DIGESTION AND ABSORPTION OF NUTRIENTS 93 



soft, moist surface for the passage of food. Outside the mucous 

 membrane are rings of circular muscle running around the gullet. 



125. Functions of the throat and gullet. The food is quickly 

 forced out of the throat cavity into the gullet, and is pushed slowly 

 down the gullet by the successive contractions of the rings of muscle 

 just described. After being swallowed from the throat, the food 

 does not drop into the stomach, for the walls of the gullet are 

 pressed together by surrounding organs, except when this tube is 

 opened by the passing food. In fact, after practice, one can swallow 

 when standing on one's head, and most quadrupeds (horse, dog, cow), 

 when feeding, hold the head below the level of the stomach. 



IV. THE STOMACH AND ITS FUNCTIONS 



126. Position, size, shape. The stomach is a curved 

 muscular pouch, which lies about midway between the upper 

 and lower ends of the trunk, with its larger end lying toward 

 the left side of the body, where it communicates with the 

 gullet (Fig. 26). When moderately filled, this organ holds 

 3J to 4 quarts. The small intestine is con- 

 tinuous with the right end of the stomach, 



the communication between the two (known 

 as the pylorus, from Greek, meaning gate- 

 keeper) being controlled by a ring of 

 muscle. 



127. The lining of the stomach and the 

 gastric glands. If one examines with a 

 lens the mucous lining of the stomach, a 

 countless number of small openings are 

 seen which look like pin pricks. These 

 are the pores through which a digestive 



fluid known as gastric juice is discharged from the gastric 

 glands (Fig. 31). This digestive fluid is composed of water 



FIG. 31. Three 

 gastric glands. 



