Extensor carpi ulnaris muscle

Extensor carpi ulnaris is a muscle located in the human forearm that acts to extend and adduct the wrist.

Being an extensor muscle, extensor carpi ulnaris is on the posterior side of the forearm.

Origin and insertion
It originates from the lateral epicondyle of the humerus and the posterior border of the ulna, and crosses the forearm to the ulnar (medial) side to insert at the base of the 5th metacarpal.

Action
The Extensor carpi ulnaris extends the wrist, but when acting alone inclines the hand toward the ulnar side; by its continued action it extends the elbow-joint.

The muscle is a minor extensor of the carpus in carnivores, but has become a flexor in ungulates. In this case it is described as ulnaris lateralis.