Theabovequotationssumupprettywellthestatementsofallpreviouswriters。Furthermore，therearesomewritersonNaturalHistorywhohavenotventuredtolaydownthelawinsuchprecisetermsasregardstheveins，butwhoallalikeagreeinassigningtheheadandthebrainasthestarting-pointoftheveins。Andinthisopiniontheyaremistaken。
Theinvestigationofsuchasubject，ashasbeenremarked，isonefraughtwithdifficulties；but，ifanyonebekeenlyinterestedinthematter，hisbestplanwillbetoallowhisanimalstostarvetoemaciation，thentostranglethemonasudden，andthereupontoprosecutehisinvestigations。
Wenowproceedtogiveparticularsregardingthepropertiesandfunctionsoftheveins。Therearetwoblood-vesselsinthethoraxbythebackbone，andlyingtoitsinnerside；andofthesetwothelargeroneissituatedtothefront，andthelesseroneistotherearofit；
andthelargerissituatedrathertotherighthandsideofthebody，andthelesseronetotheleft；andbysomethisveinistermedthe\'aorta\'，fromthefactthatevenindeadbodiespartofitisobservedtobefullofair。Theseblood-vesselshavetheiroriginsintheheart，fortheytraversetheotherviscera，inwhateverdirectiontheyhappentorun，withoutinanywaylosingtheirdistinctivecharacteristicasblood-vessels，whereastheheartisasitwereapartofthemandthattoomoreinrespecttothefrontwardandlargeroneofthetwo，owingtothefactthatthesetwoveinsareaboveandbelow，withtheheartlyingmidway。
Theheartinallanimalshascavitiesinsideit。Inthecaseofthesmalleranimalseventhelargestofthechambersisscarcelydiscernible；thesecondlargerisscarcelydiscernibleinanimalsofmediumsize；butinthelargestanimalsallthreechambersaredistinctlyseen。Intheheartthenwithitspointedenddirectedfrontwards，ashasbeenobservedthelargestofthethreechambersisontheright-handsideandhighestup；theleastoneisontheleft-handside；andthemedium-sizedoneliesinbetwixttheothertwo；andthelargestoneofthethreechambersisagreatdeallargerthaneitherofthetwoothers。Allthree，however，areconnectedwithpassagesleadinginthedirectionofthelung，butallthesecommunicationsareindistinctlydiscerniblebyreasonoftheirminuteness，exceptone。