Extensor carpi radialis longus

Arising from the lower third of the lateral supracondylar ridge of the humerus the muscle passes down the forearm, behind brachioradialis and beneath the thumb muscles, to be inserted as a flattened tendon into the base of the second metacarpal.

Nerve supply of extensor carpi radialis longus:

By the radial nerve (C6, 7) above the elbow, before the posterior interosseous branch is given off

Action of extensor carpi radialis longus:

Its action is indicated by its name. It is indispensable in the action of ‘making a fist’, and its tendon can be felt and often seen when this is done.