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'The Nictitating Membrane' (Cooper's Juvenile)
The eyelids of a bird are not used in blinking. Instead the eye is lubricated by the nictitating membrane, a third concealed eyelid that sweeps horizontally across the eye like a windscreen wiper, as seen here. (Juvenile Cooper's Hawk).

The eyelids of a bird are not used in blinking. Instead the eye is lubricated by the nictitating membrane, a third concealed eyelid that sweeps horizontally across the eye like a windscreen wiper, as seen here. (Juvenile Cooper's Hawk).

Copyright Howard Cheek