Plica semilunaris of the conjunctiva

Infobox Anatomy
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Latin = plica semilunaris conjunctivae
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Caption = Front of left eye with eyelids separated to show medial canthus. (Plica semilunaris labeled at center left.)


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The plica semilunaris is a small fold of bulbar conjunctiva on the inner corner of the eye. It is loose, so that eye movements are not restricted.

It is the vestigial remnant of the nictitating membrane (the "third eyelid"), which is present in other animals.

The plica semilunaris also secretes rheum, commonly known as sleep: the hardened crust that forms on the eye during sleep. This helps to stop foreign bodies such as dust and pollen entering the eye and damaging the sensitive cornea.

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