands. The =interdigital pouch= (Sinus cutaneus interdigitalis) is a peculiar tubular invagination of the integument which opens at the anterior part of the interdigital cleft. On sagittal section it appears as a bent tube, an inch or more (ca. 2.5 to 3 cm.) in length, and about a fourth of an inch (ca. 6 to 7 mm.) in diameter. The pouch extends downward and backward, and then curves sharply upward between the distal ends of the proximal phalanges. Its deep blind end is somewhat ampullate. The subcutis forms a capsule around it. The skin of the pouch is thin and pale; it bears fine colorless hairs, the follicles of which receive the secretion of several sebaceous glands. The coil glands here are compound and very large; they open into the hair-follicles or directly into the pouch. The secretion of the glands is a colorless fatty substance. The skin is covered in great part by wool, which is similar in structure to hair, but is finer, curly, and usually contains no medullary cells. The follicles of the wool are curved, and are arranged more or less distinctly in groups of ten or a dozen, several of which open in common on the surface. A considerable part of the face and the limbs is covered with short, stiff hair, and long hairs occur more or less interspersed among the wool. The claws resemble those of the ox. The horns, when present, are more or less prismatic, distinctly ringed, and vary in length and curvature in different breeds. Their structure is similar to those of the ox.

The olfactory and gustatory organs resemble in general those of the horse.

SENSE ORGANS AND INTEGUMENT OF THE PIG

THE EYE

The posterior part of the orbital margin is formed chiefly by the orbital ligament, which extends from the extremely short supraorbital process to the small eminence at the junction of the malar and the zygomatic process of the temporal.

Cilia occur only on the upper eyelid. The inner canthus is prolonged by a groove on the infraorbital region. The tarsal glands are very short and curved. The conjunctival epithelium is of the transitional type with many goblet cells.

The deep part of the cartilage of the third eyelid is broad and spoon-like, the superficial part somewhat anchor-shaped. In addition to the gland which surrounds the deep part of the cartilage, there is a deeper gland of Harder (Glandula palpebræ tertiæ profunda), which is surrounded by a distinct capsule and a blood-sinus. This gland is brownish or yellowish-gray in color, elliptical in outline, and about an inch (2 to 3 cm.) in length. It is situated deeply below the attachment of the inferior oblique muscle.

The caruncula lacrimalis has the form of a ridge; it divides into two branches which join the skin at the inner commissure. It is red in color and contains numerous large coil glands.

The lacrimal gland is mucous in type. There is no lacrimal sac, and the two lacrimal ducts pass through separate openings at the infraorbital margin. The naso-lacrimal duct is usually short and opens into the inferior meatus at the posterior end of the inferior turbinal.[229]

The eyeball appears small, partly on account of the narrowness of the palpebral opening; it closely approaches the spherical form. The cornea, although in reality almost circular, appears oval when viewed from the front, the inner end being much the broader. The chorioid has no tapetum. The iris is usually dark grayish-brown or yellowish-brown, but sometimes has a blue tinge. The pupil is a transverse oval in ordinary light, but almost circular when dilated; granula are not present. The optic papilla is nearer the posterior pole than in the horse and ox, and has a distinct central artery and vein.

THE EAR

The external ear differs considerably in size, thickness, and position. It may be carried vertically, inclined inward, or hang downward. It is relatively wide and is little curved except at the base. The concave surface presents several cutaneous ridges which correspond approximately with the long axis of the ear. The anterior border of the concha is strongly recurved in its lower part, and divides into two branches, one of which passes almost horizontally backward in the cavum conchæ, while the other continues the general direction of the border. The posterior border is slightly concave above, strongly convex below, forming a prominence somewhat analogous to the lobule of the human ear. The osseous external auditory meatus is very long and is directed downward and inward. The tympanic membrane is almost circular.

The tympanic cavity proper is small, but it is continuous with the numerous cells of the large bulla ossea. The Eustachian tube is short; its pharyngeal opening is situated in the upper part of the wall of the pharynx immediately behind the posterior nares. It is somewhat infundibular, and is bounded internally by a thick fold of mucous membrane (Torus tubarius).

THE SKIN AND APPENDAGES

The thickness of the skin in improved breeds is 1 to 2 mm. Fat usually accumulates in the subcutis and forms a distinct and often extremely thick panniculus adiposus over the greater part of the body.

The sebaceous glands are in general small and much fewer than in the other animals. The sweat glands, on the other hand, are large, yellow or brownish in color, and are in many places visible to the naked eye. At the inner side of the carpus there are small cutaneous diverticula, the so-called carpal glands, into which numerous compound coil glands open. Large glands also occur in the skin of the digits and interdigital space. Compound tubular glands are present in the skin of the snout. Large sebaceous and sweat glands are found at the entrance to the preputial diverticulum.

