The siamang inhabits Sumatra. It presents several points of resemblance to the orang-outang, but is also in several respects strongly distinguished from that animal. The arms are longer even than the orang’s, and the peculiar use which the orang makes of his long arms is more strikingly shown in the progression of the long-armed siamang, for the body inclining slightly forward, when the animal is on level ground the long arms are used somewhat like crutches, and they advance by jerks resembling the hobbling of a lame man whom fear compels to make an extraordinary effort. The skull is small, and much more depressed than that of the orang or chimpanzee. The face is naked and black, straggling red hairs marking the eyebrows. The eyes are deeply sunk, a peculiarity which, by the way, seems characteristic of arboreal creatures generally;[37] the nose broad and flat, with wide-open nostrils; the cheeks sunk under high cheekbones; the chin almost rudimentary. “The hair over the whole body is thick, long, and of a glossy black colour, much closer on the shoulders, back, and limbs than on the belly, which, particularly in the females, is nearly naked. The ears are entirely concealed by the hair of the head; they are naked, and, like all the other naked parts, of a deep black colour. Beneath the chin there is a large, bare sac, of a lax and oily appearance, which is distended with air when the animal cries, and in that state resembles an enormous goitre. It is similar to that possessed by the orang-outang, and undoubtedly assists in swelling the volume of the voice, and producing those astounding cries which, according to Duvancelle’s account, may be heard at the distance of several miles.” This, however, may be doubted, for M. Duvancelle himself remarks of the wouwou, that, “though deprived of the guttural sac so remarkable in the siamang, its cry is very nearly the same; so that it would appear that this organ does not produce the effect of increasing the sound usually attributed to it, or else that it must be replaced in the wouwou by some analogous formation.” The habits of the siamang are interesting, especially in their bearing on the relationship between the various orders of anthropoid apes and man; for, though the gibbon is unquestionably the lowest of the four orders of the anthropoid apes in intelligence, it possesses some characteristics which bring it nearer to man (so far as they are concerned) than any of its congeners. The chief authorities respecting the ways of the siamang are the French naturalists Diard and Duvancelle, and the late Sir Stamford Raffles.