(named after the 16th-century Italian physician L. Botallo), or arterial duct, the upper division of the sixth arterial arch, which joins the pulmonary artery with the dorsal aorta in the embryos of terrestrial vertebrates.
The ductus botalli receives most of the blood from the right ventricle of the heart (or from the right side of the single ventricle) and carries it into the aorta, missing the as yet nonfunctioning blood-circulation cycle. In the majority of animals, the ductus botalli stops functioning after birth, grows over, and becomes a ligament; only in caudates and apodal amphibians, the tuatara, alligator, and certain tortoises is the ductus botalli preserved in the adult.
In man, the ductus botalli is a blood vessel that joins the pulmonary artery and the aorta in the fetus. With the initiation of pulmonary respiration (at birth), it empties and becomes a connective-tissue cord (ligament). In rare cases, when the ductus botalli remains open, a surgical operation is necessary because of severe disruption of blood circulation.