What structure separates the two cerebral hemispheres and extends into the longitudinal fissure?

• A. Falx cerebri
• B. Corpus callosum
• C. Thalamus
• D. Cerebellum

Answer: (A)

The structure that separates the two cerebral hemispheres and extends into the longitudinal fissure is the falx cerebri. It is a sickle-shaped fold of dura mater, the tough outer layer of the meninges that protects and surrounds the brain. The falx cerebri lies in the midline of the cranial cavity and helps anchor the two hemispheres of the brain, providing stability. By its position, it also prevents excessive movement of one hemisphere over the other, which is crucial for maintaining the integrity and function of the cerebral hemispheres.

The other structures mentioned do not serve this specific purpose. The corpus callosum is a large bundle of nerve fibers connecting the left and right hemispheres, facilitating communication between them, but it does not separate the hemispheres. The thalamus is a central relay station for sensory information and is located deep within the brain, playing a different role in processing and relaying signals rather than separating hemispheres. The cerebellum is located at the back of the brain and is primarily involved in motor control and coordination, not in the separation of the cerebral hemispheres.