the.com/midbrain

means The small, ancient relay station atop the brainstem that handles reflexive eye movement, visual and auditory orienting, and helps regulate alertness and motor control.

from Straightforward anatomical compounding: 'mid-' plus 'brain,' naming its physical position in the brain's stem — between the hindbrain below and the forebrain above. The formal term is 'mesencephalon,' from Greek 'mesos' (middle) and 'enkephalos' (brain, literally 'in the head'), coined in the era when anatomists were busy carving the brain into Greek-labeled regions. 'Midbrain' is simply the English plain-speech version sitting beside its Greek cousin.