LIVER. 173 



^5- 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 micro- 

 scopically, exhibit a rounded or polygonal shape, and measure, on 

 the average, T oV^ of an inch in diameter ; they possess one, and 

 sometimes two, nuclei ; they also contain globules of fat, pigment 

 matter, and animal starch. The cells constitute the secreting struc- 

 ture 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, and superior and 



inferior me sent eric 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 entering the liver, penetrate its substance, divide into smaller 

 and smaller branches, occupy the spaces between the lobules, com- 

 pletely 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 have distinct membranous walls, or whether they 

 originate in the spaces between the cells by open orifices, has not been 

 satisfactorily determined. 



