[Structural basis of peripheral innervation mechanisms in the walls of the biliary tract].

Several types of giant neurons exist in the extrahepatic bile ducts in the dog. The intrinsic innervation of the ducts wall has the characteristics as follows: 1) within the nerve, fascicless axons and nerve terminals come into a different relation to the glial cytoplasm; 2) two categories of the nerve terminals are identified by their glial accompaniment--"closed" and "open" types; 3) separation of the nerve terminals containing synaptic vesicles from the several effector elements is usually about several thousand A and with no synapses; typical synaptic complexes were identified between nerve terminals and neurons, although not as commonly as would have been expected considering the large amount of nerve terminals surrounding some of the neurons; 4) within the interstitial space the terminals are often of the "open" type. The morphological data suggest that the peripheral vegetative fibers may form transitional provisional "functional" nerve endings.