THE PERICARDIUM 291 



It should be remembered that large pericardial effusions 

 thrust the heart forwards against the chest wall, so that the 

 introduction of a cannula at the border of the sternum is 

 certain to result in injury to the heart. The fluid collects 

 posteriorly and on each side of the heart, and on this account 

 the operation i paraccntesis pcricardii is best carried out at the 

 left extremity of the dull area and through the fifth intercostal 

 space. As a rule the instrument will pass through the left 

 pleural sac, but this injury is not followed by any bad results. 

 The instrument is thrust backwards and slightly medially, and 

 its entry into the pericardial sac is indicated by the cessation 

 of resistance to its passage. 



Inferiorly, the pericardium is supported by the diaphragm, 

 which separates it from the upper surface of the liver. Peri- 

 cardial effusions may displace the liver in a downward direction, 

 so that its lower border may be palpated below the costal 

 margin. 



Superiorly, the upper limit of the pericardial sac surrounds 

 the ascending aorta and the pulmonary artery and comes 

 into relation with the left bronchus. In pericardial effusions, 

 the bronchus may be compressed, thus increasing the re- 

 spiratory embarrassment, or it may be thrust upwards so as to 

 compress the left recurrent (laryngeal) nerve, as it hooks round 

 the inferior aspect of the arch of the aorta (Purves Stewart). 



In adhesive mediastinitis, the fibrous layer of the pericardium 

 becomes firmly anchored to the sternum and costal cartilages 

 in front and to the posterior thoracic wall behind. When the 

 ventricles contract, the left interspaces are drawn inwards on 

 the front of the chest, and a similar indrawing may be 

 observed in the lower left interspaces on the dorsal aspect of 

 the body. In this condition, the heart is called upon to work 

 at an obvious disadvantage, and, in order that it may efficiently 

 perform its functions, it requires to undergo a great amount of 

 hypertrophy, which is usually accompanied by some degree of 

 dilatation. 



On the other hand, adhesions arising within the pericardial 



