78 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



ever, large quantities of saliva are swallowed with the food and 

 it continues its action in the stomach while the food is stored in 

 the cardiac end and only ceases its activity when the food is 

 thoroughly mixed with the acid gastric juice. The conversion 

 of starch into sugar is continued and concluded in the small 

 intestine. 



Deglutition. 



The act of deglutition is commonly divided into three periods, 

 depending upon the part through which the food is passing. 

 During the first period the bolus passes from the mouth through 

 the isthmus of the fauces, during the second through the pharynx, 

 and during the third through the esophagus into the stomach. 

 A brief reference to the anatomy of these parts is necessary. 



Fauces. The isthmus of the fauces is the opening at the back 

 of the mouth, bounded below by the base of the tongue, above 

 by the soft palate and uvula, and laterally by the pillars of the 

 fauces, between which are the tonsils. The anterior pillars are 

 easily seen when the mouth is opened widely, and consist of the 

 palatoglossi muscles with their covering mucous membrane. 

 The posterior pillars approach each other more nearly than the 

 anterior, and consist of the palatopharyngei muscles and their 

 covering mucous membrane. 



Pharynx. The pharynx extends from the basilar process 

 of the occipital bone above about four and a half inches down- 

 ward. It communicates with the posterior nares, the mouth, 

 the Eustachian tubes, the larynx and esophagus. The tube is 

 made up of two coats, an external muscular and an internal 

 mucous. The muscular coat consists of the three constrictors 

 and the stylopharyngeus. The mucous coat is covered in its 

 upper part with columnar ciliated and in its lower part by pave- 

 ment epithelium. 



Esophagus. The esophagus runs a course of about nine 

 inches from the end of the pharynx, at a point behind the cri- 



