610 ANATOMY OF VERTEBRATES. 



CHAPTER XXXV. 



TEGUMENTAKY SYSTEM AND APPENDAGES OF MAMMALIA. 



357. Derm.- -The main constituent of the skin of Mammals 

 consists of an interlacement of fibres of the white or sclerous 

 kind, fig. 486, f, continuous with those of the subjacent areolar 

 tissue, z, but more or less abruptly defining a firm sheet of strong 

 and tough fasciculate framework investing the body : the looser 

 central or initial texture, i, includes, in its larger meshes, fat, 

 sweat-glands, A, bulbs of hair, of bristles, or of spines, with seba- 

 ceous follicles, according to the species : it is traversed by the 

 nerves of the sensitive or tactile papillae, d, by sweat-ducts and by 

 arteries, veins, and absorbents : it is covered by the epiderm, c, a. 

 With the sclerous fibres of the derm are blended a varying pro- 

 portion of the yellow elastic fibres, and of unstriped muscular 

 tissue, especially in relation to the roots of the hairs or spines. 



The texture of the derm is firmest at its periphery, where its 

 surface is best defined : its thickness varies in relation to the 

 bulk of the species and to other circumstances ; it is such, e.g., in 

 certain Perissodactyles and the Hippopotamus, as to have suggested 

 the name of ' Pachyderm ' for an artificial group of Ungulates in 

 the Cuvierian system. In the full-grown Giraffe the corium 

 hardly exceeds half an inch in thickness at any part : in the 

 Indian Hhinoceros, of about the same weight, the average thick- 

 ness of the derm is between two and three inches : it is thinner 

 on the less exposed surfaces and at the bending of the joints. In 

 the large specimen which I dissected the integument 011 the 

 middle line of the abdomen presented a general thickness of three- 

 fourths of an inch : on the inner side of the extremities, it was 

 about one-fourth of an inch in thickness. It was connected to 

 the abdominal parietes by a loose cellular tissue, and by a closer 

 one to most of the other parts of the body ; but the parts to 

 which the stiff and ponderous hide most firmly adhered were the 

 spinous processes of the posterior lumbar and sacral vertebrae, 

 and the anterior extremities of the iliac bones, at which places 

 the corium was blended with the periosteum, and was thin. 

 The derm adhered over the jugal bones to a kind of movable 



