THE DIGESTIVE SYSTEM 157 



dependent upon the construction of the temporomaxillary 

 articulation. 



The movements of mastication, though originating in 

 an effort of the will and under its control, are, for the most 

 part, of an automatic or reflex character, taking place 

 through the medium of the medulla oblongata and in- 

 duced by the presence of food within the mouth. The 

 nerves and nerve-centers involved in this mechanism are 

 the following : 



Afferent, or Excitor Nerves: i. Lingual branch of the 

 fifth pair. 2. Glossopharyngeal. 



Efferent, or Motor Nerves: i. Third branch of the fifth 

 pair. 2. Second hypoglossal. 3. Facial. 



The medulla oblongata not only generates motor im- 

 pulses, but co-ordinates them in such a manner that move- 

 ments of mastication may be directed toward the accom- 

 plishment of a definite purpose. 



Insalivation. Insalivation is the incorporation of the 

 food with the saliva, secreted by the parotid, submaxillary, 

 and sublingual glands. This process will be explained 

 in the chapter devoted to the Glandular System. 



Saliva. Saliva is a colorless liquid, viscid in character, 

 having a specific gravity of 1.005; its composition is: 



Water ...',., 995. 1 6 



Albuminous matter 1.34 



Potassium sulphocyanide 0.06 



Calcareous magnesium and calcareous phosphates . . . 0.98 



Sodium and potassium chlorides 0.84 



Mixture of epithelium . 1.62 



1000.00 



The viscidity of the saliva is due to the mucin which 

 it contains. Saliva also contains an enzyme, called pty- 

 alin, which acts upon the starchy particles of food to con- 

 vert them into dextrin and sugar; and, finally, by the 

 process of hydrolysis into dextrin and maltose. The 



