Section 40. A special justice of a district court who does not serve full-time in accordance with the provisions of section six A shall sit on the Boston municipal court department by assignment in the same manner as if he were serving full-time. When such a special justice, who is part-time, so-called, holds court, or a session thereof or an inquest, or certifies a bill of costs to the treasurer of the commonwealth, that fact, and the fact which gave him jurisdiction, shall be entered upon the general records of the court, but need not be stated in the record of any case heard by him.

Except in the central division of the Boston municipal court department, the district court of Dukes county and the district court of Nantucket, no justice or special justice who does not serve full-time shall hear and determine any civil cases other than supplementary proceedings, summary process, small claims, and proceedings relating to juveniles and mentally ill persons in any district court without the authorization of the chief justice of the district courts. The chief justice of the district courts shall give such authorization for specified limited periods of time in specified district courts and only as the public convenience may require, and may give such authorization by general rule applicable to the hearing and determination of interlocutory proceedings, or whenever full-time justices or special justices assigned to hear such civil cases, who serve full-time in accordance with the provisions of section six A, are absent or otherwise unable to sit. No such authorization shall be required for the rehearing of matters of law arising in civil causes by any justice assigned to the appellate division of a district court.