We all know how it goes from 1 to 9. After that, a repetition of symbols begins and we deal with 1+Z-digit numbers (lets leave numbers beyond of Z out of it for the sake of not encouraging nit-pickers). I assume this point is chosen because two hands have 10 fingers, so it makes sense that the biggest number we can most easily form in an symbolic way is the number most easiest to use for addition, subtraction, multiplication and division and which by that sort of is the skeleton of primary calculations, I suppose anyway. But what if we had 12 fingers? Would we have two more unique number-symbols and would the two-digit numbers begin with 13? Would it make any difference except of course having different number-names and having bigger "intervals" between the "bones" (formerly 10, now 13) of simple calculation? I guess what this hypothetical comes down to is: Has the number 10 as the "skeleton"-number any mathematical justification or is just an arbitrary choice caused by the number of our fingers? Right now it seems so to me and I find it fascinating how weird it still seems when I try to actually imagine it.