To determine which number has an odd middle digit, we analyze each number:
- 10 → Middle digit: 0 (Even)
- 26 → Middle digit: 6 (Even)
- 37 → Middle digit: 3 (Odd)
- 64 → Middle digit: 4 (Even)
Since 64 is the only two-digit number where the middle digit (4) is odd, it is the correct answer.