The extensor carpi radialis longus is a spindle-shaped muscle. It has a narrow tendon, which is much longer than its belly. The upper portion of this muscle is covered by the brachioradialis, while its distal part is crossed over by the abductor pollicis longus and the extensor pollicis brevis muscle.
The extensor carpi radialis longus muscle arises from the lateral epicondyle of humerus and the lateral intermuscular septum of upper arm. Then it extends downwards all along the lateral border of forearm, lying between the brachioradialis and the extensor carpi radialis brevis muscle. In the third distal portion of forearm, it becomes a narrow tendon, which runs under the extensor retinaculum. It is inserted into the base of the dorsal surface of the second metacarpal bone (of index finger side).
Action/Function
Despite its name "extensor", it is a weak flexor of the elbow-joint, assisting the brachialis muscle. It also extends the hand at the wrist joint, aiding in its abduction.
Innervation
It is innervated by the radial nerve (C5-C6-C7), which springs from the brachial plexus.
Blood Supply
The extensor carpi radialis longus muscle receives oxygenated blood from branches originating from the radial collateral and recurrent artery.
Below, two schematic pictures showing the radialis muscles of right forearm.
