• The spinal column has a suggestion of the curves seen in man, but the balance of the head on the neck, the weight of the long arms, form of pelvis and weak gluteal and calf muscles, collec tively preclude an habitual erect bipedal gait, though the animals often stand erect. Divergence from the Old World monkeys and likeness to man is seen in the absence of ischial callosities and cheek-pouches and in the presence of the vermiform appendix. The development of laryngeal air-sacs, apparently a point of dif ference, is in reality a likeness, since man retains homologous vestiges of these in the laryngeal ventricles. In the chimpanzee and gorilla (but not in the orang) the central bone of the wrist becomes fused with the scaphoid during embryonic life, as in man. The menstrual cycle has the same phases as man and in the chim panzee the interval is the same. In this animal the period of gesta tion is nine months and the placenta is essentially of the human type. The secondary placenta, present in Old World monkeys, is absent. Even the brain, though roughly only about one-third the size of that of man, is essentially a miniature of the human brain, no part or organ of one being absent in the other, but the differ ences being differences of proportion of certain parts. The suscep tibility of anthropoids to many human diseases to which other animals are relatively immune, indicates the close chemical similar ity, and the well-known precipitin tests by G. F. Nuttall show the blood of these apes to be essentially identical with that of man, while differing from that of Old World monkeys.
Of the three great apes, the least man-like is the orang-utan (Malay, "man of the forest") which inhabits swampy coastal forests of parts of Borneo and Sumatra. This animal is completely arboreal, rarely descending to the ground, and exhibits exaggerated brachiating adaptations. It is a large ape, over 4 ft. high, with heavy body and short feeble legs but very long arms extending to the ankles when the animal stands erect. The digits of both hands and feet are elongated and hook-like, except the relatively short thumb and great toe. Though the orang is rather deliberate in his motions and does not leap through the trees, as does the gibbon, the elongation of the arms permits an extended reach from branch to branch and enables it to progress with consid erable rapidity. Among structural characters the following may be noted : there are but 12 pairs of ribs as in man ; the cranium is rounded and lacks the prominent supraorbital crest of the African anthropoids; the carpus retains the central bone as in monkeys and gibbons; the laryngeal air-sacs are enormously de veloped, extending far down under the arms and on the chest in adult animals; the hair is coarse and sparse but very long and bright red in colour ; a feature frequently, but not always, present in old males is a pair of prominent ridges of connective tissue on the cheeks. The orang feeds on fruits, especially the durian. There is probably only one species, with several local varieties. It is usually known as Simia satyrus (or Pongo pygmaeus). A fossil jaw ascribed to Simia, in the Upper Pliocene of India, and a molar tooth (Paleosimia) from the Miocene indicate the ancient differ entiation of the orang line.
The chimpanzee, variously known as Anthropopithecus and Pan, and the gorilla (Gorilla) both inhabit the great forests of central Africa, the chimpanzee having far the wider range. The latter is smaller, more agile and more completely arboreal in habit. The gorilla, probably owing to its great weight (males exceed 400 lb.), is largely terrestrial, though it climbs readily and in the west coast species the females and young are said to sleep in nests built in trees. Though the arms are somewhat longer than those of the chimpanzee, the hands have shorter fingers and are less adapted for brachiation ; the feet show distinct secondary adaptation to walking on the ground. The foot of the
mountain gorilla (G. beringei) of the eastern Congo presents the closest approach to the human foot found among primates. In both chimpanzee and gorilla the ribs number 13 pairs, one more than in man, but the total number of presacral vertebrae is the same, and a 13th rib in man is not uncommon. In both apes the hair is mainly black. In the chimpanzee the skin is usually light-coloured in early life, tending to become dusky later; in the gorilla the face is intensely black. In both animals a heavy brow-ridge overhangs the eyes and in the gorilla the cranial form in adult males becomes greatly altered by the development of huge crests for muscle-attachment. The gorilla has well-marked alae of the nose, separated from the cheeks by distinct grooves. See CHIMPANZEE, GORILLA.
The earliest known forerunner of the gibbons and possibly also of the great apes and man is the fossil lower jaw named Proplio pithecus haeckeli, from the Lower Oligocene of Fayurn, Egypt. This little jaw, while no bigger than that of a small monkey, already shows the relatively great depth characteristic of all anthropoids and of early man ; its molar teeth also have the five main cusps arranged substantially as in the higher forms. Many nominal species of fossil anthropoid apes of the genera Dryo pithecus, Sivapithecus and others are known.
MAN The origin and evolution of man is fully discussed in other articles (ANTHROPOLOGY ; BRAIN ; MAN, EVOLUTION OF, etc.).
BiBuoGRAPHY.—General: W. H. Flower and R. Lydekker, Mam mals, Living and Extinct (1891) ; H. 0. Forbes, A Handbook to the Primates (1894) ; various authors, Harmsworth Natural History, vol. i. (Iwo) ; D. G. Elliot, A Review of the Primates (1912) ; W. L. H. Duckworth, Morphology and Anthropology (1915).
Tree Shrews: W. E. L. Clark, Proc. Zool. Soc. Lond. (.1924-25-26 27) Tarsioids: W. D. Matthew and W. Granger, Bull. Am. Mus. Nat. Hist. (1915) ; various authors, "Discussion on the Zoological Position of Tarsius," Proc. Zool. Soc. Lond. (1925) ; H. H. Woollard, Proc. Zoal. Soc. Lond. (1925).
Lemuroids: A. Milne Edwards and A. Grandidier, "Histoire Natur elle des Mammiferes" A. Grandidier, Histoire Physique . . . de Madagascar (1875) ; H. F. Standing, Trans. Zool. Soc. Lond. (1908) ; H. G. Stehlin, Abhand. Schweiz. Palaeont. Gesell (1912) ; R. I. Pocock, Proc. Zool. Soc. Lond. (1918) ; W. K. Gregory, Mem. Am. Mus. Nat. Hist. (192o) ; J. P. Hill, A. Subba Rau, and F. Ince, Proc. Zool. Soc. Lond. (1928).
New World Monkeys: See general works above; also R. I. Pocock, Proc. Zool. Soc. Lond. (192o) ; W. K. Gregory, Origin and Evolution of the Human Dentition (1922).
Old World Monkeys: R. I. Pocock, Proc. Zool. Soc. Lond. (1926). Anthropoid Apes and Man: See general works above; also Sir A.
Keith, Engines of the Human Body (192o) ; Brit. Med. bourn. (1923) ; W. K. Gregory, Origin and Evolution of the Human Dentition (1922) ; also K. Landsteiner and Miller, J. Experim. Medicine (1925) ; Proc. Am. Philos. Soc. (1927) ; Quart. Rev. Biol. (1927) ; C. F. Sonntag, Morphology and Evolution of Apes and Man (1924) ; G. Elliot Smith, Essays on the Evolution of Man (1924) ; W. Koehler, The Mentality of Apes; R. M. Yerkes, Almost Human.