Abductor pollicis brevis
The abductor pollicis brevis muscle is located in the hand between the wrist and the base of the thumb. It originates from the flexor retinaculum and the tubercles of the scaphoid and trapezium bones. It inserts in the outer side of the base of the proximal phalanx of the thumb. This muscle is positioned just beneath the skin, slightly overlapping the flexor pollicis brevis and mostly covering the opponens pollicis. It is flat, thin, elongated, and triangular in shape. The abductor pollicis brevis is the largest muscle of the thenar eminence muscle group, which is comprised of several muscles that control the thumb. The main function of the muscle is to abduct the thumb, or move it away from the palm. This muscle is also involved in the extension and opposition of the thumb. Opposition refers to the ability of the thumb to rotate and touch the other fingers. The recurrent branch of the median nerve controls the abductor pollicis brevis muscle. Its blood supply comes from the superficial palmar arch, which is a branch of the radial artery.