Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/249

231 DIGESTIVE ORGANS 231 the hepatic venous canals. These trunks run towards the posterior border of the liver, and open into the inferior vena cava. From this description of the vascular arrangements within the liver, it will be seen that the intralobular capillaries are continuous with three vascular trunks, two which carry blood to them, the portal vein and the hepatic artery, and one which conveys the blood away from them, the hepatic vein. The communication in each case is so free that the capillaries can be artificially injected from any one of these vessels. The secreting cells of the liver, hepatic cells, form the proper parenchyma of the organ. They are situated within the lobules, and occupy the spaces of the capillary network. The cells vary in diameter from -g^th to TT5 ^th inch; they have the form of irregular polyhedrons, with from four to seven sides, and with the angles sometimes sharp, at other times rounded. They do not appear to possess definite walls, but have a distinct nucleus. The cell protoplasm is granular, and usually contains fat drops, and yellow particles, apparently bile pigment. The general arrangement of the cells is in rows or columns, and when sections are made through a lobule, transverse to the long axis of the central vein, the columns of cells are seen to converge from the periphery to the centre of the lobule, and to form a net work. T&amp;gt; L 4.1 n Fio. 11. Transverse section through By many observers the cells lobuleg of human liver to show &, are regarded as in contact with columns of secreting ceils. c,c, , . 111 MI central veins; i, interlobular vein the intralobular capillaries, with a fine sheuth of connective without the intervention of tissue&amp;lt; x 10&amp;gt; an intermediate membrane. By others, and more especially by Lionel Beale, the secreting cells are regarded as inclosed in a tubular network, the wall of which is formed by a basement membrane. Beale states that the diameter of the network is usually about K^^th f an ^ ncu in most mammals. According to this view, the cells are not in direct contact with the capillary blood-vessels, but separated from them by the basement membrane. In some parts of the lobule Beale has been able to demonstrate the basement membrane as distinct from the wall of the capillaries, but usually they are incorporated together. At the periphery of the lobule the membrane becomes continuous with the wall of the interlobular duct. The hepatic or bile duct is the tube that conveys the bile out of the liver. It leaves the transverse fissure as two branches, one from the right, another from the left lobe, which almost immediately unite at an acute angle. It closely accompanies within the liver the ramifications of the portal vein and hepatic artery, and its terminal branches pass between the lobules to form the interlobular branches of the duct. If the hepatic duct be injected, not only does the injection fill the interlobular ducts, but it flows into a set of excessively minute passages within the lobules them selves. These passages are arranged so as to form a polygonal network, which may appropriately be called the intralobular biliary network. This network has a most in timate relation to the polyhedral hepatic calls, for the passages lie between the flattened sides of adjacent cells, so that each cell is inclosed in a mesh of the network. The German observers, who first directed attention to these passages, named them bile-capillaries, but it is probable that they are merely intercellular passages bounded by the protoplasm of the hepatic cells. The intralobular biliary network differs from the intra lobular blood capillary network, not only in the character of the fluid conveyed, but in other important particulars. The bile passages have a tranverse diameter of about y^th of that of the blood capillaries; the passages are in relation to the sides of the cells, the blood capillaries to their angles, so that the two systems of networks are not in contact with each other, but are separated by intervening hepatic cell sub stance ; the passages have not, in all probability, an inde pendent wall, such as is possessed by the blood capillaries. As these passages can be injected from the hepatic duct, and as they convey bile from the interior of the lobule into the duct, it is obvious that they must be continuous with the lumen of the interlobular branches of the duct, at the periphery of the lobules. The wall of the larger bile ducts is formed of a fibro- elastic tissue, with a proportion of non-striped muscular fibre ; it is lined by a columnar epithelium. Opening into the larger ducts are numerous orifices, which communicate with branched ceecal tubes and follicles, situated within and clustered around the walls of the larger ducts, often in con siderable numbers. Some of these appendages to the duct doubtless serve as glands for the secretion of mucus, but others are probably, as Beale supposed, mere diverticula of the duct, in which the bile may be temporarily retained, as in the gall bladder. The lymphatics of the liver form a superficial and a deep set. The superficial set ramifies beneath the serous coat, where they form a network. The deep lymphatics accompany the portal vein and hepatic artery as far as the intervals between the lobules, where they form interlobular lymphatics, which, like the corresponding branches of the portal vein, run around the lobule. The nerves of the liver arise from the coeliac plexus of the sympathetic and from the left pneumogastric. They accompany the portal vessels in their distribution, and supply the muscular coats of the vessels. The Gall Bladder is a reservoir for the bile, situated Gall in a fossa on the under surface of the right lobe of the liver, and in a notch in its anterior border (fig. 8). It is pyriform in shape ; its larger end, or fundus, projects beyond the anterior border ; its opposite end, or neck, gives origin to the cystic duct, which is directed towards the transverse fissure; after a course of H inch it joins the hepatic duct, and forms the common bile duct, ductm communis choledochus. At its neck, the gall bladder bends on itself in a sigmoid curve. The gall bladder is 3 or 4 inches long, and can hold from one to two ounces of bile. It is attached to the liver partly by areolar tissue t and partly by the peritoneum, which is reflected over its free surface. Structure. In addition to its partial serous coat, the gall bladder has a fibrous and mucous coat. The fibrous coat consists of interlacing bands of connective tissue, with which non-striped muscular fibres are sparingly inter mingled. The mucous membrane lining the gall bladder is deeply bile-stained, and presents on its free surface an alveolar appearance, due to the presence of multitudes of minute folds, which form a reticulum with intermediate depressions. The surface is covered by columnar epithe lium. The mucous lining of both the neck of the gall bladder and cystic duct is thrown into folds, which in the duct have an oblique direction, and form the spiral valve. Racemose glands, for the secretion of mucus, occur in the wall of the gall bladder, cystic duct, and common bile duct. The gall bladder is supplied with blood by the cystic branch of the hepatic artery. It receives lymphatics and nerves continuous with those which belong to the liver. The common bile duct, formed by the junction of the cystic and hepatic ducts, is about 3 inches long, and con veys the bile into the duodenum. It lies in the gastro-