At the midclavicular line, the inferior extent of the lung corresponds to which rib level?

• A. Fifth
• B. Sixth
• C. Seventh
• D. Eighth

Answer: (B)

The key idea is how far the lung extends downward along the chest wall at a given vertical line. The lung base rests on the diaphragm, and along the midclavicular line its lower edge reaches the level of the sixth rib. This is the standard anterior reference point for the lung’s inferior border in quiet anatomy, because the diaphragm meets the chest wall around that height before you move laterally. By contrast, the same diaphragmatic boundary shifts as you move away from the midclavicular line—toward the midaxillary line it lies lower (about the eighth rib), and posteriorly even further down—reflecting the curved shape of the diaphragmatic dome. So at the midclavicular line, the inferior extent of the lung corresponds to the sixth rib.