GIBBON, the collective title of the smaller man-like apes of the Indo-Malay countries, all of which may be included in the single genus Hylobates. Till recently these apes have been generally included in the same family (Simiidae) with the chimpanzee, gorilla and orang-utan, but they are now regarded by several naturalists as representing a family by themselves - the Hylobatidae. One of the distinctive features of this family is the presence of small naked callosities on the buttocks; another being a difference in the number of vertebrae and ribs as compared with those of the Simiidae. The extreme length of the limbs and the absence of a tail are other features of these small apes, which are thoroughly arboreal in their habits, and make the woods resound with their unearthly cries at night. In agility they are unsurpassed; in fact they are stated to be so swift in their movements as to be able to capture birds on the wing with their paws. When they descend to the ground - which they must often do in order to obtain water - they frequently walk in the upright posture, either with the hands crossed behind the neck, or with the knuckles resting on the ground. Their usual food consists of leaves and fruits. 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. The union of the index and middle fingers by means of a web extending as far as the terminal joints is the distinctive feature of the siamang, which is the largest of the group, and black in colour with a white frontal band. Black or puce-grey is the prevailing colour in the second group, of which the hulock (H. hulock) of Assam, H. lar of Arakan and Pegu, H. entellöides of Tenasserim (fig.), and H. agilis of Sumatra are well-known representatives. A female of the Hainan gibbon (H. hainanus) in confinement changed from uniform sooty-black (without the white frontal band of the black phase of the hulock) to puce-grey; but it is probable that this was only an individual, or at most a sexual, peculiarity. The range of the genus extends from the southern bank of the Bramaputra in Assam to southern China, the Malay Peninsula, Java, Sumatra and Borneo.
The Tenasserim Gibbon (Hylobates entellöides).
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)