Final answer:
The adult derivatives of the diencephalon's wall include the thalamus, hypothalamus, and the retina. The thalamus and hypothalamus form the walls of the third ventricle, and the optic cup within the embryonic diencephalon develops into the retina.
Step-by-step explanation:
The diencephalon is a region of the adult brain that carries the same name it had during embryonic development. In adults, the diencephalon is comprised of several structures: the thalamus, the hypothalamus, and the epithalamus, which includes the pineal gland. Additionally, the diencephalon embryologically gives rise to other structures such as the optic nerves and the retina. The thalamus and hypothalamus form the walls of the third ventricle, with the thalamus located on either side of the midline, contacting in the middle, and the hypothalamus situated inferiorly and anteriorly, leading down to the pituitary gland. The optic cup, which develops within the embryonic diencephalon, eventually becomes the retina of the eyes, illustrating a rare instance where central nervous system (CNS) tissue becomes a peripheral structure in the mature nervous system.