388 



THE LIVER. 



d a 



various sizes, and join together. 



Blood-vessels. — The hepatic veins commence in the centre of each 

 lobule by the convergence of its capillaries into a single independent 



Fig. 275. 



Fig. 275. — Longitudinal Section of a 

 Portal Canal, containing a Portal 

 Vein, Hepatic Artery, and Hepatic 

 Duct, from the Pig (after Kier- 

 nan). About 5 diameters. 



P, branch of vena portre, situated in 

 a portal canal, formed amongst the he- 

 patic loliules of the liver ; ^j, p, larger 

 Ijranches of portal vein, giving oft' 

 smaller ones (?', i), named interlobular 

 veins ; there are also seen within tlie 

 large 230i'tal vein numerous orifices of 

 interlobular veins arising directly from 

 it ; a, hepatic artery ; d, biliary dnct ; 

 at c, c, the venous -wall has been par- 

 tially removed. 



intralobular vein (figs. 276, h ; 

 277, 2 ; and 278, 1), as already 

 stated. These minute intralobu- 

 lar veins open at once into the 

 sides of the adjacent sublobular 

 veins (fig. 277, 1), which are of 

 Uniting into larger and larger 

 vessels, they end at length in hepatic venous trunks, which receive no 

 intralobular veins. Lastly, these venous trunks, converging towards the 

 posterior border of the liver, and receiving in their course other sub 

 lobular veins, terminate in the vena cava inferior, as already described. 

 In this course the hepatic veins and their successive ramifications are 

 unaccompanied by auy other vessel. Their coats are thin ; the sub- 

 lobular branches adhere immediately to the lobules, and even the 

 larger trunks have but a very slight areolar investment connecting 

 them to the substance of the liver. Hence the divided ends of these 

 veins are seen upon a section of the liver as simple open orifices, the 

 thin wall of the vein being surrounded closely by the solid sutfstance of 

 the gland. 



The portal vein and hepatic artery, which, accom]'>anied by the emerg- 

 ing hiliarii ducts, enter the liver at the transverse fissure, have a totally 

 diil'erent course, arrangement, and distribution, from the hepatic vein. 

 Within the liver the branches of these three vessels lie together in 

 certain canals, called portal ccinals, which are tubular passages formed 

 in the substance of the gland, commencing at the transverse fissure, 

 and branching upwards and outwards from that part in all directions. 

 Each portal canal (even the smallest) contains one principal branch of 

 the vena portee, of the hepatic artery, and of the biliary duct (fig. 275) ; 

 the whole being invested within the larger portal canals by the capsule 

 of Glisson. 



The portal vein subdivides into branches which ramify hetween the 

 lobules, anastomosing freely aronnd them, and are named interlohiilar 

 or peripheric veins. From these, still finer vessels pass into the lobules 

 at their circumference (fig. 278, 3), and end in the capillary network 

 from which the intralobular or central (hepatic) veins take origin. 



