▁tib ia ▁b ones ▁of ▁the ▁leg ▁were ▁indeed ▁larger ▁than ▁the ▁hum er us ▁b one ▁of ▁the ▁arm , ▁unlike ▁Gal en ' s ▁original ▁find ings . ▁ ▁Mus cular ▁system ▁▁▁ ▁V es al ius ' ▁most ▁impress ive ▁contribution ▁to ▁the ▁study ▁of ▁the ▁mus cular ▁system ▁may ▁be ▁the ▁illustr ations ▁that ▁accomp any ▁the ▁text ▁in ▁De ▁fab rica , ▁which ▁would ▁become ▁known ▁as ▁the ▁" mus cle ▁men ". ▁ ▁He ▁describes ▁the ▁source ▁and ▁position ▁of ▁each ▁mus cle ▁of ▁the ▁body ▁and ▁provides ▁information ▁on ▁their ▁respective ▁operation . ▁ ▁V asc ular ▁and ▁circul atory ▁systems ▁▁▁ ▁V es al ius ' ▁work ▁on ▁the ▁v asc ular ▁and ▁circul atory ▁systems ▁was ▁his ▁greatest ▁contribution ▁to ▁modern ▁medicine . ▁In ▁his ▁dis sections ▁of ▁the ▁heart , ▁V es al ius ▁became ▁convinced ▁that ▁Gal en ' s ▁claims ▁of ▁a ▁por ous ▁Inter vent ric ular ▁sept um ▁were ▁false . ▁This ▁fact ▁was ▁previously ▁described ▁by ▁Michael ▁Ser vet us , ▁a ▁fellow ▁of ▁V es al ius , ▁but ▁never ▁reached ▁the ▁public , ▁for ▁it ▁was ▁written ▁down ▁in ▁the ▁" Man us cript ▁of ▁Paris ", ▁in ▁ 1 5 4 6 , ▁and ▁published ▁later ▁in ▁his ▁Christian ism i ▁Rest itut io ▁( 1 5 5 3 ), ▁a ▁book ▁regarded ▁as ▁her et ical ▁by ▁the ▁In quisition . ▁Only ▁three ▁copies ▁surv ived , ▁but ▁these ▁remained ▁hidden ▁for ▁dec ades