Metencephalon

At week four of development, the neural tube develops to form three primary ventricles: forebrain, midbrain, and hindbrain. At week five, the secondary brain ventricles form. The forebrain develops into the telencephalon and diencephalon. The midbrain becomes the mesencephalon. Finally, the hindbrain, becomes the metencephalon and myelencephalon. Essentially, the metencephalon becomes the pons and cerebellum and contains many ascending and descending tracts, as well as the reticular formation. The pons is the bridge to the cerebellum, which plays key functions in motor coordination and perhaps even somatosensory function.