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
_Palceotherium_. The ulna is complete and much larger than in any
of the _Equidae_, while it is more slender than in most of the true
_Palaeotheria_; 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 _Equidae_. The femur is more
like that of the _Palaeotheria_ 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 _Equidae_. 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 _Equidae_; and the metacarpal
bones are longer than the metatarsals, as in the _Palaeotheria_.

In its general form, _Plagiolophus_ resembles a very small and slender
horse[1], and is totally unlike the reluctant, pig-like creature
depicted in Cuvier's restoration of his _Palaeotherium minus_ in the
"Os semens Fossils."

[Footnote 1: 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 must have had a five-toed
"atavus" at some earlier period.

No such