288 



THE MAINTENANCE OF THE INDIVIDUAL 



The Stomach. The stomach of vertebrates is likewise subject to 

 considerable variation. In the case of grain-eating birds a distended 

 esophageal region, the crop, is developed for the storage of food. 

 Below this region is the stomach proper, divisible into a glandular 

 stomach, which secretes digestive enzymes, and a muscular gizzard, 



or grinding stomach, 

 that compensates for 



esophagjxs 



rtcmen, 



psalterium 



ahomasutn 



Stomach of a ruminant. What is the function 

 of the valve and what is the significance of "chew- 

 ing the cud" ? (After Walter.) 



the absence of teeth. 



A second example of 

 an outstandingly differ- 

 ent type of stomach ap- 

 pears in the compound 

 stomach of ruminants 

 as, for example, a cow. 

 Here there are four 

 parts, namely, the ru- 

 men, recticulum, psalte- 

 rium, and abomasum, 

 the first two being 

 derivatives of the esoph- 



agus. The more solid food is temporarily stored in the rumen, or 

 paunch, as fast as it is ingested, gradually being passed on into the 

 reticulum where it is mixed further with digestive juicfes and softened. 

 From time to time, ball-like masses of this food are regurgitated from 

 the reticulum and thoroughly mixed with saliva by chewing. This 

 process is commonly known as "chewing the cud." After a time the 

 food is swallowed a second time and if the chewing has sufficiently 

 reduced the mass to a small slippery wad, it passes directly into the 

 psalterium and thence to the abomasum, where it undergoes gastric 

 digestion. 



The human stomach as compared with the compound stomach of 

 the ruminants is of a more simple type, although divisible both 

 histologically and physiologically into several parts. The esophagus 

 enters an expanded cardiac region the entrance of which is guarded 

 by a ringlike sphincter muscle. The stomach is always curved to 

 some extent, the inner or concave surface being known as the lesser 

 curvature and the outer or convex as the greater curvature. The blind, 

 rounded part of the stomach lying to the left and usually opposite the 

 entrance of the esophagus is called the Jundus, while the region closest 

 to the point of entrance of the esophagus is called the cardiac portion ; 



