"As to the convolutions, the brains of the Apes exhibit every stage of progress, from the almost smooth brain of the Marmoset, to the Orang and the Chimpanzee, which fall but little below Man. And it is most remarkable that as soon as {147}all the principal sulci [or grooves] appear, the pattern according to which they are arranged is identical with that of the corresponding sulci of Man. The surface of the brain of a Monkey exhibits a sort of skeleton map of Man's, and in the Man-like Apes the details become more and more filled in, until it is only in minor characters, such as the greater excavation of the anterior lobes, the constant presence of fissures usually absent in Man, and the different disposition and proportions of some convolutions, that the Chimpanzee's or the Orang's brain can be structurally distinguished from Man's.... And the difference between the brains of the Chimpanzee and of Man is almost insignificant when compared with that between the Chimpanzee's brain and that of a Lemur." (_Huxley._) The Anthropoid Apes have no cheek-pouches. The larynx has large dilatations of the shallow depressions--called ventricles--of the mucous membrane on each side of its inner surface--which may extend down as far as the arm-pits, and be connected with powerful voice possessed in most of the species. The stomach is simple, like that of Man, and not sacculated, as in the last family (the _Cercopithecidæ_). The uterus and other structures connected with the reproductive system resemble those in the human subject. The length of gestation varies probably in the different genera, and is unknown in many of the species. The period for which the young are suckled by the mother lasts about six months. "The proportions of the limbs to one another and to the body do not sensibly change after birth; but the body, limbs, and jaws enlarge to a much greater extent than the brain-case." (_Huxley._) Observations are still required, in regard to most of the species, as to the age at which they arrive at maturity, and are able to reproduce. {148}The _Simiidæ_--the most intelligent of the animal kingdom--are all diurnal animals, and essentially arboreal. Many of the members of the family have, when walking, a tendency to tread on the outer edge of the foot, turning, therefore, the toe inward on account of the free motion which is possible between the various bones of its ankle, whereas, in the human foot, these bones are more solidly bound together. When climbing, the power of turning in the sole is, as is evident, of the greatest advantage to the Ape. Their food is chiefly vegetable; a few species exhibit slight carnivorous tendencies.