28 THE EXTINCT BATRACHIA, REPTILIA 



Teeth none. 



Quadratum immoveably fixed by articulation with the large pro and opisthotics. 



Cranial canity not ossified anteriorly; no ali or orbitosphenoid. 



Palatine bones attached anteriorly. 



No postorbital or supratemporal elements. 



Two sacral vertebra; : ischia and pubes more or less transverse, the latter sometimes not 



in contact. 

 Costal and vertebral elements usually united into a dorsal shield : dorsal corium ossified. 

 Circulatory and Nervous Systems, much as in Lacertilia. 



PTEROSAURIA. 



Limbs differentiated, one digit excessively elongated for aerial progression. 



Postorbital and supratempoial roof wanting. 



Sacrum of from three to five vertebra?. 



Inferior pelvic elements distinct, the pubes set parallel, directed forwards and not joined. 



Neural arches consolidated. 



Palatine elements united ; one premaxillary. 



LACERTILIA. 



The distal parts of limbs differentiated ; no supratemporal or postorbital bones. 

 Quadratum not in contact with prootic, articulating freely with opisthotic ; no quadrato- 



jugal. 

 Opisthotic sessile not distinct. 

 Sternum composed of but two elements, which are continuous with remainder of scapidar 



arch. 

 Cranial caAdty not ossified anteriorly to prootic. 

 Palatine bones solidly attached to maxillae; a symphysis mandibuli. 

 Squamosal usually present; premaxillary usually single. 

 Limbs ambulatory, when present. 



Sacrum of two vertebra;, when present ; ribs single headed. 

 Neural arches not united by suture, chevron bones present. 

 Pubes and ischia transverse, united in pairs. 

 Circulatory System. Heart with imperfect septum atriorum, no communication between 



aorta roots. 

 Nervous System. Cerebellum without lateral lobes or plicae. 



