. Bulletin of the British Museum (Natural History), Geology. no CLASSIFICATION OF BABOONS couple is exerted tending to topple the animal from the branch (Fig. 31). The moment of the couple is Wh, where W is the weight of the animal and h the distance by which the weight-line is displaced. If the animal is not to fall, this couple must be resisted by an equal and opposite frictional couple exerted by the extremities, especially the feet. This frictional couple, in turn, is determined largely by the dia- meter of the branch spanned (d), and the amount of pressure that can be exerted normal to th
. Bulletin of the British Museum (Natural History), Geology. no CLASSIFICATION OF BABOONS couple is exerted tending to topple the animal from the branch (Fig. 31). The moment of the couple is Wh, where W is the weight of the animal and h the distance by which the weight-line is displaced. If the animal is not to fall, this couple must be resisted by an equal and opposite frictional couple exerted by the extremities, especially the feet. This frictional couple, in turn, is determined largely by the dia- meter of the branch spanned (d), and the amount of pressure that can be exerted normal to the branch surface by the action of the digital flexors and hallucal adduc- tors (Vi and V2). Long phalanges in digits II-V, and a long and abductable hallux increase the possible size of d, while powerful flexors of the digits and adductors of the hallux increase V^ and Vg, respectively. The apparently disproportionately large hallux of the mandrill and other big, semi-arboreal monkeys, can be accounted for by the fact that while d is increased as the length of the hallux and other digits, W increases as the cube of linear body-dimensions. Thus, the hallux needs to be long relative to general body dimensions. In ground-walking and running, on the other hand, a long, abducted hallux and long digits would be of little value, and probably in fact a positive handicap. It is quite clear that the Olorgesailie Simopithecus most closely resembled the highly terrestrial gelada in those characters of the foot which are good indicators of. Fig. 31. Forces acting upon a foot gripping a horizontal branch with the hallux, when the animal's weight-line is displaced beyond the branch. (Modified after Gray, 1943) •. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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