Abductor pollicis longus muscle

The Abductor pollicis longus lies immediately below the Supinator and is sometimes united with it.

Origin and insertion
It arises from the lateral part of the dorsal surface of the body of the ulna below the insertion of the Anconæus, from the interosseous membrane, and from the middle third of the dorsal surface of the body of the radius.

Passing obliquely downward and lateralward, it ends in a tendon, which runs through a groove on the lateral side of the lower end of the radius, accompanied by the tendon of the Extensor pollicis brevis, and is inserted into the radial side of the base of the first metacarpal bone.

It occasionally gives off two slips near its insertion: one to the greater multangular bone and the other to blend with the origin of the Abductor pollicis brevis.

Action
The chief action of the Abductor pollicis longus is to carry the thumb laterally from the palm of the hand.

By its continued action it helps to extend and abduct the wrist.

Variations
More or less doubling of muscle and tendon with insertion of the extra tendon into the first metacarpal, the greater multangular, or into the Abductor pollicis brevis or Opponens pollicis.