136 THE ABDOMEN. 



tended the bladder extends up into the abdominal cav- 

 ity, as does the uterus also when enlarged. 



Salivary Digestion. Although most of the digestive or- 

 gans are situated in the abdomen, the food enters the body 

 through the mouth, where its prehension is a voluntary 

 act. Here digestion also begins and from the first the 

 process is a double one, mechanical and chemical, me- 

 chanical digestion consisting largely of muscular move- 

 ments by which the food is ground up and carried through 

 the digestive tract. Thorough mastication or grinding 

 of the food by the teeth is necessary, while the tongue 

 assists by moving the food about and by mixing it 

 thoroughly with the saliva, a viscid fluid composed of 

 water and salts and having a slightly alkaline reaction. 

 The saliva is secreted by the parotid, sublingual, and 

 submaxillary glands, and serves to soften and dissolve the 

 food and by virtue of its unorganized ferment, ptyalin, to 

 convert starch into sugar. Upon proteins and fats it has 

 practically no digestive action. Moderate warmth and 

 an alkaline medium favor its action, while extremes of 

 heat or cold or an acid medium hinder it. There is little 

 absorption in the mouth, though starch, nicotine, and 

 alcohol may be absorbed in small quantities. 



The Pharynx. When the food is ready for deglutition 

 or swallowing, it is thrust back into the pharynx, a some- 

 what conical, musculo-membranous sac, situated, base 

 upward, behind the nose and mouth and behind, but 

 somewhat above, the larynx. The pharynx is about four 

 and a half inches long and ends on a level with the 

 cricoid cartilage in the esophagus or gullet. It is at- 

 tached to the vertebrae at the back and opens in front 

 into the mouth. The posterior nares, the Eustachian 

 tubes, and the larynx also open into it, the last being pro- 

 tected by the epiglottis, which closes during deglutition 

 to prevent food from entering the air passages, just as 

 the soft palate is drawn back to prevent regurgitation of 

 food into the nose. There are three coats to the 

 pharynx; 1. a mucous coat continuous with that of the 



