PHYLUM CHORDATA 



377 



are weak as compared with the fore-limbs, and the pelvis does not exhibit 

 any resemblance to that of Birds, but appears to come nearer to tliat of the 

 Crocodiles. The astragalus sometimes unites with the tibia. There is no trace 





WH^ 



of any exoskeleton. The brain, as shown by 

 casts of the interior of the skull, bore interesting 

 resemblances to that of Birds in the relations of 

 the cerebellum and optic lobes, the latter being 

 separated from one another by the approximation 

 of the cerebellum to the fore-brain, instead of 

 being in close apposition with one another as in 

 existing Reptiles. 



The Pterosauria are confined to formations of 

 the Jurassic and Cretaceous periods. 



Fig. 1020. — Rampho- 

 rhyncliuSj restored. 

 (After Zittel.) 



in form and structure ; 



Pythonomoepha. 



The Pythonomorpha (Fig. 1021) were large 

 marine Reptiles with extremely elongated snake- 

 like bodies, but ' with well-developed limbs, 

 which were modified as swimming-paddles. The 

 vertebrfe, which are very numerous, are proccelous, 

 sometimes with, sometimes without, zygosphenes 

 and zygantra. The sacrum is absent as a ride. 

 A sternum has been found in one genus. The 

 skull resembles in form that of a Lizard, both 

 the quadrate is mobile, there is a parietal foramen ; 



the premaxillse are united. There is no inferior -temporal arch, the quadrato- 



Fig. 1021.— Edestosaurus (Pythonomorpha). Pectoral arch and fore-limbs, c. coracoid with 

 pro-coracoid ; h. humerus ; rfic. metacarpus ; r. radius ; %c. scapula ; w. ulna ; /, first digit ; 

 K, fifth digit. (From Zittel, after Marsh.) 



jugal being absent. The quadrate is movable, articulating with the squamosal 

 and epiotic. The rami of the mandible are united by ligament at the symphysis. 

 The pectoral arch (Fig. 1021) comprises discoidal coracoids (c) which meet 



