The Bird in the Egg AGS 
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 develop- 
ment begins superficially and works inward, not, as would 
be thought, starting at the shoulder and ending at the 
digits. 
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-reaching rays of the fin-like 
fore limbs, and it is believed that the pelvic girdle had 
its origin in the spliced scales of some fish-like ancestor 
of old, which had scales like those of some of the fossil 
ganoids. These probably covered over the cartilage girdle 
and then sunk in. 
An example of one out of many reptilian structures 
which appear for a time and then vanish, is found in the 
procoracoid bone which has apparently much to do with 
the development of the typical coracoids, but which is 
absent or reduced to a mere process in the adult bird.* 
Strangely enough, in the embryo of the common chick 
the coracoid 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 the bones complete their development as 
they began,—two wholly independent structures. 
Again, in the embryo of a tern, faint vestiges of teeth 
* This process is quite pronounced in the case of the Ostrich. 
