154 



ANIMAL BIOLOGY 



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 separate 

 covering of skin from the other digits, as 

 may be seen in a plucked bird. The de- 

 generate hand of the fowl is of course 

 useless as a hand (what serves in its 

 place ?) but 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? FlG ^ _ A FossIL BlRD (archa;opteryx} 



(\Vhy does rigidity Of found in the rocks of a former geological 



trunk require flexibility 



Question: Find two resemblances to reptiles in 

 Of neck?) 'Why does this extinct bird absent from skeletons of extant birds. 



