The ear may be affected by disease, including infection and traumatic damage. Diseases of the ear may lead tohearing loss,tinnitus andbalance disorders such asvertigo, although many of these conditions may also be affected by damage to the brain or neural pathways leading from the ear.
The human ear has been adorned byearrings and other jewelry in numerous cultures for thousands of years, and has been subjected to surgical and cosmetic alterations.
The outer ear is the external portion of the ear and includes the fleshy visibleauricle, the ear canal, and the outer layer of the eardrum (also called the tympanic membrane).[1] Since the outer ear is the only visible portion of the ear, the word "ear" often refers to the external part (auricle) alone.[2]
The auricle consists of the curving outer rim called thehelix, the inner curved rim called theantihelix, and opens into the ear canal. Thetragus protrudes and partially obscures the ear canal, as does the facingantitragus. The hollow region in front of the ear canal is called the concha. The ear canal stretches for about 1inch (2.5cm). The first part of the canal is surrounded bycartilage, while the second part near the eardrum is surrounded bybone. This bony part is known as theauditory bulla and is formed by thetympanic part of the temporal bone. The ear canal ends at the external surface of the eardrum, while the surrounding skin containsceruminous andsebaceous glands that produce protectiveearwax.[3] Earwax naturally migrates outward through ear canal, constituting a self-cleaning system.[4][5][6][7]
The middle ear lies between the outer ear and the inner ear. It consists of an air-filled cavity called thetympanic cavity and includes the threeossicles and their attaching ligaments; theauditory tube; and theround andoval windows. The ossicles are three small bones that function together to receive, amplify, and transmit the sound from the eardrum to the inner ear. The ossicles are themalleus (hammer),incus (anvil), and thestapes (stirrup). The stapes is the smallest named bone in thebody. The middle ear also connects to the upperthroat at thenasopharynx via thepharyngeal opening of the Eustachian tube.[3][12]
The three ossicles transmit sound from the outer ear to the inner ear. The malleus receives vibrations from sound pressure on the eardrum, where it is connected at its longest part (the manubrium or handle) by a ligament. It transmits vibrations to the incus, which in turn transmits the vibrations to the small stapes bone. The wide base of the stapes rests on the oval window. As the stapes vibrates, vibrations are transmitted through the oval window, causing movement of fluid within thecochlea.[3]
The round window allows for the fluid within the inner ear to move. As the stapes pushes thesecondary tympanic membrane, fluid in the inner ear moves and pushes the membrane of the round window out by a corresponding amount into the middle ear. The ossicles help amplify sound waves by nearly 15–20 times.[1]
Inner ear
The outer ear receives sound, transmitted through theossicles of the middle ear to theinner ear, where it is converted to a nervous signal in thecochlea and transmitted along thevestibulocochlear nerve.
The inner ear sits within the temporal bone in a complex cavity called thebony labyrinth. A central area known as thevestibule contains two small fluid-filled recesses, called theutricle andsaccule. These connect to thesemicircular canals and thecochlea. There are three semicircular canals angled at right angles to each other which are responsible for dynamic balance. The cochlea is a spiral shell-shaped organ responsible for the sense of hearing. These structures together create themembranous labyrinth.[13]
The bony labyrinth refers to the bony compartment which contains the membranous labyrinth, contained within the temporal bone. The inner ear structurally begins at the oval window, which receives vibrations from the incus of the middle ear. Vibrations are transmitted into the inner ear into a fluid calledendolymph, which fills the membranous labyrinth. The endolymph is situated in two vestibules, the utricle and saccule, and eventually transmits to the cochlea, a spiral-shaped structure. The cochlea consists of three fluid-filled spaces: thevestibular duct, thecochlear duct, and thetympanic duct.[3]Hair cells responsible fortransduction—changing mechanical changes into electrical stimuli are present in theorgan of Corti in the cochlea.[13]
Blood supply
The outer ear is supplied by a number of arteries. Theposterior auricular artery provides the majority of the blood supply. Theanterior auricular arteries provide some supply to the outer rim of the ear and scalp behind it. The posterior auricular artery is a direct branch of the external carotid artery, and the anterior auricular arteries are branches from thesuperficial temporal artery. Theoccipital artery also plays a role.[13]
