Figure 18.

The images show an aortopulmonary window (panel A), with origin of the right pulmonary artery on the aortic side of the window (panel B). This is well explained by inadequate growth of the aortopulmonary septum from the dorsal wall of the aortic sac (see Figure 4A), leaving a fold between the walls of the aorta and the pulmonary trunk at the margins of the pericardial cavity (star in panel C). Note the separate formation of the aortic and pulmonary roots, implying normal septation and separation of the intermediate and proximal components of the developing outflow tract.