The hairs are sparsely scattered in improved breeds—indeed, in some cases the skin is almost bare. The long hairs or bristles are arranged usually in groups of three. They are most developed on the neck and back. The bristles about the snout and the chin are sinus hairs.

The =claws= and their matrix resemble those of the ox, but the bulbs are more prominent and form a greater part of the ground surface; they are also better defined from the sole, which is small. The claws of the accessory digits are more developed and their parts better differentiated than those of the ox.

The olfactory region is extensive in correlation with the large size of the olfactory bulbs; the mucous membrane here is brown in color.

SENSE ORGANS AND INTEGUMENT OF THE DOG

THE EYE

The posterior margin of the orbit is formed by the orbital ligament, as in the pig. The orbital axes if produced backward would include an angle of about 79°, the optic axes an angle of about 92.5° (Koschel).

The lower eyelid has no distinct cilia. The inner angle is wide, the lacus lacrimalis shallow, and the caruncula lacrimalis small and yellowish-brown. The conjunctival epithelium is cylindrical, with many goblet cells. The gland which surrounds the deep end of the cartilage of the third eyelid is large and pink; it is a mixed gland.

The lacrimal gland is flat and lies chiefly under the orbital ligament. It is pink in color and mixed in structure. The naso-lacrimal duct is variable in arrangement and may differ on the two sides. It may open into the inferior meatus immediately after its emergence from the osseous lacrimal canal; thence it continues forward and opens on the lateral wall of the nostril below the inferior turbinal fold.

The eyeball is almost spherical and is relatively large, especially in the small breeds. The sclera is thick in the ciliary region, where it contains a well-developed venous plexus; in the vicinity of the equator it is thin, and the chorioid shows through it. The cornea is almost circular. The chorioid is richly pigmented, and presents a well defined =tapetum cellulosum=; this is somewhat triangular in outline and has a metallic luster. Its color is often golden green, shading to blue peripherally, but the blue tone may predominate, and in other cases it is mainly golden yellow or reddish-yellow. The appearance is due to several layers of peculiar flattened polygonal cells. The ciliary muscle is more developed than in the other species. The iris is commonly light or yellow brown, but not rarely has a blue tinge; the color often differs in the two eyes. The pupil is round; its edge is either smooth or bears minute round prominences. The retina presents a round area centralis external to the optic papilla. The latter is variable in outline; commonly it has the form of a triangle with the angles rounded off, but is often round or oval. Branches of the central vessels of the retina radiate from the middle of the papilla. The surfaces of the lens are not so strongly curved as in the other domestic animals, and there is little difference in the radius of curvature of the two surfaces.

THE EAR

The external ear differs greatly in size and form in the various breeds; in most it is relatively wide and thin and the greater part of it hangs down over the opening. The anterior border has a prominence (Spina helicis) at its lower part, and below this it divides into two branches (Crura helicis). One of these continues down to a blunt point, while the other turns in to the cavity of the concha. The posterior border forms a pouch below its middle, and is thick and rounded in its basal part. Here the conchal cartilage bears a pointed process (Processus uncinatus), which projects upward and backward. The outer wall of the cavum conchæ is supported by a quadrilateral plate (Tragus) above and a semiannular cartilage below. The concave surface presents several cutaneous folds, and in the cavum conchæ there are ridges and irregular prominences. There are long hairs on the borders, apex, and the folds of the concave surface, but the skin of the cavum conchæ is bare. The annular cartilage is a complete ring. The osseous external auditory meatus is wide and extremely short.

The auricular muscles are thin. The scutularis is extensive and is divisible into interscutularis and fronto-scutularis. It partly covers the occipitalis muscle, which is oval and unpaired and ends in the fascia of the frontal region. The scutulo-auriculares superficiales, inferior et accessorius, and the cervico-scutularis are not differentiated as separate muscles. The cervico-auricularis superficialis and the parieto-auricularis both bifurcate and are inserted into the base of the concha and the scutiform cartilage. The parotido-auricularis is narrow and almost long enough to meet the opposite muscle. The tragicus consists of two parts; of these the lateral one is long and arises from the border of the mandible above the angular process. The helicis and the verticalis auriculæ are well developed.

