the lower
mammalia. In consequence of this cranial enlargement, the face and eyes
are swung downward, as it were, so that the line of vision is not straight
ahead, but depressed below the horizontal. In order to look to the front
and to the immediate foreground to which it is progressing or to where its
food or enemies may be, the monkey must bend back its head; if it is
still, it finds greater ease in the upright sitting posture which it
assumes readily and naturally.

The next division, called the Cercopithecidae, includes the baboons of the
Old World. These animals also run upon all fours, and their feet are
handlike as before, but the tail is much reduced. The general appearance
of the head is doglike, and the brain-case arches little more than it does
in the monkeys, but the face projects forward as a long muzzle, with
terminal nostrils close together. In some respects the baboons stand
somewhat away from the line leading from the lower to higher anthropoids;
in other characters they approach the latter, for in the teeth especially
they are identical with the apes and with the human species.

The Simiidae, or true apes, possess an overwhelming importance, far beyond
that of the baboons and monkeys. There are only four principal kinds now
existing, namely, the gibbon, orang-outang, chimpanzee, and the gorilla,
of which the first is much less familiar than the others. The known
species of gibbons occur in Indo-China and the Malay Peninsula. The
typical animal stands about three feet high; its overarching braincase,
enlarged in conformity with the much greater brain development, has pushed
the eyes and face still further around underneath, so that if the animal
walks upon all fours the eyes look almost straight into the ground.
Therefore it must bend back its head at an extremely uncomfortable angle
if it is to remain upon all four feet, but it prefers to raise itself up
into the human sitting posture, or, when it walks, it stands erect upon
its hind limbs. Hence we who are accustomed to think of ourselves as the
only erect animals must revise our opinion, for we find in the gibbon an
organism that is nearly, if not quite, as advanced in this respect as we
are. One peculiar difference may be pointed out,--the walking gibbon
stretches out its great long arms to the sides in order to preserve its
balance. The animal seems awkward to us, perhaps, but it is possible that
the human method of balancing the body by vigorou