Corpus: Extensor carpi radialis longus muscle

The muscle originates from the lateral supracondylar ridge at the lower third of the humerus and from the lateral intermuscular septum. The muscle is partially covered by the brachioradialis muscle towards the top. The extensor carpi radialis longus tapers into a flat tendon in the lower third of the forearm, which runs distally in close association with the tendon of the extensor carpi radialis brevis. It follows the lateral side of the radius, lies beneath the abductor pollicis longus and the extensor pollicis brevis muscles, and enters the second tendon compartment of the extensor retinaculum during its course. 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 deep branch of 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 joint (extension or dorsiflexion), and a slight abduction of the hand towards the radius.