The lobules present considerable variety of form dependent upon their situation and upon the manner in which they are examined. For instance, the section of a lobule divided trans versely has an irregularly pentagonal or hexa gonal figure, and longitudinally a foliated ap pearance. The lobules of the centre of the liver are angular and smaller than those of the surface, on account of the pressure to which, from their position, they are submitted by sur rounding lobules. They are also more an-. gular in some animals than in man. The sur face of the liver of the cat, in which the portal vein is injected, has a beautiful reticulated ap pearance produced by angular meshes of an hexagonal figure; the hexagonal outline being formed by the interlobular fissures, reddened by the injection in the minute branches of the portal vein, and the included area by the lo bule viewed upon its transverse diameter. a section of the liver made from the free margin to the posterior border in the direction of the hepatic veins, the lobules are found to be larger than in a section made transversely to those vessels. The lobules of the exterior, par ticularly on the concave side and posterior border, are for the same reason larger from lying obliquely to the surface and correspond ing in direction with the course of the sub lobular veins. They are also more rounded from the absence of compression by surround ing lobules. But one appearance described by Kiernan is peculiarly characteristic of the lo bules which form the surface of the liver, the superficial lobules. The word surface in this instance does not refer simply to the periphery of the organ, but also to the various canals channelled through its interior for the passage of the portal vein, hepatic ducts, and hepatic artery, and also for the main trunks of the he patic vein, " all these canals being" as it were " tubular inflections inwards of the super ficies of the liver." The superficial lobules (fig. 34, 2, fig. 35) are not terminated by a rounded extremity like those of the centre, but are flat and apparently incomplete, and as though cut across by a transverse incision. This peculiar form gives to the anatomist a natural surface which affords all the advantages for ob servation of a transverse section, and enables him to detect by external examination the rela tive condition of both the central portion and surface of the lobule. In these lobules also the intra-lobular hepatic vein, instead of being entirely concealed within the lobule, commences directly from the flat surface. A knowledge of this structure, says Kiernan, "enables us in in jecting the hepatic veins to limit the injection to this system of vessels, which is effected by withdrawing the syringe when the injection ap pears in minute points upon the surface of the liver." Occasionally double lobules, or lobules having two intra-lobular veins, are seen upon the surface.
" Each lobule," according to Kiernan, "is composed of a plexus of biliary ducts, of a venous plexus formed by branches of the portal vein, of a branch (intra-lobular) of art hepatic vein, and of minute arteries; nerves and absorb ents, it is to be presumed, also enter into their formation, but cannot be traced into them." " Examined with the microscope, a lobule is apparently composed of numerous minute bodies of a yellowish colour, and of various forms, connected with each other by vessels. These minute bodies are the acini of Malpighi." " If an uninfected lobule be examined and contrasted with an injected lobule, it will be found that the acini of Malpighi in the former are identical with the injected lobular plexus of the latter, and the bloodvessels in both will be easily distinguished from the ducts." Gussost's CAPSULE is the web of cellular tissue which envelopes the hepatic artery, portal vein, and ductus communis choledochus during their passage through the right border of the lesser omentum, and which accompanies them along the portal canals and interlobular fissures to their ultimate distribution in the substance of the lobules. It forms for each of the lobules a
distinct capsule which invests it on all sides with the exception of its base, and is then ex panded over the whole of the exterior of the organ, constituting the proper capsule of the liver. Glisson's capsule serves to maintain the portal vein, hepatic artery, and hepatic ducts in connection with each other, and attaches them also to the surface of the portal canals; it con nects the trunks of the hepatic veins to the surface of the canals in which they run ; it sup ports the lobules and binds them together, and by its exterior expansion it invests and protects the entire organ. But Glisson's capsule, ob serves Kiernan, " is not mere cellular tissue ; it is to the liver what the pia mazer is to the brain; it is a cellulo-vascular membrane, in the vessels divide and subdivide to an extreme degree of minuteness ; which lines the portal canals, forming sheaths for the larger ves sels contained in them, and a web in which the smaller vessels ramify ; which enters the inter lobular fissures, and with the vessels forms the capsules of the lobules, and which finally enters I the lobules, and with the bloodvessels expands itself over the secreting biliary ducts. Hence arises a natural division of the capsule into three portions, a vaginal, an interlobular, and a lobu lar portion." The vaginal portion If the capsule is loose and abundant ; it occupies the portal canals and incloses the portal vein, hepatic duct, and hepatic artery. In the larger canals (fig. 36, 8,) it completely surrounds these vessels, but in the smaller ones (fig. 37,) is situated only on that side of the portal vein upon which the duct and artery are placed, the opposite side of the vein being in contact with the capsular surfaces of the lobules. It constitutes a me dium for the ramification of the vaginal plexus formed by the vein, artery, and duct, previously to their entrance into the cellular interval of the interlobular fissures.
The interlobular portion forms the cellular capsule for each of the lobules and the bond of uMon between their contiguous surfaces. It supports the plexiform ramifications of the por tal vein, hepatic artery, and duct, and is the medium of vascular communication between all the lobules of the liver.
The lobular portion forms sheaths for the minute vessels which enter the lobules, and a cellular parenchyma for the substance of those bodies.
The portal vein is formed by the union of the venous trunks which return the blood from the cbylopoietic viscera, viz., the superior and in ferior mesenteric, the splenic, and gastric veins. Commencing behind the pancreas where all these veins converge, the portal trunk ascends along the right border of the lesser omentum, lying behind the hepatic artery and ductus coin munis choledochus to the transverse fissure. [At the transverse fissure it bifurcates into two 'trunks which enter the right and left lobes, divide and subdivide as they take their course through the portal canals, until they are ultimately lost in the substance of the lobules. The branches of the portal vein are accompanied throughout their course by branches of thehepatic duct and hepatic artery, and they are inclosed and connected to the capsular surfaces of the lobules forming the portal canals, by Glisson's capsule. The branches of the portal vein are divisible into vaginal, interlobular, and lobular.