The lung fissures are divisions from the surface to the hila of lung tissue which divide it into lobes. They include the:
- oblique fissures on both sides
- the horizontal fissure on the right
The oblique fissure divides the left lung into superior and inferior lobes. On the right, the oblique fissure demarcates along a similar route, but the presence of the horizontal fissure results in the following arrangement:
- superior lobe rests superior to oblique and horizontal fissures
- middle lobe rests superior to oblique fissure but inferior to horizontal fissures
- lower lobe rests inferior to oblique fissure
In a significant proportion of the population, the fissures are incomplete and the lobes merge. Conversely, a minority display accessory lobes due to the creation of new fissures e.g. the meso-azygous fissure.