Well, mine are rectangular on both the front and rear housing, and larger but still rectangular on the center housing.  Since my engine is in pieces, I can tell you that these holes connect to the round holes that are below the exhaust ports.  My guess would be that these are channels for exhaust to heat the intake manifold, but I admit that I don't really know for sure.  I'm sure someone here does though.

Cheers,
Rusty (converting from bent mechanical flap handle to electric flaps)