COMMON BRACHIOCEPHALIC TRUNK 



631 



to the coronary groove, in which it curves around to the right and backward. It 

 then descends in the right longitudinal groove almost to the apex of the heart It 

 usually gives off a circumflex branch as it turns downward; this branch (Ramus 

 circumflexus) passes back in the coronary groove, and anastomoses with the cor- 

 responding branch of the left artery. 



The left coronary artery (A. coronaria sinistra) arises from the left posterior 

 smus of the aorta, emerges behind the origin of the pulmonary artery, and divides 

 into two branches. The descending branch (Ramus descendens) passes down the 



Pulmonnry veins 



Right coronary 

 artery 



Great coronary vein 



Left coronary artery, 

 circumflex branch 



Left coronary artery, 

 descending branch 



Great coronary vein 



Fig. 552. — Cardi.4c Vessels of Horse; Left Side. 



The dotted lines indicate part of the left coronary artery which is concealed by the left auricle. The ligamentum 



arteriosum is shown but not marked. 



left longitudinal groove toward the apex. The circumflex branch (Ramus circum- 

 flexus) runs backward in the coronary groove, in which it winds around to the right 

 side. 



2. COMMON BRACHIOCEPHALIC TRUNK 



The common brachiocephalic trunk (Truncus brachiocephalicus communis)^ 

 is a very large vessel which arises from the convexity of the arch of the aorta within 

 the pericardium. It is directed forward and upward. Its length in horses of 

 medium size is usually about two inches (ca. 5 cm.), but it is sometimes only half 

 an inch or less (ca. 1 cm.). It is crossed on the left by the left vagus and cardiac 

 nerves, and the left recurrent nerve runs between it and the trachea. It divides 

 opposite to the second intercostal space or third rib into the brachiocephalic and 

 left brachial arteries. 



The brachiocephalic artery (A. brachiocephalica) is directed forward and some- 

 what dorsally in the anterior mediastinum, beneath the trachea. Opposite the 

 first rib it gives off the bicarotid trunk and is continued as the right brachial artery. 

 The latter (A. subclavia dexter) turns ventrally and bends around the anterior 



^ Also known as the anterior aorta. 



