The cranium, or skull, is the bony structure that protects the structures found inside our head, and it’s divided into two parts: the viscerocranium and the neurocranium. Viscera- refers to the organs within the body cavities, so the viscerocranium is the lower and anterior part of the skull that forms the orbits, the nasal cavities, and the oral cavities; in other words, the facial skeleton. Neuro-, on the other hand, refers to the nervous system, so the neurocranium, also called the cranial cavity, is the superior and posterior part of the skull that houses the brain, and its membranous coverings - the cranial meninges - and also blood vessels and the proximal parts of the cranial nerves.
Let’s look at the viscerocranium first, which is actually made up of 15 bones! Only three of them are unpaired bones, and they sit on the midline: the mandible, ethmoid, and vomer; then there are six pairs of paired, symmetrical bones: the maxillae, the inferior nasal conchae, as well as the zygomatic, palatine, nasal, and lacrimal bones. Most of these bones articulate with each other by fibrous - or immovable - joints; except for the mandible, which articulates only with the temporal bones by a synovial - or movable - joint.
Next, the neurocranium is made up of eight bones: the frontal, ethmoid, sphenoid, and occipital bones, which are singular and placed in the midline; then two temporal and two parietal bones, which are bilaterally paired. All these bones articulate by fibrous joints. In addition, the neurocranium can be further divided into the calvaria - or skullcap - and the cranial base, which would be like the roof and the floor of the neurocranium, respectively. The cranial base is where the foramen magnum is found, where the spinal cord is continuous with the brain.
