GIBBON, the collective title of the smaller man-like apes of the Indo-Malay countries, all belonging to the genus Hylobates (see PRIMATES), which consti tutes the family Hylobatidae.
One of the distinctive features of this family is the presence of small naked callosities on the but tocks. The extreme length of the limbs and the absence of a tail are other features of these small apes, which are arboreal in their habits, and make the woods re sound with their unearthly cries at night ; in agility they are un surpassed. When they descend to the ground—which they do to obtain water—they walk in the upright posture, either with the hands crossed behind the neck, or with the knuckles resting on the ground. Their food consists of leaves and fruits. Gib bons may be divided into two groups, the one represented by the siamang, Hylobates (Symplialangus) 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. entelloides of Tenasserim, and H. agilis of Sumatra are representatives. The range of the genus extends from the southern bank of the Bra maputra in Assam to southern China, the Malay Peninsula, Java, Sumatra and Borneo.