Precommissural fornix is a filamentous mass that detaches from the vault (fornix)
in front of the ventricular intercavity and disappears into the septal region. The wire mass connects the seahorse (hippocampus) to the acetylcholine-producing so-called
septal nuclei. These, in turn, send threads via the fornix back to the hippocampus. The septal nuclei will thus "irrigate" the hippocampus with acetylcholine.