The lever is interesting also. There is a 'trigger' under the rear gear lever. Pull the trigger and this allows the rider to move the derailleur past the outer stop aligning the small sprocket so the chain can be de-railled onto the 'C' chain holder. This allows the rear wheel to be taken out and replaced by a race mechanic when a flat occurs. The mechanic then pushes the rider off while the rider de-rails back onto the appropriate sprocket.

Here is a poor photo - you can just see the trigger under the gear lever.