INTRODUCTION 



XV 



IfneE'Cf)!' 



several small pieces originally, but now forming a 

 thin plate, becomes welded on to the top of the bones 

 of the foot. It it these last which are always, but 

 wrongly, described as the "leg-bones." Really, they 

 answer to the bones of our own feet which lie be- 

 tween the ankle and the 

 toes. Finally, we have 

 the toes, about which 

 there can be no mistake. 

 The great lengthen- 

 ing of the foot-bones 

 has been brought about 

 by the evolution of the 

 bird from a climbing 

 to a walking animal. 

 Originally they were 

 five in number, but are 

 now, like the toes, re- 

 duced to four. Of 

 these four, three are 

 now welded together — 

 Nos. I, II, III— to 

 form a single "cannon- 

 bone," answering to 

 that of the horse; but 

 in the young bird their 

 originally separate con- 

 dition can still be traced 

 (see Fig. 1). The first 

 of these foot-bones answering to the hind-toe is now 

 reduced to a mere "button" of bone slung by liga- 

 ments on to the cannon-bone." The leg of the old 



c^"- 



cO' 



Fig.. 2. — Diagram of the leg of 

 an adult bird, ' showing the 

 condition of the limb after 

 the separate elements have 

 become welded. 



