The Extensor pollicis longus
is much larger than the Extensor pollicis brevis
muscle, the origin of which it partly covers.
Origin and insertion
It arises from the lateral part of the middle third of the dorsal surface of the body of the ulna below the origin of the Abductor pollicis longus
, and from the interosseous membrane
It ends in a tendon, which passes through a separate compartment in the dorsal carpal ligament, lying in a narrow, oblique groove on the back of the lower end of the radius.
It then crosses obliquely the tendons of the Extensores carpi radialis longus and brevis, and is separated from the Extensor pollicis brevis by a triangular interval, the anatomical snuff box in which the radial artery is found; and is finally inserted into the base of the last phalanx of the thumb.
The radial artery
is crossed by the tendons of the Abductor pollicis longus
and of the Extensores pollicis longus
Extensor pollicis longus extends the terminal phalanx of the thumb; in combination with the Extensor pollicis brevis, it helps to extend and abduct the wrist.