THE LUNGS 349 



become adherent. The right lung is divided into three lobes. 

 The lower lobe is very similar to the lower lobe of the left 

 lung and is limited above by the oblique fissure, but a trans- 

 verse fissure cuts off a middle lobe from the antero-inferior 

 part of the upper lobe. 



The apex of the lung can be mapped out on the surface of 

 the body in the way described on page 344. It has already 

 been shown that the costo-mediastinal lines of pleural reflection 

 differ slightly on the two sides, and a similar difference, slightly 

 exaggerated, exists between the anterior borders of the two 

 lungs. The anterior border of the right lung corresponds 

 exactly to the line of pleural reflection, but the anterior border 

 of the left lung deviates widely from the line of pleural reflec- 

 tion below the level of the fourth chondro-sternal articulation 

 (PI. II.). As a result, there is a relatively large area of the 

 pericardium which is only separated from the chest wall by 

 the pleural sac. This area, together with the portion of the 

 pericardium which is uncovered by pleura (p. 290), is therefore 

 dull to percussion and constitutes the area of superficial cardiac 

 dulness (p. 296). A small, tongue-like process of lung tissue 

 projects medially in the fifth intercostal space from the notch 

 in the anterior border of the left lung (Fig. 106). It some- 

 times becomes consolidated in phthisis or pneumonia of the 

 upper lobe, and it then gives rise to an increased area of 

 cardiac pulsation. 



In quiet respiration, a definite interval exists between the 

 lower border of the lung and the lower limit of the pleural 

 sac. This interval increases in extent as it is traced laterally, 

 and so, whereas it only amounts to ij inches in the nipple 

 line, it may be as much as 3^ or even 4 inches in the 

 mid-axillary line. On the posterior surface of the body, the 

 interval again decreases, and, in the scapular line, it is about 

 ij inches in depth. In forced inspiration, the lower borders 

 of the lungs descend almost to the lower limit of the pleural 

 sac, and areas which were dull or tympanitic to percussion 

 during quiet breathing become resonant. 



