138 Mammals of Eastern Asia 
The type species of the genus is the White-handed Gibbon, 
Hylobates lar. 
At least four species of Gibbons exist on the continental 
mainland of Asia, and the Sunda Islands Gibbon, H. moloch, 
on Java and Borneo. The mainland species are the Siamang, 
H. syndactylies, the White-handed Gibbon, H. lar, the Hoolock 
Gibbon, H. hoolock, and the Black or Crested Gibbon, H. con- 
color. In addition, H. agilis may be separated from H. lar as a 
full species. 
The Siamang, Hylobates syndactylies, is distinguished from 
all other Gibbons by the fact that the second and third toes are 
contained in a common web of skin. There is an inflatable sac 
in the throat. The head is uncrested. The color of this Gibbon 
is black, unrelieved by any white on the brows. The length of 
the head and body is about 3 feet ; the span across the arms about 
5 feet. 
The Siamang occurs in Tenasserim and the Malay Peninsula 
between 2000 and 6000 feet, and on Sumatra. The form in 
Sumatra is typical, the peninsular race being distinguished as 
H, s. continents . 
The Black, Crested, or Indo-Chinese Gibbons, Hylobates 
concolor, are sharply set apart from all other Gibbons by pos- 
session of an erect mat of hairs or crest on the head and by 
the extremely long clitoris of the female sexual organs, a 
condition analogous to that in the Spider Monkeys of tropical 
America. 
As in H. syndactylies, there is no white band of hairs across 
the brows. The female has a patch of dusky on the crown of the 
head. Baby Crested Gibbons of both sexes are pale yellowish 
gray. Males become and remain black; females turn very dark 
and then lighten to buff or grayish buff. In the typical race 
found on Hainan Island and the hilly parts of Tonkin and 
northern Annam, the males are wholly black, the females pale 
gray. Related races are found in Indo-China, and the Crested 
