um . ▁Next , ▁the ▁left ▁common ▁car ot id ▁ar tery ▁origin ates ▁from ▁the ▁a ort ic ▁arch ▁to ▁the ▁left ▁of ▁the ▁bra chio ce phal ic ▁tr unk , ▁then ▁asc ends ▁along ▁the ▁left ▁side ▁of ▁the ▁tra che a ▁and ▁through ▁the ▁superior ▁medi ast in um . ▁Finally , ▁the ▁left ▁sub c lav ian ▁ar tery ▁comes ▁off ▁of ▁the ▁a ort ic ▁arch ▁to ▁the ▁left ▁of ▁the ▁left ▁common ▁car ot id ▁ar tery ▁and ▁asc ends , ▁with ▁the ▁left ▁common ▁car ot id , ▁through ▁the ▁superior ▁medi ast in um ▁and ▁along ▁the ▁left ▁side ▁of ▁the ▁tra che a . ▁An ▁an atom ical ▁variation ▁is ▁that ▁the ▁left ▁verte br al ▁ar tery ▁can ▁arise ▁from ▁the ▁a ort ic ▁arch ▁instead ▁of ▁the ▁left ▁sub c lav ian ▁ar tery . ▁ ▁The ▁arch ▁of ▁the ▁a ort a ▁forms ▁two ▁curv atures : ▁one ▁with ▁its ▁convex ity ▁up ward , ▁the ▁other ▁with ▁its ▁convex ity ▁forward ▁and ▁to ▁the ▁left . ▁Its ▁upper ▁border ▁is ▁usually ▁about ▁ 2 . 5   cm . ▁below ▁the ▁superior ▁border ▁to ▁the ▁man ub rium ▁stern i . ▁Blood ▁flows ▁from ▁the ▁upper ▁curv ature ▁to ▁the ▁upper ▁regions ▁of ▁the ▁body , ▁located ▁above ▁the ▁heart ▁- ▁namely ▁the ▁arms , ▁neck , ▁and ▁head . ▁ ▁Com ing ▁out ▁of ▁the ▁heart , ▁the ▁thor ac ic ▁a ort a ▁has ▁a ▁maximum ▁diameter