Answer
The cranium is a bony box of eight bones that sits on top of the human skeleton. Its major function is to protect the brain from injury-- accidental or intentional. Both the shape of the whole structure and of the individual bones, as well as the nature of and result of the ossification process, facilitate this major function of the cranium. The eight bones of the cranium are the frontal, the sphenoid, the ethmoid and the occipital ( which are unpaired) plus the parietal and temporal bones, which are paired. The external cranial bones are joined to form a type of box. However, this is not a cuboid box with flat surfaces, but a spheroid "box: with gently rounded surfaces. A consequence of this shape is that the force of a blow delivered to the head will be dissipated, and potential injury to the brain by concussion or tissue injury will be lessened.
The nature of the ossification of cranial bones results in the flat bones of the cranium having three layers-- two outer layers of hard compact bone and a middle layer of spongy cancellous bone. This arrangement also serves to soften any physical blow delivered to the cranium and is an added measure of protection for the brain.
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Cranium
