Common Integument

The thickness of the skin of the ox is greater than that of any of the other domesticated animals; in general it is about 3 to 4 mm., but at the root of the tail and the point of the hock it is about 5 mm. and on the brisket 6 to 7 mm. The variably developed prominence at the anterior part of the pectoral region known as the brisket consists of a fold of skin (Plica colli ventralis longitudinalis), which contains posteriorly a mass composed of coarse fibrous trabeculæ and fat.

The cutaneous glands are fewer and less developed than in the horse. Except about the natural openings, at the point of the hock, and the flexion surface of the fetlock, the sweat glands do not form a coil, but are enlarged at the deep end and are variably flexuous. The sebaceous glands are best developed about the natural openings and on the udder, but there are none on the teats. The naso-labial glands form a thick layer under the bare skin of the muzzle. They are compound tubular glands and are lined with cubical epithelium. The openings of their excretory ducts are easily seen.

The hairs are extremely variable in color and size in the different breeds and in different individuals. The hair of the frontal region is often curly, especially in the bull. There is no mane, and the long hairs of the tail occur only at the end, where they form the “brush” (Cirrus caudæ).

The claws, four in number on each limb, cover the ends of the digits. Those of the chief digits conform in a general way to the shape of the third phalanges, and each may be regarded as having three surfaces. The abaxial or outer surface is convex from side to side, and is marked by ridges parallel with the coronary border. Its anterior part is concave from edge to edge, and the angle which it forms with the ground is about 30°. The interdigital or inner surface is concave and grooved; it touches the opposite claw only at its ends. The inferior or ground surface consists of two parts, viz., a slightly concave sole, which is pointed in front and widens behind, and a prominent bulb of soft thin horn, which is continuous above with the skin. The claw may be regarded as consisting of three parts—periople, wall, and sole. The periople surrounds the coronary border in the form of a flat band, which is about half an inch wide, except at the heels, where it widens to cover the entire surface. The wall forms most of the abaxial or outer part of the claw and is reflected in front upon the interdigital surface. It thins out toward the bulb or heel, which appears, as stated above, to consist of the thin expansion of the periople. The sole occupies the angle of inflection of the wall; it is continuous without demarcation with the periople of the bulb. The perioplic matrix bears relatively long papillæ. The coronary matrix is much less developed than in the horse and its papillæ are short. The sensitive laminæ are much narrower and are more numerous than in the horse; secondary laminæ are not present. The matrix of the sole is not marked off behind from that of the periople; its papillæ are very small and close together. The matrix of the bulbs is separated from the flexor tendon by a mass of elastic, fatty tissue, which is analogous with the plantar cushion of the horse. The papillæ here are long and often compound.

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.