Henry Gray (18251861). Anatomy of the Human Body. 1918.
may be traced over the costal surface of the lung, the apex and base, and also over the sides of the fissures between the lobes, on to its mediastinal surface and the front part of its root. It is continued from the lower margin of the root as the anterior layer of the pulmonary ligament, and from this it is reflected on to the pericardium (pericardial pleura), and from it to the back of the sternum. Above the level of the root of the lung, however, the mediastinal pleura passes uninterruptedly from the vertebral column to the sternum over the structures in the superior mediastinum. Below, it covers the upper surface of the diaphragm and extends, in front, as low as the costal cartilage of the seventh rib; at the side of the chest, to the lower border of the tenth rib on the left side and to the upper border of the same rib on the right side; and behind, it reaches as low as the twelfth rib, and sometimes even to the transverse process of the first lumbar vertebra. Above, its cupula projects through the superior opening of the thorax into the neck, extending from 2.5 to 5 cm. above the sternal end of the first rib; this portion of the sac is strengthened by a dome-like expansion of fascia (Sibsons fascia), attached in front to the inner border of the first rib, and behind to the anterior border of the transverse process of the seventh cervical vertebra. This is covered and strengthened by a few spreading muscular fibers derived from the Scaleni.
FIG. 966 Lateral view of thorax, showing the relations of the pleuræ and lungs to the chest wall. Pleura in blue; lungs in purple. (See enlarged image)
In the front of the chest, where the parietal pleura is reflected backward to the pericardium, the two pleural sacs are in contact for a short distance. At the upper part of the chest, behind the manubrium, they are separated by an angular interval; the line of reflection being represented by a line drawn from the sternoclavicular articulation to the mid-point of the junction of the manubrium with the body of the sternum. From this point the two pleuræ descend in close contact to the level of the fourth costal cartilages, and the line of reflection on the right side is continued downward in nearly a straight line to the xiphoid process, and then turns lateralward, while on the left side the line of reflection diverges lateralward and is continued downward, close to the left border of the sternum, as far as the sixth costal cartilage. The inferior limit of the pleura is on a considerably lower level than the corresponding limit of the lung, but does not extend to the attachment of the diaphragm, so that below the line of reflection of the pleura from the chest wall on to the diaphragm the latter is in direct contact with the rib cartilages and the Intercostales interni. Moreover, in ordinary inspiration the thin inferior margin of the lung does not extend as low as the line of the pleural reflection, with the result that the costal and diaphragmatic pleuræ are here in contact, the intervening narrow slit being termed the phrenicocostal sinus. A similar condition