peritoneum vs rib cage

peritoneum

noun
  • In mammals, the serous membrane lining the cavity of the abdomen and that is folded over the viscera. 

  • In animals, the membrane lining the coelom cavity. 

rib cage

noun
  • The enclosed area created by and within the ribs. 

  • A part of the skeleton within the thoracic area consisting of ribs, sternum and thoracic vertebrae. 

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