n :  an arterial trunk or either of its two main branches that carry blood to the lungs:  a  :  a large arterial trunk that arises from the conus arteriosus of the right ventricle, ascends in front of the aorta, and branches into the right and left pulmonary arteries - called also pulmonary trunk   b  :  a branch of the pulmonary trunk that passes under the arch of the aorta to the right lung where it divides into branches - called also right pulmonary artery   c  :  a branch of the pulmonary trunk that passes to the left in front of the descending part of the aorta, gives off the ductus arteriosus in the fetus which regresses to the ligamentum arteriosum in the adult, and passes to the left lung where it divides into branches - called also left pulmonary artery  .
 
 
 
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