The wing membrane of a bat, specifically the membranous tissue connecting the hand and arm bones to form the wing.
From Greek χείρ (cheír) 'hand' and πτερύγιον (pterýgion) 'small wing,' describing how bat wings are essentially modified hands.
Bat wings aren't like bird wings at all—they're stretchy membranes between elongated finger bones, so cheiropatagium perfectly describes bat anatomy as 'hand-wings' that evolved from mammalian fingers.
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