THE DIGESTION 



227 



into capillaries. Thus the portal vein (Latin porta, a gate, 

 since it enters under a kind of archway) both begins and 

 ends in capillaries, for it begins in the capillaries of the 

 digestive tract and ends in the capillaries of the liver. After 

 these capillaries have passed in among the cells, they unite 

 again to form the hepatic veins, which go directly to the 

 ascending vena cava. There is another large blood vessel 

 in the portal circulation. This is the hepatic artery, which 

 enters the liver directly from the aorta and supplies the 

 liver cells with arte- 

 rial blood with which 

 to repair themselves 

 and carry on their 

 work (Plate VII). 

 The capillaries from 

 this artery unite with 

 those of the portal 

 vein in forming the 



hepatic Vein. A COW'S FIG. 179. Diagrammatic Representation of Two 

 v . Hepatic Lobules. 



liver, cut in two, 



The left-hand lobule is represented with the intralobular 

 vein cut across: in the right-hand one the section takes 

 the course of the intralobular vein. /, interlobular 

 branches of the portal vein; h, interlobular branches 

 of the hepatic veins; s, sublobular vein; c, capillaries 

 of the lobules passing inwards. The arrows indicate 

 the direction of the course of the blood. The liver-cells 

 are represented in only one part of each lobule. 



shows in places small 

 gaping holes, which 

 are branches of the 

 hepatic veins. 



404. Minute Anat- 



omy of the Liver. If you examine the surface of a 

 piece of liver obtained from the butcher, you will find 

 it to be of a dark red color, and mottled over with 

 little areas, each measuring about one twentieth of an 

 inch across. These are the round lobules of the liver 

 arranged around a branch of the hepatic vein (Fig. 1/9). 

 The capillaries of the portal vein and hepatic artery and 

 the branches of the bile duct pass between these cells. 

 Study carefully Figure 180, which represents a segment of a 

 lobule. When you understand the circulation in a lobule, 



