▁occur , ▁this ▁can ▁result ▁in ▁co arct ation ▁of ▁the ▁a ort a . ▁The ▁du ct us ▁ar ter ios us ▁connect s ▁to ▁the ▁final ▁section ▁of ▁the ▁arch ▁in ▁fo etal ▁life ▁and ▁the ▁lig ament um ▁ar ter ios um ▁when ▁the ▁du ct us ▁ar ter ios us ▁re gress es . ▁ ▁Vari ation ▁There ▁are ▁three ▁common ▁variations ▁in ▁how ▁ar ter ies ▁branch ▁from ▁the ▁a ort ic ▁arch . ▁In ▁about ▁ 7 5 % ▁of ▁individuals , ▁the ▁branch ing ▁is ▁" normal ", ▁as ▁described ▁above . ▁In ▁some ▁individuals ▁the ▁left ▁common ▁car ot id ▁ar tery ▁origin ates ▁from ▁the ▁bra chio ce phal ic ▁ar tery ▁rather ▁than ▁the ▁a ort ic ▁arch . ▁In ▁others , ▁the ▁bra chio ce phal ic ▁ar tery ▁and ▁left ▁common ▁car ot id ▁ar tery ▁share ▁an ▁origin . ▁This ▁variant ▁is ▁found ▁in ▁approximately ▁a ▁ 2 0 % ▁of ▁the ▁population . ▁In ▁a ▁third ▁variant , ▁the ▁bra chio ce phal ic ▁ar tery ▁spl its ▁into ▁three ▁ar ter ies : ▁the ▁left ▁common ▁car ot id ▁ar tery , ▁the ▁right ▁common ▁car ot id ▁ar tery ▁and ▁the ▁right ▁sub c lav ian ▁ar tery ; ▁this ▁variant ▁is ▁found ▁in ▁an ▁estimated ▁ 7 % ▁of ▁individuals . ▁ ▁C lin ical ▁significance ▁The ▁a ort ic ▁kn ob ▁is ▁the ▁prominent ▁shadow ▁of ▁the ▁a ort ic ▁arch ▁on ▁a ▁front al