Nictitating membrane: Difference between revisions
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{{Short description|"Third eyelid" of some animals that protects and moistens the eye while maintaining vision}} |
{{Short description|"Third eyelid" of some animals that protects and moistens the eye while maintaining vision}} |
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[[File:Bird blink-edit.jpg|thumb|right|upright=2.0|The nictitating membrane of a [[masked lapwing]] as it closes over the left eye, originating from the [[Medial (anatomy)|medial]] [[canthus]]]] |
[[File:Bird blink-edit.jpg|thumb|right|upright=2.0|The nictitating membrane of a [[masked lapwing]] as it closes over the left eye, originating from the [[Medial (anatomy)|medial]] [[canthus]]]] |
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The '''nictitating membrane''' (from Latin ''[[wikt:nicto|nictare]]'', to blink) is a transparent or [[translucent]] third [[eyelid]] present in some animals that can be drawn across the [[eye]] from the [[Medial (anatomy)|medial]] [[canthus]] to protect and moisten it while maintaining vision. All [[Anura (frog)|Anura]]<ref>{{Cite book|last1=Rolleston|first1=George|last2=Jackson|first2=William Hatchett|title=Forms of Animal Life : A Manual of Comparative Anatomy, with Descriptions of Selected Types.|publisher=Clarendon Press|date=1898|pages=401}}</ref> (tailless amphibians), and some reptiles, birds, and [[shark]]s have full nictitating membranes; in many [[mammal]]s, a small, [[vestigial]] portion of the nictitating membrane remains in the corner of the eye. Some mammals, such as [[cat]]s, [[beaver]]s, [[polar bear]]s, [[pinniped|seals]] and [[aardvark]]s, have full nictitating membranes. Often called a '''third eyelid''' or '''haw''', it may be referred to in scientific terminology as the [[Plica semilunaris of the conjunctiva|''plica semilunaris'']], ''membrana nictitans'', or ''palpebra tertia''. |
The '''nictitating membrane''' (from Latin ''[[wikt:nicto|nictare]]'', to blink) is a transparent or [[translucent]] third [[eyelid]] present in some animals that can be drawn across the [[eye]] from the [[Medial (anatomy)|medial]] [[canthus]] to protect and moisten it while maintaining vision. All [[Anura (frog)|Anura]]<ref>{{Cite book|last1=Rolleston|first1=George|last2=Jackson|first2=William Hatchett|title=Forms of Animal Life : A Manual of Comparative Anatomy, with Descriptions of Selected Types.|publisher=Clarendon Press|date=1898|pages=401}}</ref> (tailless amphibians), and some reptiles, birds, and [[shark]]s have full nictitating membranes; in many [[mammal]]s, a small, [[vestigial]] portion of the nictitating membrane remains in the corner of the eye. Some mammals, such as [[cat]]s, [[beaver]]s, [[polar bear]]s, [[pinniped|seals]] and [[aardvark]]s, have full nictitating membranes. Often called a '''third eyelid''' or '''haw''', it may be referred to in scientific terminology as the [[Plica semilunaris of the conjunctiva|''plica semilunaris'']], ''membrana nictitans'', or ''palpebra tertia''. |
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== Description == |
== Description == |
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[[File:Nictitating membrane - Nickhaut - Membrana nittitante - (Balearica pavonina - Weltvogelpark 2013).jpg|thumb |
[[File:Nictitating membrane - Nickhaut - Membrana nittitante - (Balearica pavonina - Weltvogelpark 2013).jpg|thumb|The nictitating membrane (completely closed) of a [[black crowned crane]], right eye]] |
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The nictitating membrane is a transparent or [[translucent]] third [[eyelid]] present in some animals that can be drawn across the [[eye]] for protection and to moisten it while maintaining vision. The term comes from the Latin word ''[[wikt:nicto|nictare]]'', meaning "to blink". It is often called a ''third eyelid'' or ''haw'', and may be referred to in scientific terminology as the [[Plica semilunaris of the conjunctiva|''plica semilunaris'']], ''membrana nictitans'', or ''palpebra tertia''. Unlike the upper and lower [[eyelid]]s, the nictitating membrane moves horizontally across the eyeball. |
