The central rear room contains a roofed shrine chamber -- a room within a room -- that is called the pib na (the "underworld house" within the "sacred mountain"). In each of the three buildings, the doorjamb texts give the name for the building, apparently derived from the central motif that decorates the extraordinary carved panel on the inside back wall of each pib na.
...The motif in the Temple of the Foliated Cross (the na te kan), commemorates the earthly realm, in keeping with its location on the east, the life-giving direction of the rising sun. This motif depicts the maize plant, the sustainer of life, from which sprout human heads (in the creation myth of the Popol Vuh, human beings were fashioned by the gods from maize dough).
Robert J. Sharer, The Ancient Maya, p. 284
"In each temple, the central image was flanked on the one side by a short figure encased in a heavy cloth costume, and on the other by Chan-Bahlum wearing simple dress. From there the action moved to the two exterior panels, following the path of the king from the Otherworld to the natural one. On the outer panels the king is shown returning in triumph from his transformational journey: he has changed from heir to the reigning monarch of Palenque."
Linda Schele and David Freidel, A Forest of Kings: The Untold Story of the Ancient Maya, p. 239