1. Ventral View of Developing Heart – Day 40
UNSW Embryology

2. Ventral View of Developing Heart – Day 40
Opening of Sinus Venosus
Primordial Left Atrium
Primordial Right Atrium
Fused Dorsal and Ventral Endocardial Cushions
Primordial Left Ventricle
Primordial Right Ventricle

4. Growth of the Septum Primum

5. Growth of the Septum Primum
Foramen Primum

6. Growth of the Septum Primum
Myocardium differentiated from splanchnic mesenchyme near the venous pole
Foramen Primum

7. Growth of the Septum Primum
Foramen Primum

8. Growth of the Septum Primum
Originates from left sided mesenchyme from the original cardiogenic fields
Foramen Primum

10. Perforation of the Septum Primum

11. Perforation of the Septum Primum
Growth of the Ventricular Septum

12. Perforation of the Septum Primum Growth of the Ventricular Septum
Valve of the Sinus Venosus
Openings of the pulmonary veins
Ventricular Septum

13. Growth of the Ventricular Septum
Early studies believed that the ventricular septum formed from coalescence of trabeculae of the primordial ventricle
Ventricular Septum

14. Growth of the Ventricular Septum

15. Growth of the Ventricular Septum
Later studies have suggested that the muscular septum originates from fusion of the external R and L ventricular walls as the ventricles grow
Ventricular Septum

17. Growth of the Septum Secundum

18. Growth of the Septum Secundum
Ventricular Trabeculation

19. Growth of the Septum Secundum Ventricular Trabeculation
Foramen Ovale
Foramen Secundum

20. Growth of the Septum Secundum
Forms as a superior interarterial fold

21. Growth of the Septum Secundum

22. Growth of the Septum Secundum
Also originates from left sided mesenchyme from the original cardiogenic fields

23. Ventricular Trabeculation

24. Ventricular Trabeculation
Trabeculae