62 PHYSIOLOGY AT THE FARM. 



from both these sources has no other channel for return to the 

 general vascular system but the hepatic veins. Thus the 

 trunks of the hepatic veins, as they enter the abdominal vena 

 cava, correspond not merely to the hepatic artery, but to all 

 the arterial trunks which supply arterial blood to the chylo- 

 poetic viscera, namely, the gastric, the splenic, the anterior 

 mesenteric, the posterior mesenteric. But it is believed now, 

 that within the substance of the liver the blood of the hepatic 

 artery, after nourishing the several component textures of the 

 liver by its minute ramifications, is collected by a small set 

 of veins which pour their blood into the minute divisions of 

 the portal vein as these are about to secrete the bile ; so that 

 the blood which nourishes the liver contributes, like the blood 

 of the other chylopoetic viscera, to the secretion of the bile. 

 It may be remarked that while the arteries are commonly 

 given off from the trunks in pairs, there are in the abdominal 

 aorta three remarkable azygous arteries that is, arteries 

 without corresponding fellows namely, the cceliac axis, the 

 anterior mesenteric, and the posterior mesenteric ; and that 

 these three azygous arteries are wholly spent upon the chylo- 

 poetic viscera, including the liver ; and further, that the vena 

 cavce hepaticce, or great veins of the liver, correspond to these 

 three azygous arteries in the sense that these veins return to 

 the abdominal vena cava the blood which had been carried 

 out from the aorta by these three arteries. 



But to return to the mode in which the blood-vessels of the 

 liver are connected with the pin-head lobules of the organ. It 

 is remarked that the base of each lobule rests on a small ven- 

 ous trunk, and that a minute vein descends from the body of 

 the lobule through the middle of its base to join this minute 

 trunk. This minute trunk and its branch are radicles of the 

 hepatic veins. These minute trunks on which the pin-head 

 lobules rest gradually unite into larger veins which pursue an 



