_Minute Structure of the Liver._--The liver is made up of an enormous number of _lobules_ of a conical form (see fig. 3). If the portal vein is followed from the transverse fissure, it will be seen to branch and rebranch until minute twigs called _interlobular veins_ (fig. 2, i) ramify around the lobules. From these _intralobular capillaries_ run toward the centre of the lobule, forming a network among the polygonal hepatic cells. On reaching the core of the conical lobule they are collected into a central or _intralobular vein_ (fig. 2, c) which unites with other similar ones to form a _sublobular vein_ (fig. 3, s). These eventually reach the hepatic radicles, and so the blood is conducted into the vena cava. In man the lobules are not distinctly separated one from the other, but in some animals, e.g. the pig, each one has a fibrous sheath derived from Glisson's capsule (fig. 3, ct.). _Embryology._--The liver first appears as an entodermal hollow longitudinal outgrowth from the duodenum into the ventral mesentery. The upper part of this forms the future liver, and grows up into the _septum transversum_ from which the central part of the diaphragm is formed (see DIAPHRAGM). From the cephalic part of this primary diverticulum solid rods of cells called the _hepatic cylinders_ grow out, and these branch again and again until a cellular network is formed surrounding and breaking up the umbilical and vitelline veins. The liver cells, therefore, are entodermal, but the supporting connective tissue mesodermal from the septum transversum. The lower (caudal) part of the furrow-like outgrowth remains hollow and forms the gall bladder. At first the liver is embedded in the septum transversum, but later the diaphragm and it are constricted off one from the other, and soon the liver becomes very large and fills the greater part of the abdomen. At birth it is proportionately much larger than in the adult, and forms one-eighteenth instead of one-fortieth of the body weight, the right and left lobes being nearly equal in size. [Illustration: FIG. 3.--Vertical section through two hepatic lobules of a pig. c, c, Central veins receiving the intralobular capillaries. s, Sublobular vein. ct, Interlobular connective tissue forming the capsules of the lobules. i, i, Interlobular veins.]