The falx cerebri is a strong crescent-shaped sheet that represents an invagination of the meningeal layer of the dura mater into the longitudinal fissure, found between the medial surfaces of the cerebral hemispheres. This sheet descends in the midline of the brain, separates the cerebral hemispheres and incompletely divides the cranial cavity into right and left halves.
Anteriorly, the falx cerebri is attached to the crista galli of the ethmoid bone, and runs posteriorly in the sagittal plane, as far back as the internal occipital protuberance. Its posterior part blends with another dural fold called the tentorium cerebelli, which separates the occipital lobe of the brain from the underlying cerebellum.
This article will discuss the anatomy and function of the falx cerebri.
|Definition||The falx cerebri is an invagination of dura mater into the longitudinal fissure of the brain, that separates the cerebral hemispheres|
Anterior part: Crista galli of ethmoid bone
Superior margin: Groove for superior sagittal sinus
Posterior part: Internal occipital protuberance
Superior margin: Superior sagittal sinus
Inferior margin: Inferior sagittal sinus
Posterior part: Straight sinus
|Function||Separates the cerebral hemispheres
Houses the dural venous sinuses
Constrains the brain and limits displacement and rotation inside the cranium
Determines the suture sites
The brain and spinal cord are enveloped by the meninges, which serve to protect them from mechanical trauma, provide support to blood vessels and a passageway for the cerebrospinal fluid (CSF). From innermost to outermost, the meninges consist of the following three layers: pia mater, arachnoid mater, and dura mater.
The dura mater is a strong, double-layered membrane, composed of the periosteal layer, which adheres to the periosteum of the neurocranium, and the meningeal layer, which surrounds the brain and spinal cord. In some regions and fissures of the brain, the meningeal layer of dura mater projects inwards to form four dural partitions: the falx cerebri, falx cerebelli, tentorium cerebelli, and sellar diaphragm.
The falx cerebri is the largest of the four partitions of the dura mater, and represents an invagination of the meningeal layer of dura into the longitudinal fissure of the brain. This crescent-shaped sheet of tissue occupies this fissure and separates the two cerebral hemispheres. It begins anteriorly from the crista galli of the ethmoid bone, and runs in the midline along the entire internal surface of the cranium, and extends posteriorly all the way to the internal occipital protuberance.
The anterior part of the falx cerebri is narrow and thin, and is fixed to the crista galli. Its convex superior margin is attached to the lips of the groove for superior sagittal sinus, while its concave inferior margin is free. The posterior part of the falx cerebri is broad and attaches to the internal occipital protuberance, while blending with the superior surface of the tentorium cerebelli.
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Similarly to the dura mater, the falx cerebri is supplied by branches of the maxillary, internal carotid, ascending pharyngeal and vertebral arteries.
More specifically, the anterior part of the falx cerebri is supplied by the anterior division of the middle meningeal artery, anterior ethmoidal and pericallosal arteries.
The posterior part of the falx is supplied by the posterior division of the middle meningeal artery, meningohypophyseal trunk of the internal carotid artery, and posterior cerebral, pericallosal, and posterior meningeal arteries.
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The falx cerebri contributes to the formation of several dural venous sinuses:
- The convex superior margin of the falx cerebri houses the superior sagittal sinus, which runs along the midline of the internal surface of the calvaria, in the groove for superior sagittal sinus.
- The concave inferior margin of the falx cerebri runs in the interhemispheric space and contains the inferior sagittal sinus.
- The posterior part of the falx cerebri contains the straight sinus, more specifically along the line of attachment of the falx cerebri and tentorium cerebelli.
The falx cerebri separates the cerebral hemispheres and houses the dural sinuses, into which the blood and cerebrospinal fluid drain. However, it’s exact function is not entirely certain. The function of the falx cerebri may be to constrain the brain and limit its displacement and rotation inside the cranium. Being a dural fold, the falx is stiffer than the surrounding tissue and plays an essential role in supporting the brain by suppressing the movements of the brain inside the skull during acceleration.
In addition, it is thought that the dural folds, and especially the falx cerebri and the tentorium cerebelli, play an important role in the development and functional loading of the cranium. In other words, dural folds determine the cranial suture sites and their absence is accompanied by a lack of suture formation.
Now that you’ve mastered the falx cerebri, check out the study unit below to find out more about the meninges of the brain, or take the quiz to consolidate what you learned so far!
Subfalcine herniation, also known as cingulate herniation, is the most common type of cerebral herniation. It can be caused by anything that increases the intracranial pressure in one compartment of the brain, such as a tumor, localized hemorrhage (e.g. epidural hematoma), or an increase in cerebrospinal fluid (CSF) volume. In each case, the mass creates a compressing effect and pushes the brain tissue in a downward and medial direction, causing the displacement of the ipsilateral cingulate gyrus under the free margin of the falx cerebri.
The herniated cingulate gyrus can compress the ipsilateral anterior cerebral artery resulting in contralateral leg weakness. If the herniation occurs in the dominant hemisphere, the cingulate gyrus can also compress the arcuate fasciculus. Since this fasciculus connects the Broca’s and Wernicke’s areas, its compression can cause different types of aphasias.
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