The calcar, also known as the calcaneum,[1] is the name given to a spur of cartilage arising from inner side of ankle and running along part of outer interfemoral membrane in bats,[1][2] as well as to a similar spur on the legs of some arthropods.[3]
The calcar serves to help spread the interfemoral membrane,[4] which is part of the wing membrane between the tail and the hind legs.
Calcar (femorale) also refers to the dense, vertically oriented bone present in the posteromedial region of the femoral shaft inferior to the lesser trochanter.