A CASING IN POINT
On the McLaren, like on most other cars, the rear wing central pillar goes through and around the exhaust pipe (interestingly, Mercedes does not use this installation) and connects to the gearbox casing.
The casing houses the gearbox itself as well as other various components (oil pump, torsion bars, rockers, heave spring, anti-roll bar, etc.), some of which can be seen on the bottom picture.
