The abductor digiti minimi is a small muscle found in both the hands and the feet. Located on the same side of the hand and foot as the pinky finger and little toe along the outer surface of each appendage, this muscle is responsible for abduction. Abduction, in this case, is the action of pulling the smallest finger and toe laterally away from the other digits of the hand or foot — hence the name, abductor digiti minimi.
In the hand, this muscle is situated on the palm side beneath the pinky finger, running between the wrist and the metacarpophalangeal joint, the large knuckle at the base of the finger. It can easily be felt along the border of the palm and felt flexing when moving the pinky away from the other fingers. Here the abductor digiti minimi originates on the pisiform bone, a tiny bone roughly the size and shape of a pea found just distal to the wrist on the ulnar side of the hand, where the ulna bone in the forearm meets the carpal bones in the hand at the wrist. It then runs along the outside of the palm and inserts at the base of the proximal or nearest phalanx bone in the little finger along its outer or medial side.
The abductor digiti minimi in the foot is an analogous muscle to that in the hand. It stretches between the ankle and the base of the pinky toe along the outside of the foot on its plantar surface, or sole. Originating on the lateral surface of the calcaneus or heel bone on its plantar side, this muscle runs along the lateral side of the foot toward the little toe, just before which it narrows into a tendon. This tendon attaches alongside the flexor digiti quinti brevis on the bottom of the proximal phalanx of that toe along its outer surface.
Both abductor digiti minimi muscles perform the same function, which is abduction of the smallest toe, by pulling outwardly on that toe during contraction. That of the foot, however, has an additional function of assisting in toe flexion, or curling it downward. This is due to its shared attachment with the flexor digiti quinti brevis, which flexes the pinky toe only. Because the two muscles are interwoven where they meet the proximal phalanx of the fifth toe, the abductor digiti minimi is necessarily involved in this motion.