The two main types of neural tissue is,
• White matter
• Gray matter
The surface of the cerebrum contains several foldings called gyri (raised ridge of the folding), and it consists of the nerve cells (grey matter) and it is also called as cerebral cortex. White matter (nerve fibres) is present in the interior of the hemispheres. These foldings are separated by sulces (shallow grooves) or fissures (deep grooves).
Thus, the blanks can be filled with white matter, gray matter.