These were referenced from a book called Anatomy for the artist by Barcsay. It's a good book for figuring out the shape of things and how limbs and other body parts can move. There are downsides though, for example eventhough he is very good at drawing male anatomy his females look really bizarre. I actually had a laughing fit over the way he draws breasts (if you've seen Botticelli's "Birth of Venus" you know what I mean)! And he tends to draw all the faces looking the same too, but you can easily practice drawing them from somewhere else.
Couldn't resist drawing my sleeping fat cat!