Figure 3. Episcopic images showing the rotation of the boundary of the distal OFT with the pharyngeal mesenchyme.

A) Shows the aortic sac with cranial and caudal components at early E11.5, which give rise symmetrically to the fourth and sixth arch arteries, respectively. The asterisk shows the intermediate part of the sac, with the dorsal wall separating the systemic and pulmonary parts of the sac. B) Is from a CS14 human embryo showing a comparable arrangement. C,D) Show views of a mid E11.5 OFT cut transversely through the closing AP foramen (arrow in D), close to the aortic sac, as shown in the inset in C. The oblique orientation of the protruding dorsal wall of the aortic sac is shown as the dashed line in D. E) Is an over view of an E11.5 heart, showing the orientation of section of A and F. F) Is a view made by removing the parietal wall of the aorta, as in Fig 2F, just prior to closure of the AP foramen. The dotted line shows the border between the intra- and extrapericardial aortic components. The upper double headed arrow shows the walls distal to the foramen, derived from the protrusion, while the lower double headed arrow shows the adjacent wall of the aorta proximal to the foramen, derived from the fused distal cushions.