Green’s Dictionary of Slang

(US) the labia majora.

1960		in E. Cray Erotic Muse (1992) 190: The next time I saw her she was pulling off a hound, / And the jaws of her twat were a-drippin’ on the ground.
1966		B. Jackson Get Your Ass in the Water (1974) 151: Now Lil had nipples on her titties just about as thick as your thumb, / Lil had jaws on her pussy that would make a dead man come.
1984		A. Sample (con. late 1950s-early 1960s) Racehoss 240: Dem britches she had on wuz so tight I could see the jaws! Had lips fat as Sugar Ray Robinson’s boxing gloves.