The correct option is White matter.
Explanation
The cerebral hemispheres are structurally divided into two distinct regions based on the composition of neuronal tissue: the outer cortex and the inner medullary region.
- White Matter: The inner part of the cerebral hemisphere consists of fibers known as tracts. These tracts are composed of myelinated axons. The myelin sheath, which is lipid-rich, gives this tissue an opaque white appearance, leading to the designation "white matter." Its primary function is to connect different parts of the grey matter to each other.
- Grey Matter: The outer layer of the cerebral hemisphere is called the cerebral cortex. It contains a high concentration of neuronal cell bodies, which gives it a greyish appearance. It is referred to as grey matter.
- Cortex: This term specifically refers to the outer layer of the cerebrum (grey matter), not the inner region.
- Pia: The Pia mater is the innermost layer of the meninges (protective membranes) that closely adheres to the surface of the brain. It is a connective tissue layer, not the inner neural tissue itself.
Key Takeaway: In the cerebrum, the outer layer is Grey Matter (cell bodies), and the inner region is White Matter (myelinated axons).