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 vertebrae. 

 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 



