Common goldeneye showing the transparent nictitating membrane characteristic of diving animals The nictitating membrane of a blue shark 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.
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The nictitating membrane of a masked lapwing 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. The nictitating membrane also covers the eye and acts as a contact lens in many aquatic birds when they are under water. When sleeping, the lower eyelid rises to cover the eye in most birds, with the exception of the horned owls where the upper eyelid is mobile.
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The nictitating membrane (completely closed) of a black crowned crane, right eye 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.
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Instead the eye is lubricated by the nictitating membrane, a third eyelid that moves horizontally. The nictitating membrane also covers the eye and acts as a contact lens in many aquatic birds. The bird retina has a fan shaped blood supply system called the pecten. Eyes of most birds are large, not very round and capable of only limited movement in the orbits, typically 10-20°.
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Third eyelid on a domestic dog 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.Gormezano, I. N. Schneiderman, E. Deaux, and I. Fuentes (1962) Nictitating Membrane: Classical Conditioning and Extinction in the Albino Rabbit Science 138:33–34.
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Groundsharks, like this blacknose shark, have a nictitating membrane which can be drawn over the eye to protect it. Carcharhiniformes, the ground sharks, with over 270 species, are the largest order of sharks. They include a number of common types, such as catsharks, swellsharks, and the sandbar shark. Members of this order are characterized by the presence of a nictitating membrane over the eye, two dorsal fins, an anal fin, and five gill slits.
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Langer SZ, Trendelenburg U. J Pharmacol Exp Ther. 1966 Jan;151(1):73-86 with Ullrich TrendelenburgDemonstration by the histochemical fluorescence method of the prolonged disappearance of catecholamines from the denervated nictitating membrane of the cat. Weiner N, Langer SZ, Trendelenburg U. J Pharmacol Exp Ther. 1967 Aug;157(2):284-9Time course of the development of supersensitivity to various amines in the nictitating membrane of the pithed cat after denervation or decentralization.
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Close-up of a cherry eye Cherry eye is a disorder of the nictitating membrane (NM), also called the third eyelid, present in the eyes of dogs and cats.Gelatt, K. N. (2000). Essentials of Veterinary Ophthalmology. Baltimore: Lippincott Williams & Wilkins.
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The plica semilunaris is a small fold of tissue on the inside corner of the eye. It is the vestigial remnant of the nictitating membrane, i.e., third eyelid, an organ that is fully functional in some other species of mammals.Owen, R. 1866–1868.
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The nasal capsules are trumpet-shaped and well-separated from orbits. Circumnarial skin folds are present, but the rostral process of the neurocranium (braincase) is absent, although a precerebral fossa is present. Finally, the braincase bears a supraorbital crest. The eyes lack a nictitating membrane.
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SGTX causes depression of spontaneous movement, mydriasis, and relaxation of the nictitating membrane in cats at i.v. dose levels of 0.15-0.2 mg/kg. Further, it produces hypotension of 1–2 hours in duration that is not prevented by treatment with atropine or propranolol.
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The nictitating membrane (mid-blink) of a bald eagle Fully developed nictitating membranes are found in fish, amphibians, reptiles, birds and mammals, but are rare in primates.Paul Miller, Why do cats have an inner eyelid as well as outer ones? Scientific American. 20 Nov 2006.
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The plica semilunaris of conjunctiva is a vestigial remnant of a nictitating membrane in humans. The 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. It can, however, be seen clearly when gently opening the eye of the healthy animal when it is asleep, or 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.
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All geckos except those in the subfamily Eublepharinae (eyelid geckos) possess brilles. Some groups of bony fish have a transparent eyelid known as the adipose eyelid. Some reptiles, mammals and birds have a translucent third eyelid that moves horizontally across the eye called the nictitating membrane.
