3/4 REPTILIA. 



each superior maxilla carries an enormous tusk-like tooth 

 growing from a persistent pulp. In Oudenodon, on the other 

 hand, the mouth is beak-shaped (fig. 323, B), and seems to 

 have possessed no teeth of any kind. Dicynodon and Oudeno- 

 don are known only from strata of supposed Triassic age in 

 India and South Africa. Rhynchosaurus also, if truly refer- 

 able here, is Triassic, occurring in Europe. 



ORDER VIII. PTEROSAURIA. This order includes a group 

 of extraordinary flying Reptiles, all belonging to the Mesozoic 

 epoch, and exhibiting in many respects a very extraordinary 

 combination of characters. The most familiar 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 

 vertebrae 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 are always armed 

 with teeth, and these were implanted in distinct sockets. In 

 some forms (Ramphorhynchus) there appear to have been no 

 teeth in the anterior portion of the jaws, and these parts seem 

 to have been sheathed in horn, so as to constitute a kind of 

 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. 324) consists of a humerus, ulna and radius, carpus, and 

 hand of four fingers, of which the inner three are short and 

 unguiculate, whilst the outermost is clawless and is enormous- 

 ly elongated. Between this immensely-lengthened finger, the 

 side of the body, and the comparatively small hind-limb, there 

 must have been supported an expanded flying-membrane or 

 " patagium," which the animal must have been able to employ 

 as a wing, much as the Bats of the present 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 little question as to their being genuine Reptiles. The only 

 Reptile, however, now existing, which possesses any power of 

 sustaining itself in the air, is the little Draco volans, but this 

 can only take extended leaps from tree to tree, and cannot be 

 said to have any power of flight properly so called. That 

 the Pterodactyles, on the other hand, possessed the power of 

 genuine flight, is shown by the presence of a median keel upon 



