These extraordinary animals, typified by
_Brontotherium_ (fig. 243) itself, agree with the existing Tapirs
of South America and the Indian Archipelago in having the fore-feet
four-toed, whilst the hind-feet are three-toed; and a further
point of resemblance is found in the fact (as shown by the form
of the nasal bones) that the nose was long and flexible, forming
a short movable proboscis or trunk, by means of which the animal
was enabled to browse on shrubs or trees. They differ, however,
from the Tapirs, not only in the apparent presence of a long tail,
but also in the possession of a pair of very large "horn-cores,"
carried upon the nasal bones, indicating that the animal possessed
horns of a similar structure to those of the "Hollow-horned"
Ruminants (_e.g._, Sheep and Oxen). _Brontotherium gigas_ is
said to be nearly as large as an Elephant, whilst _B. Ingens_
appears to have attained dimensions still more gigantic. The
well-known genus _Titanotherium_ of the American Miocene would
also appear to belong to this group.
[Illustration: Fig. 243.--Skull of _Brontotherium ingens_. Miocene
Tertiary, United States. (After Marsh.)]
The family of the Horses (_Equidoe_) appears under various forms
in the Miocene, but the most important and best known of these
is _Hipparion_. In this genus the general conformation of the
skeleton is extremely similar to that of the existing Horses,
and the external appearance of the animal must have been very
much the same.
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