This bisected brain shows the major features of the midbrain and brain stem. The corpus callosum is just been the cortex of the brain and connects the left and right hemispheres. The lateral ventricle is a fluid filled space found below the corpus callosum and just about the fornix. The septum pellucidum is a thin membrane that separates the two sides of the lateral ventricle. It takes a careful incision to keep this small membrane intact.
The third ventricle is a fluid filled space between the fornix and the thalamus.