midbrain

mid·brain

noun \ˈmid-ˌbrān\

Definition of MIDBRAIN

: the middle division of the three primary divisions of the developing vertebrate brain or the corresponding part of the adult brain that includes a ventral part containing the cerebral peduncles and a dorsal tectum containing the corpora quadrigemina and that surrounds the aqueduct of Sylvius connecting the third and fourth ventricles—called also mesencephalon

Illustration of MIDBRAIN