Posteriorly, on the inside, a "flexor retinaculum" runs between the medial malleolus (network of nerve tissues and muscle around the ankle) and the calcaneus (Achilles tendon) and forms sheaths for tendons passing beneath the foot. "Peroneal retinacula" connect the lateral malleolus and the calcaneus, providing sheaths for tendons on the outside of the ankle. There is a corresponding flexor retinaculum in the wrist and palm of the hand.