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Structure. The substance of the liver is composed of lobules held together by extremely 

 fine areolar tissue, and of the ramifications of the portal vein, hepatic duct, hepatic artery, hepatic 

 veins, lymphatics, and nerves, the whole being invested by a serous and fibrous coat. 



The serous coat (tunica serosa) is derived from the peritoneum, and invests the greater part 

 of the surface of the organ. It is intimately adherent to the fibrous coat. 



The areolar or fibrous coat (capsula fibrosa [Glissoni]) lies beneath the serous investment and 

 covers the entire surface of the organ; it is called the capsule of Glisson; the latter term has also 

 been retained for the heavy fibrous tissue, at the portal fissure, that envelops and accompanies 

 the vessels into the liver. It is difficult of demonstration, excepting where the serous coat is 

 deficient. The areolar tissue which surrounds and binds together the liver lobules is continuous 

 with the areolar coat. 



The Lobules 1 (lobuli hepatis) (Fig. 1076). The lobules form the chief mass of the hepatic 

 substance; they may be seen either on the surface of the organ or by making a section through 

 the gland. They are small granular bodies about the size of a millet seed, measuring from one- 

 twentieth to one-tenth of an inch in diameter. In the human subject their outline is very irreg- 

 ular, but in some of the lower animals (for example, the pig) they are well defined, and when 

 divided transversely have a polygonal outline. If divided longitudinally they are more or less 

 foliated or oblong. The bases of the lobules are clustered around the smallest radicles of the 

 hepatic veins (sublobular veins}, to which each is connected by means of a small branch which 

 issues from the centre of the lobule (intralobular vein). The remaining part of the surface of 

 each lobule is imperfectly isolated from the surrounding lobules by a thin stratum of areolar tissue 

 in which are ducts and a plexus of vessels, the interlobular plexus (Figs. 1074 and 1075). In 

 some animals, as the pig, the lobules are completely isolated from one another by this interlobular 

 areolar tissue. 



If one of the sublobular veins be laid open, the bases of the lobules may be seen through the 

 thin wall of the vein on which they rest, arranged in the form of a tesselated pavement, the 

 centre of each polygonal space presenting a minute aperture, the mouth of an intralobular vein 

 (Fig. 1072). 



FIG. 1071. The hepatic cells at different stages of digestion. (Heidenhain.) 



Microscopic Appearance. Each lobule is composed of irregular, anastomosing chains of cells, 

 hepatic cells (Fig. 1071), surrounded by a dense capillary plexus, composed of vessels which 

 penetrate from the circumference to the centre of the lobule, and terminate in a single straight 

 central vein, which runs through its centre, to open at its base into one of the radicles of the 

 hepatic vein. These structures are supported by a delicate meshwork of retiform connective 

 tissue. Within the chains of the cells are the minute commencements of the bile ducts. There- 

 fore, in the lobule we have all the essentials of a secreting gland; that is to say, (1) cells, by 

 which the secretion is formed; (2) bloodvessels, in close relation with the cells, containing the 

 blood from which the secretion is derived; and (3) ducts, by which the secretion, when formed, 

 is carried away. Each of these structures will have to be further considered. 



1. The hepatic cells are epithelial in nature and of more or less cuboidal or polygonal form. 

 They vary in size from the T oV?r to the -^^ of an inch in diameter; they consist of a granular 

 protoplasm without any cell wall, and contain one or sometimes two distinct nuclei. In the nu- 

 cleus is a highly refracting nucleolus with granules. Embedded in the protoplasm are numerous 

 brownish particles, the coloring matter of the bile, oil globules, and glycogen granules in varying 

 quantities. Secretory capillaries are to be found in the cells. The cells adhere together by 

 their surfaces so as to form rows, which radiate from the centre to the circumference of the 

 lobules. As stated above, they are the chief agents in the secretion of the bile. 



2. The Bloodvessels. The blood in the capillary plexus around the liver cells is brought 

 to the liver principally by the portal vein, but also to a certain extent by the hepatic artery. For 

 the sake of clearness the distribution of the blood derived from the hepatic artery may be con- 

 sidered first. 



The hepatic artery, entering the liver at the transverse fissure with the portal vein and hepatic 

 duct, ramifies with these vessels through the portal canals. It gives off vaginal branches which 



1 According to Mull (Jour, of Anat., vol. v, No. 3), the lobule as here described is not his structural unit, which 

 refers to all the tissue surrounding each terminal branch of the portal vein. 



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