What anatomical feature separates the left and right hemispheres of the brain?

The correct anatomical feature that separates the left and right hemispheres of the brain is the corpus callosum. The corpus callosum is a large bundle of neural fibers located under the cerebral cortex, connecting the two hemispheres and allowing for communication between them. It plays a crucial role in integrating sensory and cognitive processes by enabling the transfer of information from one side of the brain to the other.

While the other options listed contribute to various functions and structures in the brain and central nervous system, they do not serve the purpose of separating the hemispheres. The tentorium cerebelli is a protective fold of dura mater that separates the cerebellum from the occipital lobe but does not separate the two cerebral hemispheres. The ventricles are fluid-filled spaces within the brain that have roles in cushioning and producing cerebrospinal fluid but do not separate hemispheres. The medulla oblongata is part of the brainstem responsible for vital functions like breathing and heart rate, but it is not involved in the separation of the hemispheres. Thus, the corpus callosum is the key structure in this context as it directly relates to the question asked.