Oil Channels

According to RAVE flow of oil from the block to the head is via a small (5mm) internal channel at the front of the engine. Oil then travels up into the rocker shaft where it lubes the rockers before exiting at the rear of the head down a similar 5mm channel.
What confuses me is on my cylinder block there is no channel for the oil to flow back into. The head gasket has a hole to allow the oil out of the head but the block has nothing.

Is this normal? It doesnt make sense (to me at least) why the flow of oil is blocked at the head gasket.

there are two holes as same gasket fits both sides which are opposite way round to each other ,oil exits down push rod holes into sump,rocker shafts have hole each end for same reason