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Pictograph of a child (人) with an opening in the top of its head (囟). Represents the soft spot (fontanel) at the top of young infant heads. The 囟 component is written like 臼.
Components
Evolution

Oracle script
(~1250-1000 BC)
Bronze script
Late Shang dynasty (~1100 BC)
Seal script
Shuowen (~100 AD)
Clerical script
Eastern Han dynasty (25-220 AD)Regular script
ModernDefinitions
Component uses
Sources
季旭昇《說文新證》p.687