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Iversen LL, Langer SZ. Br J Pharmacol. 1969 Nov;37(3):627-37.Monoamine oxidase and catechol-O-methyl transferase activities in cat nictitating membrane and rat and guinea-pig vas deferens after sympathectomy. Iversen LL, Jarrott B, Langer SZ. Br J Pharmacol. 1968 Nov;34(3):693P-694P.
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Squalomorphii is a superorder of cartilaginous fishes, generally characterized by lacking traits such as an anal fin, nictitating membrane, or suborbital shelves in the cranium. Also called squalea, or squalean sharks. There are about 163 living species in 11 families. Squalean sharks are divided into four orders: the Hexanchiformes, Squaliformes, Squatiniformes, and Pristiophoriformes.
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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 for protection and to moisten it while maintaining vision. Some reptiles, birds, and sharks have full nictitating membranes; in many mammals, a small, vestigial portion of the membrane remains in the corner of the eye. Some mammals, such as cats, camels, 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.
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Accessory abducens nucleus is a small cluster of neurons in the pontine reticular formation of the rat and rabbit. In the rabbit, motoneurons that are involved in the nictitating membrane response are found in the accessory abducens nucleus. Crosby et al. (1962) questioned whether, in the human, it exists independently of the accessory facial nucleus.
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John Murray: London. 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. 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.
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Because of the size of the head, the neck is relatively short to provide better support. Lacking a lacrimal apparatus, the eye relies on the harderian gland to keep it moist. A durable nictitating membrane protects the eye globe. The animal's field of vision is compromised by the location and limited mobility of the eyes.
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The eyes are covered by a nictitating membrane which allows the beaver to see under water. The nostrils and ears are sealed while submerged. Their lips can be closed behind their front teeth so that they can continue to gnaw underwater. A thick layer of fat under its skin insulates the beaver from its coldwater environment.
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Infected cats typically contract conjunctivitis within a 2-5 day incubation period. Clinical signs of infection are hyperaemia of the nictitating membrane (severity varies), blepharospasm, and discharge from the eye. The infection is not deadly, but if left untreated may cause blindness and pain for the cat. Infection is commonly spread among cats by ocular secretion.
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Comparative Anatomy and Physiology of Vertebrates. London. Its associated muscles are also vestigial. Only one species of primate, the Calabar angwantibo, is known to have a functioning nictitating membrane. The orbitalis muscle is a vestigial or rudimentary nonstriated muscle (smooth muscle) of the eye that crosses from the infraorbital groove and sphenomaxillary fissure and is intimately united with the periosteum of the orbit.
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The nictitating membrane acts a sweeping wiper across the eye. The eagle iris is a pale yellow color, much lighter than human eyes. Both eagles and humans have a white area called the sclera, but in the case of eagles, it is hidden below the eyelid. Eyelid openings are oval-shaped in humans, while they are round in the case of birds' eyes.
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Birds, reptiles and sharks blink with a nictitating membrane from one side of the eye to the other. Blinking provides moisture to the eye by irrigation using tears and a lubricant the eyes secrete. The eyelid provides suction across the eye from the tear duct to the entire eyeball to keep it from drying out. Blinking also protects the eye from irritants.
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During the millisecond before contact with wood, a thickened nictitating membrane closes, protecting the eye from flying debris. These membranes also prevent the retina from tearing. The nostrils are also protected; they are often slit- like and have special feathers to cover them. Woodpeckers are capable of repeated pecking on a tree at high decelerations in the order of (1000 g).
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Cherry eye is typically diagnosed by examination of the conjunctiva and nictitating membrane. 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. This mass may be unilateral or ‘’bilateral’’. Both eyes may develop cherry eye at different times in the animal's life.
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Sharks do not have moveable upper or lower eyelids, but the tiger shark—among other sharks—has a nictitating membrane, a clear eyelid that can cover the eye. A reflective layer behind the tiger shark's retina, called the tapetum lucidum, allows light-sensing cells a second chance to capture photons of visible light. This enhances vision in low-light conditions.
