Such buildings and structures shall be and remain the property of the municipal corporations in undivided interests proportionate to the contributions made by each in the original construction cost of such building or structure. Such monumental buildings as were erected jointly by any township, village, city or county and any post or posts or the department of Michigan, of the order known as the grand army of the republic shall be forever dedicated as memorial buildings to the memory of the union soldiers of the war of the rebellion, and all relics, documents, books, papers and library belonging to any such grand army post, or which may be deposited afterwards for such purpose, shall be cared for therein by proper supervision, by the public authorities, in a proper room or rooms kept for that purpose, and which shall at all reasonable times be kept open and free to the public. In case any surviving organization of the descendants of such union soldiers become and remain an incorporated body, such incorporated organization may, at its option, and said municipal corporation is hereby authorized and required, if so desired, to permit the said incorporated organization to maintain, so far as possible, the same relations to the municipal corporation in said buildings, as the posts or department of the grand army of the republic might or could do. The amount of money contribution by any post or department of the grand army of the republic to the construction of said building, shall be and remain so long as may be necessary a perpetual fund devoted to the maintenance of such building as a memorial building.