250 THE HISTORY OF CREATION, 
half of the Thick-skinned animals—rhinoceroses, tapirs, and 
paleeotheria—manifest the closest relationships to horses, 
and have like them odd-toed feet; whereas the other 
half of the Thick-skinned animals—pigs, hippopotami, and 
anoplotheria—on account of their double-toed feet are much 
more closely allied to ruminating animals than to the 
former. Hence we must, in the first place, among Hoofed 
animals distinguish the two orders of Paired-hoofs and Odd- 
hoofs, as two natural groups, which developed as diverging 
branches out of the old tertiary primary group of Primary 
Hoofed animals, or Prochela. 
The order of Odd-hoofed animals (Perissodactyla) com- 
prises those Ungulata in which the middle (or third) toe of 
the foot is much more strongly developed than the others, 
so that it forms the actual centre of the hoof. This order 
includes the very ancient, common, primary group of all 
Hoofed animals, that is, the Primary-hoofed animals (Pro- 
chela), which are found in a fossil state in the oldest Eocene 
strata (Lophiodon, Coryphodon, Pliolophus). Directly allied 
to this group is that branch which is the actual primary 
form of the Odd-hoofed animals, namely, the Palcotheria, 
fossils of which occur in the upper Eocene and lower 
Miocene. Out of the Paleotheria, at a later period, the 
rhinoceroses (Nasicornia) and rhinoceros-horses (Elasmo- 
therida) on the one hand, and the tapirs, lama-tapirs, and 
primeval horses, on the other, developed as two diverging 
branches. The long since extinct primeval horses, or 
Anchitheria, formed the transition from the Palzotheria 
and tapirs to the Miocene horses, or hipparions, which 
are closely allied to the genuine living horses. 
The second main group of Hoofed animals, the order of 
