Chapter II: The Monkeys and Apes--Sub-Order Anthropoidea

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.

THE MARMOSETS AND TAMARINS. FAMILY HAPALIDÆ.

Of the New World, or Platyrrhine, Apes, the Marmosets come to be described first, as they have many characters which mark them out as the lowest of the _Anthropoidea_, and rank them nearer to the _Lemuroidea_ than any of the others. They are specially characterised by having only thirty-two teeth, their dental formula being I2/2, C1/1, P3/3, M2/2. In the actual number of their teeth they agree with their Eastern relations, but with this {130}difference, that in the latter the pre-molars are two, and the molars three, above and below on each side. Their flattened nose, with its wide partition between the nostrils, and their non-prehensile bushy tails, are also distinguishing characters. The face is nude, the ears large and sometimes fringed. Their hind-limbs are proportionately larger and longer than their fore-limbs, while the nails of their fingers and toes are not flattened as in the Old World Apes, but all form sharp curved claws, except on the much shortened great toe. The thumb is elongated and lies parallel, but quite unopposable to, nor indeed is it separable at will from, the rest of the digits. The fore-foot, consequently, "is a mere paw, and the term 'hand' is not applicable to it."... The plantar surface of the hind-foot "is very long, and the digits are very short. It follows from these facts that the term 'quadrumanous' is not applicable in any sense to the Marmosets." (_Huxley._) These animals have no callosities over the ischial (or buttock) bones, and no cheek-pouches. In their smooth and rounded skull superciliary ridges are conspicuously absent; and the ear-capsules have, as has been already observed, no external bony canal for conducting sound vibrations to the inner ear. The hyoid bone resembles that of the Lemurs.

This family has been divided into two genera, distinguished from each other only by a variation in the relative length of their incisor and canine teeth, which is so slight as to render it doubtful whether these differences really warrant the generic separation of the two groups. As, however, the distinction has been maintained by nearly all writers upon these animals, the arrangement has been followed here, and the various species of the family will be described as true Marmosets (_Hapale_) and {131}Tamarins (_Midas_). They are most numerous in the equatorial forests of South America.

THE MARMOSETS. GENUS HAPALE.

_Hapale_, Illiger, Prodr. Syst. Mamm., p. 71 (1811).

The members of this genus, which are often kept in captivity as pets, are very small animals, covered with thick and silky fur, and having bushy tails, equal to or even exceeding the length of their body. The head is round, the eyes large and watchful, the face short and nude, and often abundantly whiskered. The mouth is large; the ears also large and often fringed, and the neck sometimes clothed, with long hair. They are distinguished from the Tamarins (_Midas_) by having their upper incisor teeth long, narrow, and protruding outwards and forwards; the incisors of the lower jaw are also very long, and its canines small and shorter than the incisors, both being protrusive, as among the Lemurs. The cranial region of the smooth skull is conspicuously large in comparison with its facial portion, but the cerebrum shows a low type of organisation, and indicates a small degree of intelligence in its possessor; it is smooth and almost devoid of convolutions; the cerebrum, too, unlike that of the _Lemuroidea_, completely covers the cerebellum. The orbits are large, and almost completely walled in from the temporal depression behind. The stomach in form resembles that found in the higher groups, but its orifices for the entrance and exit of food are nearer to each other than in any of the other American Monkeys.

The female produces two or three young at a birth, instead of one, as is the general rule among the _Anthropoidea_. The species vary much in coloration, and some of them resemble the Lemurs in being ring-tailed.

{132}The Marmosets are all gentle and playful in disposition, and are, on this account, very largely brought to Europe as pets; but they are very delicate, and rarely survive long in confinement after the advent of the Northern winter. They are arboreal, living in troops, and feeding on insects and fruit, and not disdaining flesh, especially of fishes, when they can obtain it. They emit a characteristic chirping noise.