MONKEYS, a general name for the ani mals of the highest mammalian order, the Pri mates (q.v.), excepting mankind and the lemurs; ordinarily also excepting the anthropoid apes (see Am) and the baboons (q.v.). The term in fact, then, is suitably limited to three families, considered in their broadest sense, the Hapalidte, Cebida and Cercopithecidce. General characters are as follows: the short hallux, or great toe,, is opposable to the other digits of the foot, so that the feet become converted functionally into hands. The polies, or thumb, of the fore limbs may be absent, but when developed it is usually opposable to the other fingers. These animals may thus be called ufour-handedn or quadruma nous; hence the old designation Quadrumaaa. The limbs are nearly of equal length. There is only one pair of mammary glands, which are pectoral in position. In many cases the cheeks are dilated into pouches. The teeth consist of two incisors in each side of each jaw. The premolars, or false molars, vary in number. The true molars number three in each side of each jaw, the latter teeth being furnished with tubercles of various sizes and shapes, adapted for crushing fruits and vegetables. The canine teeth are generally stroll? and of large size. A diastetna or interval exists between the lower canine and the first lower premolar tooth, and between the upper canine and outer incisor teeth; this interval admitting of the large ca nines being brought into apposition when the jaws are closed.
For information as to the probable descent and geological history of monkeys, see PRI MATES.
The small American monkeys of the family Hapalida., more usually called marmosets (q.v.), seem to be lowest in the scale of structure and nearest the lemurs, and are by some naturalists separated from the Cebidat in a group Arcto pithecini. They are least in size of the race, have the tail long, hairy and not prehensile; no cheek-pouches or natal callosities; the fore limbs shorter than the hind ones; the thumb not op posable; the ears hairy and of large size; the body covered by a close fur. Their dental formula gives four incisors, two canines, six premolars and four molars in each jaw—this dentition resembling that of the Old World monkeys, and also that of man himself. The molars are provided with blunt processes. They are confined to tropical America, and wholly arboreal, feed on insects and fruit, and are tamable, gentle and intelligent. See MARMOSET.
Next to these come the Cebida, called New World monkeys, because the family is confined to the American continent, and also known ay Platyrhini, because of the broad partition in the nose which widely separates the nostrils and causes them to open somewhat laterally, though this term is often applied to the also.
They are characterized by the possession of an extra premolar on each side of each jaw ; and by the length and strong prehensility of the tail in most forms — an arrangement by which the end of the tail (naked there on its underside) curls without effort around a limb and clings firmly to it, giving so great assistance in climb ing that many of these monkeys exhibit wonder ful agility among the trees, grasping and swinging by their tails alone, leaving all four feet (or hands) free. The ears are rounded and with most of the face are destitute of hair, there are no cheek-pouches or callosities on the buttocks, so characteristic of the Old World forms. The hind limbs are generally the longer in this section. In the spider monkeys, however, the fore limbs are longer than the hinder mem bers. The thumbs are not generally opposable, and may be wanting; and the thumb in these monkeys nearly approaches the other fingers in size and form when present. Unlike other mon keys, they have the thumb placed in nearly the same plane as the other fingers, so that the mere position of the thumb renders it unfitted. The great toe is generally of large size, and is more capable of being opposed tp the other digits than the thumb. The diet is mainly of a vege table nature, and their life almost exclusively arboreal, a fact which, more than any question of climate, seems to limit them in range to the region of the tropics, between the plains of northern Mexico and those of southern Brazil, since several species dwell in the cold regions of high mountains. Of the Cebid.e the spider monkeys (Ateles) present very typical examples. In these forms the tail reaches its greatest de velopment as a prehensile organ. The limbs are exceedingly slender, and the thumb is rudi mentary. (See SPIDER-MONKEY.) The capu chin monkeys, or Sapajous (q.v.) form the type of the genus Cebus, and include many species, as also does the genus Callithrix (see SQUIRREL4 MONKEY). The howling monkeys (Mycetes) are so named from the loud howling noises they are capable of producing, through the posses sion of a bony °drum.," which opens into the larynx, and which greatly increases the reso nance of the voice. Other genera are Pithecia, the sakis, or hooded monkeys; Uacavia, the Woolly monkeys; Chrysothrix or golden mon keys; and Nictiptthecus, the Dorocouli monkeys.