il50 MANUAL OF ZOOLOGY. 



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 

 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 pataigiura 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 difl5- 

 culty as to the position of the Pterosauria 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 

 the Lower Lias to the Middle.Chalk inclusive, the Lithographic 

 Slate of Solenhofen (Upper Oolite) being particularly rich in 

 their remains. Most of them appear to have attained no very 

 great size, but the remains of a species from the Cretaceous 

 rocks have been considered to indicate an animal with more 

 than twenty feet expanse of wing, counting from tip to tip. 



In the genus Pterodactylus proper, the jaws are provided 

 with teeth to their extremities, all the teeth being long and 

 slender. 



In Dimorphodon, the anterior teeth are large and pointed, 

 the posterior teeth small and lancet-shaped. 



In Ramphorhynchus, the anterior portion of both jaws is 

 edentulous, and may have formed a homy beak, but teeth 

 are present in the hinder portion of the jaws. 



Order IX. — Dinosauria. — The last order of extinct Reptiles 

 is that of the Dinosauria, comprising a group of very remarkable 

 Reptiles, which show many points of decided affinity to the 

 Birds on the one hand, and to the so-called Pachydermatous 



