The pulmonary artery passes craniodorsad and slightly to the left from
the cranial end of the conus arteriosus. One to one and a half
centimeters from the conus it divides into right and left branches (Fig.
116, _j_). Just before the division the dorsal surface of the pulmonary
artery is connected by the short =ligamentum arteriosum=, or ligamentum
Botalli, with the aorta. This is the remnant of a canal which in fœtal
life forms a free communication between the pulmonary artery and the
aorta; this canal is known as the =ductus Botalli=. The ligament is
almost or quite obliterated in the adult cat.
The left branch of the pulmonary artery passes to the left lung,
crossing ventrad of the thoracic aorta. It then divides into branches
which pass to the lobes of the left lung. The point of division of the
left branch of the pulmonary artery lies craniad of all the lobes of the
lung, so that the lobes of the left lung are said to be all
=hyparterial=, i.e., below (or caudad of) the artery.
The right branch passes under (dorsocaudad of) the aortic arch, and
reaches the right lung at about the junction of the cranial lobe with
the remainder of the lung. The cranial lobe of the right lung is
therefore said to be =eparterial=, since it is craniad of the pulmonary
artery; the other lobes are hyparterial. The right branch divides at its
entrance to the lung and is distributed to its lobes.