Where is the crista terminalis located?

• A. On the open flap of the right atrium
• B. On the left atrial wall
• C. In the right ventricle near the outflow tract
• D. In the interventricular septum

Answer: (A)

The crista terminalis is a muscular ridge located on the interior surface of the right atrium. It runs from the region near the superior vena cava ostium down to the inferior vena cava, dividing the smooth posterior wall (sinus venarum) from the rough anterior wall that contains the pectinate muscles. This location within the right atrial wall makes it a key landmark inside the chamber, and the SA node sits near its upper end.

So, the best answer places it on the inner surface of the right atrium, not in the left atrium, not in the right ventricle, and not in the interventricular septum. The other options describe structures in the wrong chambers or locations.