THE CORONARY ARTERIES. 477 



opposite this part has a somewhat oval figure ; but below the attachment of the 

 valves it is circular. This portion of the aorta is contained in the cavity of the 

 pericardium, and, together with the pulmonary artery, is invested in a tube of 

 serous membrane, continued on to them from the surface of the heart. 



Relations. The ascending aorta is covered at its commencement by the trunk 

 of the pulmonary artery and the right auricular appendix, and, higher up, is 

 separated from the sternum by the pericardium, the right pleura, and anterior 

 margin of right lung, some loose areolar tissue, and the remains of the thymus 

 gland ; behind, it rests upon the right pulmonary artery and left auricle. On the 

 right side it is in relation with the superior vena cava and right auricle ; on the 

 left side, with the pulmonary artery. 



PLAN OF THE RELATIONS or THE ASCENDING AORTA. 



In front. 



Pulmonary artery. 

 Right auricular appendix. 

 Pericardium. 

 Right pleura and lung. 

 Remains of thymus gland. 



Right side. >^*""~""~"*N. Left side. 



Superior vena cava. / \ Pulmonary artery. 



Right auricle. 



Behind. 



Right pulmonary artery. 

 Left auricle. 



BRANCHES OF THE ASCENDING AORTA. 



The only branches of the ascending aorta are the coronary arteries. They 

 supply the heart, and are two in number, right and left, arising near the com- 

 mencement of the aorta, immediately above the free margin of the semilunar 

 valves. 



THE CORONARY ARTERIES. 



The Right Coronary Artery, about the size of a crow's quill, arises from the 

 anterior sinus of Valsalva. It passes. forward between the pulmonary artery and 

 the right auricular appendix, then runs obliquely to the right side, in the groove 

 between the right auricle and ventricle, and, curving around the right border of 

 the heart, runs along its posterior surface as far as the posterior interventricular 

 groove, where its divides into two branches, one of which (transverse) continues 

 onward in the groove between the left auricle and ventricle, and anastomoses with 

 the left coronary ; the other (descending] courses along the posterior interven- 

 tricular furrow, supplying branches to both ventricles and to the septum, and 

 anastomosing at the apex of the heart with the descending branches of the left 

 coronary. 



This vessel sends a large branch (marginal] along the thin margin of the right 

 ventricle to the apex, which in its course gives off numerous small branches to 

 the anterior and posterior surfaces of the ventricle. It also gives off a branch 

 (infundibular] which ramifies over the front part of the conus arteriosus of the right 

 ventricle. 



The Left Coronary, larger than the former, arises from the left posterior sinus of 

 Valsalva ; it passes forward between the pulmonary artery and the left auricular 

 appendix, and divides into two branches. Of these, one (transverse] passes trans- 

 versely outward in the left auriculo-ventricular groove, and winds around the left 

 border of the heart to its posterior surface, where it anastomoses with the trans- 



