In this family are included the Gibbons, the Orangs, the Gorillas, and the
Chimpanzees, the most highly organised and the nearest to Man in structure
of all the _Anthropoidea_. To {144}these groups the term "Ape," has been by
many writers chiefly restricted, the remaining families of the Old World,
and all of the Western Hemisphere, being designated "Monkeys" as a
convenient method of nomenclature. The outward resemblance of the _Simiidæ_
to Man has made the various members of the family objects of the greatest
interest, not alone to the naturalist, but to every intelligent person; and
has naturally suggested a constant inter-comparison between the characters
of both.
They are all essentially arboreal climbing animals, yet when they come to
the ground they progress in a semi-erect position of their own accord.
Their front-limbs are always so much longer than their hind-limbs, that
when walking on a level surface their fingers reach the ground, without
stooping lower than their semi-erect attitude. Their front-limbs vary in
length in the different genera; so does the thumb; but their great-toe is
always smaller in proportion to the foot than it is in Man, and, unlike
his, is opposable to the other toes. As they belong to the Catarrhine
group, their nose has a narrow partition between the nostrils, which are
directed downwards. In all, an external tail, cheek-pouches, and (except
among the Gibbons) ischial callosities are wanting. All are covered with
hair, some more thickly than others, but no Ape has on its head the long
abundant locks which Man possesses.
The form of the skull varies very greatly in the _Simiidæ_. It is, however,
always longer than broad. In its frontal region it is never so rounded and
elevated as in Man. The roof of the eye-sockets projects into the fore part
of the brain-cavity, and considerably reduces its capacity. The
pre-maxillary bones (carrying the incisor teeth) are relatively more
distinct and much larger than in Man, "the sutures {145}separating them
from the maxillary bones remaining visible after the adult dentition has
been obtained." (_Mivart._)[1] The _Simiidæ_ have a bony meatus or canal to
the ear. The back part of the head, which among the Guenons is flat, is
convex among the _Simiidæ_. The palate is long and narrow, and the margins
of the jaws nearly parallel. The lower jaw is always in one piece, the two
halves being firmly ossified in the middle. The dental formula of the
Man-like Apes is I2/2, C1/1, P2/2, M3/3 (_i.e._, 32 teeth in all); their
inner upper incisors are larger, and the lower are smaller than the outer
pair; the canines are large, and between them and the neighbouring incisor
above there is a vacuity (or diastema), and, below, between them and the
nearest pre-molar. The upper pre-molars have three roots, and the lower,
two; the upper molars have four tubercles, their crowns being relatively
wide; the lower molars have five tubercles, but the posterior has no hind
talon.
The opening for the passage of the spinal cord is situated towards the
posterior portion of the base of the cranium, and is thus further from the
centre than in Man.
Except among the Gibbons, the vertebral column shows in the sacral region
indications of that curve--or concavity in the back between the two
convexities of the neck and loins--which is one of the distinctive
characters of the human skeleton. The processes for the interlocking of the
vertebræ, which are large in the lower Anthropoids, are much reduced in the
Man-like Apes, and become inconspicuous in Man.
The breast-bone is flat, and resembles that of Man, and, in all, except the
Orang, is composed of two bones. The {146}arm-bone is often shorter than
the fore-arm. The _radius_ and _ulna_ can be completely rotated. The
articulating surface of the _trapezium_, the wrist-bone (_carpus_), to
which the thumb is attached, has a rounded face like that of the
_ento-cuneiform_ bone in the ankle (_tarsus_), a form which, as already
pointed out (Vol. I., p. 11), was in the Lemuroids correlated with an
opposable great-toe, so here it is correlated with a true opposable thumb.
In the Monkeys and Lemuroids this bone is not generally rounded, and they
have not the thumb opposable in the strict sense that it is among the
higher Apes.
