he seven
grinders, which, as I have said, is frequently absent, and, when it does
exist, is small in the horse, is a good-sized and permanent tooth, while
the grinder which follows it is but little larger than the hinder ones.
The crowns of the grinders are short, and though the fundamental pattern
of the horse-tooth is discernible, the front and back ridges are
less curved, the accessory pillars are wanting, and the valleys, much
shallower, are not filled up with cement.

Seven years ago, when I happened to be looking critically into the
bearing of palaentological facts upon the doctrine of evolution, it
appeared to me that the _Anchitherium,_ the _Hipparion,_ and the modern
horses, constitute a series in which the modifications of structure
coincide with the order of chronological occurrence, in the manner in
which they must coincide, if the modern horses really are the result
of the gradual metamorphosis, in the course of the Tertiary epoch, of a
less specialised ancestral form. And I found by correspondence with the
late eminent French anatomist and palaeontologist, M. Lartet, that he
had arrived at the same conclusion from the same data.

That the _Anchitherium_ type had become metamorphosed into the
_Hipparion_ type, and the latter into the _Equine_ type, in the course
of that period of time which is represented by the latter half of the
Tertiary deposits, seemed to me to be the only explanation of the facts
for which there was even a shadow of probability. [3]

And, hence, I have ever since held that these facts afford evidence of
the occurrence of evolution, which, in the sense already defined, may be
termed demonstrative.

All who have occupied themselves with the structure of _Anchitherium,_
from Cuvier onwards, have acknowledged its many points of likeness to a
well-known genus of extinct Eocene mammals, _Palaeotherium._ Indeed, as
we have seen, Cuvier regarded his remains of _Anchitherium_ as those of
a species of _Palaeotherium._ Hence, in attempting to trace the pedigree
of the horse beyond the Miocene epoch and the Anchitheroid form, I
naturally sought among the various species of Palaeotheroid animals
for its nearest ally, and I was led to conclude that the _Palaeotherium
minus (Plagiolophus)_ represented the next step more nearly than any
form then known.

I think that this opinion was fully justifiable; but the progress of
investigation has thrown an unexpected light on the question, and has
brou