THE LUNGS. 199 



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In people with straight backs and flat chests (often seen in phthisis), the sloping 

 downward of the ribs is marked; in those with rounded backs the chest is apt to be 

 round, as in emphysema, and then the ribs are more horizontal. 



Another point to be noticed is the lateral extent of the apex of the lung in 

 relation to the length of the clavicle. The lung does not extend farther out on the 

 clavicle than one-fourth its length. The clavicular origin of the sternomastoid 

 muscle extends out one-third of the length of the clavicle, so that the lung is behind 

 the clavicular origin of the sternomastoid and care should be taken not to percuss 

 too far out. If the finger is laid in the supraclavicular fossa in percussion it should 

 be pressed downward and inward, not backward. 



Posteriorly the scapula rises to the second rib and its spine has its root opposite 

 the fourth rib or spinous process of the third thoracic vertebra. Therefore a small 

 portion of the lung is above the upper edge of the scapula and percussion in the 

 supraspinous fossa gives a clear resonant note. 



Behind the middle of the first piece of the sternum passes the trachea, crossed 

 by the left innominate vein. The trachea of course contains air; the lungs slope 



Collapsed lung 



FIG. 217. Formalin-hardened body, showing the right lung collapsed and compressed by a large 



pleural effusion. 



inward from the sternoclavicular joints to meet nearly or quite in the median line 

 and so continue to the level of the fourth rib; hence it follows that the percussion 

 note on the sternum nearly down to this point is resonant and if it be found to be 

 dull one should look for an aneurismal or other tumor which is displacing or 

 covering the lungs and trachea at this point and thereby subduing their resonance. 



Below the fourth rib the area of the absolute heart dulness becomes evident. 

 (This will be alluded to in describing that organ later on. ) 



In performing abdominal operations, as those involving the gall-bladder and 

 kidney, the surgeon may be tempted to prolong his incision upward into the lower 

 edge of the chest-walls, and it is necessary to know how far he can proceed without 

 opening the pleural cavity. This necessitates his knowing how far from the lower 

 edge of the chest the pleura lies. It reaches to the seventh rib in the mammary line, 

 the ninth in the axillary line, and the twelfth posteriorly, extending to its extreme 

 lower edge. 



In the axillary line the pleura is about 6 cm. (2| in.) away from the edge , of 

 the thorax. This distance gets less as one proceeds forward to the sternum and 

 backward toward the spine. 



