brainpan vs encephalon

brainpan

noun
  • The brain or mind. 

  • The skull. 

encephalon

noun
  • The area of central nervous system that includes all higher nervous centers, enclosed within the skull and continuous with the spinal cord; the brain. 

How often have the words brainpan and encephalon occurred in a corpus of books? (source: Google Ngram Viewer )