Figure 4  .

(A) The membranous septum is revealed by transillumination in this view of the right atrium and right ventricle. The hingeline of the tricuspid valve divides the membranous septum into atrioventricular (AV) and interventricular (IV) components. (B)This four chamber section shows the more apical attachment of the tricuspid valve compared to the mitral valve resulting in an offset arrangement (arrows). The cardiac septum is profiled showing the thin valve of the oval fossa. Superiorly, the rim is an infolding of the atrial wall (arrow). (C) A cut taken slightly more cephalad passes through the aortic root producing the so-called five chambers section that shows the aortic valve wedged between the atrioventricular valves. Note the thin membranous septum (small arrow) and the moderator band (thick yellow arrow).