Thanks again, Doitsu!
What's going wrong it that I can't find a way to click on something and be transported elsewhere within the book, except in the Contents... and I can't see why the mechanism I try to copy from that, doesn't work.
Thanks for the advice on not starting link ids with a number. Mine do though start with letters.
I do try to put images nearest where they will be most discussed, but an image of a skeleton will contain useful points that multiple chapters will want to refer to.