This machine, described in the brochure as a "tri-promeneur", has a single enclosed chain which is used to transmit power from both the pedals and the water-coooled engine. The 1904 model forecar had two chains.

Bruneau Motocyclettes and Tricars
Photographed at Bad Münstereifel Oldtimer Motorcycle Rally, 2010, by Uwe Goedereis, friend of Craig Howell Licence: CC BY-NC-SA 2.0