capitulum vs protuberance

capitulum

noun
  • A small protuberance on a bone which articulates into another bone to form a ball-and-socket joint. 

  • The head-like mouthpart apparatus of a tick, including the palpi, mandibles, and hypostome. 

  • A densely clustered inflorescence composed of a large number of individual florets arising from a platform-like base. 

protuberance

noun
  • A bulge, knob, swelling, spine or anything that protrudes. 

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