In humans, the calcaneus (from the Latin calcaneum, meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In humans, the calcaneus is the largest of the tarsal bones and the largest bone of the foot. The tarsal bones of the ankle are arranged in proximal and distal groups somewhat like the carpal bones of the wrist. Because of the load-bearing role of the ankle, however, their shapes and arrangement are conspicuously different from those of the carpal bones, and they are thoroughly integrated into the structure of the foot. In the calcaneus, several important structures can be distinguished: The posterior half of the bone is the tuber calcanei. On its lower edge on either side there are its lateral and medial processes (serving as the origins of the abductor hallucis and abductor digit minimi). The calcaneal (Achilles) tendon is inserted into a roughened area on its superior side, the cuboid bone articulates with its anterior side, and on its superior side are three articular surfaces for the articulation with the talus bone. Between these superior articulations and the equivalents on the talus is the tarsal sinus (a canal occupied by the interosseous talocalcaneal ligament). On the medial side of the bone, below the middle talar facet, is the sustentaculum tali (which serves for the attachment of several other ligaments). On the lateral side is commonly a tubercle called the peroneal trochlea, under which is a groove for the tendon of the peroneus longus. The talus, calcaneus, and navicular are considered the proximal row of tarsal bones. In the calcaneus, an ossification center is developed during the 4-7th week of fetal development. With normal axial alignment in the hind-foot, the axes of the tibia and calcaneus lie on a vertical line (pes rectus). If the calcaneal axis is turned medially the foot is in an everted position (pes valgus), and if it is turned laterally the foot is in an inverted position (pes varus).