nictitatingmembrane

nic·ti·tat·ing membrane (nĭkʹtĭ-tā'tĭng) also nic·tat·ing membrane (nĭkʹtā'tĭng) n.

A transparent inner eyelid in birds, reptiles, and some mammals that closes to protect and moisten the eye. Also called third eyelid.

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