how can I build a multiplexer in simulink?

Hi everybody. I want to simulate a real-time system in simulink in which some blocks are feed by delay block. But the initial values of these block should be determined by an input value from the workspace. My idea is to apply a multiplexer that fist time passes data from the first input port to the output and the other times passes data from the second input port to the output. Now, my problem is that which block in simulink can operate as multiplexer so that be capable of controlling the output. can anybody help me? thanks.