This arises from an oblique area on both bones of the forearm and the intervening interosseous membrane. Its radial origin lies immediately distal to the posterior oblique line. The ulnar origin, in line with it, is more proximal in the forearm. The muscle belly emerges from the depths and spirals around the radial extensors of the wrist and brachioradialis to reach the base of the first metacarpal, into which it is inserted by a round tendon. This tendon is split longitudinally into three or four separate bands, one of which commonly passes beyond the metacarpal bone and expands into the belly of the abductor pollicis brevis.
Nerve supply Abductor pollicis longus:
By the posterior interosseous nerve (C6, 7) in the forearm.
Action of abductor pollicis longus:
Its name indicates that it abducts the thumb; its old name was extensor ossis metacarpi pollicis. Former anatomists considered that it extended the thumb. Its unaided action lies somewhere between abduction and extension. It can assist in flexing and abducting the wrist.