34 THE STRUCTURE AND LIFE OF BIRDS chap. 



PCO 



(5) Birds have a single coracoid ; in reptiles it is 

 divided into two, the coracoid proper and precoracoid. 

 But in the Rhea we find a very conspicuous, though 

 rudimentary, survival of the latter, and in the Ostrich 

 the bone is complete. 



(6) The bird's feather 

 corresponds to the horny 

 coating of the reptile's 

 scale. The snake moults, 

 when, as we say, he 

 " sheds his skin." 



In 1 861 there was 

 found in the Lithographic 

 Stone at Solenhofen in 

 Bavaria the form of an 

 animal very different from 

 any that had ever been 

 seen either alive or as 

 fossils. This stone be- 

 longs to the Jurassic sys- 

 tem and, consequently, 

 was deposited in the 

 Secondary or Mesozoic 

 period, and long, too, 

 before that period was 

 concluded. Here was a 

 feathered creature pre- 

 served in the form of a 

 bas-relief, with the detail standing out so distinct and 

 clear, that something even of the minute structure of 

 the feathers might be seen. As Sir Richard Owen 

 showed, it was a bird of a very primitive form. The 



CO 



% 



Fig. 



-Coracoid of Rhea. 



coracoid ; pco, precoracoid ; sc, 

 capula. 



