tegmentum

https://doi.org/10.1351/goldbook.11282
Floor of the midbrain.
Notes:
  1. In the embryo this term refers more generally to the anterior portion of the neural tube.
  2. The tegmentum is the site of the nuclei of several cranial nerves.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 811 (https://doi.org/10.1515/pac-2015-1202)