36 



A HISTORY OF BIRDS 



with scales as to the head, neck and trunk, the feathers being 

 restricted to the parts on which they occur in the fossil ! A 

 contention as wildly improbable surely as it would be to insist 

 that from the absence of all traces of muscles these primitive 

 creatures had not yet acquired muscular tissue ! 



Nevertheless, we have, in this primitive type, not only a 

 remarkable link in the chain of evidence as to the source from 

 which birds derived their origin, but also a most valuable key 

 to some essentially avian characters which would otherwise 

 have had to be explained on mere conjecture. In so far as 

 the reptilian characters are concerned the principal features are 



A 



III. II. — The Skeletons of Two Extinct Fossil Birds, Hesperornis (A) 



AND ICHTHYORNIS (B) 



In Hesperornis all that remains of the wing is a vestige of the humerus, 

 seen in the figure lying across the ribs. 



the teeth and tail. The former were small and appear to 

 have been lodged in sockets, while the tail, on account of its 

 length and the number of the vertebras, must unquestionably 

 be regarded as reptilian. As to the avian characters, these will 

 be dealt with later (p. 263). 



Not, unfortunately, until the cretaceous period do we meet 

 again with bird remains, and these have now become stamped 

 with the stereotyped avian characters in all save that the jaws 

 still bore teeth. 



The two most conspicuous and most perfectly preserved of 



