Overview
The fornix is a C-shaped outflow bundle of white matter, originating from the hippocampus in the mesial temporal lobe and is the main efferent system of the hippocampus. It is part of the limbic system, associated with the processes of cognition, memory consolidation, emotions and sexual responses. It is one of the commissural fibres connecting the cerebral hemispheres.
Structure & Course
The fornix extends from the hippocampus to the mammillary bodies of the hypothalamus and the anterior nuclei of the thalamus. It is a curvilinear bundle of white matter fibres that begins as a group of myelinated fibres called the alveus.
- Alveus – Found medially to the floor of the temporal horn of the lateral ventricle. The fibres travel posteromedially and join to form the fimbria of the hippocampus.
- Fimbria – The fimbria of each hippocampus thickens and then splits off from the hippocampus to form the crus (leg) of the fornix.
- Crura – The two crura arch anterosuperiorly under the splenium of the corpus callosum.
- Body – The two crura continue anterior and merge in the midline to form the body. The body arches over the thalamus under the septum pellucidum, which connects it to the corpus callosum
- Columns – The body of the fornix extends anteriorly and bifurcates into left and right columns of the fornix. Each column turns towards in front of the interventricular foramen of Monro and passes through the hypothalamus to reach the mammillary body.
Connections
- Hippocampal commissure (of psalterium Davidi or David’s lyre) – connects the crura across the midline
- Precommissural fornix – Composed of the fibres that descend in front of the anterior commissure. They relay onto the septal nuclei (medial olfactory area), the ventral striatum, orbital cortex and the cingulate gyrus. Some fibres also reach the habenular nuclei
- Postcommissural fornix – Fibres that pass behind the anterior commissure and relay onto the mammillary bodies and the anterior nuclei of the thalamus.
- Dorsal fornix – A small amount of fornical fibres pass above the splenium of corpus callosum to reach the structures above the corpus callosum
Relations
- Superiorly: septum pellucidum anteriorly, splenium of corpus callosum posteriorly
- Inferiorly: thalamus anteriorly
- Medially: third ventricle (lies inferior to the body of the fornix)
- Laterally: medial aspects of the cerebral hemispheres
- Anteriorly: anterior commissure
- Posteriorly: posterior commissure, splenium of corpus callosum
Arterial Supply
- Mainly from the short medial central arteries, derived from the proximal anterior cerebral artery
