The bony structure that encloses and protects the brain, consisting of eight bones that fuse together during development. It includes both the neurocranium (brain case) and provides attachment sites for muscles of mastication and facial expression.
From Greek 'kranion' meaning skull, from 'kara' (head). The term was used by ancient Greek physicians like Hippocrates to distinguish the brain case from other parts of the skull.
Your cranium grows rapidly in the first two years of life, expanding from about 350ml to 1000ml capacity, which is why babies have soft spots (fontanelles) where the bones haven't fused yet! The skull bones are incredibly efficient - they're only about 7mm thick on average but can withstand tremendous impact because of their curved, dome-like architecture.
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