on the gait of animals-第4部分

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not　be　a　biped。　As　in　a　man　or　a　quadruped；　the　thigh　and　the　rest



of　the　leg　would　be　attached　immediately　to　quite　a　small　hip；



consequently　the　whole　body　would　be　tilted　forward。　As　it　is；



however；　the　hip　is　long　and　extends　right　along　to　the　middle　of



the　belly；　so　that　the　legs　are　attached　at　that　point　and　carry　as



supports　the　whole　frame。　It　is　also　evident　from　these　considerations



that　a　bird　cannot　possibly　be　erect　in　the　sense　in　which　man　is。　For



as　it　holds　its　body　now　the　wings　are　naturally　useful　to　it；　but



if　it　were　erect　they　would　be　as　useless　as　the　wings　of　Cupids　we



see　in　pictures。　It　must　have　been　clear　as　soon　as　we　spoke　that



the　form　of　no　human　nor　any　similar　being　permits　of　wings；　not



only　because　it　would；　though　Sanguineous；　be　moved　at　more　than



four　points；　but　also　because　to　have　wings　would　be　useless　to　it



when　moving　naturally。　And　Nature　makes　nothing　contrary　to　her　own



nature。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　12







　　We　have　stated　above　that　without　flexion　in　the　legs　or　shoulders



and　hips　no　Sanguineous　animal　with　feet　could　progress；　and　that



flexion　is　impossible　except　some　point　be　at　rest；　and　that　men　and



birds；　both　bipeds；　bend　their　legs　in　opposite　directions；　and



further　that　quadrupeds　bend　their　in　opposite　directions；　and　each



pair　in　the　opposite　way　to　a　man's　limbs。　For　men　bend　their　arms



backwards；　their　legs　forwards；　quadrupeds　their　forelegs　forwards；



their　back　legs　backwards；　and　in　like　manner　also　birds　bend



theirs。　The　reason　is　that　Nature's　workmanship　is　never



purposeless；　as　we　said　above；　but　everything　for　the　best　possible　in



the　circumstances。　Inasmuch；　therefore；　as　all　creatures　which



naturally　have　the　power　of　changing　position　by　the　use　of　limbs；



must　have　one　leg　stationary　with　the　weight　of　the　body　on　it；　and



when　they　move　forward　the　leg　which　has　the　leading　position　must



be　unencumbered；　and　the　progression　continuing　the　weight　must



shift　and　be　taken　off　on　this　leading　leg；　it　is　evidently



necessary　for　the　back　leg　from　being　bent　to　become　straight　again；



while　the　point　of　movement　of　the　leg　thrust　forward　and　its　lower



part　remain　still。　And　so　the　legs　must　be　jointed。　And　it　is　possible



for　this　to　take　place　and　at　the　same　time　for　the　animal　to　go



forward；　if　the　leading　leg　has　its　articulation　forwards；



impossible　if　it　be　backwards。　For；　if　it　be　forwards；　the



stretching　out　of　the　leg　will　be　while　the　body　is　going　forwards；



but；　if　the　other　way；　while　it　is　going　backwards。　And　again；　if



the　flexion　were　backwards；　the　placing　of　the　foot　would　be　made　by



two　movements　and　those　contrary　to　one　another；　one；　that　is；



backwards　and　one　forwards；　for　in　the　bending　together　of　the　limb



the　lower　end　of　the　thigh　would　go　backwards；　and　the　shin　would　move



the　foot　forwards　away　from　the　flexion；　whereas；　with　the　flexion



forwards；　the　progression　described　will　be　performed　not　with



