The gall-bladder is a pear-shaped sac lying behind the right lobe of the liver, 4 inches long, 1.5 inches broad, and holds 1.5 ounces. The fundus comes beyond the lower margin of the liver. Four vessels enter and leave the under side of the liver ;. they are the

Portal vein.                                      Hepatic vein.

Hepatic artery.                                Hepatic duct.

It is supplied with blood by the hepatic artery and the portal vein ; the former brings blood from the descending branch of the aorta to nourish the structures of the organ ; the latter brings blood which has traversed the capillaries of the stomach, intestines, spleen and pancreas, and is laden with the products of digestion. In the liver the portal vein breaks up, after the manner of an artery, into smaller veins, and these again into capillaries, which form a close network between the cells of the liver.

The capillaries of the liver unite to form small veins, which form larger ones that terminate in the hepatic vein, and by it the blood is carried to the inferior vena cava.