"Of the various genera of the _Simiidæ_, the Gibbons are most remote from Man. The Orangs come nearest in the number of the ribs, the form of the cerebral hemispheres, and certain other characters of the brain and skull; but they differ from him much more widely in other characters, especially in the limbs, than the Gorilla and the Chimpanzee do. Of the Chimpanzees the Gorilla is more Man-like in the proportions of the leg to the body, and of the foot to the hand; and likewise in the size of the heel, the curvature of the spine, and the absolute capacity of the cranium. The true Chimpanzees approach Man most closely in the skull, dentition, and proportionate length of the arms." (_Huxley._) The _Simiidæ_ are confined to the Ethiopian and Indian Regions. The Gorillas and Chimpanzees live exclusively in the Tropical Regions of Western and Central Africa; the Gibbons range into all the four provinces of the Indian Region; while the Orangs are confined to two islands of the Indo-Malayan Sub-region. THE GIBBONS. GENUS HYLOBATES. _Hylobates_, Illiger, Prodr. Syst. Mamm., p. 67 (1811). The group of Tree-walkers, as the term _Hylobates_ signifies, {149}embraces the smallest-sized, the slenderest-bodied, the longest-limbed, and the most perfectly arboreal of all the Man-like Apes. All are covered with thick woolly hair, which, on the arms and fore-arms, converges (except in _H. agilis_) towards the elbow. Their head is small and round, and the face compressed. Except the Orangs, the Gibbons have the longest arms of all the Apes, so long that when they stand erect the points of their fingers can touch the ground. Compared with the spinal column, their arms are as 19 to 11, while the legs are one-third longer than it. The fore-arm is much longer than the arm itself; the hand is longer than the foot, and the thumb is very long in proportion to the hand. The knee is free from the side of the body, and the great-toe is well developed and nearly one-half the length of the foot. The nails of both the thumb and the great-toe are flat. Callosities, which are wanting in all the other genera, are present in _Hylobates_, but are very small. In the skull the occiput is convex; the orbits are very large and deep, and the supra-orbital ridges prominent. The canine teeth are much larger than the others, and equally large in both sexes. They are generally the last of the permanent teeth to come in, but in the Gibbons they generally precede, or are developed along with, the last molar.