Myelencephalon

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 myelencephalon becomes the medulla oblongata, which functions to regulate autonomic functions, such as breathing, heart rate, and blood pressure, and reflexes.