Green’s Dictionary of Slang

dissected, subjected to a post-mortem.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: To be ottomised, to be dissected; you’ll be scragged, ottomised, and grin in a glass case, you’ll be hanged, anatomised, and your skeleton kept in a glass case.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1859		Matsell Vocabulum.
1895		C. Crowe Aus. Sl. Dict. 55: Ottomised, to be dissected.