Little and ring finger flexion. Artwork of the muscles of the forearm and hand from the front, with red arrows showing the direction of movement of the little and ring (fourth and third) fingers during flexion. Finger flexion is controlled by the flexor digitorum superficialis, flexor digitorum profundus, and lumbrical muscles. Some muscles act on more than one finger. This is best demonstrated by flexing the little finger, causing involuntary flexion of the ring finger. This is because the ring and middle fingers, unlike the little and index fingers, lack independent extensor muscles to keep them extended as the other fingers flex. The nerve used is the ulnar nerve. This is the left hand. For the right hand, see C016/6793.