introitus vs introitus vaginæ

introitus

noun

  • The entrance to a hollow organ or canal; often specifically the entrance to the vagina. 

  • A piece of music played before a mass; a musical introduction of any sort. 

introitus vaginæ

noun

  • The entrance to the vagina. 

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