Question

The flaplike lateral wall of each atrium is called the

Answer 1

You mean like the tricuspid and mitral (bicuspid) valves?

Answer 2

Question is asking about the flaplike lateral wall of each atrium. Atrium is basically an open roofed entrance hall or central court in an ancient Roman house. The central area in a building is usually open to the sky. The flaplike lateral wall of each atrium is called the auricle.

So the final answer is “Auricle”.