Final answer:
The fourth ventricle of the brain is located in the brainstem, not in the cerebral hemispheres, and is involved in circulating cerebrospinal fluid.
Step-by-step explanation:
The fourth ventricle is a part of the ventricular system in the brain and is not situated within the cerebral hemispheres. Rather, it is located in the region of the brainstem and is between the cerebellum and the pons and upper medulla. It is responsible for circulating cerebrospinal fluid through the central nervous system and into the subarachnoid space through median and lateral apertures.
Hence, the answer for the question about where the fourth ventricle is located would be option B. brainstem.