Said board may, by contract or otherwise, under such regulations as the board shall prescribe, build, repair and maintain, or cause to be built, repaired, or maintained all bridges and culverts needed within said district; provided, however, that the county commission of the county in which said special road district is located may, in its discretion, out of the funds available to it for that purpose, construct, maintain, or repair, any bridge, or bridges, or culvert or culverts in such road district, or districts, or it may, in its discretion, appropriate out of the funds available for that purpose money to aid and assist the commissioners of said special road district, or districts, which shall be expended by the commissioners of said special road district, or districts, as above provided.