The opposable thumb is valuable to man. A thumb in true opposition is not only opposite the fingers, but it is far forward from them and is rotated so that the pulp faces that of the fingers and the nail parallels the palm. Any tenoplasty to produce this must adhere to two essential principles. The tendon must pull subcutaneously in the right direction toward the pisiform bone and it must be inserted in the dorso-ulnar aspect of the base of the proximal phalanx of the thumb to give pronation. This may be accomplished by using any of various muscles for motor power, and for the tendon either the extensor pollicis brevis tendon or any one of various tendons prolonged by tendon grafts. The tendon used is made to pull in the right direction either by passing it through a tendon pulley constructed at the pisiform bone or by passing it around the tendon of the flexor carpi ulnaris.