78 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



However, it must be admitted that the practical effect of 

 ptyalin in digestion is not very considerable in the mouth 

 mainly because the food is not kept in the mouth long 

 enough. However, 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 con- 

 tinued and concluded in the small intestine. 



Deglutition. 



The act of deglutition is commonly divided into three pe- 

 riods, 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 anat- 

 omy 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, 

 and 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 

 downward. 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 con- 

 strictors and the stylopharyngeus. The mucous coat is cov- 



