Fossil and recent brains are cited which do not agree with the concept that midbrain exposure is always the sign of a poorly developed cerebrum and overlap always related to neocortical expansion. That forebrain and hindbrain are in contact in all 3 known brains of mesozoic mammals suggests that, between already macrosmatic but still palae-encephalic cerebrum and still palaeocerebellar cerebellum, the midbrain was still of reptilian type. The midbrain extending between forebrain and hindbrain in early cenozoic mammals had acquired mammalian characteristics with the beginnings of a neocortex. While in most phylogenies it became and stayed submerged with neocortical advance, the tectum became secondarily exposed - in Microchiroptera in the Paleocene, in an edentate more recently - through drives in the midbrain centers themselves.