*The Pleural Cavity is filled with a small amount of fluid which forms a thin film of liquid between the pleural layers. This is vital in that in prevents separation of the two pleural layers and lubricates the surface, so the lungs can move easily within the thoracic cavity. | *The Pleural Cavity is filled with a small amount of fluid which forms a thin film of liquid between the pleural layers. This is vital in that in prevents separation of the two pleural layers and lubricates the surface, so the lungs can move easily within the thoracic cavity. |