third eyelid

• غشاء شفاف أو شبه شفاف يغطي العين في بعض الحيوانات كالطيور والزواحف وبعض الثدييات، يتحرك أفقيًا عبر العين لحمايتها وترطيبها؛ وفي الإنسان هو بنية ضامرة تُعرف بالثنية الهلالية.

A transparent or translucent nictitating membrane found in the eyes of many animals, such as birds, reptiles, and some mammals, which moves horizontally across the eye to protect and moisten it; in humans, it is a vestigial structure known as the plica semilunaris.

1. Nictitating membraneC1formal

   A transparent or translucent third eyelid present in some animals, such as birds, reptiles, and some mammals, that moves horizontally across the eye for protection and moisture.

   الجفن الثالث

   • Cats have a third eyelid that helps protect their eyes from dust.
   • The veterinarian checked the dog's third eyelid for signs of infection.
   • Birds use their third eyelid to keep their eyes clean while flying.