THE LACERTILU. 1G3 



The LacertiUa all possess teeth, which may be confined 

 to the preraaxilliB, maxillo3, and dentary piece of the man- 

 dibles ; or may, in addition, be developed on the palatine and 

 pterygoid bones. These teeth are simple in structure, and 

 their crowns have very various forms, being sometimes sharp 

 and conical {Monitor) ; or blade-like, with serrated edges 

 ( L/uana) ; or with broad, crushing, and spheroidal crowns 

 ( G'jdodus). As a general rule, the teeth become anohylosed 

 i<j the adjacent bone with age ; and in the upper and lower 

 jaws they thus become attached, either by their sides to the 

 parapet of the jaw, when the dentition is said to he 2^lsuro- 

 dont ; or by their bases to the summit of the parapet, when 

 the dentition is acrodont. The extinct Protorosauria are 

 said to be thecodont, or to have the teeth lodged in alveoli. 

 New teeth are usually developed at the bases of the old ones. 



The Laeertilia are divisible into numerous groups, the leading distinctive 

 characters of which are exhibited in the following table : 



I. — The pterygoid and quadrate bones united. 

 A. A columella and an interorbital septum in the sliull. 

 Kionocraiiia (Stannius). 



a. Amphicoelous vertebraj (K. Amphiccdia). 



a. Dentition acrodont or pleurodont. 



1. Ascalaboia. 



2. Rhynrhocephala. 



3. Homceosauria* 



b. Dentition thecodont (?). 



4. Proloro^auria.* 



b. Proocelous vertebrae ( IC. proccdia). 



a. Not more than nine cervical vertebrae. 



a. The nasal bone, single. 



5. Platynoia. 



b. The nasal bones, two. 



1. The integument of the head not 



covered with epidermic plates. 



6. Munota, 



2. The integument of the head covered 



with epidermic plates. 

 Y. Laceriina. 



8. Chalddea. 



9. Scincoidea. 



b. More than nine cervical vertebriB. 



10. DoHchosauria.'* 



11. Mosa-iauria, 

 a No columella ; no interorbital septum. 



12. Amphisbwnoida. 



II. — The pterygoid and quadrate bones disunited. 



13. Cliamcdeonida, 



* The columella has not been observed in these groups, 

 9 



