This word doesn't come from Latin at all. It's related via common Indo-European. It's a kind of coincidence that the forms are still so close, in Latin and English (old English)
Middle English mous, from Old English mus "small rodent," also "muscle of the arm" (compare muscle (n.)); from Proto-Germanic mus (source also of Old Norse, Old Frisian, Middle Dutch, Danish, Swedish mus, Dutch muis, German Maus "mouse"), from PIE mus-, the old Indo-European name of the mouse, retained in several language families (source also of Sanskrit mus "mouse, rat," Old Persian mush "mouse," Old Church Slavonic mysu, Latin mus, Lithuanian muse "mouse," Greek mys "mouse, muscle").
*Modern French "souris": *
French opted for popular Latin sōrīx from the Latin sōrex/sōrīcem .
*Modern Spanish "ratón" and Portuguese "rato": *
unknown etymology, when many Indo-European languages have the stem "rat", it's not clear where it comes from (Italian ratto, French rat, German Ratten)
It's a late term, as before the XII c. the "rat" and the "mouse" were called with the same word, from the Latin mus.
Modern Italian "topo":
From the Romagnol dialect "talpa" meaning a mole.
hic = this masculine thing (Hic est psittacus ebrius)
haec = this feminine thing (Haec est mustela callida)
hoc = this neuter thing (Hoc est crustulum sordidum)
All of these are nominative, as in "Hic est mus"; if you need an accusative (ablative, etc.) equivalent, it takes a different form.