nimals which are supposed to be thus related, and
not merely with the fragments upon which the genera and species of the
palaeontologist are so often based. M. Gaudry has arranged the species of
_Hyoenidoe, Proboscidea, Rhinocerotidoe_, and _Equidoe_ in their order of
filiation from their earliest appearance in the Miocene epoch to the
present time, and Professor Ruetimeyer has drawn up similar schemes for
the Oxen and other _Ungulata_--with what, I am disposed to think, is a
fair and probable approximation to the order of nature. But, as no one is
better aware than these two learned, acute, and philosophical biologists,
all such arrangements must be regarded as provisional, except in those
cases in which, by a fortunate accident, large series of remains are
obtainable from a thick and widespread series of deposits. It is easy to
accumulate probabilities--hard to make out some particular case in such a
way that it will stand rigorous criticism.

After much search, however, I think that such a case is to be made out in
favour of the pedigree of the Horses.

The genus _Equus_ is represented as far back as the latter part of the
Miocene epoch; but in deposits belonging to the middle of that epoch its
place is taken by two other genera, _Hipparion_ and _Anchitherium_;[2]
and, in the lowest Miocene and upper Eocene, only the last genus occurs.
A species of _Anchitherium_ was referred by Cuvier to the _Paloeotheria_
under the name of _P. aurelianense_. The grinding-teeth are in fact very
similar in shape and in pattern, and in the absence of any thick layer of
cement, to those of some species of _Paloeotherium_, especially Cuvier's
_Paloeotherium minus_, which has been formed into a separate genus,
_Plagiolophus_, by Pomel. But in the fact that there are only six full-
sized grinders in the lower jaw, the first premolar being very small;
that the anterior grinders are as large as, or rather larger than, the
posterior ones; that the second premolar has an anterior prolongation;
and that the posterior molar of the lower jaw has, as Cuvier pointed out,
a posterior lobe of much smaller size and different form, the dentition
of _Anchitherium_ departs from the type of the _Paloeotherium_, and
approaches that of the Horse.

[Footnote 2: Hermann von Meyer gave the name of _Anchitherium_ to _A.
Ezquerroe_; and in his paper on the subject he takes great pains to
distinguish the latter as the type of a new genus, from Cuvier's
_Paloeo