Each lung is divided into sections called lobes that are separated from each other by various fissures.

Right lung

The right lung is divided into three lobes (superior, middle and inferior) by the two following fissures:

Right oblique fissure (also called the major or great fissure) - the superior fissure of the right lung that separates the inferior lobe from the middle and superior lobes. This fissure begins at the level of the spinous process of the fourth thoracic vertebra (T4), goes obliquely forward and downward along the costal surface and then crosses the fifth intercostal space and further follows the contour of the sixth rib to reach the sixth costochondral joint;
Horizontal fissure (minor fissure) - a short fissure that separates the superior and middle lobes. It arises from the right oblique fissure at the midaxillary line. The horizontal fissure goes along the fourth rib and fourth intercostal space forward and downward to reach the anterior border of the right lung.

Left lung

In contrast to the right lung, the left lung has two lobes and one fissure. It is divided into the superior and inferior lobes by an oblique fissure called the left oblique fissure, which appears more vertical than the right oblique fissure.

The left oblique fissure arises between the spinous processes of the third and fourth thoracic vertebrae (T3, T4) or from the spinous process of the third thoracic vertebra (T3). Like the right oblique fissure, the left oblique fissure also crosses the fifth intercostal space and follows the contour of the sixth rib to reach the inferior border of the left lung and sixth costochondral joint.

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Lobes and fissures