Green’s Dictionary of Slang

cleft (of flesh) n.

the vagina.

1748–49		Cleland Memoirs of a Woman of Pleasure (1985) 12: Oh! let me view the small, dear, tender cleft! [Ibid.] 30: Her thighs were spread to their utmost extension, and discovered between them, the mark of their sex, the red-center’d cleft of flesh.
1888–94		‘Walter’ My Secret Life (1966) VII 1373: I wanted Winifred to go up the lane, and there let me feel her little cleft.
1890–1904		Farmer & Henley Sl. and Its Analogues.