MeSH definition : A fold of the mucous membrane of the CONJUNCTIVA in many animals. At rest, it is hidden
in the medial canthus. It can extend to cover part or all of the cornea to help clean
the CORNEA.;
MeSH synonym : third eyelids; third eyelid; membranes, nictitating; membrane, nictitating; nictitating membranes; eyelid, third; eyelids, third;
MeSH annotation : ptosis of X ref THIRD EYELID: coord IM with EYELID DISEASES /vet (IM), not BLEPHAROPTOSIS; ptosis of entry term THIRD EYELID: coord IM with EYELID DISEASES /vet (IM), not BLEPHAROPTOSIS;
Wikipedia link : https://en.wikipedia.org/wiki/Nictitating membrane;
A fold of the mucous membrane of the CONJUNCTIVA in many animals. At rest, it is hidden
in the medial canthus. It can extend to cover part or all of the cornea to help clean
the CORNEA.