CHAP, in.] METABOLIC PROCESSES OF THE BODY. 741 



which, taking origin at the surface of the lobule from the inter- 

 lobular portal veinlets, are disposed in a network with meshes 

 elongated in a radial direction, and converge at the centre of the 

 lobule to form the intralobular veinlet falling into the sublobular 

 (hepatic) vein, and secondly of radiating columns of cells filling up 

 the radiating meshes of this vascular network. Hence in a section 

 of a hardened and prepared uninjected liver, in which the blood 

 vessels are largely emptied, the areas of the sections of lobules are 

 indicated by the radially converging columns of cells, and (according 

 to the animal employed) are more or less distinctly marked out by 

 the septa of connective tissue, in which may be seen here and 

 there the lumina of the larger interlobular veins. In lobules, in 

 which the section has passed through the middle of the lobule, the 

 lumen of the central intralobular vein will also be visible ; but 

 often the section will cut a lobule so superficially as to miss the 

 intralobular vein altogether ; and it is only when the section 

 happens to pass through the middle of the lobule in the plane of 

 the long axis of the flask, that the origin of the intralobular vein 

 in the middle of the body of the flask and its course along the 

 neck to the sublobular vein is displayed. 



447. If the section be extensive enough there may be seen 

 here and there sections of the portal vein, hepatic artery and bile- 

 duct running in Glisson's capsule. Sections of the branches of 

 the hepatic vein formed by the union of sublobular veins may also 

 be seen. These may be recognised by the absence or by the 

 extreme scantiness of any connective-tissue wrapping to the vein, 

 even in the case of the larger branches. The wall of the vein 

 too is very thin and consists of hardly more than the tunica 

 intima resting on a thin connective-tissue basis, muscular fibres 

 being so very scanty that the tunica media may be said to be 

 absent. 



The walls of the portal vein on the contrary are thick and 

 muscular ; the trunk is more abundantly supplied with muscular 

 fibres than is any other vein in the body ; and the branches within 

 the liver are, in diminishing degree, thick and muscular. This 

 is intelligible when we reflect that the blood is distributed into 

 capillaries from the portal vein as from an artery, and that the 

 portal vein is like an artery subject to vaso-motor impulses. 

 Neither in the trunk nor in the branches (except in the small 

 veins of the intestinal walls) are any valves present, and these are 

 also absent from the branches of the hepatic vein. 



The branches of the hepatic artery are very much smaller than 

 the branches of the portal vein, and even much smaller than the 

 branches of the. bile-duct in company with which they run. As 

 they proceed in their course they supply the walls of the portal 

 veins and of the bile-ducts arid the substance of Glisson's capsule, 

 and eventually discharge their blood into the portal veinlets. It 

 has been maintained that some of the finer branches run directly 



