Left lung

The left lung is divided into two lobes, an upper and a lower, by the oblique fissure, which extends from the costal to the mediastinal surface of the lung both above and below the hilum. The left lung, unlike the right does not have a middle lobe. However the term lingula is used to denote a projection of the upper lobe of the left lung that serves as the homologue. This area of the left lobe - the lingula, means little tongue (in Latin) and is often referred to as the tongue in the lung. There are two bronchopulmonary segments of the lingula: superior and inferior. It is thought that the lingula of the left lung is the remnant of the middle lobe, which has been lost through evolution.

There is a large and deep concavity called the cardiac impression, on the mediastinal surface to accommodate the pericardium. On the same surface, immediately above the hilum, is a well-marked curved furrow produced by the aortic arch, and running upward from this toward the apex is a groove accommodating the left subclavian artery; a slight impression in front of the latter and close to the margin of the lung lodges the left innominate vein.

Behind the hilum and pulmonary ligament is a vertical furrow produced by the descending aorta, and in front of this, near the base of the lung, the lower part of the esophagus causes a shallow impression.