[2] Between these superior articulations and the equivalents on the talus is the tarsal sinus (a canal occupied by the interosseous talocalcaneal ligament).

This eminence is concave above, and articulates with the middle calcaneal articular surface of the talus; below, it is grooved for the tendon of the flexor hallucis longus; its anterior margin gives attachment to the plantar calcaneonavicular ligament, and its medial margin to a part of the deltoid ligament of the ankle-joint.

It separates the two oblique grooves of the lateral surface of the calcaneus (for the tendons of the peroneal muscles).

Their specific functions include plantarflexion of the foot, flexion of the knee, and steadying the leg on the ankle during standing.

The calcaneus also serves as origin for several short muscles that run along the sole of the foot and control the toes.