In the head, the eyes are always directed directly forwards and the snout is typically relatively short. As is the rule for higher primates, a rhinarium (a naked, moist area of skin around the nostrils that is present in most mammals) is al-
ways completely absent. The nostrils are relatively close-set and typically downward-pointing (with the notable exception of the Mentawai Islands snub-nosed leaf-monkey Simias concolor), and in some species the nose is prominently developed. Cheek pouches are never present. As in all other Old World monkeys and apes, the dental formula is I2/2 C1/1 P2/2 M3/3. The canine teeth are typically large, stabbing teeth (although generally less prominent than in cheek-pouched monkeys), and the rear edges of the upper canines are honed against the leading edges of the anterior premolars in the lower jaw. In both upper and lower jaws, all molar teeth are bilophodont. Colobine monkeys typically walk and run quadrupedally in the trees and, in some cases, on the ground. In the trees, they are typically agile climbers. In contrast to cheek-pouched monkeys, the legs are typically somewhat longer than the arms. In the hand, the thumb is generally reduced, and in the colobus monkeys it is virtually vestigial. Fine manipulative actions of the hand are thus largely precluded. Well-developed hardened sitting pads (ischial callosities) are present on the buttocks, and these are supported by broad, roughened bony flanges (ischial tuberosities) on the pelvis. Reflecting the predominance of arboreal habits, the tail is usually relatively long, although it is reduced to a short appendage in some species, for example in the snub-nosed leaf-monkey.
In many species, coloration of the body fur is relatively inconspicuous or even cryptic, generally being darker dor-sally and paler ventrally. In several species, infants have a distinctive coloration. The face is usually virtually naked, although there is occasionally tufts of hair on the cheeks and/or chin. Body size ranges from the olive colobus (Pro-colobus verus), with a head and body length a 19.0 in (48.0 cm) for males and 18.5 in (46.5 cm) for females, and a tail length of 22.5 in (56.0 cm) for males and 23 in (57.5 cm) for females, to the proboscis monkey (Nasalis larvatus), with a head and body length of 30 in (74.5 cm) for males and 25 in (62.0 cm) for females, and a tail length of 26.5 in (66.5 cm) for males and 23 in (57.5 cm) for females. Body mass ranges from 10 lb 6 oz (4.7 kg) for males and 9 lb 4 oz (4.2 kg) for females in the olive colobus (Procolobus verus) to 45 lb (20.4 kg) for males and 21 lb 10 oz (9.8 kg) for females in the proboscis monkey (Nasalis larvatus).
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