These Gibbons have many interesting points about them, and one of the most curious is that they have no air or laryngeal pouches, and yet their general anatomy, especially of the muscles of the throat, neck, and body, is the same as that of the Siamang, which has been noticed above to have a vast pouch. The brain is small, especially behind, but why it is difficult to imagine, for the Spider Monkey, which lives in the New World, and whose feats of agility resemble those of the Gibbons, has a very large back portion of the brain, large even in proportion to that of man; and the importance of this difference is all the greater when it is remembered that all the last investigations into the actions of the nerves arising from the sides of the brain towards the back connect them with motions of the hands and fore-limbs especially. But it is possible that the back of the brain in the Siamang appears to be smaller than it really is, because of the large size of the cerebellum. The skulls of the Gibbons are very man-like, and more so than those of the other Apes, and this is because of their faces and jaws being smaller in comparison with the brain case. If the young of all the great Apes be examined, their skulls will appear much more human than those of the adults, because the brain and face grow up to a certain point together and equally; but with age the brain does not increase in size proportionally with the face, which grows on, and finally preponderates in size. But if the skulls of the young Apes be compared one with the other, that of the Siamang will really not look as human as that of the Gorilla or Chimpanzee. [Illustration: AGILE GIBBON.] The Gibbons have a very small appendage to the blindgut, and they have hard bare pads or callosities on the seat, and these structures connect them with the next group of Monkeys, which cease to be man-shaped; and indeed the Gibbons and Siamangs, although man-shaped (Anthropomorpha), occupy neutral ground between the Orangs and the Cynomorpha. Formerly, in those ages when the Orang lived on the continent of India, the Gibbons roamed far over the vast land surfaces of the period, and lived in Southern France. Portions of the skeleton of an Ape as large as a man, but which resembled the Hylobates, were found there, and named _Dryopithecus_, in strata of Mid-Tertiary age.