The invention relates to a device for fixing the open oral cavity of a rodent, having a base plate (12), comprising a supporting surface which serves for placement of at least the head of a rodent, having a first retaining bracket (16) protruding from the base plate (12) for fixing the upper jaw of the rodent and with a second retaining bracket (18) protruding from the base plate (12) for fixing the lower jaw of the rodent, wherein the first and the second retaining bracket (16, 18) can be fixed to the base plate (12) with variable spacing therefrom.
