Base of lung

The base of the lung is broad, concave, and rests upon the convex surface of the diaphragm, which separates the right lung from the right lobe of the liver, and the left lung from the left lobe of the liver, the stomach, and the spleen.

Since the diaphragm extends higher on the right than on the left side, the concavity on the base of the right lung is deeper than that on the left.

Laterally and behind, the base is bounded by a thin, sharp margin which projects for some distance into the phrenicocostal sinus of the pleura, between the lower ribs and the costal attachment of the diaphragm.

The base of the lung descends during inspiration and ascends during expiration.