I found a different skull that I wanted to print so I sliced it up for printing. The jaw should fit better on this model.
Print all the pieces and glue them together.
There is an alternate Mandible Top that has a strap for a rubber band. So if you screw a hook in the bottom of the skull then you can use that strap to hold the mandible on.
I got the original from Grabcad and then sliced it up to print. http://grabcad.com/library/skull-1