Muscle · Forearm

Extensor indicis

Musculus extensor indicis

A narrow deep muscle at the back of the forearm whose single tendon runs to the index finger alone, joining the common extensor tendon on that finger's ulnar side. Its purpose is independence: the four tendons of extensor digitorum are tied to one another across the back of the hand, so lifting one finger tends to lift its neighbours, and a finger with its own private extensor escapes that. The index has one and the little finger has one; the middle and ring fingers do not, which is exactly why those two are the hardest to raise on their own.