Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 126, § 9

The yards shall be of sufficient extent for the convenient employment of the persons confined therein, and shall be enclosed by fences of sufficient height and strength to prevent escapes and to prevent all persons who are without from access to or communication with any person confined therein. If such house of correction is not provided, the jail or a part thereof may be used for that purpose; but if so used it shall be provided with a sufficient yard, so enclosed.