Slow reply I know! ...Living in Tasmania, Australia at the mo', so I'm a few timezones away.
Pics:

Hard to make out - but the first is a rather shoddy screen grab from my mobile phone. Note the mud! I carried on riding for about 1 hr after the 'off', as I didn't think it was all that serious - and got the wound covered in mud as a result. The guy in A&E spent about 30 mins actually pulling it apart and cleaning the mud out of it.. Owwwch..! (Much to his derision.) The photo was taken while cold, shivering and probably a little in shock at the time - and waiting for my lift to arrive (who was, inevitably, late!). And yes - I was on my own! I couldn't find a mirror anywhere and I knew something felt damp and fleshy down there, but I just thought it was probably a bad graze - I couldn't quite work out what was going on when I saw the photo. Little did I realise that my chin was kinda hanging off...
....and the aftermath. Back home, clean, dry and kinda sore. It doesn't look too bad in this photo, I suppose - yet!

I was riding the same tracks the Aussie MTB squad train on - and having waay too much fun. I think that's why I came off. It was so much like the 'European' style of singletrack riding I'm used to from the UK - which is why they train here. Unfortunately rocks are - and probably always will be - my nemisis. Bastard things..!