154 



BEGINNERS' ZOOLOGY 



Fig. 289. — Breast- 

 bone and Shoul- 

 der Bones of 

 Cassowary. 



five carpals of the chick being reduced to two in the fowl 

 (Figs. 287, 288). The thumb or first digit has a covering 

 of skin separate from that of the other 

 digits, as may be seen in a plucked bird. 

 The degenerate hand of the fowl is of 

 course useless as a hand (what serves 

 in its place?) but it is well fitted for 

 firm support of the feathers in flying. The 

 two bones of the forearm are also firmly 

 joined. There are eighteen movable 

 joints in our arm and hand. The bird 

 has only the three joints which enable 

 it to fold its wing. The wrist joint is 

 the joint in the forward angle of the wing. 



Since the fore limbs are taken up with loco- 

 motion, the grasping function has been as- 

 sumed by the jaws. How does their 

 shape adapt them to this use ? For 

 the same reason the neck of a bird 

 surpasses the necks of all other ani- 

 mals in what respect? Is the trunk 

 of a bird 

 flexible or 

 inflexible ? 

 There is 

 thus ^cor- 

 relation between struc- 

 ture of neck and trunk. 

 Explain. The same 

 correlation is found in 

 which of the reptiles ? 

 (Why does rigidity of 

 trunk require flexibility 

 of neck ?) Why does 



FlG. 290. — A Fossil Bird (archaopUryx) 



found in the rocks of a former geological 

 epoch. 



Question: Find two resemblances to reptiles in 

 thiscxtinct bird absent from skeletons of extant birds. 



