40 THE STRUCTURE AND LIFE OF BIRDS CH. Ill 



The socket of his thigh-joint is not completely 

 closed with bone : in the skeleton of the crocodile as 

 in that of the bird, the cup of the socket has a hole at 

 the bottom, the membrane which was there during 

 life having disappeared. Several of the ribs have 

 uncinate processes. 



These resemblances, to which others might be added, 

 do not prove that the crocodile is the ancestor of the bird. 

 The heart and the gizzard were probably developed 

 independently after birds and crocodiles had arisen 

 from some common and more primitive stock. It 

 would be unwise to say that birds are descended from 

 any existing class of reptiles. But the facts justify us 

 in drawing the inference that birds and reptiles are 

 related; that they had common ancestors with less of 

 specialised character than either of themselves, and 

 that from these ancestors each class has developed in 

 accordance with its own mode of life. In the same 

 way Englishmen and Chinamen come from the same 

 stock ; neither race is descended from the other. The 

 Darwinian theory of the descent of man is that if 

 you trace upward the pedigrees of men and monkeys, 

 the lines will meet, not that men are descended from 

 monkeys. 



Books on the Subject. 

 See at the end of Chapter II. 



Also Newton's Dictionary of Birds, " Fossil Birds " ; Pycraft, 

 Nat. Science, November and December, 1894, " Archaeopteryx " ; 

 Owen, Philosophical Transactions, 1863, "Archaeopteryx." 



