It arises from the distal third of the dorsal part of the
body of the 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. 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. Like the
extensor digiti minimi (i.e. the extensor of the little finger), the tendon of the extensor indicis runs and inserts on the ulnar side of the tendon of the common extensor digitorum. The extensor indicis lacks the
juncturae tendinum interlinking the tendons of the extensor digitorum on the dorsal side of the hand.
Variation The extensor indicis proprius does not show much variation. It exists as a single tendon most of the time. Double tendons of the extensor indicis proprius was also reported. It is known that the extensor indicis proprius inserts to the index finger on the ulnar side of the extensor digitorum. However, the insertion on the radial side of the common extensor digitorum infrequently seen, namely the
extensor indicis radialis. ==Function==