Cranium

The cranium is the head bone that contains the brain.

Location of the cranium

The cranium is the head bone, with the primary function of protecting the brain. The only other head bone is the hyoid bone.

The cranium communicates with the vertebrae through the occipital foramen.

Structure of the cranium

The average cranium is 21 to 22 centimetres long and 17 centimetres wide. It is considered as a bone in its own right but it is actually composed of eight bones that fuse in childhood. The sutures are still visible in adulthood.

The structural bones are composed of:

• The occipital bone at the back and lower base of the cranium which contains the foramen linking to the vertebrae;
• the frontal bone, located at the front of the cranium;
• the two parietal bones located at the side and top;
• the two temporal bones located beneath the parietal bones;
• and the sphenoid and ethmoid bones, which lie more internally, and contribute to the formation of the sinus cavity.

Some other bones are occasionally considered to be part of the cranium, particularly:

• the inferior maxilla which is mobile;
• the small functional bones, especially the ear bones (the hammer, anvil and stirrup) used in hearing.