402 ANATOMY OF VERTEBRATES. 



teeth upon each pterygoid bone. The chief exception to the 

 typical dentition of the present family is made by the large 

 scincoid lizards of Australia, which, on that account, have received 

 the generic name of Cyclodus. The dentition of the Cyclodus 

 nigroluteus is exemplified in the lower jaw, fig. 272. In the upper 

 jaw, the single premaxillary bone has depressions for twelve teeth, 



272 



Lower jaw and teeth of Cyclodus nigroluteus. v. 



of which only the alternate ones are usually in place ; they are of 

 very small size, with the fang compressed laterally, and the crown 

 antero-posteriorly, so as to resemble a true incisor in form, the 

 summit sloping to an edge from behind forwards, with the middle 

 of the cutting surface a little produced. Each superior maxillary 

 bone has depressions for fourteen teeth ; they quickly increase in 

 size, and exchange their conical for a sub-hemispherical crown ; 

 the eighth to the thirteenth inclusive are the largest teeth ; they 

 are set obliquely, and pretty close together. In the lower jaw 

 there are two small incisors, at the anterior part of each pre- 

 mandibular bone corresponding with those of the premaxillary ; 

 these are succeeded by five or six conical teeth, and the rest 

 correspond in size and form with the tuberculate molars of the 

 upper jaw. All the teeth are attached, after the Pleurodont type, 

 by their base and outer margin to shallow depressions on the 

 outer side of the external alveolar parapet. The germs of the 

 successional teeth, c, fig. 272, are developed at the inner side of the 

 base of their predecessors, , which they excavate, undermine, 

 and displace in the usual manner. 



Certain genera of the Iguanian family of Lizards, e. g. Istiurus, 

 Lophyrus, Calotes, and Otocryptis, have the teeth soldered, like 

 those of Mosasaiirus, to the summit of the alveolar ridge, and 

 thence are called ( Acrodonts : ' in all these lizards the maxillary 

 and mandibular teeth may be divided into anterior laniary and 

 posterior molary teeth. In other Iguanians the teeth are lodged 

 in a common shallow oblique alveolar groove, and are soldered 

 to excavations on the inner surface of the outer wall of the 

 groove : these are called ( Pleurodonts.' Most of them possess 

 pterygoid as well as maxillary teeth : but the following genera, 



