What structure separates the cerebellum from the cerebrum in the posterior fossa?

• A. Tentorium
• B. Falx cerebri
• C. Cisterna magna
• D. Cavum septum pellucidum

Answer: (A)

The separation between the cerebellum and cerebrum in the posterior fossa is formed by the tentorium cerebelli, a dural fold that acts as a horizontal shelf separating the cerebellum (infratentorial) from the cerebral hemispheres (supratentorial). This structure creates the boundary between the two compartments and has a notch for the brainstem to pass through.

The other options aren’t responsible for this separation: the falx cerebri divides the cerebral hemispheres in the longitudinal fissure, not the cerebellum and cerebrum; the cisterna magna is a CSF-filled space behind the medulla, not a separating membrane; the cavum septum pellucidum is a potential space within the ventricles, not a barrier between cerebellum and cerebrum.