Colour. Generally black throughout, with the exception of a white or grey band across the eyebrows. This band is usually, but not always, interrupted in the middle. Many individuals, however, both males and females, vary in colour from brownish black to light yellowish grey, the frontal band beiug always couspicuously paler. The crown, back, and outside of the limbs are often paler-coloured than the lower parts of the body, the skin of the naked part of the face below the frontal band being almost always dark-coloured. Blyth thought that the males only were black, the females always paler; but this is certainly not the case; the females, however, are more frequently pale-coloured than the males.
Dimensions. From crown to rump about 20 inches, fore limb (including hand) 23, hand alone 6, leg and foot 19, foot 6; height from crown to heel about 32 inches. An adult male skull is 4·45 inches long from the occiput to the alveolar margin of the pre-maxillaries at the base of the middle upper incisors, 3·35 in basal length from the lower or anterior edge of the foramen magnum to the same, and 2·9 in breadth across the widest part of the zygomatic arches.
Distribution. The hill-ranges south of Assam; Sylhet, Cachar, Manipiur, Irawadi valley near Bhamo, Chittagong, and Arakan in hill-forest. It is uncertain how far the species is found to the east-ward. According to Anderson it inhabits Martaban. Pemberton's assertion that this species occurs at the base of the Himalayas in the lower ranges of Bhutan is probably a mistake. The type described by Dr. Harlan came from the Garo hills.
Habits. Good accoimts of this animal are given by Burrough, in Harlan's original description, by Blyth and by Anderson. Like most other Gibbons, the Hoolock is usually found associating in flocks, often comprising fifty to a hundred individuals, or even more. An old male, however, is occasionally found solitary.
Gibbons are thoroughly arboreal, and Hoolocks are almost, if not entirely, confined to hill-forest. They move chiefly by means of their long arms, by which they swing themselves for prodigious distances from branch to branch and from tree to tree. They descend hill-sides at a surprising pace, their descent being accomplished by grasping bamboos or branches that bend beneath their weight, and allow them to drop until they can seize the ends of other bamboos or branches lower on the slope, and take another mighty swing downwards. They also ascend with great rapidity, swinging themselves from tree to tree.
When walking on the ground, the Hoolqck rests on its hind feet alone, with the sole flat on the ground and the great toe widely separated from the other digits. The arms are usually held upwards, sometimes horizontally, their great length giving the animal a very peculiar aspect. Gibbons walk rather quickly, with a waddling gait, and can easily be overtaken by men when on the ground.
The food of these Apes consists of fruit, leaves, young shoots, spiders (of which they are very fond), insects, birds' eggs, and