The inner ear is supplied by the anterior tympanic branch of the maxillary artery; the stylomastoid branch of the posterior auricular artery; the petrosal branch of middle meningeal artery; and thelabyrinthine artery, arising from either theanterior inferior cerebellar artery or thebasilar artery.[13]
Functions
How sounds make their way from the source to the human brain
Sound waves travel through the outer ear, are modulated by the middle ear, and are transmitted to thevestibulocochlear nerve in the inner ear. This nerve transmits information to thetemporal lobe of the brain, where it is registered assound.[14]
Sound that travels through the outer ear impacts on the eardrum, and causes it to vibrate. The three ossicles bones transmit this sound to a second window (theoval window), which protects the fluid-filled inner ear. In detail, the pinna of the outer ear helps to focus a sound, which impacts on the eardrum. The malleus rests on the membrane, and receives the vibration. This vibration is transmitted along the incus and stapes to the oval window. Two small muscles, thetensor tympani andstapedius, also help modulate noise. The two musclesreflexively contract to dampen excessive vibrations. Vibration of the oval window causes vibration of the endolymph within thevestibule and the cochlea.[14]
The inner ear houses the apparatus necessary tochange the vibrations transmitted from the outside world via the middle ear into signals passed along the vestibulocochlear nerve to the brain. The hollow channels of the inner ear are filled with liquid, and contain a sensoryepithelium that is studded withhair cells. The microscopic "hairs" of these cells are structural protein filaments that project out into the fluid. The hair cells aremechanoreceptors that release a chemicalneurotransmitter when stimulated. Sound waves moving through fluid flows against thereceptor cells of the organ of Corti. The fluid pushes the filaments of individual cells; movement of the filaments causes receptor cells to become open to receive thepotassium-rich endolymph. This causes the cell to depolarise, and creates anaction potential that is transmitted along thespiral ganglion, which sends information through the auditory portion of the vestibulocochlear nerve to thetemporal lobe of the brain.[14]
The human ear can generally hear sounds with frequencies between 20Hz and 20kHz (the audio range). Sounds outside this range are consideredinfrasound (below 20 Hz)[15] orultrasound (above 20 kHz)[16] Although hearing requires an intact and functioning auditory portion of thecentral nervous system as well as a working ear, human deafness (extreme insensitivity to sound) most commonly occurs because of abnormalities of the inner ear, rather than in the nerves or tracts of the central auditory system.[citation needed]
Providing balance, when moving or stationary, is also a central function of the ear. The ear facilitates two types of balance: static balance, which allows a person to feel the effects ofgravity, and dynamic balance, which allows a person to sense acceleration.[citation needed]
Static balance is provided by two ventricles, the utricle and the saccule. Cells lining the walls of these ventricles contain fine filaments, and the cells are covered with a fine gelatinous layer. Each cell has 50–70 small filaments, and one large filament, thekinocilium. Within the gelatinous layer lieotoliths, tiny formations ofcalcium carbonate. When a person moves, these otoliths shift position. This shift alters the positions of the filaments, which opension channels within the cell membranes, creatingdepolarisation and anaction potential that is transmitted to the brain along the vestibulocochlear nerve.[14][17]
Dynamic balance is provided through the three semicircular canals. These three canals are orthogonal (at right angles) to each other. At the end of each canal is a slight enlargement, known as theampulla, which contains numerous cells with filaments in a central area called thecupula. The fluid in these canals rotates according to the momentum of the head. When a person changes acceleration, the inertia of the fluid changes. This affects the pressure on the cupula, and results in the opening of ion channels. This causes depolarisation, which is passed as a signal to the brain along the vestibulocochlear nerve.[14] Dynamic balance also helps maintain eye tracking when moving, via thevestibulo-ocular reflex.[citation needed]
Theotic placode on a developing embryo (about four weeks old)The ear develops in the lower neck region and moves upwards as themandible develops (six weeks).
