Tentorium cerebelli

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What it is
A tent-shaped sheet of dura roofing the posterior cranial fossa: it separates the occipital lobes above from the cerebellum below, is attached to the transverse sinus grooves and petrous ridges, and has a U-shaped free edge (the tentorial notch) around the midbrain.
Function
Supports the occipital lobes so they do not press on the cerebellum and divides the cranial cavity into supratentorial and infratentorial compartments.
Size
About 10-11 cm wide; the notch is ~3 cm wide and 5 cm long
Clinical note
Raised supratentorial pressure can squeeze the uncus of the temporal lobe through the notch (uncal herniation), stretching the oculomotor nerve and dilating the pupil.

Nearby nervous structures Cerebellar vermis, Cerebellar white matter (arbor vitae), Cerebral aqueduct, Fornix, Fourth ventricle, Midbrain, Pons, Trigeminal nerve root (CN V), Trochlear nerve root (CN IV), Vestibulocochlear nerve (CN VIII)