Tuberculum cinereum

The tuberculum cinereum, more properly named "trigeminal tubercle", is a raised area between the rootlets of the accessory nerve and posterolateral sulcus. It overlies the spinal tract of trigeminal nerve.
It is an elevation in the lower part of medulla, lateral to the fasciculus cuneatus, produced by a mass of grey matter called the spinal nucleus of trigeminal nerve.