Fourth Ventricle - Roof and Floor

Roof and Floor

The fourth ventricle has a "roof" dorsally and a "floor" ventrally. The roof of the fourth ventricle is formed by the cerebellum (superior and inferior medullary vela), the floor by the rhomboid fossa, and the side "walls" formed by the cerebellar peduncles. Among the prominent features of the floor of the fourth ventricle are the:

1. facial colliculus: formed by the internal part of the facial nerve as it loops around the abducens nucleus in the lower pons;
2. sulcus limitans: which represents the border between the alar plate and the basal plate of the developing neural tube;
3. obex: represents the caudal tip of the fourth ventricle; the obex is also a marker for the level of the foramen magnum of the skull and therefore is a marker for the imaginary dividing line between the medulla and spinal cord.
4. "median sulcus" - divides the floor in to right and left halves.It extends from cerebral aqueduct of the midbrain to central canal of the spinal cord.
5. "stria medullaris" - fibers derived from arcuare nuclei, which emerge from the median sulcus and run transversely across the floor to enter into the inferior cerebellar penducle.
6. "medial eminence" - elevations on either side of the median sulcus.
7. "sulcus limitans" - medial eminence is laterally bounded by sulcus limitans.
8. "vestibular area" - lateral to sulcus limitans vestibular nuclei is overlied by this.
9. The upper end of the sulcus limitans widens into a triangular depression called "suprior fovea" above suprior fovea sulcus limitans presents a flattend grey area called "locus cerulus".
10. The lower end of the sulcus limitans widens into a triangular depression called "Inferior fovea".
11. Other features are the Hypoglossal triangle and vagal triangle.