2/2 STOMACH OF ARTIODACTYLES CHAP. 



can see how this may be purely adaptive, the push of the hind- 

 legs in running needing a firmer support. In Hyomoschus this 

 is the case. The hind-limbs are provided with a cannon bone, 

 while the metacarpals of the fore-feet are still free. 



The number of dorso-lumbar vertebrae is less in the Artio- 

 dactyle than in the Perissodactyle Ungulates. Whereas the former 

 have but nineteen, the latter have, as a rule, twenty-three such 

 vertebrae. 1 The number of ribs varies from twelve (Camelus, 

 Hydropotes) through thirteen (Cervus, Gazella) to fourteen in 

 Dicotyles, Giraffa, etc. 



The curious form of teeth known as " selenodont " is character- 

 istic of the Artiodactyla, though only found well developed in the 

 modern forms, and of those only in the Pecora. The more primitive 

 forms had " bunodont " teeth with typically four tubercles (if we 

 except the tritubercular and but little-known Pantolestes) ; and the 

 intermediate " buno-selenodont " type characterises such groups as 

 the Anthracotheriidae. 



While the stomach of the Perissodactyles is always a simple 



sac, it is complicated, or shows signs of complication, in the 



Artiodactyles. That of the Hippopotamus is divided into two 



chambers ; there are three in Tragulus, and four in the typical 



. Ruminants such as Oervus t Oms, etc. 



Had we to deal only with the still living genera of Artio- 

 dactyles, it would be easy to sort them into two groups on the 

 characters of the teeth ; for the Pigs and Hippopotamus are pro- 

 vided with tubercular molars ; they are bunodont. The Deer, 

 Camels, Oxen, Giraffes, etc., have selenodont molars. Besides, the 

 latter are " Ruminants," and have a more complicated stomach. 

 The existing Chevrotains forbid a more trenchant division, since 

 they are, as will be pointed out in due course, somewhat inter- 

 mediate in structure ; the feet are more Pig-like, and the stomach 

 is not so typically Ruminant. In any case such a division is pre- 

 vented by certain extinct families which are perhaps ancestral to 

 both. They have teeth which are not quite bunodont and not 

 quite selenodont. These teeth have been termed buno-selenodont 

 or buno-lophodont. 



The distribution of the living Artiodactyles presents us with 

 some interesting facts. The vast preponderance of species occurs 

 in the Old World 34 in America as against over 250 species 



1 Titanotherium (see p. 266) is exceptional. 



