CT Observation of the First Metacarpal Adduction in a Carcass of the Chimpanzee

Abstract

We examined the adduction movement of the first metacarpal during the manipulating action of the chimpanzee (Pan troglodytes) by using the computed tomography (CT) techniques. We demonstrated by nondestructive method that the first metacarpal adducted and its shaft rotated from the first carpometacarpal joint. The trapezium and the other carpals did not move in the adductor action of the first metacarpal and did not contribute to the gripping action. The movement area of the first metacarpal was three-dimensionally restricted to the medial region of the second metacarpal. Some reports pointed out that the first metacarpal and the first phalanges did not act as a highly-functioned grasper in the chimpanzee unlike in the human and some fossil hominids, and our CT sections also explained that the first metacarpal movements and the thumb opposability were not sufficient to grasp object for the chimpanzee.