Abductor pollicis longus muscle
The abductor pollicis longus muscle is a muscle in the forearm that serves to abduct and extend the thumb at the carpometacarpal joint - between the bones of the wrist and the first bone of the thumb below the first knuckle.
The abductor pollicis longus originates from the middle of both the radius and ulna. It attaches at the posterior surface of the ulna, the middle third of the posterior surface of the radius and interosseous membrane between the two.
The abductor pollicis longus is innervated by the posterior interosseous nerve (C6 and C7).
The abductor pollicis longus gets its name from the action it performs. Pollicis means of the thumb, so abductor pollicis is an abductor of the thumb. Longus, meaning long, distinguishes it from the abductor pollicis brevis muscle, both of which perform similar motions at different joints.