The horizontal fissure of the right lung lies at approximately which rib level?

• A. Third
• B. Fourth
• C. Fifth
• D. Sixth

Answer: (B)

The rhythm of lung fissures marks the lobes that each side contains. The right lung has two fissures: a horizontal fissure that separates the upper and middle lobes and an oblique fissure that separates the middle and lower lobes. The horizontal fissure runs along the anterior chest wall at about the level of the fourth rib (near the 4th costal cartilage by the sternum) and then arches laterally toward the midaxillary line to meet the oblique fissure around the level of the 5th rib. Because of this anterior positioning, the fissure is typically described as lying at the level of the fourth rib. This landmark helps explain why the right lung’s upper lobe ends around the 4th rib anteriorly, with the middle lobe beginning just below that level.