In man and some of the apes, the thumb has the function of a contra finger. This function is made possible by a great freedom of movement of the first metacarpal and a highly developed and differentiated thumb musculature. The grasp function of the hand is dependent on the oppositional capacity and adductive power of the thumb, and is severely limited by a paralysis or dysfunction of the intrinsic thumb muscles. Whereas loss of the function of the adductor pollicis can be partially compensated for by the adductive action of the extensor pollicis longus, in paralysis or dysfunction of the...