426 PHYSIOLOGY CHAP. 



thoracic wall beneath which there is pulmonary substance, and a 

 dull sound where there are viscera which contain no air. The 

 lower border extends in normal expiration from the sternal margin 

 on both sides almost to the insertion of the sixth rib, in the 

 axillary line almost to the upper border of the seventh (Fig. 189). 

 The anterior margin of the left lung, in ordinary expiration, 

 reaches the line that goes from the median point of the insertion 

 of the fourth rib to the insertion of the sixth (see line ft"). 



In deep inspiration the inferior borders of the lungs pass 

 beyond the sixth and reach the seventh rib (see line mn) ; posteriorly 

 they reach the eleventh ; the anterior margin of the left lung 

 comes forward to the line ii'. 



FIG. 189. Displacement of pulmonary borders in respiratory movements. (Landois.) The line atb 

 indicates the lower border of the lungs when all the respiratory muscles are at rest. The line 

 mn indicates the right pulmonary border in deep inspiration ; hi in deep expiration. The 

 triangle tt't" corresponds with area of absolute dulness of heart when thorax is at rest. 

 In deep inspirations this area is reduced to the small triangle fit' owing to advance of internal 

 border of left lung ; in deep expiration, on the contrary, the triangle extends to tee' by the 

 retraction of this border. The line dd'd" limits the area of relative dulness of heart, the heart 

 being separated from the thoracic wall by a thin sheet of lung. 



In very energetic expiration the lower borders of the lungs 

 rise to the line hi ; the anterior margin of the left lung protrudes 

 as far as the line ee'. 



In pleuritis exudativa, when the pleural layers become 

 roughened on the surface, their friction during the respiratory 

 movements gives rise to a characteristic murmur of friction, which 

 the physician uses in diagnosis. 



With direct auscultation, and with the stethoscope, a 

 murmur is heard on inspiration throughout the whole extent of 

 the lungs, which is known as the vesicular murmur, because it de- 

 pends on the dilatations of the alveoli and the friction of the air 

 that traverses the bronchioles. The murmur is rougher in children 

 up to the age of twelve, because the pulmonary infundibuli are 



