Chap, x.i THE LUNG. 179 



edge of the right lung then continues vertically down- 

 wards behind the middle line of the sternum to the 

 sixth chondro-sternal articulation, where it slopes off 

 along the line of the sixth rib. The edge of the left 

 lung keeps close to that of the right as far as the fourth 

 chondro-sternal articulation, where it turns off to the 

 left, following a line drawn from the fourth cartilage 

 to the apex of the heart. In the child, owing to the 

 thymus, the lungs are more separated in front. The 

 two edges in no place come in contact. The right 

 reaches the middle line, but the left only reaches the 

 left edge of the sternum (Symington). The lower 

 border of the lung corresponds to a slightly convex 

 line drawn round the chest from the sixth chondro- 

 sternal articulation in front to the eleventh dorsal 

 spine behind. In the mammary line this line would 

 correspond to the sixth rib, in the mid-axillary line 

 to the ninth rib, and in a line continued vertically 

 downwards from the inferior angle of the scapula with 

 the tenth rib. The pleura extends farther down than 

 the lung, reaching in front to the level of the seventh 

 chondro-sternal union, behind to the eleventh dorsal 

 spine, and at the sides to a point some two and a half 

 inches above the lower margin of the thorax. Thus* 

 it will be seen that the pleura and diaphragm may 

 be wounded in many places without the lungs being 

 involved. The lowest part of the pleura is only sepa- 

 rated from the kidneys by the thin layer of the 

 diaphragm. The pleura is in relation with the eleventh 

 rib posteriorly, but not with the twelfth. It extends 

 lower down in the child than in the adult, reaching 

 the costo-vertebral joint of the twelfth rib. 



In penetrating wounds involving the pleura, aii 

 may enter the pleural cavity, producing pneu mo- 

 thorax, and this air may be subsequently pressed by 

 the respiratory movements into the subcutaneous 

 tissues through the wound in the parietal pleura, and 



