I &2 
APES AND MONKEYS. 
yellowish, while the loins, the outer surface of the thighs, and the tip of the tail 
are reddish chestnut; the face, hands, and feet being completely black. 
THE BLACK-HEADED UAKARI. 
The Howling Monkeys. 
Genus Mycetes. 
The howling monkeys, or howlers, derive their name from their vociferous 
cries, which are sufficient in the living condition to distinguish them from all the 
other American monkeys. To produce this extraordinary noise—of which more 
anon—there is a peculiar hollow shell of bone joining on to the upper part of the 
windpipe, corresponding to the so-called hyoid bone of man, which is a very small 
and solid structure. The resonance of the voice within this cavity communicates 
to the cry its peculiar intensity. In order to provide space for this bony shell 
the sides of the lower jaw-bone are extremely deep, and by this character, as well 
as by the extreme flatness of the part containing the brain, the peculiar skull may 
always be recognised. A front view of the head of a howler is given in the wood- 
cut on the next page, to illustrate the form of the nostrils in the American monkeys. 
The howlers differ from the two preceding groups, and agree with the spider- 
monkeys and their allies, in having prehensile tails, in which the under surface of 
the extremity is naked. In addition to the presence of the large bony swelling* 
at the top of the windpipe, they may be at once distinguished from all other 
prehensile-tailed monkeys by the extreme obliquity of the plane of the face and 
