While the photo I used isn't quite clear enough to make out the orifice, the black arrows point to the area where they should be found.
The outermost brass tubes that extend down from the top of the carb (aka the "airhorn") on the secondary side, enter the fuel-filled reservoirs (red arrows, filled by those orifices).
Fuel is picked up as the secondaries begin to open and enters the airstream through two small holes just beneath (usually- the holes can also be above) the secondary air valve. This acts as an auxiliary fuel circuit, as well as a passive accelerator 'pump' to enrichen the fuel/air mixture as the secondaries just begin to tip in.
Without this, a bog will occur when the secondaries are called on.