PEDIGREES — THE FOUNDERS OF THE HOUSE. 231 



locomotion. Compare, for instance, the ankle- 

 joint of a dinosaur with that of a young fowl, 

 tig. 7, and then the bones of the foot in the 

 same. 



Note in the dinosaur the curious upright spike 

 of bone marked "a.a." This is an upstanding 

 process of a bone known as the astragalus. More 

 bones were really originally present in this 

 region of the foot, but they have all fused or 

 combined together to form one — once on a time 

 they v^ere distinct. Capping the bundle of three 

 bones immediately below is seen a plate-like 

 structure Avhich represents a second row of bones 

 at one time quite distinct. The joint, or seat of 

 movement between the foot and the leg, lay be- 

 tween these two rows of fused ankle-bones. 

 Turn now to the bones of the young fowl's foot 

 and leg and ankle-joint, and a precisely similar 

 arrangement will be seen. The fowl, however, 

 goes a step further. The three long bones of the 

 foot, permanently distinct in the dinosaur, be- 

 come completely merged together in the adult 

 fowl to form but a single shaft. An ankle-joint 

 such as that just described occurs in some other 

 reptiles, and in all birds. 



These are the principal points of resemblance 

 between the two, but they are points of very 

 great significance. 



The fore-limb, someone will exclaim, is very 

 different in this old reptile and the bird. Quite 

 so. Like the shoulder-girdle, it has in the bird 

 undergone considerable modification and trans- 

 formation to fit it for the purposes of flight. 

 The fore-limb of the dinosaur has required no 



