Concerning the bone, the os coccygis, there is an interesting story in Midrash Kohelet (fol. 114, 3), which may be appropriately inserted here. Hadrian (whose bones may they be ground, and his name blotted out) once asked Rabbi Joshua ben Chanania, "From what shall the human frame be reconstructed when it rises again? B " From Luz in the backbone, B was the answer. " Prove this to me,8 said Hadrian. Then the Rabbi took Luz, a small bone of the spine, and immersed it in water, but it was not softened; he put it into the fire, but it was not consumed; he put it into a mill, but it could not be pounded; he placed it upon an anvil and struck it with a hammer, but the anvil split and the hammer was broken. (See also Zohar in " Genesis, " 206, etc. etc.)