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SCIENCE PRIMERS. 



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of the skull is called the brain ; the narrower, rod-like, 

 or band-like mass which runs down ^^e vertebral canal 

 in the neck and back is called the spinal cord. 

 They have separate names, but they are quite joined 

 together, and the rounded brain tapers off into the 

 band-like cord in such a way that it is difficult to say 

 where the one begins and the other ends. 



II. In the skull, besides the larger openings we have 

 spoken of, you will find several small holes leading from 

 the outside of the skull into the inside of the brain- 

 case. Some of these holes are filled up during life by 

 blood-vessels, but in others run those delicate white 

 threads or cords which you have already learnt to call 

 nerves. Nerves are in fact branches of nervous 

 material running out from the brain dr spinal 

 cord. Those from the brain pass through holes in the 

 skull, and at first sight seem to spread out very irregu- 

 larly. Those which branch off from the spinal cord are 

 far more regular. A nerve runs out on each side be- 

 tween every two vertebrae, little rounded gaps being left 

 for that purpose where the vertebrae fit together, so that 

 when you look at a spinal cord with portions of the 

 nerves ^till connected with it, it seems not unlike a 

 double comb with a row of teeth on either side. The 

 nerves which spring in this way from the spinal cord 

 are called spinal nerves, and soon after thv^y leave 

 the vertebral canal they divide into branches, and so 

 are spread nearly all over the body. In any piece of 

 skin or flesh you examine, never mind in what part of 

 the body, you will find nerves and blood-vessels. If 

 you trace the nerves out in one direction, you will find 

 them joining together to form larger nerves, and these 

 again joining others, till at last all end in either the 



