THE CONTENTS OF THE THORAX. 103 



anterior and inferior pulmonary margins. The movement of the anterior margin is due to the 

 anteroposterior expansion of the lung (costal breathing) ; the inferior margin moves on account 

 of the vertical expansion of the lung (diaphragmatic breathing). 



During expiration the anterior margin of the right lung extends from the attachment of the 

 second costal cartilage along the right sternal margin to the lower border of the fifth rib. The 

 inferior margin is situated in the mammary line at the sixth rib, crosses the seventh rib in the 

 axillary line and the ninth rib in the scapular line, and reaches the vertebral column at the level 

 of the spinous process of the tenth dorsal vertebra. The anterior border of the left lung runs 

 from the attachment of the second rib to the upper border of the fourth rib somewhat external 

 to the left sternal margin. From the fourth intercostal space it deviates outward, forming the 

 cardiac notch (incisura cardiaca), approaches nearer to the sternum in the fifth intercostal space, 

 and becomes continuous with the inferior pulmonary margin at the sixth chondrocostal articula- 

 tion. From this point the inferior pulmonary margin passes outward and backward as upon 

 the right, but at a slightly lower level, although this is of no clinical importance. During deep 

 inspiration the anterior margins of the lungs correspond to the pleural limits. The right lung 

 consequently extends somewhat beyond the median line, while the left one barely reaches it. 

 This is the situation in which the two lungs are in closest proximity, being separated only by 

 a very narrow portion of the mediastinum. The inferior margin runs obliquely outward and 

 downward from the sternal line at the lower border of the sixth rib. In the mammary line it 

 is at the level of the upper border of the seventh rib, crosses the eighth rib in the axillary line and 

 the tenth rib in the scapular line, and reaches the vertebral column at the level of the spinous 

 process of the eleventh dorsal vertebra. [The lungs in the midaxillary line are probably a little 

 lower than here stated, reaching the eighth rib in expiration, the ninth in inspiration. ED.] 

 The posterior boundary between the superior and inferior lobes (incisura interlobaris) is indi- 

 cated upon both sides of the chest by the interscapular line, which is drawn between the two 

 inner extremities of the scapular spines with the arms hanging vertically downward. This line 

 also indicates the level of the hilus. The lungs cannot be percussed posteriorly for a handbreadth 

 to either side of the vertebral column, since the long muscles of the back, situated in the dor- 

 sal grooves of the thorax, hinder the transmission of auscultatory phenomena. Upon the left 

 side the lateral boundary between the upper and the lower lobe is furnished by the fifth or the 

 sixth rib; anteriorly, along the left sternal margin, only the upper lobe is present. Upon the 

 right side the middle lobe is situated anteriorly and anterolaterally below the fourth rib. Even 

 during deep inspiration the anterior margin of the left lung does not completely fill the costo- 

 mediastinal sinus in the region of the cardiac notch. The middle and the inferior lobes rest 

 upon the diaphragm upon the right side; upon the left side only the inferior lobe is in relation 

 with the diaphragm. 



If the diaphragm is pushed upward by tympanites, by ascites, or by abdominal tumors, the 

 inferior pulmonary margin will be found at a higher level than usual. When the volume of 

 the lung becomes greatly increased, as in emphysema, the inferior pulmonary margin extends 

 downward beyond the normal limit. It should also be mentioned that the inferior margin of 

 the lung is more easily determined by percussion upon the right side, since the pulmonary reson- 

 ance passes directly into the hepatic dulness, while upon the left side the stomach cannot always 

 be differentiated from the lung by typical differences in the percussion-note. 



