Section 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.