Hippocampal commissure
Commissura hippocampi
A thin triangular sheet of crossing fibres between the two crura of the fornix, under the splenium of the corpus callosum, linking the hippocampi.
At a glance
- English
- Hippocampal commissure
- Latin (TA2)
- Commissura hippocampi
- System
- Brain and spinal cord
- Region
- Head
- Side
- Single, on the midline
About the hippocampal commissure
The hippocampal commissure, also called the commissure of the fornix, is one of the fibre bundles that join the two cerebral hemispheres across the midline. It is a small one, made of fibres that pass from the hippocampal formation of one side to that of the other. It lies under the back of the corpus callosum, close to the splenium, in the roof of the third ventricle and the bodies of the lateral ventricles.
To place it, follow the fornix. On each side the fibres leaving the hippocampus collect as the fimbria and then rise as a crus, curving up behind the thalamus. As the two crura approach each other beneath the corpus callosum, a thin, three-cornered plate of transverse fibres links them of transverse fibres, which is the commissure. Further forward the crura come together as the body of the fornix. The plate is often called the psalterium or lyre (lyra Davidis), because the diverging crura and the fibres strung between them resemble the frame and strings of a small harp. Its upper surface is closely applied to the underside of the corpus callosum.
In development, the hippocampal commissure forms early, together with the anterior commissure, in the commissural plate, a thickening of the lamina terminalis at the front end of the forebrain. The corpus callosum then grows across in the same plate, and the septum pellucidum and fornix are shaped out of the tissue between them.
Its fibres allow the two hippocampi, and especially the entorhinal and subicular areas that feed them, to exchange information, which is thought to help in combining memories laid down on each side. In humans the commissure is small compared with other mammals, in which it is a major route. It is cut together with the corpus callosum in a complete callosotomy for epilepsy, and absence of the corpus callosum in development is often accompanied by changes in this commissure.
Function and supply
- Begins at
- Arises from the hippocampal formation and the fornix crus of one side.
- Ends at
- Crosses the midline beneath the splenium of the corpus callosum to the crus and hippocampal formation of the other side.
- Function
- Connects the two hippocampal formations across the midline, allowing exchange of memory-related signals between the hemispheres.
- Blood supply
- Branches of the posterior pericallosal artery and posterior choroidal arteries from the posterior cerebral artery.
Anthromica
See the hippocampal commissure where it really sits, with every layer of the body around it.
- Every layer, one body. Peel from muscle to bone, nerve, vessel and organ, and turn it any way.
- English and Latin. Every structure named the way your exam names it.
- Quiz until it sticks. Short drills on the structures you keep missing.
Free to start. No card.
