1200 THE DIGESTIVE SYSTEM. 



The circulation within the liver is, therefore, arranged differently from that of other 

 glands, and in order to understand properly the structure of the liver, it is necessary to 

 give some account of the relations which it presents to the blood vessels which pass to and 

 from it. 



The vena portae and the arteria hepatica propria pass up to the liver between the two 

 layers of the hepato-duodenal ligament, anterior to the foramen epiploicum. Here they 

 are accompanied by the bile-duct, which lies to the right, whilst the artery is placed to 

 the left, and the portal vein posterior to both. In this order they enter the porta 

 hepatis, and there become rearranged, so that the vein lies behind, the artery in the 

 middle, and the duct in front. Each breaks up into two chief branches a right and 

 a left and several smaller ones, which enter the liver substance, surrounded by a 

 prolongation of the connective tissue coat of the liver (O.T. Glisson's capsule). Within 

 the organ the three vessels run and divide together, so that every branch of the portal 

 vein is accompanied by a corresponding (but much smaller) branch of the hepatic artery 

 and of the hepatic duct : and the three, surrounded by a prolongation of the fibrpus capsule, 



Hepatic 

 cells ' 



Veins Bile-ducts 



FIG. 943. DIAGRAM illustrating the arrangement of the blood-vessels (on left) and of the hepatic cells and 

 bile-ducts (on right) within a lobule of the liver. The first diagram shows the interlobular veins 

 running around the outside of the lobule, and sending their capillaries into the lobule to join the central 

 vein. In the second diagram the bile capillaries are seen, with the hepatic cells between them, 

 radiating to the periphery of the lobule, where they join the interlobular bile-ducts. 



and accompanied by branches of the hepatic nerves and lymph vessels, run in special 

 tunnels of the liver substance, which are known as portal canals (Fig. 941, B). 



The hepatic artery has but a small part to play in the hepatic circulation within the 

 liver, and it is distributed in the following way. Reaching the porta hepatis of the liver 

 it breaks up into branches which accompany the branches of the bile-ducts and of the 

 portal vein into the interior, and it supplies minute branches, known as the vaginal and 

 capsular branches, to the fibrous tissue which accompanies these vessels, and which also 

 invests the surface of the liver. The terminal branches of the artery end in the branches 

 from the portal vein which go to the liver lobules. 



The portal vein within the liver divides, like an artery, into numerous branches, which 

 pass in all directions in company with small branches of the bile-ducts. 



Finally, the small terminal branches form an elaborate mesh work, whose vessels 

 anastomose freely with one another, around the periphery of the liver lobules, and are 

 known as interlobular vessels. From this meshwork small capillary-like channels pass 

 into the interior of each lobule between columns of liver cells, towards a channel placed in 

 the centre of the lobule, called the central vein. From the central veins the blood is 

 carried into larger channels or sublobular veins, which pass to the hepatic veins, and so 

 to the inferior vena cava. 



The hepatic veins, formed by the union of the sublobular vessels, gradually unite with 

 one another, and run towards the inferior vena cava. Their mode of termination is 

 variable, but presents the following general arrangement : The left lobe is drained by a 

 vessel which joins the superior part of the inferior vena cava. The right lobe is drained by 

 one or two vessels which join the superior part of the inferior vena cava, and by a series of 

 small vessels, 4 to 12 in number, which pass from the inferior portion of the right lobe to 

 the inferior vena cava. The caudate lobe and central portion of the liver are drained by 



