THE VEINS 325 



(1). The first of these systems consists of the three venae 

 cavse, with the veins opening 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. 



In dissecting the veins it is convenient to follow them from 

 the la/rger to the smaller trunks, and they will he 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, 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 ligatured imrnediately to stop the bleeding. 



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. 



