NEW WORLD MONKEYS The American monkeys are differentiated from those of the Old World by the widely separated nostrils facing laterally, whence the name "platyrrhine" (flat-nosed). The head is rounded with relatively small jaws and the ears lack the pointed tip common in Old World monkeys. The buttocks do not bear callosities and the thumb is never truly opposable to the other digits. The op posable great toe of the hind-foot bears a flattened nail, but the nails of the other digits of both hand and foot are frequently com pressed laterally and in the marmosets become claws.
The American monkeys are all arboreal. The recent genera in habit the tropical forests of South America, a few species extend ing northward into Central America, spider-monkeys and certain marmosets even to Mexico. Except from Ecuador northward, the Andes limit the western range of monkeys, though some howlers, spider-monkeys and sapajous reach an elevation in Guatemala of 6,000 to 7,00o feet. A fossil cebid Homunculus, found in lower Miocene formations in Patagonia, indicate the great antiquity and former wide range of the family.
recent Cebidae, which comprise all the platyr rhine monkeys except the marmosets, are divided into some ten quite distinct genera. Of these the most central or primitive type is probably Callzcebus, of which numerous species, known as titis or teetees inhabit the forests of Brazil and neighbouring countries. They feed on fruits, insects and small birds and are extremely vociferous. They are very small, with long, bushy, non-prehensile tails. Rather closely related to these are the dourocoulis (Aotus or Nyctipithecus), the only truly nocturnal monkeys. The huge, closely-approximated eyes and short face, surrounded by a ruff of pale fur, give these little animals a peculiarly owl-like expres sion. Aotus lives on fruits and insects which it hunts at night, re maining hidden during the day. Some species are reputed to have remarkable vocal powers, but. in captivity they are often very silent. The nose is more prominent than in any other American monkey, the nostrils resembling those of catarrhine forms. This is probably correlated with the close approximation of the en larged eyes. Its behaviour in captivity and the anatomy of the olfactory parts of the brain, indicate that smell is well-developed, perhaps more so than in the higher members of the family. This
is probably of more service to nocturnal than to diurnal forms, but is nevertheless probably a primitive character. Both titis and dourocoulis use the hands in holding food but do not exhibit the manifold manipulations of these organs seen in the sapajous.
Two genera of small monkeys, placed in the sub-family Pithe cinae, are Pithecia, the said and Brachyurus or Cacajao, the uakari, both with several species. They are characterized by ex tremely procumbent incisors. The sakis have long, loose fur, that of the head often directed forward on the crown and forming a thick beard about the jaws. The tail is bushy and non-prehensile. The uakaris are the only short-tailed American monkeys. The face is naked and in one species is a brilliant vermilion; the body is covered with pale sandy or straw-coloured long hair.
The squirrel-monkeys (Saimiri or Chrysothrix), are extremely diminutive. The face is short and round and the back of the head projects markedly, its balance on the neck giving a particularly human appearance. The cerebrum, relatively very large, is slightly convoluted, but overhangs the cerebellum to a greater extent than in any other primate, even man. These monkeys are chiefly insec tivorous, and associate in small groups. Some half-dozen species are known, ranging from the Amazonian forests to Costa Rica. They are richly coloured little animals often seen in captivity.
Cebus is aptly called by H. 0. Forbes "the typical genus of the American monkeys." The common names sapajou and capu chin are applied to these familiar monkeys. They are vivacious and relatively hardy, individuals having been known to survive in captivity for 25 years in the north temperate zone. The thumb is well-developed, though not opposable and the hands are used in a great variety of manipulations. The tail is slightly prehensile and usually carried curved toward the underside. With the superior functional adaptation of the hands is correlated a large, highly-developed brain and an intelligence comparable to that of the Old World monkeys. Over 20 species have been described, some extending as far north as Nicaragua. In Colombia Cebus apella is found at nearly 7,00o feet.