One of two movable protective folds that cover the anterior surface of the eyeball when closed. They are separated by the palpebral fissure. The upper (palpebra superior) is the larger and more movable. It is raised by contraction of the levator palpebrae superioris muscle. Angles formed at the inner and outer ends of the lids are known as the canthi. The cilia, or eyelashes, arise from the edges of the eyelids. The posterior surface is lined by the conjunctiva, a mucous membrane.

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