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Most reptiles including birds possess a nictitating membrane, a translucent third eyelid which is drawn over the eye from the inner corner. Notably, it protects a crocodilian's eyeball surface while allowing a degree of vision underwater. However, many squamates, geckos and snakes in particular, lack eyelids, which are replaced by a transparent scale. This is called the brille, spectacle, or eyecap.
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The mri are a tall and slender humanoid species. Their skin is golden in color and their hair is coarse and golden-brown, generally worn shoulder-length. Their eyes are yellow, with epicanthic folds and a functional nictitating membrane to protect them against wind-blown grit. Their ears are slightly pointed, with a tuft of hair at the tip resembling that of a lynx.
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The blackspot shark is a relatively slender species with a streamlined appearance, growing to a length around . The snout is fairly long, pointed or slightly rounded at the tip. The eyes are large, oval, and set horizontally, and are protected by a nictitating membrane on the lower side. The flaps of skin beside the nostrils are triangular, and the furrows on the upper lip are short.
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The eyes are large, with a rudimentary nictitating membrane (protective third eyelid) and a prominent ridge beneath. The five gill slits are positioned somewhat dorsally on the body. The dorsal, pelvic, and anal fins are of roughly equal size. The dorsal fins are placed far back on the body, with the first originating behind the pelvic fin origins and the second originating behind the anal fin origins.
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The third Generation of Progress.New York: Raven Press; 1987 p.151-8 He was among the first to demonstrate co-transmission in the 1970s Possible involvement of a transmitter different from norepinephrine in residual responses to nerve stimulation of cat nictitating membrane after pre-treatment with reserpine. Langer SZ. J.Pharmacol Exp Ther 1976;196:697-713/ and also played a pivotal role in developing the atypical antipsychotic, aripiprazole.
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The botulinum neurotoxin is lethal because it causes paralysis. Field identification involves locating birds showing flaccidity in the legs, wings and neck, as well as the presence of protuberant nictitating membrane. The presence of several dozen, or even hundreds, of fresh waterbird carcasses is the stereotypical sign an outbreak has occurred. In this case the specimens need to be taken to disease laboratory to determine the cause of mortality.
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This species, like other dippers, is equipped with an extra eyelid called a "nictitating membrane" that allows it to see underwater, and scales that close its nostrils when submerged. Dippers also produce more oil than most birds, which may help keep them warmer when seeking food underwater. The song consists of high whistles or trills peee peee pijur pijur repeated a few times. Both sexes of this bird sing year round.
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Adults are usually found in the eyelids, tear glands, tear ducts, or the so-called "third eyelid" (nictitating membrane). Occasionally, they are found in the eyeball itself, either under the conjunctiva (the membrane that covers the white part of the eye) or in the vitreous cavity of the eyeball.Xue, C., N. Tian, and Z. Huang (2007) "Thelazia callipaeda in human vitreous." Canadian Journal of Ophthalmology 42(6):884-885.
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The Izak catshark has a very long caudal peduncle and distinctively ornate dorsal markings. The body of the Izak catshark is firm and stout, tapering dramatically towards the tail. The head is very short, wide, and flattened, with a blunt snout. The horizontally oval eyes are placed high on the head and have thick ridges beneath; each has a rudimentary nictitating membrane and is followed by a spiracle.
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The eyes have a special nictitating membrane for underwater protection. The pied cormorant can often be seen spreading its wings after diving to help dry the feathers, as it has inadequate waterproofing. This lack of feather waterproofing may help the cormorant spend longer underwater due to decreased buoyancy effects. There are two recognized subspecies; Phalacrocorax varius varius (New Zealand) and Phalacrocorax varius hypoleucus (Australia) with slight variation in physical characteristics.
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When the animal completely submerges, the nictitating membranes cover its eyes. In addition, glands on the nictitating membrane secrete a salty lubricant that keeps the eye clean. When a crocodilian leaves the water and dries off, this substance is visible as "tears". The ears are adapted for hearing both in air and underwater, and the eardrums are protected by flaps that can be opened or closed by muscles.
