<p> The cercopithecoid monkeys, though sharing a common body-plan, exhibit considerable behavioral, ecological, and anatomical diversity. The theme of this work is the relationship between anatomy, postural behavior, and habitat use, concentrating upon the distal forearm, wrist and hand. It incorporates an initial review of the relevant empirical and theoretical literature, and original research including anatomy, naturalistic and experimental observation, and a first detailed description of fossil forelimb material of the "giant" extinct baboon, <i>Theropithecus oswaldi</i>. Two modes of contact between hand and substrate in monkeys are distinguished. Palmigrady is characteristic of predominately arboreal species, while species that habitually walk on the ground do so using a distinctive <i>digitigrade</i> gait. The vervet monkey (<i>Cercopithecus</i> [now <i>Chiorocebus</i>] <i> aethiops</i>, s.l.) occupies many tropical, seasonal habitats, and, uniquely, is both polymorphic and polytypic with respect to hand posture. The author's fieldwork found that as expected, digitigrady is apparently favored by vervets living in drier, more open habitats. The mid section of the dissertation reviews in depth the copious and often confusing literature on primate, especially cercopithecoid, taxonomy, and the many contradictory schemes that have attempted to categorize primate positional behavior.</p><p> Variation in the intermetacarpal and other wrist joints in human subjects provides background for recognition of character states distinguishing obligate digitigrade (patas and baboon) from palmigrade (colobus) monkey genera. It is then demonstrated that, consistent with the observation of hand posture variation in living subjects, anatomical variation among individual vervet skeletons encompasses both types. Unexpectedly, the large fossil <i> T. oswaldi</i> (but not <i>T. geiada</i>) shows palmigrade features in some aspects of carpal structure. This theme is pursued in the most extensive section of the dissertation, which includes a detailed description and interpretation of fossil forelimb specimens assigned to <i>Theropithecus oswaldi</i>, from the sites of Olorgesailie (Kenya) and Olduvai Gorge (Tanzania) . The descriptions include notes comparing the fossils with extant cercopithecoids, and interpreting similarities and differences. These comparisons suggest that <i>T. oswaldi</i> did not closely resemble extant baboons in locomotor behavior, and may have been palmigrade on the ground. Finally, the concluding sections describe an innovative set of techniques that were used successfully to collect electromyographic and cineradiographic data on monkeys locomoting in a controlled laboratory setting, with a view to confirming the functional interpretation of anatomical features of living and fossil forms, and the naturalistic behavior of living vervets.</p><p>