XVII SPECIES OF GIBBON 57a 
compared with other Anthropoids is the fact of the large size of 
the canines, which are of equal or nearly equal size in the two 
sexes. The molars on the other hand have been particularly 
at § 
Fic. 272.—Hoolock. Hylobates hoolock. x §. 
compared to those of Man. The brain is simpler than in the 
higher forms. But it is not clear that this may not be a case 
of diminished complexity of convolution going hand in hand 
with Smallness of size. 
The Gibbons range through south-eastern Asia from Assam 
and Burmah to Hainan. The number of species is a little 
doubtful. It is clear that in the first place we may distinguish 
the Siamang, H. syndactylus, which indeed some regard as a 
separate genus. It is mainly to be defined by the syndactylous 
character of the second and third toes; they are united by skin 
as far as the last joint. The Hainan species, H. hainanus, is 
probably distinct, and the following names have been given to 
various other species or races, viz. H. agilis, H. leuciscus, H. leuco- 
genys, H. lar, H. hoolock. These animals can walk erect; and 
when they do so, the big toe is separated as in unsophisticated 
or at least unbooted man. The voice is well known to be loud, 
