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 : 875

Anguidae ( Fig. 29Y –AB)

Anguids have a crescent-shaped and medially concave ectopterygoid, similar to that of gekkotans ( Villa et al., 2018a). The lateral surface of the bone has two concave articulation surfaces: one for the posterior process of the maxilla on the anterior end and a larger one (roughly twice as large as the former) for the pterygoid flange posteriorly. The two articulation surfaces come nearly in contact with each other. In lateral view, the posterior end appears bifurcated, because of the presence of two pointed projections (lappets) clasping the pterygoid flange. The dorsal projection is longer and larger than the ventral one. In Pseudopus apodus , the anterior end also appears slightly forked, because of the presence of a small and anterolaterally directed expansion clasping ventrally the posterior process of the maxilla ( Fig. 29 AA). The mediodorsal surface of the bone is smooth.

GENERAL FEATURES OF THE BRAINCASE

The sphenoid, the basioccipital, the prootics, the supraoccipital and the otooccipitals fuse together to form the braincase ( Figs 30 , 31 , 32 , 33 , 34 ). The fusion is generally linked to ontogeny, with separated bones in juveniles that fuse in older individuals. On the posterior side of the region, the foramen magnum is defined by the basioccipital ventrally, the supraoccipital dorsally and the otooccipitals laterally. The otooccipitals and the basioccipital form the occipital condyle. On each side, the recessus scalae tympani is enclosed by the basioccipital and each otooccipital. The recessus opens externally with a ventrolaterally directed lateral opening and internally with a medial opening into the cranial cavity and a dorsomedial opening (the perilymphatic foramen) into the cochlear cavity. The external opening of the cochlear cavity is the wide fenestra ovalis, located between the prootics and otooccipitals. The paired anterior, horizontal and posterior semicircular canals are present on each side of the ossified braincase. The anterior canal passes through the prootic and the supraoccipital, the horizontal canal goes from the dorsal portion of the prootic to the base of the paraoccipital process of the otooccipital, and the posterior canal develops between the supraoccipital and the otooccipital.

Figures

Figure 29. Ectopterygoids. A–E, Laudakia stellio (MDHC 245), left ectopterygoid in anterior (A), dorsal (B), ventral (C), medial (D) and lateral (E) views. F–J, Chamaeleo chamaeleon (MNHN 2002–24), right ectopterygoid in anterior (F), dorsal (G), ventral (H), medial (I) and lateral (J) views. K–L, Ac. erythrurus (UAM.R.ACVII), right ectopterygoid in ventral (K) and dorsal (L) views. M–N, Lacerta agilis (MDHC 176), left ectopterygoid in ventral (M) and dorsal (N) views. O–P, Z. vivipara (UAM.R.Lv24), right ectopterygoid in ventral (O) and dorsal (P) views. Q–R, Ab. kitaibelii (MDHC 239), right ectopterygoid in ventral (Q) and dorsal (R) views. S–T, Chalcides ocellatus (MDHC 250), right ectopterygoid in ventral (S) and dorsal (T) views. U–V, Ophiomorus punctatissimus (MDHC 427), right ectopterygoid in ventral (U) and dorsal (V) views. W–X, Tr. aurata (MDHC 280), right ectopterygoid in ventral (W) and dorsal (X) views. Y–Z, Anguis gr.An. fragilis (MDHC 102), right ectopterygoid in ventral (Y) and dorsal (Z) views. AA–AB, Pseudopus apodus (MDHC 215), left ectopterygoid in ventral (AA) and dorsal (AB) views. Abbreviations: al, anteromedial lappet of the posteromedial process; alp, anterolateral process; asm, articulation surface with the maxilla; asp, articulation surface with the pterygoid flange; dl, dorsal lappet of the posteromedial process; plp, posterolateral process; pmp, posteromedial process; vl, ventral lappet of the posteromedial process; vp, ventral process. Scale bars = 1 mm.

Figure 30. Braincases. A–E, Ac. erythrurus (UAM.R.ACVII), braincase in anterior (A), right lateral (B), posterior (C), dorsal (D) and ventral (E) views. F–J, Lacerta bilineata (MDHC 15), braincase in anterior (F), right lateral (G), posterior (H), dorsal (I) and ventral (J) views. The parasphenoid rostrum is broken in both specimens. Abbreviations: ap, alar process; asc, anterior semicircular canal; b, basioccipital; bp, basipterygoid process; ca, crista alaris; fma, foramen magnum; fo, fenestra ovalis; glhv, groove of the lateral head vein; hsc, horizontal semicircular canal; o, otooccipital; oc, occipital condyle; p, prootic; pap, paroccipital process; povc, posterior opening of the Vidian canal; rvj, recessus vena jugularis; sp, sphenoid; su, supraoccipital; tc, trabecula cranii. Scale bars = 1 mm.

Figure 31. Braincases (continued). A–E, Po. bocagei (UAM.R.PB48), braincase in anterior (A), left lateral (B), posterior (C), dorsal (D) and ventral (E) views. F–J, Ab. kitaibelii (MDHC 239), braincase in anterior (F), right lateral (G), posterior (H), dorsal (I) and ventral (J) views. Abbreviations: aovc, anterior opening of the Vidian canal; cc, cochlear cavity; cp, crista prootica; ip, incisura prootica; pp, posterior process of the prootic; psc, posterior semicircular canal; vf, vagus foramen. Scale bars = 1 mm.

Figure 32. Braincases (continued). A–E, Chalcides chalcides (MDHC 398), braincase in anterior (A), right lateral (B), posterior (C), dorsal (D) and ventral (E) views. F–J, Chalcides ocellatus (MDHC 250), braincase in anterior (F), right lateral (G), posterior (H), dorsal (I) and ventral (J) views. Abbreviations: ci, crista interfenestralis; ctr, crista trabecularis; ctu, crista tuberalis; lrst, lateral opening of the recessus scalae tympani; rst, recessus scalae tympani; sc, supraoccipital crest; st, sphenooccipital tubercle. Scale bars = 1 mm.

Figure 33. Braincases (continued). A–E, Ophiomorus punctatissimus (MDHC 427), braincase in anterior (A), left lateral (B), posterior (C), dorsal (D) and ventral (E) views. Abbreviations: ff, facial foramen. Scale bars = 1 mm.

Figure 34. Braincases (continued). A–E, Anguis gr. An. fragilis (MDHC 102), braincase in anterior (A), left lateral (B), posterior (C), dorsal (D) and ventral (E) views (the parasphenoid rostrum is broken). F–J, Pseudopus apodus (MDHC 215), braincase in anterior (F), right lateral (G), posterior (H), dorsal (I) and ventral (J) views (the anterior end of the sphenoid and the basipterygoid processes are broken). Scale bars = 1 mm.