Cooling the heads?

When I had my intake off yesterday, I noticed that the two back cooling ports were blocked off on the intake. And I remembered that the last intake I had was the same way.

So... how does coolant flow through the heads? There's only 2 open coolant ports on the intake, so coolant only flows in to the heads but not out? Would it be beneficial to open the ports in the back and put in some hoses to the front of the intake to get some more coolant flow?