The man-like Apes, the history of whose discovery has just been
detailed, have certain characters of structure and of distribution in
common. Thus they all have the same number of teeth as man--possessing
four incisors, two canines, four false molars, and six true molars in
each jaw, or 32 teeth in all, in the adult condition; while the milk
dentition consists of 20 teeth--or four incisors, two canines, and four
molars in each jaw. They are what are called catarrhine Apes--that is,
their nostrils have a narrow partition and look downwards; and,
furthermore, their arms are always longer than their legs, the
difference being sometimes greater and sometimes less; so that if the
four were arranged in the order of the length of their arms in
proportion to that of their legs, we should have this series--Orang (1
4/9:1), Gibbon (1 1/4:1), Gorilla (1 1/5:1), Chimpanzee (1 1/16:1). In
all, the fore limbs are terminated by hands, provided with longer or
shorter thumbs; while the great toe of the foot, always smaller than in
Man, is far more movable than in him and can be opposed, like a thumb,
to the rest of the foot. None of these apes have tails, and none of
them possess the cheek pouches common among monkeys. Finally, they are
all inhabitants of the old world.

The Gibbons are the smallest, slenderest, and longest-limbed of the
man-like apes: their arms are longer in proportion to their bodies than
those of any of the other man-like Apes, so that they can touch the
ground when erect; their hands are longer than their feet, and they are
the only Anthropoids which possess callosities like the lower monkeys.
They are variously coloured. The Orangs have arms which reach to the
ankles in the erect position of the animal; their thumbs and great toes
are very short, and their feet are longer than their hands. They are
covered with reddish brown hair, and the sides of the face, in adult
males, are commonly produced into two crescentic, flexible