yz, 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." The number of ribs varies from twelve (Camelus, 
Hydropotes) through thirteen (Cervus, Gazella) to fourteen in 
Dicotyles, Giraffa, ete. 
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 Anthracotheridae. 
While the stomach of the Perissodactyles is always a simple 
sac, 1t is complicated, or shows signs of complication, in the 
Artiodactyles. That of the Hippopotamus is divided into two 
chambers; there are three in 7ragulus, and four in the typical 
Ruminants such as Cervus, Ovis, ete. 
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 Vitanotheriwm (see p. 266) is exceptional. 
