There is an origin from the common extensor tendon; as the muscle slopes downwards it is completed by an aponeurotic sheet of origin from the subcutaneous border of the ulna. This aponeurosis arises in common with that of flexor carpi ulnaris, the two passing in opposite directions into the extensor and flexor compartments. The tendon of the muscle lies in the groove beside the ulnar styloid as it passes on to be inserted into the base of the fifth metacarpal. Note the symmetry of insertion with flexor carpi ulnaris, which acts on the fifth metacarpal by way of the pisometacarpal ligament.
Nerve supply of extensor carpi ulnaris:
By the posterior interosseous nerve (C6, 7) in the forearm.
Action of extensor carpi ulnaris:
Its action is indicated by its name. It is indispensable in ‘making a fist’. Acting with flexor carpi ulnaris it produces ulnar deviation (adduction) at the wrist.