The two lungs are not symmetrical. The right lung has three lobes, and the slightly smaller left lung has only two.
In the right lung, the superior lobe and the middle lobe are separated by a depression called the horizontal fissure. Inferiorly, an oblique fissure separates the middle lobe and inferior lobe.
In the left lung, the fissure that separates the superior lobe and inferior lobe is also called the oblique fissure.
