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The nictitating membrane of a masked lapwing as it closes over the left eye, originating from the medial canthus. The nictitating membrane (from Latin nictare, to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision.
The plica semilunaris is a small fold of bulbar conjunctiva on the medial canthus of the eye.It functions during movement of the eye, to help maintain tear drainage via the lacrimal lake, and to permit greater rotation of the globe, for without the plica the conjunctiva would attach directly to the eyeball, restricting movement. [1]
The Harderian gland is a gland found within the eye's orbit that occurs in tetrapods (reptiles, amphibians, birds and mammals) that possess a nictitating membrane. [ 1 ] The gland can be compound tubular or compound tubuloalveolar , and the fluid it secretes ( mucous , serous or lipid ) varies between different groups of animals.
In squamate reptiles both the nictitating membrane and the eyelids have been suggested as the evolutionary origin of the brille, but embryonic studies supports the fusion of the dorsal and ventral eyelids. [1] Brille means "spectacles" or "glasses" in German, Norwegian, and Danish.
Cherry eye is typically diagnosed by examination of the conjunctiva and nictitating membrane. [2] The most obvious symptom of cherry eye is a round fleshy mass in the medial canthus of the eye, similar in appearance to the fruit it is named for. [ 8 ]
The nictitating membrane as it covers the eye of a masked lapwing. Many birds show plumage patterns in ultraviolet that are invisible to the human eye; some birds whose sexes appear similar to the naked eye are distinguished by the presence of ultraviolet reflective patches on their feathers.
David A. McCormick, as a graduate student with Professor Richard F. Thompson, initially identified the cerebellum as the essential structure for learning and executing eyeblink CRs. Some scientists think that the interposed nucleus is the site critical to learning, retaining, and executing the conditioning blink response.
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