106 The Bird 
few thousand years during which man has reigned seems 
but a day. 
When we study the early structure of some creature, 
say a bird, we find that before it emerges from the egg 
the skull is soft and cartilaginous, open and quite differ- 
ent in shape from what it will be eventually, and it is 
most startling to find a living creature—a shark—with 
Fic. 82.—Skull of Bald Eagle. Bones light and spongy, fitting for a very active 
aerial life; orbit very large and brain-case capacious, showing great advance 
beyond reptilian condition. 
a skull which never gets beyond this condition. It is 
as if the curtain of eternity had been, for a moment, drawn 
aside for us, and a glimpse given into the past—a past 
so remote and clouded that our keenest searches seem 
to reveal but dim, skeletal forms of weird shapes, which 
yet we know must have blended and_ imperceptibly 
merged, through millions of years, into the present life 
of the earth. 
Looking at the chicken’s skull as a whole, we notice 
a number of uses which the various parts serve. The 
