THE CAPUCHINS, HOWLERS, AND SPIDER-MONKEYS. I51 
Monkeys there are no cheek-pouches, nor ischial callosities. Ex- 
cept in the Spider-Monkeys the hind-limbs are longer than the 
fore-; ‘while the thumb, even where it is best developed, is 
capable of but a partial opposition to the other fingers, bending 
almost in the same plane with the latter, so as to be more like 
a fifth finger.” (A@ivart.) Nevertheless, all its muscles, except 
the long flexor, are present. The great-toe is large and can be 
moved from and to the side of the other digits, but is not 
opposable to them. 
The skull is smooth and has no muscular crests; the ex- 
ternal bony tube to the ear is not ossified. ‘The two extremes 
in its form are presented by the Howling Monkeys (AJ/oua/ta) 
and the Squirrel-Monkeys (Chrysothrix), as pointed out by 
Professor Huxley in his ‘‘ Anatomy of Vertebrated Animals” : 
“In the former the face is very large and prominent, with a low 
facial angle. The roof of the brain-case is depressed ; the 
plane of the occipital foramen [for the passage of the spinal 
cord] is almost perpendicular” to the axis of the base of the 
skull. In Chrysothrix, on the contrary, the face is relatively 
small, with a high facial angle; the brain-case is moderately 
arched ;” and the plane of the occipital foramen is horizontal. 
The dentition of the Ced:de is very characteristic of the 
family. The dental formula is 13, Cl, P3, M# and the teeth 
thirty-six in all—a larger number than is found in any of the 
Old World forms, or in the species of the last family (the 
Hapalide) ; for they possess an extra pre-molar tooth above 
and below on each side. Their molar teeth are four-cusped ; 
and in the upper molars of the Spider-Monkeys (Aé/es) and 
of the Howlers (A/owatta) there is an oblique cusp, such as is 
found in the molars of the ZLemurocdea, joining the hind inner 
to the front outer cusp. Among the Cedde the brain varies 
