THE SKIN. 



i3«5 



The epidermis or cuticle, the outer portion of the skin, consists entirely of 

 epithelium and, being partly horny, affords protection to the underlying corium with 

 its vessels and nerves. The thickness of this layer varies in different parts of the 

 body. Usually from .08-10 mm., it is greatest on the flexor surfaces of the hands 

 and feet, where it reaches from .5-9 mm. and from 1.1-1.3 mm. respectively 

 (Drosdoff). 



The cuticle consists of two chief layers, the deeper stratum germinativiim, con- 

 taining the more active elements, and the stratum corneum, the cells of which undergo 

 cornification. Between these layers lies a third, the stratum intermedium, that is 



Fig. 1 149. 



Stratum conieum 



Spiral duct of 

 sweat gland 



Stratum lucidum 



Stratum 

 granulosum 



Stratum 

 germinativum 



Portion of section of skin from sole of foot, showing layers of epidermis. X 70. 



ordinarily represented by only a single row of cells to which the name, stratum 

 granulosum, is usually appHed. This layer' marks the level at which the conversion 

 of the epithelial elements into horny plates begins and also that at which the 

 separation effected by blistering usually occurs. 



On the palms and soles, where the epidermis attains not only great thickness 

 but also higher differentiation, four distinct layers may be recognized in vertical sec- 

 tions of the cuticle. From the corium outward, these are: (i) the stratum germina- 

 tivum, (2) the stratum gr-anulosum, (3) the stratum hicidum and (4) the stratum 

 corneum. The first two represent the portion of the epidermis endowed with the 

 greatest vitality and powers of repair and the last two the horny and harder part. 



The stratum germinativum, or stratum Malpighi, rests upon the outer sur- 

 face of the corium, by the papillae of which it is impressed and, hence, when 

 viewed from beneath after being separated, commonly presents a more or less 

 evident net-work of ridges and enclosed pits, the elevations corresponding to the 



