Flexor pollicis brevis is one of the thenar muscles of the hand. It arises from the flexor retinaculum and the tubercle of the trapezium. It inserts into the base of the proximal phalanx of the thumb via the radial sesamoid bone.
It is innervated by the recurrent branch of the median nerve (C8 and T1).
The action of flexor pollicis brevis is to flex the metacarpophalangeal joint of the thumb.