The nictitating membrane is a transparent or [[translucent]] third [[eyelid]] present in some animals that can be drawn across the [[eye]] for protection and to moisten it while maintaining vision. The term comes from the Latin word ''[[wikt:nicto|nictare]]'', meaning "to blink". It is often called a ''third eyelid'' or ''haw'', and may be referred to in scientific terminology as the [[Plica semilunaris of the conjunctiva|''plica semilunaris'']], ''membrana nictitans'', or ''palpebra tertia''. Unlike the upper and lower [[eyelid]]s, the nictitating membrane moves horizontally across the eyeball. |
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In many species, any stimulus to the eyeball (such as a puff of air) will result in reflex nictitating membrane response. This reflex is widely used as the basis for experiments on [[classical conditioning]] in rabbits.<ref>Gormezano, I. N. Schneiderman, E. Deaux, and I. Fuentes (1962) Nictitating Membrane: Classical Conditioning and Extinction in the Albino Rabbit ''Science'' '''138''':33–34.</ref> |
In many species, any stimulus to the eyeball (such as a puff of air) will result in reflex nictitating membrane response. This reflex is widely used as the basis for experiments on [[classical conditioning]] in rabbits.<ref>Gormezano, I. N. Schneiderman, E. Deaux, and I. Fuentes (1962) Nictitating Membrane: Classical Conditioning and Extinction in the Albino Rabbit ''Science'' '''138''':33–34.</ref> |
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== Distribution == |
== Distribution == |
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Fully developed nictitating membranes are found in [[fish]], [[amphibian]]s, [[reptile]]s, [[bird]]s and mammals, but are rare in [[primate]]s.<ref name="butler05">{{cite book| publisher = John Wiley & Sons| isbn = 978-0-471-73383-6| last1 = Butler| first1 = Ann B.| first2 = William |last2= Hodos| title = Comparative Vertebrate Neuroanatomy: Evolution and Adaptation| url = https://archive.org/details/comparativeverte00butl_744| url-access = limited| date = 2 September 2005|page=[https://archive.org/details/comparativeverte00butl_744/page/n239 215]}}</ref><ref>Paul Miller, [http://www.scientificamerican.com/article.cfm?id=why-do-cats-have-an-inner Why do cats have an inner eyelid as well as outer ones?] Scientific American. 20 Nov 2006. (Accessed 2 Nov 2011)</ref> In humans, the [[Plica semilunaris of conjunctiva|plica semilunaris]] (also known as the semilunar fold) and its associated muscles are [[homology (biology)|homologous]] to the nictitating membranes seen in some other mammals and other vertebrates.<ref>The Eye: Basic Sciences in Practice by John V. Forrester, [https://books.google.com/books?id=8T4aIZnWBkAC&pg=PA82 p. 82]</ref> In most primate species, a plica semilunaris is generally not present, although fully developed nictitating membranes can be found in [[lemur]]s and [[Lorisoidea|lorisoid]] primates.<ref>{{cite book | last = [[William Charles Osman Hill|Osman Hill]] | first = W. C. | year = 1953 | title = Primates Comparative Anatomy and Taxonomy I—Strepsirhini | publisher = Edinburgh University Press | series = Edinburgh Univ Pubs Science & Maths, No 3 | page = 13 | oclc = 500576914}}</ref><ref>{{cite book|last = Ankel-Simons|first = F.|title= Primate Anatomy|edition = 3rd|publisher = Academic Press|year = 2007|isbn = 978-0-12-372576-9|page=471}}</ref> Some mammals, such as [[camel]]s, [[polar bear]]s, [[pinniped|seals]] and [[aardvark]]s, have full nictitating membranes, and many mammals retain a small, [[vestigial]] portion of the membrane in the corner of the eye. A gland of the third eyelid (nictitans gland) or [[Harderian gland|Harder's gland]] is attached to the nictating membranes of some animals and may produce up to 50% of the [[tear film]].<ref name=":0" /> |
