Final answer:
The mediastinal surface of each lung faces medially and includes the hilum and, on the left lung, the cardiac notch to accommodate the heart.
Step-by-step explanation:
The portion of each lung directed medially is the mediastinal surface. The mediastinal surface of each lung faces medially and includes the hilum and, on the left lung, the cardiac notch to accommodate the heart. This surface is home to a concave structure known as the hilum, through which blood vessels, lymphatic vessels, nerves, and the bronchus enter the lung.
On the left lung, this mediastinal surface features a cardiac notch, which is a depression that allows space for the heart. The lungs are separated into lobes, with the right lung comprising three lobes and the left lung two lobes. The structural differences in the lungs, including the cardiac notch on the left lung and the positioning of the lobes, accommodate for the heart's location and size.