2 Introduction 



this affinity. This large reptilian group embraces a number of forms, particu- 

 larly those of carnivorous habits, that without doubt regularly progressed in a 

 bipedal manner, and it was from the obvious similarity between these and the 

 birds that Huxley concluded that "there could be no doubt that the hind quarters 

 of the Dinosauria woriderfully approached that of birds in their general structure, 

 therefore, that these extinct reptiles were more closely allied to birds than any 

 which have lived." Other anatomists have held that these resemblances in 

 structure are simply adaptive, and came to be evolved in the dinosaurs from 

 community of habit with birds, but very recently Professor H. F. Osborn has 

 reexamined the evidence and has detected a number of additional points of agree- 

 ment in skeletal characters, and concludes that this hypothesis is not to be dis- 

 carded, but is to be "very seriously considered" in connection with the origin of 

 birds. Still more recently (1905) Professor E. Ray Lankester, director of the 

 British Museum [Natural History], says: "The reptiles which come nearest to 

 them in structure are the Dinosaurs, especially these Dinosaurs (like Iguanodon) 

 which walked on their hind legs and had only three toes to the foot." 



In any event it seems safe to assume that if not more intimately related, the 

 dinosaurs and birds must at least have had a common ancestor. Within the 

 past few months, Mr. W. P. Pycraft, the eminent avian anatomist of the British 

 Museum, has presented an interesting speculation regarding the probable ap- 

 pearance of the ancestral or incipient birds anterior to Archaeopteryx. He 

 says: "From what we know of other types of vertebrates we may safely 

 assume that these ancestral birds were of small size, and were probably also 

 arboreal. And from the unmistakable signs of the shortening of the body in 

 modern birds, the trunk was also relatively longer, as it certainly was in Archse- 

 opteryx. From these two inferences we conclude, with some degree of proba- 

 bility, that these creatures, these 'birds in the making,' had substituted leaping 

 for climbing about the trees. And from this there was but a short passage to 

 leaping from tree to tree. In these movements we may reasonably suppose that 

 the fore limbs were used for grasping at the end of the leap. The use of the fore 

 limb for this work would naturally throw more work upon the inner digits 

 1-3 so that the work of selection would rapidly tend to the increased develop- 

 ment of these, and the gradual decrease of the two outer and now useless members. 

 Correlated with this trend in the evolution, the axillary membrane the skin 

 between the inner border of the arm and the body became drawn out into a 

 fold, while a similar fold came to extend from the shoulder to the wrist, as the 

 fore limb, in adaptation to this new function, became more and more flexed. 

 While the fingers, upon which safety now depended, were increasing in length, 

 and growing more and more efficient, they were, at the same time, losing the 

 power of lateral extension, and becoming more and more flexed upon the fore 

 arm. And the growth in this direction was probably accompanied by the develop- 

 ment of connective tissue and membrane along the hinder, post-axial border of 

 the whole limb, tending to increase the breadth of the limb when extended 

 preparatory to parachuting through space from one tree to another, the long 

 claws being used to effect a hold at the end of the leap. The hind limbs, though 



