Overview of the Skull

The human skull divides into cranial bones and facial bones. The cranial bones form the brain case, or cranial vault, which protects the brain and houses the middle and inner ear structures. The facial bones underlie facial structures, form the nasal cavity, enclose the eyeballs, and support the teeth of the upper and lower jaws.

The adult skull consists of twenty-two individual bones: eight cranial bones and fourteen facial bones. Twenty-one of these bones are immobile and united into a single unit. The mandible, or lower jaw, is the only moveable bone of the skull, allowing for jaw movement during chewing and speech.

The eight cranial bones include paired parietal and temporal bones, plus four unpaired bones: the frontal, occipital, sphenoid, and ethmoid bones. These bones form the brain case and are typically referred to as the flat bones of the skull. Together they create the cranial vault that surrounds and protects the brain.

The fourteen facial bones include six paired bones—maxilla, palatine, zygomatic, nasal, lacrimal, and inferior nasal conchae—and two unpaired bones: the vomer and mandible. These bones form the upper and lower jaws, nose, nasal cavity, nasal septum, and orbit. The palatine bones separate the nasal cavity from the mouth cavity.

Sutures are immobile joints between cranial and facial bones filled with dense, fibrous connective tissue. The long sutures follow irregular, tightly twisting paths that interlock adjacent bones, adding significant strength to the skull for brain protection. This interlocking design enhances the skull's ability to withstand impact and stress.

The cranial cavity is formed by the cranial vault and cranial base working together. The cranial vault, bounded superiorly by the calvaria or skullcap and laterally and posteriorly by skull bones, encloses the brain. The cranial base forms the inferior boundary, creating a protected chamber for the brain and associated structures.

The ethmoid and sphenoid bones are positioned inferiorly within the skull and contribute to multiple structures. Although classified as cranial bones, the ethmoid bone also forms part of the nasal septum and walls of the nasal cavity and orbit. Both bones are essential components of the internal skull structure supporting brain protection and sensory functions.