 The root of the lung is connected by the structures that form it to the heart and the trachea.The rib cage is separated from the lung by a two-layered membranous coating, the pleura.The hilum is the large triangular depression where the connection between the parietal pleura (covering the rib cage) and the visceral pleura (covering the lung) is made, and this marks the meeting point between the mediastinum and the pleural cavities.