§ 140. Workmen's compensation board. The workmen's compensation board in the department of labor is hereby continued. Such board shall consist of thirteen members, at least four of whom shall be attorneys and counsellors-at-law duly admitted to practice in this state. The members of the board shall be appointed by the governor, by and with the advice and consent of the senate. The members of the board in office, together with the additional members and the members appointed to fill vacancies, if any, at the time this section takes effect, shall continue, notwithstanding the appointment of any of the members for a term expiring on a different date, to hold office for terms to be assigned by the governor by and with the advice and consent of the senate; two such terms to expire on December thirty-first, nineteen hundred fifty; two to expire on December thirty-first, nineteen hundred fifty-one; two to expire on December thirty-first, nineteen hundred fifty-two; two to expire on December thirty-first, nineteen hundred fifty-three; two to expire on December thirty-first, nineteen hundred fifty-four; two to expire on December thirty-first, nineteen hundred fifty-five; and one to expire on December thirty-first, nineteen hundred fifty-six. The members next appointed, except to fill a vacancy created otherwise than by expiration of term, shall be appointed for terms of seven years. The governor shall designate one of the members of the board as chairman and another as vice-chairman.