ARTIODACTYLA, 755 
nature of the tarsal bones, the tendency that ‘the stomach 
has to be complex (as in Camels and Ruminants), are im- 
portant characteristics. There are others of less obvious 
importance, such as the absence of the alisphenoid canal, 
which in Perissodactyla encloses the external carotid artery 
as it passes along the alisphenoid. 
There are primitive extinct Artiodactyla which connect 
the four modern groups—Suina, Tylopoda, Tragulina, 
and Pecora. Thus they unite the bunodont types, such 
as pigs, with cone-like tubercles on the crowns of the 
molars, and the selenodont types, such as cattle, with the 
tubercles expanded from before backwards, and curved in 
crescents. 
Group 1. Suina—hippopotamus, pigs, and peccaries. The molars are 
bunodont ; the third and fourth metacarpals and metatarsals are 
not completely fused as ‘‘ cannon bones.” 
Hippopotamide.—Huge African mammals, included in the single 
‘ genus Hippopotamus. They spend the day in the rivers and 
lakes, swimming and diving well, but usually remaining concealed. 
At night they come on land and browse on grass and herbage. 
The skin is extremely thick, with a few hairs restricted to the 
snout, head, neck, and tail. There are four toes on each foot, all 
reaching the ground. The rootless incisors continue growing ; 
so do the large curved canines; the dental formula is =3+*43 
4 1-3, 143° 
The stomach ‘has three,chambers ; there is no ceecum. 
Suidee.—The Old World boars and pigs, ‘characterised by the mobile 
snout and terminal nostrils. There are four well-developed 
digits on the narrow feet, but the second and fifth do not reach 
the ground in walking. The incisors are rooted; the upper 
canine curves outwards or upwards. The stomach is almost 
simple, but has more or less of a cardiac pouch and several 
short blind saccules ; there is a cecum. 
Examples.—Sus, eee Babirusa, Som the male with remarkable 
canines, the upper pair growing upwards from their base 
through the skin, arching backwards as far as the forehead, 
and sometimes forwards and downwards again, the lower pair 
with a more or less parallel course; Phacocherus, the wart-hog. 
Dicotylide.—The New World peccaries (Décoty/es), with a snout 
like that of pigs, with four toes on the fore-feet, and three behind. 
The incisors are rooted, the upper canines are directed down- 
wards, the dental formula is 83, The stomach is complex, and 
3133 Plex, 
there is a caecum. 
Group 2.—Tylopoda, comprising the family Camelidze—the camels 
of the Old’ World and the llamas of S. America. The limbs 
