mamma vs sternum

mamma

noun
  • The milk-secreting organ of female humans and other mammals which includes the mammary gland and the nipple or teat; a breast; an udder. 

  • An accessory cloud like a mammary in appearance, which can form on the underside of most cloud genera. 

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 mamma and sternum occurred in a corpus of books? (source: Google Ngram Viewer )