https://en.m.wikipedia.org/wiki/Corpus_callosum

The corpus callosum (Latin for "tough body"), also callosal commissure, is a wide, thick nerve tract, consisting of a flat bundle of commissural fibers, beneath the cerebral cortex in the brain. The corpus callosum is only found in placental mammals. It spans part of the longitudinal fissure, connecting the left and right cerebral hemispheres, enabling communication between them. It is the largest white matter structure in the human brain, about 10 in (250 mm) in length and consisting of 200–300 million axonal projections.

https://en.m.wikipedia.org/wiki/Lateral_ventricles

The lateral ventricles are the two largest ventriclesof the brain and contain cerebrospinal fluid.[1] Each cerebral hemisphere contains a lateral ventricle, known as the left or right lateral ventricle, respectively.