Part missing to connect hose to thermostat housing?

Hello. So, I recently had a lot of work done to my vehicle but somehow a part is missing that connects a hose to the back of the thermostat housing. The hose goes from there and splits into two and I think each end goes to the head to keep it cool?? Don't quote me. My friend says there is a "nipple" that allows the main part of that hose to connect to the thermostat housing.
Can you tell me exactly what part I need and what to call it? Thank you