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The demons in Strange include non-human and near human forms. Near human demons are distinguishable by their inhuman eye colouring which varies from blood red, silver or gold. These demons are capable of concealing their eye colour with a sort of nictitating membrane which makes the eyes appear human. They are capable of interbreeding with humans and many such demons have assimilated themselves into human society to cover their activities.
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The Squaliformes are an order of sharks that includes about 126 species in seven families. Members of the order have two dorsal fins, which usually possess spines, they usually have a sharp head, no anal fin or nictitating membrane, and five to seven gill slits. In most other respects, however, they are quite variable in form and size. Most species of the squaliform order live in a saltwater or brackish waters.
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Rhineura floridana; the Harderian gland is marked H. gl. in diagram B (horizontal section of head) and C (horizontal section through right eye). 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. The gland can be compound tubular or compound tubuloalveolar, and the fluid it secretes (mucous, serous or lipid) varies between different groups of animals.
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Adult Slitheen are tall, rather fat with long forearms, powerful claws, and infantile face. They do not appear to have eyelids, but have a nictitating membrane. They have a highly developed sense of smell, able to track a single target across a few city blocks, smell adrenaline and hormones in people, and can sense if one of their own dies. Female Raxacoricofallapatorians can produce poisons within their bodies to use against their enemies.
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The eyes can focus independently, and are specialised with three types of photoreceptive cells, all with fine structural characteristics of retinal cone cells used for both day and night vision, and a tapetum lucidum which reflects onto the retina to enhance vision in the dark. There is also a third eyelid on each eye, the nictitating membrane. Five visual opsin genes are present, suggesting good colour vision, possibly even at low light levels.
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Like the Calabar angwantibo, the golden angwantibo weighs between 266 and 465 grams and has a stumpy tail, abbreviated index fingers, a specialised grooming claw on each foot and a white line on its face. It can be distinguished from its cousin largely by its colour. The fur on its back is red-gold, with a more muted red on its belly. Unlike the Calabar angwantibo, the golden angwantibo has no nictitating membrane.
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The Hexanchiformes are the order consisting of the most primitive types of sharks, and numbering just seven extant species. Fossil sharks that were apparently very similar to modern sevengill species are known from Jurassic specimens. Hexanchiform sharks have only one dorsal fin, either six or seven gill slits, and no nictitating membrane in the eyes. Shark teeth similar to those modern hexanchids are known from Devonian deposits in Antarctica and Australia, as well as Permian deposits in Japan.
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It has orangish-yellow fur on its back, grey or white fur on its belly, and a distinctive white line on its forehead and nose. Like other lorids, this angwantibo has a very short index finger, which allows it to get a strong grip on tree branches. The second toe on each foot has a specialised claw that the angwantibo uses for grooming. The Calabar angwantibo is the only primate to have a functioning nictitating membrane (third eyelid).
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The irises of the eyes are golden to brown, and the transparent nictitating membrane is pale blue. The bill is black, with a blue cere, and the feet are white with black talons. A short tail and long, narrow wings with four long, finger-like feathers, and a shorter fifth, give it a very distinctive appearance. In flight, Northern Territory, Australia The sexes appear fairly similar, but the adult male can be distinguished from the female by its slimmer body and narrower wings.
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Woodpeckers tighten their nictitating membrane a millisecond prior to their beak impacting the trunk of a tree to prevent shaking-induced retinal injury.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. The membrane can be used to protect the eye while attacking prey, as in sharks. Nictitating membranes can protect eyes from ultraviolet radiation, as they do in polar bears to prevent snow blindness.
