Fornix

The fornix is the main efferent system of the hippocampus and an important part of the limbic system. It is one of the commissural fibres connecting the cerebral hemispheres.

Roughly C-shaped, the fornix extends from the hippocampus to the mamillary 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. The alveus joins to form the fimbria of the hippocampus. The fimbria of each hippocampus thickens and then splits off from the hippocampus to form the crus (leg) of the fornix.

The fornix is composed of four parts: 

  • crura: best seen at the splenium of the corpus callosum at the level of the superior colliculus on coronal images
  • commissure: connects the crura
  • body: from the merging of the crura, provides one of two major paths through which the hippocampi communicate with each other
  • columns (anterior pillars): curves anteriorly and dives into the hypothalamus (mammillary bodies)
Fibre tracts

At the level of the anterior commissure, the fornix divides into anterior and posterior fibres. The anterior fibres (called precommissural fibres) end in the septal region and nucleus accumbens 1,2. The posterior fibres (called the postcommissural fornix) end through the mammillary body of the hypothalamus.

The fornix connects:

  • the hippocampus to the mammillary bodies
  • the hippocampus to the septal nuclei and the nuclei accumbens
  • the mammillary bodies to the anterior nuclei of the thalamus
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

  • transection of the fornix at the level of its body can lead to memory loss 1,2

Neuroanatomy
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Article Information

rID: 33871
Section: Anatomy
Tags: refs, cases
Synonyms or Alternate Spellings:

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