EPITHELIUM, 



33 



commonly smaller than those which are free. Each of such 

 cells encloses, at nearly mid distance between its base and 

 apex, a flat nucleus with nucleoli (B, fig. 5) ; the nuclei 

 being arranged at such heights in contiguous cells as not 

 to interfere with each other by mutual pressure. 



4. The fourth variety of epithelium cells, usually 

 cylindrical, but occasionally of some other shape, are pro- 

 vided at their free extremities with several fine pellucid 

 pliant processes or cilia (figs. 6 and 7). This form of epi- 

 thelium lines the whole respiratory tract of mucous mem- 

 brane and its prolongations. It occurs also in some parts 



Fig. 6.* 



i9- 7-t 



of the generative apparatus ; in the male, lining the vasa 

 cfferentia of the testicle, and their prolongations as far as 

 the lower end of the epididymis ; and, in the female com- 

 mencing about the middle of the neck of the uterus, and ex- 

 tending to the fimbriated extremities of the Fallopian tubes, 

 and for a short distance along the peritoneal surface of the 

 latter. A tesselated epithelium, with scales partly covered 

 with cilia, lines, in great part, the interior of the cerebral 

 ventricles. 



If a portion of ciliary mucous membrane from a living or 

 recently dead animal be moistened and examined with a 

 microscope, the cilia are observed to be in constant motion, 



* Fig. 6. Spheroidal ciliated cells from the mouth of the frog ; 

 magnified 300 diameters (Sharpey). 



t Fig. 7. Columnar ciliated epithelium cells from the human nasal 

 membrane ; magnified 300 diameters (Sharpey). 



D 



