10 



THE ELEMENTARY TISSUES 



of the ciliated epithelial cells presents on its free surface twenty 

 or more small, hair-like, protoplasmic appendages, called cilia. 

 During life these small processes are in constant rapid motion, 

 waving in a direction toward the outlet of the cavity in which 



FIG. 5. Ciliated epithelium of the human trachea. 



a, layer of longitudinally arranged elastic fibers; b, basement membrane; c, deep- 

 est cells, circular in form; d, intermediate elongated cells; e, outermost layer of cells 

 fully developed and bearing cilia. Xsso. (Kirkes after Kolliker.) 



they are found. In the genital organs they are important in 

 bringing together the male and female elements of reproduction, 

 while in the respiratory tract they are concerned in aiding the 

 passage of the mucus and in the expul- 

 sion of foreign bodies. 



(b) Goblet cells are found on all sur- 

 faces covered by columnar epithelium, 

 but especially in the large intestine. 

 They secrete mucin, the main constit- 

 uent of mucus, which so distends the 

 cell that it ultimately bursts and sets 

 free its contents. 



(c) Pigmented epithelium is ordinary 

 epithelium, the protoplasm of which has become invaded and 

 colored by foreign matter, such as fat, proteid, etc. Such cells 

 are constant in the deeper layers of the epidermis, especially of 



FIG. 6. Goblet cells. 

 (Halliburton after Klein.} 



