_Brachyurus_, Spix, Sim. et Vespert. Bras., p. 11 (1823); W. A. Forbes,
P. Z. S., 1880, p. 644.
_Ouakaria_, Gray, P. Z. S., 1849, p. 9.
The species of this genus are at once recognised by their short tail, being
the only American Monkeys in which this organ is short. The fur is short
and silky; the face short, and often brightly coloured. The mammæ are
situated on the breast. In the skull the lower jaw is dilated behind, and
certain bones, the parietal and the malar, are in contact with each other
for a more or less considerable extent on the side walls of the skull. (Cf.
W. A. Forbes, P. Z. S., 1880, p. 639, figs. 5 and 6.) In Old World Monkeys
this contact _never_ (except slightly in _Hylobates_) takes place. This is
a useful mark for discriminating between the skulls of New and Old World
Monkeys. (_Forbes._) The shortness of the tail is due, not to a reduction
in the number of the vertebræ, which may be 15 to 17, but in their size.
In the brain the cerebrum exhibits the more important grooves
characterising the brain of the higher Apes (_Simiidæ_) well developed; the
cerebellum (or hind brain) is also well developed. Thus in its general
characters the brain of the Uakarís approaches most nearly to that of the
genera _Cebus_ and _Pithecia_ (next to be described). By reason of its
greater complication and development, it departs widely from that of the
Titis (_Callithrix_) and the Squirrel-Monkeys (_Chrysothrix_).
A relationship to the Howlers (_Mycetes_), suggested by the external
appearance of the Uakarís and the form of their lower {175}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.