I'm a beginner in origami folding (I have folded a few models so far) and I'm having some problems with Apatosaurus from Hans Birkeland http://origamiarts.wordpress.com/2008/0 ... atosaurus/. I'll be glad if someone could help me and give me some directives

I'm stuck at steps 13-16 (altought I'm not sure if I have done in a right manner step 11 because step 12 was a bit difficult from what I obtained hehe).
What I have right now (I have tried two prototypes so to speak):

A "zoom" of the backbone in the second prototype:

It looks fine, but the view from the top is not very attractive, so I am not sure if I'm doing it right:

A view from below shows (what I see as


Finally, an image from step 17. I'm not sure if this is the fold explained (the upper part is folded, while the bottom isn't)

Also, I have difficulties to fully understand step 19 :S. I'm I supposed to turn up the tail at the two points indicated? How is this step done?
Thank you very much for your attention and help!