Certain Scotch bishops appointed by James I., with the distinct understanding that they were to hand over a fixed portion of the revenue to the patron. A tulcan is a stuffed calfskin, placed under a cow that withholds her milk. The cow, thinking the “tulcan” to be her calf, readily yields her milk to the milk-pail.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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