REPTILTA. PTEROSAURIA. 213 



symphysis, and there is an ossified ring in the sclerotic. The 

 occurrence of a postfrontal and its union with the jugal 

 behind the orbit, are characteristic reptilian features. 



The ribs have capitula and tubercula, and sternal and 

 abdominal ribs occur. The sternum has a well-developed keel, 

 and the scapula and coracoid are large and bird-like. There 

 are no clavicles or interclavicle. 



The anterior limbs are modified to form wings by the great 

 elongation of the fifth digit, to which a membrane was at- 

 tached. The second, third and fourth digits are clawed and 

 are not elongated in the way that they are in bats. The 

 pollex, if present at all, is quite vestigial. 



The pelvis is weak and small, and though the ilia are pro- 

 duced both in front of and behind the acetabula, in other 

 features the pelvis is not bird-like. The ischia are short and 

 wide, and the pubes are represented only by the pre-pubes. 

 The posterior limbs are small and the fibula is much reduced. 

 The pes is quite reptilian in type, and has five separate slender 

 metatarsals. The two best known genera are Pterodactylus, in 

 which the tail is short, and Rhamphorhynchus, in which it is 

 long. The Pterosauria are found throughout the Jurassic and 

 Cretaceous formations in both Europe and North America. 



