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Abstract

A description is given of the contrasting features which serve to distinguish the meniscus-containing wrist joints of hominoids from those of monkeys. The form and relationships of the hominoid ulnar styloid process, triquetral and pisiform are strikingly modified. Correlated changes, clearly adaptive to suspensory locomotion, occur in the midcarpal joint: the apposed articular heads of the hamate and capitate are remodelled into a globular projection about which the proximal carpal row locks during extension, with its accompanying conjunct rotation. There is little doubt that Dryopithecus(Proconsul)africanus possessed a meniscus-containing wrist joint, with associated midcarpal modifications, and was thus well adapted for suspensory locomotion. The structural grade achieved by D.africanus was considerably in advance of that shown by Hylobates and marginally superior to that of Pongo, indicating an earlier derivation of the lines leading to these Asiatic apes. The lineages of the African great apes and man might have diverged from the D.africanus grade, but there is some evidence favoring a later separation.