Which two structures make up most of the diencephalon?

1. They define the walls of the third ventricle. 2. One sits below the other. 3. The diencephalon is composed primarily of the thalamus and hypothalamus. 4. So the answer is thalamus and hypothalamus. _Source: OpenStax 'Anatomy and Physiology 2e', Ch 13 'Anatomy of the Nervous System'_