Page:The New International Encyclopædia 1st ed. v. 12.djvu/391

LIVER. 347 LIVER. some of the lower animals, e.g. the pijr. each lobule of the liver is completely surrounded by this connective tissue, lu man the amount of connective tissue is small and does not form a complete investment for each lobule. The de- markation of the lobules is, therefore, not at all sharp. The structure of a liver-lobule may be described as follows: At the centre of each lobule is the central vein which is a branch of the hepatic vein. Passing out in a radiating manner from this central vein is a dense network of capillaries in the meshes of which lie the cords of liver-cells. These liver-cells are polyhedral in shape, granular, and contain rather large nuclei. In the connective tissue which lies at the junc- tion of three or more lobules is found the group of vessels known as the portal canal and con- sisting of the hepatic arteiy, the portal vein, and the bile-duet. The smaller bile-ducts consist of a single layer of columnar epithelium surrounded by a thin layer of connective tissue. In the larger ducts there is a well-defined mucosa con- sisting of a single layer of epithelium resting 'upon a stroma, outside of which are a few smooth — C SH.'nO. OF LIVER OF HUG, Showing very dIagTammaticall.v the lobules; a, interlob- ular connective ti^isue: b, e, braucUes of portal vein and hepatic artery ; d, bile-ducts ; e, interlobular vein. nuisele-cells and some fibrous tissue. Usually at some distance from the portal system in the con- nective tissue between two adjacent lobules is the suhlobular vein, a branch of the hepatic vein, into which the central veins empty. The blood-supply of the liver is very large, being conveyed by two distinct systems — the por- tal system and the hepatic .system. The portal vein and the hepatic artery enter the liver .at the hilus. and. entering the organ, divide and sub- divide, following the extensions inward of Glis- son's capsule. Upon reaching the boundary of the lobules the vessels break up into the intra- lobular capillaiy network ■ already referred to. Distinct up to the time of entering the lobule, the blood of the two systems mingles at some point within the lobule capillaries and empties into the above-mentioned central vein, whence it finds its way into the hepatic vein. Bile capillaries ex- tremely minute in size originate within the lobules and follow the cords of liver-cells to the periphery of the lobules, where they empty into the smaller bile-ducts. Lymphatics accompany the blood-vessels, forming in the capsule a super- ficial lymphatic system, in the substance of the liver proper a deep lymphatic system. The ner-es of the liver enter the organ at the hilus in company with the blood-vessels and lym- phatics. They are composed mainly of non- meduUated fibres, although some medullated fibres are intermingled. They branch following the subdivisions of Glisson's capsule, and reach the periphery of the lobules. Extremely minute Vol. XII.— 23. fibrils enter the lobules to terminate in end- arborizations among the liver-cells. The two distinct functions, that of the pro- duction of bile and the formation of sugar, which are now generally recognized as being per- '""'^i'k^^^^ SECTION OP INJECTED HUMAN UVBB, The capillaries having Iwell filleil from the central vpIh (a);,6, branches of portal vein. formed by the liver have led some physiologists to suppose that this gland is composed of two dis- tinct portions or anatomical elements, and Kobin has adopted this theoiy and calls one portion of the liver a biliary organ, and the other a glyco- genic or sugar-forming organ. The lobules and hepatic cells, with their different vessels, he re- gards as performing the glycogenic function, and the little racemose glands which are attached to the biliary duets along their course as the bile- producing organs; and others have entertained ideas of the independence of the sugar-making and bile-producing portions of the organ. Rut from the fact that bile is commonly foimd in the lobules, and that the biliary capillaries are con- nected with the excretory biliary ducts, the eon- elusion seems to be unavoidable that the bile is formed in the lobules, and. moreover, by the hepatic cells. It therefore becomes a question as to what are the functions of the little race- mose glands attached to the larger bile-duets. They have much the form of mucous glands in other parts of the body, and from the exami- nations of Sappey. who has found the bile to Ik; viscid in proportion to the number of these glands in the duets containing it. they appear to l>c r-i — 4). ?^^^ SECTIOX OF LIVER OF DOG. Including portion of lobule and Interlobular or con- nective tissue (.'tl: ft. piirtal vein; c. In^patic artery; d. bile-ducts; e. small perlplieral bile-veascl; /,', blood-chan- nels ; h, hepatic tissue. reallv mucous glands. In the rabbit, an anim.tl in which these glands are not found in this situ- ation, the bile is quite fluid, and free from its ordinary viscidity. It has generally been thought that the bile is' secreted exclusively from the