Lord Brahma has four heads. Vedas are the Vani of Brahma, each Ved came from each mouth of Brahma. the 4th ved Atharva was discovered later by Rishi Atharv . At the end of each yuga Brahma undergoes in a state of meditation and from each mouth he preaches vedas , once in the same state a Danav heard the 4th ved and he took the next birth as Rishi Atharv .
Name of four vedas :