A comparative atlas of the skull osteology of European lizards (Reptilia: Squamata) Author Villa, Andrea Author Delfino, Massimo text Zoological Journal of the Linnean Society 2019 2019-11-30 187 3 828 928 https://academic.oup.com/zoolinnean/article/187/3/829/5528353 journal article 10.1093/zoolinnean/zlz035 0024-4082 14829109 Anguidae ( Fig. 19 AE–AI) Free postfrontal and postorbital are present in anguids. The former is roughly T-shaped in dorsal view, with a slightly concave anterior margin, and a straight and slender body ( Fig. 19 AE–AH). In Anguis gr. An. fragilis , the body is roughly subrectangular, but its posterior end is usually poorly ossified and, therefore, it can appear more pointed ( Fig. 19 AE–AF). Pseudopus apodus has a triangular body with a pointed end in dorsal view ( Fig. 19 AG–AH). A long anteromedial process develops from the medial corner of the anterior margin: it is moderately ( Anguis gr. An. fragilis ; Fig. 19 AE–AF) or distinctly ( Pseudopus apodus ; Fig. 19 AG–AH) robust and roughly three times longer than the short anterolateral process. A concave articulation surface is visible on both the medial and the lateral margins, continuing also on the posterior margin of the processes. These surfaces contact the frontal/ parietal complex and the postorbital, respectively, and are less expanded in juveniles. Both the dorsal and ventral surfaces are smooth, but foramina can pierce the body of the bone. The postorbital ( Fig. 19 AI) is reduced to a medially concave and blade-like bone in anguids. It has smooth outer and inner surfaces and a laminar and pointed posterior process. The anterior end is more thickened and presents a small hint of the strongly reduced anterolateral process, bending anterolaterally. The development and the thickness of this latter process are higher in Pseudopus apodus than in Anguis gr. An. fragilis . The concave medial surface articulates with the postfrontal, whereas a shallow concavity lodging the anterior end of the squamosal is barely visible laterally. As also reported by Klembara et al. (2017) , the postorbital can expand medially with a variably developed and laminar ossification in adults and subadults of Pseudopus apodus ( Fig. 19 AI). SQUAMOSAL The squamosal( Fig.20 ) is a paired and anteroposteriorly elongated bone. An anterior process forms the anterior end, whereas the posterior portion can be composed by a single posterior process or by a ventrally developed quadrate process and a posterodorsally developed dorsal parietal process. The morphology of this bone is highly variable between different groups.