Around its second to third week, the developing embryo consists of three layers: ectoderm,mesoderm, and endoderm. The first part of the ear to develop is the inner ear,[20] which begins to form from the ectoderm around the embryo's 22nd day,[19] derived from two thickenings calledotic placodes on either side of the head. Each otic placode recedes below the ectoderm, forms anotic pit and then anotic vesicle.[21] This entire mass is eventually surrounded by mesenchyme to form the bony labyrinth.[21][22]
Around the 28th day, parts of the otic vesicle begin to form the vestibulocochlear nerve.[21][23] These formbipolar neurons, which supply sensation to parts of the inner ear (namely the sensory parts of the semicircular canals, macular of the utricle and saccule, and organ of Corti).[21]
Around the 33rd day, the vesicles begin to differentiate. Posteriorly, they form what will become the utricle and semicircular canals. Anteriorly, the vesicles differentiate into a rudimentary saccule, which eventually becomes the saccule and cochlea. Part of the saccule eventually gives rise and connects to the cochlear duct, which appears approximately during the sixth week and connects to the saccule through theductus reuniens.[19]
As the cochlear duct's mesenchyme begins to differentiate, three cavities are formed: thescala vestibuli, thescala tympani and thescala media.[19][22] Both the scala vestibuli and the scala tympani contain an extracellular fluid calledperilymph, while the scala media contains endolymph.[22] Thevestibular membrane and thebasilar membrane develop to separate the cochlear duct from the vestibular duct and the tympanic duct, respectively.[19]
Molecular regulation
Most of the genes responsible for theregulation of inner ear formation and itsmorphogenesis are members of thehomeobox gene family such asPax, Msx and Otx homeobox genes. The development of inner ear structures such as thecochlea is regulated byDlx5/Dlx6,Otx1/Otx2 andPax2, which in turn are controlled by the mastergene Shh. Shh is secreted by thenotochord.[24]
Middle ear
The middle ear and its components develop from the first and secondpharyngeal arches.[21] The tympanic cavity and auditory tube develop from the first part of thepharyngeal pouch between the first two arches in an area which will also go on to develop thepharynx. This develops as a structure called thetubotympanic recess.[21] The ossicles (malleus, incus and stapes) normally appear during the first half of fetal development. The first two (malleus and incus) derive from the first pharyngeal arch and the stapes derives from the second.[19] All three ossicles develop from theneural crest.[21] Eventually, cells from the tissue surrounding the ossicles will experienceapoptosis and a new layer of endodermal epithelial will constitute the formation of the tympanic cavity wall.[19][20]
Outer ear
Unlike structures of the inner and middle ear, which develop from pharyngeal pouches, the ear canal originates from the dorsal portion of the firstpharyngeal cleft.[19][21] It is fully expanded by the end of the 18th week of development.[22] The eardrum is made up of three layers (ectoderm, endoderm and connective tissue). The auricle originates as a fusion of six hillocks. The first three hillocks are derived from the lower part of the first pharyngeal arch and form the tragus, crus of the helix, and helix, respectively. The final three hillocks are derived from the upper part of the second pharyngeal arch and form the antihelix, antitragus, and earlobe.[19][21][22] The outer ears develop in the lowerneck. As themandible forms, they move towards their final position level with the eyes.[18][23]
Growth
The ears of newborn humans are proportionally very large, even more so than the head's largeness as compared to the body. Ears grow quickly until about the age of nine, then continue to grow steadily in circumference (about 0.5 millimeters a year) throughout life, with the increase in length more extreme in males.[25][26]
Uniqueness
Ears are individually almost unique, with the odds of two people having matching ears being very low.[27] Additionally, the ear's proportions are normally retained for life, and have thus been employed forforensic identification since the 1950s.[28]
Normal hearing levels are 20decibels, hearing less than this is either partial hearing loss or total hearing loss.[29] This may be a result of injury or damage,congenital disease, orphysiological causes. When hearing loss is a result of injury or damage to the outer ear or to theossicles of the middle ear, it is known asconductive hearing loss.[30] When hearing loss is a result of injury or damage to the inner ear structures such as thecochlea, auditory nerve, and potentially to the vestibulochoclear nerve, it is known assensorineural hearing loss.[30]
Otitis media complications can lead to hearing loss.
