80 HUMAN PHYSIOLOGY. 



about twenty feet, and varies in thickness, in different situations, from the 

 Y% to the T J^ 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 muscular fibres and elastic tissize, 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 the soles of the feet ; they average the y l^ 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 extra-vascular structure, a product 

 of the true skin, and 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 closely applies itself to the papillary layer of the true skin, 

 and is composed of large, nucleated cells, the lowest layer of which, the 

 " prickle cells," contain 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 atmosphere, are hard and horny in texture ; it varies in 

 thickness from */ of an inch on the palms of the hands and feet, to the 

 F i0 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 (l) 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, which is oval in shape, and 

 about the ? l^ 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. 



The Root of the hair is embedded in the hair follicle, formed by a tubular 

 depression of the skin, extending nearly through to the subcutaneous tissue ; 

 its walls are formed by the layers of the corium, covered by epidermic cells. 



