 The 5th pair of vessels only form in some cases without any known contribution to the final structure of the great arteries.The right 6th almost completely regresses with only the proximal part contributing to the base of the pulmonary arteries, while the left 6th forms the ductus arteriosus, which disappears after birth.Abnormalities in the development of the great arteries during embryonic development may lead to congenital cardiovascular defects, such as