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Congenital Heart Disease 143

Majority of the ventricular septal defects are located
in the membranous part of the septum because of its
complex origin from three sources as mentioned above.
6. What do you know about the formation of the atrial
septum?
As the endocardial cushions develop, there is a
developing septum from the dorsocranial atrial wall that
grows toward the cushions (Fig. 2). This is the septum
primum, and the intervening space is called the foramen
primum.

Fig. 2: Development of the atrial septum