Jim,
That was a fast and correct reply. I turned the switch a few degrees so the two holes on one side show. There are 2 holes on the opposite side for the power to continue on to wherever.
When I was a child many of the houses had this kind of wiring (though we never did). The wires were separate, a black one and a white one. They ran up, down and/or across the walls on the INSIDE of the room. There were "porcelain" spreaders to keep the wires about 1 1/2 inches apart. The wires that ran horizontally were normally in the attic.
It didn't look too neat. It certainly was not too safe. However, it sure made for easy installation.
The Good Ole Days???
Enjoy,
JimB