The neurocranium, sometimes called the braincase, is composed of both the upper and front portions of the skull that protect the brain, and the rounded base of the skull that shields the brain stem. It is one of two groups of bones of the skull; the other part, the viserocranium, includes the interorbital region of the eyes and the associated bone structures behind the nose and mouth. The braincase is composed of six separate cranial bones. These bones are the frontal, parietal, ethmoid, and occipital bones, and include the paired temporal and sphenoid bones. They are connected by sutures, which are the fibrous joints of the skull.
One of the largest bones of the neurocranium is the frontal bone. It is the portion of the skull located behind the forehead of the face and the beginning of the hairline. The frontal bone borders the orbits of the eyes and the nasal cavity.
Another large bone that helps to form the neurocranium is the parietal bone. This bone comprises the upper rounded roof and sides of the skull. The edges of the parietal bone align with parts of the frontal and occipital bones, as well as pieces of the temporal and sphenoid bones.
Below the parietal bone is the occipital bone; the lower curve of the back of the skull is shaped by this bone. One of the functions of the occipital bone of the neurocranium is to protect the brain stem from injury. Communications between the brain and the spinal cord are transmitted by nerves that travel through a large hole in the center of the occipital bone called the foramen magnum.
The sides of the neurocranium are partially formed by the temporal bones. They are located on both sides of the head above and behind the ears. These bones create the part of the face called the temple. Part of the temporal bone is soft and spongy; the other part is composed of very dense and hard bone tissue.
A small section of both sides of the neurocranium is shaped by the sphenoid bones. The sphenoid bone is directly in front of the temporal bone and adjacent to the eye socket. It is one of the many tiny bones that form the orbit of the eye.
The smallest part of the neurocranium, the ethmoid bone, is below the frontal bone and behind the nose. This very porous piece of bone separates the nasal cavity from the brain. If an injury to the nose occurs, the bone may break into fragments that can cause an injury resulting in the leakage of a clear liquid called cerebral spinal fluid (CSF) into the nasal cavity. When CSF is suspected to be leaking, immediate evaluation and treatment by a physician may prevent bacteria from traveling into the CSF that cushions the brain and spinal cord.