FIGURE 2-19 Diencephalon The diencephalon (center) is composed of the thalamus, shown at right, and the hypothalamus and other structures, shown at left. Thalamic regions connect to discrete cortical regions. Below the thalamus, at the base of the brain, the hypothalamus (hypo-, below) and pituitary lie above the roof of the mouth. The hypothalamus is composed of many nuclei, each with distinctly different functions.