266 



THE SKIN 



It is because of the resulting spinous appearance that the polyhedral 

 cells have been termed prickle cells (Schultze). 



In the thinner portions of the epidermis the prickle cells are imme- 

 diately covered by several layers of hard flattened cells whose nuclei 

 have partially or wholly disappeared, and whose cytoplasm has been 

 changed into a horny, keratin-containing mass. The flattening and 

 desiccation of these cells becomes more pronounced as they approach 



the surface. In the 

 thin portions of the 

 epidermis the change 

 from the prickle cell 

 layer to the horny lay- 

 er is abrupt. 



In the thicker por- 

 tions of the epidermis, 

 as in the palms of the 

 hands, the change is 

 more gradual, and re- 

 sults in the appearance 

 of two additional cell 

 layers, in the cytoplasm 

 of whose cells are in- 

 termediate products of 

 chemical metamorpho- 

 sis, keratohyalin and 

 eleidin, which may be 

 considered as the prede- 

 cessors of the keratin 

 or pareleidin which is 

 peculiar to the cells of 

 the horny portion. 



Granular Layer 

 (Stratum Granulo- 

 surn). In the thicker 

 parts of the cuticle the 

 most superficial prickle 

 cells become slightly 



flattened, and coarse granules appear within their cytoplasm. These 

 cells form the granular layer (stratum granulosum), a double cell layer 

 which occupies the superficial portion of the rete mucosum. 





FIG. 263. SKIN FROM SOLE OF HUMAN FOOT, SHOW- 

 ING SPIRAL DUCTS OF Two SWEAT GLANDS OPENING 



THROUGH THE EPIDERMIS. 



The stratum germinativum is represented by the 

 dark, wavy line; below this is the stratum papillnre of 

 the derma, above the stratum lucidum. 



