Axial CT of the brain

1. A Falx cerebri.

2. B Right middle cerebellar peduncle.

3. C Right cerebellar hemisphere.

4. D Left tentorium cerebelli.

5. E Pons.

The falx cerebri is a scythe-shaped fold of dura mater in the longitudinal fissure between the two cerebral hemispheres. It attaches anteriorly to the crista galli of the ethmoid and posteriorly to the upper surface of the tentorium cerebelli. The tentorium cerebelli is a tent of dura that separates the cerebellum from the inferior portion of the occipital lobe, thus defining the supratentorial and infratentorial spaces.

The cerebellum is connected to the rest of the central nervous system by three pairs of nerve tracts known as cerebellar peduncles. The inferior cerebellar peduncles connect the medulla spinalis and medulla oblongata with the cerebellum. They form a thick strand between the lower part of the fourth ventricle and the roots of the ninth and tenth cranial nerves. The middle cerebellar peduncles connect the pontine nuclei to the contralateral cerebellum. Their fibres are arranged in three fasciculi – superior, inferior and deep. The superior cerebellar peduncles connect the cerebellum to the midbrain. They form the upper lateral boundaries of the fourth ventricle. The anterior medullary velum connects the superior cerebellar peduncles, and between them they also form the roof the fourth ventricle.