The origin of Fromm's arteries in trout gills.

In trout gills two small arteries paralleling the main afferent filament vessel have been described by Fromm (1974). In search of their origin from branchial arteries the orifices of numerous small vessels were detected in the efferent branchial artery (EBA) by scanning electron microscopy. These small vessels are bordered by specialized endothelial cells that seem to have grown out against the blood stream into the EBA. By studying serial sections, the small vessels originating from the EBA were confirmed to be the roots of Fromm's arteries.