It arises from the distal third of the dorsal part of the body of ulna and from the interosseous membrane.

It runs through the fourth tendon compartment together with the extensor digitorum, from where it projects into the dorsal aponeurosis of the index finger.

[1] Opposite the head of the second metacarpal bone, it joins the ulnar side of the tendon of the extensor digitorum which belongs to the index finger.

[2] Split tendons of the muscle inserting on both ulnar and the radial side of the common extensor digitorum was also reported.

[3] This article incorporates text in the public domain from page 456 of the 20th edition of Gray's Anatomy (1918)