What is the Falx Cerebri?

The falx cerebri is a structure inside the human skull that divides the two hemispheres of the brain, also known as the cerebrum. This structure should not be confused with the falx cerebelli, a similar structure that divides the cerebellum. Like other aspects of the cranial anatomy, the falx cerebri is designed to protect and insulate the brain to reduce the risk of injury in response to trauma and infection, while also providing pathways for blood vessels, fluid drainage, and nerves.

This structure is made up of dura mater. Dura mater is one of the thick layers of material that is located between the inner skull and the brain. It can also be found encasing the spinal cord. It is very strong and tough, designed to resist impact and prevent the leakage of cerebrospinal fluid. Dura mater could be considered the outerwear for the brain and spinal cord, used to protect these delicate structures from injury.

In several locations, the dura mater makes folds, also known as reflections. Instead of simply lining the skull, the dura mater protrudes into the skull cavity. The falx cerebri is one such site. The dura mater forms a shape like a sickle that is narrow in front and wider in the back of the brain. It separates the hemispheres of the brain and also houses the sagittal sinuses that provide a pathway for cerebrospinal fluid drainage around the brain. These cavities can be found at the top of the falx cerebri, as well as the bottom. In addition, the structure houses blood vessels that supply the brain.

In the front of the skull, the falx cerebri attaches to a ridge of bone known as the crista galli or “rooster's crest.” In the back of the brain, it connects with the tentorium cerebelli, a structure that separates the cerebellum from the cerebrum. As people age, the composition of the falx cerebri changes and it tends to calcify, stiffening and growing harder.

Depictions of surgical procedures on the brain on television often show surgeons cutting through a thin layer of skull to directly access the brain. This is not actually the case. Surgeons must first peel the scalp back from the skull, make an incision in the bone, and then cut through the layers of dura to access the brain. The falx cerebri is one of the structures that can be used as an orienting landmark, as the signs of the superior sagittal sinus can be seen once the skull is opened.