Flexor Digitorum Superficialis

The flexor digitorum superficialis is a large muscle located beneath the flexor carpi ulnaris. It arises from three immovable muscles - one from the middle inside of the humerus (upper arm bone), one from the middle inside of the ulna (longest forearm bone), and one from the radius (shortest forearm bone). Its movable end is in the tendons of the fingers and acts to flex the fingers and, by a combined action, to flex the hand.