Housing the cerebellum and pons and many ascending and descending tracts of the reticular formation, it is the rostral (anterior) part of the rhombencephalon (or hindbrain), and sits above the medulla oblongata. It also contains part of the fourth ventricle as well as parts of the fifth (trigeminal), sixth (abducens), seventh (facial) and eighth (vestibulocochlear) cranial nerves. It is involved in a wide range functions, including arousal, balance, circulation, control of precise movements (e.g., of the tongue and lips in aid of speech production), maintenance of muscle power, and sleep and dreaming. At five weeks in the embryo, the rhombencephalon divides into two, with the metencephalon becoming the primary vesicle and the myelencephalon behind it forming a secondary one. By three months, the metencephalon differentiates into the pons and the cerebellum.
See Arousal, Brain (or encephalon), Cerebellum (anatomy), Cranial nerves, Diencephalon, Medulla oblongata, Mesencephalic reticular activating system, Mesencephalon, Muscle tone (or power), Pons, Prosencephalon, Red nucleus, Rhombencephalon, Sleep-waking cycle, Telencephalon, Ventricle, Vesicle