Corpus: Extensor pollicis brevis muscle

The origin of the muscle is on the posterior surface of the radius and the interosseous membrane of the forearm. Its tendon passes through the first tendon compartment of the extensor retinaculum and attaches to the proximal phalanx of the thumb.

The innervation is by the deep branch of the radial nerve with fibers from the C6 to C8 segments.

The extensor pollicis brevis muscle causes extension and abduction of the thumb's proximal phalanx.