MAMMALIA 



633 



They swallow their food partially chewed and, because of the struc- 

 ture of the stomach, they are able to regurgitate it later for further 

 chewing. For this reason such animals can consume large quantities 

 of bulky food in a short time, then retire to the shade and chew 

 while reclining. The stomach of such an animal is greatly modified 

 by having four divisions. Following the esophagus is the pouchlike 

 rumen at the left, then the small middle reticulum, at the right, is 

 another pouchlike part, the omasum or psalterium, which continues 

 on to the right and posteriorly into the more elongated al) omasum, 

 which in turn joins the duodenum. On the first trip to the stomach, 

 the food passes into the rumen, is stored and moistened. It then goes 

 in small quantities at a time into the reticulum, and this "cud" 



Psa/fer/u/n 



Esophagus 



Aboma^um 



Hunjerj 



Fig. 344. — A ruminant stomach. The arrows indicate the direction of tlie move- 

 ment of the food in the formation and regurgitation of a cud. (From Wolcott, 

 A-nxinal Biology, published by McGraw-Hill Book Company.) 



may pass back to the mouth from here. After it is chewed and re- 

 swallowed it passes through a valve at the entrance to the stomach 

 into the omasum, and on to the abomasum. 



Order Perissodactyla. — This is the group of odd toed mammals in 

 which the axis of the foot is through the third toe. There are no 

 modern forms which are natives of this country with the possible ex- 

 ception of the horse, and this is very indirect. In the horse, ass, and 

 zebra, the foot is reduced to one hoofed toe. The ass and zebra are 

 African and Asiatic forms. Tapirs are piglike with four toes in 

 front and three behind. They are found in southern Asia, and in 

 Central and South America. The rhinoceros is a large Asiatic and 

 African form. 



