198 



THE SKIN 



The layer of stratified epithelium composing the epidermis 

 differs from that of the mucous membranes in that its superficial 

 cells contain an abundance of keratin, a peculiar horny material. 

 The production of keratin in the cells of stratified epithelium 

 appears to -be more or less dependent upon the desiccation which 

 occurs in those cells which form the comparatively dry cutaneous 

 surface. The cornification can scarcely be demonstrated in the 

 stratified squamous epithelium of the moistened mucous membrane 

 of the mouth, esophagus, etc. ; it is present though not pronounced 

 in the partially moistened margins of the eyelids, lips, labia minora, 



glans penis, etc. In the epidermis, 

 however, cornification is pronounced 

 and characteristic in all portions of 

 the body. 



The thickness of the cornified 

 a layers appears to be in proportion 

 to, if not entirely dependent upon, 

 the amount of mechanical violence 

 to which the cutaneous surface 

 is subjected. Accordingly the in- 

 creased thickness of the epidermis 

 covering the palms and soles is 

 found to be due almost entirely to 

 an increase in the superficial horny 

 portion of the epidermis, the ger- 

 minal layers being no more pro- 

 nounced than in other portions of 

 the body. 



The epidermal tissue is divisible 

 into a superficial horny portion con- 

 sisting of flattened, desiccated, corni- 

 / fied cells the stratum corneum or 

 horny layer and a deeper proto- 

 plasmic, so-called "mucous" portion, 



FIG. 178. EPIDERMIS OF THE FOOT. , . , . , , , -, -, T 



which consists of polyhedral and 



a, flattened cells; 6, stratum luci- 

 dum; c, granular layer; d, germinal Cylindrical Cells stratum niUCOSlim, 



, cylindrical cell layer; /, re te mucosum, rete Malpighii. 



Cylindrical Cell Layer (Stratum 

 Cylindricum). The deepest cells 

 of the stratum mucosum are elongated in a direction nearly 

 perpendicular to the basement membrane upon which they rest ; 



layer; 



derma. Picro-carmine. Moderately 



magnified. (After Ranvier.) 



