FOOD AND DIGESTION. 337 



To understand the distribution of the blood-vessels in the liver, it 

 will be well to trace, first, the two blood-vessels and the duct which enter 

 the organ on the under surface at the transverse fissure, viz., the portal 

 vein, hepatic artery, and hepatic duct. As before remarked, all three 

 run in company, and their appearance on longitudinal section is shown 

 in fig. 268. Running together through the substance of the liver, they 

 are contained in small channels called portal canals, their immediate in- 

 vestment being a sheath of areolar tissue continuous with Glisson's cap- 

 sule. 



To take the distribution of the portal vein first : In its course through 

 the liver this vessel gives off small branches which divide and subdivide 

 between the lobules surrounding them and limiting them, and from this 

 circumstance called inter -\obulstf veins. From these small vessels a 

 dense capillary network is prolonged into the substance of the lobule, 



p 



Fig. 269 Capillary network of the lobules of the rabbit's liver. The figure is taken from a very 

 successful injection of the hepatic veins, made by Harting: it shows nearly the whole of two lo- 

 bules, and parts of three others ; p, portal branches Tunning in the interlobular spaces; h, hepatic 

 veins penetrating and radiating from the centre of the lobules. X 45. (Kolliker.) 



and this network gradually gathering itself up, so to speak, into larger 

 vessels, converges finally to a single small vein, occupying the centre of 

 the lobule, and hence called intra-lobular. This arrangement is well 

 seen in fig. 269, which represents a transverse section of a lobule. 



The small intra-lobular veins discharge their contents into veins 

 called 5^5-lobular (h h h, fig. 270), while these again, by their union, 

 form the main branches of the hepatic veins, which leave the posterior 

 border of the liver to end by two or three principal trunks in the infe- 

 rior vena cava, just before its passage through the diaphragm. The 

 swS-lobular and hepatic veins, unlike the portal vein and its companions, 

 have little or no areolar tissue around them, and their coats being very 

 thin, they form little more than mere channels in the liver substance 

 which closely surrounds them. 



The manner in which the lobules are connected with the suUobular 



