314 DISSECTION OF THE BABBIT 



veins on each side, which converge to open 

 into the dorsal surface of the left auricle. 



d. Vessels arising from the left ventricle. 



i. The aorta conveys arterial blood from the heart 

 to all parts of the body. It arises from the 

 middle of the base of the heart, dorsal to 

 the root of the pulmonary artery, runs for- 

 wards about half an inch, and then arches 

 over to the left side, and runs back along the 

 left side of the vertebral column. Its thoracic 

 portion is readily seen on turning aside the 

 left lung. 



The ductus arteriosus is a ligamentous 

 band, connecting the aorta with the pulmonary 

 artery, just before the division of the latter 

 into right and left branches. During em- 

 bryonic life it forms a tubular connection 

 between the two vessels. 



B. The Veins. 



The veins form three distinct systems, communicating 

 with one another only through capillaries, and containing 

 different kinds of blood. 



(1) The first of these systems consists of the three venaB 

 cavae, with the veins openmg into them : these bring to the 

 right auricle venous blood from the body generally, and from 

 the liver. 



(2) The second or portal system collects the blood from 

 the walls of the alimentary canal, and from the pancreas and 

 spleen, and conveys it to the liver. 



(3) The third or pulmonary system conveys arterial blood 

 from the lungs to the left auricle. 



Ill dissecting the veins it is convenient to follow them from 

 the larger to the smaller trunks, and they will he described 

 in this order ; it must be remembered, however, that the floto 

 of blood is in the reverse direction. Care must be taken not 

 to cut the veins, as the blood obscures the dissection, and the 



