Whenever different parts of any municipality or any two municipalities are separated by an intervening valley or ravine, and the commissioners of the county in which such municipality or municipalities are located shall decide it necessary that a public bridge, to connect the territories thus separated, be constructed, the county may contract with the municipality or municipalities for the laying out and construction of the bridge by such municipality or municipalities, and may pay to the municipality or municipalities such portion of the cost thereof as the county commissioners shall deem reasonable.
16 P.S. § 2655