I'll take a shot. Dennis, it is an extension of the bow side bone on bone you mention. As you draw on the string side, you CAN find a place where the "triangle" is complete and you establish bone on bone support on the string side too.
Visualize a triangle starting at the bow hand, running up the bow arm and across the shoulders (both of them) -- all one straight line and this is one side of the "triangle."
Next, there is a line along the arrow line, string hand, wrist and forearm to the string elbow -- the second side of the triangle. Think of this as a chain that is pulled straight by the bow weight.
The third side of the triangle is the upper string arm bone (humerus) -- the third side of the triangle. This bone is held in position by the back of the shoulder and string side rhomboid (back tension).
When you achieve this triangle, you will feel like the bow weight has reduced substantially. Your muscle use actually reduces as all your muscles have to do is hold the bones in alignment to maintain the triangle.
Many (Most?) find that the shaking that happens at full draw is because they are trying to hold the full bow weight with the arm muscles. The long muscles in the arm fatigue much faster than the posterior deltoid (string side shoulder) and rhomboid muscles.
Learning this is why so many of us "obnoxious" coaches recommend LIGHT weight bows to LEARN with.
Find that bone on bone triangle and I think your shakes will reduce substantially if not disappear completely. When learning this (if you decide to pursue it) use an arm guard as I can almost guarantee a string slap or two until it "clicks" for you.
See if that helps.
Arne