abnormal eyelid morphology abnormal nictitating membrane morphology 2014-12-04T20:44:25Z MP:3000004 MPheno.ontology abnormal nictitans morphology abnormal palperbra tertia morphology abnormal third eyelid morphology any structural anomaly of the translucent fold of the mucous membrane of the conjunctiva present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility; in many mammals, a small, vestigial portion of the membrane remains in the corner of the eye; in mice, the nictitating membrane is very small and composed of a very thin core of cartilage covered by loose connective tissue cynthia.smith