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pli·ca sem·i·lu·na·'ris of con·junc·ti·'va[TA]
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
See nictitating membrane.
third eyelid eversion
the free margin of the third eyelid is rolled outwards because of a curvature of the cartilage. More prevalent in large breeds of dogs and may be an inherited defect in St. Bernards and German shorthaired pointers.
third eyelid protrusion syndrome
see cherry eye.