Figure 3.

Early and late E12.5 hearts, with midseptal plane indicated. At the earlier stage, separation of aortic and pulmonary roots only extends through the distal outflow tract. Within the medial portion, the primordia of the aortic and pulmonary valves lie on a common transverse plane (pink) through the outflow. By late E12.5, separation of the aortic and pulmonary roots extends through this region. The two vessels adopt divergent orientations, as revealed by the symmetrical arrangement of their valve planes (yellow and mauve, respectively).