Explanation:
The inter-atrial septum in the human heart can be best described as a thin muscular wall.The interatrial septum is the wall of tissue that separates the right and left atria of the heart. On cross-sectional echocardiography the normal interatrial septum is recorded as a thin wall of echoes behind the aorta and separating the right and left atria.Hence, the correct option is (A).