During atrial septation, perforations in the septum primum result in which structure?

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During atrial septation, the septum primum grows toward the endocardial cushions and leaves an opening called the ostium primum. As it fuses, small perforations appear in the septum primum and then coalesce to form a midline opening known as the ostium secundum, or foramen secundum. This is the fetal interatrial passage that allows blood to flow from the right atrium to the left. The septum secundum later forms to the right of the primum, creating the foramen ovale with the primum acting as a flap over it. So perforations in the septum primum give rise to the foramen secundum.