MUTTON-in-long-coats,
Women A Leg of Mutton in a Silk Stocking, a Woman's leg.
· 
· 
Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
The Vulgar Tongue originally collected by Grose, 1811.
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).