:*< ZOOLOGY. 



3. This operation is an important <>nr, inasmuch a< the 

 more the food is masticated the easier will lie the digestion. 

 When sucli instruments an- wanting in animals whose I'ood 

 still requires trituration, this is efl'retrd by other means. The 

 gi//ard, tor example, in jnuny birds is sufficiently strong to 

 answer this purpose. 



Insalivation. 



57. Whilst the food is undergoing trituration in the 

 mouth, it iml)ibes saliva, which sometimes even dissolves it. 



58. The saliva is formed partly in little mucous cavities 

 hollowed out of the mucous membrane of the mouth, partly 

 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 

 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 amygdala', or tonsils. 



The mixed saliva coming from these various souret >. is 

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

 tion, there exist a peculiar principle called ptyaline and 

 animal diastase, various salts, as sea salt or chlorin 

 sodium, tartrate of soda, and a little uncombined soda, ren- 

 dering the saliva alkaline. 



The saliva thus mixed with the food facilitates mastica- 

 tion, assists in deglutition, and obviously aids in the digestion 

 of some kinds of food. 



Deglutition. 



59. In mammals, between the buccal cavity and the 

 pharynx, is a moveable muscular partition, the jir/nlulnua 

 palate, (Fig. 23,) which, during mastication, separates the 

 two cavities t'roi u each other; but so soon as this is accom- 

 plished, the elementary mass or bolus being pressed back- 

 wards by the tongue, the pendulous palate is drawn upwards 

 and backwards, so as to permit of the passage of the food 

 or drink through the isthmus into the pharynx. At this 



