70 The Bird 
ply a copy of the primitive flakes or joints of the tiny 
muscle-beginnings, and is comparable to the joints or 
rings in the body of a beetle, butterfly, or earthworm. 
In a short time all the squares will fuse together, and not 
until later will they separate again into divisions which 
will ultimately form the real bones of the spinal column. 
Every little chick, before it hatches, goes through the 
same strange changes,—living reminders of the evolution 
which has gone on in past ages of the earth. It is inter- 
Fic. 46.—Muscle-plates, or false vertebre, of third-day embryo chick. 
Magnified 25 diameters. 
esting to note that the vertebre of the embryo chick 
pass through a stage when they are biconcave,—a condi- 
tion found both in Amphioxus and Archzopteryx. 
This digression upon the back-bone history may seem 
out of place, but in reality such a bird’s-eye survey of 
the past, imperfect as it is, will add a new interest to 
our handful of chicken-bones. 
