The diencephalon is continuous rostrally with the mesencephalon without a clear boundary. With its nuclei and connecting pathways, it surrounds the third ventricle and can be subdivided into four sections. From ventral to dorsal, these are:
- Hypothalamus
- Subthalamus
- Subthalamus
- Epithalamus
The wall of the third ventricle also contains circumventricular organs, which are closely connected to the hypothalamus.