The ventral metacarpo- and metatarso-phalangeal sesamoid bones: comparative anatomy and evolutionary aspects.

A study of comparative anatomy was made to determine the distribution of metapodo-phalangeal sesamoid bones among the different mammalian species for a better understanding of the variations and origins of these bones in man, and that in the context of renewed interest in non-metrical characteristics of the post-cranial skeleton in physical anthropology. The material used included 457 non-primate mammalian skeletons divided into 18 orders, 63 families, and 161 genera, 211 non-human primate skeletons divided into 37 genera, and 2,500 human radiographs (1,250 hands and 1,250 feet). 2 sesamoid bones were constantly observed for each metapodo-phalangeal joint in almost all mammalian orders. Modifications of the general mammalian pattern were observed only in man and a small number of primate genera, all closely related to man and called anthropoid apes; these modifications consist of the more or less complete disappearance of some or all sesamoid bones and often of a morphological heteropody. All the genera concerned use brachiation or probably have brachiating ancestors. Some morphological characteristics could apparently be related to specific modes of locomotion, namely the shape, more or less oblong, pear-like or round, according to genera or digits, and the possible fusion of the 2 sesamoid bones of the same digit to form a unique ossified structure.