The pleural cavity is a closed space (like the inside of a balloon) within which the lung has grown. As the lung grows into the space, it picks up a layer of pleura (outside of balloon) and this is called the visceral pleura. The remainder of the pleura is called the parietal pleura. Pleura is a membrane that is single celled. Normally it produces a small amount of fluid that fills the gap between the parietal and visceral layers of pleura.
Subdivisions of the Thoracic Cavity
In preparation for studying the internal organs of the thoracic cavity, we will subdivide it artificially into several parts. It is thought that doing this will aid memorizing what is located in each subdivision. First, when looking at a cross section, we can subdivide the cavity into left and right pleural cavities and an intermediate area called the mediastinum.