THE LIVER. 1057 



Vessels. The blood-supply of the liver follows a double course through the 

 portal vein and hepatic artery. The greatest amount of blood flowing through 

 the liver, thus differing from other organs, comes from the veins of the digestive 

 tract and of the spleen, which unite into a great vessel, the vena portarum or portce. 



The hepatic artery and portal vein, accompanied by numerous lymphatics and 

 nerves, ascend to the transverse fissure between the layers of the gastro-hepatic 

 omentum. The hepatic duet, lying in company with them, descends from the 

 transverse fissure between the layers of the same omentum. The relative position 

 of the three structures is as follows : the hepatic duct lies to the right, the hepatic 

 artery to the left, and the portal vein behind and between the other two. Thev 

 are enveloped in a loose areolar tissue, the capsule of Glisson, which accompanies 

 the vessels in their course through the portal canals in the interior of the organ. 



In the transverse fissure this portal vein splits into two trunks, the right and 

 left, for lobes of the same name. At the point of division is an enlargement, the 

 sinus vena? portce. They enter the liver substance and subdivide dichotomously into 

 smaller branches, which do not anastomose. They end in the interlobular connec- 

 tive tissue in three to five twigs, and form a rich plexus around each lobule, inter- 

 lobular '-//<*. These lose themselves in a capillary network, which penetrates the 

 lobule in a ray-shaped manner, and are collected at its centre into a little vein, the 

 vena centralis or mtralobufar vein. These are the roots of the hepatic veins. 



The characteristic point of the blood-current of the portal system consists in 

 this : it must first pass through a capillary circulation before it enters the inferior 

 vena cava. 



Accompanying the portal vein is the hepatic artery, a branch of the coeliac 

 axis, which divides at the transverse fissure into a right and left branch. The 

 twigs of the chief branches follow those of the portal vein, which accompany them 

 singly or doubly. The hepatic artery supplies chiefly the connective tissue and 

 the capsule of the liver. In the serous covering it anastomoses with the phrenic 

 and internal mammary arteries. 



The intralobular veins form, so to speak, the pedicles of the lobules, and, after 

 their exit from each empty at an acute angle into bigger veins, the sublobular. 

 These larger veins unite with each other and form numerous valveless hepatic veins, 

 which, draining the blood from the circulation of the portal vein and hepatic 

 artery, make their way to the posterior surface of the liver and empty, as three 

 large trunks and a number of small ones, into the vena cava. These hepatic veins 

 have no cellular investment, and their walls are directly adherent to the surround- 

 ing liver substance, while the branches of the portal vein, hepatic artery, and 

 hepatic duct are enclosed by loose connective tissue, and the three go together in 

 a portal canal. 



"V\ hen the arterial, portal, and biliary twigs are seen in the same connective tissue 

 sheath, the portal twigs are the strongest, and the arteries have the smallest lumen. 



On section of a piece of liver the open solitary holes are the cut hepatic veins, 

 unable to collapse on account of their close relation to the liver-tissue. For this 

 reason hemorrhage is so dangerous in wounds of the liver. The branches of the 

 portal vein collapse on cross-section. 



According to Sappey. there are five sets of accessory portal veins. The liver 

 does not receive all its blood from the hepatic artery and vena portse. 



The first group occupies the lesser omentum, and consists of venules from the 

 lesser curvature of the stomach. When the pyloric vein rises high it joins this 

 group, which is distributed to the lobes just in front of and just behind the trans- 

 verse fissure. 



The second group is more important, and consists of twelve to fifteen little veins 

 rising from the fundus of the gall-bladder and distributed to the fossa vesicalis. 

 Two cystic veins here usually open into the right branch of the portal vein. 



The third group includes all the venules rising in the walls of the portal vein, 

 hepatic artery, and hepatic duct. They lose themselves in the subjacent lobules. 



The fourth group consists of veins descending from the middle portion of the 



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