The clerk of the court for Essex county shall, not less than twenty-eight days before the first Mondays of January and May, and the second Monday of September respectively, issue writs of venire facias for forty-five veniremen from whom the court shall select twenty-three grand jurors to serve in said court, who shall serve for each sitting thereof for four months and until another grand jury has been impanelled in their stead.
Mass. Gen. Laws ch. 277, § 2G