6o THORAX 



examination of the venae cavre will show that the lower inch 

 of the superior vena cava lies within the fibrous pericardium 

 and that it is ensheathed, except along its postero-medial 

 border, by a covering of the serous layer, whilst the inferior 

 vena cava can scarcely be said to have any intra-pericardial 

 course, for it joins the lower and posterior part of the right 

 atrium immediately after piercing the fibrous layer, but the 

 margin of the orifice by which it enters is surrounded by the 

 serous layer except along a narrow line posteriorly. The 

 left pulmonary veins are covered by the serous layer on their 

 superior, anterior, and inferior aspects, but not posteriorly ; 

 and the right pulmonary veins, which enter the left auricle as 

 soon as they have pierced the fibrous pericardium, are in rela- 

 tion with the serous layer merely along the medial and lateral 

 borders of the orifices in the fibrous layer through which 

 they enter. 



Dissection. After the examination of the reflections of the serous layer 

 of the pericardium is completed, the dissectors should study the vessels and 

 nerves which supply the walls of the heart. They are the coronary arteries 

 and the cardiac veins and nerves, and they lie in the coronary and longitudinal 

 sulci of the heart, which have been noted already. To display them the 

 visceral pericardium superficial to them must be cut and turned aside, the fat 

 which lies in the sulci around the vessels must be removed, then the main 

 vessels can be traced to their origins and terminations, and an endeavour 

 should be made to preserve the fine nerves which accompany the vessels. 



Arteriae Coronarise. The coronary arteries are the nutrient 

 vessels of the heart. They spring from dilatations of the com- 

 mencement of the aorta which are called the sinus aortce 

 (Valsalva). There are three sinuses of the aorta, an anterior 

 and two posterior, and only two coronary arteries, a right and 

 a left ; the right artery springs from the anterior sinus, and 

 the left from the left posterior sinus. 



The right coronary artery passes anteriorly from the anterior 

 aortic sinus, between the pulmonary artery and the right 

 auricle ; turns downwards and to the right, in the coronary 

 sulcus, to the lower part of the right margin of the heart, round 

 which it curves. Then it proceeds to the left, in the posterior 

 part of the coronary sulcus, till it reaches the posterior end 

 of the inferior (posterior) longitudinal sulcus, where it divides 

 into a small transverse and a large interventricular branch. 

 The transverse branch continues to the left till it anastomoses 

 with the circumflex branch of the left coronary artery. The 

 interventricular (descending) branch runs anteriorly in the 



