Anguidae

Villa, Andrea & Delfino, Massimo, 2019, A comparative atlas of the skull osteology of European lizards (Reptilia: Squamata), Zoological Journal of the Linnean Society 187 (3), pp. 828-928 : 903

Anguidae ( Figs 49K–N, 50S–V, 51D, E)

Anguids have a free angular, whereas the other bones are fused into a compound bone. The angular ( Fig. 49K–N) is slender with pointed anterior and posterior ends. The latter end is slightly larger than the former and a clear constriction is visible at the beginning of the posterior-half of the bone in lateral view. The constriction is slightly more evident in Anguis gr. An. fragilis ( Fig. 49K, L) than in Pseudopus apodus ( Fig. 49M, N). The angular ridge runs along the ventral margin, having a thickening roughly at midlength. The dorsoventrally directed posterior alveolar foramen pierces this expansion in the middle. The anterior-half of the lateral surface is covered by the articulation surface with the dentary, whereas the posterior one is smooth. The compound bone ( Figs 50S–V, 51D, E) can be split into two portions in young individuals, but in adults only the anterior expansions of the surangular and the prearticular remain unfused. The articular condyle is subquadrangular and slightly mediolaterally elongated in dorsal view ( Fig. 51D, E). A robust but short tubercle is present on its anteromedial corner. The retroarticular process is short, stocky and quadrangular in medial view. It expands in the ventromedial direction and, therefore, the posterior portion of the compound bone appears concave in medial view. A low or very low longitudinal lateral crest is visible on the lateral surface of the process ( Fig. 50T, V). The articulation surface with the angular is visible on the lateral surface of the bone, reaching roughly midlength ( Fig. 50T, V). The posterior surangular foramen is shifted dorsally, near the dorsal margin, and in Pseudopus apodus the anterior one is shifted anteriorly, lying in the articulation surface with the dentary. Because of this latter shift, the anterior surangular foramen of Pseudopus apodus is not visible in lateral view. At the base of the retroarticular process, a ridge-like ventral expansion is present on the ventral surface of the bone: this expansion is very low in Anguis gr. An. fragilis ( Fig. 50S), but can be moderately or well developed in Pseudopus apodus ( Fig. 50U). The adductor fossa is strongly reduced, very narrow and anteroposteriorly elongated. In Anguis gr. An. fragilis , it is slightly longer than it is in Pseudopus apodus .