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These muscles are seven in number; two for each of the three middle fingers, and one for the little finger. Four are situate on the back of the hand, and three only in the palm. They are inserted into the metacarpal bones, and send a tendon to the tendon of the extensor communis. According to their office, they are, to each finger, an adductor and an abductor. The index has a dorsal abductor and a palmar one. The middle finger has two dorsal muscles for adductor and abductor; the ring finger has a dorsal adductor and a palmar abductor; and the little finger has only one interosseous abductor, which is palmar. These muscles produce abduction and adduction of the fingers, which they can also extend, owing to their connexion with the extensor tendons.