CH. III.] 



STRATIFIED EPITHELIUM 



31 



ureters is, however, the transitional par excellence. In this variety 

 there are two or three layers of cells, the upper being more or less 

 flattened according to the full or collapsed condition of the organ, 

 their under surface being marked with one or more depressions, into 

 which the heads of the next layer of club-shaped cells fit. Between 

 the lower and narrower parts of the second row of cells are fixed the 



FIG. 44. Epithelium of the bladder, a, one 

 of the cells of the first row ; b, a cell of 

 the second row ; c, cells in situ, of first, 

 second, and deepest layers. (Obersteiner.) 



FIG. 45. Transitional epithelial cells 

 from a scraping of the mucous 

 membrane of the bladder of the 

 rabbit. (V. D. Harris.) 



irregular cells which constitute the third row; sometimes a fourth 

 row is present (fig. 44). If a scraping of the mucous membrane of 

 the bladder is teased, and examined under the microscope, all these 

 forms may be made out (fig. 45). Each cell contains a large nucleus, 

 and the larger and superficial cells often possess two. 



Stratified Epithelium. 



The term stratified epithelium is employed when the cells forming 

 the epithelium are arranged in a considerable number of super- 

 imposed layers. The shape and size of the cells of the different 

 layers, as well as the number of the 

 layers, vary in different situations ; but 

 the superficial cells are, as a rule, of the 

 squamous, or scaly variety, and the 

 deepest of the columnar form. 



The cells of the intermediate layers 

 are of different shapes, but those of the 

 middle layers are more or less rounded. FIG. 46. Epithelium scales from the in- 

 The superficial cells are broad and over- 

 lap by their edges (fig. 46). Their chemical composition is different 

 from that of the underlying cells, as they contain keratin, and are 

 therefore horny in character. 



The really cellular nature of even the dry and shrivelled scales 

 cast off from the surface of the epidermis can be proved by the 



