mamilla vs sternum

mamilla

noun
  • A nipple-shaped protuberance. 

  • The small projection of a mammary gland; a nipple. 

sternum

noun
  • The breastbone, consisting of the manubrium, gladiolus, and xiphoid process. 

  • The sclerotized ventral plate of spiders, between the coxae, marking the floor of the cephalothorax. 

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