Causes of conductive hearing loss include an ear canal blocked by earwax, ossicles that are fixed together or absent, or holes in the eardrum. Conductive hearing loss may also result from middle ear inflammation causing fluid build-up in the normally air-filled space, such as byotitis media.Tympanoplasty is the general name of the operation to repair the middle ear's eardrum and ossicles. Grafts from muscle fascia are ordinarily used to rebuild an intact eardrum. Sometimes artificial ear bones are placed to substitute for damaged ones, or a disrupted ossicular chain is rebuilt in order to conduct sound effectively.[citation needed]
Hearing aids orcochlear implants may be used if the hearing loss is severe or prolonged. Hearing aids work by amplifying the sound of the local environment and are best suited to conductive hearing loss.[31] Cochlear implants transmit the sound that is heard as if it were a nervous signal, bypassing the cochlea. Activemiddle ear implants send sound vibrations to the ossicles in the middle ear, bypassing any non-functioning parts of the outer and middle ear.[citation needed]
Congenital abnormalities
Anomalies and malformations of the auricle are common. These anomalies include chromosome syndromes such asring 18. Children may also present cases of abnormal ear canals and low ear implantation.[20] In rare cases, no auricle is formed (atresia), or is extremely small (microtia). Small auricles can develop when the auricular hillocks do not develop properly. The ear canal can fail to develop if it does not channelise properly or if there is an obstruction.[20] Reconstructive surgery to treat hearing loss is considered as an option for children older than five,[32] with a cosmetic surgical procedure to reduce the size or change the shape of the ear is called anotoplasty. The initial medical intervention is aimed at assessing the baby's hearing and the condition of the ear canal, as well as the middle and inner ear. Depending on the results of tests, reconstruction of the outer ear is done in stages, with planning for any possible repairs of the rest of the ear.[33][34][35]
Approximately one out of one thousand children suffer some type of congenital deafness related to the development of the inner ear.[36] Inner ear congenital anomalies are related to sensorineural hearing loss and are generally diagnosed with acomputed tomography (CT) scan or amagnetic resonance imaging (MRI) scan.[32] Hearing loss problems also derive from inner ear anomalies because its development is separate from that of the middle and external ear.[20] Middle ear anomalies can occur because of errors during head and neck development. The first pharyngeal pouch syndrome associates middle ear anomalies to the malleus and incus structures as well as to the non-differentiation of theannular stapedial ligament. Temporal bone and ear canal anomalies are also related to this structure of the ear and are known to be associated with sensorineural hearing loss and conductive hearing loss.[32]
Vertigo refers to the inappropriate perception of motion. This is due to dysfunction of thevestibular system. One common type of vertigo isbenign paroxysmal positional vertigo, when anotolith is displaced from the ventricles to the semicircular canal. The displaced otolith rests on the cupola, causing a sensation of movement when there is none.Ménière's disease,labyrinthitis,strokes, and other infective and congenital diseases may also result in the perception of vertigo.[37]
The ear drum may become perforated in the event of a large sound or explosion, when diving or flying (calledbarotrauma), or by objects inserted into the ear. Another common cause of injury is due to an infection such as otitis media.[42] These may cause a discharge from the ear calledotorrhea,[43] and are often investigated byotoscopy andaudiometry. Treatment may includewatchful waiting, antibiotics and possibly surgery, if the injury is prolonged or the position of the ossicles is affected.[44] Skull fractures that go through the part of the skull containing the ear structures (the temporal bone) can also cause damage to the middle ear.[45] Acholesteatoma is a cyst of squamous skin cells that may develop from birth or secondary to other causes such as chronic ear infections. It may impair hearing or cause dizziness or vertigo, and is usually investigated by otoscopy and may require a CT scan. The treatment for cholesteatoma is surgery.[46]
There are two principal damage mechanisms to the inner ear in industrialised society, and both injure hair cells. The first is exposure to elevated sound levels (noise trauma), and the second is exposure to drugs and other substances (ototoxicity). A large number of people are exposed to sound levels on a daily basis that are likely to lead to significanthearing loss.[47] TheNational Institute for Occupational Safety and Health has recently published research on the estimated numbers of persons with hearing difficulty (11%) and the percentage of those that can be attributed to occupational noise exposure (24%).[48] Furthermore, according to theNational Health and Nutrition Examination Survey (NHANES), approximately twenty-two million (17%) US workers reported exposure to hazardous workplace noise.[49] Workers exposed to hazardous noise further exacerbate the potential for developingnoise-induced hearing loss when they do not wearhearing protection.[citation needed]
Tinnitus
Tinnitus is the hearing ofsound when no external sound is present.[50] While often described as a ringing, it may also sound like a clicking, hiss or roaring.[51] Rarely, unclear voices or music are heard.[52] The sound may be soft or loud, lowpitched or high pitched and appear to be coming from one ear or both.[51] Most of the time, it comes on gradually.[52] In some people, the sound causes depression, anxiety, or concentration difficulties.[51]
