MAMMALIA 



337 



herbivorous diet. In the upper jaw the canines are usually 

 degenerate. There are generally no incisors, never more than 

 a single pair, and in their place is a thickened calloused pad. 

 The canines of the lower jaw have taken the form of incisors. 

 The molars are selenodont, with crescent-shaped cusps; the 

 stomach is usually divided into four compartments (Fig. 273), 

 the rumen or paunch, which receivers the food when it is eaten; 

 from here it is regurgitated and chewed again as cud. It is 

 then passed into the second division of the stomach, the reticulu7n, 

 from which it passes into the third division, the omasum; and 

 from there to the true stomach or abomasum. These animals 



Fig. 273. — Stomach of a ruminant (sheep), showing the four compart- 

 ments: a, Esophagus; b, paunch; c, honeycomb or reticulum; tl, liber 

 psalterium or manjrplies; e, true digestive stomach; /, beginning of the in- 

 testine. (After Owen.) 



are usually large and many of them bear horns, which are larger 

 (or exclusively) on the males. 



The Chev'rotain belongs to the primitive Asiatic and African family 

 Tragu'lidw. It is the smallest ungulate living to-day. It has both deer- 

 like and pig-like characteristics. It is hornless and the stomach has but 

 three divisions. 



The camels and llamas {CamcVida') ha\-e long limbs, with no trace of 

 second and fifth toes. The rumen has smooth walls, and from it are devel- 

 oped the water cells (Fig. 274). Camels are wonderfully adapted to their 

 desert home by the sole pads on their feet; by their sandy color; by their 

 long necks, which give long range of vision and enable them to reach the 

 desert shrubs on each side of their path; by their cartilaginous mouth, which 

 enables them to eat the hard and thorny plants of the deserts on which no 

 other animal could subsist; by their small ears; by the valve-like folds by 



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