P.D.
You may possibly have athlete's foot. I have it, and this is on of the results. If there is any itching/burning associated with it, you may want to try one of the anti-fungal foot creams. When treating, soak your feet and rub the rough, cracked areas with a pumice stone (the black ones do the best on that part of the foot) to remove the extra skin build up and apply the cream twice a day. If you aren't experiencing any itching/burning, then it probably is just a plain old case of extreme dryness. Good luck!