POLYHEDEAL OR SPHEROIDAL EPITHELIUM. 29 



Polyhedral or spheroidal epithelium is characteristic of many secret- 

 ing glands. Columnar and ciliated epithelium are for the most part 

 found covering the inner surface of mucous membranes ; which are 

 membranes moistened by mucus and lining passages in communication 

 with the exterior, such as the alimentary canal and the respiratory and 

 generative passages. 



The detailed study of most of these may be reserved until the 

 organs in which they occur are respectively dealt with. 



The hairs and nails and the enamel of the teeth are modified epithelial 

 tissues. 



