630 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



aortse. Here is forms three pouch-like dilatations, the sinuses of the aorta. These 

 correspond to the cusps of the aortic valve, and the coronary arteries arise from the 

 left posterior and anterior sinuses. At the arch the diameter is about two inches 

 (ca. 5 cm.), and beyond this it diminishes rather rapidly in width. 



It is convenient to divide the aorta into thoracic and abdominal parts. The 

 thoracic aorta (Aorta thoracica) (Figs. 553, 554) lies within the pericardium to the 

 point of attachment of the ligamentum arteriosum, and is enclosed with the pulmon- 

 ary artery in a prolongation of the epicardium. Beyond this it is between the two 

 pleural sacs. It is crossed on the right by the oesophagus and trachea, on the left 

 by the left vagus nerve. The left recurrent nerve winds around the concavity of the 



Right branch of 



pulmonary 



Pulmonary veuis artery 



Vena azygos 





Great coronary vein- 



Small coronary vein 



Rigid coronary artery 



Veins are black, arteries white. 



Fig. 551. — Cardiac Vessels of Horse; Right Side. 



The circumflex branch of the coronary artery is largely concealed by the great coronary 

 vein. 



arch from the lateral to the medial side, and the vena azygos and thoracic duct lie 

 along the dorsal part of its right face. The trachea causes it to deviate to the left, 

 but beyond this it becomes median. The abdominal aorta (Aorta abdominalis) 

 (Fig. 575) is related dorsally to the lumbar vertebrae, the ventral longitudinal 

 ligament, and the left psoas minor muscle; in the hiatus aorticus it is related to the 

 cisterna chyli. On its right is the posterior vena cava, and on its left the left kidney 

 and ureter. 



BRANCHES OF THE THORACIC AORTA 

 I. CORONARY ARTERIES 



The two coronary arteries, right and left, are distributed almost entirely to 

 the heart, but send some small twigs to the origins of the great vessels. 



The right coronary artery (A. coronaria dextra) arises from the anterior sinus 

 of the aorta. It passes forward between the conus arteriosus and the right auricle 



