When a die is thrown, the total number of outcomes is 6. Since we want the dice not to show a 1, the remaining outcomes are 5, 2, 3, 4, 5, and 6 (so, 5 possible outcomes).
For each die, the probability of not showing 1 is:
\[
P(\text{not showing 1}) = \frac{5}{6}
\]
Since four dice are thrown simultaneously, the probability that none of the dice shows 1 on its face is:
\[
P(\text{none of the dice shows 1}) = \left( \frac{5}{6} \right)^4 = \frac{625}{1296}
\]
Thus, the probability that none of the dice shows the number 1 is \( \frac{625}{1296} \).