Complete the passage describing the four major regions of the adult brain. The cerebrum is the largest and most superior region of the brain, making up more than 80% of total brain mass. The outermost layer of the cerebrum forms the central cortex. It consists of two hemispheres separated along the midline by the longitudinal fissure, this region, the core of the brain. It contains the thalamus and provides relay centers for control of visceral activities and for some sensory and motor pathways. Inferiorly, this region communicates with the brainstem, which consists of three distinct subdivisions. From superior to inferior, these include the midbrain, pons, and medulla, collectively, they control automated behaviors. The cauliflower-like cerebellum lies posteroinferior to the occipital lobe and dorsal to the pons and medulla. This region functions as an integration center, fine-tuning constitutes the conscious mind.