28 THE EXTINCT BATRACHIA, REI'TILIA Teeth none. Quadratum immoveably fixed by articulation with the large pro and opisthotics. Cranial cavity not ossified anteriorly; no ali or orbitosphenoid. Palatine bones attached anteriorly. No postorbital or supratemporal elements. Two sacral vertebrae 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. Circulator y 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 vertebne. 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 scapular arch. Cranial cavity not ossified anteriorly to proetic. Palatine bones solidly attached to maxillie; a symphysis mandibuli. Squamosal usual].) present; premaxillary usually single. Limbs ambulatory, when present. Sacrum of two vertebrae, when present ; ribs single headed. Neural arches not united by suture, chevron bones present. Pubes and ischia transverse, united in pairs. Circulator y System. Heart with imperfect septum atriorum, no communication between aorta roots. Nerroto System. Cerebellum without lateral lobes or plicae.
