page_title: Nictitating membrane
hierarchical_section_title: Nictitating membrane
caption_attribution_description: English: The blinking eye of a Masked Lapwing in Cairns, Queensland, Australia. The nictitating membrane closes from only one side, and is translucent. The eyelids themselves do not close during blinking, but do so for sleep. Français&#160;: Le clignement de l'œil d'un vanneau soldat (sous-espèce nord, Vanellus miles miles). La membrane nictitante, translucide, est la seule à se fermer sur l'œil. L'oiseau ne ferme ses paupières que pour dormir.
context_page_description: The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus for protection and to moisten it while maintaining vision. Some reptiles, birds, and sharks have full nictitating membranes; in many mammals, a small, vestigial portion of the membrane remains in the corner of the eye. Some mammals, such as cats, camels, polar bears, seals and aardvarks, have full nictitating membranes. Often called a third eyelid or haw, it may be referred to in scientific terminology as the plica semilunaris, membrana nictitans, or palpebra tertia.
context_section_description: The nictitating membrane (from Latin nictare, to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus for protection and to moisten it while maintaining vision.  Some reptiles, birds, and sharks have full nictitating membranes; in many mammals, a small, vestigial portion of the membrane remains in the corner of the eye. Some mammals, such as cats, camels, polar bears, seals and aardvarks, have full nictitating membranes. Often called a third eyelid or haw, it may be referred to in scientific terminology as the plica semilunaris, membrana nictitans, or palpebra tertia.
caption: The nictitating membrane of a masked lapwing as it closes over the left eye, originating from the medial canthus
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