50 THORAX 



The Pericardium. This is a fibre-serous sac which occupies 

 the middle mediastinum. It surrounds the heart and the roots 

 of the great vessels which enter and leave the heart. 



The Fibrous Pericardium. The fibrous or outer part of 

 the pericardium is conical in form. Its base rests upon the 

 diaphragm, principally on the central tendon but also 

 upon the muscular portion, particularly upon the left side. 

 Near the median plane it is blended with the central tendon, 

 and can be separated from it only by the aid of the edge 

 of the scalpel ; more laterally the areolar tissue which 

 connects the pericardium and the diaphragm is easily broken 

 down by the handle of the knife. The diaphragm separates 

 the pericardium mainly from the upper surface of the liver, but 

 also, towards the left and anteriorly, from the fundus of the 

 stomach. The apex of the fibrous sac blends with the outer 

 coats of the aorta, the pulmonary arteries and the superior 

 vena cava. The anterior surface lies behind the body of the 

 sternum and the cartilages of the ribs from the second to the 

 sixth inclusive, but it is separated from them by the lungs and 

 pleurae, except (i) in the median plane of the anterior medi- 

 astinum, where condensations of the areolar tissue of the medi- 

 astinum, called the superior and inferior sterno-pericardiac 

 ligaments, connect the anterior surface of the fibrous sac to 

 the upper and lower ends of the body of the sternum 

 respectively, and (2) in the region of the sternal extremity of 

 the left fifth costal cartilage, where the left pleura retreats 

 somewhat towards the left side, and the pericardium comes 

 into direct relation with the sternum and the left transversus 

 thoracis muscle. This portion of the pericardium is the 

 so-called bare area. It is usually of small extent, and frequently 

 it does not extend beyond the margin of the sternum, but it is 

 of importance because through it the surgeon attempts to tap 

 the pericardium when the sac is distended with fluid. 



The lateral walls of the pericardium are in relation with 

 the mediastinal pleura, the phrenic nerve and the pericardiaco- 

 phrenic vessels intervening (O.T. comes nervi phrenici). The 

 posterior surface lies anterior to the descending aorta and the 

 oesophagus medially, whilst laterally it is supported posteriorly 

 by the lungs and pleurae. At the junction of the upper parts of 

 the lateral and posterior surfaces, on each side, two pulmonary 

 veins enter the pericardium and receive sheaths from its 

 fibrous wall. 



