Definition of third eyelid in English:
Informal term for nictitating membrane.
- Crocodilians' eyes are immobile spheres covered by three eyelids: the third eyelid, the nictitating membrane, is transparent, but protects the eye from water.
- Eversion of the nictitating membrane is a condition in which the third eyelid protrudes.
- These membranes, essentially a third eyelid, can cover the exposed portion of the eye, since, as in all sharks, the upper and lower eyelids of catsharks cannot completely cover the eyeball.
Definition of third eyelid in:
- US English dictionary