Lorenzo Lotto, Detail from The Legend of St. Brigid: The Boar Tamed
This episode is on p. 137 of Cogitosus' Vita in Acta Sanctorum (February vol. 1). A wild boar besets what the text calls a grex ("flock") of pigs. Here of course we have a flock of sheep. Pigs or sheep, the saint's response is the same. She blesses the boar, and then in the upper register we see the effect of her blessing: The boar, no longer wild, grazes peacefully among the other animals.
The herdsman in the picture is absent from Cogitosus.
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Source: Web Gallery of Art