The liver is an organ which has po 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 much 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, hut which is immediately returned to the blood. The other function of the liver is the production of bile, which, although a true excretion, answers a salutary purpose.
As the bile-ducts increase in size they contain numerous follicles and cluster-like glands which are called racemose (the binary acini of Robin), and they continue to occupy the biliary passages as far as the durtus COMM minis cholrdorhus, 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 of an inch in length. The larger of these glands are formed of groups of these follicles, and are from 4 to 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 off very fine branches, called rasa vusorum, to the walls of the portal vein, to those of the hepatic vein, to its own branches, and all exceedingly 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 from 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 duct us 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 cystic duct, connecting it with the hepatic duct, is the smallest of time three larger duets, 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 submueous tissues. They secrete mucus mixed with bile. The idea has been entertained by some that these biliary racemose glands found in different parts of tho binary ducts were the bile-producing glands, while the hepatic cells were the organs for se creting sugar, or, in other words, for the con version of the glycogenic 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 pneuinogastric, the phrenie, and from the solar plexus of the' great sym pathetic. They all penetrate the gland at the great transverse 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 vessels 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-duets, 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 lymphatic spaces. and are similar in structure to those which are found in various parts of the body. See LY\rPtrATIc.