Extensor pollicis longus muscle

The extensor pollicis longus muscle is a muscle in the forearm that serves to extend the interphalangeal and metacarpophalangeal joints of the thumb - the joints at both knuckles of the thumb.

Origin
The extensor pollicis longus originates from the ulna, at middle third of the posterior ulna just below the abductor pollicis longus muscle and the adjacent interosseous membrane.

Insertion
The extensor pollicis longus inserts at the base of the distal phalanx of the thumb.

Innervation
The extensor pollicis longus is innervated by the posterior interosseous nerve (C7 and C8).