There are several ways to describe the human brain. Three functional brain layers is one way. Three brain parts is another.
Some scientists speak about these three parts as:
1. The cerebrum (including two hemispheres and the mammalian or
2. Two cerebellums
3. One brain stem
This model lumps the neocortex with its two hemispheres and the mammalian brain into one part, the two cerebellum portions as one part, and the brain stem as one part.