Christie has signed a permanent deal while Riggott has joined on loan for three months with a guarenteed move in the summer. The initial fee of £3m could rise to £5m, probably due to appearances.
Speaking to Boro's official website boss Steve McClaren said "From day one I've always wanted to build a good young squad. These players are an investment in the club's future. They both have great potential and a desire to improve so they are for the future as well as the now."
There has been no additional word on the late swoop for Michael Ricketts from Bolton, indeed some reports deny that Bolton have received an official written bid from Boro.
With only hours left until the transfer deadline it would appaear that the 24-year-old will be staying at the Reebok.