Morphology and classification of subdivisions of the intrahepatic vascular and biliary systems in sheep.

Tensol casts and histology were used to demonstrate sub-divisions of the portal and hepatic veins, and arterial and biliary systems. Portal and hepatic venous subdivisions were most readily identified. Based upon size, location, sequence of branching and histological characteristics a nomenclature for the sub-divisions of the portal vascular system was proposed. The names of distributing, primary, terminal, secondary (long and short) and tertiary veins were adopted to identify portal veins branches. The same criteria allowed the identification of three hepatic vein branches, central, sublobular and hepatic; the central hepatic veins and to a much lesser extent the sublobular hepatic veins drained the sinusoids. Casts of the arterial system demonstrated the arterial blood supply to the biliary system, to the sinusoids and portal vein vasa vasorum but they were of little use in identifying subdivisions. Arterial subdivision identification is possible by using accompanying portal veins as morphological markers and designating the subdivision after the vein. This approach is also applicable to the biliary system and provides a more accurate means of subdivision identification than does the broader division into ductules, intermediate and large ducts.