The right lung is divided into three lobes by two fissures:

The right oblique fissure (also the major fissure or great fissure) is the fissure that divides the inferior lobe from the middle lobe and also from the superior lobe. This fissure begins at the level of the spine of the fourth thoracic vertebra (T4), crosses the fifth intercostal space, and then follows the contour of the sixth rib to the sixth costochondral junction.
The horizontal fissure (also the minor fissure) is a short fissure that divides the superior and middle lobes. The horizontal fissure arises from the right oblique fissure close to the midaxillary line and follows the level of the sternal end of the fourth costal cartilage. Further, it passes posteriorly to the hilum on the mediastinal surface of the right lung.

The left lung is divided into two lobes by an oblique fissure - the left oblique fissure, which is more vertical than the right oblique fissure. This fissure arises from the medial surface of the hilum, ascends obliquely backward, crossing the posterior border of the left lung. Further, the fissure passes anteriorly downwards across the costal surface and, finally, ascends on the medial surface to the hilum.

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Lung fissures