Fimbria of the hippocampus

Overview
With regard to the brain, the fimbria  is a prominent band of white matter along the medial edge of the hippocampus.

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.