I'd like to see how PhysX is integrated into the Engine.

I’m currently implementing a simple physics engine using PhysX 4.0, for a personal project.
I’d like to know how PhysX is integrated in Unreal Engine.
I’m browsing through the source codes but it seems like I’m unable to find all the header/source files related to physX.

Can please someone kindly guide me to the folders where the physX related source codes are located?
Thank you!