Corpus: Extensor carpi radialis brevis muscle

The muscle originates from the lateral epicondyle of the humerus. It is overlaid by the extensor carpi radialis longus muscle towards the top. The muscle tapers into a flat tendon around the middle of the forearm, which runs distally in close association with the tendon of the aforementioned muscle. Further along its course, the tendon passes beneath the abductor pollicis longus muscle and the extensor pollicis brevis muscle to the wrist and enters the second tendon compartment of the extensor retinaculum during its course. The tendinous insertion of the extensor carpi radialis brevis muscle is the base of the third metacarpal bone. The tendinous insertion of the extensor carpi radialis longus muscle is the dorsal base of the second metacarpal bone.

The innervation of the extensor carpi radialis longus muscle is provided by the radial nerve from the brachial plexus (segments: C6-C7).

The extensor carpi radialis longus muscle facilitates flexion at the elbow joint, extension of the hand at the wrist (dorsiflexion), and a slight abduction of the hand towards the radius.