EPITHELIUM. 



tions. It occurs also in some parts of the generative apparatus ; 

 in the male, lining the vasa efferentia of the testicle, and their 

 prolongations as far as the lower end of the epididymis; and 



FIG. 6. 



FIG. 7. 



FIG. 6. Spheroidal ciliated cells from the mouth of the frog ; magnified 300 diameters 

 (Sharpoy). 



FIG. 7. Columnar ciliated epithelium cells from the human nasal membrane ; 

 magnified 300 diameters (Sharpey). 



in the female commencing about the middle of the neck of the 

 uterus, and extending to the fimbriated extremities of the 

 Fallopian tubes, and for a short distance along the peritoneal 

 surface of the latter. A tessellated epithelium, with scales 

 partly covered with cilia, lines, in great part, the interior of 

 the cerebral ventricles, and of the minute central canal of the 

 spinal cord. 



If a portion of ciliary mucous membrane from a living or 

 recently dead animal be moistened and examined with a micro- 

 scope, the cilia are observed to be in constant motion, moving 

 continually backwards and forwards, and alternately rising 

 and falling with a lashing or fanning movement. The ap- 

 pearance is not unlike that of the waves in a field of wheat, 

 or swiftly running and rippling water. The general result of 

 their movements is to produce a continuous current in a de- 

 terminate direction, and this direction is invariably the same 

 on the same surface, being usually in the case of a cavity 

 towards its external orifice. 



Uses of Epithelium. The various kinds of epithelium serve 

 one general purpose, namely, that of protecting, and at the 

 same time rendering smooth, the surfaces on which they are 

 placed. But each, also, discharges a special office in relation 

 to the particular function of the membrane on which it is 

 placed. 



In mucous and synovial membranes it is highly probable 

 that the epithelium cells, whatever be their forms and what- 

 ever their other functions, are the organs in which by a regular 

 process of elaboration and secretion, such as will be afterwards 



