book1.docx
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book1.docx
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book1
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
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