Oh Greg just woke up so here it is. "How do you make a Maltese Cross?"
The answer: "Poke it in the eyes." Now get your parents to explain it.
You can see the Maltese Cross on the tomb in this picture. The twisted column is copied after some of the columns in the Vatican. There are skulls on either side of the white bust.
The floors are all tombstones of the Saints or heroes of the day. So as you walk through the Cathedral your feet are walking on and covering fabulous inlaid marble tombstones with Latin inscriptions. This was 15 euros well spent to go through the Museum.