The extensor indicis (or extensor indicis muscle, latin: musculus extensor indicis) is a flat, small muscle of the forearm that belongs to the posterior muscle group, lying in the second or deep layer.
The extensor indicis originates from the distal third of the posterior surface of the ulna and from the interosseous membrane of the forearm.
The extensor indicis descends obliquely to the second finger and inserts at the bases of the intermediate and distal phalanges of the second digit of the hand.
The major function of the extensor indicis is to extend the second finger, also known as the index finger.
The extensor indicis is innervated by the radial nerve.