In the skull the cranial portion exceeds the facial. Professor Mivart observes that in this group the facial part is relatively smaller than in many of the higher Old-World Apes. The skull has no external bony canal (or meatus) to the ear; and its frontal bones possess large air-cavities. In the Capuchins the incisor teeth are erect, and are always shorter than the canines. The molars are four-cusped, and have, on their crowns, two transverse ridges and the oblique ridge, already described in the Lemuroidea, from the front inner cusp to the hind outer cusp. These animals have also one milk-molar tooth more than in Man.
The outer surface of the main brain (cerebrum) is almost as much convoluted as in the Old World Apes.
The Capuchins range from Costa Rica to Paraguay, and are represented by about eighteen species. They are very gentle and docile animals.
F. Cuvier observes in his "Histoire Naturelle des Mammiferes," that of all the Quadrumana—indeed, of all the Mammals—there are none so difficult to characterise as the Capuchins of America, whose colours vary almost with every individual. No two authors agree in the number of species the genus contains. Brisson recognised three, Linnæus four, Gmelin six, Buffon two, and George Cuvier supposed it possible that they all belonged to but one species. Two causes help to produce this diversity of opinion; one is, as remarked above, the natural disposition which these animals have to vary, and to become lighter or darker in colour according to circumstances, and the other is the extremely close relationship that exists between the different species of the genus. Observations, however, are not yet numerous enough, nor exact enough, to enable those who have only studied the species alive in Europe, or had skins, to decide with such imperfect data as to their sex, age, and habitat. Not until some naturalist has made a prolonged study of these animals in their native country, and watched their conduct and relations in the living state, can we hope to attain to any certain knowledge of how many species the genus contains; and of the differences between the old and young of both sexes at different periods from youth to age.
I. THE WHITE-THROATED CAPUCHIN. CEBUS HYPOLEUCUS.
Saï á gorge blanche, Buffon, Hist. Nat. Mamm., p. 64, pl. 15, fig. 9 (1767); Fr. Cuv., Hist. Nat. Mamm., livr. xvi.; Audeb., Hist. Nat. Singes, fam. v., sect. 2, pl. 5 (1797).
Simia hypoleuca, Humb., Obs. Zool., i., p. 337 (1811); Pucher., Rev. et Mag. de Zool. (2), 1857, p. 348.
Cebus hypoleucus, Geoffr., Ann. Mus., xix., p. 111 (1812); Gray, Cat. Monkeys Brit. Mus., p. 50 (1870); Schl., Mus. Pays Bas, vii., p. 190 (1876).
Cebus leucocephalus, Gray, P. Z. S., 1865, p. 827, fig. 4; Sclater, P. Z. S., 1872, p. 4; Alston in Godman and Salvin, Biol. Centr. Am. Mamm., p. 13 (1879).
Characters.—Hair very silky, smooth and stiff, and thicker above than below. Face and forehead nude, flesh-coloured; hands and feet nude, of a violet hue, as also the thinly-haired skin of the under side of the body. The tip of the tail for a short distance being naked, distinguishes this species from all others. Shoulders, arms, and sides of the head behind the ears pure white; chest and throat yellowish; rest of the body deep black.