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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.
It is loose, thus eye movements are not restricted by it. Only one species of primate, the Calabar angwantibo, is known to have a functioning nictitating membrane. [4] With ocular allergies, the lacrimal caruncle and plica semilunaris may be inflamed and pruritic (itchy) due to histamine release in the tissue and tear film.
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.
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.
The islands are difficult to get to, [107] and are colonised by few animal species, indicating that some animals absent from these islands may have caused tuatara to disappear from the mainland. However, kiore (Polynesian rats) had recently become established on several of the islands, and tuatara were persisting, but not breeding, on these ...
The eyelids of a bird are not used in blinking. Instead the eye is lubricated by the nictitating membrane, a third concealed eyelid that sweeps horizontally across the eye like a windscreen wiper. [12] The nictitating membrane also covers the eye and acts as a contact lens in many aquatic birds when they are under water. [5]
Combined with the five-kingdom model, this created a six-kingdom model, where the kingdom Monera is replaced by the kingdoms Bacteria and Archaea. [16] This six-kingdom model is commonly used in recent US high school biology textbooks, but has received criticism for compromising the current scientific consensus. [ 13 ]
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 ]