Section 13-223. Medical board a

(1) There shall be a medical board of three
  physicians. One of such physicians shall be appointed by the  board  and
  shall  hold office at the pleasure of such board, one shall be appointed
  by the commissioner of health and shall hold office at the  pleasure  of
  such  commissioner, and the third shall be appointed by the commissioner
  of citywide  administrative  services  and  shall  hold  office  at  the
  pleasure of such commissioner.
    (2)  The  board,  the  commissioner  of health and the commissioner of
  citywide administrative services shall each have power to appoint one or
  more but not exceeding four alternate physicians, who shall hold  office
  at the pleasure of such appointing board or official. Whenever the board
  of  trustees  of  the  retirement system shall so direct, the functions,
  powers and duties of the medical board, in addition to  being  performed
  and  exercised  by  the three physicians appointed pursuant to paragraph
  one of this subdivision, shall be performed and exercised by one or more
  groups of three physicians as hereinafter prescribed. Each such group of
  three physicians shall function separately as the medical board and each
  such group may consist partly of a  physician  or  physicians  appointed
  pursuant  to  such  paragraph  one  and  partly of one or more alternate
  physicians or may consist entirely of  alternate  physicians;  provided,
  however, that one of the physicians or alternate physicians in each such
  group shall be appointed by the board, one by the commissioner of health
  and one by the commissioner of citywide administrative services.