Every person desirous of being decerned executor of a deceased person as disponee, next of kin, creditor, or in any other character whatsoever now competent, or of having some other person, possessed of such character, decerned executor to a deceased person, shall . . . . . . F1 present a petition to the commissary for the appointment of an executor; which petition . . . . . . F2 shall be subscribed by the petitioner or by his agent F3or by an executry practitioner F4or a recognised financial institution providing executry services within the meaning of section 23 of the Law Reform (Miscellaneous Provisions)(Scotland) Act 1990.