OF EVOLUTION. 33 



The Hadrosaurus, as it is called, is the represent- 

 ative of a large group of reptiles, the dino- 

 saurs, or terrible reptiles, many of whose mem- 

 bers depart just in that much from other reptiles 

 as is indicated by the above characters supposed 

 to belong to birds. In other words, we have 

 here both small and giant animals, whose pro- 

 gression was either largely, or mainly, effected by 

 the hinder appendages alone ; in which the pubic 

 bone of the pelvis was directed backward, more 

 or less in a direction parallel with that of the 

 ischium ; in which the tibia was provided with a 

 well-developed cnemial crest ; and in which, finally, 

 the ankle-joint of the foot and the disposition of 

 the toes were in accordance with the disposition 

 seen in birds. Many of these animals, further- 

 more, had the pneumatic character of the bones 

 of birds, ensuring a certain amount of lightness 

 to an otherwise ponderous frame. These singular 

 creatures, one of which, the Iguanodon, is repre- 

 sented in the diagram before you, first appeared 



in the Triassic age, or in the period immediately 



(3) 



