E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The test of the brawns head. A little boy one day came to the court of King Arthur, and, drawing his wand over a boars head, declared, Theres never a cuckolds knife can carve this head of brawn. No knight in the court except Sir Cradock was able to accomplish the feat. (Percys Reliques.)