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The false catshark was first described by Portuguese ichthyologist Félix de Brito Capelo in the Jornal do Sciências Mathemáticas, Physicas e Naturaes in 1868. He based his account on a long adult male caught off Setubal, Portugal. Brito Capelo thought the specimen resembled a member of the genus Triakis, except lacking a nictitating membrane (though it is now known that this species does in fact have this trait). Thus, he assigned it to the new genus Pseudotriakis, from the Greek pseudo ("false").
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The eyes of most frogs are located on either side of the head near the top and project outwards as hemispherical bulges. They provide binocular vision over a field of 100° to the front and a total visual field of almost 360°. They may be the only part of an otherwise submerged frog to protrude from the water. Each eye has closable upper and lower lids and a nictitating membrane which provides further protection, especially when the frog is swimming.
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In some animals, it acts as an accessory to the lacrimal gland, secreting fluid that eases movement of the nictitating membrane. Research has proposed that the gland has several other functions, including that of a photoprotective organ, a location of immune response, a source of thermoregulatory lipids, a source of pheromones, a site of osmoregulation, inter alia. In mammals, the gland secretes an oily substance used to preen the fur. The presence or absence of this gland is one of the cues used by palaeontologists to determine when fur evolved in the ancestors of mammals.
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This allows for binocular vision with stereopsis that vastly improves depth perception. Though its hearing does not match its visual acuity, mating calls are said to be heard for several miles. Eagles blink up as their top eyelid is larger than the bottom one; the additional inner eyelid is known as a nictitating membrane, which “grows in the inner corner of the eye, next to the tear duct”. Eagle tears moisten the eyes and contain the chemical lysozyme which protects against salt water and also destroys bacteria, thus preventing eye infections.
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Diagnosis of FVR is usually by clinical signs, especially corneal ulceration. Definitive diagnosis can be done by direct immunofluorescence or virus isolation. However, many healthy cats are subclinical carriers of feline herpes virus, so a positive test for FHV-1 does not necessarily indicate that signs of an upper respiratory tract infection are due to FVR. Early in the course of the disease, histological analysis of cells from the tonsils, nasal tissue, or nictitating membrane (third eyelid) may show inclusion bodies (a collection of viral particles) within the nucleus of infected cells.
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A shyshark has a stout, spindle-shaped body and a short head comprising less than one-fifth of the total length. The head is broad and dorsally flattened, with a rounded snout. The large, oval eyes have cat-like slit pupils, a rudimentary nictitating membrane (protective third eyelid), and a prominent ridge running underneath. A distinguishing trait of this genus are the large nostrils partially covered by greatly expanded, triangular flaps of skin that overlap the mouth and cover a pair of deep grooves between the nasal excurrent (outflow) openings and the mouth.
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But cats cannot see the same richness of hues and saturation of colors that humans can. A 2014 study found that, along with several other mammals, cats lenses transmit significant amounts of ultraviolet (UVA 315–400 nm) light, which suggests that they possess sensitivity to this part of the spectrum. Cats have a third eyelid, the nictitating membrane, which is a thin cover that closes from the side and appears when the cat's eyelid opens. This membrane partially closes if the cat is sick, although in a sleepy state this membrane is often visible.
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Foreign bodies embedded in the palpebral conjunctiva or the nictitating membrane can cause persistent irritation and ulceration. Often the shape and distribution of the lesion is suggestive of this aetiology, but even in the absence of a characteristic lesion their presence should be considered and sought out. Bacterial and fungal infection occurs readily after the initial ulceration, as disruption of the corneal epithelium allows attachment and colonisation of the underlying tissues by normal corneal commensals. Commonly isolated bacteria include Staphylococcus, Streptococcus and Pseudomonas, and empirical anti-microbial therapy should be effective against these bacteria.
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In anesthetized cats, doses of 0.06–0.12 mg/kg, iv., also caused respiratory and cardiovascular disturbances: although the details were concentration-and time- dependent, the ultimate effects were ones of sustained respiratory stimulation and elevated blood pressure; the hypertension was not inhibited by atropine, but was antagonized by hexamethonium. Candicine caused contraction of the cat nictitating membrane. A concentration of 0.012 mg/mL applied to the isolated guinea pig atrium caused a decrease in the amplitude and rate of contractions, these effects being enhanced by eserine, but inhibited by atropine pre- treatment.
