buttock vs shoulder blade

buttock

noun
  • Each of the two large fleshy halves of the posterior part of the body between the base of the back, the perineum and the top of the legs. 

  • The convexity of a ship behind, under the stern. 

shoulder blade

noun
  • Either of the large flat bones at the back of the shoulder. 

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