Green’s Dictionary of Slang

myrtle n.

[ety. unknown; ? link to muddle v.]

1. (Aus.) sexual intercourse.

[Aus]Baker Popular Dict. Aus. Sl.

2. (Aus.) the female genital area.

S.J. Baker Aus. Vulgarisms [t/s] 11: myrtle: [...] 2. The female pudend.