contrary　motions；　but　with　one　forward　motion。



　　Now　man；　being　a　biped　and　making　his　change　of　position　in　the



natural　way　with　his　two　legs；　bends　them　forward　for　the　reasons



set　forth；　but　his　arms　bend　backwards　reasonably　enough。　If　they　bent



the　opposite　way　they　would　be　useless　for　the　work　of　the　hands；



and　for　taking　food。　But　quadrupeds　which　are　also　viviparous



necessarily　bend　their　front　legs　forwards。　For　these　lead　off　first



when　they　move；　and　are　also　in　the　forepart　of　their　body。　The　reason



that　they　bend　forward　is　the　same　as　in　the　case　of　man；　for　in



this　respect　they　are　like　mankind。　And　so　quadrupeds　as　well　as　men



bend　these　legs　forward　in　the　manner　described。　Moreover；　if　the



flexion　is　like　this；　they　are　enabled　to　lift　their　feet　high；　if



they　bent　them　in　the　opposite　way　they　would　only　lift　them　a



little　way　from　the　ground；　because　the　whole　thigh　and　the　joint　from



which　the　shin…bone　springs　would　lie　under　the　belly　as　the　beast



moved　forward。　If；　however；　the　flexion　of　the　hind　legs　were　forwards



the　lifting　of　these　feet　would　be　similar　to　that　of　the　forefeet



（for　the　hind　legs；　too；　would　in　this　case　have　only　a　little　room



for　their　lifting　inasmuch　as　both　the　thigh　and　the　knee…joint



would　fall　under　the　position　of　the　belly）；　but　the　flexion　being



backwards；　as　in　fact　it　is；　nothing　comes　in　the　way　of　their



progression　with　this　mode　of　moving　the　feet。　Moreover；　it　is



necessary　or　at　least　better　for　their　legs　to　bend　thus　when　they　are



suckling　their　young；　with　a　view　to　such　ministrations。　If　the



flexion　were　inwards　it　would　be　difficult　to　keep　their　young　under



them　and　to　shelter　them。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　13







　　Now　there　are　four　modes　of　flexion　if　we　take　the　combinations　in



pairs。　Fore　and　hind　may　bend　either　both　backwards；　as　the　figures



marked　A；　or　in　the　opposite　way　both　forwards；　as　in　B；　or　in



converse　ways　and　not　in　the　same　direction；　as　in　C　where　the　fore



bend　forwards　and　the　hind　bend　backwards；　or　as　in　D；　the　opposite



way　to　C；　where　the　convexities　are　turned　towards　one　another　and　the



concavities　outwards。　Now　no　biped　or　quadruped　bends　his　limbs　like



the　figures　A　or　B；　but　the　quadrupeds　like　C；　and　like　D　only　the



elephant　among　quadrupeds　and　man　if　you　consider　his　arms　as　well



as　his　legs。　For　he　bends　his　arms　concavely　and　his　legs　convexly。



　　In　man；　too；　the　flexions　of　the　limbs　are　always　alternately



opposite；　for　example　the　elbow　bends　back；　but　the　wrist　of　the



hand　forwards；　and　again　the　shoulder　forwards。　In　like　fashion；



too；　in　the　case　of　the　legs；　the　hip　backwards；　the　knee　forwards；



the　ankle　in　the　opposite　way　backwards。　And　plainly　the　lower　limbs



are　opposed　in　this　respect　to　the　upper；　because　the　first　joints　are



opposites；　the　shoulder　bending　forwards；　the　hip　backwards；　wherefore



also　the　ankle　bends　backwards；　and　the　wrist　of　the　hand　forwards。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　14







