EPITHELIUM. 



[CH. III. 



This transformation is a normal process continually going on 

 throughout life, the discharged mucin contributing to form mucus. 

 The cells themselves may recover their original shape after dis- 

 charge, and repeat the process later on. 



Ciliated Epithelium. 



The cells of ciliated epithelium are generally of columnar 

 shape (fig 40), but they may occasionally be spheroidal (fig. 41). 



Fig. 40. Ciliated epithelium from the human 

 trachea, a, large fully formed cell ; 

 6, shorter cell ; c, developing cells with 

 more than one nucleus. (Cadiat.) 



Fig. 41. Spheroidal ciliated 

 cells from the mouth of 

 the frog, x 300 diame- 

 ters. (Sharpey.) 



Each cell is surmounted by a bunch of fine tapering filaments. 

 They were originally called cilia because of their resemblance in 



Fig. 42. Ciliated epithelium of the human trachea, a, layer of longitudinally arranged 

 elastic fibres ; b, basement membrane ; c, deepest cells, circular in form ; rf, inter- 

 mediate elongated cells ; e, outermost layer of cells fully developed and bearing cilia. 

 X 350. (Kolliker.) 



shape to eyelashes. They differ from eyelashes in being 

 extremely small, and in not being stiff; they are in fact composed 



