The Intake manifold is an amazing piece of plumbing. The large arrow indicates the electronic 'fly-by-wire' throttle. Air enters from the front right-hand side of the engine, passes through here in the direction of the curved arrows into the plenum. From the plenum the air is drawn efficiently into the runners aided by a generous bell mouth (marked by the small, straight arrows) on each runner. The whole system is about as efficient as a typical aftermarket intake system.