Final answer:
The hypothalamus is not found in the brainstem; it is part of the forebrain. The brainstem is comprised of the midbrain, pons, and medulla oblongata.
Step-by-step explanation:
The structure that is not found in the brainstem is the hypothalamus. The brainstem consists of the midbrain, pons, and medulla oblongata. It does not include the hypothalamus, which is part of the forebrain. The brainstem is responsible for several vital functions, including regulating the cardiovascular and respiratory systems. It also serves as a connection point between the forebrain and the spinal cord, and provides sensory and motor pathways to the cranial nerves.