EXCRETION. 



487 



man and from i.i to 1.17 square meters in woman. It varies in thickness 

 in different localities of the body from J to -^^ of an inch. The skin 

 consists of two principal layers: viz., a deep layer, the derma or corium, 

 and a superficial layer, the epidermis. 



The derma or corium may be subdivided into a reticulated and a pa- 

 pillary layer. The reticulated layer consists of white fibrous and yellow 

 elastic tissue, non-striated muscle-fibers, woven together in every direction 

 and forming an areolar network, in the meshes of which are deposited 

 masses of fat and a structureless amorphous matter; the papillary layer con- 

 sists mainly of club-shaped elevations or projections of the amorphous 

 matter constituting the papillae. The reticulated layer serves to connect 

 the skin with the underly- 

 ing structures and to afford 

 support for the blood-ves- 

 sels, nerves, and lymphat- 

 ics which are distributed 

 to the papillae (Fig. 225). 



The epidermis is an 

 extra-vascular structure 

 consisting entirely of epi- 

 thelial cells. It may also 

 be subdivided into two 

 layers the Malpighian or 

 pigmentary layer, and the 

 corneous or horny layer.^ * 

 The former is closely ap- 

 plied to the papillary layer 

 of the true skin and is 

 composed of large nucle- 

 ated cells, the lowest layer 

 of which, the "prickle 

 cells," contains the pig- 

 ment granules which give 

 to the skin its varying 

 hues in different individ- FIG. 225. SECTION PERPENDICULARLY THROUGH THE 

 uals and in different races HEALTHY SKIN, a Epidermis or scarfskin. b. Rete mu- 

 . ,, , cosum, or rete malpighn. c. Papillary layer, a. Derma, 



of men; the corneous layer corium> or true sk i n . e. Pannicuius aiposus, or fatty tis- 



is Composed Of flattened sue. /, g, h. Sweat-gland and duct, i, k. Hair, with its 



cells which from their ex- follicle and P a P illa ' * Sebaceous s land - , 

 posure to the atmosphere, etc., are hard and horny in texture. 



The Sweat-glands. These glands are tubular in shape, the inner 

 extremity of each being coiled upon itself a number of times, forming a 

 little ball situated in the derma or the subcutaneous connective tissue. From 

 this coil the duct passes up in a straight direction to the epidermis, where 

 it makes a few spiral turns, after which it opens obliquely on the surface. 

 The gland consists of a basement membrane lined with epithelial cells. 

 It is supplied abundantly with blood-vessels and nerves. The sweat 

 glands are extremely numerous all over the cutaneous surface, though 

 they are more thickly*' disposed in some situations than others. They 



