THE HIPPOPOTAMIDiE. 319 



the great distributional provinces except the Australian* and 

 Novo-Zelanian. JPorcus is peculiar to part of the Malay Ar- 

 chipelago, Dlcotyles to South America, and Phacoclioerus to 

 South Africa. 



A great variety of swine-like TTngulata existed during the 

 deposition of the older tertiary strata, and are the earliest 

 known members of the group. 



b. The IIlppopotainid(B are represented at present only by 

 the genera JELippopotamus and Ghceropus. These animals 

 have a huge head, a heavy body, covered with a thick integu- 

 ment, provided with scanty hairs, and short, stout, tetradactyle 

 limbs, all the four toes of which rest on the ground. The 

 female has inguinal teats, and the male is devoid of a scrotum. 



The dental formula of the adult JSlppopotamfius is i. ^ 



c. W p.m. ^ m. 3-^, while Chmropus has only two incisors in 



the lower jaw. The tubercles of the molar teeth, when ground 

 down by mastication, present a double trefoil pattern, and the 

 hindermost inferior molar is trilobed. The incisors are straig-ht 

 and tusk-like. The very large and curved canines are directed 

 downward in the upper jaw, upward in the lower. Their mu- 

 tual attrition wears the anterior face of the extremity of the 

 upper, and the posterior face of that of the lower, flat. 



The milk dentition consist of d.i. J^ d.c. i^J d.m. ^t The 



06 1 • I 4.4 



last lower deciduous molar is trilobed, and the first deciduous 



molar persists a long time, and seems not to be replaced. 



The stomach is divided into three or four compartments, 

 and there is no coecum. The liver has a gall-bladder, and the 

 kidneys are lobulated. 



The skeleton is very pig-like, but in some respects ap- 

 proaches the Ruminants. The centra are slightly convex in 

 front, and concave behind, in the cervical region, but not else- 

 where. The prezygapophyses overlap the postzygapophyses 

 in the posterior dorso-lumbar vetebr^e. On the other hand, the 

 transverse processes of the last lumbar vertebrae articulate 

 with those of the preceding and succeeding vertebra, as in 

 the Horse and other Perissodactyles. 



In the skull the orbits are nearly complete jDosteriorly. and 

 they become almost tubular by the outward production of the 

 frontal and lachrymal bones. 



The nasals and premaxillae unite for a great extent. The 



♦ The Papuan pig may have been introduced from the westward. 



