The Ulna’s connected to the-

Adding some finer detail to my original base mesh in order to optimise the sculpting potential (the layers of skin are going to deform to reveal the underneath as in the pic):

 

And the arm muscle with the skin deleted so you can see what’s going on:

I’m hoping to have bits of muscle detach (maybe hanging on one end) in order to reveal the bone underneath.. Here it is with some muscle sections deleted: