Further Absorption, Division and Septation:
The sinus venosus valve which guards the opening of the vena cavae into the right ventricle is absorbed. The sinoatrial node, the primary cardiac pacemaker, is a remnant of this structure.
Early on during the looping stage, a portion of the bulbus is merged with the right ventricle to give the right ventricle proper.
Longitudinal division of the bulbus and truncus arteriosus occur somewhat later from the bulbar ridges, yielding the adult aorta and pulmonary artery (Figure 2.05).. This occurs through the joining of spiral ridges (spiral aortic pulmonary septum) on the inside of the common outflow tube. This helical separation causes the aorta and pulmonary artery to be wound around one another in the adult.
The right aortic arch develops into the aorta in mammals, while it is the left aortic arch which does this in birds.
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