Page:The New International Encyclopædia 1st ed. v. 12.djvu/390

* LIVEB. 346 LIVER. the terminations of the liepatic artery before passing into the lobules, ll is very important to bear in mind this peculiarity of distribution, whidi is often overlooked. The branches of each hepatic vein, the vessel which carries tlie blood from the liver to the ascending great vein (as- cending vena cava ), by which it is returned to the heart and lungs, have their origin within the lobules. Their capillary extremities arise from the capillary ramifications of the portal vein, and, passing toward thi^ centre of the lob- ule, converge into three or four radicles, which, uniting at the centre, form the infinlobulnr vfins, which are the commencement of the hepatic veins. These intralobular veins, which are in the centre of each lobule, are from xbVs ^'^ tot "^ ^° inch in diameter, and they follow the long axis of the lobule, receiving vessels in their course till they empty into larger vessels situated at the base of the lobules, called by Kiernan sub-lobular veins. They collect the blood from all parts of the liver, and. increasing in size by union with one another, they at last form the three hepatic veins which discharge the blood from the liver into the a.seending vena cava. Now. these hepatic veins -are a long way from the influence of the heart's action, lying as they do between the portal circulation and the veins going to the heart; but a provision has been made to assist in the pro- pulsion of their contents, and they are supplied with a muscular coat, comi)ospd of unstriated muscular fibres. The most essential elements of the lobule, or of the liver, are the hepatic cells, which are the true secreting elements of the gland. They are minute, polygonal-shaped bodies about YthTf "f ■''" hich in their longest and tcW in their shortest diameter, having one nucleus, or sometimes two nuclei, with some granular matter. (See Cell.) They are surrounded by an independent network of extremely minute ves- sels rrf.Vrrij °^ ^^ •"'"h in diameter, of uniform size throughout, called the biliary capillaries, and in ■which the bile first makes its appearance. The liver is an organ which has jio analogue in any of the other organs of the body. It has two distinct functions, and a cellular arrange- ment entirely unlike that seen in any other gland. It is excretory on the one hand and secreting on the other, and it is its secreting function which has been so long overlooked, and the knowledge of which has also thrown so nnich light on the physiology of what are called ductless glands, like the spleen (q.v. ) and the lymphatic glands. The liver, in one of its functions, is a ductless gland. It secretes (that is, not merely sepa- rates, but forms) a substance which is not car- ried away by any excretory vessel, but which is immediately retuined to the blood. Tlie other function of the liver is the production of bile, which, although a true excretion, an.swers a salutary purpose. As the bile-ducts increase in size they contain numerous follicles and cluster-like glands which are called racemose (the biliary acini of Robin), and they continue to occupy the biliary passages as far as the ijiirfrin cnmniiinif! cholerlorhus. or the common bile-duct, which empties into the in- testinal canal. Those which are found in the smallest ducts are simple follicles from ^^^ to ■j^ of an inch in length. The larger of these glands are formed of groups of these follicles. and are from -j^ to y^of an inch in diameter. The nutrition of the liver is provided for by the hepatic artery, which has three sets of branches. As soon as it enters the sheath formed by the capsule of Glisson, it sends oH' very tine branches, called vasa vasoniDi, to the walls of the portal vein, to those of the hepatic vein, to its own branches, and an exceedinglj' rich and beautiful network of branches to the hepatic duct. When the hepatic artery is well injected it almost com- pletely covers the duct with its ramifications. The hepatic duct proper, or that single vessel so called lying outside of the liver, is formed by the union of two ducts, one fiom the right and one from the left lobe of the liver. It is about an inch and a half long, and joins the duct from the gall-bladder, called the cystic duct, to form the common duct, or ductus communis cholcdochus, which is about three inches long and of the size of a goose-quill, and empties, in common with the pancreatic duct, into the intestine, a little below the middle of the duodenum, or about 5 inches below the stomach. The gall-bladder is an elongated, pear-shaped sac about 4 inches in length and one in breadth, having a capacity of about one and a half fluid ounces. The cj'stic duct, connecting it with the hepatic duct, is the smallest of the three larger ducts, and is about one inch in length. In the gall-bladder there are also numerous small racemose glands similar to those above mentioned as existing in the biliary ducts generally. They consist each of from 4 to 8 follicles lodged in the submucous tissues. They secrete nuicus mixed with bile. The idea has been entertained by .some that these biliary racemose glands found in diff'erent parts of tho biliai'y ducts were the bile-producing glands, while the hepatic cells were the organs for se- creting sugar, or, in other words, for the ecu version of the gl3'cogenic matter of the liver into glucose, or grape-sugar; but this view has not been found tenable. The nerves of the liver are derived from the pneumogastrie, the phrenicj and from the solar plexus of the great sym- pathetic. They all penetrate the gland at the great transver.se fissure, and follow the blood- vessels in their course of distribution to the various parts of the organ, but their terminal distributions are not yet well understood. The lymphatic ves.sels of the liver are numerous and consist of two layers. The outer or superficial layer is situated immediately beneath the serous or peritoneal covering. The inner or deeper layer forms a plexus surrounding the lobules, having entered the liver along with the portal veins, hepatic arteries, and bile-ducts, enveloped in sheaths of Glisson"s capsule. In their course they invest the branches of both ducts and blood- vessels with a delicate network of tubes, and on arriving at the surface of the lobules they enter them and form another remarkable network of lymphatic passages, traversing the lobule in every direction. Every blood-capillary is envel- oped in a lymphatic sheath in very much the same manner that the interlobular vessels are enveloped in the sheath of Glisson's capsule. These lymphatic sheaths surrounding the other vessels are otherwise called the perivascular Ij'mphatie spaces, and are similar in structure to those which are found in various parts of the body. See Ltmpii.tic. Histology. The macroscopic divisions of the liver which are known as lobes are subdivided microscopically into lobules by extensions inward of the connective tissue of Glisson's capsule. In