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Overall view of the lower-left portion of the combustion chamber and injector. Note the radial baffles.

The silver circles which look like flat-head screw heads are igniter fuel housings. The F-1 Engine Familiarization Training Manual (R-3896-1) [direct link to 16.8 meg PDF] describes how two igniter fuel housings are located in each of the 12 outer compartments and one in the center compartment. Fed by individual igniter fuel feed tubes from the igniter manifold, they injected igniter fuel into the compartments. The igniter fuel (from the hypergol manifold) was composed of 85% triethylborane and 15% triethylaluminum, and ignited upon contact with oxygen, causing spontaneous combustion and establishing thrust chamber ignition.