The four dural folds are: falx cerebri, tentorium cerebelli, falx cerebelli, and diaphragma sellae. These folds are formed by the inner layer of the dura mater, one of the meninges that surround the brain and spinal cord. They provide support and compartmentalize the brain.
Here's a more detailed look at each:
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Falx Cerebri: This is a large, sickle-shaped fold that lies in the longitudinal fissure, separating the left and right cerebral hemispheres. It attaches anteriorly to the crista galli of the ethmoid bone and posteriorly to the tentorium cerebelli.
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Tentorium Cerebelli: This tent-shaped fold separates the cerebrum from the cerebellum. It attaches to the petrous part of the temporal bone, the occipital bone, and the sphenoid bone. It creates a space called the tentorial notch (or incisura) through which the brainstem passes.
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Falx Cerebelli: This is a small, sickle-shaped fold that projects downward from the tentorium cerebelli, separating the two cerebellar hemispheres.
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Diaphragma Sellae: This is the smallest of the dural folds. It is a horizontal shelf of dura mater that covers the pituitary gland and the sella turcica of the sphenoid bone. It has a small opening for the passage of the infundibulum (pituitary stalk).
These dural folds not only provide structural support to the brain but also help to limit its movement within the skull, protecting it from injury. They also form venous sinuses, which drain blood from the brain.
