INTEGUMENT 



43 



basal layer of this epithelium is composed of columnar cells, 

 while the cells of the upper layers are polygonal in outline, 



Fig. 19. — Section of skin of Rana pipiens, showing a mucous gland. C, 

 stratum compactum; Co, stratum corneum; Ch, chromatophores; E, epidermis; 

 S, stratum spongiosum. 



becoming definitely flattened next to the stratum corneum. 

 When the stratum corneum is lost at molting, its place is taken 

 by the outermost layer of the 

 stratum germinativum, and new 

 cells, formed by cell divisions in 

 the basal layer, are pushed up 

 from below. All of the cells of the 

 epidermis originate in the basal 

 layer. A peculiar histological 

 characteristic of the cells of the 

 stratum germinativum is the pres- 

 ence of delicate processes, called 

 intercellular bridges, connecting 

 adjacent cells (Fig. 20). 



Pigment cells or chromatophores °[ Rana V ipicns : y ^ hX l magnified, 



° . showing intercellular bridges. C, 



OCCUr in Small numbers in the stratum corneum; G, stratum 



epidermis. Cutaneous innerva- germinativum. 

 tion is supplied by nerves terminating in the lower layers of the 

 epidermis. The epidermis is pierced by ducts leading from glands 

 located in the corium. 



Fig. 20. — Section of epidermis 



