Fornix

The fornix is a thin, C-shaped white matter bundle located on the medial aspect of the cerebral hemispheres. It is a major pathway of the limbic system, connecting the hippocampal formation with structures in the diencephalon and basal forebrain.

Fibres from the hippocampus collect in the alveus and then the fimbria. As the fimbria enlarges, it continues as the crus of the fornix. The right and left crura curve superiorly and anteriorly beneath the splenium of the corpus callosum and continue as the body of the fornix, which arches above the thalamus and beneath the septum pellucidum. Anteriorly, the body divides into the right and left columns of the fornix, which descend into the basal forebrain.

At the anterior commissure, fibres of the columns divide into precommissural fibres, which pass anterior to the commissure and postcommissural fibres, which pass posteriorly and include subicular projections to the mammillary bodies and anterior thalamic nuclei.