The tympanic cavity is very roomy, extending ventrally into the large but simple cavity of the bulla ossea. The tympanic membrane is extensive and oval. The promontory is very pronounced. The auditory ossicles are large. The Eustachian tube is short, and has a fibrous outer wall. Its pharyngeal opening is an oblique slit situated on the lateral wall of the naso-pharyngeal meatus, and is margined internally by a thick mucous fold.

The cochlea has three and a half turns and is more sharply pointed than in the ungulates.

THE SKIN AND APPENDAGES

The skin varies greatly in thickness in different breeds. It is remarkably loose on the dorsal aspect of the neck and trunk, where it can be raised in extensive folds. The coat is also subject to extreme variation in length, thickness, color, etc. The hairs are arranged in groups of three to a large extent. The sebaceous glands are best developed in the short and rough haired breeds. They are largest and most numerous at the lips, anus, dorsal surface of the trunk, and sternal region. The sweat glands are relatively better developed in the long and fine haired breeds. The largest are found in the digital pads. Coil glands occur in the skin of the muzzle, the perineum, and the paranal pouches.

On the flexion surface of the carpus and digit there are hairless, cushion-like pads. The carpal pad (Torus carpalis) is situated medial and distal to the accessory carpal bone. The metacarpal and metatarsal pads (Torus metacarpalis, metatarsalis) are the largest and are situated behind the distal ends of the metacarpal or metatarsal bones and the greater part of the first phalanges. They are somewhat heart-shaped, with two unequal lateral lobes, and the apex distal. The metapodiophalangeal joints rest on them when the paw supports the weight. The digital pads (Tori digitales) are oval and are much smaller; they similarly support the second digital joints. That of the first digit is small on the fore limb, and usually absent from the hind limb. Each receives two suspensory bands from the tubercles at the distal end of the corresponding second phalanx. The pads have a basis of fibro-elastic tissue and fat, which is intimately adherent to the skin and is connected by trabeculæ with the bones and tendons. The epidermis is thick and largely keratinized, and is studded with numerous rounded papillæ which are readily seen with the naked eye. The corium has large papillæ, and contains sweat glands and lamellar corpuscles.

The =claws= (Ungues) correspond in form to the ungual part of the distal phalanges which they inclose. The horn of the claw consists of a body or wall and a sole. The former is strongly curved in both directions, and is compressed laterally. Its root or coronary border fits into the depression under the bony collar or ungual crest of the third phalanx and is covered by skin. The lateral borders converge and inclose the sole anteriorly. The matrix presents a coronary part which bears papillæ only near the coronary border. On the dorsal surface it is thickened to form a ridge, and the corresponding part of the horny covering is thick and maintains the pointed character of the claw. The matrix of the sides of the wall bears small laminæ which converge to the matrix of the sole. The latter is papillated. When the flexor muscles are inactive, the distal phalanges and the claws are maintained in dorsal flexion by two elastic ligaments. These arise from the tubercles at the proximal end of the second phalanx and converge to the dorsal aspect of the ungual crest of the third phalanx.

OLFACTORY AND GUSTATORY ORGANS

The =olfactory region= lies above the lamina transversa, which separates it from the naso-pharyngeal meatus. The mucous membrane is distinguished by its thickness and yellow color, and is very extensive. It covers about half of the large ethmoturbinals, and one-third to one-half of the septum nasi. The ethmoturbinal which projects into the frontal sinus and the adjacent inner wall of the sinus is olfactory in character. Olfactory nerve-fibers ramify in the vomero-nasal organ (of Jacobson).

The gustatory apparatus presents no special features of importance.

INDEX

Abdomen, muscles of, 245 of dog, 326 of pig, 313 muscles of, 301, 313

Abdominal aorta, 536 branches of, 566 of dog, 638 artery, anterior, 541 posterior, 579 subcutaneous, 580 cavity of horse, 352 of ox, 390 fascia of horse, 245 muscles of dog, 326 of horse, 245 of pig, 301, 313 panniculus, 245 plexuses, 713 tunic of horse, 245 of pig, 313 veins, 598

Abducent nerve, 683

Abduction of joints, 172

Abductor cruris posterior muscle, 327 digiti quinti muscle, 324, 329 hallucis muscle, 329 pollicis brevis et opponens pollicis muscle, 324

Abomasum of ox, 390, 392 cavity of, 396 of sheep, 409

Accelerator urinæ, 499

Accessory carpal bone, 84 fibro-cartilage of patella, 105 organs, 330 pancreatic duct of dog, 431 of horse, 373 pillars of rumen, 393 spleens of horse, 379 thyroids of dog, 468 of horse, 458 of ox, 464

