The human left lung is divided into two lobes, an upper and a lower, by the oblique fissure

Oblique fissure

In the lung, the oblique fissure separates the inferior lobe of either lung from the remainder of the lung. The oblique fissure extends from the spinous process of T2...

, which extends from the costal

Rib

In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...

 to the mediastinal surface of the lung both above and below the hilum

Hilum of lung

Above and behind the cardiac impression is a triangular depression named the hilum, where the structures which form the root of the lung enter and leave the viscus. These include the pulmonary artery, superiormost on the left lung, the superior and inferior pulmonary veins, lymphatic vessels and...

.

As seen on the surface, this fissure begins on the mediastinal surface of the lung at the upper and posterior part of the hilum, and runs backward and upward to the posterior border, which it crosses at a point about 6 cm. below the apex.

It then extends downward and forward over the costal surface, and reaches the lower border a little behind its anterior extremity, and its further course can be followed upward and backward across the mediastinal surface as far as the lower part of the hilum.

Impressions

On the mediastinal surface, immediately above the hilum, is a well-marked curved furrow produced by the aortic arch

Aortic arch

The arch of the aorta or the transverse aortic arch is the part of the aorta that begins at the level of the upper border of the second sternocostal articulation of the right side, and runs at first upward, backward, and to the left in front of the trachea; it is then directed backward on the left...

, 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

Descending aorta

The descending aorta is part of the aorta, the largest artery in the body. The descending aorta is the part of the aorta beginning at the aortic arch that runs down through the chest and abdomen. The descending aorta is divided into two portions, the thoracic and abdominal, in correspondence with...

, and in front of this, near the base of the lung, the lower part of the esophagus

Esophagus

The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...

causes a shallow impression.

External links

- "Mediastinal surface of the left lung."

• Diagram and quiz at cancer.gov
• Slide at mgccc.cc.ms.us - "lobes (left lung)"
• Diagram at md.chula.ac.th