The "body in buddha" x-ray showed an iron band supporting the head. There is an explanation in the above paper.
Sokushinbutsu (即身仏) are a kind of Buddhist mummy. In Japan the term refers to the practice of Buddhist monks observing asceticism to the point of death and entering mummification while alive.
Mendicants, these two extremes should not be cultivated by one who has gone forth. What two? Indulgence in sensual pleasures, which is low, crude, ordinary, ignoble, and pointless. And indulgence in self-mortification, which is painful, ignoble, and pointless. Avoiding these two extremes, the Realized One woke up by understanding the middle way of practice, which gives vision and knowledge, and leads to peace, direct knowledge, awakening, and extinguishment.
Buddhism has died many times and been reborn many more times. Just as it has in you. Be careful clinging to signs. Be careful of certainty. We mummify ourselves in many ways other than the literal.