Prof. Huxley on the Animals hetween Birds and Reptiles^ 71 



As in the case of birds, the tertiary formations yield no trace of 

 reptiles which depart from the type of the existing groups. But 

 otherwise than is true of birds, the newest of the Mesozoic forma- 

 tions, the chalk, makes us acquainted with reptiles which, at first 

 sight, seem to approach birds in a very marked manner. These are 

 those flying reptiles the Pterodactyles, which resemble the great 

 naajority of birds in the presence of air-cavities in their bones, in the 

 wonderfully bird-like aspect of their coracoid and scapula, and in 

 their broad sternum with its median crest. Furthermore, in some 

 of the Pterodactyles, the praemaxillae and the symphysial part of 

 the mandibles were prolonged into beaks, which appear to have 

 been sheathed in horn, while the rest of each jaw was armed with 

 teeth. 



But horn-sheathed beaks are found in reptiles as well as in birds ; 

 the structure of the scapulo-coracoid arch and of the sternum, and 

 the pneumaticity of the bones vary greatly among birds themselves ; 

 and these characters of tbe Pterodactyles may be merely adaptive 

 modifications. 



On the other hand, the manus has four free digits, the three inner 

 of which are strongly clawed, while the fourth is enormously pro- 

 longed, in total contrast to the abortion of the corresponding digit in 

 birds. The pelvis is as wholly unlike that of birds as is the hind 

 limb and foot, 



Thus it appears that Pterodactyles, among reptiles, approach birds 

 much as Bats, among mammals, may be said to do so. They are a 

 sort of reptilian Bats * rather than links between reptiles and birds ; 

 and it is precisely in those organs which in birds are the most cha- 

 racteristically ornithic, the manus and the pes, that they depart most 

 widely from the ornithic type. 



Clearly, then, the passage from reptiles to birds is not from the 

 flying reptile to the flying bird. Let us try another line. I have 

 already observed that in the existing world the nearest approxima- 

 tion to reptiles is presented by certain land birds, the Ostriches and 

 their allies, all of which are devoid of the power of flight by reason 

 of the small relative size of their fore limbs and of the character of 

 their feathers. 



Can we find any extinct reptiles which approached these flight- 

 less birds, not merely in the weakness of their fore limbs, but in other 

 and more important characters ? 



I imagine that we can, if we cast our eyes in what at first sight 

 seems to be a most unlikely direction. 



. The Dinosauria, a group of extinct reptiles, containing the genera 

 Iguanodon, Hadrosaurus, Megalosautnis, Poihilopleuron, Scelidosaurus, 

 Plateosaurus, &c., which occur throughout the whole series of the Me- 

 sozoic rocks, and are, for the most part, of gigantic size, appear to me 

 to furnish the required conditions. 



In none of these animals is the skull or the cervical region of 



* It will be understood that I do not suggest any direct afiinity between 

 Pterodactyles and Bats. 



