Sorry, it was just an extra bone.

Actually, I think I got it right: https://en.wikipedia.org/wiki/Vertebra

You're correct. My neophyte Latin chops be exposed. Let me explain what I just learned with my figurative antennae (plural, not antenna which also ends in 'a' and is singular), something about first and second declensions and neutered...

No that's plenty enough. Carry on!