just think what is brain?

The brain
The brain is a relatively small organ, weighing about 1,500 grams and constituting about 2 percent of total body weight. Three major divisions of the brain are recognized: (1) the massive, paired cerebral hemispheres ( cerebrum), derived from the telencephalon; (2) the brain stem, from which all true cranial nerves emerge, consisting of the thalamus and hypothalamus, the midbrain, the pons, and the medulla oblongata (also known as the diencephalon, the mesencephalon, the metencephalon, and the myelencephalon); and (3) the cerebellum (“little brain”), derived from the pons, or metencephalon. The terms telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon denote five distinct embryonic subdivisions derived from separate vesicles in the rostral neural tube.