A STUDY OF BONES. 63 



waving tail of the Solenhofen bird, with its 

 single pair of quills, must have been a com- 

 paratively ineffectual and clumsy piece of 

 mechanism for steering an aerial creature 

 through its novel domain. Accordingly, the 

 bones soon grew fewer in number and shorter 

 in length, while the feathers simultaneously 

 arranged themselves side by side upon the 

 terminal hump. As early as the time when 

 our chalk was deposited, the bird's tail had 

 become what it is at the present day 

 a single united bone, consisting of a few 

 scarcely distinguishable crowded rings. This 

 is the form it assumes in the toothed fossil 

 birds of Western America. But, as if to 

 preserve the memory of their reptilian origin, 

 birds in their embryo stage still go on pro- 

 ducing separate caudal vertebrae, only to 

 unite them together at a later point of their 

 development into the typical coccygean bone. 

 Much the same sort of process has taken 

 place in the higher apes, and, as Mr. Darwin 

 would assure us, in man himself. There the 