　　This　is　the　way　then　the　limbs　bend；　and　for　the　reasons　given。



But　the　hind　limbs　move　criss…cross　with　the　fore　limbs；　after　the　off



fore　they　move　the　near　hind；　then　the　near　fore；　and　then　the　off



hind。　The　reason　is　that　（a）　if　they　moved　the　forelegs　together　and



first；　the　animal　would　be　wrenched；　and　the　progression　would　be　a



stumbling　forwards　with　the　hind　parts　as　it　were　dragged　after。



Again；　that　would　not　be　walking　but　jumping；　and　it　is　hard　to　make　a



continuous　change　of　place；　jumping　all　the　time。　Here　is　evidence



of　what　I　say；　even　as　it　is；　all　horses　that　move　in　this　way　soon



begin　to　refuse；　for　example　the　horses　in　a　religious　procession。　For



these　reasons　the　fore　limbs　and　the　hind　limbs　move　in　this



separate　way。　Again；　（b）　if　they　moved　both　the　right　legs　first　the



weight　would　be　outside　the　supporting　limbs　and　they　would　fall。　If



then　it　is　necessary　to　move　in　one　or　other　of　these　ways　or



criss…cross　fashion；　and　neither　of　these　two　is　satisfactory；　they



must　move　criss…cross；　for　moving　in　the　way　we　have　said　they



cannot　possibly　experience　either　of　these　untoward　results。　And



this　is　why　horses　and　such…like　animals　stand　still　with　their　legs



put　forward　criss…cross；　not　with　the　right　or　the　left　put　forward



together　at　once。　In　the　same　fashion　animals　with　more　than　four　legs



make　their　movements；　if　you　take　two　consecutive　pairs　of　legs　the



hind　move　criss…cross　with　the　forelegs；　you　can　see　this　if　you　watch



them　moving　slowly。　Even　crabs　move　in　this　way；　and　they　are



polypods。　They；　too；　always　move　criss…cross　in　whichever　direction



they　are　making　progress。　For　in　direction　this　animal　has　a



movement　all　its　own；　it　is　the　only　animal　that　moves　not　forwards；



but　obliquely。　Yet　since　forwards　is　a　distinction　relative　to　the



line　of　vision；　Nature　has　made　its　eyes　able　to　conform　to　its　limbs；



for　its　eyes　can　move　themselves　obliquely；　and　therefore　after　a



fashion　crabs　are　no　exception　but　in　this　sense　move　forwards。



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　　Birds　bend　their　legs　in　the　same　way　as　quadrupeds。　For　their



natural　construction　is　broadly　speaking　nearly　the　same。　That　is；



in　birds　the　wings　are　a　substitute　for　the　forelegs；　and　so　they



are　bent　in　the　same　way　as　the　forelegs　of　a　quadruped；　since　when



they　move　to　progress　the　natural　beginning　of　change　is　from　the



wings　（as　in　quadrupeds　from　the　forelegs）。　Flight　in　fact　is　their



appropriate　movement。　And　so　if　the　wings　be　cut　off　a　bird　can



neither　stand　still　nor　go　forwards。



　　Again；　the　bird　though　a　biped　is　not　erect；　and　has　the　forward



parts　of　the　body　lighter　than　the　hind；　and　so　it　is　necessary　（or　at



least　preferable　for　the　standing　posture）　to　have　the　thigh　so　placed



below　the　body　as　it　actually　is；　I　mean　growing　towards　the　back。



If　then　it　must　have　this　situation　the　flexion　of　the　leg　must　be



backwards；　as　in　the　hind　legs　of　quadrupeds。　The　reasons　are　the　same



as　those　given　in　the　case　of　viviparous　quadrupeds。



　　If　now　we　survey　generally　birds　and　winged　insects；　and　animals



which　swim　in　a　watery　medium；　all　I　mean　that　make　their　progress



in　water　by　dint　of　organs　of　movement；　it　is　not　difficult　to　see



that　it　is　better　to　have　the　attachment　of　the　parts　in　question



oblique　to　the　frame；　exactly　as　in　fact　we　see　it　to　be　both　in　birds



and　insects。　And　this　same　arrangement　obtains　also　among　fishes。



Among　birds　the　wings　are　attached　obliquely；　so　are　the　fins　in　water



animals；　and　the　feather…like　wings　of　insects。　In　this　way　they



divide　the　air　or　water　most　quickly　and　with　most　force　and　so　effect



their　movement。　For　the　hin