The pleura surround the root of the lung quite similar to the cuff (sleeve) of the coat around the wrist. It goes down as a fold termed pulmonary ligament. The pulmonary ligament stretches from the root of the lung as far down as the diaphragm between the lung and the mediastinum. The fold is full of loose areolar tissue and include few lymphatics.
The functionality of pulmonary ligaments are as follows:.
A. It gives a dead space into which the pulmonary veins can enlarge during increased venous return as during exercise.
B. It enables the descent of the root of the lung with all the descent of diaphragm during motivation. Consequently, the apex of lung comes down from the rough suprapleural membrane making an empty space below the membrane. Now the apex of lung can enlarge into this empty space.