In the anatomy of the brain of vertebrates, the<unk>  (or forebrain) is the rostral-most portion of the brain. The<unk> , the mesencephalon (midbrain), and rhombencephalon (hindbrain) are the three primary portions of the brain during early development of the central nervous system.
At the five-vesicle stage, the<unk>  separates into the diencephalon (prethalamus, thalamus, hypothalamus, subthalamus, epithalamus, and pretectum) and the telencephalon (cerebrum).  The cerebrum consists of the cerebral cortex, underlying white matter, and the basal ganglia.
When the embryonic<unk>  fails to divide the brain into two lobes, it results in a condition known as holoprosencephaly.
Prosencephalon
Rhombencephalon
Cerebral peduncle
Hypophysial fossa
Diencephalon
Periaqueductal gray
Fourth ventricle
Lingula of cerebellum