Either of two masses of grey matter, the largest part of the diencephalon, lying between the cerebral hemispheres on either side of the third ventricle, relaying sensory information and acting as a centre for pain perception.
Source: PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 812 (https://doi.org/10.1515/pac-2015-1202)