@LEGI easiest way is to duplicate faces that you want to make back face for. Then flip their polygons. In 3DS Max there is flip in editable_poly face tab. I don't know about other software.
It's the tri's. So yeah, you need to drop another 300ish. A polygon is simply a face, if you consider that most faces will be made up of 4 vertices, each one of those is 2 tris. IF you triangulated your mesh, you would see all 600 odd faces.
i actually find this is kinda demonic. :poly122: not to mention ox head and horse face this duo actually is a gatekeeper of hell. http://en.wikipedia.org/wiki/Ox-Head_and_Horse-Face
@Carbonated I don't see in your screens the areas you're seeing inside the model. Usually this is due to your face normals being inside-out. One one side of a polygon is "viewable/rendered" and receives light. If you go Display>Polygons>Face Normals, you will now see a spike representing the normal and its' set direction…