The mammal fauna of the Indian region of Asia is much more highly developed than that of the Palaearctic. The Quadrumana are represented by several peculiar genera, amongst which are Semnopithecus, Hylobates and Simia.
Gibbons may be divided into two groups, the one represented by the siamang, Hylobates (Symphalangus) syndactylus, of Sumatra and the Malay Peninsula, and the other by a number of closely allied species.
Hainanus) in confinement changed from uniform sooty-black (without the white frontal The Tenasserim Gibbon (Hylobates entelloides).
The ungko (Hylobates agilis) is not so common.
This is Huxley's argument, some prominent points of which are the following: As regards the proportion of limbs, the hylobates or gibbon is as much longer in the arms than the gorilla as the gorilla is than the man, while on the other hand, it is as much longer in the legs than the man as the man is than the gorilla.