Next, in the backward order in
time, is the _Miohippus_, which corresponds pretty nearly with the
_Anchitherium_ of Europe. It presents three complete toes--one large
median and two smaller lateral ones; and there is a rudiment of that
digit, which answers to the little finger of the human hand.
The European record of the pedigree of the horse stops here; in the
American Tertiaries, on the contrary, the series of ancestral equine
forms is continued into the Eocene formations. An older Miocene form,
termed _Mesohippus_, has three toes in front, with a large splint-like
rudiment representing the little finger; and three toes behind. The
radius and ulna, the tibia and the fibula, are distinct, and the short
crowned molar teeth are anchitherioid in pattern.
But the most important discovery of all is the _Orohippus_, which comes
from the Eocene formation, and is the oldest member of the equine
series, as yet known. Here we find four complete toes on the front-limb,
three toes on the hind-limb, a well-developed ulna, a well-developed
fibula, and short-crowned grinders of simple pattern.
Thus, thanks to these important researches, it has become evident that,
so far as our present knowledge extends, the history of the horse-type
is exactly and precisely that which could have been predicted from a
knowledge of the principles of evolution.
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