372 



ABDOMEN 



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 right lobe of 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 that furrow it crosses the fossa for the umbilical 

 vein and enters the left lobe of the liver. As it crosses the 

 fossa for the umbilical vein the left branch of the portal 

 vein is joined in front by the ligamentum teres, whilst the 

 ligamentum venosum is attached to it behind. 



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 

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

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

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

 the vena cava. Trace the hepatic 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, the areolar tissue is so scarce around the 

 large veins that it is hardly appreciable to the naked eye ; 

 it is entirely absent from the smaller veins, and their walls 

 rest directly against the hepatic lobules. 



A section should now be made through the liver substance 

 and the cut surface examined. The portal veins can be readily 

 distinguished from the hepatic veins. The following are the 

 points of difference : 



PORTAL VEINS. 



1. Are always accompanied by a 



branch of the duct and a branch 

 of the hepatic artery. 



2. Mouths usually collapsed. 



3. Walls thicker. 



4. Walls separated from the liver 



substance by the fibrous cap- 

 sule. 



HEPATIC VEINS. 



1. Are solitary and not accom- 



panied by any other vessel. 



2. Mouths usually open and gaping. 



3. Walls exceedingly thin. 



4. Walls apparently in direct 



apposition with the liver 

 substance. 



Structure of the Liver. Very little of the structure of 

 the liver can be learned in the dissecting-room. It is com- 

 pletely enveloped by a fibrous capsule (O.T. Glisson's). This is 

 thick where the peritoneum is absent, but very thin where that 



