282 



HISTOLOGY 



averaging 0.7 mm. high and 0.7 mm. in diameter, and that the entire liver 

 (of 175 c.c.) contains 480,000 of them (Amer. Journ. Anat, 1906, vol. 5, 

 pp. 227-308). There has been prolonged discussion as to whether the 

 lobules should be regarded as centering about the terminal branches of the 

 portal vein or around those of the hepatic vein, for, although it was fre- 

 quently stated that they were arranged like a bunch of grapes, there was 

 no unanimity as to what formed the stem. If the human liver is examined 

 (Fig. 277) it is seen that the lobules are not definitely marked out as in the 

 pig, but the liver retains to a greater extent its embryonic appearance. 

 Scattered about through the section, but at quite uniform distances from 

 one another, there are islands of connective tissue containing branches 

 of the portal vein, hepatic artery, and bile duct. The strands of connective 



Branch of portal vein. 



Large interlobular bile duct. 



Central veins. 



nterlobular connective 

 tissue. 



Central vein. 



FIG. 277. FROM A TANGENTIAL SECTION OF THE HUMAN LIVER. X 40. 



The three central veins in cross section mark the centers of three lobules, which are not sharply separated, 

 at the periphery, from their neighbors. Below and at the right the lobules are cut obliquely and their 



boundaries are not seen. 



tissue which conduct the portal branches were named portal canals by 

 Kiernan (Trans. Roy. Soc. London, 1833, pp. 711-770). If the connective 

 tissue should spread from one canal to another, connecting those nearest 

 together, it would mark out lobules like those in the pig's liver, and this 

 sometimes takes place pathologically in man. Normally the portal canals 

 stand as isolated "boundary stones." 



Within each lobule thus marked out there is a central vein or enlarged 

 sinusoid, toward which the capilliform sinusoids between the hepatic 

 trabeculae converge. Occasionally there are two veins, side by side. 

 These central veins empty at right angles into suUobular veins (Fig. 278), 

 which come together to form the main branches of the hepatic vein. All 

 these veins, in contrast with the portal branches, have very little connective 

 tissue around them, and they are not associated with bile ducts or arteries; 



