Bats (around 1,200 species) are the only truly flying mammals, although several gliding mammals are referred to as “flying” (such as the flying squirrel and flying lemur). The “wings” of bats consist of double membranes of skin stretching from the sides of the body to the hind legs and tail that are actually skin extensions of the back and belly. The wing membranes are supported by the elongated fingers of the forelimbs (or arms).