Below you can find the Red blood cells are made in this substance that fills the medullary cavity of the bones Jeopardy Words Answer. The answer to Red blood cells are made in this substance that fills the medullary cavity of the bones has 6 letters. This clue belongs to the Science & nature category and is part of Jeopardy Word Level 909. If you scroll near the bottom you will find other clues and answers part of level 909