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HUMAN ANATOMY. 



THE CORONARY ARTERIES. 



9 



The coronary arteries, which supply the heart, are two in number, and arise from 

 the right and left prominences at the base of the aorta which mark the corresponding 

 sinuses of Valsalva. 



The left coronary artery (a. coronaria sinistra) lies at its origin (Fig. 679) 

 behind the base of the pulmonary aorta, and passes forward between that vessel and 

 the left auricular appendix to reach the anterior interventricular groove, in which it 

 divides into two branches. The larger of these (ramus descendens anterior) descends 

 in the, groove to the ape.x of the heart, giving off branches which supply the anterior 

 surface of both ventricles, while the smaller one (ramus circumflexus) passes backward 

 in the left portion of the auriculo-ventricular groove and gives of^ branches to the 

 left auricle and ventricle. Branches to the left auricle also arise from the main stem 

 of the artery, as well as twigs to the walls of the aortae. 



Fig. 689. 



Left pulmonary artery 



Superior left pulmonary vein 



Inferior left pulmonary vein 



Termination of left 

 coronary vein 



Circumflex branch of left 

 coronary artery 



Left ventricle 



Superior vena cava 



Superior right pulmonary vein 

 Right pulmonary artery 



Inferior right pulmonary vein 



Inferior vena cava 



Coronary sinus 



Right coronary vein 



Right coronary artery 



Posterior descending branch 

 of right coronary artery 



Middle cardiac vein 

 Right ventricle 



Postero-inferior surface of injected heart, viewed from below and behind. 



The right coronary artery (a. coronaria dextra) passes outward fro»i its origin 

 in the right portion of the auriculo-ventricular groove, in which it lies, until it reaches 

 the posterior interventricular groove, down which it (ramus descendens posterior) is 

 continued towards the apex of the heart (Fig. 689). In its course it gives off num- 

 erous branches, which are distributed to the right auricle and ventricle and to the 

 portion of the left ventricle which adjoins the posterior interventricular groove. 

 Usually a large branch, the marginal artery, descends along the right border of the 

 heart (Fig. 679) and gives branches to both surfaces of the right ventricle. 



The peculiarities of the ultimate distribution of these arteries have been described 

 in connection with the heart (page 703). 



Variations. — The two coronary arteries may arise by a common stem ; one of tliem may 

 be wanting, or supernumerary vessels may occur. 



