Corpus: Fornix of cerebrum

The fornix of the cerebrum is a C-shaped projection tract of the brain that connects the hippocampus to the mammillary bodies.

The fornix lies ventrally and rostrally (according to Forel) to the corpus callosum and is an efferent fiber bundle of the hippocampus, which is part of the limbic system. The fornix cerebri consists of:

• Fornix column
• Body of the fornix
• Crus of fornix
• Commissure of fornix

The fiber tracts of the fornix form fimbriae inside the hippocampus. The right and left fiber cords form two initially separate thighs (crura), which meet in the midline of the brain to form the fornix body. The lower edge of the pellucid septum touches the upper side of the fornix body.

The fornix body continues anteriorly and divides again near the anterior commissure into a left and right part, the two fornix columns. These consist of a free part (pars libera), which runs freely through the third cerebral ventricle and forms the anterior boundary of the foramen of Monro, and a covered part (pars tecta), which is covered by tissue of the hypothalamus. The fibers in front of and behind the commissure take different courses:

• The postcommissural fornix runs through the hypothalamus to the mammillary bodies, then to the anterior thalamic nuclei, which project to the cingulate gyrus.
• The precommissural fibers end at the septal nuclei and the nucleus accumbens of each cerebral hemisphere.

The fornix is supplied with blood by branches from the anterior cerebral artery and the pericallosal, callosomarginal, and anterior communicating arteries.

The function of the fornix is not yet (2024) fully understood. It connects the limbic system with integrative nuclei of the hypothalamus, constituting part of the Papez circuit.

Damage to the fornix (e.g., due to tumors or herpes encephalitis) leads to anterograde amnesia, long-term memory disorders, and loss of spatial orientation. Recognition of objects is not affected.