nictitating membrane

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nictitating membrane

(in reptiles, birds, and some mammals) a thin fold of skin beneath the eyelid that can be drawn across the eye

Nictitating Membrane

 

a third eyelid, located in the inner corner of the eye in some Euselachiae (fishes) and the majority of terrestrial vertebrates. The nictitating membrane is formed from a fold of the conjunctiva and is located behind the upper and lower eyelids. In terrestrial vertebrates, a transparent nictitating membrane periodically covers the cornea to clean and moisten it. Nictitating membranes are most highly developed in reptiles and birds. Among mammals, a third eyelid is absent in Echidna and Cetacea; apes and humans have rudimentary nictitating membranes in the form of semilunar folds.

nictitating membrane

[′nik·ə‚tād·iŋ ′mem‚brān]
(vertebrate zoology)
A membrane of the inner angle of the eye or below the eyelid in many vertebrates, and capable of extending over the eyeball.
References in periodicals archive ?
I've never been happier to see a working nictitating membrane.
Clinical signs include discomfort, ocular irritation, lacrimation, conjunctivitis, eye scratching, ophtalmia, keratitis, corneal opacity, and inflammation of the nictitating membrane, which may protrude beyond the eyelids (Magalhaeset al.
Lung, nasal turbinate, nasal septum, larynx, trachea, bronchus, tracheobronchial lymph node, nictitating membrane, tonsil, heart, liver, spleen, kidney, pancreas, duodenum, jejunum, colon, adrenal gland, brain, and olfactory bulb samples were obtained, were fixed in formalin, and processed to obtain sections for staining with hematoxylin and eosin.