This Sub-order, though containing animals of much higher organisation than
the _Lemuroidea_, embraces species presenting many different grades of
intelligence, and ranging in size from the Pigmy Marmoset, not larger than
a small Kitten, to the {124}ponderous Gorilla and the genus _Homo_. In
external characters the Monkeys and Apes have in general a shorter and less
Dog-like nose than the Lemurs, thin lips and a more distinct face; while
their eyes, situated on the face, are invariably directed forwards, and
never outwards, or to the side. The opening of their nostrils is either
outward (as in those inhabiting the New World), or downwards (as in the
bulk of the Old World species). All of them are covered with hair; the tail
may be long, short, or wanting. The proportions of the fore-limbs to the
hind- vary much in the different groups. The great toe, as well as the
thumb, is (except in a few species) fully opposable, so that in the
majority of members of the Sub-order, the foot is as good a prehensile
organ as the hand. From this circumstance comes the designation,
_Quadrumana_, or "four-handed," so often applied to these animals. In a few
species the thumb is rudimentary or absent, but the fore-finger, the
absence of which characterised some of the Lemurs, is always present and
well developed, and the corresponding digit in the foot (except in the
Marmosets) has a flat nail instead of a claw. The mammæ of the
_Anthropoidea_ are always situated on the breast. If we examine the
structures underlying the skin, we find that in the skull the orbits are
entirely shut in by a bony wall, so that the finger cannot be passed into
the temporal depression behind, as could be done in the Lemurine skull, and
that the lachrymal foramen opens within the cavity for the eye. In the
present Sub-order there is no toothless space in the mid-line of the upper
jaw, the incisor teeth being set close together; but there is always a
vacuity, except in Man, between the incisors and the canine tooth. The
lower canine teeth do not resemble in form the incisors, nor do they
protrude horizontally, as in the Lemurs. {125}The two halves of the lower
jaw are always co-ossified together, when the animal is full grown. The
_humerus_, or arm-bone, never has an entepicondylar foramen on the inner
side of its lower portion, and the bones of the fore-arm (the _ulna_ and
_radius_) are never ossified together, nor are those of the lower leg (the
_tibia_ and _fibula_); so that there is perfect freedom for every movement
necessary for grasping and walking, or for rotating the hand or foot on the
wrist and ankle.
With regard to the brain, the anthropoid cerebrum, or fore-brain, is
greatly convoluted, and differs from that of the Lemurs by its
proportionately larger size, the cerebellum, or hind-brain, being as a rule
entirely covered by it.
The uterus and structures for the nutrition of the young prior to birth
differ greatly in this Sub-order from the conditions existing in the
_Lemuroidea_. The uterus is a simple and not a two-horned sac, and its
inner layer, in which the foetal and maternal structures intermingle during
the growth of the embryo, is shed after the birth of the young, which is
not the case in the Lemurs.
"The resemblance of Monkeys to Man," says Mr. Darwin, "is greatly caused by
the relative position of the features of the face. The eyes are arched
over; they are separated by a long nose, the end of which in some is very
human. The mouth is not carried back, but occupies the same general
position as in Man, and the forehead, so often wrinkled, is usually
prominent and like that of a child. The likeness is increased by the fact
that anger, sorrow, pleasure, and satisfaction, are displayed by the Monkey
by nearly similar movements of the muscles and skin, chiefly above the
eyebrows and round the mouth. Some few expressions are indeed almost the
same, as in the weeping of certain kinds of Monkeys, and in the
{126}laughing noise made by others, during which the corners of the mouth
are drawn backward and the eyelids wrinkled. In Man the nose is much more
prominent than in most Monkeys; but we may trace the commencement of an
aquiline curvature in the nose of the Hoolock Gibbon, and this in the
Great-nosed Monkey (_Nasalis larvatus_) is carried to a ridiculous
extreme."
In regard to the distribution of the _Anthropoidea_, excluding Man
(_Hominidæ_), two families (the _Hapalidæ_ and _Cebidæ_) are known only
from the New World; and two others (the _Cercopithecidæ_ and _Simiidæ_) are
exclusively confined to the Old World. No fossil remains of Eastern
Hemisphere forms have as yet been found in the Western, or _vice versâ_, a
fact which indicates, doubtless, a separation of great antiquity between
the two groups. The various species of these families are to be found
chiefly in the warmer regions on both sides of the equator. In the New
World some species range as far north as to 20° N. lat. in Mexico; and
South, to 30° below the equator. In the Eastern Hemisphere, the Old World
species predominate in the tropical and sub-tropical regions; but certain
forms have spread as far north as Thibet and Japan, and others have made
the high altitudes of the Himalaya Mountains their home; while to the
southward they extend in Africa nearly to the Cape of Good Hope. No
indigenous species have ever been found in New Guinea, Australia, New
Zealand, or in the Pacific, or West Indian Islands.
