In anatomy, a fornix is any arch-shaped structure found within the body, but the most common use of the term is to refer to a fornix located within the brain. It is a C-shaped bundle of fibers, also known as axons, which carry signals from the hippocampus to other parts of the brain, including the septal nuclei and the hypothalamus. This fornix resembles a conjoined pair of C-shaped objects, placed at an angle and touching at the top edge. The bottom edges of both objects angle outward, causing them to touch both hemispheres of the brain.
The fibers actually begin in the hippocampus, and at their origin point they are known as the fimbia. They then come together and meet at their top edge, merging together to form the body, and then split again when they reach the back end, forming the anterior pillars. This structure is located in the midbrain and makes its arch directly above the thalamus.
Fornix is the Latin word for arch or vault, and this structure of the brain is so named solely because of its unique shape. While the exact function and importance in overall brain physiology is not clear, it has been demonstrated that surgical transsection – the cutting of the fornix along its body – can cause memory loss in humans. There is some debate over what type of memory is affected by this damage, but it has been found to most closely correlate with recall memory rather than recognition memory. This means that damage to it can cause difficulty in recalling long-term information such as details of past events, but it has little effect on the ability to recognize objects or familiar situations.
While the most common definition will refer to this particular brain structure, the term itself can also be used to refer to other arch-like structures in the body. Two of the most notable are the uterine fornix, which includes several recessed areas located in the deepest part of the vagina and is created by the protrusion of the cervix into the vaginal cavity, and the fornix conjunctivae, which refers to a series of aching membrane liners in the eye that are in turn connected to a membrane cover. Generally, if the term is used without any preceding or following word but simply noted as the fornix, it will almost inevitably refer to the arching brain structure described above.