Professor Owen describes the _Hipparion_, or Three-hoofed Horse, as the
first representative of a family so useful to mankind. This animal,
in addition to its true hoof, appears to have had two additional
elementary hoofs, analogous to those which we see in the ox. The object
of these no doubt was to enable the Hipparion to extricate his foot
with greater ease than he otherwise could when it sank through the
swampy ground on which he lived.