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Unit2Osteology

.Introdduction

Thegeneralframeworkofthebodyisbuiltupmainlyofaseriesofbones,supplemented,however,incertainregionsbypiecesofcartilage;thebonypartoftheframeworkconstitutestheskeleton.

Intheskeletonoftheadultthereare206distinctbones,asfollows:

AxialSkeletonVertebralcolumn26

Skull22

Hyoidbone1

Ribsandsternum25

—74

AppendicularSkeletonUpperextremities64

Lowerextremities62

—126

Middleearbones6

Total206

1.classification

 Bonesaredivisibleintofourclasses:

Long,Short,Flat,andIrregular

LongBones.—Thelongbonesarecylindrical,withacentralcavitytermedthemedullarycanal.Theyarefoundinthelimbs.

ShortBones.—Whereapartoftheskeletonisintendedforstrengthandconstructedofanumberofshortbones,asinthecarpusandtarsus.

FlatBones.—,thebonesareexpandedintobroad,flatplates,asintheskullandthescapula.

IrregularBones.—Theirregularbones-consistofcancelloustissueenclosedwithinathinlayerofcompactbone.

2.SurfacesofBones.

Processabroad,rough,unevenelevation;

Spineasharp,slenderpointedeminence;

Tuberosityalargeroughenedprocess

Fossaaflattenedorshallowsurface

Sulcusagroovethataccommodatesavessel,nerve,ortendon

Sinusacavityorhollowspaceinabone

Headaprominent,roundedarticulatingendofabone

Facetaflattenedorshallowarticulatingsurface

Crestanarrowridgelikeprojection

3.Structure

Boneiscomposedoftwokindsoftissue,oneofwhichisdenseintexture,termedcompacttissue;theotherconsistsofslenderfibersandlamella,whichjointoformareticularstructure,termedcancelloustissue.

Periosteumadherestothesurfaceofeachofthebones.Boneduringlifeispermeatedbyvessels,andisenclosedinafibrousmembrane,bymeansofwhichmanyofthesevesselsreachthehardtissue.

Marrownotonlyfillsupthecylindricalcavitiesinthebodiesofthelongbones,butalsooccupiesthespacesofthecancelloustissueandextendsintothelargerbonycanals,whichcontainthebloodvessels.

VesselsandNervesofBone.Thebloodvesselsofboneareverynumerous.Thoseofthecompacttissuearederivedfromacloseanddensenetworkofvesselsramifyingintheperiosteum.Nervesaredistributedfreelytotheperiosteum,andaccompanythenutrientarteriesintotheinteriorofthebone.

Axialskeleton

1.Thevertebra

Thevertebralcolumnisaflexuousandflexiblecolumn,formedofaseriesofbonescalledvertebra.   

  Thevertebraarethirty-threeinnumberandthereareseveninthecervicalregion,twelveinthethoracic,fiveinthelumbar,fiveinthesacral,andfourinthecoccygeal.

Atypicalvertebraconsistsoftwoessentialparts—ananteriorsegment,thebody,andaposteriorpart,thevertebralarch;theseencloseaforamen,thevertebralforamen.Thevertebralarchconsistsofapairofpediclesandapairoflamina,andsupportssevenprocesses—viz.,fourarticular,twotransverse,andonespinous.

Thecervicalvertebra

cervicalvertebra（Fig）arethesmallestofthetruevertebra.Thespinousprocessisshortandbifid,thetwodivisionsbeingoftenofunequalsize.Thetransverseprocessesareeachpiercedbytheforamentransversarium,which,intheuppersixvertebra,givespassagetothevertebralarteryandveinandaplexusofsympatheticnerves.

FirstCervicalVertebra（Fig.）isnamedtheatlasbecauseitsupportstheglobeofthehead.Itschiefpeculiarityisthatitisring-likeandhasnobody,nospinousprocess

SecondCervicalVertebra（Fig）isnamedtheaxisbecauseitformsthepivotuponwhichthefirstvertebra,carryingthehead,rotates.Themostdistinctivecharacteristicofthisboneisthestrongodontoidprocesswhichrisesperpendicularlyfromtheuppersurfaceofthebody.

TheSeventhCervicalVertebra—Themostdistinctivecharacteristicofthisvertebraistheexistenceofalongandprominentspinousprocess,hencethenamevertebraprominens.

Thethoracicvertebra

Thethoracicvertebra（Fig）areintermediateinsizebetweenthoseofthecervicalandlumbarregions;theyincreaseinsizefromabovedownward.Theyaredistinguishedbythepresenceoffacetsonthesidesofthebodiesforarticulationwiththeheadsoftheribs,andfacetsonthetransverseprocessesofall,excepttheeleventhandtwelfth,forarticulationwiththetuberclesoftheribs.

Thelumbarvertebra

Thelumbarvertebra（Fig）arethelargestsegmentsofthemovablepartofthevertebralcolumn,andcanbedistinguishedbytheabsenceofaforameninthetransverseprocess,andbytheabsenceoffacetsonthesidesofthebody.

