Crista terminalis is a ridge located between the sinus venarum and which part of the right atrium?

• A. Fossa ovalis
• B. Pectinate muscle
• C. Crista terminalis
• D. Sinoatrial node

Answer: (C)

This question tests understanding of the boundary inside the right atrium between its smooth and rough parts. The crista terminalis is the prominent ridge that separates the smooth posterior wall, known as the sinus venarum (derived from the sinus venosus), from the rough anterior wall that is lined with pectinate muscles. So the ridge lies at the junction with the pectinate-muscle region of the right atrium. That’s why the correct description is the pectinate muscle area. The fossa ovalis is in the interatrial septum, not at this boundary, and while the sinoatrial node is near this region, the crista terminalis itself marks the division between sinus venarum and the pectinate muscle–bearing wall.