Fig. 5. Pharyngeal arch artery defects in Fgf8 domain-specific mutants at E10.5. Stage-matched embryos are shown photographed at the same magnification. (A,B) Ventrolateral views of the right (A) and left (B) sides of an ink injected E10.5 control embryo. Remodeling toward a left dominant system is already evident. Pharyngeal arch arteries (PAAs) are numbered, the dorsal aorta and aortic sac are labeled (DoA, AS respectively). (C,D) An Fgf8/AP2-IRESCre mutant with bilateral aplasia of the fourth and sixth PAAs. The third PAA is abnormally enlarged and provides blood flow from the heart to the DoA (see also Fig. 7, rows K, L). There are sprouts from the DoA visible on the left side (red arrowheads). (E-H) Fgf8/AP2-IRESCre mutants with bilateral hypoplasia of the entire PAA system (E,F), or aplasia of the fourth PAAs (G,H); the red arrowhead highlights a sprout from the AS on the left side.