442 



DISSECTION OF THE THOKAX. 



below, so as to freely admit the hand into the pleural cavity. 

 When the general cavity has been examined, the anterior 

 mediastinum, or the space between the two pleural sacs behind 

 the sternum and in front of the pericardium, will be cleared. With 

 one hand in the pleural sac as a guide to its anterior limit, it will 

 be found easy to mark the limits of the mediastinum, and the 

 pleurae can be readily separated in the middle line, and from the 

 pericardium, which they overlap. The portion of sternum with 

 the ribs and cartilages of the right side have been left on for the 

 preservation of the anterior mediastinum, but after it has been 

 Open right examined the ribs should be removed on the right side as on the 

 left, and the pleural sac opened and its limits defined. Finally 

 the right half of the sternum with the attached costal cartilages 

 will be removed and kept aside with the left portion for future 

 examination. It, unfortunately, often happens in subjects for 

 dissection, that the pleura is thickened and adherent to the lung. 

 Should the dissector find it is so on the left side, he should 

 at once open the right in case the membrane may be healthy on 

 that side. 



THE PLEURAE are two serous membranes, or closed sacs, which are 

 reflected around the lungs in the cavity of the thorax. One occu- 

 pies the right, and the other the left half of the cavity ; they 

 approach each other along the middle of the chest, forming a 

 thoracic partition or mediastinum. 



Each pleura is conical in shape ; its apex projects into the neck 

 above the first rib (fig. 162, p. 447) ; and its base is in contact with 

 the diaphragm. The outer surface is rough, and is connected to the 

 lung and the wall of the thorax by areolar tissue ; but the inner 

 surface is smooth and free. Surrounding the lung, and lining the 

 interior of one half of the chest, the serous membrane consists of a 

 parietal part, which is variously called 



1. Costal pleura, where it lines the chest- wall ; 



2. Phrenic pleura, where it covers the diaphragm ; 



3. Pericardial pleura, where it covers the pericardium ; and 



4. Cervical pleura, where it passes into the neck. 

 The visceral pleura is the pulmonary pleura. 



Difference in There are some differences in the shape and extent of the two 

 sac of right, pleural bags. On the right side the bag is wider and shorter than 

 and of left on ^ ne ^ e ^ ' an( ^ on ^ ne latter it is narrowed by the projection of 

 side - the heart to that side. 



The continuity of the bag of the pleura may be traced horizontally 

 from any given point, over the lung and chest wall, back to the same 

 spot in the following manner : Supposing the membrane to be 

 followed outwards from the sternum, it lines the wall of the chest 

 from wall of as ^ ar as tne spinal column ; here it is directed forwards to the root 

 of the lung, and is then reflected over the viscus, as the visceral or 

 pulmonary pleura, covering its surface, and extending into the 

 fissures between the lobes. From the front of the root of the lung 

 the pleura may be followed over the side of the pericardium back 

 again to the sternum. 



Sac of the 

 pleura : 



form 



outer 

 surface ; 

 inner 

 surface ; 



disposition. 



The con- 

 tinuity is 

 here traced 



chest to 

 lung 



