H) carry the line of evolution toward the anthropoid types, but in the baboons (Pl. I, G), which are secondarily terrestrial, the humerus is distinguished by the enlargement of the deltopectoral crest and the swollen form of the greater and lesser tuberosities. Then come the anthropoids, headed by the gibbon (Pl. I, F), in all of which the shaft of the humerus is long and cylindrical, the head large and globular, the deltopectoral crest reduced and the great tuberosity reduced to a peculiar low protuberance, which with its fellow the lesser tuberosity flanks the bicipital gutter. At the distal end there is no trace of the entepicondylar foramen and the short supinator crest is directed obliquely upward toward the shaft. Suppose now we pick up a human humerus (Fig. 4 and Pl. I, A) and compare it with each one of this series. It is assuredly very different from all the primitive quadrupedal types; it differs conspicuously from the secondarily quadrupedal baboon in its long cylindrical shaft, globular head and reduced tuberosities. When we come to the gibbon's humerus, however, we see a marked increase in resemblance to the human specimen, and when we compare the latter point by point with those of the chimpanzee and the gorilla, we recognize in the proximal end and shaft surprisingly close agreements; only the distal end shows a thinner outer border of the supinator crest, a less pronounced ridging of the trochlea and a few other rather inconspicuous but perhaps important points of difference. In preparation for the present paper I took the few anthropoid humeri and the first human humerus that happened to come to hand and laid them out in the series shown in these photographs (Pls. I-IV). I think there can be no question of the strong structural resemblance of this human humerus to the brachiating types of the recent anthropoids. The measurements of these specimens (Table I) show this human humerus to be surprisingly close to that of this particular chimpanzee. In other words, although no longer a brachiating animal, man retains a humerus of brachiating habitus so nearly allied in structure to those of the anthropoid apes, especially the gorilla and the chimpanzee, that the ascription of these resemblances to convergent evolution would be a bold petiol principii. In conclusion, it has been shown by many investigators that in the anatomy of the locomotor apparatus as a whole man is indubitably nearer to the brachiating chimpanzee and to the formerly brachiating gorilla than to the pronograde or arboreal quadrupedal monkeys. The observations on the comparative osteology of the humerus recorded in the present paper tell in the same direction. That man now differs from the chimpanzee in the relative lengths of his limb segments is not to be wondered at, in view of millions of years of divergent specialization. His long legs, short arms, highly progressive thumb and perfected foot belong to his long continued and relatively recent terrestrial habitus, but the biramous internal construction of his foot, the essential musculature of his foot and hand and a host of adjustments to the upright gait in brain, in skeleton and in viscera, are part of his heritage from primitive brachiating ancestors. These characters, along with many striking peculiarities of the dentition and of the brain, to say nothing of physiological tests, tie him irrevocably to the primitive brachiating apes and at the same time separate him from all the known pronograde monkeys. REFERENCES TO LITERATURE (1) BOULE, MARCELLIN. L'Homme fossile de la Chapelle-aux-Saints. Ann. de Paléontologie, T. VI, 1911, pp. 111-172, Pls. I–IV; T. VII, 1912, pp. 85-190, Pls. V-XVI. (2) 1915. La Paléontologie Humaine en Angleterre. L'Anthropologie, T. XXVI, Nos. 1-2, pp. 1-67. (3) GREGORY, WILLIAM K. Studies on the Evolution of the Primates. 1916. Bull. Amer. Mus. Nat. Hist., Vol. XXXV, Art. XIX, pp. 239-355 (4) 1920. On the Structure and Relations of Notharctus, an American Eocene Primate. Mem. Amer. Mus. Nat. Hist., N.S., III, Part II, Pls. XXIII-LIX. (5) DARWIN, CHARLES. 1874. The Descent of Man. 2d edition. (6) References to most of these papers are given in my earlier papers, especially The Origin and Evolution of the Human Dentition. Baltimore. 1922.* * See also Straus, W. L., Jr., 1927, "Growth of the Human Foot and its Evolutionary Significance," Contrib. to Embryol., No. 101, Vol. XIX, Carnegie Inst. Washington, Publication No. 380, pp. 93-134; and McMurrich, J. Playfair, 1927, "The Evolution of the Human Foot," Amer. Jour. Phys. Anthrop., Vol. X, No. 2, pp. 165–171. Weidenreich F., 1921-22, Der Menschenfuss. Zeitschr. f. Morphol. u. Anthropol., Bd. 22, Heft 1-2, S. 51-282. |