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 
sinus of the aorta, emerges behind the origin of the pulmonary artery, and divides 
into two branches. The descending branch (Ramus descendens) passes down the 
Pulmonary veins 
Great coronary vein 
Left coronary artery, 
circumflex branch 
Right coronary \ 
artery 
Left coronary artery, 
descending branch 
Great coronary vein 
Fie. 5 
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. 
2.—Carpiac VEesseLs oF Horse; Lert Sipe. 
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 em.), but it is sometimes only half 
an inch or less (ca. 1 em.). 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 
1 Also known as the anterior aorta. 
