Extensor carpi ulnaris ORIGINATES from the lateral epicondyle of the humerus and posterior border of the ulna, and crosses the forearm to the ulnar (medial) side to INSERT at the base of the metacarpal. It extends the wrist, but when acting alon
Extensor Digitorum: Origin - lateral epicondyle of humerus. Insertion - extensor expansions of medial four digits. Action - extends medial four digits at metacarpophalangeal joints, extends hand at wrist joints.