Citroen C3 Horn?

Hi Sorry i think i posted a question as an answer in a previous question so I have added my question correctly now.
My girlfriends C3 horn HDi 2003 is not working, she has just bought the car (with a full years MOT).
Can anyone tell me where the horn should be located as I can not see it anywhere.
The warning fuse is ok so I was goinig to check out the switch on the steering wheel. Does the centre of the steering wheel just pull/prise off? I am a little concerned about pulling too hard with it having air bag.

any help appreciated.