The Descent of Man

pons, like those of the European boar in the
prime of life, whilst the upper tusks are so long
and have their points so much curled inwards,
sometimes even touching the forehead, that
they are utterly useless as weapons of attack.
They more nearly resemble horns than teeth,
and are so manifestly useless as teeth that the
animal was formerly supposed to rest his head
by hooking them on to a branch! Their convex
surfaces, however, if the head were held a little
laterally, would serve as an excellent guard;
and hence, perhaps, it is that in old animals
they "are generally broken off, as if by fighting."
(40. See Mr. Wallace's interesting account
of this animal, 'The Malay Archipelago,' 1869,
vol. i. p. 435.) Here, then, we have the curious
case of the upper tusks of the Babirusa regularly
assuming during the prime of life a structure
which apparently renders them fitted only for
defence; whilst in the European boar the lower
tusks assume in a less degree and only during