536 SPECIAL PHYSIOLOGY. 



est portal canals, the parts are not so distinct. The hepatic veins do 

 not lie in the portal canals, but pursue a separate course through the 

 liver, the branches of these being seen, on a section, passing along 

 through the gland, immediately surrounded by the lobules. As the 

 portal veins diverge from the portal fissure, whilst the hepatic veins 

 converge to the posterior border of the gland, their branches cross 

 each other ; moreover, they have very different relations to the hepatic 

 lobules. 



Each minute lobule has one aspect, which is named its base, whilst 

 its other surfaces are called its sides. The bases of all the lobules rest 

 upon the so-called sublobular veins, which are branches of the hepatic 

 vein, the inner surface of which, as shown when they are opened, is 

 marked by the polygonal outlines of the bases of the lobules. When 

 divided transversely, the lobules are polyhedral; when cut longitu- 

 dinally, they present a foliated appearance, and are seen to be sup- 

 ported on the sublobular hepatic veins, like sessile leaves upon a leaf- 

 stalk. 



The sides of the lobules are turned towards each other in the inter- 

 lobular spaces, towards the portal canals, or to the surface of the liver. 

 The portal veins, ramifying in the portal canals, give off branches 

 which enter the interlobular spaces, and are hence named interlobular 

 veins ; from these, still finer branches penetrate the sides of the lob- 

 ules, and end, within them, in the so-called lobular venous plexus, or 

 lobular capillary network. From this network proceeds a small vein, 

 occupying the centre of each lobule, named the intra-lobular vein, and 

 belonging to the hepatic venous system ; it opens by a minute orifice, 

 situated in the middle of the base of the lobule, into the corresponding 

 sublobular vein. 



It will thus be seen, that the blood of the portal vein is conveyed, 

 by the portal interlobular veins, to the sides of the lobules, and thus 

 reaches their internal vascular plexus, from which it is collected by the 

 hepatic intralobular veins, and so passes out, at the bases of the lob- 

 ules, into the sublobular hepatic veins, by which it is ultimately con- 

 veyed away. 



From the peculiar distribution of the branches of the portal and 

 hepatic venous systems, in each lobule, it follows that a congested state 

 of either, influences the mottled color of the liver in a characteristic 

 manner. Thus when the hepatic system is congested, a rather frequent 

 occurrence, the centre of each lobule is dark, and the circumference 

 paler ; whilst in portal congestion, which is rare, and occurs chiefly in 

 children, the centre of each lobule is pale, and the marginal part dark. 

 From the great size of the portal vein, as compared with the hepatic 

 artery, it is evident that the liver is chiefly supplied by venous blood. 

 But even the arterial blood furnished to this organ, by the hepatic 

 artery, appears to become venous and portal, before it reaches the 

 plexus within the lobule. The hepatic artery is a nutrient vessel, sup- 

 plying the framework, and not the secreting tissue, of the liver; its 

 branches terminate in a capillary network, in the coats of the blood- 

 vessels and ducts, in the areolar tissue of the capsule of Glisson, the 

 interlobular tissue, and the areolar coat of the liver ; from these parts, 



