the skin-covered structure that protects the front of the eye; limits light entering the eye; and spreads tears over the cornea.
Birds have one upper and one lower eyelid - the latter being more moveable. Birds also have a nictitating membrane between both eyelids and the cornea. It has its own lubricating duct equivalent to the human tear duct to clean and protect the eye. Thus in total, birds have three eyelids.
the moveable folds of skin and muscle that can be closed over the eyeball; also called palpebrae.
The lid or cover of the eye, a movable fold of skin and muscle that can be closed over the eyeball or opened at will. Each eye has an upper and a lower lid. An eyelid is also called a palpebra. See the entire definition of Eyelid
Skin-fold covering the eye.
An eyelid is a thin fold of skin and muscle that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily.
