5 6 



ELEMENTARY PHYSIOLOGY 



arrangement of the small branches and capillaries of the four 



vessels of the liver. It will 

 now be convenient to trace 

 the branches of these vessels 

 separately, in order to learn 

 their relations to each other. 



The branches of the portal 

 vein give off small veins which 

 surround the lobules and separate 

 them from each other. These 

 small veins are consequently call- 

 ed the interlobular veins. The 

 interlobular veins give off still 

 smaller branches, which run to- 

 ward the centres of the lobules, 

 and give rise to a close network 

 of capillaries. These capillaries 

 then unite to form other small 

 veins which collect the blood and 

 convey it into vessels which oc- 

 cupy the centres of the lobules, and 

 which are called the intralobular 

 veins. The intralobular veins 

 then convey the blood to the 

 bases of the lobules, and into the 

 larger sublobular veins, around 

 which the lobules are placed. 

 The sublobular veins unite to 

 form the hepatic vein, which 

 vein carries the blood direct to 

 the ascending vena cava. Thus 

 the interlobular veins are the dis- 

 tributing branches of the portal 

 vein ; and the intralobular veins 

 and the sublobular veins may 

 be regarded as the collecting 

 branches of the hepatic vein ; the 

 two sets of branches being united 

 by the capillaries of the lobule. 



The hepatic artery, as already 

 stated, brings bright arterial blood 

 to the various structures of the 

 liver, for these structures, like 

 all other parts of the body, need 

 a supply of oxygen gas. The 

 branches of this artery are dis- 

 tributed like those of the portal 

 vein ; and the blood brought by 

 them is, after circulation through 



Fig. 143. Transverse Section of a capillary systems, returned either 

 small Portal Canal and its Vessels. into the subdivisions of the portal 



i, portal vein; 2> interlobular branches ; 3, other vein or into the capillary network 

 branches; 4, hepatic duct ; 5, hepatic artery. of the lobules. Thus the bright 



Fig. 142. Longitudinal Section of a 

 Portal Vein and Canal. Magnified 

 about 5 diameters. 



a, portions of the canal from which the vein has 

 been removed ; b, side of the portal vein in con- 

 tact with the canal ; c, the side of the vein which 

 is separated from the canal by the hepatic artery 

 and duct, with areolar tissue (Glisson's capsule) ; 

 d, internal surface of the portal vein, through 

 which are seen the outlines of the lobules and the 

 openings, e, of the inteilobular veins ; g, hepatic 

 artery ; h, hepatic duct. 



