564 MANUAL OF ZOOLOGY. 



a very extraordinary combination of characters. The most fa- 

 miliar members of the order are the so-called " Pterodactyles," 

 and the following are the characters of the order : 



No exoskeleton is known to have existed. The dorsal vertebrce 

 are proccelous, and the anterior trunk-ribs are double-headed. 

 There is a broad sternum with a median ridge or keel, and ossified 

 sternal ribs. The jaws were generally armed with teeth, and 

 these were implanted in distinct sockets. In some forms (Ram- 

 phorhynchus] there appear to have been no teeth in the ante- 

 rior portion of the jaws, and these parts seem to have been 

 sheathed in horn, so as to constitute a kind of beak. In the 

 genus Pteranodon, from the Cretaceous rocks of North America, 

 comprising gigantic examples of the order, the jaws are com- 

 pletely destitute of teeth, and appear to have been encased in 

 a horny beak. 



A ring of bony plates occurs in the sclerotic coat of the eye. The 

 pectoral arch consists of a scapula and distinct coracoid bone, 

 articulating with the sternum as in Birds, but no clavicles have 

 hitherto been discovered. The fore-limb (fig. 317) consists of a 



Fig. 317. Pterodactyius brevirostris. Skeleton and restoration. 



humerus, ulna and radius, carpus, and hand of four fingers, of 

 which the inner three are short and unguiculate, whilst the outer- 

 most is clawless and is enormously elongated. Between this im- 

 mensely-lengthened finger, the side of the body, and the compara- 

 tively small hind-limb, there must have been supported an ex- 

 panded fiy ing-membrane, or " patagium," which the animal must 

 have been able to employ as a wing, much as the bats of the pres- 

 ent day. Lastly, most of the bones were "pneumatic " that is 

 to say, were hollow and filled with air. 



By the presence of teeth in distinct sockets, and, as will be 

 seen hereafter, especially in the structure of the limbs, the 

 Pterodactyles differed from all known Birds, and there can be 



