352 DISSECTION OF THE RABBIT. 



(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. 



In dissecting the veins it is convenient to follow them from 

 the larger to the smaller trunks, and they will be described in 

 this order ; it must be remembered, however, that the flow of 

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

 cut the veins, especially at the anterior end of the thorax, as 

 the blood obscures the dissection, and the vessels themselves, 

 when empty, are difficult to follow, owing to the thinness of 

 their walls. If by chance a large vein is cut, it must be liga- 

 tured immediately, to stop the bleeding. 



During the dissection of the veins take great care not to 

 damage or remove the arteries or nerves lying near them. 



1. The system of the venae cavse. 



a. The right anterior vena cava has already been 



seen. It is formed by the union of the jugular 



and subclavial veins, immediately in front of 



the first rib. 



' i. The azygos cardinal vein is a median vein which 



runs forwards in the mid-dorsal line of the 



thorax, lying close to the vertebral column 



and along the right side of the aorta. It 



receives branches from the posterior seven 



or eight intercostal spaces of both sides of 



the body. Opposite the level of the auricles 



it passes round the right side of the oesophagus 



and trachea, to open into the vena cava close 



to the auricle. 



ii. The right anterior intercostal vein is a small 

 vein returning blood from the anterior four 

 or five intercostal spaces of the right side, 

 and opening into the vena cava just in front 

 of the azygos vein. 



