266 A Study of the Structural Unit of the Liver 
THE Hepatic LOBULE AND THE PorTAL UNIT. 
It is seen from what has been said above that the final branches of the 
portal and hepatic veins are always as far from one another as possible 
throughout all stages of their development as well as in the adult liver. 
At all times this distance is half the diameter of a lobule and since this 
is in the neighborhood of one millimeter the distance is about half a mil- 
Fic. 28. Reconstruction of the vasicular system of tne liver of a human 
embryo 24 mm. long (No. 6). X 20. All of the important vessels are fully 
formed. The stage is the same as that shown in section, Fig. 27. Uv, umbili- 
cal vein; vp, vena portae; ru, recessus umbilicalis; ra, ramus arcuatus; rd, 
ramus descendens; ra, ramus angularis; 7, r, right arborization of ru; re, left 
arborization of the recessus umbilicalis; vh, vena hepetica; dv, ductus venosus; 
ds, vena dextra superior; di, vena dextra inferior; md, vena media dextra; 
ms, vena media sinistra; ss, vena sinistra superior; si, vena sinistra inferior; 
vc, vena cava. 
limeter, the normal length of a capillary blood-vessel. It is also appar- 
ent, as indicated by Fig. 1, that the liver breaks up into two sets of units 
arranged respectively around the terminal twigs of the two sets of veins. 
