E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
le fils de la Folie et de Pulcinello. A supposititious Italian dancer, sent to amuse Bettina in the court of the Grand Duke Laurent. Bettina was a servant on a farm, in love with the shepherd Pippo. But when she was taken to court and made a countess, Pippo was forbidden to approach her. Bettina languished, and to amuse her a troop of Italian dancers was sent for, of which Saltarello was the leader. He soon made himself known to Bettina, and married her. Bettina was a mascotte (q.v.), but, as the children of mascottes are mascottes also, the prince became reconciled with the promise that he should be allowed to adopt her first child. (La Mascotte.)
Hence a Saltarello is an assumed covert to bring about a forbidden marriage and hoodwink those who forbade it.