Development of the nervous system
The nervous system starts to form as early as the third week of embryonic development. By the fourth week, the neural tube has formed and is starting to close. This tube will become the spinal cord and brain. The primitive brain is divided into three major sections: the prosencephalon or the forebrain, mesencephalon or the midbrain, and rhombencephalon or the hindbrain.
The prosencephalon gives rise to the telencephalon, which later becomes the cerebral cortex and basal ganglia. The diencephalon gives rise to the optic cup, which becomes the eyes, the thalamus, the hypothalamus, and the mammillary bodies. The mesencephalon gives rise to the tectum, the cerebral aqueduct, the red nucleus, the crus cerebrum, and the substantia nigra. Finally, the rhombencephalon develops into the metencephalon, which later gives the pons and cerebellum, and the myelencephalon, which later becomes the medulla oblongata.