TheSacralandCoccygealVertebra

Thesacralandcoccygealvertebraconsistatanearlyperiodoflifeofnineseparatesegmentswhichareunitedintheadult,soastoformtwobones,fiveenteringintotheformationofthesacrum,fourintothatofthecoccyx.Sometimesthecoccyxconsistsoffivebones;occasionallythenumberisreducedtothree.VertebralCanal.（Fig.）runsthroughoutthegreaterpartofthebone;above,itistriangularinform;below,itsposteriorwallisincomplete,fromthenon-developmentofthelaminaandspinousprocesses.Itlodgesthesacralnerves,anditswallsareperforatedbytheanteriorandposteriorsacralforaminathroughwhichthesenervespassout.

2.TheSternum

Thesternum（Fig）iselongated,flattenedbone,formingthemiddleportionoftheanteriorwallofthethorax.Itconsistsofthreeparts,namedfromabovedownward,themanubrium,thebodyandthexiphoidprocess;Thesuperiorborderisthethickestandpresentsatitscenterthejugularorpresternalnotchandarticulateswiththemanubrium,thejunctionofthetwoformingthesternalangle.

3.TheRibs

Theribsareelasticarchesofboneandtwelveinnumberoneitherside.Thefirstsevenareconnectedbehindwiththevertebralcolumn,andinfront,throughtheinterventionofthecostalcartilages,withthesternum（Fig）;theyarecalledtrueribs. Theremainingfivearefalseribs;Eachribhastwoextremities,aposteriororvertebral,andananteriororsternal,andaninterveningportion—thebody. Theheadismarkedbyakidney-shapedarticularsurface,dividedbyahorizontalcrestintotwofacetsforarticulationwiththedepressionformedonthebodiesoftwoadjacentthoracicvertebra.Theneckistheflattenedportionwhichextendslateralwardfromthehead.Ontheposteriorsurfaceatthejunctionoftheneckandbody,andnearerthelowerthantheupperborder,isaneminence—thetubercle.theinferiorborderofribsisagroove,thecostalgroove,fortheintercostalvesselsandnerve.

Thecostalcartilages（Fig.）arebarsofhyalinecartilagewhichservetoprolongtheribsforwardandcontributeverymateriallytotheelasticityofthewallsofthethorax.

2.TheSkull

Theskullisdivisibleintotwoparts:

（1）thecranium,whichlodgesandprotectsthebrain,consistsofeightbones,and

（2）theskeletonoftheface,offourteen.

Cranium,8bones   Occipital.

TwoParietals.

Frontal.

TwoTemporals.

Sphenoidal.

Ethmoidal.

Face,14bonesTwoNasals.

TwoMaxilla.

TwoLacrimals.

TwoZygomatics.

TwoPalatines.

TwoInferiorNasalConcha.

Vomer.

Mandible.

Cranium

Frontalbone

Thefrontalboneformstheanteriorroofofthecranium,theforehead,theroofofthenasalcavityandthesuperiorarchoftheorbits.

Paritealbones

Theparietalbonesform,bytheirunion,thesidesandroofofthecranium.Theyfuseatthemidlinealongthesagittalsutureandmeetthefrontbonealongthecoronalsuture.

Temporalbones

Thetemporalbonesaresituatedatthesidesandbaseoftheskull.Eachconsistsoffiveparts,thesquama,thepetrous,mastoid,andtympanicparts,andthestyloidprocess.

Sphenoidbone

Thesphenoidboneissituatedatthebaseoftheskullinfrontofthetemporalsandbasilarpartoftheoccipital.Itsomewhatresemblesabatwithitswingsextended,andisdividedintoamedianportionorbody,twogreatandtwosmallwingsextendingoutwardfromthesidesofthebody,andtwopterygoidprocesseswhichprojectfromitbelow.

Ethmoidbonei

Theethmoidboneisexceedinglylightandspongy,andcubicalinshape;itissituatedattheanteriorpartofthebaseofthecranium,betweenthetwoorbits,attheroofofthenose,andcontributestoeachofthesecavities.Itconsistsoffourparts:

ahorizontalorcribriformplate,formingpartofthebaseofthecranium;aperpendicularplate,constitutingpartofthenasalseptum;andtwolateralmassesorlabyrinths.

Occipitalbone

Theoccipitalbone（Figs.）,situatedatthebackandlowerpartofthecranium,istrapezoidinshapeandcurvedonitself.Itispiercedbyalargeovalaperture,theforamenmagnum,throughwhichthecranialcavitycommunicateswiththevertebralcanal.

Facialbones

maxilla

Themaxillaform,bytheirunion,thewholeoftheupperjaw.Eachassistsinformingtheboundariesofthreecavities,viz.,theroofofthemouth,thefloorandlateralwallofthenoseandtheflooroftheorbit.

mandible

Themandible,thelargestandstrongestboneoftheface,servesforthereceptionofthelowerteeth.Itconsistsofacurved,horizontalportion,thebody,andtwoperpendicularportions,therami,whichunitewiththeendsofthebodynearlyatrightangles.Thebodyiscurvedsomewhatlikeahorseshoeandhastwosurfacesandtwoborders.Theramusisquadrilateralinshape,andhastwosurfaces,fourborders,andtwoprocesses.

hyoidbone

Thehyoidboneisshapedlikeahorseshoe,andissuspendedfromthetipsofthestyloidprocessesofthetemporalbonesbythestylohyoidligaments.Itconsistsoffivesegments,viz.,abody,twogreatercornua