148 ORGANS OF RESPIRATION. 



which is confined to its appropriate half of the thorax, so as to 

 line its cavity and to cover its lung. 



The pleura, as other serous membranes, is a thin sac. Its 

 circumference is entire, like that of an inflated bladder; there 

 is, therefore, no point or line at which one may exclusively be- 

 gin an account of its course and attachments. To commence, 

 however, at the sternum ; the pleura goes thence outwardly to 

 line the lateral parietes ofthe thorax, as formed by the carti- 

 lages of thn ribs, the ribs themselves, and the intercostal mus- 

 cles. In this way it may be traced around to the dorsal verte- 

 brae, and over the convex surface of the diaphragm. In pro- 

 ceeding along the first rib, which is very oblique, it forms a sort 

 of bulging bag, which projects towards the trachea, lines the 

 lower part of the scalenus anticus muscle, and receives the up- 

 per extremity of the lung. The pleura, having reached the dor- 

 sal vertebrae from the ribs, passes from their sides forwards to 

 the posterior part of the pericardium, a very small portion of 

 which it covers. It then goes upon the posterior face of the 

 pulmonary vessels and of the bronchus to the lung, and applies 

 itself closely to the latter. It then covers the part of the lung 

 posterior to its root, and continues to advance along the round- 

 ed surface of the lung to its anterior margin: it then passes over 

 the internal surface of the lung, which is anterior to its root. 

 It afterwards covers the front of the pulmonary vessels and of 

 the bronchus, and gets in a very short space to the pericar- 

 dium. It then passes forwards on the side of the latter, and 

 having got near its middle line, goes from it to the sternum, and 

 reaches the line from which the description of its course com- 

 menced. 



There is no important difference between the two pleurae, 

 either in their mode of reflection or in the organs to which they 

 are attached*, so that the description of one will apply to the 

 other. The portion of each pleura covering the lung is called 

 Pleura Pulmonalis, and that portion which lines the thorax is 

 the Pleura Costalis-; that covering the Diaphragm is the Pleura 

 Diaphragmalis. A duplicature of the pleura commences at the 

 inferior margin of the pulmonary veins, and, descending as far 

 as the diaphragm, attaches the inferior portion of the posterior 

 margin of each lung to the side of the pericardium, in front 



