Fimbia of the hippocampus

With regard to the brain, the fimbria  is a prominent band of white matter along the medial edge of the hippocampus. It is a complex fibre bundle that runs from the lateral surface of the Hippocampal formation to other regions of the forebrain

Structure
The fimbria is an accumulation of myelinated axons (mostly efferent) that first collect on the ventricular surface of the hippocampus as the alveus (a thin layer resembling an inverted trough).

Relations
Near the splenium the fimbria separates from the hippocampus as the crus of the fornix. So that section which runs rostrally from the hippocampus forms the fornix. This is divided in turn into:
 * the precommsisural fornix, the axons of which run from the medial septum to the hippocampus and from there to the lateral septum
 * The fornix columns, which convey axons from the subiculum to the anterior thalamic nuclei and to the mammilary bodies of the hypothalamus.