56 NORMAL HISTOLOGY. 



increases the tenacity with which the cell-remains adhere to each 

 other when they become hardened and toughened on the surface of 

 the epithelial layer (Fig. 39). 



These delicate bridges connecting neighboring cells are not pecu- 

 liar to stratified epithelium, though they are more conspicuous in 

 that tissue than elsewhere. They have been observed between the 

 cells of the columnar epithelium of the intestinal mucous mem- 

 brane, and also between the cells of other elementary tissues ; e. g., 

 smooth muscular tissue. 



6. Transitional Epithelium (Figs. 40 and 41). This variety re- 

 sembles stratified epithelium in forming layers several cells in thick- 



Prickle cells from human stratified epithelium. (Rabl.) Four cells with delicate processes unit- 

 ing across an intervening space are represented. The lower right-hand cell is just below 

 the upper surface of the section, so that its surface is seen. This is covered with minute 

 spots, which are end views of the prickles directed toward the observer. The nucleus 

 of this cell is not in sharp focus, a fact indicated by the fainter outline in the figure. 



ness, but differs in the character of its superficial cells. These do not 

 undergo the horny change peculiar to stratified epithelium, but con- 

 tinue to increase in size, forming a covering of very large cells lying 

 upon those beneath. Under these largest superficial cells are pyri- 

 form cells lying with their larger, rounded ends next to the topmost 

 layer, while their deeper and more attenuated ends lie between the 

 oval or round cells that form the one or two deepest layers of the 

 epithelium and rest upon the underlying tissues. 



Transitional epithelium is found lining the renal pelves, ureters, 

 and bladder. Its structure permits of a considerable stretching of 

 the tissues beneath without rupture of the epithelial layer over 

 them, the cells of which become flattened to cover the increased 

 surface, to return to their first condition when the viscus which they 

 line is emptied. This is notably the case in the bladder, the epi- 



