190 ALLEN’S NATURALIST’S LIBRARY. 
in the male (less so in the female) for the reception of the 
vocal apparatus. ‘Their incisor teeth are small and equal, the 
canines are prominent and have an oblique ridge across the 
crown from the outer front, to the inner hind, cusp, and the 
upper molars are large. The tail is powerful and prehensile, 
naked towards the tip, where it is tactile and very sensitive. 
The thumb is movable, the face is naked, and the chin 
bearded. Some have short, and some have long, fur over their 
bodies, but it is generally more plentiful about the head. In 
appearance they are the most unattractive and repulsive of 
the American Monkeys. ‘Their intelligence is also of a very 
low order. 
The roof of the brain-case is depressed ; the plane of the 
opening for the passage of the spinal-cord from the brain is 
almost perpendicular to that of the base of the skull; the 
condyles for the articulation of the neck are situated as far 
back as possible. Sir William Flower, in his valuable mono- 
graph on the brain of JZjce/es, has shown that the frontal lobes 
are small and the cerebral hemispheres only just cover the 
cerebellum. In regard to its grooves and convolutions, the main 
brain (cerebrum) of Mycetes can be distinguished from that of 
all other Monkeys. The whole organ is small as compared with 
the size of the animal; it wants the roundness and fulness 
of that of the Spider-Monkeys (4Ze/s) and of the Capuchins 
(Cebus). Its surface markings are comparatively few and 
simple, and depart remarkably from the ordinary type seen in 
the order. In the Old World Apes there is a striking simi- 
larity in the character of the surface markings of their cerebral 
hemispheres. There is a slight ascensive development from 
Cercopithecus towards Ay/obates ; and further complications 
overlying the same primitive type—such as large proportionate 
