?2 SCIENCE PRIMERS. [§ v. 



ourney should always pas«=* through the 

 jbllowing things in the following order ; 

 ight auricle, right ventricle, pulmonary 

 [^rtery, arteries, capillaries, and veins of the 

 tings, pulmonary vein, left auricle, left ven- 

 tricle, aorta, arteries, capillaries, and veins 

 iomewhere in the body, and either superior 

 >r inferior vena cava. That is the course of the 

 circulation. But there is something still to be added, 

 f^ong the many large branches, not drawn in the 

 liagram, given off by the aorta to the lower part of 

 he body, there are two branches which are drawn 

 ,nd which deserve special notice. 

 One is a large branch carrying blood to the tube 

 .Z., which is meant in the diagram to stand for 

 ihe stomach, intestines, and some other organs. This 

 •branch, like all other branches of the aorta, divides into 

 mall arteries, and these into capillaries, which again 

 re gathered up into veins, forming at last a large vein 

 inarked in the diagram V.P. and called the vena 

 )ortae or portal vein. Now the remarkable thing 

 s that this vein does not, like all the other veins, 

 /o straight to join the vena cava, but makes for 

 ;he liver, where it divides into smaller and smaller 

 Veins, until at last it breaks completely up in the liver 

 3nto a set of capillaries again. These capillaries gather 

 ibnce more into veins, farming at last the large trunk, 

 palled the hepatic^ vein, ZT. F!, which does what 

 ihe portal vein ought to have done but did not ; it 

 opens straight into the vena cava. 



The other branch of the aorta of which we are 

 ^peaking goes straight to the liver, and is called the 



•| I From ^/ar, liver J the vein of the liver. 



