Green’s Dictionary of Slang

(US black) the clitoris.

1978		R. Charles Brother Ray 118: [B]ack on my old stompin’ grounds, I could usually find some purr tongue. (That’s the word us country boys used for clitoris.).
1992		(con. 1910s) F.M. Davis Livin’ the Blues 36: At an early age we talked about a ‘purr-tongue’ or a ‘boy-in-the-boat’.