Plica semilunaris of conjunctiva
| Plica semilunaris of the conjunctiva |
|
| Front of left eye with eyelids separated to show medial canthus. (Plica semilunaris labeled at center left.) |
| Latin |
plica semilunaris conjunctivae |
| Gray's |
subject #227 1027 |
The plica semilunaris is a small fold of bulbar conjunctiva on the medial canthus 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 such as birds, reptiles, and fish. It is rare in mammals, mainly found in monotremes and marsupials.[1] Its associated muscles are also vestigial.[2] The plica semilunaris of Africans and Indigenous Australians are slightly larger than in other peoples.[2] Only one species of primate, the Calabar Angwantibo, is known to have a functioning nictitating membrane.[3]
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