Hyperacusis is a condition where sounds are painful, usually in the ear or from headaches.[54]
Society and culture
Stretching of the earlobe and various cartilage piercings
The ears have been ornamented with jewelry for thousands of years, traditionally bypiercing of theearlobe. In ancient and modern cultures, ornaments have been placed to stretch and enlarge the earlobes, allowing for largerplugs to be slid into a large fleshy gap in the lobe. Tearing of the earlobe from the weight of heavyearrings, or from traumatic pull of an earring (for example, by snagging on a sweater), is fairly common.[55]
Injury to the ears has been present since Roman times as a method of reprimand or punishment – "In Roman times, when a dispute arose that could not be settled amicably, the injured party cited the name of the person thought to be responsible before the Praetor; if the offender did not appear within the specified time limit, the complainant summoned witnesses to make statements. If they refused, as often happened, the injured party was allowed to drag them by the ear and to pinch them hard if they resisted. Hence the French expression "se faire tirer l’oreille", of which the literal meaning is "to have one's ear pulled" and the figurative meaning "to take a lot of persuading". We use the expression "to tweak (or pull) someone's ears" to mean "inflict a punishment"."[38]
The auricles have an effect on facial appearance. In Western societies, protruding ears (present in about 5% of ethnicEuropeans) have been considered unattractive, particularly if asymmetric.[56] The first surgery to reduce the projection of prominent ears was published in the medical literature byErnst Dieffenbach in 1845, and the firstcase report in 1881.[57]
TheVacanti mouse was a laboratorymouse that had what looked like a human ear grown on its back. The "ear" was actually an ear-shapedcartilage structure grown by seeding cow cartilage cells into a biodegradable ear-shaped mold and then implanted under the skin of the mouse; then the cartilage naturally grew by itself.[75] It was developed as an alternative to ear repair or grafting procedures and the results met with much publicity and controversy in 1997.[76][77]
All mammals havethree auditory ossicles. The externalpinna intherian mammals helps direct sound through the ear canal to the eardrum. The complex geometry of ridges on the inner surface of some mammalian ears helps to sharply focus sounds produced by prey, using echolocation signals. These ridges can be regarded as the acoustic equivalent of aFresnel lens, and may be seen in a wide range of animals, including thebat,aye-aye,lesser galago,bat-eared fox,mouse lemur and others.[78][79][80]
Man able to move his ear
Some largeprimates such asgorillas andorangutans (and alsohumans) have undeveloped earmuscles that are non-functionalvestigial structures, yet are still large enough to be easily identified.[81] An ear muscle that cannot move the ear, for whatever reason, has lost that biological function. This serves as evidence ofhomology between related species. In humans, there is variability in these muscles, such that some people are able to move their ears in various directions, and it has been said that it may be possible for others to gain such movement by repeated trials.[81] In such primates, the inability to move the ear is compensated for mainly by the ability to easily turn thehead on a horizontal plane, an ability which is not common to most monkeys—a function once provided by one structure is now replaced by another.[82]
Half-Lop Rabbit Illustration by Charles Darwin, 1868
The ear, with its blood vessels close to the surface, is an essential thermoregulator in some land mammals, including the elephant, the fox, and the rabbit.[83] There are five types ofear carriage in domestic rabbits, some of which have been bred for exaggerated ear length[84]—a potential health risk that is controlled in some countries.[85] Abnormalities in the skull of a half-lop rabbit werestudied by Charles Darwin in 1868. In marine mammals,earless seals are one of three groups ofPinnipedia.
Invertebrates
Only vertebrate animals have ears, though many invertebrates detect sound using other kinds of sense organs. In insects,tympanal organs are used to hear distant sounds. They are located either on the head or elsewhere, depending on the insectfamily.[86] The tympanal organs of some insects are extremely sensitive, offering acute hearing beyond that of most other animals. The female cricket flyOrmia ochracea has tympanal organs on each side of her abdomen. They are connected by a thin bridge of exoskeleton and they function like a tiny pair of eardrums, but, because they are linked, they provide acute directional information. The fly uses her "ears" to detect the call of her host, a male cricket. Depending on where the song of the cricket is coming from, the fly's hearing organs will reverberate at slightly different frequencies. This difference may be as little as 50 billionths of a second, but it is enough to allow the fly to home in directly on a singing male cricket and parasitise it.[87]
Simpler structures allow otherarthropods to detectnear-field sounds. Spiders and cockroaches, for example, have hairs on their legs, which are used for detecting sound. Caterpillars may also have hairs on their body that perceive vibrations[88] and allow them to respond to sound.[citation needed]
^"Ear".Oxford Dictionary. Archived fromthe original on 18 July 2012. Retrieved25 February 2016.
^abcdefDrake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell; illustrations by Richard; Richardson, Paul (2005).Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone. pp. 855–856.ISBN978-0-8089-2306-0.