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The infective L3 larvae wiggle out of the straw-like feeding apparatus of the fly when it feeds on the tears of another mammal or bird host. The L3 larvae develop into adults in the eye or surrounding tissues of the host, where they may live for over one year. In the definitive host, Thelazia have been found in various tissues of the orbit (or socket) of the eye, including within the eyelids, in the tear glands, tear ducts, or the so-called "third eyelid" (nictitating membrane) or in the eyeball itself.
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The appearance of the human upper eyelid often varies between different populations. The prevalence of an epicanthic fold covering the inner corner of the eye account for the majority of East Asian and Southeast Asian populations, and is also found in varying degrees among other populations. Separately, but also similarly varying between populations, the crease of the remainder of the eyelid may form either a "single eyelid", a "double eyelid", or an intermediate form. Eyelids can be found in other animals, some of which may have a third eyelid, or nictitating membrane.
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They spread tears on the eyes, which contains substances which help fight bacterial infection as part of the immune system. Some species have a nictitating membrane for further protection. Some aquatic animals have a second eyelid in each eye which refracts the light and helps them see clearly both above and below water. Most creatures will automatically react to a threat to its eyes (such as an object moving straight at the eye, or a bright light) by covering the eyes, and/or by turning the eyes away from the threat.
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The adnexa of the eye, including the third eyelid (seen in the left corner) The eyelids are made up of three layers of tissue: a thin layer of skin, which is covered in hair, a layer of muscles which allow the lid to open and close, and the palpebral conjunctiva, which lies against the eyeball. The opening between the two lids forms the palpebral tissue. The upper eyelid is larger and can move more than the lower lid. Unlike humans, horses also have a third eyelid (nictitating membrane) to protect the cornea.
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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. It is the vestigial remnant of the nictitating membrane (the "third eyelid") which is drawn across the eye for protection, and is present in other animals such as birds, reptiles, and fish, but is rare in mammals, mainly found in monotremes and marsupials.Owen, R. 1866–1868.
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There is no nictitating membrane and the cornea is continuous with the skin surrounding the eyes. The gill slits are on the ventral surface just behind the head and there are five in all species except the sixgill stingray (Hexatrygon bickelli). The front few vertebrae are fused into a synarcual and this either articulates with the bones of the well-developed pectoral girdle or is fused to them, the suprascapulae uniting above the vertebral column. Most species have enlarged, thorn-like dermal denticles on their skin, often with a row of large denticles along the spine.
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The two types of these sensory pits are integumentary sense organs that cover the body and papillae that cover the head, primarily around the snout. When under water, crocodile have a “third eyelid” called a nictitating membrane, which is present in many other reptiles, but is unique in crocodiles because it is semitransparent and acts as goggles to improve eyesight when hunting and prevents eye damage. Crocodiles are able to make certain sounds, especially juveniles. Hatchling crocodiles are able to indicate when they will hatch by making a vocalization that can be heard by the mother.
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The Nile crocodile shares with all crocodilians a nictitating membrane to protect the eyes and lachrymal glands to cleanse its eyes with tears. The nostrils, eyes, and ears are situated on the top of the head, so the rest of the body can remain concealed under water. They have a four- chambered heart, although modified for their ectothermic nature due to an elongated cardiac septum, physiologically similar to the heart of a bird, which is especially efficient at oxygenating their blood. As in all crocodilians, Nile crocodiles have exceptionally high levels of lactic acid in their blood, which allows them to sit motionless in water for up to 2 hours.
