on the gait of animals-第4节

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the　chafer；　and　to　unsharded；　like　bees　and　wasps。　Further；　birds　that



are　not　made　for　flight　have　a　tail　that　is　of　no　use；　for　instance



the　purple　coot　and　the　heron　and　all　water…fowl。　These　fly　stretching



out　their　feet　as　a　substitute　for　a　tail；　and　use　their　legs



instead　of　a　tail　to　direct　their　flight。　The　flight　of　insects　is



slow　and　frail　because　the　character　of　their　feathery　wings　is　not



proportionate　to　the　bulk　of　their　body；　this　is　heavy；　their　wings



small　and　frail；　and　so　the　flight　they　use　is　like　a　cargo　boat



attempting　to　make　its　voyage　with　oars；　now　the　frailty　both　of　the



actual　wings　and　of　the　outgrowths　upon　them　contributes　in　a



measure　to　the　flight　described。　Among　birds；　the　peacock's　tail　is　at



one　time　useless　because　of　its　size；　at　another　because　it　is　shed。



But　birds　are　in　general　at　the　opposite　pole　to　flying　insects　as



regards　their　feathers；　but　especially　the　swiftest　flyers　among　them。



（These　are　the　birds　with　curved　talons；　for　swiftness　of　wing　is



useful　to　their　mode　of　life。）　The　rest　of　their　bodily　structure　is



in　harmony　with　their　peculiar　movement；　the　small　head；　the　slight



neck；　the　strong　and　acute　breastbone　（acute　like　the　prow　of　a



clipper…built　vessel；　so　as　to　be　well…girt；　and　strong　by　dint　of　its



mass　of　flesh）；　in　order　to　be　able　to　push　away　the　air　that　beats



against　it；　and　that　easily　and　without　exhaustion。　The　hind…quarters；



too；　are　light　and　taper　again；　in　order　to　conform　to　the　movement　of



the　front　and　not　by　their　breadth　to　suck　the　air。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　11







　　So　much　then　for　these　questions。　But　why　an　animal　that　is　to　stand



erect　must　necessarily　be　not　only　a　biped；　but　must　also　have　the



superior　parts　of　the　body　lighter；　and　those　that　lie　under　these



heavier；　is　plain。　Only　if　situated　like　this　could　it　possibly



carry　itself　easily。　And　so　man；　the　only　erect　animal；　has　legs



longer　and　stouter　relatively　to　the　upper　parts　of　his　body　than



any　other　animal　with　legs。　What　we　observe　in　children　also　is



evidence　of　this。　Children　cannot　walk　erect　because　they　are　always



dwarf…like；　the　upper　parts　of　their　bodies　being　longer　and　stouter



than　the　lower。　With　advancing　years　the　lower　increase



disproportionately；　until　the　children　get　their　appropriate　size；　and



then　and　not　till　then　they　succeed　in　walking　erect。　Birds　are



hunchbacked　yet　stand　on　two　legs　because　their　weight　is　set　back；



after　the　principle　of　horses　fashioned　in　bronze　with　their



forelegs　prancing。　But　their　being　bipeds　and　able　to　stand　is　above



all　due　to　their　having　the　hip…bone　shaped　like　a　thigh；　and　so　large



that　it　looks　as　if　they　had　two　thighs；　one　in　the　leg　before　the



knee…joint；　the　other　joining　his　part　to　the　fundament。　Really　this



is　not　a　thigh　but　a　hip；　and　if　it　were　not　so　large　the　bird　could



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　forw