MONKEY

in general, any member of the mammalian order Primates, with the exception of the tree shrews, the lemurs and their allies, the gibbons and apes, and humans. Monkeys are arranged into two main groups: those of the Old World tropics, the catarrhines, with two families, Cercopithecidae (monkeys with cheek pouches) and Colobidae (leaf monkeys); and those of the New World tropics, the platyrrhines, also with two families, Callitrichidae (marmoset) and Cebidae. Monkeys live in tropical forests, where they move about by using all four limbs. Except for the largest, such as the baboon and drills, monkeys are predominantly arboreal, leaping from limb to limb in their travels among the trees. On the ground they walk in plantigrade fashion (the entire sole of the foot touching the ground); but they are capable of sitting upright and sometimes standing erect, and consequently their hands are freed for many manipulative tasks. Most have a short, relatively flat face without great prominence of the muzzle (excepting the baboons and drills). The hands and feet are prehensile, with, typically, five digits on each, the first (thumb and big toe) being divergent from the others. Commonly, the digits have flattened nails, but those of the marmoset are an exception. Except for the night-roaming durukuli of tropical America, monkeys are active during the day, moving frequently in bands in search of vegetation, birds' eggs, smaller animals, or insects to eat. Monkeys are highly social animals and are often organized in clans headed by an old male; these clans are rigidly defined in such species as howlers and baboons. As in all primates the brain is comparatively large. This feature, combined with the freeing of the hands and a well-developed vision, allows monkeys a great latitude of activity. Among the smaller New World forms that have endeared themselves to humans because of their ingratiating antics and their tameability are the alert marmosets, often plumed and colourfully arrayed; the inquisitive squirrel and woolly monkeys; and the capuchins, or organ grinder's monkeysall of which exhibit in marked degree the curiosity and cleverness ascribed to monkeys generally. Other interesting kinds are the acrobatic spider monkeys and the noisy howlers. The Old World monkeys include many that are popular in zoos, especially the beautifully coloured African guenons (monadiana, white-nosed, green, vervet, and grivet monkeys), long-maned guerezas, mangabeys, and the chiefly Asiatic macaques. The macaques include the Barbary ape of the Rock of Gibraltarthe only macaque outside of Asia and the only monkey inhabiting any part of Europe todayand the rhesus monkey of India, which has been used considerably in medical research. The graceful Asiatic langurs include the hanuman, or sacred monkey, of India. Among the more unusual monkeys are the strikingly coloured African drills and mandrills, large ground-dwelling monkeys; the proboscis monkey of Borneo; and the related snub-nosed monkeys of western China. New World monkeys, or platyrrhines, have broad noses, with a wide septum separating the outwardly directed nostrils; each side in both jaws has three premolar teeth. Platyrrhines lack a bony ear passage, and the arrangement of some cranial bones differs from that in Old World monkeys. Usually long-tailed, a few have prehensile tails with specialized naked skin on the under surface. Old World monkeys, or catarrhines, have narrow noses and a thin septum, the nostrils being directed downward. Only two premolar teeth are present above and below on each side of each jaw, but the skull is provided with a bony auditory passage. In none of the catarrhines is the tail prehensile; it may be long, short, or lacking. All Old World monkeys have hard patches of naked skin on the buttocks (ischial callosities). In this they differ not only from the New World monkeys but also from the great apes. Monkeys differ from the lemur in that there is no restricted breeding season. After sexual maturity, males are at all times potent and nonpregnant females are under regularly monthly cycles termed menstrual cycles. The phases of each cycle may, as in many platyrrhines, scarcely be recognizable, except by behaviour, but in some platyrrhines and all catarrhines a sanguinous discharge appears at one stage. This is accompanied in many species by gross swelling of the external genitalia and neighbouring skin. Gestation varies from four and a half months in marmosets to nearly seven months in some Old World monkeys. A single young (occasionally twins) is produced and is nursed by the mother.