The third ventricle is the space formed by the expanding canal of the diencephalon. The ratio of the basal ganglia, diencephalon and brainstem combined is 11.35. The prosencephalon develops further into the telencephalon and the diencephalon. The subthalamus or prethalamus is a part of the diencephalon. The pineal body lies just above the diencephalon. The retina itself is derived from the optic cup, a part of the embryonic diencephalon. In the human brain, the telencephalon covers most of the diencephalon and the mesencephalon. The pineal gland is located in the diencephalon of the brain. The prosencephalon gradually divides into the telencephalon and the diencephalon. Research has also shown that when areas of the diencephalon are damaged, amnesia can occur. The midbrain continues with the thalamus of the diencephalon through the tentorial notch. The medial lemniscus and lateral lemniscus terminate in specific relay nuclei of the diencephalon. The epithalamus is a (dorsal) posterior segment of the diencephalon. The diencephalon expands more evenly, but caudally of the diencephalon the canal remains narrow. The basal plate becomes the diencephalon.