The structure indicated is the calcaneus bone of the foot.

The foot contains three groups of bones:

• Tarsals
• Metatarsals
• Phalanges

The calcaneus is one of seven tarsal bones. There are three groups of tarsal bones:

• Proximal group
• Intermediate group
• Distal group

There are two bones in the proximal group of tarsal bones: the talus and the calcaneus. The calcaneus is the largest tarsal bone and forms the heel through its posterior projection. Anteriorly, the calcaneus articulates with the cuboid bone, and superiorly it articulates with talus.

Three muscles insert onto the calcaneus:

• Gastrocnemius
• Soleus
• Plantaris

Learn more about the bones of the foot in this anatomy tutorial.