Thecanineandfelineearcanbedividedintotheircomponentparts,consistingofthepinnae,theexternalearcanalsorexternalacousticmeatuses,themiddleear,andtheinternalear(Fig.1).Knowledgeofthenormalstructureandfunctionoftheeariscriticaltobeabletodiagnoseabnormalitiesthateitherinvolvetheearororiginatewithinoneormoreoftheearcompartments.Inaddition,aveterinarianmustbeawareofvariousstructureswithinorassociatedwiththeearsothattheyarenotdamagedordestroyedwhiletreatingananimalwithoticdisease.Thisarticleprovidesabriefdiscussionofthevariousanatomicfeaturesoftheearandnormalphysiologyofportionsoftheear.Formorein-depthcoverageofoticanatomyandphysiology,refertothefollowingreferences.1–8
Theconformationofthepinnaeinthedogmaybeerectorpendulous.Mostcatshaveerectpinnae.Geneticmutationsinthecathaveaffectedthedevelopmentofthepinnae,andresultedinbreedsofcatswithfourears,foldedears,andcurledears.Catswiththefour-earedconditionpossessasmallextrapinnabilaterally,showreductionofthesizeoftheirglobes,andhaveaslightlyundershotjaw,withanormalbodysize.9ScottishFoldcatsareauniquebreedwithpinnaethatarefolded.Upto4weekspostnatal,ScottishFoldcatshaveerectpinnae,andthenthetipsoftheearsbegintofoldrostrally.AllScottishFoldcatswiththefolded-earphenotype,evenifheterozygotes,sufferfromsomedegreeofosteochondrodysplasiaofthedistallimbs.10TheAmericancurlcatbreedhaspinnaethatarecurledbackatthepinnalapex.
犬的耳廓构造可以是直立或是下垂的。大多数猫的耳廓是直立的。猫的基因突变影响了耳廓的发育，导致猫的品种有四耳猫，折耳猫和卷耳猫。四耳猫天生多出来一对较小的耳廓，并且眼球较小，下颌略突出，体型正常。苏格兰折耳猫是一种特别的折耳品种。[9]
后4周，苏格兰折耳猫的耳廓都是直立的，之后耳尖开始向前翻折。所有苏格兰折耳猫都有折耳表型，即使是非纯种基因，也会出现某种程度的末端肢体骨软骨发育不良。[10]美国卷耳猫的耳廓顶端向后卷曲。
Pinnaeplayanimportantroleinsoundlocalizationandalsocollectsoundwavesandtransmitthemtothetympanicmembrane.
Thepinnaearecomposedofauricularcartilagethatiscoveredonbothsidesbyhairedskincompletewithapocrinesweatglands,sebaceousglands,andhairfollicles.
Theconvexsurfaceofthepinnahasmorehairfolliclesperunitareathanthethinnerconcavesurface.11
Themusclesofthepinnaarenumerousandacttomovetheearinspecificdirections.
耳廓在声音定位中起重要作用，同时收集声波并将其传输到鼓膜。
耳廓由耳廓软骨组成，两侧覆盖着有毛皮肤，并伴有顶泌汗腺，皮脂腺和毛囊。耳廓凸面比较薄的凹面在单位面积内具有更多的毛囊。
耳廓的肌肉很多，使耳朵能向特定方向移动。
Theopeningoftheexternalearcanalfacesdorsolaterally.
Thequadrangularplateofcartilage,thetragus,formsthelateralboundaryoftheearcanal.
Theantitragusisathin,elongatedpieceofcartilagecaudaltothetragusandseparatedfromitbytheintertragicincisure.1
Theintertragicincisureistheanatomicregionusedtoguidetheotoscopicconeorotoendoscopeintotheearcanalfortheotoscopicexamination(Fig.2).
Theproximalportionoftheauricularcartilagebecomesfunnelshapedformingtheverticalearcanal.
Theverticalearcanaldeviatesmediallyjustdorsaltothelevelofthetympanumtoformthehorizontalearcanal.12
Thereisaprominentcartilaginousridgethatseparatestheverticalandhorizontalearcanalsandwhentheearisinitsnormalposition,makesoticexaminationofthehorizontalearcanaldifficultwithoutelevatingthisridgebygraspingandliftingtheearpinna(Fig.3).
Aseparatecartilaginousband,theannularcartilage,fitswithinthebaseofthisconchaltube,givingtheexternalearcanalflexibility.
Theannularcartilagehasfibrousattachmentstotheosseousexternalacousticmeatus.
Theannularcartilagecoverstheshorttubularosseousexternalacousticmeatusofthetympanicpartofthetemporalbone.
Theosseousexternalacousticmeatusendsatthetympanicannulus.
外耳道朝背外侧开口。
四边形软骨和耳屏形成耳道的外侧边界。
对耳屏是在耳轮外侧边缘由一层软骨薄片构成，通过耳屏间切迹将其分开。[1]
耳屏间切迹是引导锥形耳镜或耳内镜进入耳道进行耳镜检查的解剖区域(图2)。
耳廓软骨的近端部分变成漏斗状，形成垂直耳道。
垂直耳道在鼓室水平的背侧向内侧偏移，形成水平耳道。[12]
当耳朵处于正常位置时，有一个突出的软骨嵴将垂直和水平的耳道分开，虽然可以对耳道进行耳廓检查，但若不通过抓住和提起耳廓来抬高软骨脊，就很难检查水平耳道（图3）。
一个单独的软骨带，环状软骨，贴合在这个管状耳软骨的基部，使得外耳道的灵活可动。
环状软骨与骨外耳道有纤维性附着。
环状软骨覆盖在颞骨鼓室部的短管状骨外耳道上。
骨外耳道止于鼓室环。
Thedorsorostralmarginoftheexternalacousticmeatusisincloseappositiontoaplateauofboneformedbythezygomaticprocessofthetemporalbone(Fig.4).