Fully developed nictitating membranes are found in [[fish]], [[amphibian]]s, [[reptile]]s, [[bird]]s and mammals, but are rare in [[primate]]s.<ref name="butler05">{{cite book| publisher = John Wiley & Sons| isbn = 978-0-471-73383-6| last1 = Butler| first1 = Ann B.| first2 = William |last2= Hodos| title = Comparative Vertebrate Neuroanatomy: Evolution and Adaptation| url = https://archive.org/details/comparativeverte00butl_744| url-access = limited| date = 2 September 2005|page=[https://archive.org/details/comparativeverte00butl_744/page/n239 215]}}</ref><ref>Paul Miller, [http://www.scientificamerican.com/article.cfm?id=why-do-cats-have-an-inner Why do cats have an inner eyelid as well as outer ones?] Scientific American. 20 Nov 2006. (Accessed 2 Nov 2011)</ref> In humans, the [[Plica semilunaris of conjunctiva|plica semilunaris]] (also known as the semilunar fold) and its associated muscles are [[homology (biology)|homologous]] to the nictitating membranes seen in some other mammals and other vertebrates.<ref>The Eye: Basic Sciences in Practice by John V. Forrester, [https://books.google.com/books?id=8T4aIZnWBkAC&pg=PA82 p. 82]</ref> In most primate species, a plica semilunaris is generally not present, although fully developed nictitating membranes can be found in [[lemur]]s and [[Lorisoidea|lorisoid]] primates.<ref>{{cite book | last = [[William Charles Osman Hill|Osman Hill]] | first = W. C. | year = 1953 | title = Primates Comparative Anatomy and Taxonomy I—Strepsirhini | publisher = Edinburgh University Press | series = Edinburgh Univ Pubs Science & Maths, No 3 | page = 13 | oclc = 500576914}}</ref><ref>{{cite book|last = Ankel-Simons|first = F.|title= Primate Anatomy|edition = 3rd|publisher = Academic Press|year = 2007|isbn = 978-0-12-372576-9|page=471}}</ref> Some mammals, such as [[camel]]s, [[polar bear]]s, [[pinniped|seals]] and [[aardvark]]s, have full nictitating membranes, and many mammals retain a small, [[vestigial]] portion of the membrane in the corner of the eye. A gland of the third eyelid (nictitans gland) or [[Harderian gland|Harder's gland]] is attached to the nictating membranes of some animals and may produce up to 50% of the [[tear film]].<ref name=":0" /> |
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== Functions == |
== Functions == |
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The nictitating membrane is normally translucent. In some diving animals, including [[sea lion]]s, it is activated on land, to remove sand and other debris—its function in most animals. In [[Crocodilia|crocodiles]], it protects their eyes from water but also hinders their focus under water. In some diving animals, for example [[beaver]]s and [[manatee]]s, it is transparent and moves across the eye to protect it while under water. |
The nictitating membrane is normally translucent. In some diving animals, including [[sea lion]]s, it is activated on land, to remove sand and other debris—its function in most animals. In [[Crocodilia|crocodiles]], it protects their eyes from water but also hinders their focus under water. In some diving animals, for example [[beaver]]s and [[manatee]]s, it is transparent and moves across the eye to protect it while under water. |
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Nictitating membranes in cats and dogs do not have many muscle fibers, so they are not usually visible; chronic visibility should be taken as a sign of poor condition or ill health. The membrane can, however, be seen clearly when gently opening the eye of the healthy animal when it is asleep, or by pushing down/applying pressure on the eyeball, which will cause it to appear. In some breeds of dogs, the nictitating membrane can be prone to [[prolapse]] of the gland of the third eyelid, resulting in a condition called [[cherry eye]].<ref name=":0">Artem Cheprasov, [http://gurumagazine.org/askaguru/why-do-cats-have-an-extra-eyelid/#more-9539 Why do cats have an extra eyelid?] {{Webarchive|url=https://web.archive.org/web/20160101151132/http://gurumagazine.org/askaguru/why-do-cats-have-an-extra-eyelid/#more-9539 |date=2016-01-01 }} Guru Magazine. 7 Feb 2013. (Accessed 26 Mar 2013)</ref> |
