The vaginal branches (fig 36, 3, fig. are the small veins which off by the portal trunks during their passage through the portal canals, and which are intended to convey their blood into the substance of the lobules. In the cellular sheath of Glisson's capsule which surrounds the portal vein, they inosculate freely with each other and form, together with the va ginal branches of the duct and artery, a vascu lar plexus, named from its situation the vaginal plexus. This vaginal plexus establishes a com munication between the vaginal veins through out the portal canals, and serves to equalise the supply of blood to the lobules. Opposite each interlobular space an interlobular vein is given off, which enters between the lobules and rami fies in the interlobular fissures. In the larger portal canals (fig. 36,) the vaginal plexus com pletely surrounds the portal vein, hepatic duct and hepatic artery, and the interlobular spaces are supplied solely with branches which are derived from its ramifications. But in the smaller por tal canals (fig. 37, fig. 38) the capsule of Ohs son, upon which the plexus chiefly depends, is situated only upon that side of the vein, on which the duct and artery are placed, and the vaginal plexus consequently follows the same disposition. On the opposite side the portal vein being in contact with the lobules, gives off interlobular branches directly to the spaces. If the portal vein (fig. 38) be laid open in this situation, the form of the lobules bounded by the interlobular fissures will be distinctly ap parent through its coats, and the openings of the interlobular veins will be found to correspond with the interlobular spaces.
The interlobular veins enter the intervals of the lobules through the interlobular spaces and divide into numerous minute branches, which ramify in the capsules of the lobules and then enter their substance. They cover with their ra mifications the whole external surface of the lo bules with the exception of their bases, and of those extremities of the superficial lobules which appear upon the surfaces of the liver. The interlobular veins communicate freely with each other and with the corresponding branches of adjoining lobules, and establish a general portal anastomosis of the freest kind through out the entire liver. When the portal vein is well injected, these veins form a series of inos culations which surround all the lobules and give to the surface of the organ the appearance of a vascular network composed of irregularly pentagonal and hexagonal meshes. If the vein be only partially injected the interlobular vein in the interlobular space is alone filled, and the branches which it sends off into the neighbour ing interlobular fissures not proceeding so far as to inosculate and form meshes, have a radiated appearance and resemble a number of minute stell; these are the slellated vessels of anatomists.
The lobular veins are derived from the inter lobular veins ; they form a plexus within the lobule, and converge from the circum ference towards the centre, where they terminate in the minute branches of the intralobular vein. " This plexus, interposed between the inter lobular portal veins and the intralobular hepatic vein, constitutes the venous part of the lobule, and may be called the lobular venous plexus." (fig. 39). The irregular islets of the substance of the lobules seen between the meshes of this plexus by means of the microscope are the acini of Malpighi, and are shown by Kiernan to be portions of the lobular biliary plexus.
The portal vein collects the venous blood from the chylopoietic viscera, and then circu lates it through the lobules; it likewise receives the venous blood which results from the distri bution of the hepatic artery to the structures of the liver; these two sources of supply constitute the two origins of the portal vein, the abdominal origin and the hepatic origin.
The interlobular ducts ramify upon the cap sular surface of the lobules with the branches of the portal vein and hepatic artery. Kiernan finds these ducts to communicate freely with each other, for he says, " If the left hepatic duct be injected with size or mercury, the injec tion will return by the right duct without extra vasation and without passing into other vessels, and the injection will be found in the inter lobular and vaginal ducts as well as in the trunks. This communication between the two ducts does not take place like that which exists between the and leirrrteries through the medium of the vaginal branches of the trans verse fissure, the injection being found in inter lobular branches arising from the right duct. From this experiment, which I have frequently repeated with the same result, it appears that the right and left duct anastomose with each other through the medium of the interlobular ducts. This experiment does not always suc ceed, which probably arises from the quantity of bile contained in the ducts." The lobular ducts entering theolobule by its circumference divide and subdivide into minute branches which anastomose with each other and form a " reticulated plexus," the lobular biliary plexus (fig. 40). This plexus consti The hepatic duct bifurcates in the transverse fissure into two branches, which enter the right i and left lobes of the liver and subdivide into smaller branches, and the smaller branches accompany the divisions of the portal vein and hepatic artery through the portal canals to their I ultimate distribution in the lobules. The branches of the hepatic duct, like those of the portal vein are divisible into the vaginal, inter 1 lobular, and lobular ducts.