342 DISSECTION OF THE RABBTT. 



(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 a,rterial blood 

 from the lungs to the left auricle. 



In dissecting the veins it is convenient to folloiu them from 

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

 this order ; it must he rememhered, however, that the floiv 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 tualls. If by chance a large vein is cut, it must be 

 ligatured 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 therti. 



1. The system of the venae cavae. 



a. The right anterior vena cava has already been 

 seen. It is formed by the union of the jugular 

 and subclavian 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. 



