28 



ANATOMY FOR NURSES 



[Chap. IU 



transparent membrane raised from the surface being epithelial 

 tissue — in this situation called epidermis, because it lies upon 

 the surface of the true skin. In other situations, epithelial 

 tissue usually receives the general name of epithelium. 



We may classify the varieties of epithelium according to the 

 shape of the cells which compose them, or according to the arrange- 

 ment of these cells in layers. Adopting the latter and simpler 

 classification, we distinguish three main varieties : — 



1. The simple, consisting of a single layer of cells. 



2. The transitional, consisting of two or three layers. 



3. The stratified, consisting of many layers. 



1. 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. The 

 chief varieties are : — 



a. pavement b. columnar c. ciliated 



(a) Pavement epithelium. — This is also called squamous or 

 scaly epithelium. The cells form flat, many-sided plates or scales, 

 which fit together like the tiles of a mosaic 

 pavement. It forms very smooth surfaces, 

 and lines the heart, blood-vessels, and lym- 

 phatics, the mammary ducts, the serous 

 cavities, etc. 



(6) Columnar epithelium. — The colum- 

 nar epithelium is a variety of simple epi- 

 thelium in which the cells have a prismatic 

 shape, and are set upright on the surface 

 which they cover. In profile these cells look somewhat like a 

 close palisade. They taper somewhat toward their attached end, 

 which is set upon a basement membrane. 

 Columnar epithelium is found in its most 

 characteristic form lining the intestinal 

 canal. 



(c) Ciliated epithelium. — In ciliated epi- 

 thelium the cells, which are generally colum- 

 nar in shape, bear at their free surface little 

 hair-like processes (strongly suggestive of 



eyelashes) , which are agitated incessantly with a lashing or vibrat- 

 ing motion. These minute and delicate processes are named cilia, 



Fig. 9. — Simple Pave- 

 ment Epithelium. a, 

 from a serous membrane ; 

 6, from a blood-vessel. 



Fig. 10. — Simple CoL- 



UMN.\R EpITHELIU.M. O, 



the cells ; b, intercellular 

 substance between the 

 lower end of cells. 



