Can someone explain this port please

It's been years (decades?) since I've dealt with a 318-3 in it's natural state, but I thought the coolant for the manifold came from the rear coolant ports of the heads; and the exhaust crossovers just weren't used in that application- but they were still present in the heads? I'm never wrong, but I've been mistaken a few times... :) I'm sure somebody will refresh my memory if needed!