Hippocampal Commissure help

biferi

I know The Body Of Fornix first start in both Hipoocampi and comes out the back.
Then goes up to For the body of the Fornix.

But inbetween the 2 Fibre right befor it gets to the Body of Fornix it has Hippocampal Commissure between them connecting them.

I do not understand what it is I thought it just connected the two Fibre befor the come togather to form the Body of Fornix.

Then I thought it had something to do with the Corpus Calossum.

But I just get more mixed up?