894 THE LUXGS. 



At the root of each lung which is enclosed by its own pleura, the visceral 

 and parietal portions of this membrane are continuous with each other ; and, 

 commencing immediately at the lower border of the root, there is found a 

 triangular fold or duplicature of the serous membrane, extending vertically 

 between the inner surface of the lung and the posterior mediastinum, and 

 reaching down to the diaphragm, to which it is attached by its extremity ; 

 this fold, which serves to attach the lower part of the lung, is named liya- 

 mentum latum pulmonis. 



The upper part of each pleura, which receives the apex of the correspond- 

 ing lung, projects in the form of a cul-de-sac through the superior aperture 

 of the thorax into the neck, reaching an inch or even an inch and a half 

 above the margin of the first rib, and passing up under cover of the scaleui 

 muscles, a small slip of which, arising from the transverse process of the 

 last cervical vertebra, is described by ISibson as expanding into a dome-like 

 aponeurosis or fascia, which covers or strengthens the pleural cul-de-sac, and 

 is attached to the whole of the inner edge of the first rib. The right pleura 

 is generally stated to reach higher in the neck than the left ; but, in twenty 

 observations recorded by Hutchinson, the right lung was higher in ten cases, 

 and the left in eight, whilst in two the height was equal on the two sides. 

 Anteriorly the pleural sacs of opposite sides come nearly or altogether into 

 contact behind the second piece of the sternum, and continue so for some 

 distance ; but opposite the lower end of the sternum the right pleura passes 

 beyond the middle line or remains close to it, while the left recedes to a 

 variable distance from the sternum. Inferiorly the pleurae do not pass quite 

 down to the attachments of the diaphragm, but leave a portion of its circum- 

 ference in contact with the costal parietes. Owing to the height of the 

 diaphragm on the right side (corresponding with the greater convexity of 

 the liver), the right pleural sac is shorter than the left ; it is at the same 

 time wider. According to Luschka the right pleura, opposite a line descend- 

 ing from the axilla, reaches down to the lower border of the ninth rib, 

 while the left pleura in the same transverse vertical plane reaches to the 

 lower border of the tenth rib. 



Structure. The pleura possesses the usual characters of serous membrane. The 

 costal part of the membrane is the thickest, and may be easily raised from the ribs 

 and intercostal spaces. It is strengthened in these situations by a layer of subserous 

 areolar tissue of considerable thickness. On the pericardium and diaphragm the 

 pleura is thinner and more firmly adherent; but it is thinnest and least easily 

 detached upon the surface of the lungs. 



Luschka has described nerves in this membrane, with fine and coarse fibres, which 

 are traceable to the phrenic and sympathetic. Kolliker states that, in the pleura 

 pulmonalis of man, branches of nerves may be seen accompanying the ramifications of 

 the bronchial arteries. 



THE LUNGS. 



Form. Each lung is shaped somewhat like a cone, having its base turned 

 downwards, and its inner side much flattened. The base is broad, concave, 

 and of a semilunar form, and rests upon the arch of the diaphragm. It is 

 bounded by a thin margin, which is received in the angle between the ribs 

 and the diaphragm ; and it reaches much lower down behind and at the 

 outer side than in front and towards the middle line. The apex, forms a 

 blunted point, and, as already mentioned, reaches into the root of the neck, 

 above the margin of the first rib, where it is separated from the first portion 

 of the subclavian artery by the pleural membrane. 



