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Detail of the taped cover over the fuel inlet manifold visible at the 12:00 position of dsc59800.jpg.

Picture 2 of 2.

Liquid hydrogen from the fuel turbopump is routed through this manifold to the regenerative cooling tubes comprising the thrust chamber walls. Like the RL-10, the J-2 employs a "pass and a half" construction, with the "down" tubes being introduced at this manifold and the "up" tubes running the full length of the thrust chamber.

See the USSRC's RL-10 thrust chamber section to see an example of this "pass and a half" construction.