Thanks Skafe!
Here's some shots from Uxmal taken earlier today. Trying to show what the detail looks like there. Here's the Nun's Quad looking east-
Here's a view close up of the frieze detail-
The center shows a serpent to the left and a warrior, sans one leg, to the right. On the far right is a stack of Chac Mul or the rain god. There three, one on top of the other.
Here's the serpent's head close showing human form/face inside the serpents mouth-
Here the main throne at the south end of the Nun's Quad-
I did some research this morning before heading out turns not only were several key pieces broken off and sold sometime around the turn of the 20th century an impending visit by a noble woman resulted in the removal of anything that appeared to be phallic.