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A picture illustrating the location of the calcar on a bat.

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] This is to help spread the interfemoral membrane,[3] which is part of the wing membrane between the tail and the hind legs.

This membrane can form a basket or pouch to help catch and hold insects captured in flight.[4] The oldest known ancestor to present day bats, Icaronycteris index, apparently did not have a calcar or spur as evidenced by fossil remains.[5]

Calcar (Femorale) also refers to the dense, vertically oriented bone present in the posteroemedial region of the femoral shaft inferior to the lesser trochanter of the femur.


  1. ^ a b The Anatomy of Bats
  2. ^ The Handbook of British Mammals (ASIN B000WPL1CO)
  3. ^ Encyclopedia Smithsonian: Bat Facts
  4. ^ The Anatomy of Bats
  5. ^ Ontogeny, Functional Ecology, and Evolution of Bats (ISBN 978-0-52-162632-3)