5 
290 FOSSIL HORSES IN AMERICA. 
only three toes in the fore foot, as well as behind, and the fibula 
was coossified with the tibia at its lower end. In this genus, all the 
toes reached the ground, as shown in the accom- 
panying figure of the left fore foot of Miohippus 
annectens Marsh, the type species (Fig. 74). In 
the same deposits, the genus Anchitherium Meyer 
occurs, represented by a single species, A. anceps 
arsh. This genus is closely allied to Miohippus, 
but differs in having a deep depression in the skull 
in front of the orbit. The radius and ulna arè 
united, and the outer toes are reduced in size. In 
the eastern basin, Anchitherium Bairdi Leidy is 
abundant, and with it is found a smaller species, — 
A. celer Marsh. The animals of these two genera 
Miohippus are all larger than the species of Orohippus from — 
annectens, . . 
the Eocene, some of them exceeding a sheep in size 
The Miocene species known with certainty are as follows:— 
Miohippus annectens Marsh, Miohippus Condoni (Anchitherium 
Condoni Leidy) and Anchitherium anceps Marsh, from Oregon; 
and A. Bairdi, Leidy, and A. celer Marsh, from the eastern basin. 
During the Pliocene, or later Tertiary, a great development of : 
the horse family took place, and vast numbers of these animals — 
left their remains in the lake deposits of that epoch. The largest ! 
of these lakes had the Rocky Mountains for its western border, 
and extended from Dakota to Texas, its northern part covering 
the bed of the older Miocene basin. Another Pliocene lake, of : 
unknown limits, extended over the older Tertiary strata of eastert 
Oregon, and evidence of still others may be seen in Idaho, Ne- : 
vada and California. In all of these basins, equine remains of i 
various kinds have been found, but the most important localities 
are the region of the Niobrara river east of the mountains, and 
the valley of the John Day river in Oregon. 
The equine genera of the Pliocene which appear oF 
nearly related to their predecessors from older strata are, Anchir : 
pus Leidy, Hipparion Christol, and Protohippus Leidy, all three — 
toed forms, but with the outer digits reduced to much the oa 
proportions- as the posterior hooflets of the modern deer and 0% 
The genus Pliohippus Marsh, from the same deposits, had ` 
like those of the recent horse. Other genera, less known, 
have been proposed, are Parahippus, Merychippus, and H; 
5 
Fig. 74. 
