12 THORAX 



Each lung lies free in the pleural space except along its 

 medial surface, where it is attached to the heart by the 

 pulmonary vessels, to the corresponding bronchial tube, and 

 by a fold of pleura to the side of the pericardium. 



The dissection which has already been made shows the 

 pleura lining the deep surfaces of the costal arches and the 

 internal intercostal muscles. This part is called the costal 

 pleura, and it is part of the parietal pleura, but before it can 

 be more fully investigated and before the remaining parts of 

 the pleurae and the lungs can be examined, further dissection 

 is necessary. 



Dissection, The pleural membrane previously exposed by the removal 

 of the contents of the intercostal spaces must now be carefully separated 

 from the inner surfaces of the ribs by the gentle pressure of the fingers. 

 The separation should be carried anteriorly to the junction of the ribs 

 with their cartilages and posteriorly as far as possible. When this has 

 been done the ribs, from the second to the sixth inclusive, must be divided, 

 with bone forceps, at their junctions with their cartilages, and at the same 

 time any fibres of the transversus thoracis which may be attached to them 

 must be cut. The first and the seventh and those below the seventh viust 

 not be interfered with. Afterwards the ribs must be divided as far 

 dorsally as possible and the separated portions removed. After the separ- 

 ated parts of the ribs are detached, remove any sharp spicules of bone 

 from the cut ends of the remaining portions. 



The outer surface of the costal part of the parietal pleura will be exposed 

 in the area from which the ribs have been removed, and the dissector 

 should notice that it has the appearance of a fibrous membrane with a 

 rough surface, the roughness being due to fragments of the connective tissue 

 (endothoracic fascia) which connect it with the adjacent parts. 



After he has examined the outer surface of the pleura, the dissector 

 should divide it by a vertical incision about midway between the anterior 

 and posterior borders of the area exposed. At each end of the vertical 

 incision a transverse incision must be made. One of the two flaps so 

 formed must be thrown anteriorly, and the other posteriorly. The pleural 

 sac is now opened and the lateral surface of the lung, covered with the 

 visceral portion of the pleura, is exposed. 



The cavity of the sac and its relations to the mediastinal septum, the 

 diaphragm, and the root of the neck can be explored with the fingers ; and 

 the borders, surfaces, and the root of the lung can be examined. 



The Pleural Sacs are two in number, a right and a left. 

 They are serous sacs, and are therefore closed. After 

 opening into the interior, the dissector should notice the 

 difference between the rough outer surface of the wall of the 

 sac and its smooth and glistening inner surface, and in order 

 that he may thoroughly understand the relationship of the 

 wall of the sac to the lung, the mediastinum and the wall of 

 the thoracic cavity, he should follow the wall of the sac, with 

 his fingers, at three different levels (i) at the level of the 



