what do Oedipus'ankles reveal? can you give me soures?

A messenger enters from Corinth bringing the news that Polybus, King of Corinth, is dead – and that Oedipus has been chosen as the Corinthian king. Jocasta is delighted, for, if Polybus is Oedipus’ father, the oracle must be false: he has not died at Oedipus’ hands, but rather of sickness. Oedipus reenters, and laughs delightedly, telling the Corinthian messenger of the tragic prophecy he has avoided. The messenger tells Oedipus he had no need to worry: for he was not the son of Polybus and Merope. Rather, it was he - this very messenger - that took the baby from the shepherd, who found him as a baby in the mountains, with his ankles pierced. Oedipus suddenly realizes that the plot has thickened - and he may still be guilty.