CHAPTER XXIX 

 THE SPINAL CORD 



498. The first collection of central nerve cells is in the 

 spinal cord. The spinal cord is a soft white cylinder of 

 nervous tissue, about half an inch in diameter. It is 

 securely hung in the upper two thirds of the tube formed 

 by the bony rings of the backbone. It extends from the 

 bottom of the skull to about the level of the lowest rib, a 

 length of about eighteen inches. It is only about two 

 thirds as large as its tube, and so is not likely to be injured 

 by bending the backbone. 



499. The gray matter. When the cord is cut across, 

 the central part of its end shows the grayish outline of a 



butterfly surrounded by a 

 thick layer of a whiter 

 substance. The gray mat- 

 ter is a collection of nerve 

 cells, which give off nu- 

 merous nerve fibers like 

 the central fibers of ordi- 

 nary nerve threads. The 



A thin slice from the spinal cord with the 11 ahrmt * of an 



cells and nerves magnified 200 diameters. * TOITO O 



inch in diameter. Some 



a cells in the gray matter. 



b fibers in the gray matter. of the nerve fibers COm- 



c nerve threads in the white matter. municate with Other cells 



of the cord, and some take coverings and become ordinary 

 nerve threads. The whole is bound together by delicate 

 connective tissue. 



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