Form and Function of Hands, in Relation to Brachiation

Abstract

On the hands of apes, monkeys and man, some characteristics were observed and measured morphologically and functionally. The results obtained are shown in Tables 1-6 and Figures 3 and 4.These results show that, in manipulation (Fig. 5), hand of man is most suitable for fingering, gripping, squeezing, grasping and pinching, and hands of Pongidae and Hylobatidae are most suitable for pending, and Cercopithecidae is for hanging. It is noteworthy that gibbon, who has the ability to brachiate most skilfully and in the highest speed, has the longest thumb, compared with, not only Pongidae who is the skilfull brachiator and has shorter thumb, but Cercopithecidae and man (Table 3). Moreover, the thumb of gibbon has not opposability with other fingers, only atthe tip of the thumb, and so, when five fingers get together at the same direction, his hand can pend conveniently, and, on the other hand, when the thumb is opposite to other four fingers, his hand can grasp sufficiently. In the author's opinion, it seems that, in brachiating movement, pending is most effective, but, in the case of speedy turning during brachiation, grasping is necessary to hold the balance of body, andhand of gibbon is made fitted to this movement. Consequently, brachiation does not always result in devolution of the thumb, as is frequently said, but in speedy brachiator, such as gibbon, it is recognized that the thumb is not shortened.