The Bird in the Egg 475 



radiate fins. But as early as the tenth day, except for 

 the absence of feathers and claws, the limbs are, in appear- 

 ance, very perfect wings and feet. The most interesting 

 fact in connection with the limbs is that their develo})- 

 ment begins superficially and works inward, not, as would 

 be thought, starting at the shoulder and ending at the 

 diiiits. 



Even the deep-seated shoulder- and thigh-girdles of bone 

 (pp. 85 and 89) are not derived from the axial skeleton. 

 The former, in the long ago, was gradually pushed inward 

 from the surface by the deep-reach in.*;- rays of the fin-like 

 fore limbs, and it is believed that the pelvic girdle had 

 its origin \n the spliced scales of some fish-like ancestor 

 of old, which h;i(l scales hkc those of some of the fossil 

 ganoids. These probal)l\- co\ered o^•er the cartilage girdle 

 and then sunk in. 



An exami)lc of one out of many reptilian structures 

 whicli ap})car for a time and then vanish, is found in the 

 procoracoid bone which has a|^|)arently much to do with 

 the de\eloi)ment of tlie topical coracoids, but which is 

 absent or rcnluced to a mei-e process in the adult bird.* 

 Stran.iicly enou.iih, in the embryo of the common chick 

 the coracoitl and scapula fuse together at an early stage. 

 being then in a condition comparable only to that found 

 in the full-grown ostrich. Later this inexplicable fusion 

 is dissolved and th(^ bones complete their development as 

 they began,— two wholl\- independent structures. 



Again, in the embryo of a tern, faint vestiges of teeth 



* This process is quite pronounced in the case of the Ostrich. 