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Chick in camouflaged posture A masked lapwing blinking the left eye (the nictitating membrane is used rather than the eyelids). Note origin of the membrane from the medial canthus. A masked lapwing feeding on a sand worm Masked lapwings are shy and harmless in summer and autumn but are best known for their bold nesting habits, being quite prepared to make a nest on almost any stretch of open ground, including suburban parks and gardens, school ovals, and even supermarket carparks and flat rooftops. They can be particularly dangerous at airports where their reluctance to move from their nesting area - even for large aircraft - has resulted in several bird strikes.
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The tiger shark is a member of the order Carcharhiniformes, the most species-rich order of sharks, with more than 270 species also including the small catsharks and hammerhead sharks. Members of this order are characterized by the presence of a nictitating membrane over the eyes, two dorsal fins, an anal fin, and five gill slits. It is the largest member of the Carcharhinidae family, commonly referred to as requiem sharks. This family consists of mostly slender but powerful mid- to large-sized sharks and includes some other well-known sharks, such as the blue shark (Prionace glauca), lemon shark (Negaprion brevirostris), and bull shark (Carcharhinus leucas).
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Analogous organs in other animals similar to humans continue to perform similar functions. The coccyx, or tailbone, though a vestige of the tail of some primate ancestors, is functional as an anchor for certain pelvic muscles including: the levator ani muscle and the largest gluteal muscle, the gluteus maximus. Other structures that are vestigial include the plica semilunaris on the inside corner of the eye (a remnant of the nictitating membrane); and, as pictured, muscles in the ear and other parts of the body. Other organic structures (such as the occipitofrontalis muscle) have lost their original functions (keep the head from falling) but are still useful for other purposes (facial expression).
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The moderately large eyes are horizontal ellipsoids, which have no nictitating membrane, which is a protective, third- eyelid. Ligaments articulate the long jaws to the cranium, and the corners of the mouth have neither furrows nor folds. The jaws contain 300 trident-shaped teeth, each needle-tooth has a cusp and two cusplets; the rows of teeth are widely spaced, with 19–28 tooth rows in the upper jaw, and 21–29 tooth rows in the lower jaw. At the throat, there are six pairs of long gill slits; the first pair of gill slits form a collar, while the extended tips of the gill filaments create a fleshy frill, hence, the frilled shark name of this fish.
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One explanation for the evolution of slit pupils is that they exclude light more effectively than a circular pupil, helping to protect the eyes during daylight. On the rear wall of the eye is a tapetum lucidum, which reflects incoming light back onto the retina, thus utilizing the small amount of light available at night to best advantage. In addition to the protection of the upper and lower eyelids, crocodiles have a nictitating membrane (sometimes called a "third eye-lid") that can be drawn over the eye from the inner corner while the lids are open. The eyeball surface is thus protected under the water while a certain degree of vision is still possible.
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A new chapter was opened when Max Lewandowsky in 1899 in Berlin observed that adrenal extracts acted on the smooth muscle of the eye and orbit of cats – as the iris dilator muscle and nictitating membrane – in the same way as sympathetic nerve stimulation. The correspondence was extended by John Newport Langley and, under his supervision, Thomas Renton Elliott in Cambridge. In four papers in volume 31, 1904, of the Journal of Physiology Elliott described the similarities organ by organ. His visionary hypothesis stands in the abstract of a presentation to the Physiological Society of May 21, 1904, a little over ten years after Oliver and Schäfer's presentation: ″Adrenalin does not excite sympathetic ganglia when applied to them directly, as does nicotine.
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Darwin cites moles as an example of mammals that have organs that have become vestigial and are being phased out by natural selection: > The eyes of moles and of some burrowing rodents are rudimentary in size, and > in some cases are quite covered by skin and fur. This state of the eyes is > probably due to gradual reduction from disuse, but aided perhaps by natural > selection. In South America, a burrowing rodent, the tuco-tuco, or Ctenomys, > is even more subterranean in its habits than the mole; and I was assured by > a Spaniard, who had often caught them, that they were frequently blind. One > which I kept alive was certainly in this condition, the cause, as appeared > on dissection, having been inflammation of the nictitating membrane.
