48 



EPITHELIAL TISSUES 



broad tapering process which is embedded between the adjacent cells of 

 the deeper layers. The rounded extremities 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 specially 

 characteristic of the detached superficial cells of transitional epithelium. 

 The superficial cells, while somewhat flattened, usually have a thick- 

 ness equal to one-sixth to one-third their transverse diameter. In this 

 respect they differ markedly from the superficial scaly cells of stratified 

 squamous epithelium and are easily distinguished therefrom, even in the 



FIG. 54. ISOLATED CELLS WHICH MAY APPEAR IN HUMAN URINE. 

 A, from the vagina of a woman (stratified squamous epithelium); B, from the 

 ureter of a child (transitional epithelium); a, cells from the deep layers; 6, superficial 

 cell. Moderately magnified. 



isolated condition in which they are frequently found in the urine. 

 The concave facets on their under surface, as well as the peculiar pyri- 

 form shape and small size of the deeper cells, are sufficient to distinguish 

 the transitional cells from those of stratified epithelium. 



There is little, if any, formation of keratin in transitional epithelium. 

 This is possibly explained by the fact that, as it occurs only in the 

 urinary system, this form of epithelium is always well moistened. Differ- 

 entiation of this variety of epithelial tissue, though neglected by some 

 authors, becomes most important in the clinical examination of urine 

 where it is necessary to determine the origin of individual cells. Transi- 

 tional cells from the bladder are easily distinguished from the stratified 

 squamous cells of th*e vagina, urethra, or epidermis. 



