1398 SUKFACE AND SUKGICAL ANATOMY. 



serratus anterior afford reliable guides to the fifth rib. The infra-sternal notch is 

 the guide to the medial end of the seventh costal cartilage. The second and third 

 costal cartilages are almost horizontal; below this the cartilages ascend with 

 increasing obliquity, that of the sixth being the first to present a distinct angle. 

 The anterior end of the second intercostal space is the widest, while those of the 

 fifth and sixth are very narrow. 



The costo-chondral junctions may be indicated, on the surface, by a line drawn 

 from the superior end of the para-sternal line to a point a finger's breadth posterior 

 to the angle of the tenth costal cartilage. 



The internal mammary artery crosses- behind the medial ends of the superior 

 five intercostal spaces, about half an inch from the edge of the sternum ; as it 

 descends it approaches a little nearer to the sternum. The vessel is accompanied 

 by two veins which unite to form a single vein opposite the second interspace. 



This artery is occasionally injured in punctured wounds of the chest. At the second or third 

 intercostal space it is easily ligatured through a transverse incision, but at a lower level it is 

 generally necessary to resect a portion of one of the costal cartilages. 



THE LUNGS AND PLEURAE. 



The apex of the lung extends upwards into the root of the neck for a distance 

 of one to two inches superior to the anterior extremity of the first rib, and is mapped 

 out by a curved line drawn from the superior border of the sterno-clavicular 

 articulation across the sterno-mastoid to the junction of the medial and inter- 

 mediate thirds of the clavicle, the highest part of the curve reaching from J to 1J 

 in. above the clavicle. The apex of the right lung reaches half an inch higher 

 than that of the left lung. Intimately related to the apex of the cervical pleura 

 are the subclavian artery and the inferior cervical ganglion of the sympathetic. 



Both the cervical pleura and the subclavian artery may be injured by one of the fragments in 

 a fracture of the clavicle ; the scaleni muscles, however, affording considerable protection to the 

 pleura. In ligaturing the third part of the subclavian artery, care must be taken not to injure 

 the cervical pleura. 



To delineate the anterior border of the right lung, draw a line from the superior 

 border of the sterno-clavicular articulation to the centre of the manubrium sterni, 

 and from there vertically downwards, in or slightly to the left of the median plane 

 to the level of the sixth or seventh costal cartilage, or, it may be, even to the infra- 

 sternal notch (Fig. 1091). 



The anterior border of the left lung is mapped out by a corresponding line as 

 far as the fourth costal cartilage ; thence it is directed laterally along the inferior 

 border of the fourth costal cartilage to the para-sternal line ; it then passes downwards 

 and slightly laterally across the fourth interspace, and curves medially behind the 

 fifth costal cartilage and fifth interspace to reach the superior border of the sixth 

 costal cartilage in the para-sternal line. The inferior part, therefore, of the anterior 

 surface of the right ventricle is uncovered by lung and gives a completely dull 

 note on percussion ; this area is spoken of as the area of " superficial or absolute 

 cardiac dulness" 



The level of the inferior border of the lung is practically the same on both sides ; 

 it is mapped out by a line extending laterally from the inferior extremity of the 

 anterior border to the sixth costal cartilage in the mid-clavicular line, and thence 

 in a slightly curved direction, with the convexity downwards, across the lateral 

 aspect of the chest to the tenth thoracic spine. This line crosses the eighth rib in 

 the mid-axillary line and the tenth rib in the scapular line (Figs. 1091 and 1092). 



To indicate the position of the oblique fissure a line is drawn from the second 

 thoracic spine across the interscapular region to the root of the spine of the scapula, 

 and thence downwards and laterally across the infraspinous fossa, to end at the 

 inferior border of the lung opposite the sixth costal cartilage, a little medial to the 

 mammary line. When the arm is raised above the level of the shoulder, and the 

 hand placed on the back of the head, the inferior angle of the scapula is rotated 

 upwards and forwards so that the vertebral margin practically corresponds with 

 the line of the oblique fissure. 



