THE l^HORAX. 



335 



pouches forming the sinuses of Valsalva, one in front 

 and two posterior. 



Relations. In front is the pericardium (and the structures 

 that overlie the pericardium in the middle line). 



At its base the pulmonary artery : Behind, left auricle of 

 heart, right pulmonary artery, right bronchus, anterior 



