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
membrana nictitans(1) Semilunar fold of conjunctiva; plica semilunaris conjunctivae [NA6].
(2) Nictitating membrane.
pl. membranae [L.] membrane.
the layer of small, actively mitotic cells in the wall of the ovarian follicle.
a fold of conjunctiva supported by a T-shaped cartilage and attached at the medial canthus of the eye; the so-called third eyelid in animals. In most animal species, it moves across the cornea when the upper and lower eyelids are closed. Prolapse of the membrane so that it is held in position halfway across the eye when the eyelids are open is a nonspecific sign of ill health in cats. Spasm of the membrane so that it is drawn smartly across the eye with a slow return to a normal position is a diagnostic sign of tetanus in all species. See also nictitating membrane, third eyelid.