A tiny but important point needs to be cleared up, especially since the above diagrams are a bit confusing. The output of a register is copied onto the wires that emanate from that register and the signals almost immediately travel to their destinations, which are usually muxes or other registers. However, these values are not latched into the registers until the LD wire goes high. Moreover, when there are several inputs to a mux, only one is selected by the associated mux select wires.