paleencephalon

noun, plural pa·le·en·ceph·a·la [pey-lee-en-sef–uh-luh; especially British pal-ee-] /ˌpeɪ li ɛnˈsɛf ə lə; especially British ˌpæl i-/.

1. (no longer in technical use) the more primitive part of the brain in the evolutionary development of animals, including all parts except the cerebral cortex and its related structures.