"...on either side of the door is an elaborated serpent face in profile, the whole cast into a strikingly rectangular mould. One of these profile heads is given in Fig. 175. It is an interesting example of elaboration, since the top of the eye is formed by a small complete serpent whose tail constitutes the nose plug of the greater head.
The noteworthy features in the present connection are the teeth that project inward at the side of the door and the peculiar right-angled turn of the jaw. It should also be stated that the design does not completely fill a four-sided area and that details from other masks intrude into the open spaces."
Herbert J. Spinden, "A Study of Maya Art", p. 126.