XVII. 



THE LIVER. 



fTHHE LIVER, the largest gland of the body, is neither acinous 

 JL nor tubular, but has a peculiar structure of its own. Its 

 vascular supply is predominantly venous, and is obtained from 

 the portal system. From this blood the epithelia elaborate a 

 secretion, the bile, which does not exist as such in the blood. 



Corresponding with the lobate shape of the liver, which, how- 

 ever, is nowhere very distinctly marked, the intimate structure 

 of the liver is lobular, though in man and in most mammals the 

 lobules also are not sharply denned, but in many places appear 

 confluent. In the pig's liver the single lobules are easily dis- 

 cerned with the naked eye. The lobules are composed of epithelia 

 and capillary blood-vessels ; they are inclosed in fibrous con- 

 nective tissue, called the interstitial tissue, which is more abun- 

 dant in some places than in others, and in many localities is 

 altogether lacking. Around the lobules, in the interstitial con- 

 nective tissue, run branches of the portal veins, of the hepatic 

 artery, the bile-ducts, the lymphatics, and the larger bundles of 

 nerves. In the lobules, capillaries are found which are derived 

 from veins, and which carry, therefore, only venous blood ; while 

 the center of each lobule is occupied by the hepatic vein. The 

 system of the portal veins is arranged at right angles to the 

 system of the hepatic veins. Where the portal veins are cut 



I longitudinally, the hepatic vein appears in transverse section, 

 and vice versa. (See Fig. 296.) 

 The portal vein, upon entering the hilus of the liver, divides 

 into smaller veins, which ramify in all directions, only the 



