patagium

thumb|Patagia on a flying squirrel The patagium (: patagia) is a membranous body part that assists an animal in obtaining lift when gliding or flying. The structure is found in extant and extinct groups of flying and gliding animals including bats, theropod dinosaurs (including birds and some dromaeosaurs), pterosaurs, gliding mammals, some flying lizards, and flying frogs. The patagium that stretches between an animal's hind limbs is called the uropatagium (especially in bats) or the interfemoral membrane.

==Bats== thumb|Wing of a desert red bat (Lasiurus frantzii) In bats, the skin forming the surface of the wing is an extension of the skin of the abdomen that runs to the tip of each digit, uniting the forelimb with the body.