The rear stretcher set into the mortise and bolted through.  Becase of the fit of the stretcher, you only need one bolt to hold the entire thing in alignment

The tenon extends through the side rails 1 1/2 inches.  This allows a clean finish and makes sure that the entire side rail provides bearing surface and support.

Here the front stretcher is set in place and bolted.  The front stretcher is constructed of two 4 x 6 timbers doweled and bolted like the side rails.  The scallops are for decoration as far as I can tell.