MAMMALIA. 



575 



present, the hoofs are not compressed and there is no fusion of the 

 metapodials. In Pliocene and Pleistocene times the Hippopotamidi2 

 were found throughout Eurasia. 



Family II. — Suidae. — The pigs have a bunodont dentition with 

 many tubercles which, when worn, form irregular crowns. The canines 

 grow from persistent pulps and form tusks. The dental formula is 



Fig. 390. — The African Water-Chevrotain 

 ( Dorcatheriuin aquaticum) . 



iS^h- 



(From Flower and Lyddeker.) 



The stomach is simple and the diet omnivorous. All 

 four toes are present, but the second and fifth are shortened up and the 

 hoofs of the third and fourth are compressed into the middle line, forming 

 the "cloven hoof." The metapodials and tarsal bones are, however, not 

 yet fused and the ulna and fibula are still unreduced. The placenta 

 is diffuse. The typical pigs are confined to the old world, but the 

 peccaries (Dicotyles) are found in South America ; they differ in 

 dentition from the true pigs. 



P'amily III. — Tragulidae. — This is a small family of little Ungulata 

 called the chevrotains. In dentition they most nearly resemble the Pecora 



