50 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



fully functional, but the first, although retaining the 

 usual number of phalanges, is greatly reduced in 

 size. Finally, in Iguanodon, 1 which is fully adapted 

 to the upright position, the second, third, and fourth 

 toes are still fully functional, but not only has the 

 fifth toe disappeared, but the first is merely repre- 

 sented by a pointed metatarsal. 



Thus it is apparent that each new phase in the 

 transformation from quadruped to biped is attended 

 by partial degeneration, although the hind limbs, 

 having alone to fulfil the function of locomotion, 

 necessarily acquire a fuller development. The 

 Iguanodon is too specialized in its development 

 to have been the ancestor of birds ; but this is 

 not so with other bird-footed Dinosaurians, such 

 as Camptosaurus and Hypsilophodon, where the 

 hind foot is sufficiently primitive to have been 

 the forerunner of the bird's claw. 



Most birds have four functional toes, which have 

 retained the primitive number of phalanges, but the 

 legs of running birds exhibit more or less important 

 variations. The modifications they have undergone 

 have obviously not diminished their functional im- 

 portance, but quite the contrary. These modifications 

 have, however, been accompanied by degeneration 

 with running birds, and the first toe disappeared 

 first, as in the Cassowary and the American Ostrich, 



1 Dollo : First, second, third, fourth, and fifth Notes siir les 

 Dinosauriens de Bernissart. Bull. Mus. royal d'Hist. nat. de Belg. 

 1882, 1883, 1884. 