Acetabular angle, 94, 96 fossa, 96 notch, 96

Acetabulum of dog, 167 of horse, 96 of ox, 131 of pig, 148

Acromion of dog, 162 of ox, 127

Adduction of joints, 172

Adductor brevis muscle of horse, 282 digiti quinti muscle of dog, 324 secunda muscle of dog, 324 hallucis muscle of dog, 329 longus muscle of horse, 282 magnus muscle of horse, 282

Adductor muscle of dog, 328 of horse, 282 of ox, 308 of pig, 316 parvus muscle of horse, 282 pollicis muscle of dog, 324

Aditus laryngis of horse, 447

Adrenal bodies of dog, 484 of horse, 477 structure of, 478 of ox, 481 of sheep, 481 plexus, 714

Adventitia of seminal vesicles, 492 of vas deferens, 489

Æquator lentis, 746

Æsthesiology, 734

Air-cells of lungs, 457

Alæ nasi, 436

Alar canal, 51 cartilage, 437 of ox, 459 fold, 437 foramen, 68

Alimentary canal, 330

Alveolar arch, superior, 69 artery, inferior, 552 of dog, 635 of pig, 627 border of mandible, 64 ducts of lungs, 457 nerve of dog, 729 of horse, 681, 682 periosteum of teeth, 339 tuberosity of horse, 69 vein, 589 inferior, 587

Alveoli of horse, 58 of lungs of horse, 457 of thyroid gland of horse, 458

Alveus, 669

Amphiarthroses, 172

Ampulla ductus deferentis, 489 of semicircular canals, 758 of uterus of bitch, 523 recti of horse, 370

Amygdaloid nucleus, 676

Anal glands of dog, 432 lymph glands, 605 of ox, 626 of pig, 632 sacs of dog, 432

Anastomosis of arteries, 524

Anatomy, 17 gross, 17 macroscopic, 17 microscopic, 17 philosophical, 17 special, 17

Anatomy, systematic, 17, 18 topographic, 17, 18 veterinary, 17

Anconeus muscle, 262 of pig, 315

Angiology, 524

Angle, duodenal, of horse, 372 of mandible, 64 splenic, 372

Angular artery of eye, 550 of ox, 611 movements of joints, 171 process of mandible of dog, 159

Annular cartilage of ear, 748 ligament, 212 anterior, of horse, 263 of manus of horse, 263 of pelvic limb of horse, 274 posterior, of carpus of horse, 263

Annulus tympanicus, 753

Ansate fissure of dog, 726

Anterior angle of pancreas, 372 of scapula, 76 annular ligament of horse, 263 aorta, 537 aperture of thoracic cavity, 450 fossa of skull, 70 nares, 436

Antero-external angle of ischium, 95

Antero-internal angle of ischium, 95

Antibrachial artery of dog, 635

Anticlinal vertebræ of horse, 42

Antitragicus muscle, 751

Antitragus, 748

Antrum pylori, 358

Anus of horse, 371 of ox, 400

Aorta, 535 abdominal, 536 branches of, 566 of dog, 638 anterior, 537 arch of, 535 of ox, 609 of pig, 627 thoracic, 536 branches of, 565

Aortic orifice of heart of horse, 533 plexus, 712

Aperture, anterior, of thoracic cavity, 450 of abdominal cavity, 353 pharyngeal, of horse, 447

Apex cæci, 364

Apical lobe of lungs of ox, 462, 463

Aponeuroses, 211

Aponeurosis of external oblique muscle, 246 of internal oblique muscle, 248 of transversus abdominis muscle, 249 pharyngeal, 350

Appendages of skin, 762

Appendix testis, 485 ventriculi laryngis, 447

Aquæductus cochleæ, 759 vestibuli, 758

Aqueduct of cerebrum, 664 of Sylvius, 664

Aqueous humor, 746

Arachnoid granulations, 647

Arachnoidea, 646 spinal, 647

Arch, alveolar, superior, of horse, 69 of aorta, 535 of cricoid cartilage, 441 plantar, 581 venous, 595 zygomatic, 56, 67

Arciform ligaments, 182

Arcuate fibers, external, 657, 658 internal, 658 of cerebellum, 661

Arcus terminalis, 564 venosus plantaris, 599 volaris, 595

Area acustica, 662 of ox, 715 centralis retinæ, 746 cochlæ, 759 parolfactoria, 671 radicularis ventralis, 649 tentorial, 668 vestibularis superior, 759

Arm, bones of, 28 muscles of, 259 of ox, muscles of, 302 of pig, muscles of, 314

Arrectores pilorum, 763

Arterial circle of Willis, 546 plantaris lateralis of ox, 620 reticularis of ox, 615