MAMMALS 



321 



muscular contractions. They live on aquatic plants and 

 the herbage along rivers. 



Certain species of the even-toed mammals differ from the 

 hippopotamus in the structure of the stomach and in the 

 manner of masticating the food. For example, an ox, 

 sheep, camel, deer, etc., are said to " chew the cud." 

 Therefore, these mammals are known as ruminants. 



Fig. 210. — Stomach of a ruminant: a, gullet; 6, rumen; c, reticulum; 

 d, psalterium ; e, abomasum. 



The stomach of a ruminant is divided into four compart- 

 ments, known, respectively, as the rumen, or paunch; the 

 reticulum, or'honeycomh ; the psalterium, or hook ; and the 

 abomasum, or stomach proper (Fig. 210). While an ox is 

 grazing, the food is swallowed without mastication, and, 

 together with saliva, passed directly into the rumen, or 

 paunch, and reticulum. After the animal finishes eating, 

 the food is brought back to the mouth — a small quantity 

 at a time, which constitutes the cud — and is thoroughly 

 masticated. This time, after being swallowed, the food 

 goes to the psalterium, and thence to the abomasum, or 



herrick's zool. — 21 



