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Medical Term:

plica semilunaris of conjunctiva


  1. the semilunar fold formed by the palpebral conjunctiva at the medial angle of the eye;
  2. a fold of the conjunctival mucous membrane found in many animals; normally partially hidden in the medial canthus of the eye when at rest, it may be extended to cover part or all of the cornea in a winklike action to clean the cornea, as in birds.

Synonym(s): membrana nictitans, nictitating membrane, palpebra III, palpebra tertia, third eyelid

© Copyright 2017 Wolters Kluwer. All Rights Reserved. Review Date: Sep 19, 2016.