Stalk-like part of the brain that includes amongst its parts the medulla oblongata of the hindbrain and the tegmentum of the midbrain[ZFA,MP,generalized].
Comment:
'brainstem' is a loose term that sometimes refers to the ventral parts o the brain except for any part of the telencephalon - sometimes it includes the diencephalon or subpallial telencephalon structures (ISBN:0471888893). Here we use it in a more restriced sense, to include only the medulla oblongata, pons (when present) and the midbrain tegmentum (following the ZFA definitions).