The
nictitating membrane of a
Masked Lapwing as it closes. The membrane is a transparent or
translucent third
eyelid present in some animals that can be drawn across the
eye for protection and to moisten it while maintaining visibility. Some reptiles, birds,
sharks, and mammals have full nictitating membranes. Most mammals, however, have a small,
vestigial portion of it remaining in the corner of the eye.Photos:
99of9
The
nictitating membrane of a
Masked Lapwing as it closes. The membrane is a transparent or
translucent third
eyelid present in some animals that can be drawn across the
eye for protection and to moisten it while maintaining visibility. Some reptiles, birds,
sharks, and mammals have full nictitating membranes. Most mammals, however, have a small,
vestigial portion of it remaining in the corner of the eye.Photos:
99of9