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 : 889

Anguidae ( Figs 34, 40L, M)

In anguids, the alar process is long and wide with a rounded anterior end. The paroccipital projection is moderately long. The incisura prootica is U-shaped, very deep and wide, and the facial foramen, which opens laterally in a shallow entocarotid fossa, is also wide. The crista prootica is low ( Anguis gr. An. fragilis ; Fig. 34B) or moderately developed ( Pseudopus apodus ; Fig. 34G) and moderately robust; it can also be slightly irregular. The anteriormost and posteriormost portions of the crista are almost unrecognizable. The posterior opening of the Vidian canal opens on the ventral surface of the anterior inferior process of the prootic, ventrally to the facial foramen or slightly anteriorly. Only a reduced portion of the recessus vena jugularis is, therefore, visible posterior to it. In disarticulated specimens, the canal appears as a groove, since its lateral wall is composed by the crista ventrolateralis of the sphenoid.

OTOOCCIPITAL

The otooccipital ( Fig. 41) is a paired bone made up by the complete fusion of exoccipital and opisthotic, which are not recognizable as separate elements. Each otooccipital takes part in composing the occipital condyle. The posterior semicircular canal is visible on the posterior surface of the bone, running vertically and continuing dorsally on the supraoccipital. Few foramina are located between the ventral end of the posterior semicircular canal and the occipital condyle. The vagus foramen is the largest and most dorsally located of these foramina. The other ones are the hypoglossal foramina, whose number is highly variable. On the lateral side of the otooccipital is the well-developed paroccipital process that is roughly rectangular in posterior view. The posterior portion of the horizontal semicircular canal is visible by the base of this process. The crista interfenestralis marks the dorsal margin of the lateral opening of the recessus scalae tympani, running anteroventrally from the paroccipital process on the lateral surface of the otooccipital. The posterior portion of the inner ear is enclosed by this bone. It houses the posterior walls of the cavum capsularis and of the cochlear cavity, located dorsally and ventrally, respectively. There are no ridges or grooves separating the two cavities, but the openings of the ampullary recess ventrally and of the utricular recess dorsally are visible inside the cavum capsularis. The openings of the horizontal semicircular canal and the posterior semicircular canal are present laterally and dorsally to the cavum, respectively. Inside the cochlear cavity is the perilymphatic foramen, opening in the recessus scalae tympani. The otooccipital contacts the basioccipital ventrally, the prootic anteriorly and the supraoccipital dorsally, fusing with them.