§ 201. Duties of the corporation counsel. The corporation counsel shall be and act as the legal adviser of the common council and of the several officers, boards and departments of the city. He shall appear for and protect the rights and interests of the city in all actions, suits and proceedings brought by or against it or any city officer, board or department, including the commissioner of charities in bastardy proceedings; and such officer, board or department shall not employ other counsel. The corporation counsel may, however, with the written consent of the mayor, employ counsel, at such compensation as may be approved by the board of estimate and apportionment, to assist him in the argument and conduct of important cases or proceedings in which the city or any officer, board or department thereof is interested or a party.