Nictitating membrane
TRANSPARENT OR TRANSLUCENT THIRD EYELID IN SOME ANIMALS
Third eyelid; Nictating membrane; Nictating Membrane; Nictating eyelid; Nictitating eyelid; Nicitating membrane; Inner eyelid; Palpebra tertia; Nictitating; Semilunar fold; Nictitation; Nictitating membranes; Nictitans
The nictitating membrane (from Latin [to blink) is a transparent or translucent] third [[eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision. All Anura(tailless amphibians), and some reptiles, birds, and sharks have full nictitating membranes; in many mammals, a small, vestigial portion of the nictitating membrane remains in the corner of the eye.