Bones returned from a lengthy hiatus last week. But it was hard for fans to get too excited for the episode.

After all, it was just number-99.

But the Fox series will air a special installment this Thursday. Titled "The Parts in the Sum of the Whole," the 100th episode will take viewers back six years to the very first case on which Brennan and Booth worked together.

As usual, we'll update our site with the latest Bones quotes after the episode airs. For now, check out the following photos from it:

We've been told the final photo listed is actually a new one, set in the modern day. Why are Bones and Booth in a semi-embrace? Tune in. Find out.

Below, we've also posted the official Fox promo for the episode:

[video url="http://www.tvfanatic.com/videos/the-parts-in-the-sum-of-the-whole-promo/" title="The Parts in the Sum of the Whole Promo"] [/video]

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.