Extensor pollicis brevis muscle

The Extensor pollicis brevis lies on the medial side of, and is closely connected with, the Abductor pollicis longus.

Origin and insertion
It arises from the dorsal surface of the body of the radius below that muscle, and from the interosseous membrane.

Its direction is similar to that of the Abductor pollicis longus, its tendon passing the same groove on the lateral side of the lower end of the radius, to be inserted into the base of the first phalanx of the thumb.

Action
The Extensor pollicis brevis extends the proximal phalanx.

Variations
Absence; fusion of tendon with that of the Extensor pollicis longus.