The median nerve then passes below the arch of the flexor digitorum superficialis, a muscle which it innervates in the middle third of the forearm. Distal to this, it supplies the palmar surface of the fingers, from the base of the thumb to the radial side of the ring finger, and the dorsal surface of these fingers, distal to the proximal phalanx. The thenar motor branch supplies the abductor pollicis brevis, opponens, and superficial branch of the flexor pollicis brevis. Finally, one common palmar branch innervates the first and second lumbricals (Fig. 13.1).