Muscle · Forearm

Extensor pollicis brevis

Musculus extensor pollicis brevis

A small deep muscle of the back of the forearm lying immediately below abductor pollicis longus and travelling with it, from the back of the radius to the base of the thumb's first phalanx. It straightens the thumb at its knuckle joint, and stops there — the joint beyond it belongs to extensor pollicis longus. It shares a single fibrous tunnel at the wrist with the abductor's tendon, and the two together form the palm-side border of the shallow hollow at the base of the thumb known as the anatomical snuffbox.