ABDOMINAL CAVITY 523 



canal" It is employed to denote a channel in the liver 

 substance lined by a prolongation of the fibrous capsule, 

 and holding in its interior a branch of the portal vein, a 

 branch of the hepatic artery, and a branch of the hepatic 

 duct. 



Vessels of the Liver. Blood enters the liver (i) by the 

 hepatic artery ', (2) by the large portal vein ; whilst it is led away 

 from the liver by the hepatic veins. 



The hepatic artery is a branch of the cceliac artery. It 

 carries arterial blood for the nourishment of the liver sub- 

 stance and divides into two branches which enter the liver 

 at the extremities of the porta hepatis (p. 462). 



The portal vein carries venous blood, which it has gathered 

 from the entire length of the abdominal portion of the ali- 

 mentary canal (with the exception of the anal canal of the 

 rectum), from the spleen, pancreas, and gall-bladder. It 

 reaches the under surface of the liver at the right extremity 

 of the porta hepatis, where it divides into its two terminal 

 branches. The terminal part of the portal vein, just before 

 it divides, is slightly expanded, forming the sinus of the 

 portal vein. The right branch is a short wide vessel, which 

 immediately sinks into the liver ; the left branch^ much longer 

 and considerably smaller, extends to the left along the bottom 

 of the porta hepatis, and at the left extremity of this furrow 

 it crosses the fossa for the umbilical vein and enters the liver 

 substance. As it crosses the fossa for the umbilical vein the 

 coats of the left branch of the portal vein are joined in front 

 by the obliterated umbilical vein, whilst behind it has also 

 attached to it the obliterated ductus venosus. 



The hepatic veins, which lead the blood out of the liver, 

 have an arrangement altogether different from the vessels 

 which enter at the porta hepatis. They converge towards 

 the fossa for the vena cava, on the posterior surface of the 

 organ, and cannot be said to have any course outside the 

 liver, as they open directly into the vena cava inferior. Their 

 gaping mouths will be found at the upper end of the fossa for 

 the vena cava. Trace these veins for a short distance into 

 the substance of the gland. They are remarkable for the 

 tenuity of their walls, and also for the very small quantity of 

 areolar tissue which separates them from the hepatic sub- 

 stance ; indeed, this is so scarce that it is hardly appreciable 

 to the naked eye. In the case of the smaller veins it is 



