I was a little confused looking at this one at first. I thought her back was actually her midriff, because the line on her back looks like a navel.
Part of the reason it's confusing is the fact that, in spite of her wide hips, she has practically no ass. Based on the way her left thigh is extended back toward the viewer, you'd expect the curvature of her left cheek to be at least slightly noticeable, but it's completely flat. If you cropped the hands and knees and upper body out of this, I suspect that most viewers would assume they were looking at a drawing of someone's crotch.