Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 43, § 75

All executive and administrative powers, authorities and duties, not otherwise provided for in this chapter, shall be assigned to a suitable department by the city council by ordinance, and changes in the assignments may be made by ordinance by the affirmative vote of three members of the city council, or by the qualified voters of the city upon initiative petition.

The city council shall determine the policies to be pursued and the work to be undertaken in each department, but each commissioner shall have full power to carry out the policies or to have the work performed in his department as directed by the city council.