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Zorak tries to kill it by shooting it in the eye (unsuccessfully, as the lizard shuts its nictitating-membrane), while Niamh tries to poke her knife in from its back—which allows Zorak to shoot it in the throat. Niamh then almost faints from exhaustion and fear; Zorak, putting aside his weapons, prevents this but slips off the branch after stepping in the dead ythid's blood. Niamh, taking the weapons, explores the branch until she comes upon a tower of strange design/construction (Karn would have told her that it was built by one of Zarqa's race), where she walks into a lab with a detached head. The head's eyes open and it cries "waa-waa- waaa...", whereupon an odd-looking dwarf, Quoron, comes in and takes her as prisoner.
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Similar results were obtained with frog nerve-muscle preparations, in which it was shown that MLA blocked response of the gastrocnemius muscle to electrical stimulation of the sciatic nerve, inhibited post-synaptic action potentials in the sartorius muscle elicited by stimulation of the sciatic nerve, and reduced the amplitude of miniature end- plate potentials in the extensor digitus IV muscle. Ganglion-blocking effects of MLA were observed using the cat nictitating membrane preparation: complete inhibition of the response was produced by 4 mg/kg of "mellictine" given intravenously. No significant effects were produced by the drug in smooth muscle preparations from rabbit, guinea pig or cat, indicating the lack of activity at typically muscarinic sites. In electrically stimulated guinea pig ileum, for example, contractions were unaffected by a concentration of 5 x 10−4M of MLA.
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As Rüppell did not originally designate a holotype, in 1960 a 31-cm-long specimen caught off Jeddah, Saudi Arabia, was made the species lectotype. Other common names for this shark include blunthead shark, light-tip shark, reef whitetip shark, and whitetip shark. Once placed in the family Triakidae, the whitetip reef shark is now recognized by most authors as belonging to the family Carcharhinidae on the basis of morphological characters, such as a full nictitating membrane, well-developed precaudal pit, strong lower caudal fin lobe, and scroll-like intestinal valves. Morphological and molecular phylogenetic analyses suggest the whitetip reef shark is grouped with the lemon sharks (Negaprion) and the sliteye shark (Loxodon) in occupying an intermediate position on the carcharhinid evolutionary tree, between most basal genera (Galeocerdo, Rhizoprionodon, and Scoliodon) and the most derived (Carcharhinus and Sphyrna).
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The entorhinal cortex (EC) is an area of the brain located in the medial temporal lobe and functions as a hub in a widespread network for memory, navigation and the perception of time.Integrating time from experience in the lateral entorhinal cortex Albert Tsao, Jørgen Sugar, Li Lu, Cheng Wang, James J. Knierim, May-Britt Moser & Edvard I. Moser Naturevolume 561, pages57–62 (2018) The EC is the main interface between the hippocampus and neocortex. The EC-hippocampus system plays an important role in declarative (autobiographical/episodic/semantic) memories and in particular spatial memories including memory formation, memory consolidation, and memory optimization in sleep. The EC is also responsible for the pre-processing (familiarity) of the input signals in the reflex nictitating membrane response of classical trace conditioning; the association of impulses from the eye and the ear occurs in the entorhinal cortex.
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Birds that fish by stealth from above the water have to correct for refraction particularly when the fish are observed at an angle. Reef herons and little egrets appear to be able to make the corrections needed when capturing fish and are more successful in catching fish when strikes are made at an acute angle and this higher success may be due to the inability of the fish to detect their predators. Other studies indicate that egrets work within a preferred angle of strike and that the probability of misses increase when the angle becomes too far from the vertical leading to an increased difference between the apparent and real depth of prey. Birds that pursue fish under water like auks and divers have far fewer red oil droplets, but they have special flexible lenses and use the nictitating membrane as an additional lens.
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