712 PRIMATES 
is related to the enormous size of the vocal organs, which the rami 
of the mandible enclose and protect. The inflated hyoid bone, 
which forms a deep cup, is shown in the figure. The Howlers are 
subject to great individual and sexual variation of colours, so that 
the discrimination of species from local races is difficult. In one 
species the male is black and the female straw-coloured ; and several 
of the species have bright red or golden hair on the flanks. In 
disposition these creatures are sluggish and stupid, but their chief 
characteristic is their prodigious power of voice. Mr. Bates, in his 
Naturalist on the Amazons, observes that “when Howlers are seen in 
the forest there are generally three or four of them mounted on the 
topmost branches of a tree. It does not appear that their harrow- 
ing roar is emitted from sudden alarm; at least it was not so in 
captive individuals. It is probable, however, that the noise serves 
to intimidate their enemies.” 
Several species have been described, the Red Howler (JZ. seniculus) 
and the Ursine Howler (Jf. wrsinus) being well-known forms. 
Remains of this genus probably referable to existing types are found 
fossilised in the cavern-deposits of Brazil. An allied fossil form 
from the South American Pleistocene has been described as 
Protopithecus. 
Subfamily Pitheeiinse.—Lower incisors inclined forward at their 
summits ; hyoid bone normal ; tail long or short, non-prehensile ; 
pollex well developed. Two genera are included in this subfamily, 
readily distinguished by the length of the tail. 
Pithecia.\—The Sakis, as the representatives of this genus are 
commonly termed, are readily characterised by the length of the 
tail; the angle of the mandible is expanded, although less so than 
in Mycetes. A number of species have been described, the Black 
Saki (P. satanas) of the Lower Amazons, being one of the best 
known. While some species, like P. hirsuta, have long hair covering 
the whole of the head, body, and tail, in others only the head, or 
the cheeks and chin, are so clothed. 
Uacaria.2—The Uakari Monkeys differ from all the other 
Cebide by their short Baboon-like tail. The Bald Uakari (U. calva) 
of the Rio Negro, and the closely allied U. rubicunda of the Upper 
Amazons, are remarkable for their scarlet face, which forms a striking 
contrast to the long, silky, whitish hair covering the body. Accord- 
ing to Mr. Bates, the Uakaris live in forests which are inundated 
during a great part of the year, and never descend to the ground ; 
they appear to be rare and of local distribution. The third species, 
U. melanocephala, differs considerably from both the others. The 
cecum of U. calvw, according to Mr. F. E. Beddard, measures 
’ Geoffroy, Ann. du Muséum, vol. xix. p. 115 (1812). 
* Gray, Proc. Zool. Soc. 1849, p. 9. Amended from Ouakaria : Syn. Brachy- 
urus ; Spix, Sim. et Vesp. Brasil,'p, 11 (1823). Preoceupied by Fischer, 1814. 
