30 ANATOMY FOR NURSES [Chap. Ill 



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 epithelium lines the 

 bladder and ureters. 



3. Stratified epithelium. — This consists of main' layers of cells. 

 The cells composing the different layers differ in shape. As a rule, 

 the cells of the deepest layer are columnar in shape ; the next, 

 rounded or many-sided, whilst those nearest the surface are always 

 flattened and scale-like. The deeper soft cells of a stratified 

 epithelium are separated from one another by a system of channels, 

 which are bridged across by numerous fibres. These cells are often 

 described as prickle cells, as when separated they appear beset with 

 spines. They are continually multiplying by cell-division, and as 

 the new cells which are thus produced in the deeper parts increase 

 in size, they compress and push outward those previously formed. 





Fig. 13. — Section of Stratified Epitheliu.m. c, lowermost columnar cells; 

 P, polygonal cells above these ; fl., flattened cells near the surface. Between the 

 cells are seen intercellular channels, bridged over by processes which pass from cell 

 to cell. (Schafer.) 



In this way cells which were at first deeply seated are gradually 

 shifted outward and upward, growing harder as they approach the 

 surface. The older superficial cells are being continually rubbed 

 off as the new ones continually rise up to supply their places. 



Stratified epithelium covers the anterior surface of the eye, 

 lines the mouth, the chief part of the pharynx, the oesophagus, the 

 anal canal, part of the urethra, and in the female the vagina and 

 neck of the uterus. 



Its most extensive distribution is over the surface of the skin, 

 where it forms the epidermis. Whenever a surface is exposed 

 to friction, we find stratified scaly epithelium, and we may there- 

 fore classify it as a protective epithelium. 



