Final answer:
The truncus arteriosus, a primitive heart structure, divides to form the pulmonary trunk and aorta in the fully developed heart.
Step-by-step explanation:
The pulmonary trunk and aorta are derived from the truncus arteriosus, one of the five regions of the primitive heart tube.
This structure will eventually divide and give rise to these two important arteries in the fully developed heart. The bulbus cordis is another primitive heart structure that develops into the right ventricle of the heart, which is responsible for pumping deoxygenated blood to the lungs via the pulmonary trunk.