Inmostdogbreeds,zygomaticprocessofthetemporalboneisshortandcurvedandformsanobtuseanglewiththelongitudinalaxisoftheskull.
Inaddition,inmostdogbreeds,theretroarticularprocessofthetemporomandibularjointisnarrowandformsamoreobtuseanglerelativetotheverticalplane.
Incontrast,somedogs,suchaspitbullterriers,havealongerandbroaderzygomaticprocessofthetemporalbonethatformsarightangleorslightlyacuteangletothelongitudinalaxis.
Theretroarticularprocessismuchbroaderandlongerandformsamuchmoreacuteanglerelativetotheverticalplane(seeFig.4).
Inaggregate,thesevariationsinpitbullterriersresultinanexternalacousticmeatusthatisdeeperandpossiblybetterprotectedrelativetotheexternalsurface.
However,theclinicalsignificanceofthisdeeperlocationandmoreacuteanglescaninhibitthedepthofinsertionoftheotoendoscopewhenattemptingtoperformamyringotomyusingthevideootoscope.
外耳道背前缘与由颞骨颧骨突形成的骨平台紧密相连(图4)。
在大多数犬种中，颞骨的颧突短而弯曲，与颅骨的纵轴形成一个钝角。
此外，在大多数犬种中，颞下颌关节的后关节突较窄，相对于垂直面形成的角度更接近钝角。
相比之下，有些犬，如比特犬，其颞骨颧突更长更宽，与纵轴呈直角或近似锐角。
关节后突宽得多，长得多，相对于垂直面形成的角度更接近锐角(见图4)。
总的来说，比特犬的这些变化导致了外耳道更深，相对于外部表面有更好的保护。
然而，当试图使用耳内镜进行鼓膜切开术时，这种更深人位置和更锐角的临床意义可能会阻挡耳内镜的插入深度。
Theepidermisliningtheexternalearcanalissimilarhistologicallytothepinna;
however,inmostbreeds,hairsarefeweranddonotextendthelengthoftheearcanal.13
Averyfewfinehairsarefounddistaltothetympanicmembrane.
Thesehairsareausefullandmarkwhenflushinganeartolocatethetympanicmembraneinanabnormalear(Fig.5).
Cockerspanieldogstypicallyhaveexcessivecompoundhairfolliclesinthehorizontalearcanalcomparedwithsparselydistributed,simplehairfolliclesingreyhounddogsandmixedbreeddogs.14
外耳道的表皮层在组织学上与耳廓相似;
然而，在大多数品种中，毛发较少，且不会延长至耳道的长度。[13]
在水平耳道远端至鼓膜可见非常细小的毛发当冲洗耳朵时，这些毛发是一个有用的标志，以便于在异常的耳道中定位鼓膜(图5)
相比灵缇犬和混血犬稀疏的毛囊分布和简单的毛囊，可卡犬在水平耳道通常有过多的复合毛囊。[14]
Theexternalearcanalalsocontainssebaceousglandsandceruminousglands,whicharemodifiedapocrineglands.
Cerumenisanemulsionthatcoatstheearcanal.
Itiscomposedofdesquamatedkeratinizedsquamousepithelialcellsalongwiththesecretionsfromthesebaceousandceruminousglandsoftheears.
Thedermisoftheexternalearcanalistypical,consistingofcollagenandelasticfibersandasubcutaneouslayerthatseparatesthedermisfromthedeepercartilagelayer.
外耳道还包括皮脂腺和耵聍腺，后者是改性的顶泌腺。
耵聍是一种覆盖耳道的乳剂。
它是由脱落的角化鳞状上皮细胞以及来自皮脂腺和耵聍腺的分泌物组成。
外耳道的真皮层，典型的是由胶原蛋白和弹性纤维以及将真皮层与更深的软骨层隔开的皮下层组成。
Theexternalearandexternalcanalterminatemediallyatthetympanicmembrane.
Itisimportanttonotethatthetympanicmembraneisorientatedata45-degreeanglerelativetothecentralaxisofthehorizontalexternalacousticmeatus.
Insomebreeds,thetympanicmembraneisalsovariablyorientatedrostrally.8
Fromaclinicalperspective,thisanglecanbeusedtoadvantagewhileperformingadeepexternalearflush,allowingonetobeabletopassacatheteralongtheventralfloorofthehorizontalearcanalwithoutrupturingthetympanicmembranetoremovealltheflushingsolutionandsaline(Fig.6).
外耳和外耳道终止于鼓膜的内侧。
值得注意的是鼓膜与水平外耳道的中轴呈45度角。
在一些品种中，鼓膜会不同程度地前倾。[8]
在临床中，这个角度便于进行深部外耳冲洗,便于我们能够沿水平耳道腹侧壁探入导管，并吸出所有冲洗溶液和生理盐水，而不必撕裂鼓膜(图6)。
皮肤科之星
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