Green’s Dictionary of Slang

1. (orig. theatre) a ‘ladder’ in a pair of tights or stockings.

1859		G.A. Sala Gaslight and Daylight 354: He [...] proceeded to overhaul all parts of his apparel with as much care and circumspection as if they had been of purple and fine linen, catching up any strong rents and ‘Jacob’s ladders’ with a grave and deliberate countenance.
1882		Sydney Sl. Dict. (2 edn) 5: Jacob’s-ladder - A longitudinal flaw in the leg of a ballet-girl’s tights.

2. the vagina.

1890–1904		Farmer & Henley Sl. and Its Analogues.
1980		Maledicta IV:2 (Winter) 189: Jacob’s ladder leads to Heaven.