3G2 Trof, Huxley^s Lecture 



mandibles were prolonged into beaks, whicli 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 the 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 Eeptiles and Birds, 

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

 characteristically ornithic, the manus and the pes, that they depart 

 most widely from the ornithic type. 



Clearly, then, the passage from Eeptiles to Birds is not from the 

 flying Eeptile to the flying Bird. Let us try another line. I have 

 already observed that, in the existing world, the nearest approxima- 

 tion to Eeptiles is presented by certain land Birds, the Ostriches and 

 their allies, all of w^hich 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 flightless 

 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, Megalosaurus, Poikilopleuron, Scelidosaurus, 

 Plateosaurus, etc., which occur throughout the whole series of the 

 Mesozoic rocks, and are, for the most part, of gigantic size, appear 

 to me to furnish the required conditions. 



In none of these animals are the skull, or the cervical region of 

 the vertebral column, completely known, while the sternum and the 

 manus have not yet been obtained in any of the genera. In none 

 has any trace of a clavicle been observed. 



With regard to the characters which have been positively deter- 

 mined, it has been ascertained, that : — 



1. From four to six vertebrae enter into the composition of the 

 sacrum, and become connected with the ilia in a manner which is 

 partly ornithic, partly reptilian. 



2. The ilia are prolonged forwards in front of the acetabulum as 

 well as behind it, and the resemblance to the bird's ilium thus pro- 

 duced is greatly increased by the widely arched form of the acetabular 

 margin of the bone, and the extensive perforation of the floor of the 

 acetabulum. 



^ It will be understood that I do not suggest any direct affinity between Pterodac- 

 tyles and Bats. 



