Section 200. Corporation counsel

The corporation counsel shall be the head
  of the department of law.  He may appoint, to  hold  office  during  his
  pleasure,  a  first  assistant  and  such  other  subordinates as may be
  prescribed by the board of estimate and apportionment. In  case  of  the
  absence or disability of the corporation counsel, or of a vacancy in the
  office,  the  first  assistant  shall discharge the duties of the office
  until the corporation counsel returns,  his  disability  ceases  or  the
  vacancy  is  filled.  The corporation counsel and first assistant before
  entering upon the discharge of the duties of their  respective  offices,
  shall  each execute and file with the city clerk an official undertaking
  in such penal sum as may be prescribed by the common council.