Fig. 7. Ventricular septal defects in Bmp4^lacZ/+ and Bmp4^lacZ/S2G mutants. Hematoxylin and Eosin-stained coronal sections of an E16.5 Bmp4^S2G/S2G embryo (A,D,G), an E17.5 Bmp4^lacZ/+ embryo (B,E,H) and an E16.5 Bmp4^lacZ/S2G embryo (C,F,I). (A-C) Anterior sections at the level of the pulmonary trunk (PT) and aorta (Ao) show normal outflow tract septation. (D-F) Sections through the muscular (^*) and membranous (Mb) portion of the ventricular septum. Arrows indicate an aberrant opening where the membranous portion of the septum has not formed. (G-I) Sections through the atrioventricular valves (arrowheads) and atrial septa (arrows) showing normal development of these structures. LA, left atrium; Lu, lung; LV, left ventricle; RA, right atrium RV, right ventricle.