Mass. Gen. Laws ch. 43 § 67
The city council shall consist of the following five members: a mayor, who shall be the commissioner of administration; a commissioner of finance; a commissioner of health; a commissioner of public works and a commissioner of public property. Each commissioner shall have charge of the department of city affairs indicated by his official title, except as to the affairs and property of the city which are within the jurisdiction of the school committee. All of these officers shall be elected by and from the qualified voters of the whole city for terms of two years, except as hereinafter provided.
In case of a difference of opinion as to the departments to be in charge of any one or more of the commissioners, the matter shall be determined by a vote of a majority of all the commissioners.
Mass. Gen. Laws ch. 43, § 67