That is so gross.

I can't find a tier 1 source for the story I read fairly recently about the contents of chicken McNuggets. The closest I come is to Answer.com about "How are Chicken McNuggets Made":

http://answers.yahoo.com/question/index?qid=20081205062811AATRqmj

Here is the link to a McDonald's PDF that lists the ingredients in all of their foods:

http://nutrition.mcdonalds.com/nutritionexchange/ingredientslist.pdf

You have to scroll through the list, it isn't easy to read and there are no anchor links on the page to make it easy to go directly to what you're curious about. I found everything but McNuggets when I scrolled through, but if you read the chicken strips and chicken sandwich ingredients, you'll get the picture.