EQUIDE 381 
of North America, there were three digits in the feet (Fig. 156, d); 
but in the Indian H. antilopinum (separated by Cope as Hippo- 
dactylus) the lateral digits seem to have disappeared. There is 
some doubt whether or no Hipparion should occupy a place in the 
direct ancestry of the Horse, and Professor Cope suggests that while 
in America the intermediate place between Anchitherium and Equus 
was held by Protohippus, in Europe the same position was occupied 
by Hipparion—a view which involves the dual origin of the Horses 
of the New and Old Worlds. 
Equus1—Upper cheek-teeth with the anterior pillar (except in 
a very early stage of wear) joined by a narrow neck to the 
adjacent column (Fig. 157, c). Each foot with a single complete 
digit, but with remnants of the proximal portions of the second 
and fourth metapodials (Fig. 156, ¢); some extinct forms having 
claw-like rudiments of the terminal phalangeals of the lateral digits. 
First upper premolar very small or altogether absent in existing 
species, but in some fossil species larger and persistent; first 
lower premolar only occasionally developed in some fossil forms. 
Ears long. Tail long, with long hairs either at the end or 
throughout. <A callosity on the inner side of the fore limb above 
the carpus. 
Fossil Species. —In the Pleistocene Horses of South America 
described as Hippidiwm, as well as in the closely allied ones from 
North America for which the name Pliohippus has been proposed, 
the upper molars are shorter and more curved than in the existing 
species, while their anterior pillar is not longer antero-posteriorly 
than in Hipparion ; the lateral claw-like hoofs persisting. Some of 
the European Pliocene species (like E. stenonis) agree with these 
species in the form of the grinding surface of the anterior pillar 
of the upper molars. In one of the species from the Lower 
Pliocene of India (£. sivalensis)—which was a contemporary of 
Hipparion—and in all the existing species, the grinding surface of 
the pillar in question is greatly elongated in the antero-posterior 
direction, as in Fig. 157, «. 
Fossil remains of Horses are found abundantly in deposits of 
the most recent geological age in almost every part in America, 
from Eschscholtz Bay in the north to Patagonia in the south. In 
that continent, however, they became quite extinct, and no Horses, 
either wild or domesticated, existed there at the time of the 
Spanish conquest, which is the more remarkable as, when intro- 
duced from Europe, the Horses that ran wild proved by their 
rapid multiplication in the plains of South America and Texas that 
the climate, food, and other circumstances were highly favourable 
for their existence. The former great abundance of Hguide in 
America, their complete extinction, and their perfect acclimatisation 
1 Linn. Syst. Nat. 12th ed. vol. i. p. 100 (1766). 
