Extensor carpi radialis brevis

Origin: Humerus at the anterior of lateral epicondyle (common extensor tendon)

Insertion: Base of the 3rd metacarpal

Artery: Radial artery

Nerve: Deep branch of the radial nerve

Action: Extensor and abductor of the hand at the wrist joint

Antagonist: Flexor carpi radialis muscle

Description:
The Extensor carpi radialis brevis (Extensor carpi radialis brevior) is shorter and thicker than the preceding muscle, beneath which it is placed. It arises from the lateral epicondyle of the humerus, by a tendon common to it and the three following muscles; from the radial collateral ligament of the elbow-joint; from a strong aponeurosis which covers its surface; and from the intermuscular septa between it and the adjacent muscles. The fibers end about the middle of the forearm in a flat tendon, which is closely connected with that of the preceding muscle, and accompanies it to the wrist; it passes beneath the Abductor pollicis longus and Extensor pollicis brevis, then beneath the dorsal carpal ligament, and is inserted into the dorsal surface of the base of the third metacarpal bone on its radial side. Under the dorsal carpal ligament the tendon lies on the back of the radius in a shallow groove, to the ulnar side of that which lodges the tendon of the Extensor carpi radialis, longus, and separated from it by a faint ridge.
The tendons of the two preceding muscles pass through the same compartment of the dorsal carpal ligament in a single mucous sheath.