34. THE STRUCTURE AND LIFE OF BIRDS CHAP. 
(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. 
Fic. 12.—Coracoid of Rhea. 
co, coracoid ; pco, precoracoid ; sc, 
capula. 
(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 1861 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 
