chorion vs hymen

chorion

noun
  • The protective and nutritive membrane in higher vertebrates that attaches the fetus to the uterus. 

  • The outer membrane of seeds of plants. 

  • The outer case of an insect egg. 

hymen

noun
  • A membrane which completely or partially occludes the vaginal opening in human females. 

  • Marriage. 

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