Air cleaner snorkel connects to that with a fiber tube - it puts warm air into the engine and helps keep the engine running when it is cold. When warm, the snorkel will close that pathway off and will draw air from the front of the snorkel.
Acornridgeman is correct. My '71 Mav and '67 Mustang both had this on the exhaust manifold and I never had it hooked up. Winters in Texas don't get THAT cold and I never had a problem with never hooking it up.
Thanks for the help that was bothering me haha. I'm starting to take the engine apart so I can rebuild it