Which structure lines the thoracic walls and diaphragm?

The parietal pleura is the correct answer because it is the membrane that lines the thoracic cavity and covers the diaphragm. This serous membrane is essential for providing a smooth surface that facilitates the expansion and contraction of the lungs during respiration. It helps to reduce friction and creates a pressure differential necessary for optimal lung function.

The visceral pleura, on the other hand, directly covers the lungs themselves and does not line the thoracic walls or diaphragm, which clearly differentiates it from the parietal pleura. The pericardium is a separate structure that encases the heart and is not involved with the thoracic walls. The endothoracic fascia is a connective tissue layer that provides support and anchors chest structures but does not serve the same role as the parietal pleura in lining the thoracic cavity.

Thus, the parietal pleura is crucial for its anatomical positioning and functional role within the thoracic cavity.