Section image of stage 9, cranial view. Looping of the heart tube is evident; apart from that no major developments can be seen at this stage. Section image of stage 11, cranial view. Trabeculation of the ventricle, separation of the common atrium and development of the AV-cushions have all started at this stage. Section image of stage 14, cranial view. The four distal cushions are clearly visible, as are the developing AV-cushions. Section image of stage 14 (same embryo as previous figure, plane of section more caudad), cranial view. Here the proximal cushions in the outflow tract are visible along with the distal cushions. Section image of stage 14-15, cranial view. At this plane of section the veins entering the (by now separated) atria can be clearly seen. Section image of stage 14-15 (same embryo as previous figure, plane of section more caudad), cranial view. The AV-canal has developed at this stage. Section image of stage 14-15 (same embryo as previous two figures, plane of section more caudad), cranial view. In this figure the proximal cushions can be seen to touch the distal cushions in the outflow tract. Section image of stage 15, cranial view. In the interatrial septum, small foramina are still present. On the right an incomplete septum, possibly the venous valve of the superior cardinal vein, is visible. Section image of stage 15 (same embryo as previous figure, plane of section more caudad), cranial view. The ventricle is heavily trabeculated and the AV-cushions are by now highly developed. Section image of stage 15 (same embryo as previous figure, plane of section more caudad), cranial view. In the ventricle the cavum arteriosum and the cavum venosum can be distinguished.