MASTICATION. 33 



by glands situated around this cavity, and communicating 

 with it. These glands are composed of small granulations, 

 agglomerated. In man there exist three salivary glands on 

 each side, placed around the lower jaw; the parotid, the sub- 

 maxillary, and the sublingual. They have each an excretory 

 duct, by which their secretions are poured into the mouth in 



From Valentin.* 



variable quantities. The follicles of the mucous membrane of 

 the mouth are disseminated partly over the surface of the 

 tongue and cheeks, and partly collected into two groups, 

 situated in the isthmus or passage by which the mouth com- 

 municates with the pharynx. These little masses of follicles 

 are called amygdalae, or tonsils. 



The mixed saliva coming from these various sources is 

 composed of 993 parts of water to 1000 of saliva. In addi- 



* In the act of mastication the lower jaw (a, i) is pressed against the im- 

 movable upper one (k, g). Since the upper and lower rows of teeth are 

 arranged symmetrically, it is only the corresponding masticatory surfaces of 

 opposed teeth which work upon each other. 

 D 



