RESPIRATORY EXCURSION OF THE LUNGS. 



2I 9 



on the anterior chest-wall. The apices of the lungs extend above the 

 clavicles anteriorly to a distance of from 3 to 7 cm. ; on the posterior 

 surface they extend above the spines of the scapulae to the level of the 

 seventh spinous process. On the right side the lower border of the 

 lung, in a position of rest, begins at the right edge of the sternum at the 

 insertion of the sixth rib, and extends horizontally outward to about the 

 upper edge of the sixth rib in the mammillary line, and the upper edge 

 of the seventh rib in the axillary line. On the left side (apart from the 

 position of the heart) the lower border of the lung extends downward 

 for the same distance. In Fig. 84 the line at b indicates the lower 

 boundary of the lungs in a state of rest. Posteriorly, both lungs extend 

 to the tenth rib. 



[Fio. 84. Topography of the Boundaries of the Lungs and the Heart during Inspiration and Expiration 



(after v. Dusch). 



During the deepest possible inspiration the lungs descend anteriorly 

 below the sixth rib as far as the seventh ; posteriorly as far as the eleventh 

 rib. At the same time the diaphragm withdraws from the wall of the 

 thorax. During forced expiration the lower borders of the lungs rise 

 almost for the same distance as they sink during inspiration. In Fig. 

 84 the line m n shows the limit of the border of the right lung during 

 deep inspiration, and h 1 indicates the same border during complete 

 expiration. 



The relation between the border of the left lung and the heart de- 

 serves especial attention. In Fig. 34 may be seen an almost triangular 

 space, extending to the left of the sternum from the middle of the inser- 

 tion of the fourth rib to the sixth rib. This space represents that part 

 of the heart which lies in direct contact with the chest-wall when the 