Nictitating membranes in cats and dogs do not have many muscle fibers, so they are not usually visible; chronic visibility should be taken as a sign of poor condition or ill health. The membrane can, however, be seen clearly when gently opening the eye of the healthy animal when it is asleep, or by pushing down/applying pressure on the eyeball, which will cause it to appear. In some breeds of dogs, the nictitating membrane can be prone to [[prolapse]] of the gland of the third eyelid, resulting in a condition called [[cherry eye]].<ref name=":0">Artem Cheprasov, [http://gurumagazine.org/askaguru/why-do-cats-have-an-extra-eyelid/#more-9539 Why do cats have an extra eyelid?] {{Webarchive|url=https://web.archive.org/web/20160101151132/http://gurumagazine.org/askaguru/why-do-cats-have-an-extra-eyelid/#more-9539 |date=2016-01-01 }} Guru Magazine. 7 Feb 2013. (Accessed 26 Mar 2013)</ref> |
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== Gallery == |
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== See also == |
== See also == |
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== External links == |
== External links == |
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{{Commons category|Nictitating membrane}} |
{{Commons category|Nictitating membrane}} |
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* {{youTube|dgh6ABfdlAU|Hawk, transparent eyelids (nicitating membrane slow motion video)}} |
* {{youTube|dgh6ABfdlAU|Hawk, transparent eyelids (nicitating membrane slow motion video)}} |
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Revision as of 11:45, 25 June 2024
![](http://upload.wikimedia.org/wikipedia/commons/thumb/d/d0/Bird_blink-edit.jpg/440px-Bird_blink-edit.jpg)
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. All Anura[1] (tailless amphibians), and some reptiles, birds, and sharks have full nictitating membranes; in many mammals, a small, vestigial portion of the nictitating membrane remains in the corner of the eye. Some mammals, such as cats, beavers, polar bears, seals and aardvarks, have full nictitating membranes. Often called a third eyelid or haw, it may be referred to in scientific terminology as the plica semilunaris, membrana nictitans, or palpebra tertia.
Description
![](http://upload.wikimedia.org/wikipedia/commons/thumb/c/cd/Nictitating_membrane_-_Nickhaut_-_Membrana_nittitante_-_%28Balearica_pavonina_-_Weltvogelpark_2013%29.jpg/220px-Nictitating_membrane_-_Nickhaut_-_Membrana_nittitante_-_%28Balearica_pavonina_-_Weltvogelpark_2013%29.jpg)
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining vision. The term comes from the Latin word nictare, meaning "to blink". It is often called a third eyelid or haw, and may be referred to in scientific terminology as the plica semilunaris, membrana nictitans, or palpebra tertia. Unlike the upper and lower eyelids, the nictitating membrane moves horizontally across the eyeball.
In many species, any stimulus to the eyeball (such as a puff of air) will result in reflex nictitating membrane response. This reflex is widely used as the basis for experiments on classical conditioning in rabbits.[2]
Distribution
Fully developed nictitating membranes are found in fish, amphibians, reptiles, birds and mammals, but are rare in primates.[3][4] In humans, the plica semilunaris (also known as the semilunar fold) and its associated muscles are homologous to the nictitating membranes seen in some other mammals and other vertebrates.[5] In most primate species, a plica semilunaris is generally not present, although fully developed nictitating membranes can be found in lemurs and lorisoid primates.[6][7] Some mammals, such as camels, polar bears, seals and aardvarks, have full nictitating membranes, and many mammals retain a small, vestigial portion of the membrane in the corner of the eye. A gland of the third eyelid (nictitans gland) or Harder's gland is attached to the nictating membranes of some animals and may produce up to 50% of the tear film.[8]
Functions
The nictitating membrane is normally translucent. In some diving animals, including sea lions, it is activated on land, to remove sand and other debris—its function in most animals. In crocodiles, it protects their eyes from water but also hinders their focus under water. In some diving animals, for example beavers and manatees, it is transparent and moves across the eye to protect it while under water.
