[Rare muscle variations of the forearm].

An accessory twin-bellied muscle in both forearms of a male was observed. On the right side, the accessory muscle originated from the main muscle belly of the superficial flexor muscle of the fingers and inserted on the index finger tendon of the superficial muscle. On the left side, the accessory muscle belly originated from the medial epicondyle of the humerus and inserted on the index finger tendon of the superficial muscle. A further accessory muscle belly originated from the distal muscle belly and joined with the lumbrical muscle just before its insertion on the dorsal aponeurosis. The functional effects are discussed and compared to a similar case in literature.