The outside of the floor of the third ventricle.

Tuber cinereum

Grey area of the hypothalamus located on the underside of the midbrain and giving rise to the pituitary stalk.
The tuber cinereum is located posterior to the optic nerve cross and in front of the wart bodies and is bounded to the sides by the substantia perforata anterior. The area contains on hay. and we. side, adjacent to the wart body, nucleus tuberomammillaris.

Do not confuse tuber cinereum with tuberculum cinereum located on the outside of the medulla.