This is Leonardo da Vinci’s drawing The Copulation (c 1493) which is reproduced in
Magnetic resonance imaging of male and female genitals during coitus and female sexual arousal by Willibrord Weijmar Schultz, Pek van Andel, Ida Sabelis, Eduard Mooyaart, BMJ (1999) 319:1596 link
where it appears with this interesting and scrupulous description:
The Renaissance sketch shows a transparent view of the anatomy of sexual intercourse as envisaged by the anatomists of his time. The semen was supposed to come down from the brain through a channel which can be seen in the spine of the man. In the woman the right lactiferous duct is depicted as originating in the right female breast and ending in the genital area. Even a genius like Leonardo da Vinci distorted men’s and women’s bodies—as seen now—to fit the ideology of his time and to the notions of his colleagues, who he paid tribute to.
