Furthermore,

of animals some are horned, and some are not so.
The great majority of the horned animals are cloven-footed, as the ox,
the stag, the goat; and a solid-hooved animal with a pair of horns has
never yet been met with. But a few animals are known to be
singled-horned and single-hooved, as the Indian ass; and one, to wit
the oryx, is single horned and cloven-hooved.

Of all solid-hooved animals the Indian ass alone has an astragalus
or huckle-bone; for the pig, as was said above, is either solid-hooved
or cloven-footed, and consequently has no well-formed huckle-bone.
Of the cloven footed many are provided with a huckle-bone.