THORACIC CAVITY 19 



ribs, from the^second to the eighth 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 ninth 

 ribs and those below the ninth must not be interfered with. After- 

 wards the ribs, from the second to the eighth inclusive, must be 

 divided as near their vertebral ends as possible and the separated 

 portions removed. After the separated 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 

 then be exposed in the area from which the ribs have been 

 removed, and the dissector should notice that it has the appear- 

 ance 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 the dissector has examined the outer surface of the 

 pleura, he should divide the membrane 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 forwards, and the other backwards. The pleural sac 

 will then be opened and the lateral surface of the lung, covered 

 with the adherent visceral portion of the pleura, will be exposed. 



The cavity of the sac and its relations to the mediastinal 

 septum, to the diaphragm, and to the root of the neck, can now 

 be explored with the fingers ; and the borders, surfaces, and the 

 root of the lung can be examined. 



If the lungs are healthy and are not hardened with formalin 

 they will shrink to one third of their original bulk as soon as the 

 pleural sacs are opened. 



Pleurae. There are two pleural sacs, 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, and to 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 

 third intercostal space, (2) at the level of the fifth costal 

 cartilage, and (3) at the level of the manubrium sterni. He 

 must trace the wall of the sac in the vertical plane also. 



Commencing at the level of the third intercostal space, he 

 should place his fingers on the surface of the lung and follow 

 it forwards and medially until, behind the sternum, he reaches 

 the sharp, anterior border, which should be pulled laterally ; 

 then, turning from the lung to the parietal pleura, he should 

 place his fingers on the inner surface of the anterior flap and 



ji 2 a 



