bone of the tarsus that forms the heel
Tarsus (skeleton) The talus bone or ankle bone is connected superiorly to the two bones of the lower leg, the tibia and fibula, to form the ankle joint or talocrural joint; inferiorly, at the subtalar joint, to the calcaneus or heel bone. Together, the talus and calcaneus form the hindfoot.[1]
Chondrichthyes Chondrichthyes (/kɒnˈdrɪkθɪ.iːz/; from Greek χονδρ- chondr- 'cartilage', ἰχθύς ichthys 'fish') is a class that contains the cartilaginous fishes: they are jawed vertebrates with paired fins, paired nares, scales, a heart with its chambers in series, and skeletons made of cartilage rather than bone. The class is divided into two subclasses: Elasmobranchii (sharks, rays, skates, and sawfish) and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class).