Mammalia: Classification 735 



Fig. 568. \ highly specialized aonruminant mouth — hippopotamus. (Courtesy, 

 Museum of Comparative Zoology, Harvard University.) 



long curved tusks, especially prominent in male; molars with rounded 



•i 1 I o 



cusps (bunodont type); formula for pig, i ^ cy p -r> m - Stomach 



simple. Two Families: 



Suidae: Pig (Sus), peccary (Fig. 567). 



Hippopotamidae: Hippopotamus (Fig. 568). 



Suborder RUMINANTIA (SELENODONTIA). Usually only 



two functional digits (third and fourth), their two metacarpals or 



metatarsals fused into a single long "cannon bone," the second and 



fifth much reduced or lacking. Upper incisors small or usually lacking; 



canines small or lacking; molars with crescentic ridges (selenodont 



3 3 

 type); usual formula, iyCTip^m^ (Fig. 569). Stomach complex — 



i.e., divided into several compartments, usually four (Fig. 570). Feed- 

 ing and chewing are separated. Food, swallowed unchewed, passes into 

 the more anterior one or two compartments for temporary storage. 

 After feeding is finished, masses of the food are regurgitated into the 

 mouth and thoroughly chewed at leisure ("chewing the cud,'* or 

 rumination). It is then swallowed in a finely divided and semifluid 

 state and, by action of a valvular arrangement, is caused to pass 

 directly into the posterior division of the stomach, where it is digested. 



The several Families fall into three groups, as follows: 



TYLOPODA: 



Camelidae : Teeth exceptional in that a pair of upper incisors and 

 all four canines are present. No horns or antlers. Camels — the drome- 



