THE PLEURAE
membrane investing the surface of the lung is called the pleura pulmonalis (visceral layer of pleura); whilst that which lines the inner surface of the chest is
Each lung is invested, upon its external surface, by an exceedingly delicate serous membrane, the pleura, which encloses the organ as far as its root, and is then reflected upon the inner surface of the thorax. The portion of the serous called the pleura costalis (parietal layer of pleura). The Interspace or cavity between these two layers is called the cavity of the pleura. Each pleura is therefore a shut sac, one occupying the right, the other the left half of the thorax; and they are perfectly separate, not communicating with each other. The two pleurse do not meet in the middle line of the chest, excepting at one point in front; an interspace being left between them, which contains all the viscera of the thorax, excepting the lungs: this is the mediastinum.
Reflections of the Pleura (fig. 337). Commencing at the sternum, the pleura passes outwards, covers the costal cartilages, the inner surface of the ribs and Intercostal muscles, and at the back of the thorax passes over the thoracic ganglia and their branches, and is reflected upon the sides of the bodies of the vertebrae, where it is separated by a narrow interspace from the opposite pleura, the posterior mediastinum.
From the vertebral column, the pleura passes to the side of the pericardium, which it covers to a slight extent; it then covers the back part of the root of the lung, from the lower border of which a triangular fold descends vertically by the side of the posterior mediastinum to the Diaphragm. This fold is the broad ligament of the lung, the ligamentum latum pulmonis, and serves to retain the lower part of the organ in position. From the root, the pleura may be traced over the convex surface of the lung, the summit and base, and also over the sides of the fissures between the lobes. It covers its anterior surface, and front part of its root, and is reflected upon the side of the pericardium to the inner surface of the sternum.
Below, it covers the upper surface of the Diaphragm. Above, its apex projects, in the form of a cul-de-sac, through the superior opening of the thorax into the neck, extending about an inch above the margin of the first rib, and receives the summit of the corresponding lung: this sac is strengthened, according to Dr. Sibson, by a dome-like expansion of fascia, derived from the lower part of the Scaleni muscles.
A little above the middle of the sternum, the contiguous surfaces of the two pleura are in contact for a slight extent; but above and below this point, the interval left between them by their non-approximation forms the anterior mediastinum.
The inner surface of the pleura is smooth, polished, and moistened by a serous fluid; its outer surface is intimately adherent to the surface of the lung, and to the pulmonary vessels as they emerge from the pericardium; it is also adherent to the upper surface of the Diaphragm; throughout the rest of its extent it is somewhat thicker, and may be separated from the adjacent parts with extreme facility.
The right pleural sac is shorter, wider, and reaches higher in the neck than the left.
The arteries of the pleura are derived from the intercostal, the internal mammary, the phrenic, inferior thyroid, thymic, pericardiac, and bronchial.
The veins correspond to the arteries.
The lymphatics are very numerous.
The nerves are derived from the phrenic and sympathetic (Luschka). Kolliker states that some accompany the ramifications of the bronchial arteries in the pleura pulmormlis.
