DIGESTION 



In all probability the saliva does not digest all the starch taken as 

 food, the greater part passing unchanged from the stomach into the 

 intestine. 



. It is undoubtedly the abundant secretion of the parotid glands which 

 becomes most completely incorporated with the food during mastication 

 and which serves to unite the dry particles into a coherent mass. The 

 secretions from the submaxillary and sublingual glands and from the 

 small glands and follicles of the mouth, being more viscid and less in 

 quantity than the parotid secretion, penetrate the alimentary bolus less 

 easily and form a glairy coating on its exterior, agglutinating the 

 particles near the surface. 



When the processes of mastication and in salivation have been com- 

 pleted and the food has passed into the pharynx, it meets with the 

 products of the pharyngeal glands, which still further coat the surface 

 with the viscid secretion that covers the mucous membrane in this situ- 

 ation, thus facilitating the first part of deglutition. 



It has been observed that the saliva engages bubbles of air in the 

 alimentary mass. In mastication, a considerable quantity of air is mixed 

 with the food, and this facilitates the penetration of the gastric juice. 

 It is well known that moist bread and articles that can not become 

 impregnated in this way with air are not easily acted on in the 

 stomach. 



DEGLUTITION 



Deglutition is the act by which solid and liquid articles are passed 

 from the mouth into the stomach. The process involves first, the pas- 

 sage, by an automatic movement, of the alimentary mass through the 

 isthmus of the fauces into the pharynx ; then, rapid contraction of the 

 constrictors of the pharynx, by which it is forced into the oesophagus ; 

 and finally, a peristaltic action of the muscular walls of the oesophagus, 

 extending from its opening at the pharynx to the stomach. 



Physiological Anatomy of the Parts concerned in Deglutition. The 

 parts concerned in this process are the tongue, the muscular walls of 

 the pharynx and the oesophagus. In the passage of food and drink 

 through the pharynx, it is necessary to protect from the entrance of 

 foreign matters a number of openings that are exclusively for the passage 

 of air. These are the posterior nares and the Eustachian tubes above, 

 and the opening of the larynx below. 



The tongue is the chief agent in the passage of the alimentary bolus 

 into the pharynx ; but a study of all the muscles brought into action 

 would involve anatomical descriptions out of place in this work. The 



