18 ANATOMY OF VERTEBKATES. 



Order XXII. DIXOSAUKIA. (Extinct.) 



Cervical and anterior dorsal vertcbraj with par- and di-apo- 

 pliyses, articulating with bifurcate ribs ; a few anterior vertebrfe 

 more or less convex in front and cupped behind ; the rest 

 with flat or slightly concave articular ends ; dorsal vertebras with 

 a neural platform ; sacral vertebras exceeding two in numljer ; 

 body supported on four strong, ambulatory, unguiculate limbs. 

 Skin in some armed by bony scutes. Teeth confined to upper 

 and lower jaws ; implanted in sockets. Ventricle of heart double 

 (inferential). 



Genera, Iguanodon, Scelidusaurus, Megalosaurus. 



Order XXIII. PTEEOSAURIA. (Extinct.) 



Pectoral members, by the elongation of the anti-brachium 

 and fifth digit, adapted for flight. Vertebrte prococlian ; those 

 of the neck veiy large, those of the pelvis small. Anterior 

 trunk-ribs with bifurcate heads. Most of the bones pneumatic. 

 Head large ; jaws long, and armed with teeth. Ventricle of 

 heart double (inferential). 



Genera, Dimorplwdon, Ramplwrhynclius , Ptcrodacti/lus. 



