In response to Eric's comments about whether or not the bolt broke, I can not say for sure, but the bolts are secured with ny-lock nuts that should prevent an inadvertent loosening of the nut.

The vertical bolt in the picture attaches to a plate on the bottom side of the upper (inverted) U-shaped piece of the tongue. This plate then butts up against the edge of the square tube that forms the inner piece of the tongue and it appears to be there to prevent the two pieces of the tongue from moving fore and aft against each other, or perhaps for alignment during installation.