Origin Flexor retinaculum and tubercles of scaphoid and trapezium Insertion Lateral side of base of proximal phalanx of thumb Action Flexes thumb Innervation The flexor pollicis brevis is mostly innervated by the recurrent branch of the median nerve (C8, T1). The deep part is often innervated by the deep branch of the ulnar nerve. Arterial Supply Superficial palmar branch of the radial artery