It is a combination of the FN SCAR (Upper reciever) and the G36 (Lower Reciever) ~ though I would assume its internal workings are more 36 less SCAR.
If you are farmiliar with the SCAR you know that the bolt can be operated from either side - in this case the bolt handle is being used on the other side and we cannot see it in the pictures.
All and All I am impressed, but judging from the pictures in the news lately the Mexican Army is still not using it in "combat" just parades.
(and yes, I did make an account just to say this ... I am that bored here at work)