i 882.] 
The Horse and Jus Fossil Ancestry. 
467 
impels individuals of a species to emigrate, and thus an 
indirect harmony may be established between the two 
theories. In their direct aspects, however, they are dia- 
metrically opposite. 
V. THE HORSE AND HIS FOSSIL ANCESTRY. 
NE of the most striking pieces of palaeontological evi- 
dence in favour of Evolution is well known as being 
presented by the fossil Equidae. Not wishing to re- 
iterate at length familiar facets, we will merely sum up the 
peculiarities of this group of animals by saying that Oro- 
hippus , the' earliest known genus of this family, had its fore 
feet 4-toed, the representative of the thumb being alone 
wanting, though the middle digit is much larger than the 
others. Its hind feet were 3-toed. The remains of this 
species are found in the Eocene deposits of North America. 
In the Miocene Tertiaries occur three genera, all 3-toed 
on both fore and hind feet. One of these ( Mesohippus ) has, 
however, on the fore feet a rudiment which represents a 
fourth toe, though it is useless. In Miohippus this rudi- 
mental fourth toe has disappeared, but the three toes are 
not strikingly unequal in size, and all of them touch the 
ground and take part in the functions of a foot. We go a 
step further : in Ancitherium the foot has still three toes, all 
touching the ground, but the middle one is much larger than 
the two outer toes put together. All still touch the ground, 
though the functional importance of the outer digits must 
have been but trifling. 
Another step lands us in the Upper Miocene and the 
Lower Pliocene. Here occur the remains of another genus, 
Hipparion. Here, though there are still three toes, the two 
outer cannot touch the ground, and the middle one alone is 
to be called a&ive. 
In the later Pliocene formation we find the fossil skeleton 
of Pliohippus with a foot exactly like that of the Equus, the 
modern horse, which does not appear until the Post-Pliocene. 
In both these genera there is merely one perfect toe, which 
is enclosed in a single hoof. The two side toes which we 
