The several counties of the state, acting by and through the boards of supervisors thereof, are hereby invested, within their discretion, with full authority to expend monies and to do, within any municipalities of the county all acts regarding construction and maintenance of roads and streets that they may do within the county outside the limits of said municipalities.
The authority granted under this section shall be construed as additional and cumulative to all existing authority for the expenditure of county funds within municipalities.