The thigh-bone (_femur_) has no round ligament binding its articular head into its socket in the pelvis, a disposition which, while it affords greater flexibility and freedom to the hind-limbs in climbing, gives it much less firmness in walking on the ground. The proportionate length of the foot to its limb is greater in this genus than in any other of the _Anthropoidea_. The ankle (_tarsus_) is very short, and the bones (_phalanges_) of the toes form the longest part of the foot. The great-toe is especially short and divergent, its terminal bone being often absent, while the bones of the digits are long and curved. On account of the form of certain bones of the tarsus and their inter-mobility the foot is set obliquely to the leg through the action of one of its muscles (the _tibialis anticus_), so that the sole is pulled to the inside when walking. The outer edge of the foot, with the upper side of the fourth and fifth toes, is therefore applied to the ground in the act of progression, while the spread thumb supports most of the animal's weight. The wrist (_carpus_) contains the complete number of nine bones, as it possesses the _os centrale_ wanting in Man and the Chimpanzees. The breast-bone in the Orang is composed of ossifications {174}arranged in pairs, instead of being formed of only two bones, as in the other members of the family. Between the neck and the complex and solid sacral bone there are sixteen vertebrae, and there are twelve pairs of ribs, as in Man. The vertebral column presents slight but distinct indications of the curvature so characteristic of Man, and is nearly as much concave forward in its dorso-lumbar region as in a child. The Orang-utan has no uvula as in Man and in the Chimpanzees. It possesses enormous air sacs--dilatations of the lateral cavities (ventricles) of the larynx, found in Man--which extend over the throat, the top of the chest, and as far as the arm-pits; these may even unite in the middle line. Its great-toe and thumb lack the long flexor muscles which are present in Man and in the Chimpanzees. "Of all Apes, the Orang has the brain which is most like that of Man; indeed, it may be said to be like Man's in all respects, save that it is much inferior in size and weight, and that the cerebrum is more symmetrically convoluted and less complicated with secondary and tertiary convolutions." (_Mivart._) The cerebral hemispheres are higher in proportion to their length than in any other _Anthropomorpha_, but they are elongated and depressed, as compared with Man. (_Huxley._)