958 A MANUAL OF ANATOMY 



of the body of the sternum, from which it is separated by the peri- 

 cardium, right pleura, and anterior margin of the right lung. 

 Posterior. — The right pulmonary artery and the left auricle. Right. — 

 The superior vena cava, and the right auricle. Left. — ^The trunk of 

 the pulmonary artery. 



Branches. — ^These are the two coronary arteries, right and left. 



The right coronary artery arises from the right antero-lateral 

 sinus of Valsalva. Passing forwards between the right auricular 

 appendix and the root of the pulmonary artery, it enters the right 

 auriculo-ventricular groove, which it traverses from front to back 

 as far as the commencement of the inferior interventricular groove. 

 At this point it divides into two branches, transverse and descend- 

 ing. The transverse branch enters the posterior part of the left 

 auriculo-ventricular groove, in which it anastomoses with the 

 transverse branch of the left coronary artery. The descending 

 branch traverses the inferior interventricular groove as far as the 

 region of the apex, where it anastomoses with the descending branch 

 of the left coronary artery. 



The right coronary artery furnishes branches to the right auricle 

 and to both ventricles. One, of large size, called the right mar- 

 ginal branch, passes along the right border, or margo acutus, towards 

 the apex. 



The left coronary artery arises from the left antero-lateral sinus 

 of Valsalva, and is at first concealed by the root of the pulmonary 

 artery. It then passes forwards between the pulmonary artery 

 and the left auricular appendix, and divides into two branches, 

 transverse and descending. The transverse branch enters the left 

 auriculo-ventricular groove, which it traverses from front to back, 

 anastomosing posteriorly with the transverse branch of the right 

 coronary artery. The descending branch traverses the antero- 

 superior interventricular groove as far as the region of the apex, 

 where it anastomoses with the descending branch of the right 

 coronary artery. 



The left coronary artery furnishes branches to the left auricle 

 and to both ventricles. One, of large size, called the left marginal 

 branch, springs from its transverse branch and passes along the left 

 border, or margo obtusus, towards the apex. 



Development. — The ascending aorta, along with the trunk of the pul- 

 monary artery, is developed from the aortic bulb. 



Arch of the Aorta. — ^The arch of the aorta commences behind 

 the right border of the sternum, on a level with the upper maigin 

 of the second right costal cartilage, and it terminates on the left 

 side of the body of the fourth thoracic vertebra, at the lower border 

 of which it becomes the descending aorta. It passes upwards, 

 backwards, and to the left, sweeping over the root of the left lung, 

 and, when it reaches the left side of the body of the fourth thoracic^ 

 vertebra, it descends. The height to which the arch reaches cor-' 

 responds to the centre of the manubrium sterni, which is about 



