Interventricular septum

The ventricular septum is directed obliquely backward and to the right, and is curved with the convexity toward the right ventricle: its margins correspond with the anterior and posterior longitudinal sulci.

The greater portion of it is thick and muscular and constitutes the muscular ventricular septum, but its upper and posterior part, which separates the aortic vestibule from the lower part of the right atrium and upper part of the right ventricle, is thin and fibrous, and is termed the membranous ventricular septum. An abnormal communication may exist between the ventricles at this part owing to defective development of the membranous septum.