THORACIC CAVITY 55 



sternum, and terminates opposite the sixth right cartilage at 

 the same distance from the right margin of the sternum. At 

 the upper and left corner of the atrial area is the apex of the 

 left auricle (O.T. auricular appendage), and between the two 

 auricles are the roots of the pulmonary artery and the aorta, 

 the former anterior to the latter. The rounded portion of 

 the upper part of the right ventricle, immediately below the 

 pulmonary artery, is the conns arteriosus. 



If a finger is introduced into the cleft between the aorta 

 anteriorly and the superior vena cava posteriorly, it can be 

 passed across, from the right to the left side of the pericardial 

 cavity, through a passage, called the transverse sinus of the 

 pericardium (Figs. 24 and 27). This sinus lies anterior to the 

 superior vena cava and the atria, and posterior to the ascending 

 aorta and the stem of the pulmonary artery. The upper border 

 of a finger placed in the sinus will indicate the position of the 

 upper border of the heart. This border is formed to a slight 

 extent by the upper border of the right atrium, but mainly by 

 the upper border of the left atrium. Its position can be in- 

 dicated, on the anterior surface of the body, by a line com- 

 mencing half an inch from the side of the sternum at the lower 

 border of the second left costal cartilage, and ending at the 

 same distance from the sternum on the upper border of the 

 third right cartilage. Whilst a finger is kept in the transverse 

 sinus a pointer should be introduced into the right pulmonary 

 artery through its cut end in the root of the right lung. The 

 dissector will note, as the pointer traverses the right pulmonary 

 artery, that it passes first posterior to the superior vena cava and 

 then along the upper border of the transverse sinus, that is 

 along the upper border of the heart where that border is 

 formed by the left atrium ; therefore the position of the right 

 pulmonary artery may be indicated, on the anterior surface 

 of the body, by the right two-thirds of the line which marks 

 the position of the upper border of the heart. 



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. 



Before proceeding further the dissector should summarise 



