THE THORAX 



943 



surfaces of the lungs anterior to their roots. The phrenic nerve, 

 on each side, descends in very close contact with it. In front of it 

 are the body of the sternum and the sternal ends of the correspond- 

 ing costal cartilages. Its anterior surface is, to a greater or less 

 extent, encroached upon by the adjacent portions of the anterior 

 margins of the limgs and by the two pleurae. There is, however, 

 a small portion of this surface which is immediately related to the 

 stermmi below the Ie\el of the lower border of the fourth left costal 

 cartilage at its sternal end. Posteriorly, the pericardium hes in front 

 of the posterior mediastinum, and the oesophagus is here related 

 to it opposite the posterior aspect of the left auricle of the heart. 



Arch of Aorta 

 Superior Vena Cava 



Ascending Aorta 



Right Auricular Appendix 



Pericardium (cut) 

 Right Auricle 



Pulmonary Artery 



Left Auricular Appendix 



Diaphragm 



Left Ventricle 

 -• Pericardium (cut) 



Central Tendon 

 of Diaphragm 



Apex 



Fig. 385 The Heart (Anterior View) and Pericardium 



(The anterior part of the pericardium has been removed). 



The pericardium consists of two portions — an external or 

 fibrous, and an internal or serous. The fibrous portion is strong 

 and dense. Inferiorly it is attached to the central tendon of the 

 diaphragm, and slightly to its muscular part on the left side. 

 Superiorly it ensheathes the great vessels connected with the base 

 of the heart, with the single exception of the inferior vena cava. 

 These sheaths are eight in number. One, which is the strongest, 

 invests the whole of the ascending aorta; two invest the right 

 and left pulmonary' arteries; one surrounds the lower half of the 



