Mass. Gen. Laws ch. 43 § 69
The city council elected as aforesaid shall meet at ten o'clock in the forenoon on the first Monday of January in each year, and the members of the city council whose terms of office then begin shall severally make oath, before the city clerk or a justice of the peace, to perform faithfully the duties of their respective offices. The city council shall thereupon be organized by the choice of a president, who shall hold his office during the pleasure of the city council. The president of the city council shall be any member thereof, except the mayor. The organization of the city council shall take place as aforesaid, notwithstanding the absence, death, refusal to serve, or non-election of the mayor or of one or more of the four other members; provided, that at least three of the persons entitled to be members of the city council are present and make oath as aforesaid. Any member-elect, not present at the time fixed therefor, may make oath at any time thereafter.
Mass. Gen. Laws ch. 43, § 69