SKIN 



387 



nature, and referred to it as a rete since it forms a network between the papillae of 

 the corium (Fig. 389). Malpighi considered that the color of the Ethiopian skin was 

 confined to this layer. 



The stratum germinativum and stratum corneum are subdivisions of a 

 single thick stratified epithelium. The basal cells, which rest directly 

 upon the papillae of the corium, constitute a single row of columnar cells, 

 with elongated nuclei and no cell walls (Fig. 390). Through mitotic 

 division these cells multiply and give rise to the outer polygonal cells, 

 but it is noteworthy that mitotic figures are seldom seen. The polygonal 

 cells which form the bulk of the stratum germinativum are connected with 

 one another by slender intercellular bridges (Fig. 43, p. 53), through which 

 fibrils pass from cell to cell. Because of this striking feature, the stratum 

 germinativum was formerly called the stratum spinosum. 



Stratum 

 granulosum. 



/v 



Stratum 

 germinativum 



Corium 

 (Tunica 

 propria.) 



FIG. 390. THE DEEPER PART OF THE EPIDERMIS, FROM THE SOLE 

 OF THE FOOT OF AN ADULT MAN. X 360. 



The transition from the stratum germinativum to the stratum corneum 

 is abrupt. It may be marked by an incomplete layer of coarsely granular 

 cells, such as are highly developed in the skin of the palms and soles, where 

 they form the stratum granulosum (Fig. 390). In the stratum corneum 

 the cells acquire a horny exoplasmic membrane; the bridges become 

 short stiff spines; the protoplasm and nucleus are dry and shrunken; ane 

 in the outermost cells the nucleus wholly disappears. The cells becomd 

 flatter toward the surface, from which they are constantly being des- 

 quamated. 



