On The Parts Of Animals   

would seem, derived from the function of the part. For as man is the
only animal that stands erect, he is also the only one that looks
directly in front (proso) and the only one whose voice is emitted in
that direction.
Part 2
We have now to treat of horns; for these also, when present, are
appendages of the head. They exist in none but viviparous animals;
though in some ovipara certain parts are metaphorically spoken of as
horns, in virtue of a certain resemblance. To none of such parts,
however, does the proper office of a horn belong; for they are never
used, as are the horns of vivipara, for purposes which require
strength, whether it be in self-protection or in offensive strife. So
also no polydactylous animal is furnished with horns. For horns are
defensive weapons, and these polydactylous animals possess other means
of security. For to some of them nature has given claws, to others
teeth suited for combat, and to the rest some other adequate defensive
appliance. There are horns, however, in most of the cloven-hoofed
animals, and in some of those that have a solid hoof, serving them as
an offensive weapon, and in some cases also as a defensive one. There
are horns also in all animals that have not been provided by nature
with some other means of security; such means, for instance, as speed,
which has been given to horses; or great size, as in camels; for
excessive bulk, such as has been given to these animals, and in a
still greater measure to elephants, is sufficient in itself to protect
an animal from being destroyed by others. Other animals again are
protected by the possession of tusks; and among these are the swine,
though they have a cloven hoof.
All animals again, whose horns are but useless appendages, have been
provided by nature with some additional means of security. Thus deer
are endowed with speed; for the large size and great branching of
their horns makes these a source of detriment rather than of profit to
their possessors. Similarly endowed are the Bubalus and gazelle; for
though these animals will stand up against some enemies and defend
themselves with their horns, yet they run away from such as are fierce
and pugnacious. The Bonasus again, whoe horns curve inwards towards
each other, is provided with a means of protection in the discharge of
its excrement; and of this it avails itself when frightened. There are
some other animals besides the Bonasus that have a similar mode of
defence. In no case, however, does nature ever give more than one
adequate means of protection to one and the same animal.
Most of the animals that have horns are cloven-hoofed; but the Indian
ass, as they call it, is also reported to be horned, though its hoof
is solid.
Again as the body, so far as regards its organs of motion, consists of
two distinct parts, the right and the left, so also and for like
reasons the horns of animals are, in the great majority of cases, two
in number. Still there are some that have but a single horn; the Oryx,
for instance, and the so-called Indian ass; in the former of which the
hoof is cloven, while in the latter it is solid. In such animals the
horn is set in the centre of the head; for as the middle belongs
equally to both extremes, this arrangement is the one that comes
nearest to each side having its own horn.
Again, it would appear consistent with reason that the single horn
should go with the solid rather than with the cloven hoof. For hoof,
whether solid or cloven, is of the same nature as horn; so that the
two naturally undergo division simultaneously and in the same animals.
Again, since the division of the cloven hoof depends on deficiency of
material, it is but rationally consistent, that nature, when she gave
an animal an excess of material for the hoofs, which thus became
solid, should have taken away something from the upper parts and so
made the animal to have but one horn. Rightly too did she act when she
chose the head whereon to set the horns; and AEsop's Momus is beside
the mark, when he finds fault with the bull for not having its horns
upon its shoulders. For from this position, says he, they would have