The joints of the evolving foot. Part I. The ankle joint.

Evidence is presented to suggest that the eutherian ankle joint has been derived from a meniscus-containing joint such as that found in extant arboreal marsupials. Probable morphological derivatives of this meniscus are identifiable in the Eutheria. The form and function of the joint are described in sub-human Primates and the adaptations which characterize the joint in bipedal man are noted. These morphological findings permit some speculation about the palaeocology of the earliest mammals with particular reference to the emergence of the order Primates.