762 THE SENSE ORGANS AND SKIN OF THE HORSE 



In many places further subdivision into strata is evident on properly prepared 

 cross-sections. 



The corium consists essentially of a feltwork of connective-tissue and elastic 

 fibers. It is well su]:)plied 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 suiierficial part, the corpus papillare, is of finer texture and is free from fat. 

 Its superficial face is thickly l)eset with blunt conical prominences, the papillae, 

 which are received into corrc^sponding depressions of the epidermis. They contain 

 vascular loops and nerves, or, in certain situations, special nerve-endings. 



The papilla? are best developed where the epidermis is 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 (Glandulse cutis) are chiefly of two kinds, sudoriferous 

 and sebaceous. 



The sudoriferous or sweat glands (Glandula? sudoriferae) consist of a tuljc, 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 glandulse sudorif erse) . 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 In' a funnel-shaped pore (Porus sudoriferus) on the surface of the skin. 



The sebaceous glands (Cilandulae 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 bodies. In certain 

 situations {e. g., 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 special types occur. Some of these are to be regarded as modified sweat glands, e. g., the 

 naso-lal)ial glands of the ox, the glands of the snout of the i)ig, and the glands of the plantar 

 cushion of th(> horse. Others, e. g., the tarsal (or Meibomian) glands of the eyelids, are modified 

 sebaceous. Still others are not yet classified satisfactorily. Some of these special types have 

 been referred to in previous chapters, and others will receive attention in the special descriptions 

 which follow. The mammary glands are highly modified 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, 

 ancl another network is formed under the papillae. Small vessels from the deej) 

 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 papillae, and another at the junction of the corium and 

 sul)cutis. The lymph vessels form subpapillary and subcutaneous plexuses. 



The nerves vary widely in number in different parts of the skin. The terminal 

 fi]:)ers either end free in the epidermis and in c(^rtain ]iarts of the corium, 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, honis, etc. 



The hairs (Pili) cover almost the entire^ surface of the body in the domesticated 



