Fig. 5
From: CT imaging features of atrioventricular shunts: what the radiologist must know
At the end of the fourth week the unseptated primitive ventricle (V) is connected on one side with the primitive atrium (which is not shown and lying directly behind of the primitive ventricle on this drawing), through the atrioventricular (AV) canals. On the other side it is connected with the bulbus cordis (B). The bulbus cordis consists of the conus cordis and the truncus cordis and will give rise to the future aorta and truncus pulmonalis. In the fifth week the left and right part of the primitive ventricle start to grow, creating a median muscular ridge (interventricular septum, IVS). Initially, this ridge mainly results from the joining of the growing ventricles on each side. In a second stage, cell growth from the ventricular septum itself contributes to the size. The primitive interventricular septum grows up to the endocardial cushions, creating two chambers. However, it will stop growing before it reaches the endocardial cushions, leaving an opening that allows interventricular communication, called the interventricular foramen