The cranium, or top portion of the human skull, is a large, solid, relatively shockproof brain case made of eight sections of bone that meld after birth into a single unit, and these connections are called sutures. The structure itself is called the cranial vault. A cranium without facial bones is called the calvarium. At about eight millimeters, or one-quarter inch thick, the cranium is solid enough to prevent the brain from shifting in all but the most forceful impacts.



In all, a human skull contains 22 skull bones which form the vault, as well as other, smaller cavities for the eyes, internal ear, nose and mouth. Add to this 14 facial bones, which determine the size, shape and configuration of the face, and the human skull is a complex meld of form following function, in which evolution has reduced the size of the mandible, or jaw bone, the supraorbital process (the eyebrow area), the zygomatic area and the thickness of the nasal bone. If not, we would look like early hominids.

The skull also contains a number of areas like processes (which hold muscles and ligaments), foramina (openings for nerves and blood vessels) and sinuses, or empty spaces that make the skull light enough the human spine can support it. Fissures, or lines, are simply areas where two bones have joined.

Anatomical models of skulls range from a very simple model - bisected at the axial plane to show the calvarium and with a removable mandible, or lower jaw – to eight-part models showing the brain and detailed representations of the processes, foramina, sutures and fissures.

The neurovascular skull, an adult-sized model, is another tripartite model (calvarium, skull, mandible) with the seven cervical vertebrae attached. Mounted on a stand, both the inside and outside of the model depict the arteries (in red, on the left) and the 12 cranial nerves (in yellow, on the right), including their branches.

A transparent, tripartite skull is an excellent teaching tool, showing the internal workings of the skull as they would be seen on a CT scan, for example. The fetal skull clearly demonstrates the various plates that later join to form the cranial vault and facial bones, allowing physicians and surgeons to demonstrate the cephalohematomas which sometimes occur at birth and can cause brain damage if they do not dissipate or are removed via surgical procedures.

The superior teaching model, however, is a didactic skull. Using 19 different colors to distinguish the various skull and facial bones, this anatomical model displays all seven cervical vertebrae (C1, C2 and C7 in color) and also shows the rhombencephalon, or hindbrain, spinal cord, nerves going to the cervical spine, all the vertebral arteries (including the rear) and their confluence in the basilar artery, as well as all fissures, foramina, processes and sutures. Stand-mounted and made of unbreakable plastic, this model is essential teaching equipment in medical schools, hospitals, neurosurgeon's offices and clinics treating brain and skull injuries and defects.

Also available are pathological skull models which demonstrate conditions like microcephaly (an abnormally small skull), hydrocephaly (excess spinal fluid that puts pressure on the brain), cleft jaws or palates, and tempromandibular joint syndrome, a dysfunctional, often stress-related alignment of the jaw bone that can cause extreme ear, jaw, tooth and head pain.