[TA] muscle of posterior (extensor) compartment of forearm; origin, lateral epicondyle of humerus (humeral head) and oblique line and posterior border of ulna (ulnar head); insertion, base of fifth metacarpal bone; action, extends and adducts hand at wrist joint; nerve supply, radial (posterior interosseous). SYN: musculus extensor carpi ulnaris [TA], ulnar extensor (muscle) of wrist.