of
_Plagiolophus_ are similar to those of _Anchitherium_, and their crowns
are as thinly covered with cement; but the grinders diminish in size
forwards, and the last lower molar has a large hind lobe, convex outwards
and concave inwards, as in _Palueotherium_. The ulna is complete and much
larger than in any of the _Equidoe_, while it is more slender than in
most of the true _Paloeotheria_; it is fixedly united, but not ankylosed,
with the radius. There are three toes in the fore limb, the outer ones
being slender, but less attenuated than in the _Equidoe_. The femur is
more like that of the _Paloeotheria_ than that of the horse, and has only
a small depression above its outer condyle in the place of the great
fossa which is so obvious in the _Equidoe_. The fibula is distinct, but
very slender, and its distal end is ankylosed with the tibia. There are
three toes on the hind foot having similar proportions to those on the
fore foot. The principal metacarpal and metatarsal bones are flatter than
they are in any of the _Equidoe_; and the metacarpal bones are longer
than the metatarsals, as in the _Paloeotheria_.

In its general form, _Plagiolophus_ resembles a very small and slender
horse,[4] and is totally unlike the reluctant, pig-like creature depicted
in Cuvier's restoration of his _Paloeotherium minus_ in the "Ossemens
Fossiles."

[Footnote 4: Such, at least, is the conclusion suggested by the
proportions of the skeleton figured by Cuvier and De Blainville; but
perhaps something between a Horse and an Agouti would be nearest the
mark.]

It would be hazardous to say that _Plagiolophus_ is the exact radical
form of the Equine quadrupeds; but I do not think there can be any
reasonable doubt that the latter animals have resulted from the
modification of some quadruped similar to _Plagiolophus_.

We have thus arrived at the Middle Eocene formation, and yet have traced
back the Horses only to a three-toed stock; but these three-toed forms,
no less than the Equine quadrupeds themselves, present rudiments of the
two other toes which appertain to what I have termed the "average"
quadruped. If the expectation raised by the splints of the Horses that,
in some ancestor of the Horses, these splints would be found to be
complete digits, has been verified, we are furnished with very strong
reasons for looking for a no less complete verification of the
expectation that the three-toed _Plagiolophus_-like "avus" of the horse
mus