Posterior part of the forebrain (prosencephalon), containing the hypothalamus and other thalamic components and enclosing the third ventricle.
Compare: telencephalon
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 744 (https://doi.org/10.1515/pac-2015-1202)