The two posts that hold up the table each have two holes in them. Two brackets extending between the two posts hang free when the table is closed, but they provide diagonal support to each half of the table when open.
You can see part of the support brackets with the table in the closed position in this photo here:
http://www.mackenziegems.com/gallery/tesara04/dscn0749 It'll probably take me two weeks, but, I can take a few good photos of the underside of the table.
