510 THE THORAX AND VERTEBRAL COLUMN 



sternum by at least one inch. At the sternal ends of the 

 fourth and fifth spaces and behind the sternal ends of the 

 fifth and sixth cartilages of the left side, the pericardium is 

 only separated from the chest wall by a double layer of pleura. 

 Light percussion of this area, therefore, produces a dull note, 

 and the area will be increased in size when the anterior border 

 of the left lung is retracted owing to pressure or disease (see 

 below). 



The Heart and Pericardium. The Pericardium is a 

 fibro-serous sac which encloses the heart and the roots of the 

 great vessels. Under normal conditions its outline corresponds 

 to the outline of the heart, but, when greatly distended, it 

 becomes pear-shaped with the blunted apex superiorly. 



The Right Border of the Heart is entirely formed by the 

 right atrium (auricle). It begins above at the third right costal 

 cartilage half an inch lateral to the sternum, and descends, with 

 a slight convexity to the right, to the sixth costal cartilage. 

 Its maximum distance from the median plane is in the fourth 

 interspace and amounts to i| inches. 



The Lower Border of the Heart extends from the lower 

 end of the right border to the apex-beat (p. 502). It is formed 

 mainly by the right ventricle, but the left ventricle forms its 

 left extremity. 



The Left Border of the Heart extends upwards and 

 medially from the apex to the second left intercostal space, 

 where it lies at a distance of half an inch from the sternum. 

 It is gently convex upwards and to the left, and corresponds to 

 the rounded border of the left ventricle. 



When the heart, pleurae, and lungs are marked in on the 

 same chest (Fig. 150), it will be found that an irregularly 

 triangular area of the anterior surface of the heart is uncovered 

 by the left lung. This area is termed the area of superficial 

 cardiac dulness, and where it extends beyond the sternum it is 

 covered by pleura. 



Effusion of fluid into the pericardial sac may greatly 

 increase the size of the area of superficial cardiac dulness, and 

 the lungs and pleural reflections are displaced laterally. 

 Curschmann holds that it is not safe to perform paracentesis 

 pericardii at the lateral border of the sternum, as the fluid tends 

 to collect posteriorly and laterally, so that the heart is thrust 

 forwards against the chest-wall. He recommends that the 

 needle should be inserted in or lateral to the lateral line, and 



