Fig. 2. E18.5 Fgf8^H/– mutants exhibit lethal cardiovascular malformations. (A,E) Frontal and left oblique views of wild-type newborn heart and great vessels: the aorta (ao) arises from the left ventricle (lv) and is located to the right and posterior to the main pulmonary artery (mpa); the left aortic arch (aa) gives rise to the brachiocephalic (b), left common carotid (lcc) and left subclavian (lsc) and the aorta descends on the left (dao). The MPA arises from the right ventricle (rv). The ductus arteriosus (da) is closing (E, arrowhead). (B-D) Persistent Truncus Arteriosus results from failure of outflow tract septation. (B) Frontal view; a single vessel, the truncus (t), originates from the right ventricle (RV). (C) Left lateral view reveals origin of the left branch pulmonary artery (pa) and LCC from the truncal vessel. A right aortic arch was noted (raa). Broken lines have been superimposed to help clarify the anatomy. (D) Viewed from inside the RV, the truncal vessel overrides a large membranous ventricular septal defect (VSD, arrowhead), which is the only path of egress from the LV. The right atrium (ra) has been removed. (F-H) Double outlet right ventricle results from failure of outflow tract rotation and alignment. (F) Frontal view, MPA is anterior and towards the left of the aorta (Ao). (G) Right lateral view after removal of the right atrium and RV-free wall; note origins of Ao and MPA from the RV, there is a subaortic VSD (arrowhead), a right aortic arch and right patent ductus arteriosus (pda). (H) Left lateral view after removal of the LV free wall shows a probe passing from left ventricle through VSD into Ao; an atrial septal defect is visible from the left atrium (la, arrowhead). (I-L) D-Transposition of the great arteries results from failure of outflow tract rotation and alignment. (I) Frontal view; parallel circulation due to aberrant origin of the Ao anteriorly and from the RV and the MPA posteriorly from the LV. (J) Right lateral view shows right aortic arch (arrowhead), right descending aorta (dao) and right atrium (ra). (K) Right oblique view with probe passing from RV into Ao. (L) Left lateral view with probe passing from LV into MPA; there was no VSD. (M-P) Corrosion casts of the embryonic arterial vasculature reveal aortic arch anomalies in Fgf8^H/– mutants. (M) Dorsal view of a control embryo; note continuity between ascending and descending aorta via the left aortic arch (laa), which is derived from the embryonic left fourth aortic arch artery. (N) Right dorsal oblique view of a control embryo; the PDA is visible, as is the LAA. (O) Posterior view of a mutant with interrupted aortic arch, type B; note discontinuity between ascending and descending aortas (red arrowhead) with the carotids arising from the ascending aorta and the left subclavian and descending aorta arising from the patent ductus arteriosus. (P) Dorsal oblique view of a mutant with a right aortic arch. A left-sided PDA and right aortic arch (raa) are shown. Broken lines have been superimposed to clarify the anatomy. This is a vascular ring encompassing the trachea and esophagus, which can cause airway obstruction and swallowing difficulties.