10 



ANATOMY FOB, NUESES. 



[CHAP. TL 



scaly epithelium, and we may therefore classify it as a protec- 

 tive epithelium. 



2. Transitional epithelium. This is a modification of strati- 

 fied epithelium, consisting only of two or three layers of cells. 



FIG. 5. SECTION OF THE TRANSITIONAL EPITHELIUM LINING THE BLADDER. 

 (Highly magnified.) (E. A. S.) a, superficial ; 6, intermediate ; c, deep layer of cells. 



The superficial cells are large and flattened, having on their 

 under surface depressions into which fit the larger ends of the 

 pear-shaped cells which form the next layer. Between the 

 tapering ends of these pear-shaped cells are one or two layers 

 of smaller, many-sided cells, the epithelium being renewed by 

 division of these deeper cells. This kind of transitional epithe- 

 lium lines the bladder and ureters. 



3. Simple epithelium. This is composed of a single layer of 

 cells. The cells forming single layers are of distinctive shape, 

 and have distinctive functions in different parts of the body. 

 3 The chief varieties are the pavement, col- 

 umnar, glandular, and ciliated. 



In simple pavement epithelium the cells 

 form flat, many-sided plates or scales, which 

 fit together like the tiles of a mosaic pave- 

 ment. It forms very smooth surfaces, and 



FIG. 6. SIMPLE PAVE- , . . , , , . ,, . , , , -, -, 



MENT EPITHELIUM, a, l m es the alveoli of the lungs, the heart, 

 from a serous membrane; blood-vessels, and lymphatics; the mam- 



b, from a blood-vessel. 



mary ducts, the serous cavities, etc. 



The columnar epithelium is a variety of simple epithelium in 

 which the cells have a prismatic shape, and are set upright on 

 the surface which they cover. In profile these cells look some- 

 what like a close palisade, their edges, however, being often 

 irregular and jagged, especially where free or " wander-cells " 