^Stenström, J. Sten: Deformities of the ear; In: Grabb, W., C., Smith, J.S. (Edited): "Plastic Surgery", Little, Brown and Company, Boston, 1979,ISBN0-316-32269-5 (C),ISBN0-316-32268-7 (P)
^Purves, D. (2007).Neuroscience (4th ed.). New York: Sinauer. pp. 332–336.ISBN978-0-87893-697-7.
^Drake, Richard Lee; Vogl, Wayne; Mitchell, Adam W. M. (2005).Gray's anatomy for students. Philadelphia: Elsevier. p. 858.ISBN978-0-8089-2306-0.
^abcdeHall, John E.; Guyton, Arthur C. (2005).Textbook of Medical Physiology (11th ed.). Philadelphia: W.B. Saunders. pp. 651–657.ISBN978-0-7216-0240-0.
^Greinwald, John H. Jr MD; Hartnick, Christopher J. MD The Evaluation of Children With Sensorineural Hearing Loss.Archives of Otolaryngology–Head & Neck Surgery. 128(1):84–87, January 2002
^Niemitz, Carsten; Nibbrig, Maike; Zacher, Vanessa (December 2007). "Human ears grow throughout the entire lifetime according to complicated and sexually dimorphic patterns--conclusions from a cross-sectional analysis".Anthropologischer Anzeiger; Bericht Uber die Biologisch-Anthropologische Literatur.65 (4):391–413.doi:10.1127/anthranz/65/2007/391.ISSN0003-5548.PMID18196763.
^abShearer, A. Eliot; Hildebrand, Michael S.; Odell, Amanda M.; Smith, Richard JH (1993)."Genetic Hearing Loss Overview".GeneReviews®. University of Washington, Seattle. Retrieved16 January 2026.
^"Hearing Aids".National institute of deafness and other communication disorders. Retrieved20 March 2016.
^abcKliegman; Behrman; Jenson (2007). "367".Nelson Textbook of Pedriatics.
^Lam SM. Edward Talbot Ely: father of aesthetic otoplasty. [Biography. Historical Article. Journal Article] Archives of Facial Plastic Surgery. 6(1):64, 2004 Jan–Feb.
^Siegert R. Combined reconstruction of congenital auricular atresia and severe microtia. [Evaluation Studies. Journal Article] Laryngoscope. 113(11):2021–2027; discussion 2028–2029, 2003 Nov.
^Trigg DJ. Applebaum EL. Indications for the surgical repair of unilateral aural atresia in children. [Review] [33 refs] [Journal Article. Review], American Journal of Otology. 19(5):679–684; discussion 684–686, 1998 September
^Lalwani, A.K. (2009).Diagnóstico y tratamiento en Otorrinolaringología. Cirugía de Cabeza y Cuello. pp. 624–752.
^Davidson's principles and practice of medicine (21st ed.). Edinburgh: Churchill Livingstone/Elsevier. 2010. pp. 1151–1171.ISBN978-0-7020-3084-0.
^abAlexandru, Florin (30 January 2004)."Ear Injuries"(PDF).Council of Europe.
^Senate Public Works Committee, Noise Pollution and Abatement Act of 1972, S. Rep. No. 1160, 92nd Cong. 2nd session.
^Tak SW, Calvert GM, "Hearing Difficulty Attributable to Employment by Industry and Occupation: An Analysis of the National Health Interview Survey – United States, 1997 to 2003", J. Occup. Env. Med. 2008, 50:46–56
^Kuc, R. (2009). "Model predicts bat pinna ridges focus high frequencies to form narrow sensitivity beams".The Journal of the Acoustical Society of America.125 (5):3454–3459.Bibcode:2009ASAJ..125.3454K.doi:10.1121/1.3097500.PMID19425684.
^Mr. St. George Mivart, Elementary Anatomy, 1873, p. 396. Two ears provide stereo imaging that the brain can use to develop a 3-dimensional sound field.
^Fayez, I.; Marai, M.; Alnaimy, A.; Habeeb, M. (1994). Baselga, M.; Marai, I.F.M. (eds.)."Thermoregulation in Rabbits"(PDF).Rabbit Production in Hot Climates. Cahiers Options Méditerranéennes.8. Zaragoza: CIHEAM – International Centre for Advanced Mediterranean Agronomic Studies:33–41. Archived fromthe original(PDF) on 6 October 2021. Retrieved25 February 2018.
.jpg)
.png)
