The funds hereinafter appropriated for the purpose of Sections 65-11-39 through 65-11-59 shall be paid by the State Treasurer out of any money in the state treasury not otherwise appropriated on warrants issued by the State Auditor of Public Accounts, and the said auditor shall issue his warrants upon requisition signed by the chancery clerk of each county for the sum appropriated such county. Each county shall receive nine one-thousandths (.009) of the total appropriation made to carry out the provisions of said sections, and the balance of said appropriation shall be apportioned by the state auditor among all the counties according to the following formula: one third in the ratio which the area of each county bears to the total area of the state; one third in the ratio which the rural population of each county bears to the total rural population of the state, as shown by the federal census of 1940; and one third in the ratio which the mileage of rural delivery and star routes in each county bears to the total mileage of rural delivery and star routes in the state.