Atlas A General Orientation to Human Anatomy

Saladin:Anatomy&Physiology:TheUnityofFormandFunction,ThirdEditionAtlasAGeneralOrientationtoHumanAnatomyText©TheMcGraw−HillCompanies,2003ATLASAGeneralOrientationtoHumanAnatomyAnatomicalPosition30AnatomicalPlanes31DirectionalTerms31SurfaceAnatomy32•AxialRegion32•AppendicularRegion36BodyCavitiesandMembranes36•DorsalBodyCavity36•VentralBodyCavity36OrganSystems38AVisualSurveyoftheBody39ChapterReview52Saladin:Anatomy&Physiology:TheUnityofFormandFunction,ThirdEditionAtlasAGeneralOrientationtoHumanAnatomyText©TheMcGraw−HillCompanies,2003AtlasA30PartOneOrganizationoftheBodyAnatomicalPositionAnatomicalpositionisastanceinwhichapersonstandserectwiththefeetflatonthefloor,armsatthesides,andthepalms,face,andeyesfacingforward(fig.A.1).Thispositionprovidesapreciseandstandardframeofrefer-enceforanatomicaldescriptionanddissection.Withoutsuchaframeofreference,tosaythatastructuresuchasthesternum,thymus,oraortais“abovetheheart”wouldbevague,sinceitwoulddependonwhetherthesubjectwasstanding,lyingfacedown,orlyingfaceup.Fromtheperspectiveofanatomicalposition,however,wecandescribethethymusassuperiortotheheart,thesternumasanteriororventraltotheheart,andtheaortaasposte-riorordorsaltoit.Thesedescriptionsremainvalidregard-lessofthesubject’sposition.Unlessstatedotherwise,assumethatallanatomicaldescriptionsrefertoanatomicalposition.Bearinmindthatifasubjectisfacingyouinanatomicalposition,thesubject’sleftwillbeonyourrightandviceversa.Inmostanatomicalillustrations,forexample,theleftatriumoftheheartappearstowardtherightsideofthepage,andwhiletheappendixislocatedintherightlowerquadrantoftheabdomen,itappearsontheleftsideofmostillustrations.Theforearmissaidtobesupinewhenthepalmsfaceuporforwardandpronewhentheyfacedownorrearward(fig.A.2).Thedifferenceisparticularlyimpor-tanttodescriptionsofanatomyofthisregion.Inthesupineposition,thetwoforearmbones(radiusandulna)areparallelandtheradiusislateraltotheulna.Intheproneposition,theradiusandulnacross;theradiusislateraltotheulnaattheelbowbutmedialtoitatthewrist.Descriptionsofnerves,muscles,bloodvessels,andotherstructuresoftheforearmassumethattheforearmissupine.(Supinealsomeanslyingfaceupandpronealsomeanslyingfacedown.)FigureA.1AnatomicalPosition.Thefeetareflatonthefloorandclosetogether,thearmsarehelddownwardandsupine,andthefaceisdirectedforward.RadiusUlnaSupineProneFigureA.2PositionsoftheForearm.Whentheforearmissupine,thepalmfacesforward;whenprone,itfacesrearward.Notethedifferencesintherelationshipoftheradiustotheulna.Saladin:Anatomy&Physiology:TheUnityofFormandFunction,ThirdEditionAtlasAGeneralOrientationtoHumanAnatomyText©TheMcGraw−HillCompanies,2003AtlasAAtlasAGeneralOrientationtoHumanAnatomy31AnatomicalPlanesManyviewsofthebodyarebasedonrealorimaginary“slices”calledsectionsorplanes.“Section”impliesanactualcutorslicetorevealinternalanatomy,whereas“plane”impliesanimaginaryflatsurfacepassingthroughthebody.Thethreemajoranatomicalplanesaresagittal,frontal,andtransverse(fig.A.3).Asagittal1(SADJ-ih-tul)planepassesverticallythroughthebodyoranorgananddividesitintorightandleftportions.Thesagittalplanethatdividesthebodyororganintoequalhavesisalsocalledthemedian(mid-sagittal)plane.Theheadandpelvicorgansarecommonlyillustratedonthemedianplane(fig.A.4a).Afrontal(coronal)planealsoextendsvertically,butitisperpendiculartothesagittalplaneanddividesthebodyintoanterior(front)andposterior(back)portions.Afrontalsectionofthehead,forexample,woulddivideitintooneportionbearingthefaceandanotherbearingthebackofthehead.Contentsofthethoracicandabdominalcavitiesaremostcommonlyshowninfrontalsection(fig.A.4b).Atransverse(horizontal)planepassesacrossthebodyoranorganperpendiculartoitslongaxis(fig.A.4c);therefore,itdividesthebodyororganintosuperior(upper)andinferior(lower)portions.CTscansaretypi-callytransversesections(seefig.1.17,p.24).DirectionalTermsTableA.1summarizesfrequentlyusedtermsthatdescribethepositionofonestructurerelativetoanother.Interme-diatedirectionsareoftenindicatedbycombinationsofFrontalplaneTransverseplaneMidsagittalplaneFigureA.3AnatomicalPlanesofReference.Whatistheothernamefortheparticularsagittalplaneshownhere?1sagitta
arrow(c)FigureA.4ViewsoftheBodyintheThreePrimaryAnatomicalPlanes.(a)Sagittalsectionofthepelvicregion.(b)Frontalsectionofthethoracicregion.(c)Transversesectionoftheheadattheleveloftheeyes.(a)(b)Saladin:Anatomy&Physiology:TheUnityofFormandFunction,ThirdEditionAtlasAGeneralOrientationtoHumanAnatomyText©TheMcGraw−HillCompanies,2003AtlasA32PartOneOrganizationoftheBodytheseterms.Forexample,onestructuremaybedescribedasdorsolateraltoanother(towardthebackandside).Becauseofthebipedal,uprightstanceofhumans,somedirectionaltermshavedifferentmeaningsforhumansthantheydoforotheranimals.Anterior,forexam-ple,denotestheregionofthebodythatleadsthewayinnormallocomotion.Forafour-leggedanimalsuchasacat,thisistheheadendofthebody;forahuman,however,itistheareaofthechestandabdomen.Thus,anteriorhasthesamemeaningasventralforahumanbutnotforacat.Posteriordenotestheregionofthebodythatcomeslastinnormallocomotion—thetailendofacatbutthedors