EXTINCT REPTILES 



721 



Pterosauria or Pterodactyls. — Hying Reptiles, represented from the 

 Lower Jurassic to the Upper Chalk, exhibiting many points of resem.- 

 blance to Carinate Birds, but still distinctly Reptilian in type. They 

 resemble birds especially in some features of the skull and pectoral 

 girdle, but they differ markedly in their vertebral column, pelvis, and 

 organ of flight. An expansion of the skin seems to have been stretched 

 on the much -elongated outermost finger, and to have extended back- 



FiG. 427. — Vertical section through backbone and ribs 

 of Chelonian (I.) and Mammal (XL). — In part after 

 Jaekel. 



N.SP., Neural spine ; N.SC, neural scute ; T., tubercle of rib ; 

 CSC, costal scute over rib (R.) ; CA., capitulum of rib; 

 T.P., transverse process; CE., centrum; NA., cavity of 

 neural canal. In the Chelonian the tubercle abuts against 

 the flattened neural spine, and the capitulum against the 

 transverse process. In the Mammal, the tubercle articulates 

 with the transverse process and the capitulum with the 

 centrum. 



wards to the hind-legs and the tail. The long bones are hollow. The 

 sternum is keeled, and teeth are often present on the margin of both 

 jaws. There is botli a superior and an inferior temporal arcade. The 

 quadrate is fixed. Some were no larger than sparrows, but others — 

 the giants with which the race ended — had in some cases a spread of 

 wing of nearly 20 ft. It is probable that the resemblances of these 

 forms to Birds indicate similar habits, and not any close true affinity. 

 Examples. — Pterodactylus, Rhani f^horhynchus, Pteranodon. 



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