Anatomical Study of the Right Forearm and Hand of One Western Gorilla (Gorilla gorilla) for Comparison with Humans with Respect to Motions of the Thumb and Fingers

抄録

The right forelimb of a western gorilla (Gorilla gorilla) was dissected with particular attention to the motor function of fingers of this species. The anatomical structure of the forearm and hand of our specimen of gorilla is not much different from that of the human. The palmar aponeurosis is absent. Ligamentous fibers, instead, extend to the palm from the flexor retinaculum to form the ligamentous septa along the flexor tendons. The short thumb seems to be carefully calculated to fulfill both roles of locomotion and feeding. The underdeveloped flexor pollicis longus muscle bifurcates from the flexor digitorum profundus muscle of the index finger. The extensor indicis is also underdeveloped; its tendon does not reach the index finger but attaches to the wrist. The extensor apparatus of the fingers composed of both the extrinsic and intrinsic systems is as well developed as in the human hand. During knuckle walking with the metacarpophalangeal joints in extension and the proximal interphalangeal joints in deep flexion, the former joint of each finger seems to be stabilized with integrated functions of the finger extensor, interosseous and lumbrical muscles, and sagittal bands as well as the groove at the metacarpal head. The ulnar antebrachial branch of the median nerve with a fine motor communicating branch from the ulnar nerve innervates the ulnar intrinsic muscles of the hand, which are innervated by the deep branch of the ulnar nerve in the human.