vii THE DIGESTIVE SYSTEM AND ITS FUNCTIONS 153 



ducts leading from the lobes of the liver. The gall bladder 

 lies on the dorsal side of the liver, between the right and left 

 lobes. It is rounded or oval in outline, and usually appears 

 green from the color of the bile seen through its thin walls. 

 The gall bladder is connected with the cystic ducts, the one 

 leading to one of the hepatic ducts, the other joining the 

 common duct farther down, usually within the substance of 

 the pancreas. 



The histological structure of the liver differs considerably 

 from that of the pancreas, although both organs are to be 

 regarded as much-branched, tubular glands. The terminal 

 branches inclose the ultimate ramifications of the hepatic 

 ducts, or bile capillaries. These capillaries come to branch 

 and anastomose in an irregular manner so as to much obscure 

 the original tubular structure of the organ. 



The bile capillaries may be surrounded by five or six cells 

 in cross section, or they may run between but two cells ; they 

 also give off lateral branches which penetrate the cell bodies. 

 The secretory cells of the liver are cubical or polyhedral in 

 form, with large nuclei ; the cytoplasm contains proteid gran- 

 ules, small drops of fat, lumps of glycogen, and often pigment. 



The liver receives blood from two sources : (1) the hepatic 

 artery, which conveys arterial blood, and (2) the portal sys- 

 tem, which includes the anterior abdominal vein from the 

 ventral body wall, and the portal vein, which receives blood 

 from the stomach, intestine, pancreas, and spleen. The 

 materials absorbed by the blood from the organs of diges- 

 tion pass, therefore, through the liver before entering the 

 general circulation. All of the blood leaves the liver by 

 the hepatic veins, which lead from the dorsal side of that 

 organ to the posterior vena cava. 



The liver is well supplied with lymph vessels which form 

 perivascular lymph spaces around the capillaries. 



