EXTINCT ORDERS OF REPTILES. 449 



supposed Triassic age in South Africa and India, but Rhyncho- 

 saurus occurs in the Trias of 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 famiUar 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 ver- 

 tebrae are proccelous, and the anterior trunk-ribs are double- 

 headed. There is a broad sternum with a median ridge 01 

 keel, and ossified sternal ribs. The jaws were always armed 



Fig. 177. — Pterodaciylus hrevirostris. Skeleton and restoration. 



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

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

 guiculate, whilst the outermost is clawless and is enormously 

 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. 



