Green’s Dictionary of Slang

the vagina.

1606		Marston The Fawne I ii: Thou shalt marry a rich widdow, or a crackt Lady, whose case thou shalt make good.
c.1617		Fletcher Chances IV iii: bawd: A poor Gentlwoman That lies in Town, about Law Business, An’t like your Worships. petr.: You shall have Law, believe it. bawd: I’ll shew your Mastership my Case. petr.: By no means, I had rather see a Custard. bawd: My dead Husband Left it even thus, Sir. john: Bless mine Eyes from Blasting, I was never so frightened with a case.
1674		T. Duffet Epilogue Spoken by Heccate and Three Witches 31: I was with Templer lock’d from Night till Noon, My case he opene’d thrice and once Actions he entered three and one.
c.1680		Rochester ‘Song’ in Poems on Sev. Occasions (1685) 56: Quoth the Dutches of Cl--- to Mrs. Kn--- I’d fain have a Prick, but how to come by’y [...] To some Cellar in Sodom your Grace must retire, There Porters with Black Pots sit round a Coal-fire. There open your Case, and your Grace cannot fail Of a Dozen of Pricks for a Dozen of Ale.
1700		‘The Irish Hallaloo’ in Playford Pills to Purge Melancholy II 206: Their Wives are all nasty, and so are their C--ts: / But I’ll keep my Fiddle-stick out of their Cases, / They stink like Privies, a Pox on their Arses.
c.1720		‘The Masquerade Ball’ in Farmer Merry Songs and Ballads (1897) III 235: O! a Masquerade’s a fine Place / For opening of your Cases.
1738		Man-Midwife Unmasqu’d 5: Pray, Madam, said one, tell us where was the Place, / When first to the Doctor you open’d your Case.
1890–1904		Farmer & Henley Sl. and Its Analogues IV 337/1: The female pudendum [...] case [...] Kaze.