Page:The Osteology of the Reptiles.pdf/88

70 sometimes vestigial or absent. The prefrontals are always large, entering into the formation of the nares in the Varanidae and Mosasauridae (Fig. 54 ). They articulate with the palatine by a descending process. The nasals, usually paired, are sometimes fused with the premaxillae or with each other; they are separated from the nares in the Rhiptoglossa (Fig. 55 ). The postfrontals are rarely large in lizards and are often absent; when absent the postorbitals take their place, sometimes (Fig. 55 ) ending forward over the orbit to meet the prefrontal. The postfrontal and postorbital are not rarely found united by suture in the mosasaurs; usually, however, the two bones are indistinguishably fused or the postfrontal is absent. Posteriorly the postorbitals articulate as usual with the squamosal; below with the jugals. The postorbito-jugal and the postorbito-squamosal arch may be absent in various terrestrial lizards.

The jugal is a slender bone bordering the orbit below and extending forward to meet the lacrimal when that bone is present. It articulates with the maxilla, ectopterygoid, postorbital, and often with the tip of the squamosal. It may be vestigial or even entirely absent in lizards.

The maxilla articulates normally with the premaxilla, sometimes with the nasal and prefrontal, with the jugal, prevomer, palatine, ectopterygoid. It always bears a single row of acrodont or pleurodont, pointed or obtuse teeth.

On the palate the prevomers are paired or partially fused in the Rhiptoglossa. They articulate in front (Fig. 55 ) with the premaxillae, laterally usually with the maxillae, posteriorly with the palatines only. They very rarely bear small teeth.

The palatines (Fig. 55 ), unlike those of most other reptiles, are intercalated between the prevomers and pterygoids, articulating on the sides with the maxillae and more or less with the ectopterygoids. They sometimes bear teeth. The pterygoids have the normal articulations except that in front they articulate with the palatines only. The posterior palatine opening is usually large. They usually bear teeth.

The epipterygoid, a slender rod, is present so far as known in all lizards except the Amphisbaenia and Rhiptoglossa, articulating in a