A Hand-book to the Primates, Volume 2 (of 2)

by Henry O. Forbes

The cranium is very variable in form; the crown is high and pointed, the forehead round and elevated, and the occipital region convex. No two individuals are exactly alike. "The slope of the profile, the projection of the muzzle, together with the size of the cranium, offer differences as decided as those existing between the most strongly marked forms of the Caucasian and African crania in the human species. The orbits vary in width and height; the cranial ridge is either single or double, either much or little developed, independent of age, being sometimes more strongly developed in the less aged animal." (Wallace.) The supra-orbital ridges are prominent, without being particularly so. The contour of the head is more human in form, however, in youth than in age, when the forehead is large and convex. The canine teeth are very large and tusk-like in the male, but smaller in the female. The upper molars exhibit on their crowns complex rugosities; they have four cusps and an oblique ridge, as in Man, from the front inner, to the hind outer, cusp; the lower molars are five-cusped. The permanent canine teeth sometimes appear before the last permanent molar has come into place.

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 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.)

The colour of the hair of the Orang is a brick- or yellowish-red all over, but in old males it is sometimes darker on the limbs. Its length (twelve to sixteen inches) is greatest, and its character coarsest, on the arms, thighs, and shoulders; the face, ears, and throat are bare, and the skin of a reddish- or yellowish-brown colour; but there is a thin beard on the chin. The back of the hand and fingers are also thickly haired; on the arms the hair grows towards the elbow, as on the fore-arm, both meeting in a point at the elbow.

Between childhood and middle age the skin varies in colour from dark yellowish in the younger individuals to blackish-brown, or black, in the adults (the latter colour largely predominating). Very often the face and neck are almost or quite black, the palms light brown, and the breast and abdomen mulatto-yellow. (Hornaday.)

In size also the Orang varies greatly; the males being larger than the females. The largest male shot by Wallace measured 4 feet 2 inches. Hornaday, however, shot several exceeding 4 feet 4 inches, his tallest being 4 feet 6 inches, and one male was 3 feet 10½ inches; while his largest female measured 4 feet, and the smallest adult female 3 feet 6 inches. The breadth across the face in males varies from 11½ to 13½ inches, and in females 5½ to 6 inches. The young at birth is large in comparison with the size of the female. A male weighs often from 120 to 160 lbs.

Distribution.—The Orang-utan is confined to the islands of Borneo and Sumatra, in the East Indian Archipelago. In Sumatra it is far less common than in Borneo, and is found on the lowlands of the eastern coast, in the Palembang Residency, and the Djambi Sultanate. As far as I could ascertain, the natives of the southern portion of Palembang and of the Lampongs were quite ignorant of the animal, except as a name. In Borneo it inhabits the low forest-covered swamplands between the coast and the interior mountains, from the north of the island, round the west, southern, and eastern coasts, as far as the Mahakkam river, if not round the entire coast, as is most likely. In the dry season they retire into the depths of the forest. In the fruit season they come nearer to the coast, while at the height of the rains they frequent the river banks.