THE COMMON INTEGUMENT 885 



the openings of the cutaneous glands and the hair-follicles, and its deep surface is 

 adapted to the corium.i It is divisible into a superficial, harder, drier part, the 

 stratiim comexim, and a deeper, softer, moister part, the stratum germinativum. 

 The cells of the latter contain pigment, and by their proliferation compensate the 

 loss by desquamation of the superficial part of the stratum corneum. In many 

 places further subdivision into strata is evident on properly prepared cross-sections. 

 The corium consists essentially of a feltwork of white and elastic fibers. It is well 

 supplied with vessels and nerves, and contain the cutaneous glands, the hair-fol- 

 licles, 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 glands of the skin (Glandulae cutis) are chiefly of two kinds, sudoriferous 

 and sebaceous. The sudoriferous or sweat glands (Glandule sudoriferse) consist 

 of a tube, the lower, secretorj^ part of which is coiled in the deep part of the corium 

 or in the subcutis to form a round or oval ball (Corpus glandulae sudorif erae) . The 

 excretory duct (Ductus sudoriferus) passes almost straight up through the corium, 

 but pursues a more or less flexuous course through the epidermis, and opens into a 

 hair-follicle or by a funneUshaped pore (Porus sudoriferus) on the 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 easilj^ 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 tj'pe. They secrete a fatty substance, the sebum cutaneum, 

 which serves as a protective against moisture, and may also (by its aromatic con- 

 stituents) 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-labial glands of the ox, the glands of the snout of the pig, and the glands of the digital 

 cushion of the horse. Others, e. g., the tarsal glands of the eyelids, are modified sebaceous. Still 

 others are not yet classified satisfactorily. Some of these special types have been referred to in 

 pre\'ious chapters, and others will receive attention in the special descriptions which foUow. The 

 mammary glands are highly modified cutaneous glands, which are intimately associated in func- 

 tion 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 papillae. 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 papillae, and another at the junction of the corium and 

 subcutis. The lymph vessels form subpapillary and subcutaneous plexuses. 



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

 fibers either end free in the epidermis and in certain parts of the corium, or form 

 special microscopic corpuscles of several' kinds. 



1 To prevent a possible misapprehension, it may be stated that the epidermis primarily 

 molds the corium, and that the glands and hair-foUicles are invaginations of the epidermis. 



2 The papillse 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, eyehds, etc.) the corium contains pigment m its connective-tissue cells. 



