Quain's elements of anatomy . injection, they have demonstrated the existence of vacuoles within thecells communicating by exceedingly minute intracellular channels with theadjoining bile-canaliculi (see fig. .549). In the lower vertebrates and in the earlier stages of development in birds andmammals the liver is a tubular gland, composed of anastomosing tubules, withnarrow lumina (biliary canaliculi), and directly continuous with the ducts. Inall animals the bile-canaliculi are separated by at least a poi-tion of a cell fromthe nearest blood caijillaries. Structure of the ducts.—The minute ra
Quain's elements of anatomy . injection, they have demonstrated the existence of vacuoles within thecells communicating by exceedingly minute intracellular channels with theadjoining bile-canaliculi (see fig. .549). In the lower vertebrates and in the earlier stages of development in birds andmammals the liver is a tubular gland, composed of anastomosing tubules, withnarrow lumina (biliary canaliculi), and directly continuous with the ducts. Inall animals the bile-canaliculi are separated by at least a poi-tion of a cell fromthe nearest blood caijillaries. Structure of the ducts.—The minute ramifications between thelobules have walls composed of fibrillar connective tissue, within whichis a basement membrane, and a lining of short columnar to Heidenhain they also possess both longitudinally andcircularly disposed muscular cells in their wall. As they pass intothe lobules, the columnar epithelimn becomes shorter and flatter, thetube at the same time branching both laterally and terminally and. DUCTS OF THE LITER. 633 becoming much reduced in size so that only a very small lumen is basement membrane is no longer complete, and the intercellularbile passages open directly into the minute ducts, the hepatic cellsabutting against the flattened epithelium of the latter. In the portal canals, where they are somewhat larger, the ducts pre-sent numerous openings on the inner surface, which are scattered irregu-larly in the larger ducts, but in the subdivisions are arranged in twolongitudinal rows, one at each side of the vessel. These openings wereformerly supposed to be the orifices of mucous glands; but, while themain ducts are studded with true mucous glands of lobulated form andwith minute orifices, the openings now referred to belong to saccular andtubular recesses, which are often branched and anastomosing, and maybe beset all over with CEecal projections (Theile). The larger bile-ductshave areolar coats, containing abundant elastic tissu
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