196 The Bird 
bone supports the entire body and gives a point of at- 
tachment for the limbs, but long before limbs were found 
among animals on the earth, in fact long before bone 
existed, a sheath of cartilage surrounded and supported 
the primitive spinal cord of creatures which lived long 
ago in earlier epochs of the earth’s history. So we may 
say this protection to the nerve-trunk is the most im- 
portant, as it was the original, function of our vertebre. 
When “brainy” creatures appeared, that is, when the 
front end of the nerve-cord became enlarged, it needed 
some special protection, so a box—the skull,—first of 
cartilage, then of bone, was evolved. 
One more fact which may hark back to old, old times, 
and then we shall leave the past as perhaps trespassing 
too much on the province of the chick while he is yet 
within the egg. Birds (and all the higher classes of ani- 
mals) have what we may call two separate systems of 
nerves, although in some ways they are insolubly con- 
nected with each other. The brain and spinal cord send 
numerous branches which subdivide into countless nerve- 
lets, permeating every portion of the body, as we can 
easily prove by the feeling, on pricking our skin anywhere 
with a needle. This is the principal nervous system of 
back-boned animals, and it is by this that birds, and all 
creatures with well-developed nerves, see, hear, taste, 
smell, and by which they send messages to the muscles 
when they desire to move them. Below the vertebral 
column is another lesser system which sends nerves to 
the digestive tract and other organs, the movements and 
functions of which are not under control of the will, and 
