Michelangelo dissected corpses because he was studying the human body and creating sketches of the muscles and arteries of a human body so then others were able to study those sketches and get a better idea of how the body is on the inside therefore proving his theory about bone structure.
I kinda had to remember back to my art classes to remember what I learned about Michelangelo and then what I couldn’t piece together I looked up. Hopefully it’s right. May not be the exact answer you were looking for but I tried lol.