Which way does the thermostat face?

[plymouthcolt]

I replaced the o-ring on the t-stat. When I went to reinsert it I noticed I there is a opening about half an inch to one inch down from the top of it.

Does this opening face the rear of the engine or front? Maybe the rear as there is a opening in the cylinder wall that I'm guessing lines up with the opening on the t-stat?

[oneblueyedog]

It's only goint to fit an one way as the top flange is asymetrical.