The Anthropoidea are divisible into two sections, the Catarrhina, characteristic of the Old World, and the Platyrrhina, confined to the New. In the Catarrhina, or Old World apes and monkeys, the dental formula is the same as in Man: i 2/2, c 1/1, p 2/2, m 3/3, × 2 = 32; the nostrils are close together and the tympanic bullæ have tubular entrances. Many, but not all, have cheek-pouches opening into the mouth. The tail is never prehensile and, except in most of the large, man-like apes (Simiidæ), there are naked callosities on the buttocks. With these Old World forms we have no further concern, though it may be noted in passing that Dr. Schlosser has discovered in the Oligocene of Egypt certain monkeys (†Parapithecus) which he thus describes: “The number and structure of the teeth, character of the jaws and bodily size make complete the transition from the Anaptomorphids and Tarsiids to the Simiids.”
Section Platyrrhina. South American Monkeys
In these animals the nostrils are separated by a broad septum, and there are always three premolars above and below (p 3/3). The tail is frequently prehensile and serves as a fifth limb, being capable of supporting the whole weight of the body. There are no cheek-pouches and no callosities, and the tympanic bullæ have no bony tubes leading into them. The thumb is but partially, or not at all, opposable and in some genera is absent.
The New World monkeys are, in general, smaller and lighter than those of the eastern hemisphere; there are no very large ones and they are all arboreal and are confined to the forested parts of the Neotropical region, except the West Indies, which have none. The marmosets (Hapalidæ), the first of the two families into which the Platyrrhina are divided, are little creatures, no longer than squirrels, with long, non-prehensile tails. They are characterized by the dental formula: i 2/2, c 1/1, p 3/3, m 2/2, × 2 = 32, and are the only Primates which have no third molar above or below. The thumb is not opposable, though quite long, and the hallux, or great toe, is very small; they are thus deficient in grasping power. Instead of the flat nails common to all the other Anthropoidea, they have long, sharp claws. All other South American monkeys are included in the family Cebidæ which, in turn, is divided into four subfamilies. It is not necessary to consider these or do more than cite a few illustrative examples.
Fig. 286.—Common Marmoset (Hapale).—By permission of W. L. Berridge, London.
Fig. 287.—Sapajou (Cebus).—By permission of the New York Zoölogical Society.
Some twenty species of the genus Cebus are distributed from Central America to Paraguay; they have long, prehensile tails completely covered with hair, and well-developed thumbs. The monkeys of this genus are familiar to every one, as they are largely used by organ-grinders. The spider-monkeys (Ateles) are so called because of the great length and slenderness of their limbs; the tail is very long and perfectly prehensile, naked on the lower side near the end, which improves its grasping power. The hand has lost the thumb, but is used very effectively as a hook. The species, ten or more in number, have a wider range than those of Cebus and extend from Uruguay to Mexico.
The howling monkeys (Alouatta, more commonly, but improperly, called Mycetes) are gifted with most unusual vocal powers. Mr. Bates says of them: “Morning and evening the howling monkeys make a most fearful and harrowing roar.” “The brief evening chorus of animals then began, the chief performers being the howling monkeys, whose frightful unearthly roar deepened the feeling of solitude which crept on as darkness closed around us.”[14] The tremendous volume of sound which these small creatures are able to produce is due to a resonating apparatus, formed by the great inflation of one of the hyoid bones (see [p. 67]), normally the bony support of the tongue. The tail is long and prehensile, with the end naked beneath; the thumb is well developed.