The influence of expansion of the atrioventricular canal (yellow) on the disposition of the primary ring (red). Square—inferior transition; circle—superior transition; and triangle—transition to dead-end tract. At Carnegie stages 13 and 14, the plane of the orifice of the primary ring is itself at right angles to the plane of the atrioventricular junction (left column). With rightward expansion of the atrioventricular canal, the primary ring itself bends at a right angle, with the dorsal part then encircling the newly formed right atrioventricular junction as part of the right atrioventricular canal. The right column has been reorientated to show the view of the atrioventricular junctions as seen from the right side with the ventricular apex pointing to the left. The dorsal part retains its position on the muscular ventricular septum, while the cranial part expands leftward to encircle the outflow tract of the left ventricle (aortic ring).