TERTIARY AGE. 



505 



tusks. The figure (Fig. 919, from Marsh) gives an oblique view of 

 the skull, one eighth its natural size, and shows the pairs of horn-like 

 prominences, two of which, if not all, were horn-cores, bearing horns, 

 and also the tusks or canines. The name Uintatherium alludes to the 

 Uintah Mountains, the southern boundary of the G-reen River basin, 

 and Dinoceras to the terrible array of horns. 



There were also the earliest known species of the Horse tribe in 

 America. The modern Horse has one toe, the third one out of the 

 five in other animals, enormously enlarged and elongated ; but either 

 side of it, under the skin, there are rudiments of the second and fourth 



Fijr. 920. 



3?eet op Species of the Horse Tribe. — Fig. 920 a, Orohippus, of the Eocene (x V b )', 920 6, An- 

 chitherium, of the Miocene; 920c, Hipparion, of the Pliocene; 920 d, the modern Horse. 



toes, in the shape of long pointed bones, called splint-bones (as shown 

 in Fig. 920 d), while the first and fifth toes are wholly absent : occa- 

 sionally, a very small hoof is seen hanging outside of a horse's leg, 

 from the extremity of one of these splint-bones. In the most ancient 

 of the Horse tribe, these rudimentary toes were real toes, of full length 

 and development, though much smaller than the large middle one ; 

 and thus there is a gradation between some of the Tapir-like beasts 

 and the one-toed Horse. In the Eocene Horses of Wyoming, of the 

 genus Orohippus, of Marsh, not larger than a fox, there were four 

 toes in the fore foot, all of usable length, that is, three besides the 

 large one, as shown in Fig. 920 a, from Marsh. In the Miocene of the 

 Upper Missouri and Rocky Mountain region, and also of Oregon, there 

 are the remains of Horses of the genus Anchitherium, having three 

 usable toes (as illustrated in Fig. 920 b, also from a paper by Marsh) ; 

 this is an intermediate form between the Orohippus and the modern 

 Horse. It is like the Palceotherium in having three toes, but differs 

 in that the middle toe is much larger than the others. In the Plio- 

 cene of Niobrara and Oregon, occur Horses of still another extinct 



