Neurocranium

The neurocranium is the portion of the skull that houses the brain and related structures. It is a bone case that protects the brain from injury and provides space for the major nerves and blood vessels that enter the head.

The neurocranium is distinguished from the other part of the skull, the facial skeleton (visceral or splanchnic cranium), which includes the bones of the jaw, nose, and palate. Together, these two parts make up the cranium.

Divisions

The neurocranium is typically divided into two parts. One is the vault or roof (calvaria), which consists of several bones that form a covering. The other is the base of the skull (basis cranii), the floor on which the brain sits. The base is pierced by many openings, the largest of which is the foramen magnum, through which the spinal cord and brain connect.

Constituent bones

The bones of the neurocranium include the frontal bone, the two parietal bones, the two temporal bones, the occipital bone, and the sphenoid bone. The ethmoid bone also participates in the structure of the anterior base. Some of these bones also contribute to the formation of the face, so the boundary between the two regions is sometimes not clearly defined.

Articulation of bones

The vault bones are joined by immobile seams called sutures. Notable examples include the coronal suture between the frontal and parietal bones, the sagittal suture between the two parietal bones, and the lambdoid suture at the back. In infants, some sutures are not yet fully joined, leaving soft spots (fontanelles) between them that allow the skull to expand as the brain grows.

Development

During embryonic development, some of the bones of the neurocranium form directly from membrane that becomes bone, while those of the base initially form as cartilage and are later replaced by bone. This difference in development accounts for the different patterns of growth in the vault and base.