Section 55. The chief justice of the Boston municipal court department may employ stenographic services and provide for recording systems for the court. Said department may secure for its criminal business medical service, and the equipment necessary therefor, and for this purpose may expend annually such sum, not exceeding fifteen thousand dollars, as the chief justice of the Boston municipal court department may from time to time determine, subject to the approval of the chief justice for administration and management. Sums so expended shall be paid by the commonwealth upon vouchers approved by the chief justice of the Boston municipal court department.