112 
The Evolution of the Horse. 
for more direct evidence of the value of the theory ; and we are 
in a better position to do this in the case of the horse than in 
that probably of any other animal, as it is one of the few whose 
history can be traced, through a tolerably complete chain of links, 
as far back as the earliest Tertiary age. 1 We must, however, 
not carry away the idea that the record is yet perfect. Before 
the commencement of the Eocene period, it is wrapped in what 
appears at present impenetrable darkness and mystery. Through- 
out the vast Tertiary period, fragments here and fragments 
there stand out among the ruins, from which we endeavour to 
reconstruct our edifice, just as the skilful architect or antiquary, 
from the shattered pieces of marble or stone of an ancient 
temple, will restore to us the noble form and proportions it once 
bore. One thing may be said with certainty upon this subject : 
every fresh discovery that has been made has tended to cor- 
roborate, and nothing has been found inconsistent with this, 
the grandest and most sublime, and, at the same time, most 
reasonable view of the method by which the living beings 
around us have been fashioned into the shapes in which we now 
see them. 
A few more words may be said upon the important subject 
of specialisation, which will be so frequently referred to in what 
follows. It may be of three principal kinds : 1 . The addition 
of parts not met with in the generality of animals, and, as 
far as is known, not found in the earliest members of the 
groups which afterwards possess them — as, for example, the 
antlers of deer, the horns of oxen or the rhinoceros. 2. The 
suppression of parts commonly present — as the upper incisor 
teeth of ruminants, the tails of bears, guinea-pigs, &c, the outer 
toes of the horse, the entire hind limbs of porpoises, Sec. 3. The 
modification of the form, size, or relation of parts — as the immense 
development of the canine teeth in the walrus and male musk- 
deer, the complicated foldings of the molar teeth of elephants, &c. 
It is proposed in this paper to treat of the horse, not as an 
isolated form, but as one link in a great chain, one term in a 
vast series, one twig of a mighty tree ; and to endeavour to 
trace, as far as our present knowledge permits, what its relations 
are to the rest, and by what steps of modification in its various 
parts it has come to be the very singular and highly-specialised 
animal we have now before us, so distinct from all existing 
forms of life that, in most of the older zoological systems, it was 
1 The latest <>f t lie great periods into which geologists divide the age of 
the earth is called Tertiary, or Cainozoic. it is subdivided into Eocene, 
Miocene. Pliocene, and PleiMoccne, the last being that which immediately 
preceded the one in which we are now living. 
