70 THE OSTEOLOGY OF THE REPTILES 



sometimes vestigial or absent. The prefrontals are always large, en- 

 tering into the formation of the nares in the Varanidae and Mosa- 

 sauridae (Fig. 54 a). They articulate with the palatine by a descend- 

 ing 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 d). The postfrontals are rarely large in 

 lizards and are often absent; when absent the postorbitals take their 

 place, sometimes (Fig. 55 d) 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 extend- 

 ing forward to meet the lacrimal when that bone is present. It articu- 

 lates 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 pleuro- 

 dont, pointed or obtuse teeth. 



On the palate the prevomers are paired or partially fused in the 

 Rhiptoglossa. They articulate in front (Fig. 55 c) with the pre- 

 maxillae, laterally usually with the maxillae, posteriorly with the 

 palatines only. They very rarely bear small teeth. 



The palatines (Fig. 55 c), 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 articu- 

 lations 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 



1 [Also Dibamid«. — G. K. N.] 