The thigh-bone (_femur_) is shorter than the arm-bone (_humerus_); and the
foot is very long; yet the absolute length of the _tarsus_ is never so
great as in Man; it is the rest of the foot which is so much longer
relatively in Apes. The _ento-cuneiform_, or articulating bone of the ankle
for the great-toe, has a sub-cylindrical surface, which gives a great range
of motion to that digit, towards and from the plane of the foot.
The brain of the Apes closely resembles in general form and structure that
of Man; but the cerebral hemispheres differ in being much elongated and
depressed, and the cranial capacity of the skull, which is never less than
55 cubic inches in any normal human subject, is in the Chimpanzee 27½ cubic
inches; in the Gorilla 35 inches; in the Orang 26 inches; and in the
Gibbons very much less. The cerebrum has its surface richly convoluted; and
its posterior lobes always entirely over-arching the cerebellum, except in
the Siamang (_Hylobates syndactylus_).
"As to the convolutions, the brains of the Apes exhibit every stage of
progress, from the almost smooth brain of the Marmoset, to the Orang and
the Chimpanzee, which fall but little below Man. And it is most remarkable
that as soon as {147}all the principal sulci [or grooves] appear, the
pattern according to which they are arranged is identical with that of the
corresponding sulci of Man. The surface of the brain of a Monkey exhibits a
sort of skeleton map of Man's, and in the Man-like Apes the details become
more and more filled in, until it is only in minor characters, such as the
greater excavation of the anterior lobes, the constant presence of fissures
usually absent in Man, and the different disposition and proportions of
some convolutions, that the Chimpanzee's or the Orang's brain can be
structurally distinguished from Man's.... And the difference between the
brains of the Chimpanzee and of Man is almost insignificant when compared
with that between the Chimpanzee's brain and that of a Lemur." (_Huxley._)
The Anthropoid Apes have no cheek-pouches. The larynx has large dilatations
of the shallow depressions--called ventricles--of the mucous membrane on
each side of its inner surface--which may extend down as far as the
arm-pits, and be connected with powerful voice possessed in most of the
species. The stomach is simple, like that of Man, and not sacculated, as in
the last family (the _Cercopithecidæ_).
The uterus and other structures connected with the reproductive system
resemble those in the human subject. The length of gestation varies
probably in the different genera, and is unknown in many of the species.
The period for which the young are suckled by the mother lasts about six
months. "The proportions of the limbs to one another and to the body do not
sensibly change after birth; but the body, limbs, and jaws enlarge to a
much greater extent than the brain-case." (_Huxley._) Observations are
still required, in regard to most of the species, as to the age at which
they arrive at maturity, and are able to reproduce.
{148}The _Simiidæ_--the most intelligent of the animal kingdom--are all
diurnal animals, and essentially arboreal. Many of the members of the
family have, when walking, a tendency to tread on the outer edge of the
foot, turning, therefore, the toe inward on account of the free motion
which is possible between the various bones of its ankle, whereas, in the
human foot, these bones are more solidly bound together. When climbing, the
power of turning in the sole is, as is evident, of the greatest advantage
to the Ape. Their food is chiefly vegetable; a few species exhibit slight
carnivorous tendencies.
"Of the various genera of the _Simiidæ_, the Gibbons are most remote from
Man. The Orangs come nearest in the number of the ribs, the form of the
cerebral hemispheres, and certain other characters of the brain and skull;
but they differ from him much more widely in other characters, especially
in the limbs, than the Gorilla and the Chimpanzee do. Of the Chimpanzees
the Gorilla is more Man-like in the proportions of the leg to the body, and
of the foot to the hand; and likewise in the size of the heel, the
curvature of the spine, and the absolute capacity of the cranium. The true
Chimpanzees approach Man most closely in the skull, dentition, and
proportionate length of the arms." (_Huxley._)
The _Simiidæ_ are confined to the Ethiopian and Indian Regions. The
Gorillas and Chimpanzees live exclusively in the Tropical Regions of
Western and Central Africa; the Gibbons range into all the four provinces
of the Indian Region; while the Orangs are confined to two islands of the
Indo-Malayan Sub-region.