Bolyerine Snakes maxillary bone, split?
If you look at Fig. 2 in the paper, the bottom jaw has the split maxillary bone. Do you see how it says "MX" with two lines, instead of "MX" with 1 line on the top skull from Fig. 2? Each of those lines go to part of the split maxilla, with the joint being where it is pinched off (between teeth 5 and 6 on the drawing). There is also a CT image of the skull somewhere online that I've run across a few times (actually saw your question while looking for that image now).

I would also amend your statement a little in that it is not "as what is the point of 1/2 of jaw", it is that you can't have 1/2 of the joint(or split bone) existing. Either the maxilla is 1 piece or it is 2, but you cannot gradually go from 1 bone to 2 (similarly, either the cartilage of the joint exists or it doesn't. There can be a gradual change in how much cartilage there is, but if it's there or not is a binary question).

I hope that helps, off to look for the CT scan!