A relationship to the Howlers (Mycetes), suggested by the external appearance of the Uakarís and the form of their lower jaw, is not borne out by their internal anatomy. The caudate lobe of the liver is very large. This character distinguishes the whole of the Cebidæ from the Old World families.
The Uakarís are arboreal Monkeys, very gentle and timid. The distribution of the various species is singularly restricted, each being confined to a small and particular district.
I. THE BLACK-HEADED UAKARÍ. BRACHYURUS MELANOCEPHALUS.
Simia melanocephala (Cacajao), Humboldt, Obs. Zool., p. 317, pl. xxix. (1811).
Pithecia melanocephala, Geoffr., Ann. Mus., xix., p. 117 (1812); Schl., Mus. Pays Bas, vii., p. 227 (1876).
Brachyurus ouakary, Spix, Sim. et Vespert. Bras., p. 12, pl. viii. (1823).
Ouakaria spixii, Gray, P. Z. S., 1849, p. 10, cum fig.
Ouakaria melanocephala, Gray, Cat. Monkeys Brit. Mus., p. 62 (1870).
Brachyurus melanocephalus, W. A. Forbes, P. Z. S., 1880, p. 645, pl. lxiii.
Characters.—Head and nude face-black; back, sides, thighs, upper surface of tail, and outer and inner sides of legs more or less chestnut-brown; shoulders, arms, hands, feet, and rest of tail, black. Ears large, naked, and similar in form to those in Man.