Fig. 10: Pictorial timeline of the formation of the subpulmonary infundibulum.

Panels a–d show cranial views of the lumens of the left and right ventricles, the muscular ventricular septum, the lumen of the outflow tract with ridges and neural crest, and the arterial trunks, while panels e–h show left lateral views of the same structures. On completion of the fusion of the proximal outflow tract ridges at CS18, the neural crest cells largely disappear and myocardialization begins (Fig. 7h–n). Myocardialization proceeds from proximal to distal, opposite to the direction of septation, reaching the arterial valves at CS23. The myocardial septum, which then separates the subpulmonary and subaortic channels, also known as the embryonic outlet septum, is located on the right side of the muscular ventricular septum and is topographically part of the right ventricle. This right-sided position accounts for subsequent development into the free-standing muscular infundibulum. At CS23, the base of the subaortic channels is on the left side of the muscular ventricular septum, but the aortic root has not yet been incorporated in to the base of the left ventricle. All images are also available as preset views in the corresponding 3D-PDFs.