Ladyatheist got the answer right with her diagram
The litter size was verified in a post at A Merry Meow on Facebook, which also explained why the moggie was x-rayed.
We have an update on this cat. Her name is Grace, and she was given an x-ray because she was over due and the vets wanted to rule out problems. Neither she or the kittens were harmed and she delivered five kittens on 7-11-13.
The original X-ray (here):

h/t: Michael

It is lovely how the kitten bones fluoresce from the Gamma radiation.
+1 🙂
I really hope that is a joke. Sorry if it is ; I woke up early and the coffee didn’t include oil for my sarcasm detector.
Somehow I thought they’d be packaged more neatly. It looks very untidy in there. 😀
That’s why they call it a litter.
(http://www.youtube.com/watch?v=LekUKeFijxc)
I believe that five is correct, but if that’s not a skull just north of the green circle, what is it?
Mama’s stomach, I think. It’s pretty clearly soft tissue, not bone.
Not a vet, but I think that’s the heart, actually. Cat’s left side, nestled right under the lungs.
Grr. Trying linky again.
A hairball?
Well, almost right. I still think she has the yellow one flipped head for tail.
Look at the ribs – the larger ones would be closer to the head. There is something toward the bottom that I thought at first was the head of kitten #6 but looking again later I thought it was more likely bowel or something
Actually, the rib cage narrows at the shoulders and flares out toward the abdomen (see here).
Plus there’s a bony oval just north of the orange skull that seems to be connected by vertebrae to the yellow ribs. I take that to be the yellow skull.
oops no – the larger ones would be on the tail side, so the head I thought was a head was a head! Now the other heat that I thought was a head has me stumped.
So my odd “heads” was the Mama hearth and what not?
Luckily, I’m not a biologist!
Oops, the stomach I see above.
Well, don’t take my word for it. I’m not a biologist either.
This is why I shouldn’t be allowed to interpret x-rays, topological maps, floor plans, or anything stuck in a matrix.
But I have other qualities; for instance I’m pretty good with Monty Python quotes. As evidence that the world is unfair, this has not translated into an lavish livelihood. Yet I find a way to live on. 😀
My Monty Python quote repertoire is from the TV show, not the movies, so I’m doubly obscure
Are you trying to suggest that you’re being repressed and need help?
b&
Well, You can’t expect to wield supreme power just ’cause some watery tart threw a sword at you!
“There…are…*four*…kittens!”
What then, happened to the sixth kitten? It was written and therefore must be accounted, for the christian must have the written word defended against the presence of reality.
Cool to know the answer, I guessed 6, because I mistook the big circular thing above the green outline for the skull of another kitty.