سيفر حباهر 87

1[The students asked,] "Open Mem — what is an open Mem?"[Rabbi Rachumai responded,] "She includes from masculine and feminine."[The students followed up,] "What is a closed Mem?[He responded,] "She is fashioned like a womb above."[The students objected,] "But Rabbi Rachumai said that the belly is like a Tet[He replied,] "That one said it is like a Tet inside; I say it is like a Tet outside."