630 BLOOD-VASCULAR SYSTEM OF THE HORSE 
aorte. 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 
(ea. 5 em.), 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 cesophagus 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 veins 
Vena azygos 
Great coronary vein 
Small coronary vein 
s : 
Z Right coronary artery 
Fie. 551.—Carpiac Vessets or Horse; Ricut Sipe. 
The circumflex branch of the coronary artery is largely concealed by the great coronary 
vein. 
Veins are black, arteries white. 
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 vertebre, 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 
1, 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 
ANATOMY 
