30 



EPITHELIAL TISSUES 



The deepest cells are polyhedral, and these form the greater 

 portion of the membrane. Only the more superficial layers differ 

 therefrom. Those polyhedral cells which lie in the mid-region of 

 the epithelial layer possess a peculiar flask or pear-shape, with well- 

 rounded bodies and a broad tapering process which is embedded 

 between the adjacent cells of the deeper layers. The rounded ex- 

 tremities of the pear-shaped cells fit into peculiar indentations in 

 the deeper surface of the superficial layer of epithelial cells, 

 producing peculiar concave facets, which are particularly char- 

 acteristic of the detached superficial cells of transitional epi- 

 thelium. 



The superficial cells, while somewhat flattened, usually have a 

 thickness equal to one-sixth to one-third their transverse diameter. 

 In this respect they differ markedly from the superficial scaly cells 



FIG. 31. DIAGRAM SHOWING THE MANNER 

 IN WHICH ALL THE EPITHELIAL CELLS 

 OF PSEUDO-STRATIFIED CILIATED EPI- 

 THELIUM REACH THE BASEMENT MEM- 

 BRANE. 



Letters as in the preceding figure. 



FIG. 30. PSEUDO-STRATIFIED COLUMNAR 

 CILIATED EPITHELIUM FROM A BRON- 

 CHIAL TUBE OF MAN. 



a, a goblet cell; 6, cilia; c, superficial 

 cytoplasmic layer; d, deeper nucleated 

 layer, the nuclei of the columnal cells are 

 somewhat more deeply stained than those 

 of the basal cells ; e, basement membrane ; 

 /, connective tissue. Hematein and eosin. 

 x 550. 



of stratified epithelium and are easily distinguished therefrom, 

 even in the isolated condition in which they are frequently found 

 in the urine. The concave facets on their under surface, as well 

 as the peculiar pear-shape and small size of the deeper cells, are 

 sufficient to distinguish the transitional cells from those of strati- 

 fied epithelium. 



There is little, if any, formation of keratin in transitional epi- 

 thelium. This is possibly explained by the fact that, as it occurs 



