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.: 83, Fig. 2:11;
Freidel, David A., Linda Schele, and Joy Parker. 1993. Maya Cosmos: Three Thousand Years on the Shaman's Path. New York: W. Morrow: 64, Fig. 2:2