The shape of the snout and the associated cranial elements of _S. sordida_ vary geographically and ontogenetically. Specimens from the Caribbean lowlands have blunt snouts in lateral view; those from the Pacific lowlands have longer, more slender snouts that are pointed in lateral view, and those from the Meseta Central are intermediate in snout shape between the two lowland populations (Fig. 4). These differences in shape of the snout are dependent on the nature of the underlying cranial bones, principally the maxillaries and nasals. In specimens from the Caribbean lowlands the nasals are long, wide, and narrowly separated from the ethmoid; the anterior edge is just posterior to the nostril. The maxillary flanges are nearly vertical. In specimens from the Pacific lowlands the nasals are relatively shorter, narrower, and rather widely separated from the ethmoid; the anterior edges of the nasals do not extend so far forward as in specimens from the Caribbean lowlands. The maxillary flanges slant medially. In these cranial characters, specimens from the Meseta Central are intermediate between the two lowland populations. Superimposed on this geographic variation are ontogenetic changes, which are most noticeable in males. In smaller, and presumably younger, specimens the snouts are more pointed than in larger specimens; consequently some small males from the Caribbean lowlands resemble larger males from the Pacific lowlands, since the nasals and maxillaries of the former are not fully ossified. In addition, in small breeding males the ethmoid is only about one-half ossified, a large frontoparietal foramen is present, the anterior arm of the squamosal extends only about one-fourth the distance to the maxillary (two-thirds the distance in larger specimens), and the tegmen tympani are short, as compared with the long, thin elements in larger specimens. [Illustration: FIG. 4. Variation in the shape of the snout in _Smilisca sordida_; left column females, right column males; all from Costa Rica: (A) Camp Seattle, Rincon de Osa, Puntarenas Prov. (UMMZ 123684); (B) Quebrada Agua Buena, 3 km. SW Rincon de Osa, Puntarenas Prov. (USC 7236); (C) Rio Oro, 28.5 km. NW Villa Neily, Puntarenas Prov. (KU 91742); (D) Rio Jorco, near Desamparados, San Jose Prov. (KU 91765); (E-F) Bambu, Limon Prov. (USC 7183). x3.]