The mouse is a tiny verminous beast, which gnaws in darkness; it was the medieval symbol of greed and female lasciviousness. Heraldically, the category includes the “rat”, a larger rodent with much the same medieval reputation. Both mice and rats are found in 15th Century Italian armory: the canting arms (from Latin sorex and Italian ratto) of da Sorexina and Ratazi, respectively [Triv 329, 312].
The “dormouse” may likewise be included here: although not biologically related to the mouse, their bodies are sufficiently similar to warrant inclusion. The dormouse is distinguished from the mouse by its furry tail. It’s a period charge, found in the canting arms (Italian ghiro) of de Giramis, mid-15th C. [Triv 153].
The mouse and its cousins do not have a proper tincture, per se: if colored brown, they must be blazoned, e.g., a “brown mouse proper”. Neither do they have a default posture; the illustration shows a mouse statant. See also bat.
Edgar the Unready bears: Gules, a mouse rampant argent.
Brice le Raton bears: Lozengy sable and argent, a rat rampant gules.
Borgunna Varsdottir bears: Per bend sinister raguly Or and azure, a decrescent and a dormouse dormant counterchanged.