LIFE AND KINSHIP OF DINOSAURS. 615 



" its old Iclithyic vestment,"* two questions present themselves : — Out of what antecedent 

 vertebrate modification was the avian one evolved ? How, or under what conditions or 

 secondary influences, was such evolution efiected? 



The hypothesis of the bipedal locomotion of the Dinosauria, the advocated homology 

 of their OS pubis with the ischium of the bird, and the alleged restriction of the avian 

 antacetabular production of the iliac bone to the Binomuria among Reptiles, have been 

 superadded to the proved fact of a correspondence of structure between the shortei 

 sacrum of the Dinosaurs and the longer sacrum of Birds as grounds for the conclusion 

 that Birds are transmuted Dinosaurs, and that the feathered class made their first step in 

 advance under the low form of Sfruthiones or Cursores, incapable, as yet, of flight. The 

 kind and amount of modification required to evolve an Ostrich out of an Iguanodon may 

 be appreciated by the osteological comparisons already submitted in the present section of 

 this work. To revert only to the structure of the fore-limb. In losing its power of aiding 

 in the quadrupedal progression, and of grasping or otherwise applying the hand, it has 

 as yet, in the hypothetical first form of Birds, gained no other faculty. At best it may 

 help in the swift course of the ostrich by flapping motions similar to those of better birds 

 during their flight; or the more minute moiiodactyle hand may just serve to scratch the 

 back of the head, as in the New Zealand Kivi. In their larger extinct relatives, the 

 ]\Ioas, it is still doubtful whether more of the framework of a fore-limb existed than the 

 supporting scapular arch, and that of the simplest character. 



In all these gradations of structure of a limb unavailable for flight or any other mode 

 of locomotion we see no approach in the scapula to the Dinosaurian types of that bone ; 

 it retains in all Cursorials the strictly avian sabre-like shape and pointed free extremity, 

 without expansion and truncation there such as obtains in the alleged ancestral Reptilia.\ 

 The coracoid still further departs from any well-determined Dinosaurian type of the bone, 

 and as closely adheres to that of the Birds of flight, save such decrease of breadth and 

 of relative size as accords with its necessity to bear upon the sternum in the mechanical 

 mode of inspiration peculiar to Birds with Pterodactyles. 



What could be the conceivable conditions of the life of an Iguanodon or Megalosaur 

 which rendered a fore-limb useless or cumbersome, and concomitantly called for lengthened 

 and strengthened hind-limbs and a more vigorous and exclusive exercise of these in the 

 acts of locomotion ? The abettors and acceptors of the exposition of the operation of the 

 secondary mode of origin of species by way of ' natural selection ' are amenable to the call 

 for an explanation of such conditions, especially if such mode of origin be hypothetically 

 applied to the kinds of Birds deprived of the power of flight. But such explanation 

 would have to square with the fact that a loss of one pair of limbs had been associated, 

 on the assumption of the Dinosaurian ancestry, with an advance of the mechanical structure 



* ' Ou the Nature of Limbs,' p. 86. 



f Compare, tor example, the scapula of the Apteryx, 'Transactions of the Zoological Society,' vol. ii, 

 pi. XXX, fig. 2, g, and figs. 3 and A, with Cut, fig. 3, p. olsG. 



15 b 



