78 THORAX 



should be passed through the right and left pulmonary arteries. 

 Introduce the pointer through the cut end of the right 

 pulmonary artery, in the root of the right lung, and pass it 

 to the left until it emerges from the cut end of the left 

 pulmonary artery in the root of the left lung. The dissectors 

 will note that, as the pointer traverses the pulmonary arteries, 

 from right to left, it passes first posterior to the superior vena 

 cava, and then along the upper border of the transverse sinus 

 which runs parallel with the part of the upper border of the 

 heart which is formed by the left atrium. 



Leave the pointer which marks the levels of the right and 

 left pulmonary arteries and the upper border of the heart in 

 position, but withdraw the finger from the sinus. Now replace 

 the sternum and costal cartilages and note that the pointer, 

 which marks the position of the upper border of the heart, 

 inclines slightly downwards, as it passes from left to right, along 

 a line which extends from the lower border of the second left 

 costal cartilage to the upper border of the third right costal 

 cartilage. The position of the upper border of the heart 

 can be indicated, therefore, on the anterior surface of the 

 thorax by a line drawn from the lower border of the 

 second left costal cartilage to the upper border of the third 

 right costal cartilage, commencing and ending 13 mm. 

 (about half an inch) from the margin of the sternum. The 

 right two-thirds of the same line will indicate fairly correctly 

 the position of the right pulmonary artery. The left third 

 will similarly indicate the position of the medial part of the 

 left pulmonary artery. 



The left border of the anterior surface of the heart is 

 formed, to a slight extent, by the left atrium, but mainly by 

 the left ventricle. It is convex to the left and its position 

 is marked, on the surface of the body, by a line which com- 

 mences above at the lower border of the left second costal 

 cartilage, half an inch from the sternum, and terminates below, 

 at the apical point, in the fifth left intercostal space, or behind 

 the left sixth costal cartilage. 



Before proceeding further the dissector should summarise 

 the information he has gained regarding the relationship of 

 the apex of the heart and the borders of the sterno-costal 

 surface of the heart to the anterior wall of the thorax. 



The upper border is formed by the atria, and, as the heart 

 lies in situ^ it is concealed to a great extent by the aorta and 



