There was a good segment on this on Deer & Deer Hunting TV last week. They did an autopsy of a deer and took it down layer by layer showing where the vitals are and how the chest cavity is situated. They also mentioned that in the pics the lungs were deflated (as it was a dead deer) and when inflated are 3 times the size shown in the pics.

Just as you said there is no dead zone between the spine and the vitals but an area that can be a non-lethal spine hit.

Good post.