Schele, Linda, and Peter Mathews. 1998. The Code of Kings: The Language of Seven Sacred Maya Temples and Tombs. New York: Scribner: 171, fig. 4.38(a)
Schele, Linda, and David A. Freidel. 1990. A Forest of Kings: The Untold Story of the Ancient Maya. New York: William Morrow and Company, Inc.: 338, Fig. 8:21
Altar G, North side, (GI/CPN 13). LC 22.214.171.124.0 (August 19. AD 800). Erected by Yax Pasah. Depicts a double-headed serpent with legs; skeletal snake with K'awiil emerging on west side and fleshed snake with a Pawahtun emerging on east side.
See also SD1010