l6o HUMAN PHYSIOLOGY. 



The amount of skin investing the body of a man of average size is about 

 twenty feet, and varies in thickness, in different situations, from to T 7 of 

 an inch. 



The skin consists of two principal layers viz., a deeper portion, the 

 corium, and a superficial portion, the epidermis. 



The corium, or cutis vera, may be subdivided into a reticulated and a 

 papillary layer. The former is composed of white fibrous tissue, non-striated 

 muscle-fibers, and elastic tissue, interwoven in every direction, forming an 

 areolar network, in the meshes of which are deposited masses of fat, and a 

 structureless, amorphous matter; the latter is formed mainly of club-shaped 

 elevations or projections of the amorphous matter, constituting the papilla; 

 they are most abundant and well developed upon the palms of the hands and 

 upon the soles of the feet; they average T o of an inch in length, and may 

 be simple or compound; they are well supplied with nerves, blood-vessels, 

 and lymphatics. 



The epidermis, or scarf skin, is an extravascular structure, a product 

 of the true skin, and is composed of several layers of cells. It may be divided 

 into two layers: the rete mucosum, or the Malpighian layer, and the horny or 

 corneous. 



The former is closely adherent to the papillary layer of the true skin, and 

 is composed of large nucleated cells, the lowest layer of which, the "prickle 

 cells," contains pigment-granules, which give to the skin its varying tints 

 in different individuals and in different races of men; the more superficial 

 cells are large, colorless, and semi-transparent. The latter, the corneous 

 layer, is composed of flattened cells, which, from their exposure to the atmos- 

 phere, are hard and horny in texture; it varies in thickness from of an 

 inch on the palms of the hands and soles of the feet to 9^0 of an inch in the 

 external auditory canal. 



APPENDAGES OF THE SKIN. 



Hairs are found in almost all portions of the body, and can be divided 

 into 



1. Long, soft hairs, on the head. 



2. Short, stiff hairs, along the edges of the eyelids and nostrils. 



3. Soft, downy hairs on the general cutaneous surface. 



They consist of a root and a shaft. The latter is oval in shape and about 

 ^o of an inch in diameter; it consists of fibrous tissue, covered externally 

 by a layer of imbricated cells, and internally by cells containing granular 

 and pigment material. 



