C++ needs an intermediate variable to accept iterators in

The following generates error:

int main() {

  mat_int mat1(5, vector<int>{1,2,3});
  mat_int mat2(5, vector<int>{4,5,6});

  for (auto it1 = mat1.begin(); it1 != mat1.end() ; ++it1) {
        for (auto it11 =  *it1.begin(); it11 != *it1.end(); it11++)
            cout << *it11;
        cout << '\n';
    }
}

Compiler doesn't accept the inner loop iterators; /home/asabbah/programming/C++/vectors1.cpp:16:28: error: ‘class __gnu_cxx::__normal_iterator*, std::vector > >’ has no member named ‘begin’

However, if I insert a temp variable:

vector<int> temp = *it1;

then:

for (auto it11 = temp.begin(); it11 != temp.end(); it11++);

everything goes fine.

Any idea why is this so?