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| Septum secundum | |
|---|---|
 A labelled diagram of the developing heart, showing the relationship between the septum secundum (by the right atrium) and the septum primum (by the left atrium). | |
 Same heart as above, opened on right side. (Septum secundum visible in dark area at center top.) | |
| Details | |
| Carnegie stage | 14 |
| Days | 33 |
| Gives rise to | Atrial septum |
| Identifiers | |
| Latin | septum secundum |
| Anatomical terminology | |
The septum secundum is a muscular flap that is important in heart development. It is semilunar in shape, and grows downward from the upper wall of the atrium immediately to the right of the septum primum and ostium secundum. It is important in the closure of the foramen ovale after birth.