A membranous extension of skin that forms the wing material in animals such as bats. It typically comprises a number of patagial segments, stretching from the side of the body between the forelimb digits and sometimes the hindlimbs. [ http://www.brown.edu/Departments/EEB/EML/background/wing_anatomy.htm http://en.wikipedia.org/wiki/Patagium http://animals.about.com/od/zoologytermsktoz/g/patagium.htm ]