Green’s Dictionary of Slang

(US) the legs.

[1672		J. Phillips Maronides (1678) V 54: Than to bestir your Lordly legs / In running after Mublede pegs].
1920		T.A. Dorgan in Zwilling TAD Lex. (1993) 58: Mumbley pegs: that’s the legs.
1928		R.J. Tasker Grimhaven 180: Certain words in the English language were made to rhyme with others [...] ‘Mumbly peg’ – leg.
1931		D. Runyon ‘Earthquake’ in Runyon on Broadway (1954) 169: I judge the old mumblety-pegs are giving out.
1944		Maurer & Baker ‘“Aus.” Rhyming Argot’ in AS XIX:3.
1952		J. Jones From Here to Eternity (1998) 307: Lying on their bellies [...] the Company gave themselves over to the enchantments of mumblety-peg and the study of the bottoms of the officers’ wives and daughters.