Page:EB1911 - Volume 22.djvu/346

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332
PRIMATES


well developed, the limbs of medium length, with the front not longer than the hind pair, the nails curved, and the humerus with an entepicondylar foramen. 'The typical genus Cebus includes the numerous species of capuchins, many of which are so commonly seen in captivity. 'fThey are stouter in build and smaller in size than the spidenmonkeys, and their tails are only prehensile to a small extent, 'but are commonly carried spirally rolled. The conical upper canines project below the upper lip, and the molars have blunt low cusps. Well-known species are the white-cheeked capuchin, C. lunatus (fig. 12), of south Brazil; the true capuchin, C. capucinus, ranging from Guiana to Brazil; and the brown capuchin, C. fatuellus, of Guiana; all of these showing the black crown from which these monkeys take their popular name. The most northern representative of the group is the white-throated C. hypoleucus, which ranges to Costa Rica. The squirrel-monkeys, Chrysothrix (or Saimiris), of which C. sciureus is the most familiar representative, are not infrequently placed in the Nyctipithecimze, although their true position seems to be here. They differ from Cebus by their smaller size and more delicate build, by the tail being scarcely at all prehensile, by the smaller canines, smaller and more sharply cusped molars, and the large and closel -ap roximated orbits, whose inner walls are partly membranous gee €APUcum and SQUIRREL~MONKEY).

The second section of the sub-family includes the spider-monkeys (fig. 13), and is characterized by the completely prehensile tail, than usual. In the woolly spider-monkeys of the genus Lagothrix (fig. I4) not only is the fur woolly, but the thumb is fairly well developed; the nails are like those of Bmchyleles, but the nostrils are normal. Humboldt's spider-monkey, L. humboldti (or L. lagomca) and the dusky spider-monkey, L. infumata, both of which occur in Brazil and Amazonia, alone represent this genus.

FIG. 13.-Geoffroy's Spider-Monkey (Ateles geojroyi). with the inner surface of the tip naked, the rudimentary condition or absence of the thumb, the laterally compressed and more or less pointed nails, and the absence of an entepicondylar foramen to the humerus. The limbs, too, are very long and slender, with the front pair of greater length than the hind ones. The caecum approximates to that of the Catarrhina, having its terminal extremity pointed. The true spider-monkeys (Ateles) lack the thumb, and have the nails but slightly compressed and pointed, the limbs very long, the nasal septum of ordinary width, and the fur not woolly. Nearly all have the hair on the head, except that of the forehead, directed forwards. There are nearly a dozen species. In these monkeys so powerful is the grasp of the tail that the whole body can be sustained by this organ alone. It even serves as a fifth hand, as detached objects, otherwise out of reach, can be grasped by it, and brought towards the hand or mouth. Their pretension is in other respects exceptionally defective, owing to the loss of the thumb. Spider-monkeys are very gentle in disposition; and, by this and their long limbs and fitness for tree-life, seem to represent the gibbons of the Old World. Nevertheless, in spite of their admirable adaptation for arboreal life, their comparatively slow progression offers a marked contrast to the vigorous agility of the gibbons (see SPIDER-MONKEY). The brown spider monkey (Brachyteles arachnoid es) of south Brazil alone represents a genus connecting the preceding in some degree with the next, a rudimentary thumb bein present, while the fur is woolly, the nails are much compresseci. and the nostrils more approximated F IG. 14.—Humboldt's Woolly Spider-Monkey (Lagothrix humboldti). Some half-dozen species of the monkeys known as sakis (Pitheciq) form the typical representatives of the sub-family Pfithecinae, in which the tail, even when long, is non-prehensile, while the lower incisors are slender and inclined forwards in a peculiar manner, with a gap on each side separating them from the long canine. The hemispheres of the brain cover the cerebellum, the brain-case is elongated, and, despite the absence of a laryngeal sac, the lower jaw is deep with a large angle, thus recalling that of the howlers. There is no caecum. In all cases the thumb is well developed. The arrangement of the hair is very variable. From the other members of the group the sakis are sufficiently distinguished by the long and bushy tail; while they are further characterized by having a large head. In some cases the hair on the crown of the

FIG. 15.*L€1'I'1uI'-lilie Douroucouli (N yctipithecus felinus). head is divided by a transverse parting, so as to overhang the upper part of the face. P. satanas of Para and P. chiropotes of Guiana are well-known species. The uakaris (Uacaria or Cothurus) of Amazonia are broadly distinguished from all other Cebidae by their short or rudimentary tails; Ua. calm being remarkable for its brilliant red jaw and pale chestnut hair (see UAKARI).