The intercalated portion of the rat liver was studied by scanning electron microscopy (SEM) after removal of interlobular connective tissue by acid or alkaline hydrolysis. Biliary intercalated portions have generally been regarded as short straight links lying between the bile capillary network and the interlobular duct. The biliary system as observed by SEM lacked such specialized segments for linking. Instead, it contained long intercalated ductules taking winding and branching courses. The ductular branches frequently anastomosed with each other to form an extensive plexus along the limiting plate. The ductules repeatedly connected with the plate on their courses as well as at their terminals. This disposition of the ductules probably potentiates their tolerance to luminal obstruction. At the junction between the ductule and the limiting plate, ductular cells and hepatocytes shared the biliary lumen. The lumen sometimes approached the base of the ductule, providing a possible route for bile leakage.
The intercalated ductule was composed of low fusi-form epithelial cells throughout its length, meeting its classical criteria by light microscopy. Its basal surface was furrowed with narrow grooves along cell boundaries. The ductular cells extended numerous microplicae in the basal grooves and on their lateral surfaces, suggesting their secretory function.