228 THE INTERNATIONAL MONTHLY. 
side arches of the skull. A representative of this series has also 
been found in the " phosphorite " deposits of southern France. 
The other side branch of the rhinoceros stem developed along 
lines quite opposite to those taken by the series just described. 
It also is first recognizable in the middle Eocene in animals of 
rather small size, but of quite stout build, with slender and horn- 
less skulls and simple premolar teeth ; they had short necks and 
rather short, heavy limbs, with four toes in the front foot and 
three in the hind, a number which is all but universal in the 
perissodactyls of the Bridger. The Uinta form differs from its 
Bridger predecessor chiefly in the greater length and slenderness of 
its limbs, in the loss of one toe from the fore foot and in the 
increased complexity of the premolar teeth, which are beginning 
to assume the molar pattern. This series, like the preceding one, 
reaches its culmination in the White River, and the genus of that 
formation (Hyracodon) is one of unusual interest. In proportions 
and appearance it might almost be called a rhinoceros-horse, 
though its short, deep, and somewhat clumsy head is very different 
from the slender and graceful head seen in all the horses, even 
the earliest. All of the anterior teeth (incisors and canines) are 
very small, and could not have served as weapons, though none 
of them has been suppressed, and they are all alike in size and 
shape. The transformation of the premolars to the molar pat- 
tern is now complete, and all of the grinding teeth have the 
characteristic rhinoceros-like construction. The neck is slender 
and long, longer proportionately than in the contemporary White 
River horse ; the trunk is small and the limbs differ notably from 
those of all other rhinoceroses in their length and slenderness. 
The feet also are quite long and narrow and the lateral toes are 
so reduced that the tendency to monodactylism is very marked. 
Had this line survived, it would very probably have terminated in 
one-toed rhinoceroses ! Being almost defenceless, and having 
neither horns nor teeth that could be used as weapons, Hyracodon 
must have been dependent upon its powers of speed for safety 
from its enemies, and it had thus become a lightly built, slender, 
cursorial rhinoceros, which, judging from the modern world, 
