156 HUMAN PHYSIOLOGY. 



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

 constituting Glisson's 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 ^ 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 microscopic- 

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

 ToW f an i nc h i n diameter; they possess one, and sometimes 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: 



1. The portal vein, made up of the gastric, splenic, and superior and inferior 

 mesenteric veins. 



2. The hepatic artery, a branch of the celiac axis. 



Both the portal vein and the hepatic artery 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 the hepatic artery, upon en- 

 tering 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 center of the lobule, 

 to form the intralobular vein, which runs through its long axis and empties 

 into the sublobular vein. The hepatic veins are formed by the union of the 

 sublobular 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 



