XIII 



PHYLUM CHORDATA 



349 



are long and slender, like those of Birds. The pelvis and hind -limbs are 

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

 any resemblance to that of Birds. The astragalus sometimes unites with, the 



FIG. 960. Skull of Schaphognathus. D, pre-orbital aperture ; F>: frontal ; JK. jugal ; MX. 

 maxilla ; jV. nasal opening; P. mx. pre-maxilla ; Qu. quadrate. (After Zittel.) 



tibia. There is no trace 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. 



PYTHOXOMORPHA. 



The Pythoiiomorpha (Fig. 962) were large marine 

 Reptiles with extremely elongated snake-like bodies, 

 but having well developed limbs, which were modi- 

 fied as swimming-paddles. The vertebra?, which 

 are very numerous, are proco?lous, sometimes with, 

 sometimes without, zygosphenes and zygantra. 

 The sacrum is absent as a rule. A sternum has 

 been found in one genus. The skull resembles in 

 form that of a Lizard ; the quadrate is mobile, there 

 is a parietal foramen ; the pre-maxilla? are united. 

 There is only the supra-temporal arch. A peculiar 

 feature is that the supra-temporal or mastoid 

 serves to suspend the quadrate. The rami of the 

 are united by ligament at the symphysis. The pectoral arch 

 discoidal coracoids which meet vent rally, and a scapula which 

 resembles that of the Rhynchocephalia : a clavicle is never present. In the 



FIG. 901. Rhampho- 

 rhynchus. restored. 

 (After Zittel.) 



mandible 

 comprises 



