474 The Bird 
of this is emphasized in the development of the embryo, 
during which process a number of additional ribs dis- 
appear. The abortive ribs of the neck-bones are especially 
noticeable during the egg-life of the bird, so that in some 
species we can make out traces of as many as fifteen ribs 
all told. 
On page 97 a short account was given of the origin of 
the wings and feet, in the case 
of the chick—from a primi- 
tive fin-fold in some general- 
ized aquatic ancestor. About 
the fourth day of incuba- 
tion, sections of our embryo 
chick will show a low, round- 
ed ridge, extending the whole 
length from the neck to the 
tail. While we can never be 
absolutely certain that perfect 
homology exists between the 
two, yet it is very significant 
that soon after its develop- 
Fic. 367.—Early embryo of Canada ment it dwindles away, leay- 
Goose, showing fin-like limbs. : ; 
si ing four conical, isolated 
buds—the beginnings of the limbs of the bird. Within 
two or three days after the appearance of the limbs, faint 
streaks become visible upon the tips of the extremities, 
and these hints of the bones of fingers and toes, for such 
they are, soon push out beyond the edge, still bound 
together by their transparent membrane, and for some 
time they present the appearance of webbed paws or 
