84 HUMAN PHYSIOLOGY. 



fissure, and follows the vessels in their ramifications through its substance, 

 constituting Glissorfs capsule. 



Structure of the Liver. The liver is made up of a large number of 

 small bodies, the lobules, rounded or ovoid in shape, measuring the -fa of 

 an inch in diameter, separated by a space in which are situated blood 

 vessels, nerves, hepatic ducts and lymphatics. 



The lobules are composed of cells, which, when examined microscopi- 

 cally, exhibit a rounded or polygonal shape, and measure, on the average, 

 the I^OQ of an inch in diameter; they possess one, and at times two, nuclei; 

 they also contain globules of fat, pigment matter, and animal starch. The 

 cells constitute the secreting structure of the liver, and are the true hepatic 

 cells. 



The Blood vessels which enter the liver are (i) The portal vein, 

 made up of the gastric, splenic, superior and inferior mesenteric veins ; (2) 

 the hepatic artery, a branch of the coeliac axis ; both of which are invested 

 by a sheath of areolar tissue ; the vessels which leave the liver are the 

 hepatic veins, originating in its interior, collecting the blood distributed by 

 the portal vein and hepatic artery, and conducting it to the ascending vena 

 cava. 



Distribution of Vessels. The portal vein and hepatic artery, upon 

 entering the liver, penetrate its substance, divide into smaller and smaller 

 branches, occupy the spaces between the lobules, completely surrounding 

 and limiting them, and constitute the interlobular vessels. The hepatic 

 artery, in its course, gives off branches to the walls of the portal vein and 

 Glisson's capsule, and finally empties into the small branches of the portal 

 vein in the interlobular spaces. 



The interlobular vessels form a rich plexus around the lobules, from 

 which branches pass to neighboring lobules and enter their substance, 

 where they form a very fine network of capillary vessels, ramifying over 

 the hepatic cells, in which the various functions of the liver are performed. 

 The blood is then collected by small veins, converging toward the centre 

 of the lobule, to form the intralobular vein, which runs through its long 

 axis and empties into the sub-lobular vein. The hepatic veins are formed 

 by the union of the sub-lobular veins, and carry the blood to the ascending 

 vena cava; their walls are thin and adherent to the substance of the 

 hepatic tissue. 



The Hepatic Ducts or Bile Capillaries originate within the lobules, 

 in a very fine plexus lying between the hepatic cells ; whether the smallest 

 vessels have distinct membranous walls, or whether they originate in the 



