Green’s Dictionary of Slang

the anal sphincter, usu. in the context of breaking wind; also in fig. use, constr. with break, to collapse with emotion .

1594		Greene & Lodge Looking-Glass for London and England in Dyce (1861) 122: She is a woman that hath her twiddling-strings broke [...] she breaks wind behind.
1646		Parliament of Women B: She cannot be content to lye alone tumbling and tossing in a good featherbed, [...] sighing and groaning, as if her very twatling strings would breake.
1654		Mercurius Fumigosus 5 28 June 36: Several Makers of the Welsh Harp have been lately questioned: therefore it much behove all honest People, to have a care that their Maid-servants have no relation to the stamp, or their twatling-strings be not screwed up too high.
1654		New Brawle 1: Jack he begins and Doll doth open after, / Would break ones twatling-strings witrh laughter.
1660		Wandring Whore I 12: I settled on the Chamber-pot [...] till I made it whurra, and roar like the Tyde at London-Bridge, to the endangering the breaking of my very Twatling-strings with it straining backwards.
1664		C. Cotton Virgil Travestie (1765) Bk I 13: When Æol pluck’d th Plug from the Muzzle of his double Jug, The Winds burst forth with such a Rattle, As he had broke the Strings that twattle.
1699		N. Ward London Spy X 245: She happen’d to strain her Twatling-Strings, and let fly an unsavoury Sound.
1700		N. Ward ‘A Step to Stir-Bitch-Fair’ in Writings (1704) 252: The baby had broke his twatling-strings, to the great Offence of the Nostrils of the whole Company.
1722		Arse Musica 9: My Lady Brag-fart, who has spoil’d many a Concert with over blowing her Pipes, and straining her Twattling-strings.
1729		C. Cibber Rival Queans 45: Lyf. Break not our twatling-strings with saying it.
1750		Friar and Boy Pt I 12: I am confident you’ll break Your twattling strings with farting.
c.1825		Friar and Boy 11: Then straight her b-m did roar, / At which the very table shook, / This sham’d her more and more. / The boy replied, dear mother take / A cup before we part, / For I am confident you’ll break / Your twatlings with a f--t.