Among the most striking peculiarities of the liver may be mentioned the following facts: (1) It has a receptacle, the gall bladder, for storing the secretion until required. (2) It has a double blood supply. It receives by the hepatic artery a small supply of fresh arterial blood as well as all that coming from the spleen, pancreas and intestinal canal, collected by the tributaries of the great portal vein, and distributed by its branches to the liver. (3) A regular network is formed by the minute channels (bile capillaries), which freely anastomose between the cells. (4) Although in the embryo, and in many animals, the liver is a compound saccular gland, the arrangement of the duct radicles and the saccules is so modified in the higher animals and man, that their relationship is no longer apparent, and the structure is best understood by following its vascular groundwork.

STRUCTURE OF THE LIVER.

On the surface of the liver are seen with the naked eye small rounded markings about the size of a pin's head, which give the organ a mottled appearance. This is much more striking in some animals (giraffe, bear, pig) than others, but is easily recognizable in the livers of all mammalia. surfaces of the lobules of the liver. dark-red boundary, and their centre between these is a paler, yellowish zone. spond to the blood vessels, and have a constant relation to the lobules.

These little areas are the They are surrounded by a is marked by a dark spot, The dark parts corre

The entire liver is made up of these little lobules, and each one of them has the same construction and blood supply, and therefore forms in itself a little liver perfect in all its structural arrangements, so that the description of one such unit will suffice to give an idea of the structure of the gland. For other details, anatomical works must be referred to.

The branches of the large portal vein and those of the small hepatic artery pursue the same course through the gland, and are enclosed in a sheath of connective tissue (capsule of Glisson), which also forms the bed of the hepatic duct and its numerous tributaries. If these branching vessels be followed to their final

ramifications, they are found to pass around and between the neighboring lobules. The branches of the portal vein in this situation receive the name of the interlobular veins.

FIG. 72.

They anas

Section of Lobule of Liver of Rabbit in which the blood and bile capillaries have been injected. (Cadiat.)

a. Intralobular vein. b. Interlobular veins. c. Biliary canals beginning in fine

capillaries.

capillary vessels pass into the lobule, and, lying between the gland cells, form a network with long meshes radiating from the centre. These are the lobular blood capillaries. The vessels of this radiating capillary network become larger as they unite and converge to the centre of the lobule, where they open into a central vein which lies in immediate apposition with the gland cells. This vein is called the intralobular vein, and is the radicle of the efferent or hepatic vein, which carries the blood of the liver to the inferior vena cava.

The ultimate ramifications of the hepatic artery can be traced to various destinations. Some pass into the walls of the accom

Cells of the Liver. One large mass shows the shape they assume by mutual pressure. (a) The same free, when they become spheroid. (b) More magnified. (c) During active digestion containing refracting globules like fat.

panying vein and duct and the connective tissue which surrounds these vessels. Many of the arterial capillaries unite with offshoots from the interlobular venous plexus, and thus reinforce the lobular capillaries. Other branches form a lobular capillary plexus, which joins the capillaries of the vena porta, together with that from the walls of the vein and duct.

The blood flowing to the liver in the great vena porta and the hepatic artery is thus conducted by those vessels to the boundaries between the lobules (interlobular veins), and thence streams through the converging lobular blood capillaries to the intra

lobular vein, and is collected from the latter by the sublobular tributaries of the hepatic vein, by which it is conducted back to the general circulation, and enters the heart by the inferior vena

cava.

Between the meshes of the lobular capillaries the gland cells

Section of injected liver showing the position of portal branches (interlobular veins, VP) and radicals of hepatic veins (intralobular veins, HV) connected by lobular capil laries.

Below is a portion of the same highly magnified. (a) Liver cell with () nucleus; (6) Blood capillaries cut across, passing along angles of cells; (c) Bile capillaries between flattened sides of cells. (Huxley.)

are tightly packed. These are large, soft, polyhedral cells, with one, two, or even more nuclei, and no trace of a limiting membrane. Owing to the shape of the capillary meshes, the cells are placed in rows radiating from the centre of the lobule toward the periphery.

The blood capillaries are said to pass along the angles and edges of these cell blocks so as not to come into close relation to the bile capillaries (Fig. 71). The finely granular protoplasm of the liver cells is capable of undergoing some slight change in form while alive. In the protoplasm are situated varieties of granules, the commonest being bright, refracting fat globules, which vary in amount with the different stages of digestion;

Section of the Liver of the Newt, in which the bile ducts have been injected, and can be seen through the transparent liver cells to form a network of fine capillaries.

others of a yellow color seem connected with the coloring matter of the bile; and a third variety, less refracting and colorless, is said to be related to the glycogen.

Between the cells of the lobules there can be demonstrated very fine anastomosing canals, which appear to be formed by the juxtaposition of grooves which lie in the middle of the flat surface of two neighboring cells. Every liver cell is related to such a canal, and consequently a very dense network with peculiarly regular polygonal meshes is present, each mesh corresponding in size to one cell.

These fine intercellular canals are called lobular bile capillaries,