Where in either of the cases mentioned in the 2 last preceding sections, or in case of a mortgage in which she shall have joined with her husband, the mortgagee, or those claiming under him shall after the death of the husband cause the mortgaged premises to be sold by virtue of such mortgage, and any surplus shall remain after payment of the moneys due thereon and the costs and charges of the sale, such widow shall be entitled to the interest or income of 1/3 part of such surplus, for her life, as dower.