Definition of "introitus"

During NA therapy, 49 of the 54 women cleared their introitus of all Enterobacteriaceae.

1980, Thomas Alexander Stamey, Pathogenesis and Treatment of Urinary Tract Infections, Williams & Wilkins, page 144

Now, far be it from me to add insult to injury, but how could you be so klutzy that you "missed the introitus"?

1988 January 29, Cecil Adams, “The Straight Dope”, in Chicago Reader‎

There is nothing feminine about these male pseudohermaphrodites except their introitus, and they seem to be normally male otherwise.

1993: Daniel Carleton Gajdusek, Melanesian journal: expedition to New Hebrides, Solomon Islands, Manus, New Britain, and New Guinea, 23 January 1965 to 7 April 1965, page 90 (Study of Child Growth and Development and Disease Patterns in Primitive Cultures, Laboratory of Central Nervous System Studies, National Institute of Neurological Disease and Stroke, National Institutes of Health)

Five have an introitus (introduction) that stands outside the isorhythmic scheme;108 some of these introitus are instrumental rather than vocal […]

1954, Gustave Reese, Music in the Renaissance, W.W. Norton, page 22

As summarized in Example 3.14, nearly all of these introitus […]

1992, Jon Michael Allsen, Style and intertextuality in the isorhythmic motet 1400-1440, volume 1, University of Wisconsin-Madison, page 118