The dorsal interossei are small muscles in your hand that sit between the long bones of the palm (the metacarpals). You have four of them in each hand, and they run from one metacarpal to the next, then attach into the base of the fingers and the connective tissue that helps control finger movement. Their main job is to spread your fingers apart, meaning they move your fingers away from the middle finger. If you place your hand flat on a table and try to separate your fingers as wide as possible, you are using the dorsal interossei.