1186 DIGESTIVE SYSTEM 



The hepatic veins, by which the blood of the liver passes into the inferior vena cava, open 

 usually by two large and several small openings into that vessel on the posterior surface of the 

 gland at the bottom of the fossa vense cavae. 



Lymphatics. — The lymphatics are divided into a deep and a superficial set. The deep set 

 runs with the branches of the portal vein, artery, and duct through the liver, leaving at the portal 

 fissure, where they join the vessels of the superficial set. The etterent deep vessels after leaving 

 the portal fissure pass down in the lesser omentum in front of the portal vein, through the chain 

 of hepatic lymphatic nodes, and ultimately end in a group of nodes at the upper border of the 

 neck of the pancreas, in which the pyloric lymphatics also terminate. 



The superficial set begins in the subperitoneal tissue. Those of the upper surface consist: — 

 (1) Of vessels which pass up, principally, in the falciform ligament and right and left triangular 

 ligaments, through the diaphragm, and so into the anterior mediastinal nodes, and finally 

 into the right Ij-mphatic duct. Some Ij'mphatics of the right triangular ligament pass to the 

 posterior mediastinal lymph-nodes and into the thoracic duct. (2) Of a set passing downward 

 over the anterior border of the liver to the hepatic nodes in the portal fissure, and over the pos- 

 terior surface to reach the superior gastric and coeliac nodes. On the lower surface, the lym- 

 phatics to the right of the gall-bladder enter the lumbar nodes. Those around the gall-bladder 

 enter the hepatic nodes of the lesser omentum. Those to the left of the gall-bladder enter the 

 superior gastric nodes. 



Nerves. — The nerves of the liver are derived from the vagi (those from the left vagus 

 entering from the stomach through the lesser omentum), and from the ca?liac plexus of the 

 sympathetic (including right vagus branches) through a plexus accompanying the hepatic 

 artery. The terminations, so far as known, are chiefly to the walls of the vessels and of the bile 

 ducts. 



Structure of the liver. — The liver is, for the greater part, covered by peritoneum, beneath 

 which is found the fibro-elastic layer known as Glisson's capsule. At the portal fissure, Glisson's 

 capsule passes into the substance of the liver, accompanying the portal vessels, the branches of 

 the hepatic artery, and the bile-ducts. The hver substance is composed of vascular units 

 measuring from 1 to 2 mm., and known as liver lobules. These are in part (man) separated by 



Fig. 947. — Section of a Portal Canal. (Quain.) 



Branch of portal vein 



Bile duct ^^^ 



-Lymphatics in Glisson's capsule 



Lymphatics in Glisson's capsule ~ \ 



> 



•Branch of hepatic artery 



a small amount of interlobular connective tissue, which is a continuation of Glisson's capsule. 

 In this interlobular connective tissue are found the terminal branches of the portal vessels; 

 the hepatic artery, and the bile-ducts (figs. 947, 948). The branches of the portal vessels which 

 encircle the liver lobules are known as the interlobular veins. From these are given off hepatic 

 capillaries, which anastomose freely, but have in general a direction toward the centre of the 

 lobule, and unite to form the central or intralobular veins, which in turn unite to form the sub- 

 lobular veins, and these the hepatic veins. The intralobular branches of the hepatic arteries 

 form capillaries which unite with the capillaries of tlie intralobular portal veins. 



The liver is a modified compound tubular gland. The liver-cells are arranged in anas- 

 tomosing cords and columns occupying the spaces formed by the hepatic capillaries. The 

 bile-ducts have their origin in .so-called bile-capillaries [ductus bilifcri], situated in the columns 

 of liver-cells; they anastomose freely and pass to the periphery of the lobules to form the pri- 

 mary divisions of the bile-ducts, and these unite to form the larger bile-ducts. The branches of 

 the portal vessel are accompanied in their course through the liver by the branches of the hepatic 

 art(!ry and the bile-ducts, surrounded by extensions of (ili.sson's capsule forming the so-called 

 ' portal canals' (fig. 947). The branches of the hepatic vein are solitary, their walls are thin 

 and closely adherent to the liver substance, whence they remain wide open on sectioning the 

 liver. 



While it is customary to describe thus the liver lobules, it would be more logical to con- 

 sider as the real lobuh^s what Mall has described as the 'portal units.' Each portal unit 

 includes the territory supplied by one interlobular branch of the portal vein, and drained by 

 the accompanying biloduct. The relations of the ordinary lobules and the portal units are 

 evident in fig. 94H. The portal unit corresi)onds more nearly to the lobule of other glands, 

 where the duct is in the centre of the lobule. 



