20 SUPERFICIAL ANATOMY OF THE TRUNK. 



the shape of the chest. Thus, in a long narrow chest the lower ribs slope very much 

 downwards and are near to one another, the subcostal angle is narrow, and the 

 lateral margin of the thorax reaches nearly, or in some persons quite, as far as the 

 iliac crest. "When the chest is broad the opposite conditions are found. The sub- 

 costal angle is on the average about 70 in the male and 75 in the female, but it 

 may vary from 60 to 80 (Charpy). 



The lungs. The apex of the lung rises above the anterior end of the first rib 

 and the clavicle into the neck, where it is placed behind the interval between the 

 two heads of the sterno-mastoid, being covered immediately by the subclavian artery 

 and scalenus anticus muscle. Its highest point is on a level with the neck of the 

 first rib ; and it projects very slightly, if at all, beyond the plane of that rib. The 

 height to which it extends above the clavicle ranges in ordinary circumstances from 

 half an inch to an inch (1 2*5 cm.), but sometimes it is as much as an inch and three- 

 quarters (4 cm.), while in other cases the lung does not project at all above the bone. 

 A resonant percussion-note may, however, always be obtained in the living subject 

 for some distance above the clavicle, owing to the obliquity of the surface of the neck. 

 The distance of the apex from the clavicle is actually diminished during inspiration, 

 since that bone is then moved upwards with the anterior end of the first rib. There 

 does not appear to be any constant difference in the extent upwards of the lung on 

 the two sides, but it is not uncommon for the right lung to be somewhat higher 

 than the left. From the apex, the anterior border of each lung inclines inwards 

 behind the sterno-clavicular articulation and the manubrium, to the junction of the 

 latter with the body of the sternum, where the two almost meet in the middle line ; 

 they then descend together, the right sometimes projecting a little to the left of the 

 mid-line, as far as the fourth costal cartilage ; from this point the margin of the 

 right lung continues a nearly straight course to the level of the sixth chondro-sternal 

 articulation (sometimes even to the lower end of the body of the sternum), while 

 that of the left slopes outwards behind the fifth costal cartilage, in a direction which 

 may be indicated with sufficient accuracy by a line drawn from the fourth chondro- 

 sternal articulation of the left side to the spot on the chest-wall corresponding to the 

 apex of the heart (see below). 



The lower limit of the lung may be marked by a line, slightly convex downwards, 

 carried round the side of the chest from the sixth chondro-sternal articulation to 

 the tenth dorsal spine. In the mamillary line, the lung extends downwards to the 

 sixth rib ; opposite the posterior fold of the axilla, to the eighth rib ; and in the 

 scapular line (carried vertically downwards from the lower angle of the scapula, 

 while the arms are against the sides), to the tenth rib. At the side of the chest the 

 left lung often descends somewhat beyond these limits. This margin of the lung 

 descends considerably in inspiration, and rises in expiration. The position of the 

 great fissure in each lung may be ascertained approximately by drawing a line from 

 the second dorsal spine to the sixth rib in the nipple-line ; and the smaller fissure 

 of the right lung extends from the middle of the foregoing to the junction of the 

 fourth costal cartilage with the sternum. 



The pleura reaches considerably farther downwards than the lung. Posteriorly, 

 its lower margin corresponds most frequently to the head of the twelfth rib, or the 

 eleventh dorsal spine ; it is seldom higher than this, but often lower, in many cases 

 extending as much as an inch (2*5 cm.) beyond the spot mentioned. Being directed 

 at first horizontally outwards, its line then ascends gradually over the side of the chest, 

 and passes behind the seventh costal cartilage to the sternum, from which point it 

 slopes gradually inwards to reach the middle line at the level of the fifth cartilages. 

 As the pleurae of the two sides are almost symmetrical in front, the left extends 

 considerably farther over the pericardium than the corresponding lung. At the 

 side of the chest, the line of reflection of the pleura is generally from two to three 



