Extensor pollicis brevis muscle

The extensor pollicis brevis muscle is a muscle in the forearm used to extend the thumb at the metacarpophalangeal joint - the joint at the lower knuckle of the thumb.

Origin
The extensor pollicis brevis originates from the radius at the lower third of the posterior shaft and the adjacent interosseous membrane.

Insertion
The extensor pollicis brevis inserts at the base of the proximal phalanx of the thumb.

Action
The extensor pollicis brevis extends the thumb at the metacarpophalangeal joint.

Word origin
The extensor pollicis brevis gets its name from the action it creates. Pollicis means of the thumb, so extensor pollicis means extender of the thumb. Brevis, meaning short, indicates that it attaches to the first joint in the thumb, distinguishing it from the extensor pollicis longus muscle which attaches to the next joint.