What Is the Cranial Fossa?

The cranial fossa is a small depression or cavity in the cranium, which is the part of the human skull where the brain is located. There are three types of cranial fossae: the anterior, middle and posterior cranial fossa. These three openings are located at the cranium's base.

Cranial fossae — the plural spelling of cranial fossa — are part of the intracranial cavity, which is the exact space where the brain is located. A system of membranes called meninges line the brain while it floats on a protective, clear, colorless fluid called cerebrospinal fluid. The intracranial cavity is formed by the fusion of eight bones: the two parietal and two temporal bones, and the ethmoid, frontal, occipital and sphenoid bones.

The anterior cranial fossa is the frontmost of the cranial fossae. The frontal bone's horizontal plates, the ethmoid bone's cribriform plate, and the sphenoid bone's lesser wings and front section form the floor of the anterior cranial fossa. The anterior hollow is traversed by three sutures, which are fibrous joints only found in the skull. They are the frontoethmoidal suture, which is located behind the ethmoid bone and the frontal bone; the sphenoethmoidal suture, which comes between the sphenoid bone and the ethmoid bone; and the sphenofrontal suture, which is found between the sphenoid bone and the frontal bone.

The middle cranial fossa is separated from the anterior cranial fossa by the sphenoid bone. It is deeper than its frontal counterpart, but becomes narrow in the middle and laterally widens to the skull's sides. The sphenoid bone's lesser wings and the chiasmatic groove, which binds its superior surface, forms most of the fossa's frontal binding. The sphenoparietal, sphenopetrosal, sphenosquamosal and squamosal sutures traverse the middle fossa. This fossa is responsible for supporting the brain's temporal lobes, which form part of the sheet of neural tissue outside the forebrain known as the cerebral cortex.

The posterior cranial fossa is so named because it is the rearmost of the three cranial depressions. It is separated from the middle channel by a depression called the clivus and the part of the temporal bone known as the petrous crest. The occipital bone encloses it from the back, and its walls are formed by portions of the temporal bone. It is responsible for containing the brainstem, particularly the lower half of the brainstem known as the medulla oblongata and the bridge above it called the pons. It also houses the brain's cerebellum.