Trixie and Scampers will lie on their their backs sometimes but my cocker Peppi always lays on her back. In fact, when we go to bed she sleeps on the bed with me on her back with her head on her pillow and alot of the time she is holding her stuffed dog while she falls asleep. You can't get any more human than that!!
Everyone loves to watch her sleep like that, I will have to get a picture. One year I dressed her up as baby, put baby clothes on her and put her in a stroller. She layed down on her back with a pacifier in her mouth while I pushed the stroller and she just loved it.
I don't have any pictures of her on her back or if I do I would have to find them but I will definately have to start taking pictures of her sleeping.