Birds can actively control their nictitating membrane.[9] In birds of prey, the membrane also serves to protect the parents' eyes from their chicks while they are feeding them, and when peregrine falcons go into their 200-mile-per-hour (320 km/h) dives, they will blink repeatedly with their nictitating membranes to clear debris and spread moisture across the eyes. Woodpeckers tighten their nictitating membrane a millisecond prior to their beak impacting the trunk of a tree to prevent shaking-induced retinal injury.[10]
The nictitating membrane can be used to protect the eye while attacking prey, as in sharks.
It can also protect the eye from ultraviolet radiation, similar to its role in polar bears to prevent snow blindness.
Vestigiality
![](http://upload.wikimedia.org/wikipedia/commons/thumb/a/a9/Gray892.png/220px-Gray892.png)
Nictitating membranes in cats and dogs do not have many muscle fibers, so they are not usually visible; chronic visibility should be taken as a sign of poor condition or ill health. The membrane can, however, be seen clearly when gently opening the eye of the healthy animal when it is asleep, or by pushing down/applying pressure on the eyeball, which will cause it to appear. In some breeds of dogs, the nictitating membrane can be prone to prolapse of the gland of the third eyelid, resulting in a condition called cherry eye.[8]
Gallery
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Common goldeneye showing the transparent nictitating membrane characteristic of diving animals
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The nictitating membrane of a blue shark
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Slow motion video of a common buzzard yawning while perched on an antenna, with nictitating membrane visible (deployed asynchronously on left and right eye).
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Third eyelid on a domestic dog
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The nictitating membrane (mid-blink) of a bald eagle
See also
References
- ^ Rolleston, George; Jackson, William Hatchett (1898). Forms of Animal Life : A Manual of Comparative Anatomy, with Descriptions of Selected Types. Clarendon Press. p. 401.
- ^ Gormezano, I. N. Schneiderman, E. Deaux, and I. Fuentes (1962) Nictitating Membrane: Classical Conditioning and Extinction in the Albino Rabbit Science 138:33–34.
- ^ Butler, Ann B.; Hodos, William (2 September 2005). Comparative Vertebrate Neuroanatomy: Evolution and Adaptation. John Wiley & Sons. p. 215. ISBN 978-0-471-73383-6.
- ^ Paul Miller, Why do cats have an inner eyelid as well as outer ones? Scientific American. 20 Nov 2006. (Accessed 2 Nov 2011)
- ^ The Eye: Basic Sciences in Practice by John V. Forrester, p. 82
- ^ Osman Hill, W. C. (1953). Primates Comparative Anatomy and Taxonomy I—Strepsirhini. Edinburgh Univ Pubs Science & Maths, No 3. Edinburgh University Press. p. 13. OCLC 500576914.
- ^ Ankel-Simons, F. (2007). Primate Anatomy (3rd ed.). Academic Press. p. 471. ISBN 978-0-12-372576-9.
- ^ a b Artem Cheprasov, Why do cats have an extra eyelid? Archived 2016-01-01 at the Wayback Machine Guru Magazine. 7 Feb 2013. (Accessed 26 Mar 2013)
- ^ Frans C. Stades, Milton Wyman, Michael H. Boevé, Willy Neumann, Bernhard Spiess. Ophthalmology for the Veterinary Practitioner. 105–106
- ^ Wygnanski-Jaffe T, Murphy CJ, Smith C, Kubai M, Christopherson P, Ethier CR, Levin AV. (2007) Protective ocular mechanisms in woodpeckers Eye 21, 83–89.
External links
![](http://upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png)