COMPARATIVE AND FUNCTIONAL-MORPHOLOGY OF HOMINOID FINGERS

Comparisons of hominoid memetacarpals and phalanges reveal differences, many of which are closely linked to locomotor hand postures. The African apes display features of the metacarpals and phalanges which distinguish them from the other Hominoidea. These features are most evident in digits 3 and 4. The orangutan hand is demonstrably less well adapted to knuckle-walking and is distinctive in its adaptation to power and hook grasping of vertical and horizontal supports, respectively. Orangutan fingers possess a double-locking mechanism, and a slight ulnad shift in the axis of the hand which results in lengthened phalanges of ray 4. Hylobatid apes are more like orangutans in their finger morphology than any of the other Hominoidea, but exhibit unique features of their own. These include elongate phalanges of fingers 2-5. Human metacarpals 2-5 form 2 sets composed of 2-3 and 4-5. The heads of both metacarpals 2 and 3 are characterized by axial torsion. This reflects the enhanced manipulatory role of the 3rd finger in humans. Human distal phalanges are unique in the development of pronounced apical tufts. Multivariate analysis of metacarpal 3 and proximal 3 yields variables that array the extant apes along an arboreal-terrestrial axis, from hylobatid apes to male gorillas. The positions of taxa on this discriminant concur with observations on the locomotion of free-ranging apes.