900 THE SENSE ORGANS AND COMMON INTEGUMENT OF THE PIG 



ordinary 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 corium 

 of the horn (Corium cornus) is united to the horn process by periosteum which is 

 traversed by numerous blood-vessels. The corium at the root of the horn is thick 

 and bears long, slender papillae; in the body of the horn it becomes thin and the 

 papillae are smaller, but increase in size apically. Rudimentary papillated laminae 

 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 large 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 depth, which is situated in front 

 of the medial 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 interdigi- 

 talis) 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. 2.5-3 cm.) in length, and about a fourth of an inch (ca. 6- 

 7 mm.) in diameter. The pouch extends downward and backward, and then 

 curves sharply upward between the distal ends of the first 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. 



THE SENSE ORGANS AND COMMON INTEGUMENT OF THE PIG 



THE EYE 



The posterior part of the orbital margin is formed 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 medial 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. 