The Apes of the Old World differ in many important characters from those of
the New. Among the former, as already mentioned, the openings of the
nostrils are directed downwards, as in Man; the nose is narrow, and the
nostrils themselves are set close together, being separated from each other
by a thin septum, or partition, of cartilage. On this account, {127}they
have received the name of Catarrhine Monkeys (_Catarrhini_).[7] The New
World Monkeys, on the other hand, have the nose flat and the opening of
their nostrils directed outwards, and the one nostril widely separated from
the other by a broad cartilaginous septum, and they are therefore
designated Platyrrhine Monkeys (_Platyrrhini_).[8]
The dental formula of the Old World forms is I2/2, C1/1, P2/2, M3/3, making
a total of thirty-two teeth in all; but those of the Western Hemisphere
differ in having invariably three pre-molars, and sometimes two molars,
instead of three, so that they possess either thirty-two or thirty-six
teeth altogether. There is always a gap, or _diastema_, in the series of
the teeth in front of the upper and behind the lower canines; the latter
teeth being taller than the rest. Many of the Catarrhine Apes have large
cheek-pouches as well as bare patches, or callosities, often brightly
coloured, on the part they apply to the ground when sitting. None of the
Platyrrhine group have cheek-pouches or callosities, but in many of them
the tail is marvellously prehensile, which is not the case in any of the
Old World species. Again, in the Apes of the Eastern Hemisphere, the
ear-capsules of the skull have an external bony channel (or _meatus_) for
conveying the sound vibrations into the ear, which is absent in the
American species.
As a rule the Platyrrhine Monkeys have the fore-limbs shorter than the
hind-, and are more quadrupedal than those of the Old World. Their thumb is
also more like a finger than the same digit in their Eastern brethren.
Of the New World Monkeys, the _Hapalidæ_, or Marmosets, have thirty-two
teeth, and the _Cebidæ_, with several {128}sub-families, have thirty-six
teeth. The former include the Marmosets (_Hapale_) and the Tamarins
(_Midas_). The latter comprise the Capuchins (_Cebus_), which may be taken
as the representative genus of American Monkeys, the Woolly Monkeys
(_Lagothrix_), the Spider-Monkeys (_Ateles_ and the allied _Eriodes_), the
Howlers (_Mycetes_), the Sakis (_Pithecia_ and _Brachyurus_), the
Night-Monkeys or Douroucolis (_Nyctipithecus_), and the Squirrel Monkeys or
Saimiris (_Chrysothrix_), with the allied _Callithrix_.
"The extensive equatorial forests of the Amazon and Orinoco, and their
tributaries, constitute _par excellence_ the home of the American Monkeys,
but the majority of the genera have a very extended range, appearing in one
or more species throughout the greater portion of the tract covered by the
entire family. This is more particularly the case with the Sapajous
(_Cebus_), Spider-Monkeys, Howlers, and the species of _Callithrix_. The
range of the species, on the other hand, is not unfrequently very sharply
defined, as, for example, when a natural barrier, offering insurmountable
obstacles to further migration, suddenly interposes itself. Examples of
such limitation, as brought about by the dominant water-courses of the
equatorial forests," are numerous. Mr. Wallace cites the case of certain
species of Saki Monkey (_Pithecia_), found on either side of the Amazon
river, whose range, either southward or northward, appears to be limited by
that river. "The number of species of these American Apes found in, and
north of, the Isthmus of Panama is ten, of which only one (_Ateles
vellerosus_) extends into Mexico; _Mycetes villosus_, the Guatemalan
Howler, or 'Mono,' has thus far been found only in Guatemala and Honduras.
It is a little surprising that the range of only two of the species--the
Black-faced Spider-Monkey (_Ateles ater_) {129}and one of the Night-Apes
(_Nyctipithecus vociferans_)--extends beyond Colombia, in South America."
"None of the South American Monkeys appear to pass west of the Andean chain
of mountains south of Ecuador, and even north of the Peruvian boundary the
number of such transgressional forms is very limited. Indeed, even among
the wooded slopes, a habitation along the basal line of the mountain axis
seems to be much preferred. The greatest altitude at which Monkeys were
observed by Tschudi in Peru was 3,000 feet (_Lagothrix humboldti_); _Ateles
ater_ and _Cebus robustus_ were found at 2,500 feet. On the other hand,
Salvin and Godman state that in the district of Vera Paz, in Guatemala, the
'Mono' or Howler is most abundant at an elevation of 6,000 feet; and on the
Volcano of Atitlan, in the same country, Mr. Salvin found troops of the
Mexican Spider-Monkey (_Ateles vellerosus_) in the forest region of 7,000
feet elevation.
"The range of the Marmosets and Oustitis (_Hapalidæ_) is nearly
co-extensive with that of the Monkeys proper." (_Heilbrin._) The Pigmy and
the Silky Marmoset range as far north as Mexico.