Why do cats have 3 eyelids?
Emma Payne
Updated on April 25, 2026
The exact function of the
third eyelid
The term comes from the Latin word nictare, meaning "to blink". It is often called a third eyelid or haw, and may be referred to in scientific terminology as the plica semilunaris, membrana nictitans, or palpebra tertia. Unlike the upper and lower eyelids, the nictitating membrane moves horizontally across the eyeball.
› wiki › Nictitating_membrane