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A transparent inner eyelid in many vertebrates that closes to protect and moisten the eye. Also called third eyelid.
(Zoology) (in reptiles, birds, and some mammals) a thin fold of skin beneath the eyelid that can be drawn across the eye. Also called: third eyelid or haw
a thin membrane, present in many animals, that can be drawn across the eyeball for protection.
A transparent inner eyelid in birds, reptiles, amphibians, and some mammals that protects and moistens the eye without blocking vision.