What is "patagium"

Patagium \Pa*ta"gi*um\, n.; pl. Patagia. [L., an edge or border.]

1. (Anat.) In bats, an expansion of the integument uniting the fore limb with the body and extending between the elongated fingers to form the wing; in birds, the similar fold of integument uniting the fore limb with the body.

2. (Zo["o]l.) One of a pair of small vesicular organs situated at the bases of the anterior wings of lepidopterous insects. See Illust. of Butterfly.

n. 1 The thin membrane that extends between the limbs and body of a bat or of gliding mammals 2 A similar membrane between the body and wing of a bird

The patagium is a membranous structure that assists an animal in gliding or flight. The structure is found in bats, birds, some dromaeosaurs, pterosaurs, and gliding mammals.