Principal English Translation:
the "god-captive" -- it was a thigh bone from a sacrificed captive, with all the flesh removed, and wrapped with paper and adorned with a mask
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 2 -- The Ceremonies, No. 14, Part III, eds. and transl. Arthur J. O. Anderson and Charles E. Dibble (Santa Fe and Salt Lake City: School of American Research and the University of Utah, 1951), 57.
Attestations from sources in English:
auh in queztepolli, amatica qujqujqujmiloaia, qujxaiacatiaia: auh ynjn motocaiotiaia, malteutl = And he wrapped the thigh bone with paper, and provided it a mask. And this was called the god-captive. (16th century, Mexico City)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 2—The Ceremonies, No. 14, Part III, eds. and transl. Arthur J. O. Anderson and Charles E. Dibble (Santa Fe and Salt Lake City: School of American Research and the University of Utah, 1951), 57.