Anguidae

Anguidae View in CoL View at ENA ( Figs 49K–N View Figure 49 , 50S–V View Figure 50 , 51D, E View Figure 51 )

Anguids have a free angular, whereas the other bones are fused into a compound bone. The angular ( Fig. 49K–N View Figure 49 ) 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 View Figure 49 ) than in Pseudopus apodus ( Fig. 49M, N View Figure 49 ). 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 View Figure 50 , 51D, E View Figure 51 ) 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 View Figure 51 ). 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 View Figure 50 ). The articulation surface with the angular is visible on the lateral surface of the bone, reaching roughly midlength ( Fig. 50T, V View Figure 50 ). 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 View Figure 50 ), but can be moderately or well developed in Pseudopus apodus ( Fig. 50U View Figure 50 ). 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 .