56 DISSECTION OF THE VASCULAR SYSTEM. 



C. THE HEPATIC PORTAL SYSTEM OF VEINS. 



The Portal Vein is the large vein lying in the mes- 

 entery which collects venous blood from the stomach, 

 pancreas, spleen and intestines, and passes into the 

 under side of the liver. Within this organ it again 

 breaks up into capillaries, the blood from which is 

 finally collected into the hepatic veins which empty 

 into the post-cava. The portal can easily be found on 

 the under side of the liver; it is formed from two 

 large branches, one from the intestines and one from 

 the spleen, pancreas and stomach. It breaks up into 

 branches which enter the different lobes of the liver. 



D. VEINS BELONGING TO THE SYSTEM OF 



THE PR^-CAVA. 



1. The Prse-cava {superior vena-cava). A descrip- 

 tion of this vein has been given in the chapter on the 

 dissection of the thoracic viscera. 



2. The Vena Azygos. Make out again the course 

 of this vein, and the point where it opens into the 

 prae-cava. 



3. The Vertebral Veins. The vein on the riffht 

 side opens into the cava anterior to the azygos. Trace 

 it back to its emergence from the vertebral canal of 

 the spinal column. The vein on the left side opens 

 into the left brachio-cephalic or innominate vein. 

 They bring back blood from the brain, etc. 



4. The Sternal Veins. The vein on the right side 

 opens into the prge-cava anterior to the vertebral. 

 On the left side it opens into the brachio-cephalic be- 

 yond the vertebral. They bring back blood from the 

 sternum and the anterior wall of the thorax. 



