476 MANUAL OF ZOOLOGY. 



" 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 

 the sternum, proving the existence of unusually -developed 

 pectoral muscles ; by the articulation of the coracoid bones 

 with the top of the sternum, providing a fixed point or fulcrum 



Fig. 208. Pterodactylus brevirostris. Skeleton and restoration. 



for the action of the pectoral muscles ; and, lastly, by the 

 existence of air-cavities in the bones, giving the animal the 

 necessary degree of lightness. The apparatus, however, of 

 flight was not a " wing," as in Birds, but a flying membrane, 

 very similar in its mode of action to the patagium of the Mam- 

 malian order of the Bats. The patagium of the Bats, however, 

 differs from that of the Pterodactyles in being supported by 

 the greatly-elongated fingers, whereas in the latter it is only 

 the outermost finger which is thus lengthened out. The diffi- 

 culty as to the position of the Pterosanria is evaded by Mr 

 Seeley by placing them in a distinct class, which he terms 

 Ornithosauria, and which he regards as most nearly related to, 

 but coequal with, the class Aves. 



The Pterosauria are exclusively Mesozoic, being found from 



