What is the duplicate of the pleura called?

The correct answer is the pulmonary ligament. The pleura is a double-layered membrane surrounding the lungs, consisting of the visceral pleura (which is in contact with the lungs) and the parietal pleura (which lines the thoracic cavity). The pulmonary ligament is a reflection of the pleura, extending from the hilum of the lung to the diaphragm and providing support for the lung structures.

This connective tissue structure is crucial in maintaining the position of the lungs within the thoracic cavity and provides a pathway for blood vessels, nerves, and lymphatics to reach the lung tissue. It effectively represents the continuity of the pleural layers and is anatomically significant in various respiratory and surgical procedures.

Other options, while they represent significant structures within the thoracic cavity, do not specifically refer to the duplicate layer of the pleura. The pericardium, for example, is the membrane surrounding the heart, the thoracic diaphragm separates the thoracic and abdominal cavities, and the visceral layer refers strictly to the pleura in contact with the lung surface, without the context of its reflection or ligamentous form.