Green’s Dictionary of Slang

the buttocks; the anus [cite 1860 may refer tosouth adj. (1) though chro. may negate this].

1812		Spirit of Irish Wit 40: The hot frying pan [...] being in close union with his south pole.
1860		Bell’s Life in London 2 Dec. 6/3: Truckle, in the struggle, fell on his south pole, King falling on him.
1992		R. Puxley Cockney Rabbit.