The pleura is a thin layer which lines each of the lungs (visceral pleura). It is reflected around the lung hila onto the chest wall and pericardium (parietal pleura) and extends from the root of the neck (~3 cm above the mid-point of the clavicle) to the 12th rib overlying the kidney. The parietal layer secretes approximately 2.5 litres of serous fluid a day, which is absorbed by the visceral layer so that at any given time only a small amount of fluid lines the space.