Septum pellucidum
Nerves
The septum pellucidum (Latin for "translucent wall") is a thin, triangular, vertical double membrane separating the anterior horns of the left and right lateral ventricles of the brain.
It runs as a sheet from the corpus callosum down to the fornix. The septum is not present in the syndrome septo-optic dysplasia.
Definition from Wikipedia, CC BY-SA 4.0.